The chemistry of interesterification
processes
Albert J. Dijkstra
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario 2
What is interesterification?
• Interesterification of triglyceride oils can be defined as the exchange of fatty moieties between different triglyceride molecules (reshuffling) – In the chemical industry, we call it ester interchange
– For instance: DMT + glycol monomer + methanol
• There are three types of interesterification: – Randomization
– Directed interesterification
– 1,3-Specific interesterification
• There are two types of catalyst – Alkaline catalysts
– Lipase enzymes
A bit of history
• 1865. Charles Friedel & James R. Crafts heat a mixture of ethyl
benzoate and amyl acetate to 300°C and observe the formation
of amyl benzoate and ethyl acetate
• 1926. Christiaan van Loon discloses several catalysts for the
high-temperature interesterification process
• 1942. George B. Bradshaw & Walter C. Meuly (E.I. du Pont de
Nemours) disclose low-temperature, alkali catalysed FAME
production with glycerol co-product. The glycerol was needed
for the War effort; the FAME were used in soap production
• 1946. Frank A. Norris & Karl F. Mattil demonstrate that inter-
esterification causes the triglyceride composition to be random
• 1960. Josef Baltes proposes mechanism with glycerolate anion
as catalytically active intermediate
3 November 2015
World Congress on Oils & Fats and
31st ISF Lecture Series Rosario 3
A bit more history of
interesterification chemistry
• 1961. Theodore J. Weiss et al. propose a mechanism based on
β-keto ester formed from enolate that results from abstraction of
an α-hydrogen from fatty acid moiety
• 1972, 1973. Acetone and DMSO are found to accelerate the
interesterification reaction
• early 1980s. Alisdair Macrae (Unilever) starts with lipase
catalyzed interesterification for cocoa butter equivalents
• 2004. Linsen Liu demonstrates that acids without an α-hydro-gen do not take part in the interesterification
• 2004. I propose the ‘enolate’ mechanism
• 2005. Independent experimental support for the ‘enolate’ mechanism
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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3 November 2015 5
Reaction products
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario 5
When we randomize an equimolar A B
mixture of A3 and B3, we get equimolar 4 A + 4 B
mixture of all combinations A B
A3 + 3 A2B + 3 AB2 + B3
A A A B A B B B
A + A + B + A + B + A + B + B
A B A A B A B B
Now we assume A3 to have a much higher melting point than B3
and we cool the reaction mixture so that A3 starts to crystallize:
3 A3 + 0.04 A3 + 0.48 A2B + 1.92 AB2 + 2.56 B3
Triglyceride composition after
randomization
• The fatty acid composition of the fat blend
determines the triglyceride composition of the
reaction product
• [ABC] = mol fraction of triglyceride with fatty acids A, B and C
• [a], [b] and [c] mol fractions of fatty acids A, B and C in fat blend
• n = 1 if three fatty acids in triglyceride are the same, e.g. A3
• n = 3 if there are two different fatty acids in the triglyceride (A2B)
• n = 6 if the three fatty acids are different (ABC)
• The six permutations are: ABC. ACB, BAC, BCA, CAB, CBA
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario 6
Triglyceride composition on
directed interesterification
• First, the reaction mixture is randomized and
made to crystallize by cooling to below the
solubility of its highest melting component
• When this component then starts to crystal-
lize, residual liquid is no longer random
• By maintaining random equilibrium, more of
the highest melting component is formed
• A crystal slurry results with crystals of high
melting components in a randomized liquid
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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The formerly accepted glycerolate
mechanism starts with initiation
• The initiation step involves the nucleophilic attack of
the methanolate anion on a triglyceride molecule to
form the glycerolate anion and a fatty acid methyl
ester
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario 8
triglyceride methoxide intermediate glycerolate
+ FAME
O C R
O
O C R
O
H3C O
O C R
O
O
CH3
O C R
O
CH3
O
Then there is propagation leading to
interesterification
• The glycerolate anion forms a complex with a triglyc-
eride (nucleophilic attack) and then, the complex dis-
sociates into a novel triglyceride while regenerating
the glycerolate anion
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario 9
triglyceride glycerolate intermediate glycerolate +
novel triglyceride
O C R
O
O C R
O
O
O C R
O
O
O
O
RO
Then the reaction is terminated by
the addition of (acidulated) water
• Water is assumed to react with the sodium glycerol-
ate to yield a partial glyceride and sodium hydroxide
• But the amount of soap (or FFA) is observed to be
equimolar to the amount of sodium methanolate
• This observation can only be explained by assuming a
quantitative reaction between the sodium hydroxide
and triglyceride oil, which is most unlikely
– Soap boiling needs an excess lye and a long reaction time
– Using acidulated water prevents saponification
• The glycerolate mechanism cannot be the whole story
3 November 2015
World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario 10
We need another/additional catalytic
intermediate than just glycerolate
• This intermediate must form a free fatty acid
when reacting with water
• We observe that the amount of FAME formed
is equivalent to the amount of Na-methoxide
– Even when some of the methoxide has been
inactivated by water or FFA to give free methanol
• This intermediate must form fatty acid methyl
esters (FAME) by reacting with free methanol
• The enolate anion meets these requirements
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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What is an enolate anion?
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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• The enolate anion is formed by abstracting an α-
hydrogen atom from a fatty acid moiety
• The methoxide anion can abstract the hydrogen
• The enolate anion is stabilized by mesomerism
O C R
H
H
O
O CH3
O R
H
H
O
O CH3
O R
HO
fatty acid that is
part of glyceride enolate anion
methoxide
anion
keto-form enol-form methanol
The enolate anion reacts with water
• The glycerolate anion will react further with water and
form a partial glyceride and caustic soda
• The caustic will react with the FFA and form soap
• If the water had been acidified, the acid would
neutralize the caustic and leave the FFA as such
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
H
H CO
CH
R
O H
H
O
CO
CH
R
Oglycerolate
anion
FFA water enolate
anion
Methanol also has a hydroxyl group
• The enolate anion reacts with hydroxyl groups
• With free methanol, it reacts to give a FAME
and a glycerolate anion
• The enolate anion ‘mops up’ all free methanol
– FAME formation equivalent to sodium methanolate
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
H
CH3 CO
CH
R
O CH3
H
O
CO
CH
R
O
FAME
glycerolate
anion
methanol enolate
anion
Partial glyceride + enolate anion →
interesterification
• Enolate anion abstracts hydrogen from hydroxyl
group in partial glyceride
• Bond is formed between α-carbon and partial
glyceride
• Glycerolate anion is split off
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
CO
CH
R
O
H
O
CO
CH
R
O
Henolate
anion
partial
glyceride
glycerolate
anion
novel
triglyceride
Regeneration of enolate anion
• There is an equilibrium between enolate anion and
glycerolate anion
• High concentration of fatty acid moieties compared to free hydroxyl groups favours enolate anion
• Enthalpy difference may also favour the enolate anion
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O C R
H
H
O
O
O R
H
H
O
O
O R
HO
glycerolate
anion
enolate anion partial
glyceride
The role of acetone
• In 1972, Muller & Kock (Unilever) show that acetone
accelerates the interesterification process
• Could acetone act as proton transfer agent ?
• Proof was provided in 2005 when fully deuterated
acetone was added to an interesterification reaction
mixture and the deuterium was found to be
incorporated in the α-position of fatty acid moieties
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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acetone
enolate
anion O
CO
CH
R
CD3
O
D
D
D
O
CO
CH
R
CD3
O
D
DD
CD3
O
D
D
+ +
keto enol
What about the β-keto ester?
• Its presence has been spectrophotometrically
demonstrated
• It has been claimed as a catalytic intermediate
• Now its formation is considered to be the cause of
the loss of catalytic activity at elevated temperature
– Reaction temperature should be kept below 100°C
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
H2CO
C
CC
R2
R1O
H OO
H2CO
C
CC
R2
R1
OO
H2CO
C
CC
O
OO
H2CO
CHCC
R1O
OO
H H HR2
R2
R1
Transesterification or methanolysis
(Biodiesel production)
• When producing biodiesel (FAME), methanol is made
to react with triglycerides with sodium methanolate or
potassium hydroxide as catalyst.
• The process starts with two phases
– Oil at the bottom and methanol floating on top
• There is a period with a single phase
– High concentration of partial glycerides
• Finally, a glycerol phase settles at the bottom
– The alkalinity is concentrated in the glycerol phase
– Because polarity of glycerol favors presence of ions?
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Which catalytic intermediate when?
• In the beginning, the excess of methanol favors the
methoxy anion but energy arguments favour the
enolate anion
• With FAME formation, the methanol concentration
decreases and hydroxyl groups in partial glycerides
start playing a role
– This favours the glycerolate anion
• At the end, the alkalinity in the glycerol phase is
present as glycerolate anion
– In the organic phase, the high concentration of fatty acid
moieties causes the alkalinity to stem mainly from enolate
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Conclusions to be drawn
1. There are several catalytic anionic intermediates
– methoxy, glycerolate, enolate, hydroxy, carboxy
2. They are in equilibrium with each other, for instance
– glycerolate + FA in TAG ← partial glyceride + enolate
3. The equilibrium position is determined by
– free energy difference of the intermediates
– relative concentrations
4. Interesterification reaction favours the enolate anion
– As demonstrated by the formation of FFA on catalyst
inactivation by the addition of water
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
21
Industrial interesterification
(current practice)
• Interesterification is carried out as a batch process in
a vessel with heating coils, agitator and vacuum
connection
• The oil or oil blend to be interesterified must be
neutral but need not be bleached
• Its acidity is measured and enough caustic soda is
added to neutralize this acidity
• The batch is heated to some 80-90°C
• Vacuum is applied to dry the batch
– When the piping connecting the vessel to vacuum is no
longer warm, the batch is dry
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Industrial interesterification
(former practice)
• A continuous process has been operated
using a sodium glycerolate catalyst – Dissolve sodium hydroxide in a mixture of glycerol and
water.
– Add the solution to preheated (150°C) oil
– Spray dry mixture in vacuo
– Pump dry mixture through coil with few minutes residence
time to refining stage
• Suitable for large production volumes
• Avoids yield loss resulting from FAME
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
23
Industrial interesterification
(catalyst and yield loss)
• Sodium methanolate (methoxide) is commonly used
as interesterification catalyst
• A neutral and dry batch does not need more than
0.05 wt% catalyst (0.5 kg/tonne of oil) but most
people use more
– A low catalyst dosage leads to a low concentration of
catalytic intermediate and reduces by-product formation,
especially in second order reactions (ketone formation?)
• Using more catalyst is costly since yield loss (FAME
and FFA) is proportional to catalyst loading
• Yield loss can be the most important cost factor
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Ways to reduce yield loss
• Use sodium (or potassium) glycerolate
instead of sodium methanolate as catalyst
– Avoids the formation of FAME
• Anhydrous catalyst inactivation avoids the
formation of FFA
– Glacial acetic acid has been reported in literature
– But what about:
• Fatty acids that will be removed during deodorization
• Concentrated phosphoric acid?
• Acid activated bleaching earth?
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
25
Experimental support
• Interesterification with large excess of catalyst
– Take 50 g soya bean oil; measure FFA
– Dry under vacuum and add 0.5 g sodium methanolate (1%)
– Heat under vacuum to 100°C
– Inactivate with 5 g glacial acetic acid
– Wash with water until neutral
– Measure FFA in interesterified oil
• Amount of FFA formed: 0.82 – 0.12 = 0.70 %
• Equivalent amount of 1% NaCH3O
– 282 : 54 = 5.22 % FFA
• Far less FFA formation by anhydrous inactivation
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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There are other catalysts besides the
bases mentioned earlier
• Water can be used at high temperatures – Causes hydrolysis and subsequent esterification
when pressure is released
• Metal salts have been mentioned (Van Loon) – Are also used during manufacture of polyester
polymer from DMT and ethylene glycol
– Mechanism not well-understood
• Then there are enzymes – Especially those produced by genetically modified
micro-organisms
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Enzymatic interesterification using
1,3-specific lipase enzymes
• The process was developed to produce cocoa
butter equivalents, fats with a high content of
symmetric monounsaturated triglycerides
• Therefore, the starting material is an oil/fat with
a high oleic acid content at the 2-position
– High oleic acid sunflower seed oil
– Shea butter olein
• And exchanging the fatty acid at the 1,3-position
with a saturated fatty acid like stearic acid
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Fundamental problems of (stereo-
specific) enzymatic interesterification
• The first step in enzymatic interesterification
is the hydrolysis of a triglyceride
– Too much water causes extensive hydrolysis
– Too little water diminishes catalytic activity
• The 1,3-specific hydrolysis produces a 1,2- or
2,3-diglyceride
– These diglycerides isomerize to the more stable
1,3-diglycerides
– Loss of stereospecificity
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
29
Mechanisms of loss of specificity
(former proposal)
• Enthalpy difference between α and β positions is some 4 kJ/mol
• Mechanism requires 8 consecutive steps
• All steps are reversible
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
S
O
S
O- S
O
O- O + SO
S
- O
S
S
S
S+ S
S
S
S+ S
Mechanism of loss of specificity
(current proposal)
• Involves fewer steps than previous mechanism
• Therefore more likely
• Both mechanisms operate probably simultaneously
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
S
O
S
O- O
O
S
O
S
+ S
+ O
O
S
S
O
O
S
There are also kinetic problems
• This is the reaction that we would like:
• This is the reaction we get
• Only one out of four triglycerides is SOS
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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O
O
O
S
S
O4 8 S 4 8 O
O
O
O
S
S
O4 8 S
S
O
O
O
S
O
O
O
O 4 S 4 O
Solutions to the problems
• The kinetic problem can be alleviated by
shifting the equilibria by using a large excess
of stearic acid (or its methyl ester)
– This necessitates substantive purification
• The hydrolytic problem and the loss of stereo-
specificity can be alleviated by using a large
amount of rather dry catalyst
– This is costly when the enzyme loses its activity
• Sadly enough, in Europe, enzymatic CBE is
not allowed in chocolate 3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
33
Positioning of modification processes
• There are several modification processes that
change the physical properties of oils and fats
– Blending; simple, cheap and limited in scope
– Hydrogenation converts liquid oil into solid fat
• Makes oil more stable; expensive; forms trans isomers
– Interesterification changes physical properties
• Product properties depend only on fatty acid composition
– Fractionation generates two fractions
• Desirable fraction may have useless byproduct
• Byproduct may be used in interesterification blend
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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3 November 2015 35
Modification processes
35
Neutral oil
Bleaching
Deodorisation
Chemical
interesterification
Enzymatic
interesterification
Hydrogenation
Fractionation Deacidification
Fully refined
modified oil
Bleaching
Deodorisation
Bleaching
Industrial enzymatic interesterification
• The process is continuous
– Four reactors with immobilized enzyme in series
– The first reactor acts as guard to protect the others
– Changing from one type to another leads to the production of
unspecified material
• Can be reused based on its fatty acid composition
• The raw material should not inactivate the enzyme
– Therefore the raw material has to be neutralized, bleached,
deodorized and deacidified
– Using RBD palm oil is ideal since its ‘neutralisation’ by
physical refining comprises bleaching and deodorisation
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
36
Cost comparison chemical / enzymatic (Kellens and Calliauw, Oil modification processes, in Edible Oil Processing,
Hamm, Hamilton, Calliauw (eds), Wiley-Blackwell, 2013, Table 6.9, pp193-194)
Cost element Chemical Enzymatic
Usage/
tonne
Cost
($/tonne)
Usage/
tonne
Cost
($/tonne)
Labour 1 1.89 1 2.65
Steam 150 kg 3.75 12 kg 0.30
Electricity 15 kWh 2.25 4 kWh 0.60
Catalyst/Enzyme 1 kg 2.50 0.4 kg 22.00
Citric acid 0.5 kg 3.56
Bleaching earth 5 kg 3.30
Oil losses 18 kg 12.20 0.6 kg 0.51
Total cost, incl. Capital cost
and maintenance
40.00 40.00
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Assumptions underlying the cost
comparison
Chemical Enzymatic
Plant capacity (tonnes/day 140 100
Plant capacity (tonnes/year) 47 600 34 000
Capital investment (US$)
Equipment and engineering 1 100 000 1 000 000
Structural works 500 000 450 000
Installation 700 000 600 000
Total investment 2 300 000 2 050 000
Annual maintenance (US$) 40 000 50 000
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Comments on cost comparison
• The authors assume 1 kg catalyst per tonne of oil
instead of the perfectly viable 0.5 kg/tonne
– This would reduce catalyst cost by $ 1.25/tonne and the oil
loss by $ 4.80/tonne
• The authors include the post-treatment in the cost of
the chemical process but do not include any pre- or
post-treatment in the enzymatic process costs
– This makes a major difference because the treatment
preceding the enzymatic process is extensive
• The published cost comparison is biased in
favour of the enzymatic process
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
39
Towards a more impartial comparison
of current interesterification processes
• The enzymatic process is continuous and product
changes are awkward
– Large amount of oil involved in rinsing the reactors
– Really only suitable for single-product installations
• The chemical process can be batch or continuous
– Batch process is mandatory in multi-product situation
– In continuous process, no cross-contamination on change-over
• The chemical process is cheaper than the enzymatic
process
– Especially when raw materials are chemically refined
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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Look at the future
• Based on insight into the chemistry of the
chemical process, improvements are possible
– Yield loss is largest cost element
• Avoiding FAME formation improves yield
– Use catalyst made from glycerol and NaOH/KOH
– Also reduces sensitivity to water
• Avoiding FFA formation improves yield
– Anhydrous catalyst inactivation
– Strong acid, cationic ion exchange resin?
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
41
Take home messages
(the same as this morning)
• Understanding the chemistry of our processes
can lead to unexpected process improvements
– This also holds for “established” processes
• Understanding originates from questioning
established “truths”
– They can be myths that people got used to
• Biased reporting will eventually be exposed
– Then it may seriously backfire
3 November 2015 World Congress on Oils & Fats and
31st ISF Lecture Series, Rosario
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DIXI
(I have spoken)
3 November 2015 World Congress on Oils & Fats
and 31st ISF Lecture Series,
Rosario
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