Development of an environmentally benign process for the production of fatty acid methyl esters

Article abstract of DOI:10.1016/S0045-6535(00)00329-5

The production of fatty acid methyl esters (FAME) is an important intermediate step in oleochemistry. The oleochemical production route starts with the renewable raw materials fat and oil and ends at fatty alcohols and different special products. Fatty acid methyl esters can be formed at mild reaction temperatures by transesterification of natural triglycerides (fats and oils). This contribution will show the development of a continuous process which is considering the main principles of production integrated environmental protection. The main advantages of this process are low energy consumption and minimal waste production. The process alternatives are shown and a scope on future problems which have to be solved to reach a real additional improvement of the fatty acid methyl esters production is given.

Full text of DOI:10.1016/S0045-6535(00)00329-5

Chemosphere 43 (2001) 99±105
Development of an environmentally benign process for the
production of fatty acid methyl esters
V. Jordan a,*, B. Gutsche b
a
Fachhochschule M u nster, University of Applied Sciences, Fachbereich Chemieingenieurwesen, Stegerwaldstraûe 39, 48565 Steinfurt,
Germany
b
Cognis Deutschland GmbH, 40551 D u sseldorf, Germany
Abstract
The production of fatty acid methyl esters (FAME) is an important intermediate step in oleochemistry. The oleo-
chemical production route starts with the renewable raw materials fat and oil and ends at fatty alcohols and di€erent
special products. Fatty acid methyl esters can be formed at mild reaction temperatures by transesteri®cation of natural
triglycerides (fats and oils). This contribution will show the development of a continuous process which is considering
the main principles of production integrated environmental protection. The main advantages of this process are low
energy consumption and minimal waste production. The process alternatives are shown and a scope on future problems
which have to be solved to reach a real additional improvement of the fatty acid methyl esters production is giv-
en. Ó 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Oleochemistry; Transesteri®cation; Reactor design; Catalysis; Process design
1
. Introduction
in oleochemistry because fatty acids are interesting in-
termediates for the production of di€erent special prod-
ucts in many applications such as esters for cosmetics.
1.1. Survey on the production processes of fatty acid
methyl esters
ꢀ
The transesteri®cation at temperatures below 100 C
catalysed by alkaline catalysts has great advantages
compared to the alternative process at high tempera-
tures of 200±240°C and corresponding pressures of more
than 50 bar. The low temperature process shows lower
energy consumption and lower investment costs but the
raw materials must have a higher quality (Gutsche,
1997). The oils and fats for low temperature transeste-
ri®cation must have a very small content of free fatty
acids because the catalyst reacts with the fatty acids
under formation of soaps which do not have any cata-
lytic performance at the chosen reaction conditions. A
more detailed summary of transesteri®cation technology
is given by Jeromin (1994) and Gutsche (1997).
Fatty acid methyl esters (FAME) are important in-
termediate products in oleochemistry (Fig. 1). They can
be produced by esteri®cation of fatty acids formed by
hydrolysis of fats and oils or directly by transesteri®ca-
tion of the natural triglycerides with methanol (Jeromin,
1994; Breucker et al., 1995; Gutsche, 1997; Dieckelmann
and Heinz, 1989).
In any case the by-product is glycerol. Since the fat
splitting gives a strongly with water diluted glycerol (only
1
0% of the mass is glycerol) and the energy consumption
of the glycerol processing has to be taken into account the
transesteri®cation route on the way to fatty alcohols is
preferable. Nevertheless fat splitting is an important step
1
.2. Transesteri®cation of triglycerides
Fats and oils are natural triglycerides, i.e. fatty acid
esters of glycerol. Transesteri®cation of triglycerides is a
*
Corresponding author.
0045-6535/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 4 5 - 6 5 3 5 ( 0 0 ) 0 0 3 2 9 - 5

1
00
V. Jordan, B. Gutsche / Chemosphere 43 (2001) 99±105
Fig. 1. Oleochemical production routes.
three-step reaction system with the intermediate prod-
ucts diglyceride and monoglyceride (see reaction Eqs.
lating three equilibrium reactions each of second order if
it is a homogeneous system.
(
1a)±(1c):
Typical of oleochemistry used reaction systems show
a very special mixing behaviour. The educts triglyceride
and methanol are not completely soluble. The starting
mixture consists of two liquid phases. With the
production of the emulsifying intermediates di- and
monoglyceride the reaction system becomes quasi-
homogeneous and at higher conversions when the
monoglyceride maximum is passed the mixture splits
into an ester- and a glycerol phase. The glycerol phase
contains the solved alkaline catalyst. The mixing beha-
viour can explain the acceleration of the reaction after a
starting phase of 1 min (Fig. 2).
Triglyceride ‡ Methanol ¢ FAME
Diglyceride
‡
ꢁ1a†
ꢁ1b†
ꢁ1c†
Diglyceride ‡ Methanol ¢ FAME
Monoglyceride
‡
Monoglyceride ‡ Methanol ¢ FAME
Glycerol
‡
Fig. 2 illustrates the reaction progress using a concen-
tration±time diagram for the reaction components tri-
glyceride (TRI), diglyceride (DI), monoglyceride
(
MONO), glycerol (GLY) and FAME. This diagram
shows own results of the transesteri®cation of the pure
triglyceride trilaurate measured at 60°C in an ideally
stirred laboratory vessel. This experiment was done to
clear the kinetics of the reaction: By postulating the
order of each reaction of the system it is possible to
determine activation energies and preexponential factors
and to calculate the temperature dependent rate con-
stants of the three forward and three back reactions. The
concentrations shown in Fig. 2 were determined by gas
chromatography after quenching the samples with
acidi®ed cold ethanol to interrupt the reaction immedi-
ately. As Noureddini and Zhu (1997) have shown the
reaction progress can be simulated very well by postu-
Fig. 2. Kinetic and mixing behaviour ± transesteri®cation of
trilaurate at 60°C.

V. Jordan, B. Gutsche / Chemosphere 43 (2001) 99±105
101
The reaction can be catalysed by sodium- or potas-
sium hydroxide dissolved in methanol. In the methanolic
solution the corresponding alkoxide is formed which is
the active form of the catalyst. The reaction Eq. (2)
shows this reaction for sodium hydroxide. Beside Eq. (2)
also shows that the more e€ective catalyst should be the
alkoxide in methanolic solution.
deacidi®cation, i.e. the FFA are neutralized with sodium
hydroxide and the soaps and phospholipids are sepa-
rated on centrifuges. The oil has to be washed to sepa-
rate the soaps completely. The soapstock and the used
washing water together are treated with sulphuric acid in
a soap splitting. The fatty acid produced in the soap
splitting is a by-product of the oil re®ning process with
quite low quality. Finally the oil has to be dried and
bleached. The described process is able to produce a
high quality oil which is absolutely necessary for the use
in food applications.
NaOH ‡ CH
3
OH ¢ NaOCH
3
‡ H
2
O
ꢁ2†
If oil and fats are used as raw materials in alkaline
catalysed transesteri®cation processes the requirements
are not as high as in food industry, it should be sucient
to use deacidi®ed raw materials with low water content.
So a pretreatment was developed which is able to con-
vert the free fatty acids to fatty acid methyl esters by
esteri®cation of the fatty acids with methanol (Jordan
and Gutsche, 1999; Breucker et al., 1995). This pree-
steri®cation can be carried out very advantageously at
60±80°C in a ®xed bed reactor with a heterogeneous
catalyst. Catalyst is a strongly acidic macroporous ion-
exchange resin. The preesteri®cation process consists of
one reaction step and one distillation step to separate the
water formed by reaction. The distillation can be done
on falling ®lm evaporators.
2
. Pretreatment of oils and fats ± deacidi®cation
Natural fats and oils are not pure triglycerides. They
contain some other components like free fatty acids,
phospholipids, tocopherol, carotene and sterols. The
content of free fatty acids can reach some weight per-
cents. This is important to know because the base-ca-
talysed transesteri®cation at temperatures below 100°C
can only use deacidi®ed and water-free raw materials.
Free fatty acids (FFA) in the raw materials of the
transesteri®cation will neutralize the alkaline catalyst
and the formed soaps are inactive, i.e. with higher con-
tent of FFA the catalyst consumption increases and the
result is a higher environmental load because catalyst
and soaps leave the process with the by-product glyc-
erol. With increasing water content the activity of the
catalyst is reduced, too: Free fatty acids are formed and
furthermore the alkoxide equilibrium is unfavourably
in¯uenced.
In relation to the FFA-content in the treated oils and
fats the methanol excess must be very high because the
catalyst has a high water anity. Due to the high water
concentration at the reactive centres the esteri®cation
equilibrium is in¯uenced unfavourably and the metha-
nol excess must be very high. If low quality oils and fats
with high acid values of more than 15 are used the
methanol excess gets so high that it is interesting to think
The classical pretreatment of oils and fats is a process
normally used in oil mills for deacidi®cation and de-
gumming of the raw materials (Fig. 3). It is an alkaline
Fig. 3. Chemical oil re®ning by neutralization.

1
02
V. Jordan, B. Gutsche / Chemosphere 43 (2001) 99±105
3
about a more sophisticated reaction technology such as
counter current esteri®cation. Counter current processes
are for example used in oleochemistry to produce fatty
acid methyl esters by esteri®cation of fatty acids with
methanol (Jeromin, 1994).
‰FAMEŠ ‰GLYŠ
K ˆ
ꢁ4†
3
‰CH
3
OHŠ ‰TRIŠ
(K is the equilibrium constant and the expressions in
brackets are the concentrations of the components tri-
The main advantage of the preesteri®cation compared
to the classical re®ning is that there are no waste streams
and the free fatty acid is not lost but also converted to a
high quality product (FAME). To guarantee a longterm
activity for the catalyst the oils have to be degummed to
remove the phospholipids. This can be done by di€erent
processes (Buchhold, 1993; Alfa Laval, 1995).
3
glyceride (TRI), methanol (CH OH), glycerol (GLY)
and FAME. Eq. (4) contains the simpli®cation that the
activities are replaced by concentrations.)
Eq. (4) shows the possibility to reduce the methanol
excess if the concentration of the by-product glycerol is
kept low. The ideal solution of this problem is a reaction
with simultaneous separation of the glycerol formed by
reaction, e.g. by a glycerol selective membrane (Fig. 4).
The actual knowledge of membrane, distillation or
extraction processes do not o€er any process with the
ability to separate glycerol selectively from the reaction
mixture of the described system. But the mixing behaviour
gives the possibility to separate the glycerol if the con-
version is so high that enough glycerol is arised to form a
glycerol phase. By using intermediate settling and sepa-
ration of the glycerol phase it is possible to get near the
ideality of a continuous and selective separation of the by-
product. Freedman et al. (1984) have pointed out this
possibility and comparedone-step to multi-step reactions.
Own investigations with coconut oil and other im-
portant raw materials have shown that a two step pro-
cess can reduce the methanol excess to 60% of the excess
of the single step process. This gives a big reduction of
energy consumption in the methanol processing.
3. Development of a continuous and environmentally
benign transesteri®cation process
The transesteri®cation of deacidi®ed and waterfree
oils and fats needs only some minutes to reach the
equilibrium conversion (Fig. 2), i.e. a batch process in an
ideally stirred vessel should have complete conversion in
some minutes, too.
A batch process is easily realized (Jordan and Gut-
sche, 1999). In those simple batch processes a methan-
olic sodium hydroxide solution is normally used to
catalyse the reaction. The catalyst solution, methanol
and oil can be premixed in a tube with static mixers and
pumped into a stirred reaction vessel. The reaction is
carried out under methanol re¯ux. After completed
conversion the mixture is pumped into a settling tank
and the ester-and glycerol phase can be separated.
The one-step batch transesteri®cation has the fol-
lowing main disadvantages (Jordan and Gutsche, 1999):
Fig. 5 shows the two-step reaction process (Aûmann
et al., 1989a). The feed materials and the catalyst solu-
tion are mixed in a tubular reactor with the help of static
mixers and after a reaction time of some minutes the
mixture reaches the phase separator where the ®rst re-
action step is completed and a glycerol phase is sepa-
rated. Since the glycerol solves methanol and catalyst it
is necessary to feed new methanol and catalyst to the
second reaction step. The second step looks like the ®rst.
The feed materials are mixed in a tubular reactor and in
a second vessel the formed glycerol phase is separated.
Due to the kinetics of the reaction in a well-mixed sys-
tem the use of tubular reactors has great advantages:
·
·
·
·
If conversions of more than 99.5% have to be realized
a high methanol excess will be necessary.
If methanolic sodium hydroxide solutions are used
the catalyst consumption will be high.
Due to high catalyst dosing the salt content of the by-
product glycerol is very high, too.
The discontinuous operation mode does not allow
economical energy recovery.
If a high production output is to be realized a continu-
ous process will be more favourable. This continuous
operation mode also gives the possibility to realize en-
ergy recovery.
·
the reactors can be realized with low investment
costs; and
3
.1. Reduction of methanol excess
The transesteri®cation consists of three equilibrium
reactions running in series. The mass-action expression
of the total reaction
Triglyceride ‡ 3Methanol ¢ 3FAME
‡
look as follows:
Glycerol
ꢁ3†
Fig. 4. Reduction of excess in equilibrium reactions by removal
of by-product.

V. Jordan, B. Gutsche / Chemosphere 43 (2001) 99±105
103
Fig. 5. Transesteri®cation in two stages.
·
because of the very good mixing the catalyst dosing
can be minimized to the ratios estimated in laborato-
ry experiments.
methanol should be nearly free of water. Own labora-
tory tests showed that a water content above 0.3% in the
reaction mixture is not tolerable. In technical applica-
tions water contents below 0.1% are surely guaranteed.
With increasing water content the catalyst is converted
from the active alkoxide to the hydroxide form. Besides
in small scale fatty acids are formed and these neutralize
the catalyst. Therefore an increasing water content re-
sults in a decreasing reaction rate.
However it is necessary to guarantee a minimum ¯ow
rate. At low ¯ow rates methanol and triglyceride run in
two separated layers through the reactor and the mass
transfer resistances between the two phases are so high
that the reaction becomes very slow and the planned
conversions will not be reached. The in¯uence of mixing
on the reaction progress was shown by Noureddini and
Zhu (1997) for stirred vessels and by own measurements
in pilot scale tubular reactors.
Zellner (1989) has done a comparison of di€erent
catalysts and shown that the use of alkoxides is more
ecient than the use of hydroxides. From this if follows
that it is necessary to use a methanolic sodium alkoxide
solution instead of the cheaper hydroxides if a maximum
in environmental protection has to be guaranteed. By
the described measures the average salt content of the
by-product glycerol can be reduced to 60% of the values
of a simple process with low quality raw materials.
Therefore, plants with large loading range use con-
tinuous stirred tank reactors or loop reactors (Gutsche,
1
997).
3
.2. Optimization of catalyst dosing
The ®rst measure to use as low catalyst dosings as
possible is the reactor design. By the use of tubular re-
actors (Aûmann et al., 1989a) with excellent mixing
caused by the turbulent ¯ow and by static mixers it is
possible to work with the lowest dosing rates.
4
. Process design
Fig. 6 shows the complete transesteri®cation process.
Furthermore by the pretreatment of the raw material
it has to be guaranteed that the FFA-content is as low as
possible. The acid value of the feeded oils and fats
should be below 0.15. This is a value which is normally
guaranteed by an alkaline re®ning process and the
preesteri®cation must be able to reach these oil qualities,
too. This step guarantees that only a neglectable portion
of the catalyst reacts directly with fatty acids (see reac-
tion Eqs. (5a) and (5b)) and becomes inactive at the
chosen reaction temperatures below 100°C.
The deacidi®ed and dried oil or fat is converted in two
steps to the products FAME and glycerol. In the two-
step reaction with phase separation a light phase with
high ester content and a heavy phase with high glycerol
content are produced. The excess methanol is in both
phases and has to be separated by distillation.
The separation can be done in multistage falling ®lm
evaporator units (Jordan and Gutsche, 1999). Due to the
use of such a multistage evaporation energy recovery is
possible. The hot products are used to preheat the ®rst
evaporating steps and the energy consumption of the
evaporator units can be minimized. The separated
methanol vapours are not condensed, they are fed di-
rectly into the methanol recovery column where water
and fatty materials are separated. (Jordan and Gutsche,
Sodium Hydroxide ‡ Fatty acid
!
Sodium Soap ‡ Water
ꢁ5a†
Sodium Methylate ‡ Fatty acid
Sodium Soap ‡ Methanol
1
999). By this measure a great part of the heat of the
!
ꢁ5b†
evaporation units can be recovered and used to provide
the methanol recovery with energy.
Another aspect which has to be considered is the water
content in the reaction mixture. The oils and fats and the
The methanol-free glycerol phase is treated with acid
to split the formed soaps. By this splitting reaction fatty

1
04
V. Jordan, B. Gutsche / Chemosphere 43 (2001) 99±105
Fig. 6. Transesteri®cation process.
acid is produced and continuously separated as a light
phase from the glycerol. The acidic glycerol has to be
neutralized by caustic-soda solution. This process must
be controlled by an applicable pH-control to minimize
the dosage of acid in caustic-soda solution and to min-
imize the salt content of the produced crude glycerol,
too. The fatty acid is washed with water to separate
traces of acid and can be recycled completely to the
process by feeding into the preesteri®cation.
treatment with water to wash out the glycerol (Gutsche,
1997), but a washing step has the main disadvantage
that a strongly diluted glycerol is produced. A better
possibility seems to be a separation of the undissolved
glycerol by coalescence separators (Aûmann et al.,
1989b) (Fig. 7). The coalescence separation produces a
concentrated glycerol which can be fed into the de-
scribed glycerol treatment. The crude glycerol can be
re®ned to highly pure glycerol which is normally done
by distillation. If the produced esters are used in the
production of fatty alcohols it is necessary to separate
the non-reacted materials. A residue is produced which
contains partial glycerides and inert substances like un-
saponi®ables. Due to the presence of inert substances
After methanol separation of the ester phase the
crude ester still shows a content of glycerol dispersed in
very small droplets. Due to the small size of the droplets
a phase separation in a simple settling tank takes much
time. In some plants this separation is realized by a
Fig. 7. Final glycerol separation by coalescence separators.

V. Jordan, B. Gutsche / Chemosphere 43 (2001) 99±105
105
this residue cannot be recycled completely. A part has to
be taken out of the cycle. The ratio between recycle and
waste production is dependent on the used raw materials
and their content of inert substances.
·
·
·
The transesteri®cation is carried out in two steps with
intermediate removal of the by-product glycerol to
keep the methanol excess as low as possible.
The dosing rate of the transesteri®cation catalyst is
optimized to have a low catalyst consumption and
a low salt content in the by-product stream.
The continuous process allows energy recovery and a
decrease of energy consumption compared to batch
processes.
5
. Potentials for future improvements
In the following some ideas are discussed which will
give an additional improvement of the described
transesteri®cation of fats and oils regarding environ-
mental protection.
Nevertheless there are some potentials for future im-
provements. The most important innovation would be a
process with a heterogenously catalysed transesteri®ca-
tion. By such a new reaction technology it is possible to
produce a salt-free glycerol which will lead to a glycerol
processing with minimal waste production.
Up to now only homogeneously catalysed transeste-
ri®cations are known. The by-product glycerol has al-
ways a salt load which gives a waste stream in the
following glycerol re®ning process. It has been shown
that it is possible to keep the catalyst consumption as
low as possible but a heterogeneously catalysed reaction
would be preferable because only by this measure waste
streams are avoided.
References
Alfa Laval, 1995. Degumming and Neutralization of Fats and
Oils. Alfa Laval ± process information paper.
The preesteri®cation is designed as a one-step ®xed
bed process. Due to the adsorption of water on the
catalyst the methanol excess must be extremely high. A
reaction with simultaneous separation of the formed
water will be an important step to realize an additional
energy saving. Therefore heterogeneously catalysed
counter current processes have to be developed.
The residue produced by ester distillation cannot be
recycled completely. An utilization must be found. The
residue contains partial glycerides and inert substances
which are natural fat accompanying substances. These
substances could be used to produce active substances
for pharmaceutical or food applications, i.e. the pro-
duced residue could be used in an economically inter-
esting way.
Aꢀmann, G., Blasey, G., Gutsche, B., Jeromin, L., Rigal, J.,
Armengaud, R., Cormary, B., 1989a. EP 0 494 177.
Aꢀmann, G., Gutsche, B., Johannisbauer, W., Ridinger, R.,
Rigal, J., Armengaud, R., Cormary, B., 1989b. EP 0466 744.
Breucker, Chr., Jordan, V., Nitsche, M., Gutsche, B., 1995.
Oleochemie ± Chemieprodukte auf der Basis nachwachs-
ender Rohsto€e. Chem. Ing. Tech. 67 (4), 430±440.
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Freedman, B., Pryde, E.H., Mounts, T.L., 1984. Variables
a€ecting the yields of fatty esters from transesteri®ed
vegetable oils. J. Amer. Oil Chemists Soc. 61, 1638±1643.
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Anwendung f u r die Biodieselproduktion. Fett/Lipid 99 (12),
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6
. Conclusions
Low temperature transesteri®cation is an environ-
Jordan, V., Gutsche, B., 1999. Reduction of waste production
and energy consumption in the production of fatty acid
methyl esters. In: Christ, C. (Ed.), Production-Integrated
Environmental Protection and Waste Management in the
Chemical Industry, Wiley-VCH, Weinheim, pp. 115±121.
Noureddini, H., Zhu, D., 1997. Kinetics of transesteri®cation
of soybean oil. J. Amer. Oil Chemists Soc. 74 (11), 1457±
mentally friendly process in the oleochemical production
route to fatty alcohols. The shown process concept has
the following main advantages:
·
Semi-re®ned (degummed) oils and fats with high acid
value can be used because the free fatty acid of the
raw materials reacts in a ®rst step to fatty acid methyl
esters.
1463.
Zellner, A., 1989. Katalytische Herstellung von Raps o lmethy-
lester. Dissertation, Universit a t Gesamthochschule Duis-
burg.
·
The reaction of free fatty acids to fatty acid methyl
esters is catalysed heterogeneously.