University of Nigeria Research Publications
Aut
hor
AKPAN, Udom Mark
PG/M.Sc/04/35487
Title
Temperature Effects on sulphur Catalysed
Dimerisation of melon seed oil (Colocynthis Vulgaris)
Facu
lty
Physical Sciences
Dep
artm
ent
Pure and Industrial Chemistry
Dat
e
February, 2007
Sign
atur
e
TEMPERATURE EFFECTS ON SULPHUR CATALYSED DIMERISATION OF MELON SEED OIL
, (Colocynthis vulgaris)
AKPAN, UDOM MARK PG/M.Sc/04/35487
' DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY UNIVERSITY OF NIGERIA,NSUICKA.
FEBRUARY, 2007.
TEMPERATURE EFFECTS ON SULPHUR CATALYSED DIMERISATION OF MELON SEED OIL
(Colocynthis vulgaris)
AKPAN, UDOM MARK PGIM. Si$0&13548?
A RESEARCH PROJECT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTER OF
SCIENCE IN POLYMERIINDUSTRIAL CHEMISTRY
DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY UNIVERSITY OF NIGERIA, NSUKKA.
FEBRUARY, 2007.
APPROVAL PAGE
This research project has been approved by the Department
of Pure and Industrial Chemistry, Faculty of Physical Sciences,
University of Nigeria, Nsukka.
'DR C.O.B. OKOYE PROF J. A. IBEMESI HEAD OF DEPARTMENT SUPERVISOR
EXTERNAL EXAMINAR
CERTIFICATION
This is to certify that this research work titled: 'Temperature Effects on
Sulphur Catalysed Dimerisation of Melon Seed Oil (Colocynthis vulgaris)' was
actually carried out by ~ k ~ a n , Udom Mark (PGIM.SC104135487) of the Department
of Pure and Industrial Chemistry, University of Nigeria, Nsukka. The work
embodied in this project report is original and has not been submitted in part or dull
for any diploma or degree of this or any other university.
> L -------------- 7------ -r------ ,
PROF J. A. lBEMESl SUPERVISOR
DEDICATION
To God Almighty and to my beloved mother, Stella Etuk, who in spite of
difficulties, persevered to see me through my first and'second degrees.
ACKNOWLEDGEMENT
I express my unreserved thanks to my supervisor, Prof J.A.lbemesi whose
nature is one great thing that ever happened to me. His diligence, meticulous
nature and critical examination are qualities'l so much cherished.
My good friends and lecturers in the department mean so much to me
especially Dr. P. 0. Ukoha who agreed to read through my draft, Nnamdi Obasi for
his moral advice and encouragement, Asegbolenyin, Ejikeme and Agbo who are
never tired attending to my needs, Ugwu, Nnagbukwu, Ukwueze, and Ezema for
their contributions, in no small measure, gave me strength especially in times of
morale depression.
The department is specially acknowledged for providing some of the
reagents used for the laboratory work.
My best friend, Etima Akpan and others including my fellow post graduate '
students are acknowledged. You are all heartily appreciated for your good nature;
Members of ~ r a d u a t e Students Fellowship and Christ church Chapel, UNN
are most highly cherished for their persevering prayers.
My unending list of those due for acknowledgement cannot be exhausted.
To all those I have not mentioned, and those I have, May the Almighty God bless
and keep you in perfect peace, Amen.
Akpan, Udom Mark February, 2007 .
ABSTRACT
Dimer fatty acid was produced from melon seed oil (MSO) using su1phur.a~
catalyst. The oil was 'dimerised at the temperature values of 300, 310, 320,
330, 34-0, and 350°C, under inert atmosphere of nitrogen using 0.5% sulphur
as catalyst. Ten samples were withdrawn at five minutes interval each for
every specified temperature and analysed. The analysis of these dimer fatty
acids (DFA) reveals steady increases in the acid values, refractive indices,
and the molecular weights. The optimum yield of dimer was obtained on
dimerisation at 350°C for 30minujes, and the yield under, this condition was
48.67%. The effectiveness of sulphur catalyst, when compared with iodine
and NaHS04 used by other researchers under the same methodology and
laboratory conditions, was adjudged the best of the three types of catalysts
used for dimerisation. Thermodynamic analysis reveal that the dimerisation
proceeds in a slow exothermic process and the heat released in the process
is very appreciable when compared to the enthalpy of dimerisation catalysed
102,103 by other catalysts
viii
LIST OF TABLES '
Table
Fatty acids, their melting points, sources and common names
Percentage fatty acid components of some vegetable oils
Extracting solvents in order of decreasing polarity
lnciease in viscosity with chain length'
Density of some triglycerides
Refractive indices of fatty acids
Classes of oil and their iodine number
Proportions of dimer structures in the feedstock
composition and properties of commercial DFA
Physicochemical properties of MSO
Variation of acid value with time of dimerisation
Acid values produced by different catalysts
Variation of refractive index with time and temperature
Refractive indices produced by different catalysts
Variation of molecular weight with time and temperature
Molecular weights produced by different catalysts
Variation of viscosity of DFA with temperature
Variation of colour with time and 'temperature of DFA
Page
4.10 TLC separation of DFA samples into its components 83
4.1 1 Enthalpy at various times of dimerisation 86
4.1 2 Effect of catalysts on the enthalpy of dimerisation 86
LIST OF SCHEMES
Schetnes
1 I A molecule of triglyceride
1.2 Types of triglycerides
I .3 A molecule of tocopherol
1.4 Phosphatide molecules
1.5 Glyceride molecules
1.6 Vegetable oil refining steps
Page
1 .
4
8
9
1.7 Structure of various C36 compounds of DFA 32
1.8 Isomerisation of linoleic acids
I .9 Sequence for thermal polymerization reaction 37
1 .I 0 Diene reaction of two conjugated (9, 1 1 - ) linoleic acids 38
1 .I 1 Mechanism for sulphur catalysed isomerisation of linoleic acid 42 .
LIST OF EQUATION'S
Equation
1 .I Density
1.2 Refractive index
1.3 %Free fatty acid !
1.4 Saponification value
r1.5 Ploymerisation constant (K)
3.1 Acid value
3.2 Calculation of Normality of Na2S203.5H20
3.3 Iodine value,
3.4 Saponification value calculation from sample
3.5 Relative density
3.6 Molecular weigbt
3.7 Percentage yield of DFA
Page
25
26
28
28
LIST OF FIGURES
Figure . Page
4 Plot of acid value against time of dimerisation 66
4.2 Plot of acid value against temperature of dimerisation 67 A
4.3 Plot of acid values against temperature for different catalysts 69
4.4 Plot of refractive index against time of dimerisation 71
4.5 Plot of refractive index against temperature of dimerisation 72
4.6 Plot of refractive index against temperature for different catalysts 74
4.7 Plot of molecular weight against time of dimerisation ' 76
4.8 Plot of molecular weight against temperature of dimerisation 77 .
4.9 Plot molecular weight against temperature for different catalysts 79
4.10 Plot of bulk viscosity against temperature 81
4.1 1 Plot of lnAV against 1 /T in Kelvin 85 '
TABLE OF CONTENT
Title page
Approval page
Certification
Dedication
Acknowledgement
Abstract
List of Tables
List of Schemes
List of Equations
List of' Fiqures
Table of content
CHAPTER ONE: INTRODUCTION
Chemistry of Fats and Oils
Sources of Fats and Oils
Composition of Vegetable Oils
Extraction of Vegetable Oils
Classification of'vegetable Oils '
Refining of Vegetable Oils
Characterization of Vegetable Oils
Uses of Vegetable Oils
Page
I I
iii
i v
v
vi
vii
viii
i x
x ,
xi
xii
1.9.0 Dimer Fatty Acids (DFA)
1.9.1 Properties of DFA
1.9.2 Uses of Dimer Fatty Acids (DFA
'1.10 Thermal polymerization of Drying Oils
1. I 1 Isomerisation and dimerisation catalysts
CHAPTER TWO: LITERATURE REVIEW
2.0 Historical review
2.1 Research Objective
CHAPTER-THREE: EXPERllWlENTAL
3.1 Materials used
3.2 Extraction of Oil from MSO
3.3 Refining of the Crude MSO Extract
3.4 Characterization of the Oil
3.5 Dimerisation of MSO
3.6 Characterisation of the Dimer Fatty Acids (DFA) ,
3.7 Percentage yield of the DFA
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Extraktion of MSO
4.2 Characterization of MSO
4.3 Characterization of the crude DFA
4.4 Percentage yield of DFA
4.5 Thermodynamics of Dimerisation
Conclusion
Refrences
CHAPTER ONE
INTRODUCTION
Fats and oils are water-insoluble substances found in plants and animals. They
are essential nutrient in both human and animal diets, which supply twice the amourit
of most concentrated source of energy than that obtained from equivalent weight of
carbohydrates'. They are 'predominantly glycerides or triesters of glycerol, which
result from the combination of one unit of glycerol (OHCH20HCHOHCH2) with three
units of fatty acids.
The fatty acid as the building block of the triglycerides have its general fortnula thus:
Where R, R,, and R2 represent hydrocarbon chains of fatty acids.
Scheme 1.1 : A molecule of triglyceride
Oil production from vegetable source was rare, in the pre-historic times, and
was only known by the ancient Chinos,and the ~ i n d u s ~ . Since the discovery of this
method by other parts of the world, oils and fats have found endless use in industrial,
biochemical, and domestic proceses. The knowledge of the chemical composition.of
fats and oils and their sources are essential in the understanding of the various
domestic and industrial applications to which different oils may be put.
1 2.0 SOURCES OF FATS AND OlLS
The world report on the supply of fats and oils show that 68.1%, 28.2% and
3.B0/;, come from vegetable, terrestrial animal and marine sources respectively3. Thus,
plants and animals are the two major sources of fats and oils.
The dry (hull-covered) row-crop seeds, the kernels of hard-shell nuts and the
pulpy flesh surrounding seeds make up the possible sites for oils in plants. Apart from
the above, oils are also found in the roots, stalks, branches, and leaves of plants but
in' quantities not large enough for commercial purposes. Oils in seeds are stored in
microscopic globules throughout the cells of dicotyledonous plants or in the seed
germ or bran in monocotyledonous plants; examples: rice, melon, corn etc.
Oil content in some fruits and seeds are sometimes as high as 65%, in several
cases 35%. In most cereal, the fats and oils are concentrated in the seed embryo. The
olive however contains large &mount of fats in the kernel itself while in the oil palm,
both the pulp and the kernel contain large quantity of oil. However, the characteristic
of oils from the pulp may differ from those of the kernel.
On the whole, oils from the vegetable sources are referred to as vegetable oils.
However, both fats and oils are the same substance of different physical states at
ambient temperature and pressure. At ambient temperature, fat is solid whereas oil is
liquid.
1.3.0 COMPOSITION OF VEGETABLE OlLS
campbel14 divided the composition of vegetable oils into major and minor
components.
MAJOR COMPONENTS
The predominant component of vegetable oils is the triglycerides (scheme 1 .I).
The fatty acid defines the properties of the molecules; and over one hundred kinds
have been
these fatty
fatty acids
isolated from various vegetable and animal sources. The most abundant of
acids are palmitic, stearic, oleic, and linoleic acids5. The different types of
are shown in Table 1 .I. They are obtained by the hydrolysis of oils and
fats, or synthetically by oxidation of petroleum hydrocarbon.
Within. certain limits of composition, environmental factors can influence the
fatty acid in the oil seed. chappelow6 reported that the proportion of unsaturated fatty
acids in the glycerides of linseed, soybean and sunflower oils, for example, generally '
increase as the climate becomes colder and wetter. Cd to C10 acids are soluble ,in
water and from CIZ and above are insoluble. Therefore, longer hydrocarbon chains
confer more oiliness, (i.e hydrophobicity), hence less soluble in water than short chain
fatty acids7. The physical properties of fatty'acids and its components are largely
determined by the chain length and degree of unsaturation. The , non- polar
hydrocarbon chains account for the poor solubility of fatty acids in water
A simple triglyceride is one with identical fatty acids (R) as shown in
scheme 1.2 whereas triglycerides with different fatty acids (R, R,, R2) are referred to
as mixed triglycerides. Tristrearin and distearin are examples of simple and mixed
triglycerides, respectively.
Naturally occurring triglycerides are mixed and contain only small percent of
simple triglyceridesO. Thus, no glycerides contain only saturated or unsaturated acids.
Simple glycerides occur only when one acid occurs in large amount as in olive oil
(75% oleic acid) and castor oil (87-83% ricinoleic acid) as shown in Table I .2. Owing
to the natural biosynthesis of fats, most naturally occurring fatty acids are straight
chains and contain even number of carbon atoms as the molecules are being built up
from acetate units with two carbon atoms at a time8. This is evident from Table 1 .I,
though lsovaleric acid [(CH3)2CHCH2COOH] is the only odd number fatty acid isolated
from fats which has an isoprene carbon skeleton.
A triglycetride however can be simple or mixed as illustrated below:
Mixed triglyccridc Simple triglyccridc
Scheme 1.2: Types of triglycerides
, 3 Table 1.1 Fatty acids, their melting points, sources and common names
1 Common I names
Acetic acid I B&$C acid
.- - - -
Caproic acid
Caprylic
_ __ -1-
Caproleic I 9-Decenoic ( 10 1 I db 1 I-_ - Butter fat
acid C a ~ r i acid
Synthetic names
.
Ethanoic a'zd Butanoic acid '
Hexanoic acid
Octanoic acid
r ~ y r i s t i c I Tetradecanoic 1 14 1: S 1 54.4 1 ,Butter and
A
Decanoic acid
12 12
No. of
Carb on 2 4 6
8
10
S I db
Palmitic
Ricinoleic 9-hydroxy
Elaidic
Stearic - Oleic
Sources
--
, : 7 -
Butter fat. Butter fat
Coconut oil
No. of bonds
S S S
S
S
44.2 -
9-tetradecanoic Hexadecanoic
9-Hexadecanoic
Melting points
-- - -7.9 -3.4 '
16.7
31.6
Coconut oil Butter fat 1
Octadecanoic 9-octadecanoic
--- Linoleic
Linolenic
Eleostearic
14 16 16
I I Tatiric
18 . 18
(E) 9,12- Qctadeca
-dienoic 9,12,15- octadeca Trienoic 9,11,13-
. - Arachidi Gadoleic
Arachidonic
I d b S
Idb
octadecanoic 9-octadekvnoic
eicosatetraenoic 5,8,11,14,17eico
S Idb
18
18
18
Eicosanoic 9-eicosanoic
5,8,11,14-
sapentaenoic Docosanoic
18.5 62.9
-
69.6 1 :vl;; ;;;; ;;: cd; 1 16.3
18
'20
where: Z and E represent zusameri (cis) amd enfgegen (trans) forms. S, db, and tb represent single, double, and triple bonds respectively.
Coconut oil Butter .fat
Most fats and oils Some fish oilslbeeffat
2d bs
3dbs
, 3dbs
20 20 20
22 Erucic'
-
I i ocosahexaenoic 1 Lignoceric Tetracosanoic H-
I tb
5d bs
22 22
13-docosenoic 4,7,10,13,16,19d
Waxlfish oil .
-6.5
-12.8
-
S I db
4d bs
s
Most vegetable oils
Soybeanlcanola oil
-
-
-
I db 6d bs
-
75.4 -
49.5
Some fish oil
80.0
Peanut'oil Some fish oil
Lard
Peanut oil 33.4
- Rape seed
Some fish oil
x able 1.2 Percentage fatty acid components of some vegetable oils'o2
1 - -:c E % FATTY ACID COMPONENTS ~ - ] ~ ~ ~ 1 ( : f l C 1 8 : ~ h 0 0 1- Linseed Linum - - 6.5
1 24 22 54
Oiticia Licania rigida 5 6 - -- -.
Rubber Heavea brasiliensis 2
8 3 J 13 75 1
I tinctorius - - - - -- [ Dehydrated Ricinus castor
Sunflower
i Soybean Glycine max - - 8.3- 4- 22- 51-
-
I Sunflower
Corn 14
communis Helianthus annus
vulgaris . -
Cotton seed Gossypium vars 0.6 - 23- 2-4 24.7 40- - 27 50
Groundnut Arachis hypogaea - - b 4 60 20
-
I )
seed } O l i v e Olea. europea - - 6-14 2-4 ' 64- 7-
-
I--- I Castor Ricinus - 8 7 d-i
-
-
-
3
-
palm (pulp) !-- I P.K.O. ! .
10
Cocus nucifera Fordii aleurites
where : CI2 :0, CI4 :01 CI6 :0, CI8 :O, Cq8 : I , Cj8 :2, CI8 :3 represents Lauric acid, myristic acid, palmitic acid, stearic' acid, oleic acid, linoleic acid and linolenic acid, respectively. TOFA = Tung oil fatty acid. a = alpha eleostearic acid; b = licenic acid; c = Arachidic acid; d = Ricmoleic acid; e = caprylic and capric acid; f '= saturated acids and rosins; g = saturated acids and unidentified components ,
7-13
-&bI-T*I
11
Communis Elaeis geneensis
1 ,
I I
! I
44.5 -
85
6
- 48.5
. - -
-
17.5 -
51
- 17
8-1 1 2-6 6-8
- -
38
37.5 8
46 51
- -
e Trac.
5 2
- -
-
8.2' 1.5g
41 43
45 14- 16
3 Trac
e
5.5 1.5
- -
-
8.7e
The differences in the propertiek of oils are largely due to variations in the
structure of fatty acids contained in the oil as well as the stereochemical conformation
of the unsaturated oils, among other things. Thus, fatty acids exist in both cis and
trans conformations. The cis conformation lowers the melting point of the oil%elow its
more stable trans isomer. The degree of unsaturalion and the relative position of .
double bonds together with the presence of polar groups also contribute to the .
differences in the properties of oils.
The chain length of the fatty acids, the type of crystal. present and the number
and location of the cis and trans double bonds on the fatty acid chains also contribute
to the differences .in the properties of vegetable oils. These differences in properties I
are due to the fatty acid moiety since only one type of the glycerol moiety is present i'n
each triglyceride.
A few naturally occurring fatty acids with branch chainsc and physiological
characteristics include: Hydnocarpic acid (C16H2802), chaulmoogric acid (C1~H~202)
and Gorlic acid (C18H3002). They contain the cyclopentenyl ring system with certain
physiological activities and occur as major components of seed fats of the family
flacourtiaceae.
THE MINOR COMPONENTS
The minor components of vegetable oils are found in small quantities and
include: sterols, tocopherols, phosphatides, free fatty acids, pigments, mono-and dl-
glycerides, and vitamins.
(i) STEROLS
These are also referred to as steroid alcohols which belong to the class of
substances that contain the common steroid nucleus with an 8-10 carbon side chain
and an alcohol group. Sterols occur in fats and oils as free sterols or esters of the high
fatty acids and accounts for 0.5 - 1.5% unsaponifiable components. They are found
both in vegetable oils and animal fats though with certain biological differences.
Important steroids derived from squalene (a triterpene) include cholesterol (an animal
fat sterol) which occurs in trace amount in vegetable oils. Others are stigmasterol,
sistosterol, catnpesterol and ergosterol which are found in vegetable oils. The type
and amount of vegetable oil sterols vary with the source of the oil4. Sterols are
odourless, colourless, and generally inert crystalline alcohols with 26-30 carbon
atoms.
(ii) TOCOPHEROLS
These serve as important antioxidants in vegetable oils to retard rancidity and are
also good sources of vitamin E. There are four types of tocopherols varying in
antioxidation and vitamin E activity. Alpha tocopher~ls have the highest vitamin E
activity and the lowest antioxidant activity. Naturally 0ccurrin.g tocopherols in most
vegetable fats may be partially removed by pressing and then added after processing
to improve oxidative stability in finished products. Tocopherols can be represented
structurally as: c 1-1
HO
' kiO ' 143
~ ~ Q ~ ~ ~ ~ ) ~ - ~ ~ ~ - ~ ~ - ~ ~ CH3 I
'Tocopherol
Scheme 1.3: A molecule of tocopherol
(iii) PHOSPHATIDES
Phosphatides (also known as phospholipids) are a group of compounds which
like the oils, contain fatty acids. They also contain phosphate group, usually a
nitrogenous base, and glycerol and are fat soluble. In general, phosphatides may be
considered as triglycerides in which one of the fatty acid groups has been replaced by
phosphoric acid derivative. Lecithin and cephalin are common' ph'osphatides found in
edible fats together with inositol phosphatides. They make up the principal
phosp,holipid compdnents of plants and are almost completely removed during
vegetable oil refining. The two types of phosphatides can be represented structurally
as: CH, - OCOR I CH - OCOR I lo- CH2-0-P=O .
~cH~cH~&(cH , )~
LECITHIN (Phosphotidalcholine)
CH2 - OCOR I CH- OCOR I PI-I CHp-0-P=O
I + OCH2CH2N(CH3)2
CEPHALIN ,
(Phosphotidylethanolamine
Other types of phosphatides are : phosphotidylinositcl and phosphotidylserine and
can be represented structurally as:
ClH2 - OCOR CI-12 - OC01< I I ~ 1 - I - OCOR ' ! CN-OCOR I $- I 1 - 0 - - OCH2 - HNH2 F
1-1 0 COOH F 1 0 HO
Phosphatitlyl inositol
Schcmc 1.4 l'hophatide molecules
(iv) FREE FATTY ACIDS
These are fatty acids present in fats and oils. Several percent fatty acids may
be found in some unrefined oils and the level is reduced during refi,ning.
(v) PIGMENT
Some co1oure.d n-laterials which occur naturally in vegetable oils include the oil-
soluble carotenoids, chlorophylls and the xanthophylls (derivatives of chlorophylls).
They also include the yellow (lutein) in plant leaves, and zeaxanthin in corn
(zea mays). Also, the capsanthins (red pigment in red pepper), lycopene (red
colouring matter of tomatoes), beta carotene (a yellow-orange pigment and precursor
of vitamin A) are also found present in the vegetable oils.
Seeds exposed to frost during maturation or immature seeds may give oils that
contain higher levels of chlorophyll to a level to make the oil green. These colours are
extracted along with the oils and dissolve in them to give the range of colour from
yellow to deep red.' The pigment level in vegetable oils is reduced during ,processing
of the extracted oils to 'improve the market value of the oil.
(vi) MONO- AND Dl-GLYCERIDES
These are used frequently as emulsifiers. They are mono- and di-esters of fatty
acids and glycerols. They occur naturally in very minor amounts in both animal fats
and vegetable oils. They include alpha and beta monoglycerides as well as 1,2 - and
1,3 - diglycerides. Strl;cturally, they are represented as follows: I
CH2 -01-1 CI-12 - CO(]R2 C'kI? - C(lOR2 C:II2 - ClOOR I I I I
CM - COOR CH - COORl CI-I - 01-1 C'H - 011 I I I I CH2 - OH CH2 - 01.1 CI-I2 - COORI ' (21-12 - 01-1
Alpha-monoglyceride Beta-monoglyceride 1,2- diglycericlc 1,3 - diglyceride
Scheme 1.5: Glyceride molecules
(vii) VITAMINS
Vegetable oils are good sources of vitamin k. The vitamin is present in small
quantity and owes its reactivity to the tocopherol content of the oil. Oils also
serve as good carriers of the fat soluble vitamin A (retinal; a colo~rless
compound considered to result from cleavage of beta carotene) and vitamin D3
(cholecalciferol, a steroid) and vitamin K which include menadione and its
derivatives.
(vii) OTHER MINOR COMPONENTS
Some vegetable oils may contain traces of proteins and carbohydrates which
are almost completely removed during refining. Pesticide residues and metals
(examples, iron, copper, lead, arsenic, cadmium, and mercury), are also found i
present in the oil" as a consequence of crop treatment and environmental influences',
Polycyclic aromatic hydrocarbons are also found in some vegetable oils. In rape seed,
for example, sulphur in the form of elemental sulphur; isothiocynates also occurs. All
of these undesirable contaminants are reduced to negligible level during refining.
EXTRACTION OF VEGETABLE OILS: 1.4.0
Obtaining oils from vegetable sources is of ancient origin. The ,native in the
tropical region of the globe have long been removing these oils from various nuts after
drying them in the sun". The vegetable oil extraction techndogy has evolved in
various phases which include extraction by pressing and solvent extraction processes
amongst other methods.
1.4.1 THE PRESSING PROCESS
The pressing method of oil extraction is in two forms: First, the meal is preheated
to coagulate the protein matter which is largely responsible for the extremely fine state
of division of the oil inethe cells. Secondly, pressing, which is attributed to edible oils,
removes more oils and greater quantity of non-glyceride impurities such as
phospholipids, coloured bodies, and unsaponifiable matter. Heating in the first form
enables the very small oil droplets to coalesce, wl'ile the low viscosity facilitates the
flow from the material to the press. However, oils expressed without pre-heating
contain the least amount of impurities and is often of edible quality. Such oils are
known as cold drawn, cold-pressed or virgin oilq3.
I . L Z ' SOLVENT EXTRAC,TION PROCESS (SEP)
The method of extraction that is increasingly used for seed oil extraction is the
SEP. In this process, low boiling petroleum fraction is used for the extraction. The
boiling point of the solvent must however be optimal to minimize solvent loss at
complete re-distillation of the solvent from the oi! without employing unduly high .
temperatures. The Extractability of the oil has been foundto ,depend on the nature of
the oil, solvent, flake thickness and the pre-treatment condition of the oil seeds16.
Different factors determihe the choice of solvent for oil e~traction'~. These are:
Solvent extractive capacity
Effect of solvent on oil properties ,
Process safety
Solvent volatility '
Stability and
Economic factor.
Ideally, solvents used for extraction should dissolve only glycerides but
not undesirable components such as colouring matter, gums, and phospholipids. For
health concerns, commercial oil extraction is done almost exclusively with normal
hexane. Ethyl and isopropyl alcohols areattracting the most attention as alternative
extracting solvent^'^. Table 1.3 shows the boiling points1 ranges of common extracting
Table 1.3: Extracting solvents in order of decreasing polarity
Acetic acid CH3COOH 1 v: / Acetonitrile * C H X N
1 Ethyl acetate I CH3COOC2H5 I 1 Dichloromethane CH7C17
Methanol Ethanol
CH30H C2H50H
- - I- ~hi0r0~~i-i~~ Carbon tetrachloride
MECHANISM OF SOLVENT EXTRACTION
65 '
78
6 1 76
Benzene C6Hs Toluene . C6H5CH3
- - -
C5H12 - C6H14
N - heptane c7H16 ,
CyAohexane, ' C6H12 .
Solvent extraction of oil has been shown to be temperature dependent. The study
80 11 1
90 - 100 - 40 - 60160-80
36 69 94 8 1
on the effect of temperature on the extraction of rubber and melon seed oils shows
that; the yield increases with increase in temperature.' It reaches its maximum value at
the boiling point of the solvent16. The extraction involves several mechanisms, viz'":
(i) Freshly harvested seeds are cleaned of trash, foreign weeds, and stones which
may hirbour moisture that could accelerate the formation of free fatty acids. It is then
dried before storage. If this was not done before storage, it must be done before
extraction.
(ii) Removing hulls by cracking, aspirating or screening operation.
(iii) Cracking or roughrgrhding the kernels.
(iv) Steaming (tempering or cooking) of the meats or pre-pressed cake.
(v) Extraction of oil with suitable solvent.
(vi) Removing the solvent from the miscella (oil-solvept solution).
(vii) Filtration of the oil to remove solid particles which found their way into the
solution during extraction.
1.4 3 USE OF CARBON DIOXIDE
The latest technique of extraction is a high-pressure critical state extraction with
carbon dioxide. This is mainly applied to high value products such as essential oils, I
hops, and instant coffee1'.
1 5.0 CLASSIFICATION OF VEGETABLE OILS
Two classes of oil exist and these include: those of the mineral and those of
plant and animal origins1'. Oils from the plant and animal origins contain: Carbon,
Hydrogen and Oxygen as the major constituent elements and are known as natural
oils. Natural oils are further classified as volatile (essential) oils ands non-volatile
(fixed oils). Oils from the mineral origin are classified into petroleum, shale oils, and
coal tar; hence, are referred to as synthetic oils. Synthetic oils are complex mixture of
hydrocarbons with varying amount of Oxygen, Nitrogen, and Sulphur compounds
togeiher with ~ ~ d r o ~ e n and Carbon.
1.5.1 . VOLATILE (ESSENTIAL) OlLS
Volatile oils are the odourous substances found in various plant parts and are
also referred to as essential oils. They evaporate easily when exposed to air at
ordinary temperature. They vary from colourless to yellow or brown due to oxidation
and rancidification when exposed to air for sometime. To avoid darkening, volatile oils
are stored in a cool, dry place (in tightly stoppered amber glass c~ntainbrs)~. Example
of volatile oils include certain phenols and the/r esters such as Eugenol (oils of
15
Cloves),.Soeugenol (oils of nutmeg), Anetbole (oil of aniseed), Vanillin (oil of vanilla
bean), thymol (oil of thyme and mint) ', etc.
Volatile oils are used as flavouring and fragrance in various applications,.
blending these oils (example, mint and cinnamon for toothpaste, mouthwash, etc) also
make possible some fragranced products such as room fresheners, paper, printing
ink, paint, candle, soap, condiment, floor polish'g.
1.5 .2 NON - VOLATILE (FIXED) OILS
Fixed oils are obtained from either plants or animals. Their basic characteristic
is food storage such as essential ingredient like vitamins, proteins, etc which aid
growth and development. Fixed oils and fats are important products which are used, as
pharmaceutical components because of their emollient properties. Thus, it becomes
the principal constituent of many drugsq8.
Their composition differs from essential oils since they contain mainly
glycerides (fatty acid esters of glycerol). The degree of unsaturation of the fatty acids
involved affects the melting 'point of the ester. The more unsaturated acids give esters ,
with low melting points; as a result, non-volatile oils can be classified into fatty oils and
the fats". Fatty oils refer to those that are liquid at room temperature whereas fats are
those that are solid or semi-solid at ordinary temperature.
The classification of vegetable oils can also be based on their ability to absorb
oxygen from the air.On. this basis, fixed oils are classified as drying, semi-drying'and
non-drying oilsz0.
(i) Drying oil
These are oils dch in the glycerides of the unsaturated fatty acids particularly,
linoleic acid with few co,mpounds of oleic acid. On exposure to air, they absorb oxygen
and form a tough elastic but water resistant film. The value of drying oils depends on
their ability to polymerize or dry upon application onto a surface to form tough,
adherent, in~pervious and abrasion-resistant film. They are used as important solvents .
in paints, artificial rubbers, linoleums and varnish industriesz0. Examples are linseed,
tung (China wood) oil, castor oil, oiticia oil and tall oils amongst others; which provides
fatty acids for use in non-yellowing alkyds and find its primary Use,in the industries.
(ii) Semi - drying oil
' The intermediate between drying and non-drying oils is the semi-drying oil.
They are slow drying when compared to drying oils and their fatty acids are valuable
components for making non-yellowing alkyds. Large amounts of linoleic and other
saturated acids are" present but no linolenic acid. When exposed to the atmosphere,
they thicken but do not form a hard, dry film. The film remains sticky (tacky), and
absorbs atmospheric oxygen slowly producing a soft film after prolonged exposure to
air. Examples of'semi-drying oils include: tobacco oil, corn oil, melon oil, soybean oil,
etc. However, paints of lower grades could be made by mixing full-drying with semi-
drying oils.
(iii) Non-drying oil
Non-drying oils remain liquid at normal temperature and are incapable of
forming elastic film after long exposure to air. They are important sources of fatty
acids used in non-drying alkyds. Castor 'oil and coconut oil are best known examples.
Others include groundnut oil, palm oil and olive oils. They are occasionally used as
plasticizers for spirit and lacquersz'. Also, they .enter into soaps and cleanse'rs,
cosmetics, lubricants, leather dressing, and candles.
The drying rate of. oils can be determined as the rate at which a thin film of oil
exposed to air changes to a solid non-tacking skin. The rate m,ay be accelerated when
a small quantity of metallic compound called drier such as linoleate acids, and
naphthanates of lead, manganese and cobalt is introduced into the oil. The driers
therefore act as oxygen carriers to the sensitive centers in the oil molecules.
I 5 3 OTHER CLASSIFICATION
Oils can also be classified as being edible and non-edible. Various edible oils
such as soybean, corn, cotton seed, melon seed oils etc are basically employed for
cooking purposes, salad dressing and other table uses. Hydrogenated fats for cooking
and baking may include a wide variety of vegetable oils such as cotton seed, palm oil,
and soybean oil. The hydrogenating process improves the odour or flavour of the
original crude product as well as its keeping factor.
The non-edible oils on the other hand are oils used for soap making and those
found useful in paints and varnish industries etc. ,Some of the oils are slightly
hydrogenated to make them suitable for use. Drying oil industries 'consumes a large
percentage of non-edible oils. These drying oils are essentially unsaturated and
produce film or coating upon oxidation. They are also employed with synthetic resins
and cellulose derivatives to give special types of films.
1.6.0 REFINING OF VEGETABLE OIL
Extracted oils are 'crude' as they contain small quantities of compound other
; than triacylglycerol esters22.. Crude fats and oils contain variable amounts of non-
glyceride impurities such as sterols, phosphatides, free fatty acids, certain pigments
(carotenoids, chlorophyll, xanthophylls, etc), metals etc which are susceptible to
foaming and smoking on heating and liable to precipitation of solid materials when the
oil is heated during processing operations.
There are three basic objectives for refining and processing crude fats and
oils. These are:
(i) to remove free fatty acids (FFA); phospholipids (gums), pigments and off
flavour/odour compounds and toxic substances to produce light-coloured .
products with long shelf lives.
(ii) to obtain a mixture of triacylglycerol with the desired solid content profiles over
the range of products use.
(iii) to prepare and store semi-solid products with desired textures17.
There are various nlethods of refining and the one chosen is dictated by the end
use of the oil. The solid contaminants however are removed by filtration or
decantation. The classical oil refining procedure consists of degumming,
deacidification, decolouration, dewaxing, deodourization and acid wash.
1.6.1 DEMUNlFlCATlON OR DEGUMMING
This process involves the removal of phospholipids, which may have been
extracted alongside the oil, to avoid darkening the oil during high temperature
deodourisation. The process generally involves treatin,g the extracted oil with a limited
amount of water to hydrate the phosphatides and make them separable by
centrifugation. Super degumming step is that where citric acid, glycerin, or phosphoric
acid is. added to remove phospholipids that are not hydrated by water alone.
Sometimes the degumming is done to recover and further process the phospholipid to
yield a variety of lecithin products which are good emulsifying agents. The degumming
temperature is between 50-70°C above which there is increased solubility of the
phosphatides in the bi~. 'At.temperatures below 50°C, the high viscosity of the oil ' ,
makes separation of the phosphatides more difficult.
1.6.2 DEACIDIFICATION
The degummed crude vegetable oil is then neutralized with alkali to form sodium
salts of fatty acids which are removed (as soap stock) by continuous centrifugationz3.
Large amounts of these free fatty acids in oils are not desirable because:
(0
(ii)
(iii)
The unsaturated free fatty acids are more sensitfve to oxidation than the
corresponding glycerides and this can reduce the shelf life of the oil.
Free fatty acids interfere with hydrogenation by being selectively adsorbed '
on the surface of the catalyst through either of the carbonyl groups. This
hinders the hydrogenation process of the glycerides.
Low acidity in oils favour fast bodying and good colour in bodied oils and
vanishess.
The soap stock also occludes some phosphatides, colour and flavour compounds on
each percent free fatty acids (%FFA) present.
This process is also referred to as ALKALI REFINING and can be carried out
either with dilute or concentrated solutions. Concentrated solution of the alkali has a
more powerful demunification action than the dilute solution. It is good for
undegummed vegetable. oils because it causes greater saponification of the
glycerides than the dilute solution. Foots (soap stock) after separation may be used
for soap production. Thus, calcium chloride may be added directly to the soapstock for
prompt separation of the calcium soap (by precipitation) from a relatively pure saline
(NaCI) solution. Calcium, soaps are useful industrial ingredients for instance, as
demoulding agents22.
1.6.3 DECOLOURISATION
Bleaching is the heating of the oil with adsorbent (bleaching earth -example,
activated carbon, fuller's earth or acid activated montmorillonite clays) which ensures
an almost complete elimination of colouring matters in the vegetable oil. During
bleachirlg, phospholipids,'soaps, peroxides, aldehydes and other polar compounds
are also adsorbed alongside the pigment. The spent adsorbent is then recovered
through filtration although it is plagued with disposal problemad. The process of
decolourisation involves three basic methods:
(i)
(ii)
(iii)
Oxidative bleaching: this is mostly applicable to saturated oils. It has to do with
the blowing of air into the oil at an elevated temperature (about 1 10°C). Some
quantities of cobalt, manganese and iron salts are used to accelerate the
process8.
Adsorptive bleaching: ,bleaching earths are used which, due to its large
surface area, largely removes the pigment type molecules without damage to
the oil itself. It'is the method used for bleaching edible oils and oils for the
surface coating industries. :
Heat bleaching: oils are heated t~ high temperature under high vacuum with
the addition of stripping steam to enable some pigments like carotenes become
colourless. This method leaves the pigments in the oil which may have adverse
effect on the quality of the oil.
There are indications that the earths in adsorptive bleaching, also adsorb
polymers probably polar o ~ ~ ~ o l ~ m e r s ~ ~ . Adsorptive bleaching has been applied in
bleaching a number of oils including palm oil, melon and' ~ i l b e a n ~ ~ , although colouring
matter in soybean, linseed and rapese'ed oils resist this treatment.
Bleaching earth is by far the most widely used adsorbent ma'terial though in
many cases, the bleaching effect obtained with the carbon is greater and it adsorbs
various other substances that have objectionable taste or odour.
To minimize the loss of oil during adsorptive bleaching, solvent (e.g. hexane) is
added to increase the adsorptive capacity of the bleaching earthZ6 and the colour of
the bleached oil decreases linearly with increasing dilutions in the solvent27. The oil . '
. 21
remaining in the filtered cake may be up to 20-40% and can partly be recovered by
any or a combination of the following processes:
Blowing steam on the cake
Circulating hot water, and or hexane through the cake in the filter.
Mixing the cake with oilseed and passing it through the extraction process.
Extraction of the cake with hexane and
Boiling the cake in water containing soda and salt.
DEODOURISATION
Superheated steam is blown through the oil at hydrogenation temperature to
remove volatile odouriferous component present in the oil. These include: volatile
pesticides, aldehydes, tocophens-like natural antioxidants, and residual amount of
free fatty acidsz8. The natural antioxidants may be recovered from the deodourised
condensate and the final refined, bleached, and deodourised product is called RBD
oils (Scheme 1.6).
Deodourisation is conveniently carried out at pressure 1.5 - 9mmHg and
temperature 175 - 270°C. Removal of pesticides from the oil requires a
deodourisation temperature greater than 240°C; but in some cases, example in the
cocoa butter processing, it is essential to use low temperature preferably less than
180'~. A small amount of concentrated citric acid solution is normally added during
deodourisation to scavenge any metal present in the oil.
In scheme 1.6, the degummed oil may be subjected to minor bleaching and
then physically refined using a high temperaturelvacuum process that strips away the
compounds normally removed in the deodouriser plus the free fatty acids2'. The major
advantage of physical refining is reduction of oil loss that occur by occlusion. On the
whole, deodourisation may not be done in oils for paint industries, but a must for
edible fats and oils.
' CRUDE VEGETABLE OIL
1 Water -+ Degumn-ring -, Cmde I ,xithin 1
1 Alkali + Alkali Refining -, Soap stock
1 REFINED OIL
1 Activated -, Bleaching - Spent Earth Earth 1.
BLEACHED OIL 1 +
Deodourization -+ Deodousized Condensate Bleaching and Physical Refining
RBI)
Where RHD represent: Refining, Bleaching, and Deodourization
Schcn~e 1.6 Vegetable Oil Refining Steps
This is applicable only to a few oils like the su~;;lower oil, maize oil, and linseed , I
oils which contain some wax from the seed shells that makes the oil cloudy at low
solubility. The quantity of wax in crude oil varies from a few hundred to over 2000ppm.
Wax content in the oil has to be reduced to a level of about 10ppm (by dewaxing) to
enhance sufficient cold stability of the oil3'.
All materials that will solidify-out at ; refrigeration temperatures are removed
during dewaxing and this is accom&hed by cooling to 5OC and filtering-out any
solidified material. It can be'carried out on the micelle from a seed extraction plant or ' .
in combination with neutralization. The traditional method of dewaxing as applied to
the refined oil is similar to fractional crystallization (Winterisation).
' 1.7.0 CHARACTERISATION OF VEGETABLE OIL
Proper identification and assessment of quality and purity of vegetable oil is achieved
by characterization using a number of physical and chemical constants. Whereas the
physical constants include: melting point, density, refractive 'index, viscosity, colour,
solubility etc., the chemical constant include: iodine value, saponification value,.acid
value, and volatile fatty acid contents. 1
1.7.1 PHYSICAL CONSTANTS
(A) MELTING POINT
Oils generally,represent the melting points of their constituent fatty acids which
define its properties. Melting point increases with chain length and where only one '
double bond exists (e.g Clo : I ) , the melting point is lower if the double bond is located
after an odd number carbon than even number carbon . Also, the melting point is
lower if the double bond is located near the middle df the chain as compared to one
located at either ends. The melting points of mixed triglycerides (whether animal or
vegetable sources) consisting primarily of 16 to 18 carbon fatty acids generally rises
smoothly with increased'content of higher melting fats. Geometric isomers reveal that ,
trans fatty acids always have higher melting points than their cis counterparts for any
chain length3'.
However, the same sample of pure or mixed fatty acid triglyceride may show as
; many as five different melting points depending on its heating and cooling history".
Thus, tristearin has an amorphic (non-crystalline) solid form and three crystalline
forms with melting points at 54.7'C, 63.2OC, and 73.5OC.
Therefore, different methods exist1' for the determination of ,the melting points of
triglycerides. These are:
(i) Capillary method: ahis determines the temperature at which a sample of I
(ii)
(iii)
(iv)
2 4
fat in a closed capillary becomes completely clear and liquid.
By matter dropping point : the method determines the temperature at which a
sample becomes sufficiently fluid to flow in a specified apparatus.
By open tube-softening point: this determines the temperature at which a
solidified fat, in an open capillary tube, softens sufficiently to slip and rise to the
top of the heating bath. It is applicable to fats such as coconut oils, stearin,
hydrogenated fats and hard tallows. The results, 'sometimes, are reported as
'melting slip points'
Wiley method: determines the temperature at which a sample disc of solidified
fat assumes a spherical shape while suspended in a heating bath with an
alcohol water density gradient.
Factors that affect melting'points of different samples include:
(i) the types of the fatty acids present in the triglycerides and their locations
(ii) chain length of the fatty acids
(iii) number and location of cis and trans double bonds on the fatty acid chains.
(iv) type of crystal present.
(B) VISCOSITY
Oils owe their relatively high viscosity to the intermolecular attraction between
their fatty acid chains, which has to do with the rate of flow of the molecules against
one another. Measurement of viscosity is important in the study of the polymerization
of drying oils and also i r connection with the technical properties of polymerized oils
for the paint industry. Solution viscosity of oils has been used to elucidate the mode of
network formation in drying oils32. Generally, viscosity tends to increase slightly with
increasing chain length. The linear relationship between log viscosity and temperature
is seen in the increase of the viscosity of oils in prolonged heating due, to the
formation of dimeric and oligomeric fatty acid groups. Table 1.4 gives the viscosities 'of
some faky acids as a function of chain length.
Table 1.4: Increase in viscosity with chain length
[ ~ r y ~ ~ ~ w - k
- - Tricaproin -- Tricaprylin 8.8 --
NO.CARBON ATOMS (MPa.S)
1 Tristearin 18 23.4 -1 Trimyristin . 1 14 I Tri~almitin 16
DENSITY
17.6 20:5
This is a measure of the mass to volume ratio of the oil. It decreases with
increasing molecular weight, degree of unsaturation and free fatty acid contents., It
can be calculated using the formula in equation 1 .16
Density = 0.8475 + 0.0003*saponification value + 0.00014*iodine value 1.1
Oxidation generally leads to higher densities. High free fatty acid content tends
to decrease the density of crude vegetable oil. Up to 260°C, the density decreases by
about ~0.00064~lcrn~ per temperature increase of I0C. For most fats and oils, the
specific gravity lies between 0.90 and 0.94 at 20°C.
Table 1.5: Density of some triglycerides TRIGLYCERIDES NO. OF DENSITY
CARBON ATOMS
Trica rin Trilaurin
Trimvristin
Trilinolein 18:2 Trilinolenin 18:3
G / c ~ ~ At 15OC
1- Tripahitin Tristearin
10 12 : I 4
0.891 3 0.8801 0.8722
16 18:O
0.8663 0.8632
(D) REFRACTIVE INDEX
The refractive index generally increases with the degree of unsaturation,
average molecular weight of the oil (chain length), and the extent of conjugation of the
double bonds. It is one of the most important aids for classifying fatty acids since it is
closely related to the nature of the product (molecular weight and degree of
unsaturation) and can be determined quickly with great accuracy8. Table 1.6 gives
refractive indices of different fatty acids as it increases with chain length and
unsaturation. Prolonged. heating leads to increase in refractive index due to the
introduction of polar groups into the fatty acid chain. Equation 1.2 gives the
relationship between refractive index for fresh, non-hydrogenated oils and fats and
other oil parameters states thus:
Saponification value (S.V)
Table I .6: Refractive indices of fatty acids.
FATTY ACl DS
Tricaprin Trilaurin
Trimvristin
I ,
Tripalmitin Tristearin
(E) COLOUR
10 12 14
Triolein Trilinolein
The colour of crude vegetable ,oil is determined by the nature of oilseed being
1.4370 1.4402 1.4428
16 18:O
extracted and the power of the solvent used for the extraction. The colour is important
1.4452 1.4471
L
18:l 18:2
in judging quality and determining the degree of bleaching. In some oilseeds, the
colour disappears campletely after bleaching.
1.4645 1.4645
(F) SOLUBILITY AND MISCIBILITY
The solubility of fats and oils in organic solvents decreases with increasing
molar mass and increases with degree of unsaturation. It plays a part .in determining
the immiscibility curves of oil or fat in various solvents and may be used to check the
purity of the oil. Nearly all fats and fatty acids are easily miscible in common organic
solvents such as hydrocarbons, chlorinated hydrocarbons, ether and acetone. The
difference in solubility enables categories of glycerides to be separated by fractional
crystallization although complete separation is rarely achieved because of mutual
solubility effects. The solubility of oils in water is low. It decreases with increase in
chain length and increases with temperature.
1.7.2 CHEMICAL CONSTANTS
(A) Iodine value (Number)
The iodine value is used'to determine the degree of unsaturation by measuring
the number of milligram of iodine absorbed per gramme of an ,oil sample. The extent
of rancidity is also indicated by the amount of iodine consumed33 since iodine is added
across €he double bonds of the fatty acids. The higher the iodine number, the greater
is the unsaturated fatty acid content. The Wij's method is most commonly used for its
determination though; it can be inaccurate with conjugated systems. The effect .of
temperature on unsaturation could be expressed by the iodine number of the
triglyceride34. However, the importance of determining the iodine value is to classify
the oil according to its drying ability as indicated in table 1.7.
Table 1.7: Classes of oil and their iodine numbers
I IODINE I CLASS OF OIL I I NUMBER I I
>I 30 Drvina oil I
. t'0%0A30 Semi-drying oil Non-drying oil
(B) ACIDVALUE
The acid value is used to express the degree of acidity of the oil. It is defined as
the number of milligramme of potassium hydroxide (KOH) required to neutralize the
free acids in I g of the sample. The importance of acid value lies in the fact that it
measures the free fatty acid content in the oillfat. It is especially important for judging
the quality of raw oils and for determining the quantity of alkali required for alkali .
refining of oil at minimal saponification. Solvent selectivity towards phosphatides
affects the acid value of fatty acids and the presence of 1 O/O phosphatide.increases the
acid value by 0.30 - 0.35 M ~ K O H ~ ~ . Different extraction solvents often give different
acid values for the same oils8. One unit acid value is equivalent to 0.503% free fatty
acideg .That is:
%FFA = 0.503 * acid value 1.3
(C) SAPONIFICATION VALUE
Saponification value gives the number of miiligramme of potassium hydroxide
(KOH) required to neutralize the fatty acids resulting from complete hydrolysis of l g of
fatloil. It indicates the average molecular weight of fatty acid present and is related to
the molecular weight by the expression:
where M.W is the average molecular weight, S.V is the saponification value of the oil .
and A.V is the acid value.
Saponification value does not change appreciably by polymerization, but
increases with oxidation. Low molecular weight glycerides have high saponification
value (example coconut with S.V = 260.267) which reflects ,the presence of high
percentage of fatty acid with CIZ or less carbon atoms. A high molecular weight
glycerides have low saponification value (example, soyabean with S.V = 189 - 195)
which reflects a large percentage of C16 and C18 carbon atoms of fatty acid35.
(0') Reichert-Meissle, ~olenske and Kirschner Value
The amount of steam-volatile fatty acid which can be recovered from oils under
standard conditions is measured by Reichert-Meissle Polenske and Kirschner values.
The acids involved include: butyric-C4, caproic-C6, caprylic-C8, capric-Clo, lauric-Cq2
Butyric and caproic acids are water- soluble while caprylic and lauric acids are water-
insolubleA. The water-soluble and water-insoluble acids are measured by ~eichert
value and Polenske value, respectively. The Kirschner value measures butyric acid 6y
separati6n from caproic acid precipitating the'later as a silver salt.
1.8.0 USES OF VEGETABLE OILS
The report from Food and Agricultural Organisation in collaboration with the
World Health ~ r ~ a n i s a t i o ' n ~ ~ shows that fats and oils have both domestic and
industrial applications. As such there are both edible and non-edible uses of vegetable
oils,
1.8.1 EDIBLE USES OF OIL
Oil and fat products used for edible purposes can be divided into liquid oils and
plastic fats. The liquid oils include peanut oil, soya bean oils, sunflower oils, olive oils,
etc. the plastic fats include butter, lard, shortening, and margarine. The primary use of
fatty oils is closely related to man's desire for food. As earlier stated, fats and oils are,
the most concentrated saurces of energy in the diet and they are dlso important
sources of oil-soluble vitamins like vitamins A and D. They are also good sources of
vitamin E which is present in tocopherols.
Researches carried out by food scientists and biologists reveal that; of the two
dozen fatty acids availa'ble, two cannot be synthesized within the animal's body.
These include linoleic and linolenic acids and are referred to as essential fatty acids
(EFA). These are said to govern every life process in the body and also include
prevention of distinct heart and vascular diseases. This, therefore, promotes the
production and application of vegetable oils with high linoleic acid content such as
melon, soybean, and sunflower oils.
Generally, most seeds are grown specifically for processing to oils and protein
meals and short chain fatty acids are mostly desirable for foods and feed uses.
Hence, the principal consumer of vegetable oils and fats is the edible oil industries.
1.8.2NON-EDIBLE USES OF OIL
The non-edible uses of vegetable oils include the various industrial applications
of oils. In these applications, the level of unsaturation of the oil becomes important. As
indicated earlier, oils are classified as drying, semi-drying and non-drying (Table 1.7).
The drying and the semi-drying oils are mostly employed for the production of paints, .
soaps, and cosmetics. Only recently, have the non-drying oils been found useful in the
formation of plasticizers in paints and vanish industries aswel l as in the cosmetics
industries where they are mostly used as emulsions. The non-edible use of oil
employs the long chain fatty acid which has been in demand for production of
lubricants and polymers. On this note, linseed oil, soybean and castor oils can be
used as lubricants. Castor oil can also be used as a hydraulic fluid.
Hydroxyl fatty acids are used for thickening greases and improving the pliability
of plastic covering materials. Epoxy fatty acids are useda in the production of plastics
and coatings.
Fatty acids with conjugated unsaturation are often desired as chemical
intermediates in industrial products e.g. tung oil. Conjugated unsaturation can be
obtained by alkali isomerisation of soybean and linseed fatty acids. Novel sources of
conjugated unsaturation in vegetable oils include: valeriana officinalis (40%
unsati~ration at positions 9, 11, and 13), candendula officinalis oils (55% unsaturation '
at positions 8, 10, and 12), centranthus macrosiphon oil (65% unsaturation at
positions 9, 11, and 13), and impatiens edgeworthii oil (60% unsaturation at positions
9, 11, 13, and 15).
The following authorities have studied other uses of vegetable oils for non-
edible purposes: peterson3', who studied 'vegetable oils as diesel ,fuel' and
~aufmann~' , studied 'field evaluation of sunflower gilldiesel fuel blends in diesel
engines'. Others are ~ o n w e r ~ ' and schwab4' who studied 'liquid fuels from Mesua
ferrea linseed oil' and 'diesel fuel thermal decomposition of soybean oil', respectively.
1.9.0 DlMER FATTY ACIDS (DFA)
The term dimer fatty acids is applied to the dicarboxylic acids formed as a product
of thermal polymerization of two or more CI8 unsaturated fatty acids such as oleic and
linoleic acids. Commercial DFA products are mixtures of C36 dibasic acids containing
some trimers (C54) and hlgher oligomers. Small amounts of monomer acids (CI8 and
saturated, unsaturated and structurally modified fatty acids)42 are also present in the
product. The main constituent is substituted cyclohexanes, which arise through Diels
Alder reactions. DFA is used to synthesize a fatiy polyamide by reacting with
ethylenediamine to produce either solid or liquid polymers. The solid polymers are
largely linear products obtained by reacting dimer acids with diamines, while the liquid
polyme;s are highly branched products of tower molecular weight, which result from
the reaction of dimer acids and polyamines containing three or more amino groups43.
1 I, 1 PROPERTIES OF DFA
Dimers from fatty acids having 18 or more carbon atoms are a mixture of 36-
carbon atoms dibasic acids, 54-carbon atom tribasic acid (trimer acid), 18-carbon
atotn monomer and structurally modified monobasic fatty acids. The mixture is
characterized by increase in the acid number of the polymerized oil. These dimer
acids have the unique advantages of being hydrophobic, with high molecular weight,
and generally having sdme degree of unsaturation and are dibasic. Both the
unsaturation and the acid functionality provide sites at which further chemical
tnodification may be undertaken. The degree of unsaturation of the dimer acid may be
reduced by hydrogenation to enhance its stability.
The formation of a conjugated system in the fatty acids' leads to a rise in the
refractive index. The physical and chemical properties of the dimers of trienoic acid
suggest the formation of a bicyclic structure by an intra-molecular ring closure which
follows the 1,4-diene addition reaction. Thermal polymerization can also lead to the
formation of acyclic dimers which occurs predominantly by the free radical
mechanism. A bicyclic dimer could also be formed as shown in scheme 1 .I 1
CH3(CH2)8CH(CH2)7COOH I
CH3(CH2)7C = CH(CH2)7COOH
C143(CH2)3CH=C'I I Acyclic Dimer Acid
Monocyclic Dimer Acid
Scheme 1.7 Structure of various C36 compounds of DFA
The relative proportion of each of these structu'res in the feedstock of
d i rner i~at ion~~ is as stated in Table 1.8.
Table 1.8: Proportions of dimer structures in the feed stock..
ACYCLIC / Oleic and 40
Linoleic acid
---A-
MER STRUCTURES,
Apart from the structures above, many other structures including aromatics
\ have been found among the products of d imer i~at ion~~. Von ~ i k u s h ~ ' stated that the ,
logarithm of viscosity plotted against time for dehydrated castor and linseed oils
undergoing dimerisation, approaches a straight line; the slope gives a measure of the
polymerization rate. cannegieteaO showed that the polymerization rate constant K is
given by the expression:
where Vq and Vl = viscosities at times Tq and TI, respectively, for samples removed
during the progress of any one cook at a constant temperature. It is howev,er
impossible to obtain reliable polymerization rate data in open kettle laboratory cooks,
especially with smaller quantity of oil. Generally, the composition of a dimer influences
its properties as shown in Table 1.9.
Table 1.9: Composition and properties of commercial DFA.
I PROPERTIES , I
Dirner content (%) 'Trimer content (%)
I I Unsaponifiable
matter(%mass 1 0; " 1 1 .o ! L---
! Colour (Gardner max) 9
. I . Monobasic acid '(%) ,
i Acid number (MgKOHIg) I
1 Saponificationvalue 1 (MaKOHla)
.-
TYP€ OF DlMER FATTY ACID
~.T 1.5 r--i I
190,- I98 -- 190 - 197- 189 - 197 -- 195 - 201 191 - 199 191 - 199,
Higher dimer 87 13
: . - .-. - Viscosity - .- (at 23OC) Cst I S~ecific aravitv (1 00/25°C) k 0.91
1.9.2 USES OF DlMER FATTY: ACIDS (DF.A) !
0.91 , . Density ( K g l ~ ' L ~efractiv%-hdex (at k ° C )
DFAs are used in adhesives, ink and surface coating formulation, reactive and
Intermediate &h trimer
non-reactive polyamides, corrosion inhibitors (basically, trimers), and metal working
83 -- 15.3
952.4
~ubr icants~~. When incorporated into adhesives, dimerised fatty acids offer the
following benefits:
PA-
75 - 23.5
I --
(i) better bond stability due to flexibility that comes with the dimer building
block which allows the absorption of mechanical stress, even at very low
1.484 353.6
temperature.
953.6
(ii) better adhesion due to the improved flow behaviour between the adhesive.'
i Pour point (OC) 1 - 1 0 -4 -4 1.481
(iii) Durability of the adhesive bond is improved due to dimer's intrinsic water .
1.484
repellant, and its inertness towards dxygen and heat.
DFAs are widely used in polyamide hotmelt adhesives as conventional
polyamide tends to have too high a melting point to be of practical value as hotmelt
adhesives. The incorporation of DFA allows the synthesis of polyamides within a
practical range of melting points.
They are also used to manufacture improved biomedical apparatus which $are
essentially intended to be affixed, or adhered in any manner to a patient's skin such
as: electrode bandages,. iontophoresis devices, surgical tapes, transcutaneous
electronic nerve stimulation (TENS) devices, and ostomy appliances. These
adhesives have advantageous skin compatible properties56. These biomedical
adhesives are pressure sensitive and are inherently tacky, hydrophobic, skin
compatible, adhesive composition.
The fatty dimer acids are also used in the production- of dimer soaps (ie dimer
acid salts), dimer esters, dimer amides, dimer glycols, dimer diisocyahates or
essentially any other acid derivative which is sufficiantly reactive5". The dimeric
product of sesame oil has curative properties on skin lesions such as chronic
dermatitis, eczema, and tenia57.
1 . I 0 THERMAL POLYMERIZA~ION OF DRYING OILS
Drying oils in general are mixed glyceryl esters of oleic, linoleic, linolenic, and
eleostearic acid as well as related saturated and unsaturated acids. The process &
thermal polymerization involves heating drying oils in a n inert atmosphe.re to
temperatures in the range of 300°C and above. The amount of unsaturation
decreases rapidly, and their density and viscosity increase44. Under this condition, the
polyunsaturated CI8 fatty acids present in the oil is dimerized to form mixtures'of C36
dibasic acids with some trimers (CS4) and higher oligomers. Small amounts of
monomeric fatty acids which include Cqa saturated, unsaturated and structurally
modified fatty acids are alsc present.
Although catalysts are not necessary, their use is to lower the temperature and
time necessary for the dimerisation to occur. The reaction passes through the process
of isomerisation ,of the double bonds in the polyunsaturated fatty acids. Scheme 1.7
shows a typical alkaline isomerisation process of linoleic acids which gives a mixture
of 9, 11 and 10, 12 di,enes with many minor components. This is produced
commercially for use as conjugated linoleic acid (CLA).
CI-I~ ( C I I - I ~ ) ~ C I I = CH - CI-I = CH - CI I ~ ( C ' I 1 , )~( '001 I 10,13- Octadccadienoic acid
CI I3 (CI-12)jCI-I = CI-I - CH2 - CI-I= CI-I(C1 12)7C001-I . f
9, 12- Octaclecadienoic acid (Starting ma~erial)
( C H ~ ) ~ C I I~ - CH = CI-I - CH = CH - ( C I - I ~ ) ~ C ~ O I - I 9,11- Ocladecadienoic acid
Sclicnlc 1.8 Isomeriation of Lholeic Acid
The dimerisation process is predominantly a bimolecular additive reaction of
the unsaturated fatty acid radical where one double bond of a thermally generated
conjugated form reacts directly with one or more other non-conjugated double bonds
in a Diels-Alder type of reaction. This is shown in schemes 1.8 and 1.9for gylcerides
45 ' containing linoleic acid group. The sequence of reaction for the thermal
polymerization of methyl linoleate in the bulk has shown that the isomerisation stage is
the rate controlling stage in'the thermal polymerization of drying oils. The sequence of
reactions is given in scheme 1.8.
The observations that can be made of the change that take place during dimerisation,
when treated under the above conditions may be summarized in the following
manner:
(i) a relatively slow rearrangement of pentadiene group to conjugated diene
groups.
(vii)
the rapid reaction of the conjugated diehes with another linoleic group in
the same triglyceride, the product containing two double bonds for two
octadecadienoic acid groups.
with the rapid decline of linoleic radical content, formation of another
product by the union of a conjugated diene with a single ethenoic group not a
part of a pentadiene system and containing one double bond, for each 18-
carbon radical.
migration of a hydrogen atom from a methylene'group, wI3ich is between two
double bonds or adjacent to a single double bond, to 'a carbon atom in a
conjugated diene, thus, linking two 18-carbon units by a carbon-carbon
crosslink.
completion of chemical changes in unsaturated molecules at the stage the
viscosity is about 20 poises, followed by a slow, but steady decrease in linoleic
acid content. This is accompanied by a small increase in monoethenoic
unsaturated compounds. Finally, a rapid increase in viscosity with little change
in the constitution of acid groups occurs.
formation of new dimeric groups between different triglycerides or linkage of
dimeric groups within a triglyceride molecule to similar groups in other
N - C Relatively slow
N+N-D Minor reactions
N+D-T
where N = Non- conjugated linoleate, C = Conjugated linoleate, D = dime!., T = Trimer
Scheme 1.9 Sequcnce of thermal polynierisation
=it1 \ Non-conjugated Iinoleic acid
Scheme 1 .I 0: Diene reaction'of two Conjugated (9 , 11) linoleic Acids
1.1 1 ISOMERISATION AND DlMERlSATlON CATALYSTS
The faster rate at ,which conjugated esters are polymerized compared to the
, non-conjugated esters led to the search for means of introducing conjugation into
dryinglsemi-drying oils. This process is referred to as isomerisation and is facilitated
by the introduction of certain catalysts into the thermally polymerized oil. It is evident
that, isomerisation of the double bonds, from the na:urally occurring cis- to the
conjugated trans- configurations of fatty acids, precedes dimerisation. By so doing,
the process time and temperature of dimerisation is highly reduced and the crude'
product, which usually contains about 60 - ?o% dimmer, is formed46. The dimer
content can be enriched to obtain products up to 97% by standard separation
technique such as vacuum distillation, recrystallization, urea adduction, liquid and size '
exclusion .chromatography .etc. However, only the distillation method has wide
commercial application. The rest are used for laboratory analytical purposes.
Useful isomerisation catalysts claimed by various patents include nickel,
aluminium, alkalis, phosphoric acid (H3PO4), dioxonitrate , sulphur (iv) oxide,
nnthraquinone, phenanthre~e, silicon, selenium, montmorillonite clay, boron triflouride
(9F3). Anyaogu ( 2 0 0 3 ) ~ ~ reported the following as useful isomerisation catalysts:
iodine, sulphur, bromine, hydrogen fluoride (HF), sodium hydrogen sulphate
(NaHS04), etc. They are used to effect isomerisation ,in the polyunsaturated, non-
conjugated fatty acid, to its conjugated form and to lower the temperature and time,of
dimerisation. The neutral clay and water mixture, for example, is reported to reduce
process cbnditions to 230 - 260°C at 2 - 4 hours when conducted under pressure47v
In another case, S U Z U ~ ~ ~ ~ , employed synthetic silica-alumina to catalyze
dimerisation, and reported a process' condition of 290 - 310°C at 1 - 2 hours of
dimerisation. ~imerisation, catalysed by iodine appears to be highly efficient with
respect to time reduction4'. Wang and ~ a o ~ ' reported that by the addition of just
about 0.0025% of iodine crystal, it is possible to optimally effect the dimerisation of
soya bean oil at 350°C in just 20 minutes under argon atmosphere. chappelow6
states that if selenium or oxides of nitrogen and sulphur are used in the cis - trans
isomerkation (elaidization) of oleic acid, there is virtually, no positional isomerisation.
However, cis-trans isomerisation of linoleic acid and linolenic acid leads to conjugated
double bonds.
1 .I 1 .I SULPHUR AS AN ISOMERISATION AND DlMERlSATlON CATALYST
Cyclooctasulphur is, the most stable form of sulphur at standard temperature
and pressure (STP). The molecules are in the solid, liquid and gaseous phases. The
cyclooctasulphur can crystallize in several different lattices to display the structure of
three solid allotropes to include: orthorhombic (a - sulphur), monoclinic (P - sulphur).
and y - monoclinic suphur.
The orthorhombic a - sulphur is the STP form of cyclooctasulphur whereasthe
monoclinic p - sulphur is formed at 94.4OC from a - sulphur and it contains six Sa I
molecules i.e. 48 atoms in a unit cell with a melting point of 119.6°C . The y -
monoclinic suphur is an allotrope which can be obtained from solutions of cycloocta-S,
and from its melt.
The monoclinic P - sulphur is a yellow crystalline solid with boiling point
(1 19.6OC), it is in equilibrium with a liquid mixture of unknown composition. Around
159.4OC, almost all properties of liquid sulphur (e.g cycloocta - S, P - sulphur) suffer a
discontinuity for example, the change in density and most importantly, viscosity
amongst other physical properties. At 250°C, sulphur is still yellow, but the absorption
is now due to separation of the spectrum of SF, with that of plastic sulphur (polymeric
sulphur) which is dark yellow. Solid polymgric sulphur, obtained by quenching a thin
film of liquid sulphur at 200°C in liquid nitrogen, remains yellow. The absence of deep '
dark colour in solid and liquid polymeric sulphur at 160 and 200°C remains a puzzle,
because the free-radical chains, according to all known theories should be deeply
co~ou red~~ . At higher temperature, above 250°C, the viscosity of liquid sulphur
decreases rapidly, and almost black. Simultaneously, it becomes extremely reactive.
Thus in all, ,except the most pure sulphur (99.999+ %), the colour effect is
obscured by irreversible darkening due to reaction of organic impurities. The critical
properties indicate that liquid sulphur, as well as the vapour,.con~ist essentially of S2,
S3, and S4, with very little S5, S6, S7 where S8 and S p being the most stable form sf the
small sulphur molecules whose ground sthte depicts that of 02. The sulphur atoms (Si
and S3), have their physical and chemical properties similar to those of oxygen (02)
and ozone (03) respectively. Their excited electronic levels also correspond to those
of oxygen and ozone.
In non-polar liquids, cyclooctaslphur and other rings dissolve ,at room
temperature without decomposition. However, it should be noted that.above 150°C,
thermal dissociation of the ring by homolytic scission induces free radical reactions,
recognizable by the colour change. With H2S, Sulphur forms reactive system, as it
does with Iodine, Chlorine, Arsenic, etc. From the above, the mechanism for the
isomerisation and polymerization of drying oils catalysed by sulphur can be seen to
follow a free radical process of hydrogen abstraction by sulphur radical after
undergoing homolytic scission. This is represented in scheme 1 . I 0 (i, ii and iii).
The isomerisation reaction below (scheme 1.10) is likely to occur at the
temperature range of 160-200°C after the formation of sulphur free radicals. The
rationalization of the dienoic radicals and thermal decomposition of the fa'tty acids
occur simultaneously in the system and lead to the formation of free acids. The 9,lO-
and 10,12- isomers of octadecalinoleic acids amongst other fatty acids (oleic) are the
products of isomerisation which is followed by a deep colour change in the mixture at
the temperature range as proposed by eat^'.:
The conjugated linoleic acids produced therefore undergo dimerisation through
different mechanisms. These are: the Diels-Alder mechanism as shown in scheme 1.8
and 1.9 above, the free radical mechanism'occasioned by the numerous free radicals
produced by the catalysts' (sulphur) during isomerisation, which take part in the
dimerisation reaction. Owing to the high temperature employed in the process, free
radicals are generated through hydrogen abstraction and C - C scission especially at
the very high temperature of dimerisation. These mechanism (as shown in scheme
1.8 above) therefore enhances the formation of a mixture of mono-cyclic, bicyclic and
acyclic dimer fatty acid products as in scheme 1 .I 1.
There is catalyst regeneration, insitu, in the reaction mixture which can be
recovered by purification using either gel permeation chromatography or distillation
methods.
( i ) SS A 4S2 Formation of liquid hlotloclinic Liquid sulphur ' sulphur ~~-slllpllll~
> 1 50°C ( i i ) S 2 - 2s:': I-Iomolytic scission 01'
Sulplir~r ' Sulphur radical liquid sulphur
(iii) Hydrogen abstraction by sulphur radical and isomerisation:
Migration of the hydrogen atom during isomerisation occurs predominantly at
the methylenegroup53. Thus:
(CI 12)7 -COOH I I 2-H
/I CH CH
9, 1 1 -0ctadecalinolei'c acid 10, 12-Octadecalinoleic acid
Scheme 1.11 : Mechanism of Sulphur catalysed isomerisation of linoleic acid moiety
CHAPTER TWO I
LITERATURE REVIEW
2.0 HISTORICAL REVIEW
Thermal polymeriation of drying oils co when luld be dated prior to 1940
~ i n o ( 1 936)65, ~ a ~ ~ e l m i e r ( 1 933)6! Steger and Van ~oon (1 934)67 Brod, France, and
~vans(1940)~' gave definite evidence that the methyl or ethyl esters of drying oil acids
polymerized when heated, to form polymer which appeared to be largely dimer. A
more detailed study of the polymerization product of the methyl esters from olive,
dehydrated castor, soybean, linseed, and tung oils was carried out in 1940 by Bradely
and ~ohnson~'. Their work exposed the fact that the predominant reaction of thermal
polymerization is dimerisation leading to.dibasic acid esters. The esters of conjugated
acids dimerised much more rapidly than those of the non-conjugated acids. The
dimers of dienoic acid esters are similar in physical and chemical constants, whether
from conjugated or non-conjugated acids. Their physical and chemical constants
support earlier conclusion that the dimerisation is a 1,4-diene addition, resulting in a
monocyclic cyclohexene structure. These constants also support the Scheiber theory
that isomerisation from the non-conjugated double bonds to the conjugated form
precedes polymerization (cheiber, 1946)~'. Bradely's work also stated that the dimers
of trienoic acid esters are similar to one another, whether from conjugated or non-
conjugated acids. Their ~hysical and chemical constants suggest a bicyclic structure I
formed by an intramolecular ring closure which follows the diene reactions.
During dimerisation, side reactions occur, creating unsaturated hydrocarbons
and esters of low molecular weight. ~ h e s e ' fragments may unite with monomers to
form polymer intermediate whose molecular weight is between normal monomer and
dimer. Besides, Bradely and ~ohnson(1940)~~ reported that trienoic acid esters '
polymerization have low iodine values and high densities indicating a possible cyclic
structure.
In 1941, pure dimer of methyl linoleate was isolated by fractional molecular
distillation of the heat polymerized methyl esters of dehydrated castor oil acids by '
Bradely and ~ohnson~' . In spite of confirming the general nature of the str,ucture, the
possibility of various isomers of the proposed cyclohexane structures was recognized.
It was shown that a certain proportion of trimer was also formed'in the process ,
Drying fat was polymerized under the influence of sulphur monochloride by
Kaufman et al (1 9861~' and was discovered that the action of sulphur monochloride on
drying or semi-drying oils brought about increases in molecular weight, probably by
the mechanism of formation of dithrane rings. Also, in 1938, Kappelmeier polymerjzed
linseed and perilla oils, which contain glycerides of linoleic and linolenic acids with no
conjugated double bonds. I t was shown that a higher temperature or a longer time
was required for their polymerization to be completed.
The isomerisation of linseed oil was studied by Bradely and' Richardson
(1942)~~ on heating them for 2- 3.5 hours at 25OC with 37.5 - 50% aqueous sodium
hydroxide (NaOH). It was found that linseed oil acids gave 41% of doubly unsaturated
and 8.2% of triply unsaturated conjugated acids. It was concluded in the study that
large excess of alkali, slightly increased the rate of isomerisation and that the amount
of conjugation was decreased by long heating of the drying oil.
Blekkingh (1957')~~ studied the effect of catalysts on double bonds migration
and found that migration of the double bond during isomerisation occurred
predominantly at the methyl group when nickel catalyst is used. He stated that no a
migration was observed with elaidinization catalysts (SO2, Se, N2, and 03) or with .
alkali isomerisation.
The effect of temperature on the polymerization and isomerisation of
dehydrated castor oil was studied by Chowdhury and Mukherji (1951)73 to regulate the
polymerization during bodying and to enrich the product with conjugated isome'rs.
They dbselved that at' 250°C and abbve, polymerization predominates over
isomerisation and the optimum temperature for the formation of 9,11 - linoleic acid at
the expense of 9,12 - linoleic acid was 200°C.
~ i l v e r s t o n e ~ ~ studied the dimerisation and polymerization of unsaturated fatty
acids by heating a mixture of dehydrated castor oil fatty acids in the presence of
0.0001 - O.lwt% iodine at 250 - 350°C to give dimer-polymer mixtures. Using
0.0005wt0h iodine and heating the mixture for 2hours at 280°C he obtained a product
of 34.6% yield with a dimerl polymer ratio of 4.1.
Den offer ( 1 9 7 0 ) ~ ~ carried out dimerisation of oleic acid with a montmorillonite
catalyst, to examine sor~ie important process parameters e.g. amount of catalyst, I
water content, stirring intensity, reaction time and pH. A yield limit of approximately
60% (dimers and trimers) was obtained; the remaining 40% of the product consisted
of cis-and trans mono-Unsaturated fatty acids. lnfra red (IR) spectra of these
monomers showed the presence of small amounts of stearolactone groups which
probably resulted from skeletal isomerisation. These results indicate that a fairly large
amount of saturated fatty acids is formed probably by hydrogen transfer; in which
case, dienoic acids could be formed which are readily dimerized to cyclic dimers.
Dimethyl esters of dimeric fatty acid was studied by ~uj ihana and Masayoshi
(1971)'~ by continuous addition of methyl hydroxide to unsaturated fatty acid methyl
esters (safflower fatty &id) having two or more double bonds at 120 - 320°C. Thus,
the safflower fatty acid containing 76.3% methyl
dimerized in the presence of 150g terra alba for 2
linoleate (acid value 0.3) was
hours at 220°C with continuoQs
addition of 642g of 9g0/0 methyl hydroxide to give 1450g dimeric fatty acid dimethyl
esters (acid value 1.6, saponification value, 195.2).
Dsouza Cletus and' Ramaiah ( 1 9 7 6 ) ~ ~ studied the polymerization of sesame oil
in the presence of Pb3O4. The dimeric products upon topical application had curative
properties on skin lesions such as chronic dermatitis, eczema, and tenia.
Studies on the dimerisation of castor fatty acids and their methyl esters as well
as dimerisation of tall oil fatty acid and its by-products were carried out independently
by Suzuki et al ( 1 9 7 8 ) ~ ~ and Suzuki, Osamu and Yamashina (1978)", respectively. It
was found that a synthetic 70:29 silica-alumina had high catalytic activity for the
dimerisation of castor oil fatty acid methyl esters. Dimerisation. of ,castor fatty acids
also occurred in the presence of H3PO4 on Silica-Alumina support. Recinoleic acids
also dimerised over the H3P04 catalyst77. The mechanism involved dehydration of I
octadecadienoic acid, followed by the acid dimerisation. The tall oil fatty acids were
dirnerized over catalysts having phosphoric acid deposited on a high surface area".
'
A study of effect bf catalyst for the catalytic dimerisation of unsaturated fatty
acid or their methyl esters was carried out by Suzuki (1978)77. A synthetic silica-
alumina containing Si02-70, AI2O3-29, Fe203-0.7, C~O-0.1 and MgO-0.1% was found
to have high catalytic activity for the dimerisation of safflower oil and camellis oil and
their fatty acid methyl esters. In the dimerisation of llnsaturated fatty acid with the
catalyst, metal salts were formed which interfered with the dimerisation. Metal salts
did not form during dimerisation of the fatty acid over a catalyst prepared by
depositing H3PO4 on the s'ynthetic silica-alumina.
Oils polymerized in the presence of anthraquinone and amine catalyst have
reduced drying time. This was observed by Yasui et al ( 1 9 8 0 ) ~ ~ when he heated 350
parts of linseed oil in the presence of 3.5 parts of 2 ethylanthraquinone and 1.07 parts
of diphenylamine at 200°C for 1.5 hours to give polymerized oil with acid value 2.9
and drying time (in printing ink) 510 mins. I
Some problems in the synthesis of the mono-unsaturated fatty acid dimer were
determined by Rube Zynska (1981)" when'he carried out the dimecisation of oleic
acid by the ionic method with an activated aluminium and iron. Dimers were obtained
containing <lo% trimers with low viscosity and with iodine value similar to that of the
starting acid.
Shiina and Yukagaku (1982)80 studied the thermal reaction of safflower oil in
the presence of Manganese (11) iodide, Magnesium iodide, and iodoacetic acid, and
comparison was made of the polymerization products. Thus, safflower was heated at
220°C in the presence of .O.Z6mol Mnlz/kg qil for 0.5 - 4hours. The reaction products
obtained after 0.5 or 1 hour was mainly dimers. The main component of the dimer
separated from the reaction products obtained after 1 hour had a molecular weight,of
588 and contained a cyclohexene ring. The reaction product obtained after 4 hours
contained polymers (mol. .Wt 210000) and no dimer was observed. Dimers containing
benzene ring was the main components of reaction products obtained by heating
safflower oil with 0.1 1, mol Mg12/kg oil (200°C/hour) or O.13mol ICH2C02H.
Dimeric tall oil fatty acid was produced through dimerisation at 493 - 523K and
5x1 o5 - 13x10~ Pa with molecular weight 560 - 590 in 9 - 55% yield, depending on
the type of dimerisation catalyst. Best results were obtained with H2SO4 activated
bentonite (I 9831~'. I
Dimer acids with little discolouration were prepared by Arimoto (1987)'~, by
dimerizing tall oil fatty acids over clay catalysts. Treatment was done with H3PO4 and
HCHO, and then purification by distillation. A mixture of tall oil fatty acids (Gardner
colour 4.5, acid number 195.0, 46% oleic, 39% linoleic acid) 7009, Alabama clay 409,
and water 6g was heated for 5 hours at 240°C under nitrogen. It was cooled to 100°C
and mixed with 3ml 85% HsP04 and 2.1g para formaldehyde, then heated for 1 hour
at 1 10°C. The product was cooled to 80°C, and filtered to give 660g crude dimer acid
which was distilled in a falling-film apparatus to give 302g dimer acid (acid number
195.5, viscosity 7100cps) having Gafdner colour 5.0 initially and 6 after 60minutes at
1 80°C.
Cecehi (1987)'~ also studied the thermal and thermo-catalytic dimerisation of
the linoleic chain and stated that the yield of methyl linoleate dimer increased by 17 -
18% when dimerisation was carried out at 300°C in the presence of ruthenium
catalyst. The catalytic dimer exhibited an aliphatic stt-ucture due to chain coupling
mechanism involving hydrogen transfer, while thermal dimers exhibited mono-and bi-
cyclic structures due to a cycloaddition mechanism. The structures of the dimers were I
confirmed by mass spectroscopy. The thermo-catalytic dimerisation (combined
thermal and catalytic dimerisation) was accompanied by decarboxylation.
Tsvet Kov (1984)'~ studied the polynierization of tall oil fatty. acids in the
presence of a bentonite catalyst. The optimum parameters in the dimersation of tall oil
fatty acids in the presence of 'bentonite catalyst were: 250°C, 5 hours of dimerisation
and 20wt% catalyst. The highest dimer yield under this condition was 58.1% and the
highest viscosity was 470Cps. A correlation was established between the changes in
viscosity and yield of polymerised talloil fatty acids.
Fritz ( 1 9 8 8 ) ~ ~ described a rapid method for the analysis of monomer, dimer and
trimer cqmponents of polymerized tall oil fqtty acids by thin layer chromatography
(TLC) with flame ionization detector (FID) on a latroscan apparatus. The short and
long term precisions of the method were given as well as the correlation of TLCIFID
data with the gas liquid chromatography data for dimerised fatty acids. The TLClFlD
method is the superior technique for process control applications.
Bruetting and Spittfelle ( 1 9 9 4 ) ~ ~ carried out the dimerisation of conjugated fatty
acids. Dimer fatty acids 'were obtained by the clay catalysed dimerisation of the .
conjugated fatty acid mixture of 9, 11 - octadecadienoic acid and 10, 12 -
octadecadienoic acids. They were separated by means of HPLC into three fractions in
the form of their di-methyl esters analogous to the dimer fatty acids formed from
linoleic acid. Although conjugated fatty acids are predisposed to undergoing a Diels-
Alder reaction, no such pmducts could be detected. I
Bruetting et al (1994)"~ studied the products of dimerisation of unsaturated
fatty acids and the fraction of acyclic dimeric acids. The main fractions of the dimeric
fatty acids were obtained by the dimerisation of linoleic fatty acid with. the molecular
weight 588 and 590. This fraction was subjected to hydrogenation and epoxidation
with Se02PdlC. It was shown that these reaction products are a mixture of dimeric
acid with a 6- ring1 I-double bond and a dimeric acid with two 6-ringll-double bond
compounds. In both compounds, the double bonds can either be situated in the ring
as well as outside the ring. In dimeric acids with two rings, the ring system can be
condensed or separated by a carbon chain. Besides, dimeric acids with two 6 - rings
and one 5-ring were,found by an investigation of model compounds and model
fractions.
The immense benefits of thixotropy in coating systems have led to a great deal
of' effort, intensified towards finding novel thixotropic agents that would meet various
performance requirements. At the same time, efforts have been directed at developing
coatings or resins using either the traditional or the novel. thixotropes. These efforts
have resulted in a flood of patents and literature relating to the methods of production
and use of thixotropic agents.
he additive thixotropes such as fumed silicas, bentonites, waxes, sulphonated
and hydrogenated castor oil have been known and used from time. Given the weak
structures formed by these
formulation tedious, interest
inherent thixotropic character
thixotropes and the fact that their use makes paint
has long shifted to the development of resins with
Thus, in 1953, Winkler obtained a patent covering the ,
use of a fatty polyamide from the reaction of dimer acid and ethylene diamine in the
modification of alkyds to give a thixotropic resin112.
Thus, dimer fatty acids have been prepared in our laboratory using locally
available vegetable oils with the aim to make thixotropic Efforts are currently
focused on establishing ti ~e best catalysts for dimerising the title oils and obtaining the '
relevant kinetic and thermodynamic data. To date, Uwakwe (2006)'02, Egbo (2006)'03
worked on melon seed oil using N~'HSO' and l2 as catalysts, respectively while
lkyenge (2006)'~' and Aggeh (2006)lo5 worked on pumpkin seed oil with sulphur and
l2 as catalysts, respectively. The latter work showed sulphur to be a better catalyst
than iodine. In general, these studies showed increases in refractive index, acid value,
and the molecular weight of the fatty dimer acids with time and temp,erature of
dimerisation.
2 1 RESEARCH OBJECTIVE:
This work is an extension of the works of Uwakw- and Egbo on melon seed oil
with sulphur as catalyst with the following aims:
(i) To show its effectiveness in dimerising melon seed oil vis-a-vis NaHS04
(ii) To determine the effects of temperature on the dimerisation process, and
thus obtain some thermodynamic and kinetic parameters.
(iii) To obtain theoptimum conditions for dimerising melon seed oil with sulphur.
CHAPTER THREE
EXPERIMENTAL
3 1 MATERIALS USED
Melon Seed (Colocynthis 'vulgaris): I
Melon seeds were bought from Nsukka main market. The seeds were
winnowed and dried at about 105OC to reduce the moisture content. They were th'en
ground coarsely, to break the micelle in a mechanical grinder and stored in a clean
polyethylene bag.
Reagents:
Petroleum ether (40 - 60°C), potassium hydroxide (KOH), diethyl ether, methanol,
toluene, sulphur, carbon tetrachloride, phenolpthalene, Wij's solution, sodium
thiosulphate, potassium iodide, iodine trichloride, starch, fuller's earth, nitrogen gas.
Equipment: I
Vacuum pump, 4-necked alkyd resin kettle, heating mantle, mechanical stirrer, .
PZO Abbe refractometer, Gardner-Delta colour comparator, mechanical grinder,
chromatographic column -with tap, Ferranti portable viscometer.
3.2.0 EXTRACTION OF OIL FROM MELON SEEDS
The ground seeds were packed (in weighed batches) in the column fitted with a
tap at the lower end. Sufficient solvent (petroleum ether) was poured into the column
to properly soak the ground seed, with solvent level of about 5cm above the seeds in
the column. The upper end of the column was covered with alumirium foil to prevent
solvent loss by evaporation. The column and content were left to stand for 24 hours at
the end.of which the tap ,was opened to run off the oillsolvent solution into a 500ml
conical flask. More
oil until the solution
solvent was repeatedly introduced into the column to wash off the
became clear and the cake appeared whitish.
The oillsolvent solution was filtered and redistilled to recover the oil .which was
weighed and stored in a well stoppered container.
3.3.0 REFINING OF THE CRUDE MELON SEED OIL
400.0gm,of the oil was weighed and heated in a 1000ml beaker to 70°C.
120 .0~~ of hot water (80°C), representing 3% by weight of the oil, was added with
gradual stirring to achieve efficient.separation and avoid emulsification. The stirring
continued for about 5minutes before the mixture was poured into a separating funnel
and was left to cool overnight. The layers observed were separated to recover the oil ,
and the gum-free melon seed oil was stored in a well stoppered amber container.
3.3.2 DEACIDIFICATION:
The method of Cocks and Reeds was employed for the deacidification
process. 200.0g of the gum-free oil was weighed and heated in a clean 500ml beaker
to 80°C in an oil bath. A solution of 16.5ml of 1 M NaOH, 70ml of NaCl containing 1 gm
of NaCl in 350ml of distilled water (loOhbf stoichiometric amount of NaOH) was .
prepared. The NaOH solution was put in a dropping funnel from where it was added
drop wise to the heated oil with constant stirring, after which, the hot oillsoap mixture
was poured into a clean separating funnel and left to stand overnight. The,mixture
' separated into three layers:. an oil top layer, a soap middle layer and an aqueous :
lowest layer. The aqueous and soap layers were run-off to recover the oil. The oil was
not completely freed from soap; hence, the oil-soap mixture was left in an oven at
100°C for 2hours. More oil was recovered at the end of this process.,
Traces of soap residues and unconverted NaOH in the oil obtained from the
alkali refining process ~endered the oil impure. The oil was further purified by
dissolving it in petroleum ether and filtering under vacuum to remove the soap and
other impurities. The oil/solvent solution was washed with hot water in a separating
funnel with gradual shaking to avoid em~ls~ification of the oil. The washing was
discontinued when the aqueous extract was clear and neutral to litmus. The oil
solution was then redistilled under vacuum to remove solvent and water.
In a three- necked round bottom flask, 400.0g of the alkali refined oil and 60.0g
of fullers earth (15wt % based on oil) were mixed. The flask with its contents was
placed on a heating mantle and the temperature adjusted to 80°C and heated under
vacuum with occasional shaking at intervals of 10 minutes. The heating was stopped
after 45minutes and the mixture filtered hot by carefully allowing the supernatant'to
pass through the buchner funnel in which 'whatman gradel' filter paper was inserted.
This was 'carried out under vacuum after which the rest of the residue was filtered.
3.4.0 CHARACTERISATION OF THE OIL
The physicochemical properties of the refined melon seed oil determined
include: acid value, iodine value, molecular weight, colour, viscosity, specific gravity,
the refractive index and saponification value.
3.4.1 ACID VALUE'*
(a) Preparation of solutions:
(i) 0.1 M Potassium Hydroxide (KOH)
56.lg of KOH pellets was dissolved in a 1000ml volumetric flask and made up to
mark with distilled water. The solution was standardised with 0.1 M HCI to a I
phenolphthalein end point.
(ii)
drops
Neutral Solvent
Equal volumes of toluene and 2-propanol were mixed in a one litre flask. Three
of phenolphthalein indicator was added and the mixture neutralized with 0.1 M
KOH solution till a pink colour which persisted for about one minute was obtained. The
neutral solvent thus prepared was stored in a one litre volumetric flask.
(iii) Phenolphthalein indicator:
This was prepared by weighing I gm of phenolphthalei'n powder and dissolving it
in1 001nl of methanol (equivalent weight to 10.0g/1000ml).
(b) Determination
Procedure:
5.0g of the sample was weighed and dissolved in 50ml of neutral solvent in a
conical flask. 0.5ml of phenolphthalein indicator was also added and the solution
titrated with 0.1 M KOH till a pink colour, which persisted for about 30 seconds, was
obtained.
Calculation:
The acid value was calculated using the formula:
Acid value = 56.1 * M*V 3.1 w
where: M and V represent the Molarity and Volume of the KOH solution respectively and W is the weight of the sample.
IODINE VALUE:
The iodine value of the oil was determined using the Wij's method. I
(a) Preparation of solutions:
(i) Potassium iodide solution (KI)
150.0g of KI was dissolved in distilled water and made up to the m,ark in a Ilitre
volumetric flask.
(ii) 0.1 M Sodium thiosulphate pentahydrate (Na2S2O3.5H20):
24.83g of sodium thiosulphate pentahydrate was dissolved in distilled water
and diluted to I litre in a volumetric flask.
(iii)
(iv)
Starch indicator solution
A paste was made with 1.0g of starch
100ml of boiling water was added to
and cooled.
Wij's solution:
powder using a little quantity of water.
the paste and the mixture stirred rapidly
8.67g of iodine was weighed and dissolcved in 100mI of methanol. 7.96g of
iodine trichloride (IClj) was also weighed put and dissolved in a quantity of glacial
acetic acid. The separated solutions were carefully warmed in a water bath, mixed in
1 litre volumetric flask and made up to the mark with glacial acetic acid.
(b) Standardization of the sodium thiosulphate solution
0.21g of potassium dichromate (K2Cr207) previously dried to a constant weight ,
at l lO°C was weighed and dissolved with 25ml of water in a conical flask. 5ml of
concentrated HCI and 20ml of 15%KI solution were added and mixed thoroughly by
shaking. After standing for 5minutes, 100ml of distilled water was added and the
liberated iodine then titrated with the thiosulphate soluti.on. untii the yellow colour
disappeared. Im l of starch solution indicator was added and the titration continued
until ihe blue colour which appeared 'on the addition of the starch solution
disappeared. The strength of the thiosulphate solution is expressed as:
Normality (Na2S203.5H20) = 209.39 * W (K2Cr20z) V(Na2S203)
where W = weight of the K2Cr207 used , V = volume of thiosulphate consumed
(c) Determination
( 9 Procedure:
0.238g of the oil was dissolved in 20ml of carbon tertrachloride (CC14) in a
clean 500ml conical flask. 25ml of Wij's solution was added to the'flask containing the
oil, and also to another flask without the sample to serve as blank. The flasks were
stoppered swirled to ensure proper mixing and set in a dark place for Ihour with
occasional swirling.
At the end of the period, 20ml of KI solution and 100ml of distilled water were
added to the flasks and were titrated against the standardized thiosulphate solution to
a faint yellow colour. 2ml of starch solution was addea and the titration continued until
the colour disappeared.
(i i) Calculation: I
The iodine value of the samples were calculated using the expression below: .
Iodine value = _CVZ - VI) * M * 12.60 3.3 W
where: V2 andV1=,volumes of the blank and sample at end points respectively. M = molarity of Na2S203and W = weight of sample used.
3.4.3 SAPONIFICATION VALUE
This involves saponifying the oil with an excess of alkali and the excess
determined by back titration with standard HCI'~.
(a) Preparation of reagents
(i) Alcoholic
7.02g pf KOH
volumetric flask
potassium hydroxide solution (0.5M)
was dissolved with a little quantity of distilled water in a 250ml
and was made up to the mark with methanol. The resulting solution
was standardised using standard 0.1 M HCI to a phenolphthalein end point.
(h) 0.5M ~~d roch lo r i d acid solution
This was prepared by putting 10,7ml of 36% concentrated HCI into a 250ml
volumetric flask and making up to the mark with distilled water to get the required
0.5M HCI.
(b) Determination
Procedure:
2.0g of the sample was weighed intp a 250ml flask. 25ml of alcoholic KOH
solution was added to the sample and the same volume was measured into another
250ml flask (which serves as the blank) and these flasks, fitted with a condenser,
were heated for 1 hour,on a steam bath to saponify the oil. The contents of the flasks,
while still warm, were titrat,ed with 0.5M HCI using phenolphthalein indicator,.
(i) Calculation
The saponification value of the oil was calculated using the expression below:
Saponifiation value = [V1 - V 3 * M * 56.1 - - - 3.4 : w
where: V2 and V1 represent volumes of acid (HCI) at end point of blank and samples respectively. M represents molarity of the acid (HCI) and W represents weight of the sample used.
3.4.4 RELATIVE DENSITY I
(a) Procedure
An empty pycnometer was washed dried and weighed repeatedly to have a
reproducible weight (wl) with the lead in place. It was later filled with distilled water
and the weight again was 'determined and recorded (w~).. The pycnometer was dried
thoroughly, filled with the sample and weighed again (w3).
(b) Calculation:
The relative density of the sample was calculated as follows:
Relative density = (&-Wl) --- - - - _ _ . 3.5 (W2-WJ
where: W2, and W3 are %eights of empty pycnometer, pycnometer with water and pycnometer Wl,with the sample respectively. I
3.4.5 COLOUR (GARDNER SCALE)
The colour of the melon seed oil was determined using the Gardner-Delta
colour comparator model CG-6745, designed to perform according to ASTM method
D-1544 on the Gardner scale of measurement. The complete instrument consists of
the comparator and illuminator. The sample colour was determined by selecting the
closest match to it from a series of standard filters numbered 1 - 18 on two disks on
either side of the sample compartment, each containing nine glass filters. The number
on the filters, whose colour exactly matcheg the sample, was recorded as the colour of
the sample. Where the sample colour did not match exactly any of the filters, the
number on the closest match filter was recorded with a plus (+) or minus (-) sign after
it, mdicating that it is slightly darker or lighter than the sample colour, respectively.
3 4 6 VISCOSITY
The bulk viscosity of the melon seed oil (MSO) was determined using the
Ferranti portable viscometer. The instrument consists of a rotating outer cylinder
driven by a small motor with a second cylinder located coaxially within it. The inner
cylinder is free to rotate against a calibrated spring with a pointer to show the an'gular
deflection. The inner cylinder is suspended in jeweled bearings and the outer cylinder
driven 'at a constant speed by a specially designed two-phase synchronous motor of
high torque and is chosen appropriately to just cover the viscosity range required. The
model cylinders used for these measurements were the medium assembly viscosity
(VFVIlA) and the high assembly viscosity cylinders (VHIA).
The cylinders aft& thorough washing, drying, immersion in xylene and drying .
were immersed in the sample with the top of the outer cylinder just covering the
sample. The cylinder, in spite of being immersed to the required level, was not allowed
to have contact with either of the sides or the bottom of the.container holding the
sample. The viscometer was switched-on and the gear adjusted to one; the cylinder
begins to rotate in the
inner cylinder causing
:ample. The resulting rotation exerted a viscous drag on the l
a deflection of the meter proportionally to the viscosity. The
I
gears were changed from one to five consecbtively without stopping the motor and the
values obtained were recorded for each sample.
The viscosity in poises at a given speed and the cylinder combination used was
obtained by multiplying the instrument reading with the appropriate multiplying factor.
For VIIIIA cylinder combination, the multiplying factors are: 0.01 30, 0.0087, 0.00661 ,
0.0052, and 0.00436 and for VHIA cylinder combination are: 0.2814, 0.1874, 0.1412,
0.1 120, and 0.09353 for gears 1,2,3,4 and 5, respectively. The average value of the
viscosities spread over the five gears gave the viscosity of the sample. The
measurements were made at a constant temperature of 3I0C. The cylinders were
removed and thoroughly. cleaned after epch measurement by washing, drying,
immersion in xylene and drying again before re-assembling them for subsequent
measurement.
3.4.7 REFRACTIVE IND'EX
The refractive indices of the samples were determined using the PZO (RL2)
model of the Abbe refractometer at 2g°C. A drop of the sample was introduced at the
sample compartment and the light rays were balanced in the instrument using the fine
adjuster. The readings were properly taken by focusing, on the eyepiece of the scale.
MOLECULAR WEIGHT DETERMINATION BY CRYOSCOPY
Procedure:
5:Og of cyclohexane was weighed intd a clean 15 X 2cm boiling tube. The tube
was screw capped with a cork fitted with a stirrer and a thermometer in such a way
that the bulb of the thermometer and the loop of the stirrer were immersed in the
solvent. The tube was suspended in a 'cyl'indrical beaker of dimension 7 X 4cm which
served as an air jacket. The beaker, in turn, was suspended in a larger beaker which ' .
contained some ice flakes. The solvent was thus cooled while stirring continuously
until the temperature became constant. This temperature was read-off on the
thermometer and noted (MPt,).
Similarly, 2.0g of the sample was weighed and dissolved in 5.0g of the solvent
(cyclohexane) in the boiling tube. The tube was screw capped and the freezing point
of the solution determined as before and not6d (MPt2).
Calculation:
The molecular weight of the sample was calculated using the formula:
Molecular weight of sample = 1000 * K * W2 - - - - 3.6 w ~ " ( M P ~ ~ - M P ~ ~ ) -
where: K is the cryoscopic constant of the solvent, W1' and W2 are the weights of the sample and solvent used respectively. MPtl and MPtz are the mel'ting points of, the solvents and sample in solution respectively.
3.5.0 DlMERlSATlON OF MELON SEED 0,IL (MSO)
200.0g of the melon seed oil (MSO) was accurately weighed into a 4-necked
resin kettle fitted with mechanical stirrer, thermometer, nitrogen inlet tube and la
condenser. 1.0g (0.5%wlw) of monoclinic P- sulphur (yellow crystalline sulphur) was
weighed and added to thetoil and the mixture heated on the mantle. A steady stream
of nitrogen was released from the cylinder into the system while stirring continued and
it was heated gradually to 300°C at the first instance of dimerisation.
The temperature was maintained at 300°C for abbut ten minutes before the first
sample was withdrawn using a 20ml pipette fixed onto its filler. Subsequent
withdrawals were made at 5minutes intervals and ten samples were collected in 45
minutes. The samples were kept in clean, hell labeled sample bottles with rubber
caps.
The remains of the dimerisation products in the resin kettle was later
transferred into a different sample container and labeled 'final crude product' at the
specified temperature. The resin kettle was then cleaned-up for subsequent use.
Same procedure was adopted to dimerise the oil at five other temperature
values of 310, 320, 330, 340 and 350°C, respectively.
3.6 0 CHARACTERISATION OF THE DlMER FATTY ACIDS (DFA)
The physicochemical properties of the DFA produced were determined as described
in section 3.4 (1-8), and these were: acid value, refractive indice, viscosity, colour and
the molecular weight of th8 dimer fatty acid! The acid value was used to determine
some thermodynamic parameters of the dimer fatty acids.
3 7.0 PERCENTAGE YIELD OF THE DFA
The percentage yield of DFA was determined using thin layer chromatography
(TLC) with silica gel pre-coated plates cut into 2.5 X 5.5,cm sizes. The plates were
activated at 120°C for 2 hours before use. 0.15g of the sample was dissolved in 3ml
carbon tetrachloride (CC14) and spotted on the activated plate. The spotted sample
was developed in a solution of n-hexane, diethyl ether and acetic acid mixed in the
ratio of 7:5:0.2 contained in a TLC tank. The bands obtained, after placing the
developed sample in an iodine chamber, were carefully scraped off and extracted in 1
CC14 and filtered into a pre-weighed beaker. The solvent (CC14) was subsequently
evaporated and the beakers re-weighed. The percentage yields of the separated
bands were calculated as follows:
Percentage yield of DFA = (&-3!11 XI00 - - - 3 7 w2
' where: W3 = weight of the beaker and the separated fraction after evaporation. Wz =weight of sample used, W1 = weight of the beaker.
The separation was carried out on the optimum samples dimerised at different
temperatures (300, 310, 320, 330, 340, 350°C).
CHAPTER 4
4.0 RESULTS AND DISCUSSION
4.1 Extraction of melon seed oil (MSO):
An average weight of 180.40g of oil was extracted from 376.589 of grou-nd
melon seed which represents a yield of 47.90%. This is close to 43.54% reported in I
literaturegq. A yield of 58.68% was reported for MSO by a soxhlet extraction processg5.
The characteristics of MSO used for this research work are shown in Table 4.1
4.2.0 . CHARACTERISATION OF MSO
Table 4.1 Physicochemical properties of MSO
I Colour (Gardner Scale) . T / Relative density (at 28OC) I Absolute Viscosity
I Refractive index I Molecular weight
Acid value
Iodine Value
Saponificatiori value
0.3192 poise
The iodine value of the oil was determined to be 1 11.825 which puts the oil in
the range of semi-drying oils and is in accord with what had been reported by other
96-97 workers .
The saponification value of 194,246 p
molecular weight glycerides35 which reflects
laces the oil within the range of high
a large percentage of CI6 and CI8 I
glycerides in the oil3. This conforms to the high percentages of palmitic, stearic, oleic,
and linoleic acids in the ratio l7:18:54:12.8, respectively.
The crude MSO had an acid value of 3.3458 mgKOH/g which gave the free
fatty acids to be 1.68%. After deacidification, the acicl value and the free fatty acids
were reduced to 0.3186 mgKOH/g and 0.16%, respectively. Thus, the unattached
fatty acids present in the oil were highly reduced during the process of alkali refining.'
The high relative density of 0.912for rkfined MSO conforms to the low free fatty
acids of the oil%hich is attributed to high content of linoleic acid in the oilgG, The
refractive index of 1.4680 at 2g°C is in very close agreement with literature 102-103
values for pure MSO.
The Gardner colour 8 of the crude MSO was bleached to colour 1 with fuller's
earth. This reduction in the colour intensity corresponds to 87.5% bleaching of the
naturally occurring colouring matter in the oil.
The oil had an absolute viscosity of 39.92 centipoise at 3I0C and 448.65 as its
moleci~lar weight. The relatively high viscosity and molecular weight account for the
low saponification value which reflects a large percentage of Cis and C18 in the I
By 'these properties, the oil for this research work was found to be of good
quality.
4.3.0 CHARACTERISTICS OF THE CRUDE DFA
4.3.1 ACID VALUE (AV)
The presence of 1% phosphatide increases the acid value by 0.30 -
0 . 3 3 m ~ ~ 0 ~ ~ ' . The non-hydrated phospholipids which are difficult to remove during
degumming process are hydrolysed during dimerisation. This leads to the formation
of polar lipids together with other decomposition products which increase the acid
value of the DFA'as shown in Table 4.2.
The increase is directly proportional to time at constant temperature as well as
Table 4.2: Variation of Acid Value with time of dimerisation
to temperature at constant time of dimerisation as shown in Figs 4.land 4.2,
--
T i m (Min.) ----
0 5 10 15
1- -TO- - - -- .
25 30 35 40 45 --
respectively. Steady increase in the acid values was observed with increase in time of
dimerisation, with much more acid produced at 25 and 40 minutes, as evident from
Fig 4.2. Similarly, at any given time, acid value increased with temperature, with more
acid produced at 310 and 350°C, respectively as can be seen from Fig 4.1.
'
TEMPERATURE --- (OC) 300
0.31 86 0.9559 1.5932 2.2305 2.5492 -- 4.939 9.7188 11.312 12.5866 16.8883
31 0 1.1153 1.7526 3.8238 4.7797 7.9662 1.0.3561 15 .1358 16.729
18.0036 21.3054
320 2.0112 2.8678 5.2577 7.6476 10.834
13.2239 18.0036 19.5969 20.8714 23.1732
- -- -- 340
6.373 7.1696 9.5594 12.7459 15.1 358 19.91 55 21.5087 22.7833 22.9427 27.2444
A
330 4.461 6.373
9.2408 10.3501 13.5425 16.8883 18.8002 21.3494 21.9861 25.2172
---A- -
350 9.2408 10.0374 1 1.9493 15.61 37 - 19.91 55 22.7833 28.3596 30.271 6 31.3868 32.3428
J -5 Time (Min) .
Fig 4.1 Plot of Acid Value against Time of Dim'erisation
4 OMin 1 siiiliiis
A IOMins X 15Mins
X 20Mins @ 25Mins '
t30Mins -35Mins
-40Mins 4 45Mins
Temperature (degree celcius)
Fig 4,2 Plot of Acid Value against Temperature
The acid values obtained were compared with those of my co-workers' 102, 103
who used NaHS04 and iodine 'catalysts respectively, at the optimum time of
dimerisation of 40 miflutes, as shown in Table 4.3.
Table 4.3: Acid values produced by different catalysts after 40 minutes of dimerisation
The data in Table 4.3 are plotted in ~ i ~ 4 . 3 . The plots show that much more
TEMP ("C)
acids were produced when sulphur was used to dimerise MSO followed by iodine. ,
Since dimer fatty acid formation is associated with high acid value sulphur, therefore,
ACID VALUE Sulphur NaHSpn Ti Iodine
proves to be the best of the three catalyst systems.
4 sulphur 4 A , i NaHSO
300 310 320 330 340 350 360 '
Temperature
I
Fig 4.3 Plot of acid values of MSO aga against temperature for different catalysts
I 4.3.2 REFRACTIVE INDEX (R.1)
Prolonged heating of oil leads to an increase in refractive index due to the
introduction of polar groups into the fatty acid chain6. This is evident in Table 4.4 and
the values plotted against time and temperatures of dimerisation in Figures 4.4 and
4.5, respectively.
Table 4.4: Variation of Refractive Index with time at various temperature of dimerisation
Figure 4.4 shows that the refractive indices increased steadily with time at
TIME (Min.) --
0 - - 5 -- 10 1.5 20 25 30 -- 35 40 45
constant temperature and the increase is greater at higher time of dimerisation than
when the process is just beginning. Figure 4.5 shows the variation of refractive indices
with temperature at constant time of dimerisation. The increase observed, is such that,
TEMPERATURE
between 0-5, 10-20, 30-40 minutes, the refractive indices at all temperatures increase
distinctly. The increase bezomes negligible at 5-10 minutes, 20-30 minutes and 40-45 I
300 31 0
minutes of dimerisation. At 20-25 minutes of dimerisation, increase in the refractive
320 1.4725 1.4736 1.4737 1.474'7 1.4758 1.4759 1.4760 1.4770, 1 A781 1.4783
1.4704 1.4714, 1.471 5 1.4725 1.4736 1.4736 1.4737 1.4747 1 A758 1.4758
index is observed for 320°C and higher temperatures of dimerisation
1.471 4 1.4725 1.4726 1.4736 1.4747 1.4748 1 A748 1.4757 1,4768 1.4768
330 1.4736 1.4747 1.4748 1.4758 1.4769 1.4769 1.4770 1.4780 1.4791 1.4792
-- 340 1.4746 1.4756 1.4758 1.4768 1.4779 1.4780 1.4783 1.4783 1.4795 1.4795
350 1.4757 1.4767- 1.4768 1.4778 1.4781 1.4791 1.4791 1.4802 1:4813
m4814
'0 5 10 15 20 25 30 35 40 45 50 Time (Min)
Fig 4.4 Plot of Refractive Index against Time of Dimerisation
Temperature (degree celcius)
Fig 4.5 Plot of Refractive Index against Temperature
Comparatively, these results conform to earlier ieports102-103 on the dimerisation
of MSO using sodium hydrogen tetraoxosulphate (VI) (NaHS04) and iodine as
catalysts, respectively. Table 4.5, compares the variation in the refractive indices after
40 minutes of dimerisation'with those of my Aolleagues.
Table 4.5 Refractive indices produced by different catalysts after 40 minutes
[TEMP. I REFRACTIVE INDICES 1
The data in Table 4.5 are plotted in Fig 4.6, from which it can be seen that I
sulphur causes the highest change in refractive index than NaHS04 and iodine
catalysts, respectively.
+sulphur
l NaHSO
A iodine
I Temperature
Fig 4.6 Plot of refractive index of MSO DFA against temperature for different catalysts
4.3.3 MOLECULAR WEIGHT I
The polyunsaturated Cia fatty acids !present in the oil is dimerised to form ,
mixtures of C36 dibasic acids with some trimers (C54 and higher oligomers5' which
leads to increase in the molecular weights of DFA as shown in Table 4.6
Table 4.6: Variation of ~o lecu lar weight with time and temperature of DFA
I ~ E I TEMPERATURE f°Cl
The increases in the molecular weight with time at constant temperature as well
as with temperature at constant time are illustrated in Figs 4.7 and 4.8, respectively.
In Fig 4.7, the increase is negligible between 300°C and 310°C. It is most .
significant at 330°C when MSO is dimerised for a long period of time. There is an
appreciable increase in the molecular weight at 340°C and 350°C even at lower time
of dimerisation.
In Fig 4.8, no appreciable increase in the molecular weight was observed
between 300-31 0°C. The increase becomes significant after 31 O°C and continued to
the highest temperature of dimerisation (35boc). At 300°C the increase was only
significant at 15-20 minutes, 25-30 minutes and at 40-45 minutes. This shows that
lower temperatures require more time for dimerisation to yield higher molecular weight
products.
40 50 Time (Min)
Fig 4.7 plot of Molecular Weight against Time of Dimerisation
Temperature (degree celcius)
Fig 4.8 Plot of Molecular Weight against Temperature of Dimerisation
The increase in molecular weight was compared with those reported earlier
(using two different catalyst systems) as shown in Table84.7. A plot of these values
against temperature is given in Fig 4.9 for the different catalyst systems.
Table 4.7: Molecular weight of MSO after 40 minutes of dimerisation using different catalyst systems
It is observed from the plot that the rate of increase in the molecular weight is
Temp. (OC) A
highest when sulphur is used as catalysts than when either of the other catalysts is
Molecular Weight -- Sulphur I NaHS04 [ Iodine
used. This therefore goes further to buttress the efficacy of sulphur in dimerisation of
MSO.
+sulphur
I NaHSO
A iodine
290 300 310 . 320 330 340 . 350 360 Temperature
Fig 4.9 Plot of molecular weights of MSO DFA against Temperature for different catalyats I
4.3.4 VISCOSITY (Bulk)
The rate of flow of oil molecule against one another has t6 do with the
intermolecular attraction between their fatty acid chains. It increases slightly with
increase in the average molecular weight8 and with increasing degree of saturation.
The viscosity of oils tends to increase.on prolonged heating due to the formation of
dimeric and oligomeric fatty acid groups6. This increase is evident in Table 4.8 which
shows the absolute viscosity of the DFA obtained from the 'final crude products1: A
plot of oil viscosity against temperature is shown in Fig 4.10. From the Figure,
viscosity (in centipoise) is seen to increase stqadily with temperature as a result of the
formation of dimeric fatty acids and other by-products of thermal polymerization.
Table 4.8: Variation of viscosity of DFA with temperature of dimerisation
1 TEMPERATURE I VISCOSITY
Temperature
Fig 4.10 Plot of Bulk Viscosity against Temerature
4.3.5 COLOUR (Gardner scale)
Naturally, formation of conjugated system in the unsaturated fatty acids through
isomerisation leads to an increase in colour intensity. Table 4.9 gives these ,variations
in colour of the dimerised MSO using sulphur as catalyst. From the Table, it is evident
that the increase in colour intensity is proportional to tem~erature'at Constant time ,and
lo lirne, at constant temperature of dimerisation. It should be noted that the higher the
colour number, the darker the colour of the oil.
Table 4.9: Variation of colour with time and temperature of DFA
TEMPERATURE OC
-1-
where (+) indicates colour slightly higher than the stated value, and (-) indicates colour .slightly less than the stated value.
I
4.4.0 PERCENTAGE YIELD OF DFA
' Crude DFA usually contains some monomeric and trimeric products together
with other thermally decomposed products and the fraction of interest (dimers). Dimer
. products .obtained at the reaction time of 45 minutes for different temperatures were
separated into fractions and the results are given in Table 4.10. Product at 300°C
could not be reported as its separation yielded basically monomer.
Table 4.1 0 TLC separation of DFA samples into its components
From the table, it is evident that up to 330°C, dimerisation of MSO using
I
sulphur catalyst still contains a high proportion of inonomer molecules. Dimers are
Sample
310°C 320°C 330°C 340°C 350°C ---
obtained in higher proportions at 340°C and 350°C, respectively. Little proportions of
trimers were also obtained as the temperature increases. !
Separation of the product obtained at 350°C but at lower time of dimerisation of.
where: N1 = Not Identified, M = Monomer, D =Dimer and T = Trimer
30 minutes gave the maximum yield of 48.67% for the sulphur catalysed dimerisation
% yield of bands
of MSO. In contrast, a, maximum yield ofJ40.54% dimer was obtained for MSO at
M 96.67 96.00 82.00 63.33 39.33
Molecular weight of bands
350°C and a reaction time of 90 minutes using NaHS04 as catalyst'02, and. 46.1 % at
same temperature but at 40' minutes with iodine as catalystqo3.
M 740.74 714.29 823.53 689.66 833.33
These optimum yield results further show that sulphur is the best of the three
D 2.67 3.33 16.67 34.00 43.33
catalyst systems.
T NI Trace 1.33 2.67 17.33
D 1333.33 1263.16 1400.00 1217.39 141 1.76
T - - 1647.06 1750.00 - 1866.67 .
4..5.0 THERMODYNAMICS OF DlMERlSATlON
4.5.1 ENTHALPY OF DlMERlSATlON
The enthalpy change (AH) of dimerisation is determined using the expression:
In (AV) = -AHIRT + C 4.1
where AV = acid value
Enthalpy is the heat content ,or the energy of interaction between molecules.
The slope of the plot of In(AV) against 1/T (Fig 4.1 1) is equal to -AHIR, from which the
enthalpy change for the dimerisation of YSO was obtained for different times of
dimerisation as assembled in Table 4.11. The negative values of the enthalpy '
changes show that the dimerisation reaction is an exothermic process, as reported .in
the literature1".
+.
Fig 4.11 Plot of In(AV) against 1IT in Kelvin -2
Table 4.1 1 : Enthalpy at various time of dimerisation
.Time of Equation of the graph dimerisation (Minsl
The above enthalpies of dimerisation are compared with those obtained with NaHS04
and l 2 in Table 4.1 2.
Table 4.1 2: Effect of catalysts on the enthalpq of dimerisation of MSO
AH with Sulphur I AHwith NaHSOI I AH with Iodine ] in Kilojoules in Joules
0 -1 87.66 -1.00433
From the table, sulphur is found to liberate much more heat during dimerisation
than other two catalysts, which shows that sulphur catalysed dimerisation of MSO is
the most energetically favoured process. !
CONCLUSION
Dimerisation of melon seed oil (MSO) is found to be time and temperature
dependent with a percentage yield also being time and temperature dependent. This
work also showed that sulphur is the best of the three catalyst systems, sulphur,
iodine and sodium hydrogen sulphate studied in our laboratory.
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