Thermal and catalytic oligomerisation of fatty acids

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Applied Catalysis A: General 330 (2007) 1–11

Thermal and catalytic oligomerisation of fatty acids

Pasi Tolvanen, Paivi Maki-Arvela, Narendra Kumar, Kari Eranen, Rainer Sjoholm,Jarl Hemming, Bjarne Holmbom, Tapio Salmi, Dmitry Yu. Murzin *

Process Chemistry Centre, Abo Akademi University, FI-20500 Turku, Finland

Received 15 January 2007; received in revised form 25 May 2007; accepted 7 June 2007

Available online 23 June 2007

Abstract

Thermal and catalytic oligomerisation of technical grade linoleic acid was investigated under argon atmosphere at 280 8C. The most efficient

catalyst was H-MCM-41 followed by H-Beta 75. Several types of products, such as cyclic and aromatic compounds were formed indicating a

complex reaction network for catalytic oligomerisation of fatty acids.

# 2007 Elsevier B.V. All rights reserved.

Keywords: Linoleic acid oligomerisation; Mesoporous materials; Size exclusion chromatography

1. Introduction

Fatty acid dimers are valuable components, which can be

used as ingredients in paints and glues [1]. Furthermore, amides

of fatty acid dimers derived from tall or soybean oil are used as

epoxy coatings, printing inks and hot-melt adhesives [1,2].

Oligomerisation of fatty acids has been intensively investigated

[3–31] and the reaction has been carried out in the presence of

homogeneous [4,31,32] and heterogeneous catalysts

[3,5,7,20,27–30,37]. Additionally, it is known that fatty acids

react during distillation in the absence of any catalyst under

high vacuum at 270 8C forming fatty acid anhydrides via

dehydration [33–36]. These anhydrides formed are unstable

and form high molecular neutral compounds.

Oligomerisation of fatty acids has been traditionally

catalyzed by homogeneous catalysts, such as alkali or alkaline

metal salts [31] and iodine [4]. Oligomerisation of a mixture

containing equimolar amounts of oleic and linoleic acid in the

presence of 0.05 wt.% iodine at 260 8C has resulted in the

formation of 22 wt.% dimers after 5 h [4]. Both Lewis acids,

such as SnCl4 [32] and Brønsted acid catalysts, e.g. resin in H+

form [37] catalyze oligomerisation of fatty acids.

Heterogeneous catalysts are environmentally more friendly

and their industrial use is more attractive than the use of

* Corresponding author.

E-mail address: [email protected] (D.Yu. Murzin).

0926-860X/$ – see front matter # 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcata.2007.06.012

homogeneous catalysts, since they can be easily separated from

the products and reused. Dimerisation of fatty acids has been

investigated intensively over clays [3,5,7,20,27–29] and

typically clay materials, such as bentonite and montmorillonite,

have been used in the oligomerisation of fatty acids [5–30].

Bentonite has been found to be a very efficient catalyst for

dimerisation of oleic acid [3,7,28]. The reaction mechanism for

fatty acid transformations was found to be complex, consisting

of dimerisation, also of hydrogenation and dehydrogenation

steps [8,9]. It has been stated, that these reactions are acid-

catalyzed and, furthermore, bicyclic dimers of linoleic acid can

be formed [15]. Dimerisation of oleic acid has additionally been

carried out in continuous mode over montmorillonite as a

catalyst giving the yields of the dimers between 40 and

60 wt.%, depending on the process parameters, such as

temperature, catalyst particle size and water content [20].

Cation-exchanged clays are active in oligomerisation of

fatty acids [5,29]. The highest yield of dimers was achieved for

tall oil at 230 8C by using 6 wt.-% clay containing montmor-

illonite and LiOH or Ca(OH)2. The conversion was 71% with

the product containing a mixture of dimers [29]. A mixture of

oleic and elaidic acid as well as tall oil derived fatty acids was

dimerized over a clay containing LiOH and as a result, 65 wt.%

of different kinds of dimers (linear, alicyclic, aromatic and

polycyclic) were formed [27]. Furthermore, it was stated in [27]

that oleic acid dimers produced over a clay exchanged with

LiOH exhibited mostly a linear structure, while linoleic acid

dimers were polycyclic. Dimerisation of oleic acid has also

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http://dx.doi.org/10.1016/j.apcata.2007.06.012

Fig. 1. (a) A proposed Diels–Alder reaction for a conjugated linoleic acid [13] and (b) a reaction scheme for the formation of aliphatic dimers from oleic acid [8,9].

P. Tolvanen et al. / Applied Catalysis A: General 330 (2007) 1–112

P. Tolvanen et al. / Applied Catalysis A: General 330 (2007) 1–11 3

been studied over montmorillonite exchanged with several

different metal cations [5]. The highest yield of dimers has been

obtained over a clay containing magnesium as a cation

(42 wt.%) [5]. The cations located between the catalyst layers,

were active for isomerisation, and not the external catalyst

layer, as earlier proposed. It has thus been stated that the rate of

dimerisation was not dependent on the catalyst acidity, but

depended on the interfacial distance between the clay layers

[19].

The drawback in using clays is the large amount of by-

products formed. To avoid side reactions and to develop more

selective catalysts for oligomerisation of fatty acids, it is

necessary to know the reaction mechanism for oligomerisation

of fatty acids. Several other heterogeneous catalysts, such as

silica–alumina, SiO2, g-Al2O3 and MCM-41, were investigated

in the dimerisation of oleic acid at 255 8C [30]. The yields

of dimers were the highest with a clay montmorillonite

followed by silica–alumina > Li-montmorillonite > acid-acti-

vated montmorillonite » SiO2 > MCM-41 = g-alumina. Inter-

estingly, also an acid-activated montmorillonite exhibited a

lower activity than montmorillonite [30].

The reaction mechanism for the oligomerisation of fatty

acids over the clays is, however, not very clear, and several

different mechanisms have been proposed [6–15]. In these

experiments, mostly oleic acid or mixtures of oleic and linoleic

acids as well as conjugated linoleic acids (a mixture of 9,11-

and 10,12-linoleic acid) have been applied. The formation of

three different types of dimers has been confirmed, namely

aromatic dimers, tetra-substituted ring forms, an alicyclic

unsaturated dimer as well as alicyclic saturated dimers. It has

been proposed that conjugated linoleic acid reacts according to

a Diels–Alder mechanism, combining two molecules via

electrophilic addition in the double bond position forming a

cyclohexene ring (Fig. 1a) [13–15]. On the other hand, the

dimerisation of fatty acids was suggested to be initiated via a

cation mechanism forming cyclic dimers [13]. Clays are stated

to act as Lewis acids generating carbenium ions [38]. The

reaction proceeds thus via protonation of the double bond.

Carbenium ions were also formed in oleic acid oligomerisation

in the presence of H+ (Fig. 1b) [8,9]. It was, however, stated that

carbenium ions are not very selective in catalyzing only

oligomerisation of linoleic acid, since several side reactions can

proceed simultaneously, such as double bond isomerisation,

chain branching [39] and lactonisation.

The aim of this study was to compare the thermal

oligomerisation of technical grade linoleic acid (linoleic acid:

oleic acid ratio about 2:1) with the catalytic one. Seven different

catalysts, varying acidity and pore size were tested.

2. Experimental

2.1. Catalyst preparation and characterization

2.1.1. Catalyst preparation

The used zeolites were supplied by Zeolyst International.

Prior to their calcination at 530 8C the Na-Beta zeolites were

ion-exchanged to NH4-form with 3 M NH4Cl.

Na-MCM-41 was synthesized by using the method

described in Refs. [40,41]. As a surfactant, and as a source

for silica and aluminium tetradecyltrimethylammonium bro-

mide (Aldrich), sodium silicate solution (Merck) and sodium

aluminate (Riedel de Haen), respectively, were used. The

surfactant was removed at 540 8C. The formed Na-MCM-41

was ion-exchanged with 1 M NH4Cl solution and washed with

distilled water to remove chloride ions. H-MCM-41 was

obtained after calcination of this material at 530 8C.

Si-MCM-41 mesoporous molecular sieve was synthesized in

a 300 ml autoclave (Parr Instruments) as mentioned in the Refs.

[40,41] with some modifications. A gel mixture was prepared

by using the reagents, fumed silica (Aldrich), tetramethyl

ammonium silicate (Sachem), sodium silicate (Merck),

cetyltrimethyl ammonium bromide (Aldrich) and distilled

water. As the prepared gel, mixture was introduced into the

300 ml autoclave (Parr) and synthesis of Si-MCM-41 was

carried out in an oven at 100 8C. After the completion of

synthesis, the autoclave was quenched, and the mesoporous

material was filtered and washed with distilled water. Drying of

the sample was carried out at 110 8C for 12 h and calcination to

remove surfactant was performed in a muffle oven at 550 8C for

10 h. Alumina was supplied from UOP and Fe2O3 (FeIII oxide)

from Sigma–Aldrich (>99%).

2.1.2. Catalyst characterization

The specific surface areas of the catalysts were measured by

nitrogen adsorption using Sorptometer 1900 (Carlo Erba

Instruments). The catalysts were outgassed at 200 8C for 4 h.

Zeolites and mesoporous materials were analyzed by X-ray

powder diffractometer (Philips PW 1820) to investigate the

phase purity.

The concentration of Brønsted and Lewis acid sites was

measured by FTIR (ATI Mattson) by using pyridine (>99.5%,

a.r.) as a probe molecule [42,43]. The quantification of pyridine

was based on the molar extinction coefficient determined in

Ref. [44].

2.2. Experimental procedure

Linoleic acid oligomerisation was studied in a pressurized

reactor under argon (AGA, 99.9999%) atmosphere. The dried

catalyst, typically 0.5 g, if not otherwise stated, and 130 g

linoleic acid (Fluka, technical grade) were put into the reactor

and the reactor was closed and heated up to the desired

temperature. The monomer concentration was calculated using

the average molecular mass of technical grade linoleic acid

(65 wt.% linoleic acid, 35 wt.% oleic acid corresponding the

molecular mass of 280.7 g/mol) being 3.207 mol/l. Thus the total

molar amount of acids was initially 0.463 mol. To suppress

external and internal mass transfer resistances, small catalyst

particle (below 150 mm) and intensive stirring (1000 rpm) were

applied in the kinetic experiments. The initial sample was

withdrawn as the heating of the reactor was started. When the

desired temperature was reached, the corresponding time was

taken as zero reaction time. The time for heating up the reaction

mixture to the desired temperature varied between 20 and


35 min. Samples with a volume of 1 ml were taken out from the

reactor and stored under nitrogen atmosphere prior to analysis.

2.3. Analysis

2.3.1. SEC–HPLC analysis

The samples were analyzed by SEC–HPLC technique.

Tetrahydrofuran was used as eluent. Typically five droplets of a

sample were pipetted into a measuring flask (50 ml) and

weighed. The flasks were filled with tetrahydrofuran and the

obtained sample concentrations varied thus between 1.3 and

1.4 mg/ml. The samples were analyzed by SEC–HPLC together

with the calibration samples containing a known concentration

of soybean oil. The samples were additionally flushed with

argon prevent oxidation of unsaturated acids and kept at 4 8Cprior to their analysis.

The diluted samples were filtered with a 0.2 mm filter

(containing a membrane material PTFE, teflon) and analyzed

by SEC–HPLC equipped with three different columns (Jordi

precolumn, Jordigel DVB500A (7.8 mm � 300 mm), TSK

G3000HHR (7.8 mm � 300 mm). The two similar columns

were used in series in order to improve the separation. The

components were detected with a LT-ELS-detector (Low-

Temperature Evaporative Light-Scattering Detector, Sedex 85,

Sedere LT-ELSD). The SEC–HPLC system contained addi-

Fig. 2. (a) A typical SEC-retention curve obtained in the oligomerisation of

linoleic acid over H-MCM-41 catalyst. The monomer (1) is eluted at 17.4 min,

and dimers (2) and trimers (3) at 16.15 min and at 15.40 min, respectively. The

trimer peak was relatively broad indicating most probably the co-elution of

higher oligomers. (b) The obtained retention curve for SEC-analysis of fatty

acids. Monomer, dimers and trimers were eluting at 17.4 min, at 16.13 min and

at 15.38 min, respectively.

tionally the following parts: the degasser (DGU-14A), the

gradient pump (FCV-10ALVP), the fraction collector (Phar-

macia LKB-HeliFrac) and the system controller (SCL-10AVP).

Additionally, a correction factor was fitted to very small dimer

concentrations in the following way. The high molecular

components eluted faster than the low molecular mass

components and the peak areas were measured with an

integrator (Shimadzu Class-VP 8v.6.12 SP5)). A typical SEC

chromatogram is shown in Fig. 2a. The molecular mass of the

compounds as a function of retention time is plotted in Fig. 2b.

Additionally it should be noted, that it was necessary to

analyze a large number of samples within the same day to

achieve representative data.

A correction curve obtained from comparison of the

concentrations of soybean oil with the corresponding dimer

concentrations, was used for quantifying the dimer concentra-

tion in all of the samples (Fig. 3a). As the concentrations varied

(Table 1) within 0.2 mg/ml it was not possible to get exact

kinetic data from the areas of response peaks. In this case, an

indirect analysis could be used, i.e. the ratio Adimer/Atot could be

determined. Thereafter, it was corrected according to the

deviation from the initial concentration (Adimer denotes the

dimer peak and Atot the total peak area).

2.3.2. Analysis with gas chromatography

The sample was diluted with acetone and dried under

nitrogen flow. Thereafter, it was dissolved with a mixture of

Fig. 3. (a) Correction factors derived from the values given in Table 1, and (b)

isolation of the dimer carried out by RP-HPLC-fractionation technique. Chro-

matogram from the end sample in the oligomerisation of linoleic acid over H-

MCM-41 at 280 8C after 330 min reaction time.

Table 1

Values used in the calculations for determination of the correction factor, with a

known amount of soybean oil as standard

Concentration of

soya oil (mg/ml)

Concentration according

to peak area (mg/ml)

Value of the

correction factor (cf)

0.016 0.004 4.271

0.032 0.008 3.852

0.032a 0.009 4.419

0.048 0.014 3.416

0.063 0.020 3.088

0.063a 0.027 2.869

0.079 0.030 2.677

0.079a 0.031 2.420

0.157 0.086 1.950

0.157a 0.090 1.803

0.248 0.184 1.294

a The same amount of soya oil, but different amounts of sample.

Fig. 4. Thermal oligomerisation of linoleic acid at 280 8C under argon.

Symbols: monomer (^), dimer (&) and trimer (~).


BSTFA-TMCS (4:1) in pyridine and silylated at 70 8C for

45 min. The silylated monomers were analyzed both with a

short column and with a long column. The short column was a

HP-1 column (6 m, 0.53 mm, 0.15 mm film thickness), which

was used applying the following temperature programme:

100 8C (1.5 min)–12 8C/min–340 8C (18 min). The injector and

detector were SPI (septum equipped programmable injector) of

on-column type with the temperature program 80 8C (0.5 min)–

200 8C/min–340 8C (18 min) and FI-detector working at 340 8C,

respectively. The long column was a HP-1, (25 m, 0.20 mm,

0.11 mm film thickness) and FI detector at 300 8C was used. The

split ratio was 1:20. As internal standards, heneicosanoic acid

and bis(ethyl)hexylphtalate were used, respectively. Addition-

ally, the samples were analyzed by GC–MS.

2.3.3. Separation and confirmation of fatty acid dimer

A reversed-phase liquid chromatographic technique (RP-

HPLC) was used as an alternative method to separate the

products. Higher concentrations of samples, up to 100 mg/ml,

could be analyzed with RP-HPLC than with SEC-HPLC,

whereas with SEC-HPLC analysis the concentrations were

about 1–2 mg/ml. Samples could be fractioned by using RP-

HLPC technique. Both methanol and 95 wt.% ethanol in water

were tested as solvents, but only the latter solvent was able to

dissolve the samples completely at room temperature. A sample

with the concentration of 100 mg/ml was dissolved in an

ethanol–water mixture and analyzed by the RP-HPLC method.

The eluent flow (ethanol) was 20 ml/min and the total retention

time for the sample (precolumn, 20 mm � 75 mm, Phenom-

enex RP-18, 20 mm � 250 mm, detector: UV, 210 nm) was

16 min. The sample was fractioned into 30 pieces of 10 ml

sample tubes with 0.5 min time interval and a typical RP-HPLC

chromatogram is displayed in Fig. 3b, in which two peak areas

are clearly visble, the separated fractions at 5 min (fractions

8–9) and a broad peak at 7–11 min (fractions 12–19). These

peaks are the monomer and dimer peaks, which were additionally

analyzed by SEC–HPLC technique. The fractions 2–6, 8–9, 12–

14, 16–19, 20–24, and 25–30 were combined and evaporated

with nitrogen gas and dried in vacuum oven. These samples were

analysed by 1H-NMR (JEOL JNM-LA400) and GC–MS.

2.3.4. Study of aluminium leaching from alumina

The dissolution of Al from Al2O3 was measured from the

centrifuged reaction mixture by using laser ablation (New Wave

Research, UP-213) – ICP-MS (Perkin–Elmer Elan 6100 DRC

plus) technique. The LA-ICP-MS analysis of the samples was

done in a frozen state at�80 8C. The Laser Ablation Cryo-Cell

has been constructed in house.

3. Results and discussion

3.1. Catalyst characterization results

Seven different catalysts were used in the oligomerisation of

linoleic acid: g-Al2O3, Fe2O3, and three different H-Beta zeolites

exhibiting different Si/Al ratios, as well as two mesoporous

catalysts, mildly acidic H-MCM-41 and non-acidic Si-MCM-41

(Table 2). The X-ray powder diffraction pattern of Si-MCM-41

was similar to that of MCM-41. The BET surface area of Si-

MCM-41 was determined to be 1208 m2/g.

The catalysts exhibited both varying Brønsted and Lewis

acidities (Table 2). In the series of H-Beta zeolites, the most

acidic material was H-Beta-22 with the lowest Si/Al ratio. The

concentration of strong acid sites was H-Beta zeolites display

also Lewis acidity. The mesoporous H-MCM-41 contained a

higher amount of Brønsted acid sites than H-Beta-300. No

Brønsted acid sites were present in Si-MCM-41 and g-Al2O3

contained 7 mmol/gcat Brønsted acid sites, whereas it contained

the second highest amount of Lewis acid sites after H-MCM-41.

3.2. Oligomerisation results

Linoleic acid is known to oligomerize in the absence of any

catalyst via a thermal route [46]. Thus, a comparison of thermal

and catalytic oligomerisation of linoleic acid was performed in

this work.

3.2.1. Thermal oligomerisation of linoleic acid

Thermal oligomerisation of linoleic acid (Fig. 4) was carried

out at 280 8C under Ar (Table 3). The initial oligomerisation

rate, defined as a change in the molar total amount of the acids

Table 2

Properties of the screened catalysts

Catalyst Brønsted acid sites (mmol/gcat.) Lewis acid sites (mmol/gcat.) Specific surface area (m2/gcat.) Refs.

g-Al2O3 7 156 299 [42]

H-Beta-22 183 (120) 128 (113) 657a [42,43]

H-Beta-75 176 (114) 43 (16) 664a [42,43]

H-Beta-300 82 (10) 30 (4) 805a (4b) [42,43,45]

H-MCM-41 89 168 902c [42]

Si-MCM-41 0 – 1208c

Fe2O3 – – –

The acidity was determined by pyridine adsorption method, the desorption was performed at 200 8C and the values given in parenthesis correspond the desorption

temperature of 450 8C.a Dubinin method.b Specific surface area of a spent catalyst.c BET-method.


per time unit was calculated. The initial rate was 0.34 mmol/

min resulting in the conversion of 10% after 270 min. Initially,

only dimer was detected within the first 110 min, after which,

trimer formation started. This result differed from the initial

product distribution observed in catalytic oligomerisation

(Figs. 5–7), where trimers were visible already after 30 min.

This result might indicate a consecutive reaction pathway for

trimer formation. The thermal oligomerisation of linoleic acid

has been studied in several publications [9,22,46]. It was stated

in Ref. [46] that the reaction proceeded under an inert

atmosphere via formation of conjugated acids followed by a

reaction with another conjugated molecule according to Diels–

Alder condensation. Thermal oligomerisation of linoleic acid

can, however, take place via complex reactions leading to the

formation of monocyclic nonaromatic, aromatic and linear

dimers [22]. In Ref. [9], it was additionally suggested that

primary cyclic products are slowly converted to aromatic

compounds and cyclohexane derivatives. During the heating

period, some isomerization takes place leading to formation of

both linear fatty acids (partially hydrogenated and stearic acid),

which in turn form dimeric fatty acids. The rates for thermal

oligomerisation of different fatty acids, oleic, linoleic and

linolenic acids have been compared at different temperatures,

and it turned out that the reaction rates increased as follows:

oleic acid < linoleic acid < linolenic acid [47]. In this work, a

detailed analysis of the products in thermal oligomerisation of

linoleic acid was not performed, since the main aim was to

Table 3

Performed oligomerisation experiments

Entry Catalyst Reaction time (min) mreactant (g) mcat (g)

1 No catalyst, thermala 360 130 –

2 g-A2lO3b 300 130 0.50

3 H-Beta-22 390 130 0.50

4 H-Beta-75 390 130 0.50

5 H-Beta-300 390 130 0.50

6 H-MCM-41-Fc 390 105 0.35

7 Si-MCM-41 390 130 0.50

8 Fe2O3 390 130 0.50

Experiments were carried out at under Ar atmosphere at 280 8C and 5 bar.a Pressure varied between 4 and 5 bar.b 4 bar.c The same mass ratio reactant to catalyst used as in other experiments.

Fig. 5. Kinetics for the oligomerisation of linoleic acid at 280 8C under argon,

(a) concentration of linoleic acid, (b) the concentration of dimers and (c) dimer

concentration as a function of trimer concentration over (^) H-Beta-22, (&) H-

Beta-75 and (~) H-Beta-300.

Fig. 6. Kinetics for the oligomerisation of linoleic acid at 280 8C under argon

(a) concentration of linoleic acid, (b) the concentration of dimers and (c)

concentration of dimer as a function of trimer concentration over (^) H-MCM-

41 and (&) Si-MCM-41.

Fig. 7. Kinetics for the oligomerisation of linoleic acid at 280 8C under argon

(a) concentration of linoleic acid, (b) the concentration of dimers (solid symbol)

and trimers (open symbol) and (c) dimer concentration as a function of trimer

concentrration over Al2O3 (^) and Fe2O3 (&).


compare the rates and conversions in thermal and in catalytic

oligomerisation (see below).

3.2.2. Catalytic oligomerisation of linoleic acid

3.2.2.1. Initial oligomerisation rates. The initial catalytic

oligomerisation rates, defined as the change in the molar total

amount of acids per time unit and per gram of catalyst, were

calculated over different catalysts. The initial rates, shown in

Table 4, demonstrated that there is no correlation between the

initial rate and the catalyst acidity. Interestingly, for the H-Beta

zeolite catalyst series, the initial rate over the most acidic

catalyst H-Beta-22 was lower than over H-Beta-300 and H-

Beta-75 indicating that this catalyst most probably exhibited

too high amount of strong acid sites, on which irreversible

adsorption of linoleic acid occurred leading to catalyst

deactivation. The concentration of strong acid sites, i.e. from

which pyridine was desorbed at 450 8C, was highest for the H-

Beta-22 catalyst (Table 2). The initial rates over H-Beta-300

and H-Beta-75 were about the same, suggesting, moreover, that

that the initial rate was not correlating with the amount of

Brønsted acid sites. When using mesoporous catalysts, it can be

observed that the initial rates were in the same range as

achieved over Beta zeolites (Table 4). Moreover, when

comparing the initial rates over H-MCM-41 and Si-MCM-

41, it can be observed that the presence of Brønsted acid sites is

beneficial for the oligomerisation of linoleic acid. The larger

pores in the mesoporous catalysts do not enhance the initial

reaction rate compared to microporous zeolites.

3.2.2.2. Conversion after prolonged reaction times. The

conversion after 300 min was the highest over H-MCM-41

followed by Beta-75. In the H-Beta catalyst series, an optimum

Table 4

Kinetic results from thermal and catalytic oligomerisation of linoleic acid

Entry Initial ratea

(mmol/min/gcat.)

Conversion after

300 min (%)

Ydimer after

300 min (%)

dcdimer/dctrimer

within 0–30 min

dcdimer/dctrimer

within 30–90 min

ctrimer after

300 min (mol/l)

1 0.34b 10.1 6.5c Large Large 0.007c

2 0.42 9.8 6.9 12 Large 0.005

3 0.50 14.2 9.8 71 42 0.015

4 1.74 31.8 20.6 47 10 0.042

5 1.68 16.6 11.5 15 29 0.023

6 2.70 42.2 23.7 7.2 7.1 0.104

7 0.87 12.5 8.3 4.3 38 0.015

8 0.40 11.0 7.4 4 30 0.013

a Initial rate is calculated from the reacted amount of linoleic acid in the beginning of the experiment divided by the time interval and the mass of catalyst.b mmol/min.c After 270 min.

Fig. 8. The mass spectra of the dimers showing MS of the silylated dimers with the molecular mass of 702 g/mol and 704 g/mol.


concentration of Brønsted acid sites was observed for H-Beta-

75, which was able to convert 32% monomers followed by the

second best catalyst, Beta-300 with the conversion of 17%. As

stated above, the most acidic Beta-22 most probably contained

too large amounts of strong acid sites partially declining the

conversion of fatty acid monomers due to catalyst deactivation,

although reaction proceeded over this catalyst with about the

same rates as over the H-Beta-300 catalyst (Fig. 5a). Catalyst

deactivation was clearly shown also for the H-Beta-300

catalyst, since the specific surface area of a spent H-Beta-

300 catalyst decreased by tenfold compared to the fresh

catalyst. Deactivation over this catalyst was observed, although

it exhibited the lowest amount of strong acid sites from the three

H-Beta catalysts. Deactivation over the H-Beta-22 might be

partially explained by the high concentration of weak and

strong Lewis acid sites, these values are much larger for

H-Beta-22 than for other H-Beta zeolites (Table 2).

When comparing the mesoporous catalytic materials,

H-MCM-41 and Si-MCM-41, it can, however, be observed

that the presence of acidic sites is beneficial for transforming

fatty acids to oligomers. The conversion levels over the former

and the latter catalysts are 42% and 12.5%, respectively. When

comparing the conversion in linoleic acid oligomerisation

achieved over H-MCM-41 with the results obtained in oleic

acid oligomerisation [30] over MCM-41, it can be observed that

the most active catalyst was H-MCM-41 in the current work,

whereas for oleic acid oligomerisation, only 1% conversion was

achieved at 255 8C [30]. Although the Si/Al ratio in MCM-41

was 16 [30], most prabably this catalyst was not ion-exchanged

to the proton form, since that was not mentioned in the original

recipe [48]. The three non-acidic catalysts, Al2O3, Fe2O3 and

Si-MCM-41 gave about the same conversion as was obtained in

the thermal oligomerisation of linoleic acid (Table 4).

3.2.2.3. Product distribution in the oligomerisation of linoleic

acid. The product distribution was compared by plotting the

dimer concentrations as a function of trimer concentrations

(Figs. 5c–7c). It can be seen that over H-MCM-41 dimers and

trimers were formed almost parallelly, whereas over other

catalysts there is a delay in the trimer formation for about

30 min. This result indicates that H-MCM-41 is shape selective

catalyzing trimerisation reaction. The ratio between the

Fig. 9. 1H NMR spectra (600 MHz, CDCl3) of (a) technical grade linoleic acid,

all products from the oligomerisation of linoleic acid at 280 8C (b) over Al2O3 at

180 min, (c) over H-MCM-41 after 210 min.

Fig. 10. Enlarged part of the 1H NMR spectra (600 MHz, CDCl3) in a range of

d = 4.8–7.5 ppm showing signals from olefinic and aromatic protons, (a) the

technical grade linoleic acid, the products from the oligomerisation of linoleic

acid at 280 8C (b) over Al2O3 at 180 min, (c) over H-MCM-41 after 210 min.

Fig. 11. Kinetics in the isomerisation of oleic and linoleic acid over H-MCM-

41 at 280 8C. The concentrations of monomeric acids: (*) linoleic acid, (*)

isomer of linoleic acid, (^) oleic acid, (^) isomer of oleic acid, (&) other

linoleic and oleic acid isomers.


formation rate of dimer to trimer was calculated within the first

30 min and between 30 and 90 min reaction time (Table 4)

showing that over Beta-22 and Beta-75 more trimers were

formed with increasing time, when the slope dcdimer/dctrimer

decreased, whereas it was constant for H-MCM-41. On the

other hand the relative rate for formation of dimer increased

with increasing reaction times compared to the relative rate for

trimer formation over Beta-300, Si-MCM-41, Al2O3 and

Fe2O3. These catalysts exhibited lower amount of Brønsted

acid sites compared to H-Beta-22 and H-Beta-75.

The trimer formation after 300 min reaction time decreased,

however, as follows: H-MCM-41 > Beta-75 > Beta-300 >Beta-22 = Si-MCM-41 > Fe2O3 > thermal > Al2O3. Addi-

tionally over the most active catalyst, H-MCM-41 the amount

of trimers formed after 300 min reaction time was 2.5-fold of

that obtained over the second best catalyst, H-Beta-75

(Table 4), which indicates that mesoporous catalyst exhibits

shape selectivity catalyzing trimerisation of linoleic acid. The

corresponding ratio between the most efficient catalyst, H-

MCM-41, and the third effective catalyst for trimer formation,

H-Beta-300, was 4.5, whereas the most acidic catalyst H-Beta-

22 yielded only 0.015 mol/l trimer after 300 min being equally

active as Si-MCM-41 indicating the extensive catalyst

deactivation in H-Beta-22. The mesoporous Si-MCM-41

containing no Brønsted acid was thus surprisingly active,

being able to catalyze trimer formation. There should be both

an optimum acidity and enough acid groups for trimer

formation. Additionally, the larger pores in the mesoporous

acidic catalyst, H-MCM-41 are beneficial for trimer formation

compared to Beta-75 and this result indicates that the pore

structure is more important for trimer formation than acidity.

Detailed GC–MS and NMR analyses were performed for the

samples obtained over the most active catalyst, H-MCM-41

(Figs. 8–10). In the GC–MS case, dimers could be detected

exhibiting molecular masses of 702 g/mol and 704 g/mol,

respectively (Fig. 8). These compounds corresponded to

silylated linoleic–oleic and linoleic–linoleic acid trimers.

NMR results gave the ratio between linoleic and oleic acid

of 2:1, as it was in the original technical grade linoleic acid.

Isomerisation of linoleic acid to conjugated linoleic acid is

visible from the NMR spectra at d = 2.8 ppm, which

corresponds to the range where the CH2 group at C11 occurs.

This peak has decreased in the sample obtained over H-MCM-

41 (Fig. 9). The chemical shift ranges d = 4.8–6.5 ppm and at

d = 7.0–8.0 ppm correspond to the olefinic and the aromatic

protons, respectively. The unsaturated compounds might be

cyclohexene derivatives, indicating that the Diels–Alder

reaction during the oligomerisation. Furthermore, there were

also traces of aromatic compounds indicating cyclisation

reactions followed by dehydrogenation reaction. New types of

unsaturated compounds were formed giving signals in the range

of d = 5.5–7.5 ppm (Fig. 10). Thus, it can be concluded that the

oligomerisation over H-MCM-41 proceeded via a complex

reaction sequence forming linear and cyclic dimers, as well as

aromatic compounds. Additionally, the monomer fractions of

the samples obtained in the oligomerisation of linoleic acid

over MCM-41 samples were analyzed by GC (Fig. 11). The

results revealed that both linoleic and oleic acid were

isomerized via double bond shifts. Moreover, about 34% of

other unsaturated C18 fatty acid isomers, eluting from the GC

column within a time range of 13–15 min, were formed. Other

unidentified isomers of oleic and linoleic acids were formed

about 40%.


Iron oxide was able to catalyze trimer formation. The

concentration of trimers at 330 min reaction time was, however,

only 0.01 mol/l over this material. A part of Fe2O3 dissolved in

the reaction mixture, since the colour of the mixture was red

after centrifugation. These results are not surprising, since it is

known from litterature [49] that dissolved homogeneous iron

species together with potassium iodide can catalyze oligomer-

isation of fatty acids. Moreover, montmorillonite catalyzing

oligomerisation of fatty acids [25], contains Fe2O3.

Aluminium oxide was not a very efficient catalyst in the

oligomerisation of linoleic acid. This result is in accordance

with literature [30], according to which only below 1% dimers

of oleic acid was formed at 355 8C over g-Al2O3. The viscosity

of the sample obtained from the oligomerisation of linoleic acid

over Al2O3 after 180 min reaction time was, however, very

high. Due to the high viscosity of the samples further

investigations with NMR spectroscopy were carried out with

two samples, obtained over H-MCM-41 after 210 min and from

Al2O3 after 180 min. This further investigation with NMR

spectroscopy was performed, since the samples analyzed with

SEC were filtered prior to the analysis (see Experimental),

while in the NMR studies, the samples were not treated prior to

the analysis. The NMR spectra of linoleic acid along with

samples treated with Al2O3 and H-MCM-41 are displayed in

Fig. 10. It is clearly visible from the NMR spectra that there are

no organic higher polymers formed over Al2O3. The high

viscosity in the sample obtained from Al2O3 is thus not due to

formation of organic higher polymers, indicating that the SEC-

analyses of these samples are correct. The high viscosity could

thus originate, most probably, from dissolved aluminium ions,

which can interact with organic molecules. The dissolved

aluminium species were confirmed to be present in the

centrifuged reaction mixture by laser ablation ICP–MS

technique in the oligomerisation of linoleic acid with Al2O3.

4. Conclusions

Thermal and catalytic oligomerisation kinetics of linoleic acid

was studied in a batch reactor at 280 8C under inert atmosphere.

The products were analyzed by size exclusion chromatography,

NMR and GC–MS techniques. In thermal oligomerisation, the

conversion level was about 25% of the conversion level obtained

over the most efficient catalyst, H-MCM-41 within 300 min

reaction time. In catalytic oligomerisation three different H-Beta

zeolites with varying acidities, as well as mesoporous acidic and

nonacidic materials, namely H-MCM-41 and Si-MCM-41, were

studied. Additionally, the performances of these catalysts were

compared with the performance of g-Al2O3 and Fe2O3. The

initial oligomerisation rates did not correlate either with the

catalyst acidity or with the pore sizes of the catalysts. The highest

initial rate over H-Beta zeolites was achieved over H-Beta-75

exhibiting an optimum amount of acidic sites.

Acknowledgements

This work is part of activities at the Abo Akademi Process

Chemistry Centre of Excellence Programmes (2000–2011)

financed by the Academy of Finland. The authors acknowledge

Mr. Teemu Heikkila at the University of Turku, Department of

Physics, who performed XRD-analysis and Dr Paul Ek at Abo

Akademi University, who carried out ICP–MS analysis.

Appendix A

Since the response for the dimer fraction was not linear, it

should be corrected by using a correction factor with soya oil as

external standard. The response for soybean oil should be the

same as for the dimer. The correction factor could be related to

the ratio between the area of the dimer peak to the area of the

monomer peak (Table 1) as follows. In order to calculate cf the

real concentration (creal) was divided with the concentration

achieved by SEC (cSEC) and multiplied by a new correction

factor cf2, which explained the difference between the different

samples having different initial concentrations:

cf ¼creal

cSEC

� cf2; cf2 ¼csample;x

1:26(1)

The value 1.26 in Eq. (1) is the total concentration in the

selected reference sample (mg/ml), which was related to

the other samples. This correction factor cf2 describes the

difference between the reference sample and the sample. This

difference is inevitable, since there are no direct ways to weigh

very accurately these oils, the precision being one droplets

accuracy. After multiplying the correction factor with the peak

areas of the dimer and trimer, respectively, the values were

converted to molar concentrations (mol/l). The final correction

curve is given in Fig. 3a via applying exponential regression to

the following equation:

cf dim ¼ 3:3908

�Adimer

Atotal

��0:3329

(2)

Additionally, some simplifications were applied due to

significant challenges with SEC-analysis. Instead of treating all

the compounds of the system separately, only monomers,

dimers and trimers were analysed separately and the mass

balance was calculated as follows:

mmonomer;0 ¼ mmonomer þ mdimer þ mtrimer (3)

where m denotes the mass. Taking into account stoichiometry

the molar amounts (n) are

nmonomer;0 ¼ nmonomer þ 2ndimer þ 3ntrimer (4)

References

[1] 6th ed., Ullmann Ullmann’s Encyclopedia of Industrial Chemistry, vol.

13, Wiley–VCH Verlag GmbH & Co., Weinheim, 2003.

[2] R.W. Johnson, E. Fritz (Eds.), Fatty Acids in Industry, Marcel Dekker,

New York, 1988, p. 667.

[3] L. Kuprina, Gidroliznaya i Lesokhimicheskaya Promyshlennost 3 (1983)

23.

[4] P. Patrick, U.S. Patent 3,157,629 (1964).

[5] B. Cicel, P. Komadel, M. Nigrin, Coll. Czech. Chem. Commun. 57 (1992)

1666.

[6] W. Schwarz, J. Zajic, J. Brat, Fett Wiss. Technol. 95 (1993) 253.


[7] H. Mohring, G. Spiteller, Fett Wiss. Technol. 92 (1990) 126.

[8] W. Link, G. Spiteller, Fett Wiss. Technol. 92 (1990) 135.

[9] W. Link, G. Spiteller, Fett Wiss. Technol. 94 (1992) 9.



[12] R. Adelhardt, G. Spiteller, Fett Wiss. Technol. 95 (1993) 85.

[13] R. Brutting, G. Spiteller, Fett Wiss. Technol. 95 (1993) 193.



[16] J. Brat, W. Schwarz, J. Zajfc, Fett Wiss. Technol. 97 (Sonderausgabe 2)

(1995) 513.

[17] M.J.A.M. Den Otter, Fette Seifen Anstrichmittel 72 (1970) 667.

[18] M.J.A.M. Otter, Fette Seifen Anstrichmittel 72 (1970) 875.

[19] M.J.A.M. Den Otter, Fette Seifen Anstrichmittel 72 (1970) 1056.

[20] H.W.G. Heynen, W.H.M. van Opstal, M.J.A.M. den Otter, Fette Seifen

Anstrichmittel 74 (1972) 677.

[21] A.A. Bagaev, G.I. Tsarev, A.I. Kirianov, Izv. Vyss. Uchebn. Zaven, Lesn.

Z. 3 (1979) 78.

[22] A.K. Sen Gupta, H. Scharmann, Fette Seifen Anstrichmittel 70 (1968) 86.

[23] A.K. Sen Gupta, H. Scharmann, Fette Seifen Anstrichmittel 70 (1968)

153.

[24] D.H. Wheeler, J. White, J. Am. Oil’s Chem. Soc. 44 (1967) 298.

[25] D.H. Wheeler, A. Milun, F. Linn, J. Am. Oil Chem. Soc. 47 (1970) 242.

[26] R.A. Korus, T.L. Mousetis, J. Am. Oil Chem. Soc. 61 (1984) 537.

[27] D.H. McMahon, J. Am. Oil Chem. Soc. 51 (1974) 522.

[28] P. Vuzvusova, Plovdivski Universitet Paisii Khilendarski 26 (1989) 71.

[29] K. Ishihara, JP patent 2001278837 (2001).

[30] R.M. Koster, M. Bogert, B. Leeuw, J. Mol. Catal. A: Chem. 134 (1998)

159.

[31] A.F. Elsasser, L.A. McCargar, US Patent 6,187,903 (2001).

[32] J.K. Chowdhury, A.C. Chakraborty, A.J. Majumber, J. Indian Chem. Soc.

12 (1935) 441.

[33] B.S. Zmachimskii, A.N. Trofimov, E. Ryabova, A.M. Chashchin, Gidro-

liznaya i Lesokhimicheskaya Promyshlennost 1 (1991) 17.

[34] H. Stage, Fette Seifen Anstrichmittel 77 (1975) 174.



[37] H.G. Arlt Jr., US Patent 3,367,952 (1968).

[38] N. Laane, M. Colja, G.A. Graham, C. Beindorff, K.D. Haase, J. Klooster-

man, Rec. Trav. Chim. Pays-Bas 110 (1991) 195.

[39] K.D. Haase, A.J. Heynen, N.C.M. Laane, Proc. Jpn. Oil Chem. Soc. 1

(1988) 510.

[40] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, US Patent

5,098,684 (1992).

[41] A. Bernas, P. Laukkanen, N. Kumar, P. Maki-Arvela, J. Vayrynen,

E. Laine, B. Holmbom, T. Salmi, D.Yu. Murzin, J. Catal. 210 (2002)

354.

[42] P. Maki-Arvela, N. Kumar, V. Nieminen, R. Sjoholm, T. Salmi, D.Yu.

Murzin, J. Catal. 225 (2004) 155.

[43] D. Kubicka, N. Kumar, P. Maki-Arvela, M. Tiitta, V. Niemi, T. Salmi,

D.Yu. Murzin, J. Catal. 222 (2004) 65.

[44] C.A. Emeis, J. Catal. 141 (1993) 347.

[45] E.M. Sulman, V.V. Alferov, Yu.Yu. Kosivtsov, A.I. Sidorov, O.S. Minis-

kov, A.E. Afanasiev, H. Kumar, D. Kubicka, J. Agullo, T. Salmi, D. Yu.

Murzin, Development of method of low temperature peat pyrolysis on the

pyrolysis on the basis of aluminosilicate catalytic system, Chem. Eng. J.,

in press.

[46] B. de Surville, Compt. Rend. 235 (1952) 724.

[47] D.A. Afonin, A.A. Bagaev, G.I. Tsarev, A.I. Kiprianov, Izv. Vyss. Uchebn.

Zaven, Lesn. Z. 4 (1984) 89.

[48] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D.

Schmitt, C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B.

Higgins, J.L.J. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834.

[49] K. Matsuo, S. Kawamura, T. Toshine, US Patent 4,271,066 (1981).

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Thermal and catalytic oligomerisation of fatty acids