Methoxylation of methyl oleate in the presence of dealuminated Y faujasites in their protonic form

Article abstract of DOI:10.1007/s11746-006-5030-1

Methoxylation of methyl oleate into methyl methoxy stearate was carried out in a batch reactor at temperatures ranging from 150 to 190°C in the presence of dealuminated H-Y faujasites as catalysts. In the presence of an excess of methanol, the H-Y faujasite with a Si/AI ratio of 15 was shown to achieve the title reaction with a yield of methyl methoxy stearate that does not exceed 40% because of the parallel formation, at comparable rates, of methyl oleate isomers identified as methyl elaidate, methyl frans-vaccenate, and methyl c/s-vaccenate. Iso-merization reactions were confirmed to occur rapidly in an independent manner. FFA are also present in small amounts owing to the in situ dehydration of methanol and subsequent hydrolysis of the esters. Finally, starting from pure oleic acid leads to results similar to those obtained with methyl oleate as the starting material. Copyright

Full text of DOI:10.1007/s11746-006-5030-1

Methoxylation of Methyl Oleate in the Presence
of Dealuminated Y Faujasites in Their Protonic Form
Clément Lansalot-Matrasa, Paul Lozanoa, Daniel Piocha, Annie Finielsb,
Claude Moreaub,*, and Sylvain Claudec
aLaboratoire de Génie des Procédés et Elaboration des Bioproduits, Unité Mixte de Recherche (UMR)/Centre de Coopération
Internationale en Recherche Agricole pour le Développement (CIRAD) T64, CIRAD/Amélioration des Méthodes pour
l’Innovation Scientifique, TA 40/16, 34398 Montpellier Cedex 5, France, bLaboratoire de Matériaux Catalytiques et Catalyse
en Chimie Organique, UMR 5618 Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)/Centre National
de la Recherche Scientifique/Université Montpellier 34296 Montpellier Cedex 5, France, and cOrganisation
Interprofessionnelle des Graines et Fruits Oléagineux (ONIDOL), 75008 Paris, France
ABSTRACT: Methoxylation of methyl oleate into methyl as catalyst, methanol was shown to alkoxylate soybean oil, but
methoxy stearate was carried out in a batch reactor at tempera-
tures ranging from 150 to 190°C in the presence of dealuminated
H-Y faujasites as catalysts. In the presence of an excess of
methanol, the H-Y faujasite with a Si/Al ratio of 15 was shown to
achieve the title reaction with a yield of methyl methoxy stearate
that does not exceed 40% because of the parallel formation, at
comparable rates, of methyl oleate isomers identified as methyl
elaidate, methyl trans-vaccenate, and methyl cis-vaccenate. Iso-
merization reactions were confirmed to occur rapidly in an inde-
pendent manner. FFA are also present in small amounts owing to
the in situ dehydration of methanol and subsequent hydrolysis of
with a low yield, 21% (6).
It is well known that zeolites and related materials can con-
tribute to the development of environmentally friendly processes
(7–9). Indeed, there is continuing interest in the application of
micro- and mesoporous materials as catalysts in the synthesis of
bulk and fine chemicals because of their tunable acidic proper-
ties, shape selectivity properties, ease of separation from the re-
action medium, and recyclability.
The objective of the present work was to add methanol to the
double bond of methyl oleate in the presence of a series of dea-
the esters. Finally, starting from pure oleic acid leads to results sim- luminated large-pore zeolites in order to avoid diffusional limita-
ilar to those obtained with methyl oleate as the starting material.
tions expected to occur with small or medium pore-size zeolites.
Paper no. J11301 in JAOCS 83, 725–729 (August 2006).
EXPERIMENTAL PROCEDURES
KEY WORDS: Lubricants, methyl oleate, methoxylation, zeo-
lites.
Reactants. Methyl oleate (purity 83%) was kindly provided by
Stéarinerie Dubois (Ciron, France). Pure methyl oleate, methyl
elaidate, methyl trans-vaccenate, methyl cis-vaccenate, and
methanol, all with a purity >99 %, were from Aldrich (Lyon,
France) and used without further purification.
Rapeseed and sunflower oils are raw materials that easily can
be developed for the lubricant market after chemical transfor-
mation. Indeed, vegetable oils are known to be excellent and
completely biodegradable lubricants (1,2). However, their poor
thermal stability and poor oxidation and corrosion resistance
strongly limit their use. One of the main reasons for this insta-
bility is the presence of unsaturations on the alkyl chains. Veg-
etable oils can be modified by taking advantage of the reactiv-
ity of this double bond system. Indeed, methyl oleate derived
from rapeseed or sunflower oil can be methoxylated into
methyl methoxy stearate in the presence of strong acid cata-
lysts (Scheme 1). Three methods have been proposed to obtain
satisfactory yields of methoxylated products. The first is the di-
rect addition of methanol to the double bond of methyl oleate
using the methoxy mercuration–demercuration method (3,4).
The second, more recent, method is the methoxylation of
methyl linoleate using a 50 wt% BF3-MeOH complex and
yielding 56% of monomethoxy and 22% of dimethoxy adducts
(5). Finally, in a more conventional approach with sulfuric acid
Catalysts. Dealuminated Y faujasites in their protonic form
were obtained from Zeolyst International (Valley Forge, PA).
*To whom correspondence should be addressed at Laboratoire de Matériaux
Catalytiques et Catalyse en Chimie Organique, UMR 5618 ENSCM/CNRS/
UM1, Ecole Nationale Supérieure de Chimie de Montpellier, 8, Rue de l’Ecole
Normale, 34296 Montpellier Cedex 5, France. E-mail: claude.moreau@enscm.fr
SCHEME 1
Copyright © 2006 by AOCS Press
725
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C. LANSALOT-MATRAS ET AL.
Except where otherwise mentioned, they were calcined at 773 up to nearly complete consumption of methyl oleate over a 24-
K (1 K min−1) under flowing air (200 mL min−1) for 6 h.
h period. However, the concentration in methoxy methyl
Procedure. Experiments were carried out in a 0.1-L mag- stearate reaches a maximum at about 2 h, followed by a contin-
netically stirred autoclave (Autoclave Engineers type Magne- uous decrease, which corresponds to the formation of oleic acid
Drive), operating in a batch mode and equipped with a system owing to the in situ dehydration of methanol and subsequent
for sampling of liquid during the course of the reaction without hydrolysis of the ester.
stopping the agitation. The procedure was typically as follows:
In parallel, an important amount of methyl oleate isomers is
methyl oleate (0.074 mol), freshly activated catalyst (1.2 g), formed. This is not completely unexpected since the literature
and methanol (variable amount) were poured in the autoclave. already mentioned isomerization of FA and/or fatty esters over
After it had been purged with nitrogen, the temperature was in- zeolites and/or related materials (10–14).
creased to 453 K and the agitation speed was 1000 rpm to avoid
external diffusion limitations. Zero time was taken to be when methyl oleate with methanol in the presence of Y faujasites was
the temperature reached 323 K. followed by GC–MS analysis. Methyl 9- and 10-methoxy
Identification of methoxy methyl stearate. The reaction of
Analyses. Samples were periodically withdrawn and ana- stearates were identified through their mass spectra. According
lyzed by GC on a Hewlett-Packard 6890 gas chromatograph to the literature (5), the fragmentations take place at the α-po-
equipped with an FID and an HP5-capillary column (30 m × sition, followed by successive loss of methanol as illustrated in
0.32 mm, 0.25-µm film thickness, hydrogen as carrier gas), 423 Figure 2. Identification of methyl methoxy stearate was also
K for 30 min, 423 to 463 K at 5 K min−1. Reaction products confirmed by 1H and 13C NMR.
were identified by comparison with authentic samples and
Identification of methyl oleate isomers. Isomerization of
GC–MS analysis. Methyl heptadecanoate was used as external methyl oleate was performed in the absence of methanol (Fig.
standard. FFA were titrated with ethanolic KOH, with phe- 3). Three isomers were identified by comparison of the experi-
nolphthalein as colored indicator.
mental retention times with those of methyl elaidate and cis-
Kinetics. The initial reaction rates were deduced from the ex- and trans-methyl vaccenates, which were expected to result
perimental plots of concentrations vs. time by curve-fitting using from the cis-trans isomerization of the double bond on carbon
the Origin Graph software or from the determination of the slope 9 or from the shift of the double bond to the carbon 11 position.
at the origin. Experimental errors are estimated to 10 %.
As one can see in Figure 3, methyl cis-vaccenate is formed
more rapidly than methyl elaidate and methyl trans-vaccenate.
However, methyl elaidate tends to be isomerized into methyl
vaccenates as observed for its methyl oleate cis-isomer.
To evaluate the influence of the isomerization of methyl
RESULTS AND DISCUSSION
Catalyst screening. Experiments were performed over a series
of dealuminated Y faujasites that differ in their acidic proper- oleate on the methoxylation reaction, methoxylation of pure
ties and that have a suitable hydrophilic/hydrophobic balance samples of methyl oleate and methyl elaidate was performed
to allow adsorption of both methyl oleate and methanol. Figure under the same experimental conditions. In spite of its trans
1 illustrates the reaction network for methoxylation of methyl double-bond stereochemistry, methyl elaidate behaves as its cis
oleate at 458 K in the presence of the most acidic H-Y faujasite isomer methyl oleate, leading to the formation of methyl
with a Si/Al ratio of 15 (denoted later as HY15), and for a methoxy stearate with approximately the same yield (34–38%),
methanol to methyl oleate molar ratio of 7. From this figure, and at comparable reaction rates.
one may immediately observe that the HY15 catalyst is active
Influence of dealumination of Y faujasites. As illustrated in
Figure 4, the initial rates of disappearance of methyl oleate and
appearance of reaction products over a series of dealuminated
Y faujasites pass through a maximum for a Si/Al ratio of 15,
which corresponds to a balance between the number and the
strength of the acidic sites, as usually observed.
FIG. 1. Catalyst screening for the methoxylation of methyl oleate over HY15
(1.2 g), methyl oleate (0.074 mol), methanol (0.544 mol), 458 K, 1000 rpm,
1.7 MPa; methyl oleate (I), methyl methoxy stearate (G), isomers (L), mass
balance (N), and FFA (I). Error bars represent an error of 10%
FIG. 2. Principal fragmentations for methyl 9- and 10-methoxy stearates.
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METHOXYLATION OF METHYL OLEATE CATALYZED BY ZEOLYTES
727
FIG. 3. Isomerization of methyl oleate over HY15 (1.2 g), in the absence
of methanol; methyl oleate (0.074 mol), 458 K, 1000 rpm, 1.7 MPa;
methyl oleate (I), methyl elaidate (M), cis- (L) and trans- (I ≤) methyl
vaccenates, mass balance (N). Error bars represent an error of 10%.
FIG. 5. Effect of catalyst weight on the initial rates of disappearance of
methyl oleate and appearance of reaction products; methyl oleate
(0.074 mol), methanol (1.088 mol), HY15 (1.2 g), 458 K, 1000 rpm, 2.5
MPa; methyl oleate (I), methyl methoxy stearate (G), isomers (L). Error
bars represent an error of 10%.
Influence of the weight of catalyst. As shown in Figure 5 in
the plot of the initial reaction rates as a function of the catalyst
weight, an apparent kinetic first order is observed. As often ob-
served in heterogeneous catalysis (15), a saturation phenome-
non occurs at high coverage of the catalyst, and a nearly zero
order is observed. Under the experimental conditions used,
yields of methyl methoxy stearate are close to 30% after 3 h of
reaction for catalyst amounts exceeding 1.8 g.
Influence of the reaction temperature. Activation energies
have been calculated from the plots of the logarithms of the ini-
tial rates vs. the reciprocal of temperature (Fig. 6). The values
obtained are higher than the limit values generally accepted for
external diffusion limitation, i.e. around 40 kJ mol−1 (15). The
value of the activation energy calculated for the disappearance
of methyl oleate is 94 kJ mol−1, and the values for the forma-
tion of the isomers of methyl oleate and methyl methoxy
stearate are 162 and 85 kJ mol−1, respectively. A point worth
noting is that the selectivity in methyl methoxy stearate be-
comes more important than the formation of the isomers of
methyl oleate at low temperature because of the differences in
the activation energies of both reactions. However, this is to the
detriment of the global activity.
FIG. 6. Effect of temperature on the initial rates of disappearance of
methyl oleate and appearance of reaction products; methyl oleate
(0.074 mol), methanol (1.088 mol), HY15 (1.2 g), 458 K, 1000 rpm, 2.5
MPa; methyl oleate (I), methyl methoxy stearate (G), isomers (L). Error
bars represent an error of 10%.
Influence of the methyl oleate/methanol molar ratio. Initial
reaction rates vs. the methyl oleate to methanol molar ratio are
given in Figure 7. The total volume of the reaction mixture is
kept constant at 75 mL in order to have the same catalyst con-
FIG. 4. Effect of dealumination of Y faujasites on the initial rates of dis- FIG. 7. Effect of methyl oleate/methanol molar ratio on the initial rates
appearance of methyl oleate and appearance of reaction products;
methyl oleate (0.074 mol), methanol (0.544 mol), catalyst (1.2 g), 458
K, 1000 rpm, 1.7 MPa; methyl oleate (I), methyl methoxy stearate (G),
isomers (L), FFA (I). Error bars represent an error of 10%.
of disappearance of methyl oleate and appearance of reaction products;
total volume methyl oleate + methanol = 75 mL, HY15 (1.2 g), 458 K,
1000 rpm, 2.5 MPa; methyl oleate (I), methyl methoxy stearate (G),
isomers (L). Error bars represent an error of 10%.
JAOCS, Vol. 83, no. 8 (2006)

728
C. LANSALOT-MATRAS ET AL.
centration. As methanol is both reactant and solvent for this re-
action, it is not surprising to obtain a nonconventional evolu-
tion of initial rates and yields vs. the methyl oleate/methanol
molar ratio. The first observation is the spectacular increase of
the initial reaction rates at low methanol content, but to the
detriment of the yield in methyl methoxy stearate. The rela-
tively linear increase of the yield in methyl methoxy stearate,
from 11% for a molar excess in methanol of 2 to 40% for a
large excess of methanol, is linked to the increase of methyl
oleate concentration in the reaction mixture allowing the
methyl oleate to occupy most of the catalytic sites, then lead-
ing first to isomerization reactions and then to the degradation
of methyl methoxy stearate. In other words, yields are low be-
cause methanol is less adsorbed for high methyl oleate concen-
trations. On the other hand, when methanol is in large excess,
the initial reaction rates are lower, but with a significant in-
crease in methyl methoxy stearate yield.
FIG. 9. Reaction of methyl oleate with methanol; methyl oleate (2 g),
methanol (72 mL), HY15 (1.2 g), 458 K, 1000 rpm, 2.6 MPa; methyl
oleate (I), methyl methoxy stearate (G), methyl elaidate (M), other iso-
mers (G), mass balance (N). Error bars represent an error of 10%.
Oleic acid as starting material. For practical reasons it
could be interesting to use the oleic acid resulting from the hy-
drolysis of crude rapeseed or sunflower oil directly. Experi- major product. At complete methyl oleate conversion after 22 h,
ments were then conducted under operating conditions close to nearly similar amounts of methyl methoxy stearate and methyl
those used for the addition of methanol to methyl oleate, i.e., oleate isomers are formed. By comparison with the methoxyla-
0.074 mol of oleic acid, 1.088 mol of methanol, 1.2 g of HY15 tion of crude methyl oleate (Fig. 1), no formation of FFA is ob-
catalyst; 458 K; 1000 rpm, 2.2 MPa. The concentrations in re- served. Although methyl oleate and its trans isomer, methyl elai-
actant and products are plotted against reaction time in Figure date, are methoxylated at nearly similar initial reaction rates
8. From this figure, one may immediately see that oleic acid is within a 10% experimental error, methoxylation of methyl elai-
nearly totally converted into methyl oleate within the first hour. date seems to reach an equilibrium after 6 h, with methyl
Then, the reaction proceeds as was already observed when methoxy stearate as the major reaction product, even after 22 h
methyl oleate is the starting material, i.e., through the parallel (Fig. 10). Finally, methoxylation of methyl linoleate, with two
formation of methyl oleate isomers, methyl methoxy stearate unsaturations, was carried out under similar experimental condi-
(30% yield after 6 h), and free oleic acid.
tions as above. As illustrated in Figure 11, the initial rate of
Methoxylation of methyl elaidate and methyl linoleate. In an- methoxylation is similar to that of both methyl oleate and methyl
other series of experiments under the following operating condi- elaidate. However, it was not really expected that the formation
tions, pure fatty ester (2 g), methanol (72 mL), HY15 catalyst of a dimethoxylated adduct would be more rapid than the forma-
(1.2 g), 458 K, 1000 rpm, 2.6 MPa, methoxylation of methyl tion of a mono-methoxylated adduct with a nearly quantitative
oleate was compared with methoxylation of its trans isomer, mass balance up to a reaction time of 6 to 8 h.
methyl elaidate, and methoxylation of methyl linoleate with two
Thus, the acid-catalyzed methoxylation of methyl oleate
unsaturations. As illustrated in Figure 9, methoxylation of into methyl methoxy stearate is easily achieved in the presence
methyl oleate initially yields methyl methoxy stearate as the
FIG. 8. Reaction of oleic acid with methanol; oleic acid (0.074 mol), FIG. 10. Reaction of methyl elaidate with methanol; methyl elaidate (2
methanol (1.088 mol), HY15 (1.2 g), 458 K, 1000 rpm, 2.2 MPa; methyl g), methanol (72 mL), HY15 (1.2 g), 458 K, 1000 rpm, 2.6 MPa; methyl
oleate (I), methyl methoxy stearate (G), isomers (L), FFA (I). Error bars elaidate (M), methyl methoxy stearate (G), methyl oleate (I), other iso-
represent an error of 10%.
mers (G), mass balance (N). Error bars represent an error of 10%.
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METHOXYLATION OF METHYL OLEATE CATALYZED BY ZEOLYTES
729
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FIG. 11. Reaction of methyl linoleate with methanol; methyl linoleate
(2 g), methanol (72 mL), HY15 (1.2 g), 458 K, 1000 rpm, 2.6 MPa;
methyl linoleate (I), monomethoxylated adduct (L), dimethoxylated
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of dealuminated Y faujasites in their protonic form as catalysts.
Under optimized operating conditions of catalyst, temperature,
and methanol to methyl oleate molar ratio, the yield in methyl
methoxy stearate does not exceed 40% due to the parallel acid-
catalyzed formation, at comparable rates, of methyl oleate iso-
mers. Starting from pure oleic acid leads to results similar to
those obtained with methyl oleate as the starting material.
ACKNOWLEDGMENTS
This work was performed within the framework of the Agence de
l’Environnement et de la Maîtrise de l’Energie (Agriculture pour la
Chimie et l’Energie) No. 0201042 agreement between CIRAD,
ENSCM, NYCO (Paris, France), and ONIDOL.
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[Received January 2, 2006; accepted May 31, 2006]
JAOCS, Vol. 83, no. 8 (2006)