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Nanocrystalline KeCaO for the transesterification of a varietyof feedstocks: Structure, kinetics and catalytic properties

Dinesh Kumar, Amjad Ali*

School of Chemistry and Biochemistry, Thapar University, Bhadson Road, Patiala, Punjab 147004, India

a r t i c l e i n f o

Article history:

Received 11 June 2011

Received in revised form

22 June 2012

Accepted 30 June 2012

Available online 11 August 2012

Keywords:

Solid catalyst

Transesterification

Homogeneous contribution1H NMR spectroscopy

KoroseNowak criterion

* Corresponding author. Tel.: þ91 175 239383E-mail addresses: amjadali@thapar.edu,

0961-9534/$ e see front matter ª 2012 Elsevhttp://dx.doi.org/10.1016/j.biombioe.2012.06.

a b s t r a c t

The work presented in current manuscript demonstrated the preparation of potassium ion

impregnated calcium oxide in nano particle form and its application as solid catalyst for the

transesterification of a variety of triglycerides. The catalyst was characterized by powder X-

ray diffraction, scanning electron and transmission electron microscopic, BET surface area

measurement, and Hammett indicator studies in order to establish the effect of Kþ impreg-

nation on catalyst structure, particle size, surface morphology, and basic strength. The

catalyst prepared by impregnating a mass fraction of 3.5% Kþ in CaO was found to exist as

w40 nm sized particles, and same was employed in present study as solid catalyst for the

transesterification of a variety of feedstocks viz., mutton fat, soybean, virgin cotton seed,

waste cotton seed, castor, karanja and jatropha oil. Under optimized conditions, KeCaOwas

found to yield 98 � 2% fatty acid methyl esters (FAMEs) from the employed feedstocks, and

showed a high tolerance to the free fatty acid and moisture contents. A pseudo first order

kinetic model was applied to evaluate the kinetic parameters and under optimized condi-

tions first order rate constant and activation energy was found to be 0.062 min�1 and

54kJmol�1, respectively. TheKoroseNowakcriterion testhasbeenemployed todemonstrate

thatmeasured catalytic activitywas independent of the influenceof transport phenomenon.

Finally, few physicochemical properties of the FAMEs prepared from waste cotton seed oil,

karanja oil and jatropha oils have been studied and compared with European standards.

ª 2012 Elsevier Ltd. All rights reserved.

1. Introduction occurring triglycerides (animal fat or vegetable oils) with short

The continuously decreasing fossil fuel resources, increasing

petroleum crude oil price and the environmental concerns

have increased the interest in renewable fuels, such as bio-

diesel, in recent past [1]. Fatty acid methyl esters (FAMEs),

commonly known as biodiesel, are a non toxic, biodegradable,

eco-friendly and renewable substitute for conventional diesel

fuel. Combustion of the biodiesel in engines causes signifi-

cantly lesser emission of particulates, unburnt hydrocarbons,

carbon monoxide, carbon dioxide and SOx than conventional

diesel fuels [2,3]. Transesterification reaction of the naturally

2; fax: þ91 175 2364498, þamjad_2kin@yahoo.com (ier Ltd. All rights reserved040

chain alcohols (e.g., MeOH and EtOH) in the presence of

homogeneous catalysts such as strong bases (e.g., NaOH, KOH,

NaOMe and KOMe) [4,5] or acids (e.g., HCl and H2SO4) [6] is the

most common method for biodiesel production. The trans-

esterification reactions catalysed by alkali catalysts were

found to proceed more rapidly than acid catalysed one and

hence, don’t require harsh reaction conditions. However, the

use of homogeneous alkali catalyst presents several disad-

vantages viz., their non recyclability and deactivation by high

moisture (mass fraction > 0.3%) and free fatty acid (mass

fraction > 0.5%) contents in feedstock. Further, the use of

91 175 2393005.A. Ali)..

Table 1 e The chemical analysis of the vegetable oilsemployed as feedstock in present study.

S.no.

Feedstock Massfractionof free

fatty acidvalue (%)

Massfraction ofmoisturecontent

(%)

SaponificationKOH value(g kg�1)

Iodinevalue

1. WCO 0.5 0.26 190.4 94.7

2. KO 4.2 0.35 185.0 96.8

3. JO 8.4 0.28 195.5 101.5

b i om a s s an d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8460

homogeneous catalyst leads to the formation of alkali metal

contaminated biodiesel and hence, required huge amount of

water for its cleaning [7].

In order to reduce the biodiesel production cost to make it

cost competitive with mineral diesel fuel and to avoid fuel vs

food situation, application of waste cooking oil and non-edible

oils as a source of cheap feedstock could be advantageous.

However, such feedstocks usually contain high free fatty acid

(FFA) and moisture contents which lead to the deactivation of

homogeneous alkali catalyst by soap formation. In this contest

application of solid catalysts could be more advantageous as

these are less corrosive, easy to separate from the reaction

mixture, reusable [8,9] and effective even for the feedstocks

having higher moisture (�15%) and FFA contents (�6%) [10]. A

variety of solid catalysts for the transesterification of a wide

range of triglycerides were reported in literature, including,

immobilized lipase [11,12], calcium carbonate [13], sodium

aluminate [14], alkali earth oxides [15], sulphated zirconia [16],

tin supported ion-exchange resins [17], solid basic resin [18],

alkylguanidines heterogenized on organic polymers [19],

zeolites [20], alumina loaded with alkali metal salt [21] and

supported mesoporous materials [22]. Recently Hernandez

et al. [23], have reported the preparation of sodium supported

hydrotalcite as solid catalyst for the transesterification of used

cooking oil and sunflower oil as feedstock. Similarly, due to

ease of preparation, being less costly and non toxic, alkali

metal supported CaO [10,24,25], MgO [26], ZnO [27], calcium-

based mixed oxides catalysts (CaMgO and CaZnO) and potas-

sium loaded CaeAl mixed oxides [28,29] have been studied

extensively as solid catalysts for the transesterification of

a variety of triglycerides. A commercial biodiesel plant based

on Esterfip-H technology has been set up in France which

utilizes the mixed oxides of Zn and Al as heterogeneous

catalyst for the transesterification of triglycerides [30].

Although, same catalyst required high temperature

(200e250 �C) and high pressure (40e60 bar) but yielded pure

biodiesel and glycerol without any metal contamination [31].

In order to develop a solid catalyst that could catalyse the

transesterification reaction under ambient conditions, Wat-

kins et al. [25], have been reported the preparation of lithium

impregnated calcium oxide (Li/CaO) for the transesterification

of glyceryl tributyrate. Later, Meher et al. [24], have reported

the application of Li/CaO as solid catalyst for the trans-

esterification of high FFA containing karanja oil. The same

catalyst was found to show better activity than pure calcium

oxide owing to the formation of strong basic sites upon alkali

metal impregnation in CaO. Our group has recently reported

[10] the preparation of Li/CaO in nano particle form and

successfully demonstrated its application for the complete

transesterification of waste cotton seed oil even in the pres-

ence of mass fraction of 15% moisture and 6% FFA contents.

In continuation to our earlier work to develop a solid

catalyst for the transesterification of high FFAs containing

feedstock under ambient conditions, present study demon-

strates the preparation of Kþ impregnated CaO in nano-sized

form and application of the same as solid catalyst for the

transesterification of mutton fat (MF), soybean oil (SO), virgin

cotton seed oil (CSO), waste cotton seed oil (WCO), castor oil

(CO), karanja oil (KO) and jatropha oil (JO). The KeCaO cata-

lysed transesterification of the WCO, KO, and JO have been

studied in detail for the reaction parameter optimization, and

to study the kinetics of the reaction.

2. Experimental Section

2.1. Materials and methods

Soybean oil, mutton fat, virgin cotton seed oil, castor oil,

karanja oil and jatropha oil were procured from local shops at

Patiala. Waste cotton seed oil has been procured from the

restaurants located in Patiala. Methanol (99.8%) used in the

present study was obtained from Merck, India and methyl

oleate (99%) used as FAMEs standard was procured from Sig-

maeAldrich, USA. All other chemicals were purchased from

Loba Chemie, India and used as such without further

purification.

The free fatty acid (FFA) value, saponification, and the

iodine value of the WCO, KO and JO were determined by

following the methods as reported in literature [32] and the

moisture contents inWCO, KO and JO were determined by the

Karl Fisher titrimetric method (Table 1).

This work was performed on substrates of unknown

provenance, for which the chain of custody is not known. The

species and the cultivars cannot be specified and while the

authors believe that this work exemplifies the action of cata-

lysts on the oils and the fats e there is a reasonable concern

that there may be substrate factors that influence the results

obtained.

Potassium ion concentration in CaO and FAMEs was

determined by GBC A32AA atomic absorption spectropho-

tometer (AAS).X-raydiffraction (XRD)data forpowder samples

were collected on Panalytical’s X’Pert Prowith CuKa radiation.

The samples were scanned in the range of 2q ¼ 5e80� at the

scanning speed of 2� permin. The surface areas of the catalyst

were determined by using the adsorptionedesorptionmethod

at 77 K by the standard Brunauer-Emmett-Teller (BET)method

using Micromeritics Tristar 3000 equipment. All samples were

degassed at 473 K for 90 min under nitrogen atmosphere to

remove the physisorbedmoisture from the catalysts. The field

emission scanning electron microscopy (FESEM) has been

performed on JEOL JSM 6510LV to collect the SEM images of the

catalysts. The transmission electronmicroscopy (TEM) images

of the catalyst have been recorded on HITACHI 7500 instru-

ment. Fourier transform-nuclear magnetic resonance (FT-

NMR) spectra of FAMEs and vegetable oils were recorded on

a Bruker Avance-II (400 MHz) spectrophotometer. The basic

Table 2 e Comparison of BET surface area, particle sizeand basic strength of CaO with KeCaO.

S. no. Catalysttype

BET surfacearea (m2 g�1)

Particlesize (nm)a

Basicstrength (H_)

1. CaO 3.96 � 0.01 104 9.8 < H_<10.1

2. 1.5eKeCaO e 43 10.1 < H_<11.1

3. 2.5eKeCaO e 41 10.1 < H_<11.1

4. 3.5eKeCaO 5.84 � 0.02 39 11.1 < H_<15.0

5. 4.5eKeCaO e 45 11.1 < H_<15.0

6. 5.5eKeCaO e 42 11.1 < H_<15.0

a DebyeeScherrer method.

b i om a s s a n d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8 461

strengths of the catalysts (H_) were determined by Hammett

indicatorsusing the following indicators: neutral red (H_¼ 6.8),

bromthymol blue (H_ ¼ 7.2), phenolphthalein (H_ ¼ 9.3), Nile

blue (H_ ¼ 10.1), tropaeolin-O (H_ ¼ 11.1), 2,4-dinitroaniline

(H_ ¼ 15.0), and 4-nitroaniline (H_ ¼ 18.4).

2.2. Preparation of catalyst

The nanocrystalline KeCaO was prepared by following the

wet impregnation method. In a typical preparation, CaO (10 g)

was suspended in 40 mL deionized water and to this 10 mL

aqueous solution of potassium hydroxide of desired mass

fraction was added to obtain 1.5e5.5% Kþ in CaO. The resulted

slurry was stirred for 3 h and finally dried at 180 �C for 24 h.

The prepared catalysts were designated as xxeKeCaO,

where xx represents the mass fraction of K in CaO, e.g.

3.5eKeCaO represents the catalyst prepared by impregnating

a mass fraction of 3.5% Kþ in CaO.

Same experimental method has also been employed for

the preparation of Liþ and Naþ impregnated CaO using LiOH

and NaOH as metal precursors.

2.3. Transesterification of waste cotton seed oil

All transesterification reactions were performed in a 100 mL,

two neck round bottom flask equipped with a water-cooled

condenser, oil bath and a magnetic stirrer. In a typical reac-

tion 10 g of oil, desired amount of catalyst and methanol were

agitatedwith apropellerwithanangular velocity of 62.8 rad s�1

atdesiredtemperature.Tomonitor theprogressof thereaction,

the samples (0.25 mL) from the reaction mixture have been

withdrawn after every 15 min with the help of glass dropper,

centrifuged and subjected to proton NMR analysis to quantify

the FAMEs produced. After the course of the reaction, the

reactionmixture was filtered to remove the solid catalyst. The

liquid phase was kept in separating funnel for 12 h to separate

the lower glycerol layer from the upper FAMEs, and excess

methanol from the later was recovered by rotary evaporator.

The FAMEs, hence produced, were quantified by proton NMR

technique following the literature reported procedure [33,34].

Cotton seed oil FAMEs 1H NMR (CDCl3, d ppm): 5.3 (m,

eCH¼CHe), 3.6 (s, eOCH3), 2.7 (m, eCH¼CHeCH2eCH¼CHe),

2.3 (m, eCH2eCOe), 2.0 (m, eCH2eCH¼CHe), 1.6e1.25 (m,

e(CH2)ne), 0.95 (m, eCH¼CHeCH3), 0.87 (m, eCH2eCH3).13C

NMR(CDCl3, dppm): 174.09 (eCOeCH2e), 129.9 (eCH¼CHe), 77.1

(CDCl3), 51.2 (eOCH3), 34.1 (eCOeCH2e), 31.9 (u3 eCH2e),

29.66e29.08 (eCH¼CHeCH2e, eCH2e), 27.2 (eCH¼CHeCH2e

CH¼CHe), 25.6e24.80 (eCOeCH2eCH2e), 22.70, 22.47 (u2

eCH2e) and 14.16 (u1 eCH3).

Similar patterns were observed in the proton NMR spec-

trum of FAMEs obtained from the transesterification of other

feedstocks.

Fig. 1 e Comparative powder XRD patterns of CaO with

1.5eKeCaO, 2.5eKeCaO, 3.5eKeCaO, 4.5eKeCaO and

5.5eKeCaO (* [ calcium oxide; A [ calcium hydroxide;

and , [ calcium carbonate).

3. Results and discussion

3.1. Preparation and structural properties of KeCaO

The basic strengths of the alkaline earth metal oxides and

hydroxides increase in the order of Mg < Ca < Sr < Ba [25] and

being less expensive and less toxic CaO has been selected as

catalyst support in present study. The catalytic activity of CaO

based catalysts was found to be a function of their basic

strengths [20,35]. The basic strength (H_) of commercial CaO,

used as support in present study, was found to be 9.8e10, and

same could be enhanced upto 11.1e15.1 by impregnating 3.5%

Kþ in CaO as given in Table 2. However, a further increase in

Kþ concentration (>3.5%) was not found to enhance the basic

strength of KeCaO to any further extent.

Surface area of a solid catalyst has direct impact on its

catalytic activity, a catalyst with higher surface area is ex-

pected to result in higher catalytic activity. The surface area of

pure calcium oxide (3.96 m2 g�1) was found to increase upto

5.84m2 g�1 when it was impregnatedwith 3.5%Kþ as shown in

Table 2. This increase in surface area could be attributed to the

appearance of the defects in regular CaO structure upon

potassium ion impregnation.

The structure and crystallite size of the KeCaO with Kþ

mass fraction in the range of 0e5.5% were determined by X-

ray diffraction studies. The commercial CaO shows peaks at 2q

values of 32.23�, 37.45� and 53.98� due to the presence of

calcium oxide in cubic form (JCPDS card no. 821691), as shown

Fig. 2 e (a) FESEM, and (b) TEM images of 3.5eKeCaO.

b i om a s s an d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8462

in Fig. 1. The presence of low intensity peaks at 29.4� and 64.4�

reveals the presence ofminor amount of calcium carbonate as

calcite in commercial CaO (JCPDS 881811). Upon Kþ impreg-

nation the formation of Ca(OH)2 in hexagonal form was

depicted due to the appearance ofmajor peaks at 18.06�, 34.09�

and 47.14� in the diffraction patterns of KeCaO (JCPDS 841266).

A change of Kþ concentration was not found to affect the

structure as supported by the appearance of similar diffrac-

tion patterns for the KeCaO having Kþ concentration in the

range of 1.5e5.5% as shown in Fig. 1. The absence of KOH

characteristic peaks (27.4�, 32�, 32.3� and 33.5�) in diffraction

patterns supports a high degree of dispersion of Kþ in resulted

KeCaO surface. The crystallite size of KeCaO determined

from XRD line breadth of crystal plane (011) by following

Debye-Scherrer method [36] is given in Table 2. The crystallite

size of CaO decreased from 104 nm to 43 nm upon 1.5% Kþ

impregnation. However, a further increase of Kþ loading was

not found to affect the crystallite size significantly and same

was found to be in the range of 39e45 nm (Table 2).

FESEM studies of 3.5eKeCaO show that it has hexagonal

and irregular shaped cluster of 2e5 mm sized particles as

shown in Fig. 2a. TEM analysis of the same particles reveals

that these are made up of hexagonal shaped particles with an

average size of w 50 nm as shown in Fig. 2b.

The characterization studies reveal that 3.5eKeCaO not

only exists in nano particle form but also possesses higher

basic strength and larger surface area than pure CaO and

hence, expected to show higher activity towards the trans-

esterification reaction.

3.2. Catalytic activity

The prepared KeCaO catalyst has been employed as solid

catalyst for the transesterification of a variety of feedstocks

viz., WCO, CSO, JO, SO, CO, KO and MF with methanol.

However, WCO, KO and JO have been selected as feedstocks

for optimizing the reaction parameters to achieve the

complete transesterification (98 � 2%) in minimum possible

time.

The transesterification reactions have been performed by

varying the following parameters (i) impregnated potassium

ion concentration, (ii) catalyst concentration, (iii) reaction

temperature, and (iv) methanol to oil molar ratio. Besides, the

reusability of the catalyst, effect of moisture content on

catalytic activity and its efficiency with a variety of feedstocks

has also been studied.

3.2.1. Influence of potassium ion concentrationThe Kþ concentrationwas found to affect the basic strength of

KeCaO, which in turn could have an impact on its catalytic

activity. To determine the optimum potassium ion concen-

tration for the best catalytic activity, a series of catalysts were

prepared by varying the amount of potassium in the range of

1.5e5.5% (in CaO). The transesterification reactions of either

WCO or KO or JO were performed with methanol (12:1 meth-

anol to oil molar ratio) at 65 �C in presence of 7.5% mass

fraction of KeCaO (with respect to oil). Reaction time required

for the complete transesterification was found to decrease

from 2.5 h to 1.25 h forWCO, 3.5 he2 h for KO and 4.25 he2.5 h

for JO as the potassium mass fraction in CaO was increased

from 1.5 to 3.5%. Same reactions when performed in the

presence of pure CaO didn’t yield more than 10% conversion

even after 10 h of reaction period. This experiment suggests

that Kþ impregnation is necessary to achieve the enhanced

catalytic activity of KeCaO. A further increase in Kþ ion

concentration (>3.5%) neither increases the basic strength,

nor catalytic activity as shown in Fig. 3 and hence, 3.5% Kþ

concentration was found to be optimum to achieve the

maximum catalytic activity.

In order to justify the K impregnation over Li or Na one,

a series of catalyst has also been prepared by impregnating

3.5% Li or Na in CaO. The transesterification reactions of the

WCO with methanol in presence of these catalysts have been

performed and the FAMEs produced have been investigated

for themetal concentration. As given in Table 3, on increasing

the size of impregnated alkali metal ion (Li to K), the catalytic

activity gradually decreases. Although LieCaO was found to

be most efficient (TOF ¼ 17.7 h�1) among the prepared cata-

lysts, however the same catalyst leached out maximum Li in

FAMEs (20,000 mg kg�1). On the other hand, KeCaO was found

to showmoderate activity (TOF¼ 13.2 h�1) but withminimum

leaching of the K (200 mg kg�1) in FAMEs, and hence the same

was studied in detail in present work. A similar trend of the

metal leaching in glycerol layer was also observed and

minimummetal concentration in later was observed (Table 3)

when KeCaO was employed as catalyst. Moreover, the FAMEs

produced from KeCaO catalysed reaction were found to have

the total metal ion concentration within the EN specification

1 2 3 4 5

1.5

2.0

2.5

3.0

3.5

4.0

Tim

e (h

)

% Mass fraction of K+

in CaO

WCO

KO

JO

Fig. 3 e Effect of potassium ion concentration on the time

required for complete transesterification of WCO, KO and

JO to corresponding FAMEs.

2 4 6 8 10 12

1

2

3

4

5

Tim

e (h

)

% Mass fraction of catalyst

WCO

KO

JO

Fig. 4 e Effect of catalyst concentration on the time

required for the complete transesterification of WCO, KO

and JO to corresponding FAMEs.

b i om a s s a n d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8 463

(<5000 mg kg�1), and hence would not required further

washing for the metal removal.

3.2.2. Effect of catalyst concentrationIn order to find out the appropriate catalyst concentration,

a series of transesterification reactions with methanol (oil to

methanol molar ratio of 12:1) at 65 �C were performed by

varying the mass fraction of 3.5eKeCaO in the range of

2.5e12.5%. An increase of catalyst concentration was found to

increase the rate of reaction and, in presence of 7.5% catalyst

complete transesterification of WCO, KO and JO required 1.25,

2.0 and 2.5 h, respectively. Same could be attributed to the

increase of catalytic sites on increasing the catalyst concen-

tration. However, a further increase in catalyst concentration

was not found to increase the reaction rate significantly, and

same time was required for the completion of the reaction

even with higher catalyst concentrations as shown in Fig. 4.

3.2.3. Effect of reaction temperatureA series of transesterification reactions were conducted in the

presence of mass fraction of 7.5% of 3.5eKeCaO, to find the

optimum reaction temperature. The catalyst was able to

completely transesterified the WCO, JO and KO even at room

temperature, although required relatively longer reaction

duration as shown in Fig. 5. The time required for the

complete transesterification of the same oils was found to

Table 3 e Comparison of the metal leaching from the catalysts

S. no. Catalyst Reactiontime (min)

TOF (h�1)

1. 3.5eLieCaO 30 17.7

2. 3.5eNaeCaO 30 14.6

3. 3.5eKeCaO 75 13.2

reduce significantly when the reaction temperature was

increased from35 �C to 65 �C. At 65 �C temperature 3.5eKeCaO

took 1.25 h, 2 h and 2.5 h for the complete transesterification of

WCO, KO and JO, respectively. A further increase in reaction

temperature does not reduce the reaction time significantly as

shown in Fig. 5 and hence, 65 �C was found to be an optimum

temperature to achieve the best catalytic activity of KeCaO.

3.2.4. Effect of methanol to oil molar ratioThe effect of methanol to oil molar ratio is one of the impor-

tant parameter that affects themethyl ester yield as well as its

production cost. Theoretical minimum methanol to oil molar

ratio should be 3:1 for the complete conversion of vegetable oil

to FAMEs. Transesterification being a reversible reaction,

nevertheless, usually such reactions were performed with an

excess of methanol to shift the equilibrium in forward direc-

tion to achieve the maximum FAMEs content. Heterogeneous

catalysts usually catalysed the transesterification reaction at

slower rate and took more time for the completion of the

reaction. To achieve the higher FAMEs yield in lesser time in

such reactions, the use of higher methanol to oil molar ratios

(even upto 275:1) have been documented in literature [37e39].

To determine the optimum methanol to oil molar ratio for

the 3.5eKeCaO catalyst, the reactions were performed by

varying the methanol to oil molar ratios from 6:1 to 21:1 at

in FAMEs and glycerol layer.

Metal ion leachingin FAMEs (mg kg�1)

Metal ion leaching inglycerol (mg kg�1)

Li or Na or K Ca Li or Na or K Ca

20,000 10,000 44,000 60,000

1800 9400 30,000 50,000

200 4500 25,000 40,000

40 50 60 70

1.5

3.0

4.5

6.0

7.5

Tim

e (h

)

Temperature (o

C)

WCO

KO

JO

Fig. 5 e Effect of reaction temperature on the time required

for the complete transesterification of WCO, KO and JO to

corresponding FAMEs.

6:1 9:1 12:1 15:1 18:1 21:1

1

2

3

4

5

6

Tim

e (h

)

Methanol/oil molar ratio

WCO

KO

JO

Fig. 6 e Effect of methanol to oil molar ratio on the time

required for the complete transesterification of WCO, KO

and JO to corresponding FAMEs.

2 4 6 8 10

1.0

1.5

2.0

2.5

3.0

3.5

Tim

e (h

)

% Mass fraction of moisture contents

Fig. 7 e Effect of added moisture contents on the time

required for the complete transesterification of WCO.

b i om a s s an d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8464

65 �C in presence of 7.5% catalyst. The rate of trans-

esterification reaction increases as methanol to oil molar ratio

was increased from 6:1 to 12:1. The same reaction required

1.25 h, 2 h and 2.5 h for the completion in case ofWCO, KO and

JO, respectively, when a 12:1 methanol to oil molar ratio was

employed. Further increase inmethanol to oilmolar ratio does

not increase the reaction rate significantly as shown in Fig. 6.

Thus a mass fraction of 7.5% of 3.5eKeCaO with respect to

oil, 12:1 methanol to oil molar ratio, reaction temperature of

65 �C and agitation of the reaction mixture with a propeller

with an angular velocity of 62.8 rad s�1, were the optimized

reaction conditions for the transesterification of employed

feedstock.

3.2.5. Effect of moisture and free fatty acid contentsPresence of >0.3% mass fraction of moisture contents in

feedstock leads to the formation of soap instead of FAMEs

when transesterification reaction was catalysed by homoge-

nous catalyst [8]. The WCO employed as feedstock in present

study were found to have mass fraction of 0.3% moisture

contents and transesterification reaction of the same using

NaOH or KOH as homogeneous catalyst leads to the saponi-

fication reaction. However, same reaction when catalysed by

3.5eKeCaO yielded the complete conversion of oil to FAMEs.

In order to determine the maximum moisture resistance of

the catalyst, the transesterification reactions of WCO were

performed in presence of 0.3e10.3% mass fraction of water

with respect of oil. The catalyst was able to complete the

transesterification of WCO in 3.5 h even in presence of 10.3%

moisture contents in the reaction mixture as shown in Fig. 7.

Likemoisture contents, presence of>0.5%mass fraction of

FFAs in feedstock leads to formation of soap instead of FAMEs

when reaction is catalysed by homogeneous catalyst [40].

WCO employed in present study were found to have mass

fraction of 0.4% FFAs, and transesterification reaction of the

same using NaOH or KOH as homogenous catalyst leads to the

formation of soap instead of FAMEs. However, same reaction

when catalysed by 3.5eKeCaO yielded the complete conver-

sion of oil to FAMEs in 1.25 h. In order to determine the

maximum FFA tolerance of the prepared catalyst, trans-

esterification reactions were performed with a variety of

natural feedstocks having different FFA mass fractions (%)

viz., mutton fat (0.9%), soybean oil (0.2%), virgin cotton seed oil

(0.1%), waste cotton seed oil (0.5%), castor oil (1.8%), karanja oil

(4.2%) and jatropha oil (8.4%). As shown in Fig. 8, under opti-

mized reaction conditions the catalyst was found to yield

SO MF CSO WCO CO KO JO

1.2

1.5

1.8

2.1

2.4

Time

FFAs

Type of feedstock

Tim

e (h

)

1.5

3.0

4.5

6.0

7.5

% M

as

s fra

ctio

n o

f F

FA

s

Fig. 8 e Effect of the FFAs on the time required for the

complete transesterification of a variety of feedstocks.

Acronyms; SO [ soybean oil, MF [ mutton fat,

CSO [ virgin cotton seed oil, WCO [ used cotton seed oil,

CO [ castor oil, KO [ karanja oil and JO [ jatropha oil.

1 2 3

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 Time

TOF

Number of cycles

Tim

e (h

)

4

6

8

10

12

TO

F (h

−1)

Fig. 9 e Reusability studies of the 3.5eKeCaO catalyst

towards the transesterification of the WCO.

b i om a s s a n d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8 465

complete conversion of the feedstocks having up to 8.4% FFAs.

However, the activity of the catalyst was found to be effected

due to the presence of the FFAs in feedstock. Relatively lower

catalytic activity of the 3.5eKeCaO catalyst towards the

transesterification of karanja and jatropha oil could be

attributed to the partial deactivation of the catalyst by the

higher concentration of FFAs present in these oils. Trans-

esterification of the same oils in the presence of homogeneous

catalyst (KOH) leads to the saponification of the oils instead of

FAMEs formation.

Hence, the solid catalyst, 3.5eKeCaO, employed in present

study clearly has an advantage over the homogeneous one

owing to its application for the transesterification of the high

free fatty acid and moisture containing feedstocks.

3.2.6. Reusability of the catalyst and homogeneouscontributionAn important advantage of the solid catalysts is their reus-

ability as same could reduce the overall processing cost of

a chemical reaction. To test the reusability and activity decay,

3.5eKeCaO, employed for the transesterification of WCO

under optimized conditions was recovered by filtration,

washed with hexane and dried at 180 �C. The catalyst hence

recovered and regenerated was reused under the same

experimental, and regeneration methods. As given in Fig. 9,

the reused catalyst was also found to yield complete conver-

sion of oil to corresponding FAMEs but with partial loss of

catalytic activity as supported by the reduced turn over

frequency (TOF) of the catalyst after every successive run. A

further application (4th cycle onward) of the catalyst could not

yield the complete transesterification of oil into FAMEs even

after 12 h of reaction period.

The leaching of the active species from the support is

a frequent problem among the alkali impregnated solid

catalysts [41e43]. The leached species not only reduces the

catalytic activity after every successive run but also catalyses

the reaction in a similarmanner as homogeneous catalyst can

do.Asdiscussedearlier, the reusabilitystudydemonstrates the

gradual loss of catalyst activity and samecould be attributed to

the leaching of K from CaO support. The metal ion analysis

supportsminimal concentration of K andCa in FAMESas given

in Table 3. However, most of the leached metal ions were

settled in glycerol layer, and K and Ca concentrations in same

were found to be 25,000 and 40,000 mg kg�1, respectively.

In order to quantify the homogeneous contribution due to

leached metal ions, 3.5eKeCaO (750 mg) has been refluxed

with methanol (4.4 g) for 1.25 h at 65 �C. The catalyst has been

removed through filtration, and methanol thus obtained has

been used for the transesterification of WCO (10 g) at 65 �C.Under the mentioned experimental conditions not more than

5% FAMEs yield were obtained. Thus present study ruled out

any significant homogeneous contribution in catalytic activity

due to leached species, and also supports that employed solid

catalyst is mainly responsible for the catalytic activity.

3.3. Kinetic study

The transesterification of triglycerides in presence of excess

methanol has been reported [44,45] to follow pseudo-first

order kinetics and rate law for the same could be expressed

as given in equation (1).

�lnð1� XmeÞ ¼ kt (1)

where Xme is the FAME content at time t (min).

The kinetics of the KeCaO catalysed transesterification of

WCO has been studied by employing a 12:1 methanol to oil

molar ratio, and plotting a graph between eln(1eXme) vs t as

given in Fig. 10.

The (pseudo) first order kinetic model is followed by the

same reaction as supported by the linear nature of these plots.

The rate constants calculated from the later were found to be

0.062 min�1, 0.032 min�1, 0.011 min�1 and 0.0034 min�1 at 65,

55, 45 and 35 �C, respectively.

-1

10 20 30 40 50 60 70 80

0

1

2

3

4

-ln

( 1

-X

me)

Time (min)

65 ºC 55 ºC 45 ºC 35 ºC

Fig. 10 e Plot of eln(1 e Xme) as a function of reaction time t

at different temperatures. Reaction conditions: methanol to

oil molar ratio of 12:1, a catalyst concentration of 7.5% and

reaction temperature of 65 �C.

b i om a s s an d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8466

The activation energy (Ea) and pre-exponential factor (A)

for the same reaction were estimated by following the

Arrhenius model [46] as given in equation (2).

ln k ¼ �Ea=RTþ ln A (2)

where R is the gas constant (8.31 J K�1 mol�1) and T is the

reaction temperature in Kelvin.

A plot between ln k vs 1/T is shown in Fig. 11, and the values

of Ea and A from the same graph was found to be 54 kJ mol�1

and 7.4 � 1010 min�1, respectively. The calculated activation

energy (54 kJ mol�1) was found to be within the reported range

(33e84 kJ mol�1) for the transesterification of vegetable oils

[44,47].

2.95 3.00 3.05 3.10 3.15 3.20 3.25

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

ln

k

1/T (x 10-3

K-1)

Fig. 11 e The Arrhenius equation curve for the

transesterification of WCO employing methanol to oil

molar ratio of 12:1.

3.4. KoroseNowak criterion test

In order to establish that the measured catalytic activity is

independent of the influence of transport phenomena [48], the

KoroseNowak (KN) criterion test modified by Madon‒Boudart

[49] has been employed. In present study, the test has been

performed with KeCaO catalysts having Kþ concentration in

the range of 0.5e3.5%. The rate of the transesterification of

WCO was measured at 45 and 65 �C, employing a mass frac-

tion of 7.5% of KeCaOwith respect to oil, and 12:1methanol to

oil molar ratio. To explain the KN criterion, the logarithm of

the reaction rate (ln r) in mol h�l g�1 catalyst vs the logarithm

of the weight of Kþ (ln fw) in g�1 in KeCaO has been plotted

(Fig. 12). The values of the KNnumbers (slope) found to be 0.96,

and 1.03 at 45 and 65 �C, respectively, from the same plot. The

KN number close to unity [48], as found in present study,

denotes that reaction obeyed the KN criterion and reaction

rates are not influenced by the rates of transport.

3.5. Physicochemical properties of FAMEs

The transesterification reactions of the WCO, KO and JO were

performed under optimized reaction conditions in presence of

3.5eKeCaO. After the completion of the reaction, the catalyst

was separated through filtration and liquid phase thus ob-

tained was kept in separating funnel for 12 h to separate the

lower glycerol layer from upper FAMEs layer. Excessmethanol

from later has been recovered with the help of rotary evapo-

rator, and few physicochemical properties of the FAMEs have

been studied by following the standard test methods as given

in Table 4. The values of the studied properties of the obtained

FAMEs were found within the acceptable limits of European

standards (EN-14214) as given in Table 4. The important

highlight of the study is the occurrence of total metal ion

concentration in FAMEs within the acceptable limit of

5000 mg kg�1 even without washing.

-5.0 -4.5 -4.0 -3.5

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0 65 ºC 45 ºC

ln

r (m

ol-1

h

-1

g

-1

c

ata

ly

st)

ln fw (g )

Fig. 12 e The Koros‒Nowak criterion plot of ln fw vs ln r for

K‒CaO catalysed transesterification reaction by varying the

K mass fraction in catalyst 0.5e3.5%. Conditions: oil to

methanol molar ratio 12:1 and catalyst concentration of

7.5% mass fraction of oil.

Table 4 e Physicochemical properties of the FAMEsprepared from WCO (FCO), KO (FKO) and JO (FJO).

S. no. Parameters FCO FKO FJO EN 14214 Testmethod

1. Ester

content

(%)

>99 >99 >99 96.5 1H NMR

2. Flash

point (�C)110 115 100 100e170 ASTM

D 93

3. Pour

point (�C)6 5 �1 e ASTM

D 2500

4. Kinematic

viscosity

at 40 �C

3.94 6 4.5 1.9e6.0 ASTM

D 445

5. Calorific

value

(MJ kg�1)

40 25 39 e IS 1350

P:2

6. Ash (%) 0.02 0.02 0.01 0.02 ASTM

D 874

7. Density at

31 �C(g mL�1)

0.80 0.89 0.87 0.86e0.89 IS 1448

P:32

8. Water (%) 0.05 0.05 0.5 0.5 ASTM

D 2709

9. Iodine value 84 86 90 <120 EN 14111

10. Acid KOH

value

(g kg�1)

0.1 0.5 0.3 0.8 ASTM

D 664

11. K/Ca

(mg kg�1)

200/

4500

300/

4400

300/

4600

<5000

(total

metal)

ASTM

D 1318

b i om a s s a n d b i o e n e r g y 4 6 ( 2 0 1 2 ) 4 5 9e4 6 8 467

4. Conclusions

In present work prepared, 3.5eKeCaO, was found to exist in

the form of w40 nm size particles as revealed by powder XRD

and TEM techniques. The same was found to be an effective

catalyst for the transesterification of a variety of feedstock

having upto mass fraction of 10.26% and 8.4% of moisture and

FFA contents, respectively. Under optimized reaction condi-

tions (methanol to oil molar ratio of 12:1, catalyst concentra-

tion 7.5%, and at 65 �C) the transesterification of the waste

cotton seed oil is a pseudo first order reaction and the observed

first order rate constant and activation energy for the same

reaction was found 0.062 min�1 and 54 kJ mol�1, respectively.

The catalyst has been recovered and recycled for three

consecutive reaction cycles with the partial loss of the activity

after every catalytic run. The lixiviation study supports the

negligible homogenous contribution in catalytic activity, and

KN test also demonstrates that catalytic activity is free from

transport phenomenon. Few physicochemical properties of

the FAMEs prepared from the waste cotton seed, karanja and

jatropha oils have also been studied, and observed valueswere

found within the limits of EN 14214 specifications.

Acknowledgement

We acknowledge the financial support from CSIR, New Delhi

(gs1) (Ref. No.: 01(2503)/11/EMR-II). We also thank SAIF (Panjab

University) for powder XRD, NMR and TEM, and Matter Lab

(Thapar University) for FESEM studies.

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