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AIR3-CT94-2218
Reactivity of Fatty Esters and Glycerol : New Methods - Third Progress Report |
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Proposal No: | AIR3-CT94-2218 |
| Date Prepared: | October 1996 and April 1998 | |
| Source: |
First and Second Project Progress Reports Third Project Progress Report |
Summary
Introduction The aim of this project was to develop methyl esters of vegetable oils, as well as glycerol, in new industrial applications, using innovative and environmentally friendly methods. The project was divided into a number of tasks brought together in the following themes.
Activities
Task 1.1 Thermoplastic materials from fatty esters (or acids) and ligno-cellulosic wastes, using chemical or enzymatic modification.
Task 1.2 Glycerol derivatives in polyurethane foams swollen by water rather than CFC (prevention of ozone destruction) including preparation and analysis (molecular weight and distribution, Gardner colour, viscosity, acidity and basicity index) and evaluation of polyesters (Alkyd resins) entering the formulations. Fourteen resins having been prepared and analysed. Their evaluation in polyurethane foams has been very encouraging. Pilot-plant development has started and patenting is under consideration.
Task 2.1 Catalytic epoxidation of fatty esters and acids Fatty epoxides are mainly used as plasticizers and stabilisers (PVC). They are also oleochemical intermediates Epoxidation of Oleic Methyl Ester (OME) was studied in various solvents and in presence of several catalysts. Oxidants are hydrogen peroxide (H2O2) or t-Butylhydroperoxide. A new catalyst has been defined.
Task 2.2 Chemical opening of fatty epoxyacids and esters. Cleavage of epoxyacids and esters by reaction with carboxylic acids, monohydric alcohols and amines leads to different kinds of oleochemicals. The commercial development of these compounds may be through easy and environmentally friendly routes.
Task 3.1 Preparation of fatty unsaturated alcohols. Industrial conditions used to obtain unsaturated fatty alcohols are severe: a temperature around 300°C and pressure between 200 and 300 bars with zinc-chromite catalyst. A laboratory scale process that uses less extreme hydrogenation conditions in the preparation of methyl oleate has been set up. Processes and applications for the use of oleic alcohol in the surfactants area have been established. New and environmentally-friendly catalysts have been defined.
Task 3.2 Reductive animation of fatty acids and esters Fatty and N-methyl (or ethyl) substituted amines, used for example in the preparation of tensioactive agents, are generally obtained from the reaction of fatty acids (or esters) with ammonia, light alcohols and hydrogen or nitriles, light alcohols and hydrogen over copper or nickel catalysts. The processes have been adapted to vegetable materials.
Task 3.3 Esteramides and polyesteramides The main objective of this topic research was to synthesise and formulate products based on raw vegetable materials to temporarily protect metallic surfaces against rust.
Task 3.4 Estolides Estolides are polyesters of hydroxy-fatty acids condensed on themselves. Like dimers, they display lubricating and plasticizing properties. The current methods of estolide preparations start with rather expensive ricinoleic acid. A process starting with cheaper oleic acid as raw material, (high oleic sunflower for instance), has been set up.
Task 3.5 Selective esterification of glycerol - monoglycerides Monoglycerides enter hundreds of applications as surfactants (food, pharmacy, cosmetics). The aim is here to prepare neat monoglycerides in one step, without purification. Esterification or transesterification of glycerol with oleic acid, methyl oleate or neat oils, in presence of homogeneous catalysts, lead to mixtures of mono, di- and triester of glycerol. Generally by-products such as polyglycerol or acrolein are generated. In order to obtain pure monoesters of glycerol, molecular distillation is necessary. The aim of this study was to produce pure products using a new processes. The synthesis of glycerol monooleate was attempted with chemical or enzymatic catalysts by different teams, using esterification of glycerol with oleic acid or transesterification of methyl ester or triglyceride.
Results
Fatty acids do not react directly with cellulose. Traditionally an expensive co-reagent, trifluoroacetic anhydride, is used. In this project cheaper acetic anhydride was used as co-reagent, in a solvent-free medium, to generate in situ a mixed acetic-fatty anhydride. Such intermediate reacts with cellulosic hydroxyl groups to yield a mixed acetic-fatty cellulose ester. A strong acid catalyst (H2SO4) was also required. Highly substituted mixed cellulose esters were obtained, with an acetate/alkanoate ratio of about 2.4. Such products are highly hydrophobic, showed a good mechanical resistance and an apparent melting point (150-200°C) which allowed thermoforming.
The reaction between fatty acid methyl esters (FAME) and cellulose, in a DMF/benzene medium, is known. Here it was found that FAME react with cellulose in an anhydrous medium, in presence of basic catalysts, to yield cellulose esters in a solvent-free medium. The products are highly hydrophobic and melted partially when pressed at 250°C.
Both types of reactions have been applied to lignocellulosic wastes such as pine sawdust, wheat straw, olive stones and bagasse. The yields were 10-60 % lower than those obtained with pure cellulose (model).
Enzymatic work aimed to investigate the esterification of cellulose by fatty acids for the production of new thermoplastic materials, reverse the hydrolytic action of various enzymes, including lipases and proteases, using low water content media. In preliminary experiments, several polar and non-polar organic solvents such as pyridine, dimethylsulfoxide, acetonitrile, acetone and n-hexane, as well as various enzymes, such as subtilisin and lipase from Candida cylindracea, Mucor miehei (Lipozyme) and Candida antartica (Novozyme) have been tested. However, even after 20 days of incubation at various temperatures, in the presence of a large excess (or not) of fatty acids, the enzymatic acylation of cellulose even after various forms of pretreatment, with lauric and oleic acid was not possible. When soluble derivatives of cellulose (acetate and hydroxypropylcellylose) were used as substrates, using lipases in organic solvents such as t-butanol and acetonitrile, 13C-NMR and FT-IR spectroscopy data indicated that esterification of these two derivatives of cellulose with lauric acid was successful.
The formulation of polyurethanes able to be swollen by water instead of CFC was initiated by preparation of the polyesters. Two out of 14 alkyd resins prepared and analysed were suitable for the formulation stage and resulted in good polyurethannes foams.
Two different kinds of Ti-containing molecular sieves (Ti-Beta and Ti-MCM-41) were studied as heterogeneous catalysts for the selective epoxidation of fatty esters and acids. Major achievement was the synthesis of improved Ti-Beta catalysts that were used for the epoxidation of oleic methyl ester (OME) and oleic acid (OA) using hydrogen peroxide as oxidant. The catalyst can work efficiently under mild temperatures (50-70°C) and with only a slight excess of hydrogen peroxide (H2O2 /oil ratio of 1.1-1.2). Ti-Beta shows its higher activity and 100 % selectivity to the epoxide in acetonitrile. On the other hand, the mesoporous Ti-MCM-41 (larger concentration of silanol groups on the surface and therefore a high hydrophilicity) presented a low activity for epoxidation when using hydrogen peroxide as oxidant. However, they worked very efficiently (high activity and almost 100 % selectivity to the epoxide) when TBHP was used as the oxygen source. In this case, the absence of solvent is attractive from an industrial point of view. The results obtained with such catalysts were very competitive with respect to existing industrial processes.
Epoxidation of both rapeseed methyl esters (RME) and high oleic sunflower methyl esters (HOSME) was carried out using H2O2 (50 %) and formic acid (yield of 85-90 %); epoxidized esters produced on pilot scale from RME and HOSME have respectively oxirane values of 5.2/4.5 and iodine values of 1.7/1.5. Epoxidized oil produced on pilot scale from rapeseed oil have an oxirane value of 5.1 (70 % yield) and an iodine value of 22. Reactions with carboxylic acids were conducted under atmospheric pressure at 80°C without catalyst from epoxidized RME. Esters obtained from acetic acid and heptanoic acid have respectively oxirane value of 0.3/0.0, saponification values of 299/253 and iodine values of 22/25. GC analysis shows secondary products 20 % and 46 %, respectively.
Three catalysts (para-toluene sulfonic acid -PTSA-, sodium methylate, zinc chloride) were studied for the alcoholysis reaction of epoxidized RME and HOSME with monohydric alcohols (ethanol, heptanol). Cleavage of the oxirane group of epoxy-HOSME with alcohols (ethanol, heptanol and octanol) was preferentially done by acid catalysis at 100°C under atmospheric pressure. Analytical controls show the formation of etheralcohols with an oxirane value of 0.0. With ethanol, heptanol and octanol, obtained ethers have respectively acid values of 0.4/0.3/1.2, iodine values of 27/25/n.d, saponification values of 163/126/160, and hydroxyl values of 238/nd/121. GC analysis show secondary products (about 20 %). Moreover, transesterification reaction occurs during the cleavage of the epoxy ring. Cleavage of the oxirane group of epoxy-rapeseed oil with a primary amine (butylamine) was conducted under pressure, at high temperature (180-200°C) and without catalyst. Transesterification reaction leads to the formation of amides with a saponification value of 0.0. The cleavage of the epoxy ring leads to the formation of a fatty amine/imine mixture. GC analysis shows about 30 % of secondary products.
The selective hydrogenation of methyl oleate into oleyl alcohol was performed over RuSn- or CoSn-Al2O3 catalysts at rather low temperature and pressure (270°C, 8.0 MPa). Ruthenium based catalysts are more active and more selective than cobalt materials, though prepared according to the same procedure (sol-gel) and displaying the same surface composition. The oleyl alcohol yield obtained over RuSn is about 80 % in batch experiments performed without any solvent, while only 65 % of unsaturated alcohol is obtained in presence of cobalt catalysts.
The ethoxylates produced were evaluated by a new physical method, the "PIT" (Phase Inversion Temperature) measurement. By this simple method, all the samples could be classified according to their affinity for an oil-water mixture, which is the interesting property for industrial applications.
Stimulated by the fact that environmental legislation will soon mandate replacements of copper-chromium catalysts with non-chromium catalysts, the use of promoted nickel catalysts was investigated. In order to suppress the inhibiting effect of light alcohols, hexamethylene tetramine (HMTA) was used as methylating agent. Under these conditions, the nitrile is transformed either into dimethylalkylamine or into diethyldialkylamine with a selectivity (or a yield) higher than 90 %. Moreover, its was shown that HMTA was catalytically converted into MMA (monomethylamine), DMA (dimethylamine) and TMA (trimethylamine) during the reaction.
Work on esteramides and polyesteramides aimed to synthesise and formulate products to temporarily protect metallic surfaces against rust. To be competitive such products must have good applicability on metallic surfaces, no volatile component, no rust on surfaces after storage outside during several months be easily removed and have low toxicity and ecotoxicity. These criteria could be met by reaction products between vegetable oils and amines. Hence, transamidation between vegetable oil, or their derivatives, and various amines were investigated. The antirust property of molecules and formulations prepared was studied according to several tests (natural ageing, humidity cabinet, cast-iron chips) and compared with commercially available products.
Estolide synthesis was carried out as follows:
The reaction of ricinoleic fatty acid in presence of PTSA (catalyst) in toluene as solvent, leads to a final product with an acid value of 92, an iodine value of 95 and an hydroxyl value of 64. GC analysis show that estolides are composed of a mixture of C36 (oleate of methyl hydroxystearate), C54 (dioleate of methyl hydroxystearate) and C72 (trioleate of methylhydroxystearate). The reaction of polycondensation of oleic fatty acid was performed using an ion exchange resins as acid catalyst, at 120°C under atmospheric pressure. The hydratation degree of the resin is important. The best results were obtained with a resin hydrated at 5 %, and lead to a product with an acid value of 130 and the formation of 29 % of estolides. The reaction of acidification was performed using epoxidized HOSME with oleic at 176°C under atmospheric pressure without any catalyst and solvent. The oxirane opening leads to complete estolide formation: after neutralisation, analytical controls show that estolides are composed of a mixture of C36 (oleate of methyl hydoxystearate) and C54 (di-oleate of methyl hydoxystearate).
The selective enzymatic synthesis of glycerol fatty acid esters was studied and optimised. Six biocatalysts have been tested for the selective synthesis of monoglycerides from oleic and palmitic acid, and twelve biocatalysts for ricinoleic acid, including immobilised lipases from various microorganisms: Pseudomonas florescens, Rhizomucor miehei, Aspergillus oryzae, Mucor miehei and Candida antartica.
Experiments were carried out in a completely stirred tank reactor (STR), under fixed conditions of pressure and temperature. FTIR and GC-MS have been used for the qualitative identification of all chemical species present in the reaction media and Capillary Gas Chromatography has been used for quantification of the products. The optimisation of the processes have been achieved using the technique of the Factorial Design of Experiments, which employs the Response Methodology to find out the optimum conditions. The operating conditions have been fixed for the catalytic test: temperature, pressure, stirring speed, alcohol: acid molar ratio and initial catalyst concentration. The use of mild operating conditions made it possible to avoid side reactions, obtaining a pale yellow product, free of by-products.
In the chemical work monoesters of glycerol (or monoglycerides) were synthesised using three different methods:
The operating conditions optimized for the synthesis of glycerol 1-monooleate (1-MO) using a unifactorial 2x2 factorial plan (5-1). The yield of the reaction, catalysed by anion exchange resins, was found to depend strongly on temperature and the degree of initial hydration of the reaction medium. In the presence of the macroporous resin, Amberlyst A26 in the chloride form, a 97 % yield of 1-MO was obtained for a molar ration OA/Gly of 1/4, initial concentration of 2.13 mmol of OA/ml water and a temperature of 70°C for 3 h reaction. The reaction between oleic acid and glycidol was then studied in fatty acid medium.
A further experimental approach for preparation of glycerol 1-monooleate was based on the partial esterification of glycerol in an emulsion medium, while other work concerned the esterification of glycerol with acids and the transesterification of oil (rapeseed) with glycerol. Both of these latter routes were studied in presence of heterogeneous catalysts, which apart from their renewability, are easy to eliminate from the reaction mixture (filtration) avoiding by products formation, which usually take place during the neutralisation of homogeneous catalysts.
Esterification of glycerol with acids was carried out in presence of acid zeolites as catalysts. The influence of the catalyst topology was studied in order to define an adequate pore structure limiting the formation of tri and diglycerides. Indeed, the selective preparation of a highly pure monoester is not easy because of the presence in the glycerine molecule of three hydroxyl groups, giving rise to successive esterification reactions from the initial formed monoglycerides to diglycerides and hence triglycerides. The forecasts derived from a molecular simulation were confirmed by the reaction results. The tridirectional acid zeolites were found to be active as selective catalysts for esterification. Under optimum conditions, the best conversion was around 90 % and the selectivity to monoesters around 70 %.
Transesterification of glycerol rapeseed oil with glycerol was carried out in presence of heterogeneous basic catalysts using different solid catalysts: MCM-41 and sepiolite exchanged with caesium, magnesium oxide and mixed aluminium-magnesium oxides of different compositions derived from the hydrotalcite. The transesterification needs numerous and strong basic sites as present in the MgO and aluminium magnesium oxide to provide good yield and selectivities. In addition to the catalysts indicated above, impregnated catalysts were tested: mesoporous aluminosilicate (SAM and MCM-41) impregnated with carbonate and neutral alumina impregnated with potassium fluoride. The solids impregnated with carbonate were not basic enough or did not present enough basic sites to catalyse the transesterification reaction. On the other hand, alumina impregnated with potassium fluoride gave interesting results, under suitable conditions, giving 95 % of conversion in less than half an hour, but the selectivity to monoesters, compared to the oxide catalysts, was not improved (~70%).
To complete this study and considering that the quality of the emulsion between glycerol and triglycerides was of paramount importance to improve the selectivity to monoesters, a non-ionic surfactant was added (Triglyceride ethoxilated - Hedipin, R-60 from Merck) to the reaction mixture and, after 5 hours of reaction, 100 % of conversion - with a molar selectivity to monoesters of around 80 - was observed.
The selective synthesis of glycerol monooleate can be performed in presence of solid catalysts, less corrosive and more easily reusable than homogeneous mineral acids. The study of various acid solids (zeolite, clay, ion exchange resins) for the esterification of glycerol with oleic acid has shown that cationic exchange resins were the best catalysts for the selective preparation of monooleyl glyceride in mild experimental conditions. Indeed, a selectivity of about 90 % for an oleic acid conversion higher than 70 % is obtained. It seems that the activity and the selectivity were influenced by the resin structure. Depending on its crosslinking, the resin acts as a shape-selective catalyst. Similar results were obtained starting from dodecanoic acid. After the reaction, it was possible to extract the polymer resin, to wash it with ethanol and to reuse it in a new experiment with the same yields.
In a second part of this work, the transesterification reaction between methyloleate and glycerol was examined over basic catalysts in order to increase the rate of formation of glycerol monoester. The first step concerned the effect of the catalyst basicity over the rate. It was observed that the increase of basicity (strong basic sites), as with lanthanum oxide, really increased the reaction rate without side-reactions. Esterification or transesterification of glycerol with oleic acid, methyl oleate or neat oils, in presence of homogeneous catalysts, lead to mixtures of mono, di- and triester of glycerol. Generally by products like polyglycerol or acrolein are generated. In order to obtain pure monoesters of glycerol, molecular distillation is necessary. Glycerol monooleate synthesis was attempted with chemical or enzymatic catalysts, using esterification of glycerol with oleic acid or transesterification of methyl ester or triglyceride. The different methods gave comparable results.
Conclusions
Generally speaking, the project has completed the activities with, in addition to several papers and patents, some results are leading to industrial developments (polyurethannes from glycerol and esteramides). Some activities have resulted in the basis for future industrial development though needing further work (unsaturated alcohols). Other scientific highlights include the enzymatic esterification of cellulose, observed for the first time; the production of new materials from cellulose by chemical modification; and the identification of a very promising catalyst for epoxydation. As far as selective esterification of glycerol-monoglycerols is concerned, some promising methods are in the process of development, with some patents filed. However, this sector is very competitive.
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