The chemistry of interesterification processes - ASAGA€¦ · What is interesterification? ......

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


31st ISF Lecture Series, Rosario

4

3 November 2015 5

Reaction products



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



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



7

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



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



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


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



11

What is an enolate anion?



12

• 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



13

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



14

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



15

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



16

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



17

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



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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?



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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



20

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



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



22


(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



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(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



24

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?



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



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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



27

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



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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



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



30

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



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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



32

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


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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



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Modification processes

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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



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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



37

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



38

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



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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



40

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?



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



42

DIXI

(I have spoken)

3 November 2015 World Congress on Oils & Fats

and 31st ISF Lecture Series,

Rosario

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The chemistry of interesterification processes - ASAGA€¦ · What is interesterification? ......

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Transcript of The chemistry of interesterification processes - ASAGA€¦ · What is interesterification? ......