FR2970250A1 - Making composition of linear monocarboxylic acid alcohol esters and glycerin, comprises reacting fatty substances of animal/vegetable origin with aliphatic monoalcohol in presence of acid-base heterogeneous catalyst - Google Patents

Abstract

Manufacturing a composition of 6-26C linear monocarboxylic acid alcohol esters and glycerin, comprises reacting fatty substances of animal or vegetable origin with 1-18C aliphatic monoalcohol in the presence of at least one acid-base heterogeneous catalyst based on metallophosphate (I). Manufacturing a composition of 6-26C linear monocarboxylic acid alcohol esters and glycerin, comprises reacting fatty substances of animal or vegetable origin with 1-18C aliphatic monoalcohol in the presence of at least one acid-base heterogeneous catalyst based on metallophosphate having a structure of formula (MP (1-y)O [3+5(1-y)]/2.nH 2O) (I). M : a metal cation of at least one member comprising aluminum, gallium or indium, preferably aluminum or gallium; y : 0-1, where y satisfies an equation of 3+5(1-y)>= 0; and n : number of associated water molecules, and optionally be zero.

Description

Field of the invention

The present invention relates to a process for producing alcoholic esters of monocarboxylic acids from fatty substances of vegetable or animal origin, by a transesterification reaction.

Background Art The fatty acid esters are currently used in many applications as diesel fuels, domestic fuels, ecological solvents, basic compounds for the manufacture of sulphonates of fatty alcohols, amides, ester dimers, etc. They can be obtained from a transesterification reaction carried out according to Scheme 1 below and optionally a combined esterification and transesterification reaction, the esterification being carried out according to Scheme II below. Scheme 1: 1 triglyceride + 3 alcohols -> 3 fatty acid esters + glycerin Scheme II: Fatty acid + alcohol -> fatty acid esters + water Fatty acid + glycerine - + glyceride + water In the case of diesel fuel, which is today a major application of fat esters, a number of specifications have been established whose list, limits and methods are part of the standard EN 14214 (2003) currently applicable in Europe. The ester shall contain not less than 96.5% by mass of esters, not more than 0,8% by weight of monoglycerides, not more than 0,2% by mass of diglycerides and not more than 0,2% by mass of triglycerides, Few free fatty acids "0.5 mg KOH per g), which can be corrosive, less than 0.25% by weight bound and free glycerin and only trace metals. This implies a precise protocol to obtain the desired purity. When an ester is manufactured from oil or fat and monoalcohol, it is automatically formed, depending on the nature of the oil initially involved, from 10 to 15% by weight of a secondary product, which is glycerine. This glycerin is sold at a high price for various uses, but only when it has a high purity. This is obtained after extensive purification in units specialized in vacuum distillation.

In summary, most commercial processes for the production of esters lead relatively easily to crude products (esters and glycerin), which must, however, be thoroughly purified by various treatments which ultimately increase the price of the process. It is known to manufacture methyl esters by the conventional routes of homogeneous catalysis with soluble catalysts, such as sodium hydroxide or sodium methoxide, by reacting a neutral oil and an alcohol such as methanol (for example JAOCS 61, 343- 348 (1984)). However, we arrive at a pure product usable as a fuel and glycerin standards after many steps. In fact, the glycerine obtained is polluted by alkaline salts or alcoholates, so that the glycerin purification plant is almost as expensive as that which makes possible the manufacture of the ester. The heterogeneous catalysis processes have the advantage of producing esters and glycerine free of catalyst and therefore easy to purify. However, it is often difficult to economically obtain both an ester and a high purity glycerin. In order to improve the profitability of this process and to limit its operating costs, many teams have been interested in the development of new, more active catalysts. Basic solids exhibit high catalytic activity for the transesterification reaction of vegetable oils but may be sensitive to the presence of free fatty acids contained in the filler. This problem can be encountered especially when the oils used in the process are economically interesting, such as for example jatropha oil or used oils. Various oxides and mixed oxides possibly doped have thus been tested, for example the article by W. M. Antunes et al. (Catalysas Today, 133-135 (2008) 548-554) which describes the transesterification of soybean oil with methanol, using basic solid catalysts such as ZnO, MgO, Al2O3, or mixed oxides derived from hydrotalcites ( Mg / AI and Zn / Mg / AI). Patent FR-B-2,752,242, filed in the name of IFP, describes the use of solid and insoluble catalysts formed from zinc oxide and alumina or zinc aluminate. Nevertheless, these basic solids have a tendency to deactivation or are not stable in the presence of an excessive amount of fatty acids contained in unrefined or unrefined oils. The use of acid catalysts makes it possible to work with fillers containing a certain content of free fatty acids, which are economically more interesting. An example is the solid Fe-Zn cyanide used by P. Ratnasamy (Applied Catal A: Gen, 314, 2006, 148) which makes it possible to transesterify vegetable oils, acidic or not, with yields close to those obtained with catalysts basic. Nevertheless, the selectivity of the reaction, characterized by the formation of ethers, can be degraded by the presence on these solids of proton-bound Brdnsted acid sites.

By seeking to improve the performance of the transesterification reaction of fats of plant or animal origin, the inventors have developed a process using a heterogeneous acid-base catalyst based on metallophosphates of a Group 13 metal, exhibiting both basic sites and acidic sites.

SUMMARY OF THE INVENTION The process for the production of alcoholic esters of monocarboxylic fatty acids according to the present invention uses a heterogeneous catalyst based on metallophosphate in which the metal is chosen from group 13 of the periodic table.

DETAILED DESCRIPTION OF THE INVENTION The present invention describes a process for producing a composition of alcoholic esters of linear monocarboxylic acids of 6 to 26 carbon atoms and of glycerin in which a fatty substance of animal origin or plant, with an aliphatic monoalcohol containing 1 to 18 carbon atoms, in the presence of at least one metallophosphate-based acid-base heterogeneous catalyst having the general formula (1) MPO-yP [3 + 5 (1-A) Wherein M represents a metal cation of at least one member selected from aluminum, gallium or indium, where yy <1 - y such that 3 + 5 (1-y)> 0 - n the number of associated water molecules, n possibly being zero The metallophosphate compounds comprising at least one metal chosen from the group 13 of the periodic table are acid-base compounds, presenting at the same time basic sites resulting for example from groups pho sphates present on their surface and both acid sites related to the presence of the metal. This duality gives them interesting catalytic properties.

An advantage of the invention using metallophosphate catalysts of Group 13 of the Periodic Table is their ability to catalyze the transesterification of fatty substances with alcohols such as methanol or heavier than methanol. Thus, it is possible to form ethyl, isopropyl or butyl esters, which are of interest because often the pour points of the esters formed with ethyl, isopropyl or butyl alcohols are lower than those of the methyl esters, the gain sometimes being 10. ° C, which allows to use initially more saturated oils. An advantage of the invention using a catalyst based on metallophosphates of group 13 of the classification is in particular to allow a reduction of the reaction temperature, the contact time between the reagents or the alcohol / fat ratio relative to the art. previous, while improving the conversion rate and maintaining a high selectivity in esters.

Another advantage of the invention lies in the fact that these solids catalyze transesterification and esterification reactions according to a heterogeneous catalysis process. Thus, the catalyst is not consumed in the reaction and is not dissolved in the reaction medium. By remaining in solid form, it is easily separated from the reaction medium without loss of catalyst and without pollution of the reaction medium by dissolved species or catalyst residues. The activity and selectivity of this catalyst is not affected by the transesterification or esterification reaction: the catalyst is stable and recyclable under the experimental conditions of the reaction. This type of catalyst is compatible with use in a continuous industrial process, for example in a fixed bed and in which the catalyst charge can be used for a very long time without loss of activity. Preferably, the metal cation M of the metallophosphate compound is aluminum or gallium. Among the metallophosphate compounds of general formula MPO4, those whose atomic ratio M / P is equal to 1 are particularly interesting. Thus, the catalyst used in the process according to the present invention preferentially corresponds to the following general formula (II): MPO 4, nH 2 O in which M represents a metal cation of at least one element selected from aluminum, gallium or The type of catalyst may advantageously be prepared by one of the methods described below and known to those skilled in the art. The metallophosphate precursor MPO4, nH2O can be obtained by reacting a halide (MCI3 in the case where M is a Group 13 metal) on phosphoric acid in the presence of propylene oxide. The reaction is carried out at 0 ° C. and the gel obtained at room temperature is washed with an alcoholic solution. The solid is finally calcined to obtain the metallophosphate, at temperatures between 500 and 700 ° C., most often around 600 ° C. The catalyst used in the process according to the present invention is in the form of powders, beads, extrudates or pellets. The fatty substances used in the process of the invention correspond to natural or elaborate substances of animal or vegetable origin, predominantly containing triglycerides, commonly grouped under the terms of oil and fats. Usable oils include all common oils, such as palm oils (concrete or oleic), soybean, palm kernel, copra, babassu, rapeseed (old or new), sunflower (conventional or oleic). ), maize, cotton, peanut, jatropha curcas, castor oil, linseed oil and crambe oils and all oils derived from sunflower or rapeseed by genetic modification or hybridization or from algae or micro-algae. We can even use frying oils, rendering, various animal oils, such as fish oils, seals, tallow, lard, or fats from sewage treatment and even from poultry fat, because esters made from certain alcohols, such as ethyl, isopropyl or butyl alcohol, make it possible to gain more than 10 ° C. in the pour point and consequently to use more saturated oils at the beginning.

Among the oils used, it is also possible to indicate partially modified oils, for example by polymerization or oligomerization, such as, for example, "standolies" of linseed oil, sunflower oil and blown vegetable oils. The oils used are neutral or acid, virgin or recycled. The presence of fatty acid in the oils is not a priori detrimental because the catalytic systems based on metal phosphates of group 13, preferably aluminum or gallium, are also active for esterification and furthermore transform the fatty acids to esters. The limit value for free fatty acids contained in the oils is at an acid number close to 10 (the acid number being defined as the mass in mg of KOH required for the determination of all the free fatty acids in 1 g oil). The operability of the process under these conditions is close to that defined with a low acid number oil (ie less than 0.2 mg KOH / g). In the case of oils with a very high acid number (close to 10 mg of KOH / g), one of the possibilities is to precede the transesterification reaction with an esterification reaction of the free fatty acids present, either in using the same alcohol as that used in the transesterification process in the presence of a strong acid such as sulfuric acid or soluble or supported sulfonic acids (Amberlyst type 150 resins), or preferably using glycerin, to form a total or partial glycerol ester, using the same catalyst based on Group 13 metal phosphates, preferably aluminum or gallium, at atmospheric pressure and preferably under vacuum and at temperatures of between 150 and 220 ° C. . When using frying oils, which are a very cheap raw material for producing biodiesel, it is necessary to remove the fatty acid polymers from the reaction mixture so that the ester mixture meets the specifications of the standard. EN 14214.

Alcohol The nature of the alcohol involved in the process plays a role in the transesterification activity.

In general, it is possible to use various aliphatic monoalcohols containing, for example, from 1 to 18 carbon atoms, preferably from 1 to 12 carbon atoms. Even more preferably, the aliphatic monoalcohol contains from 1 to 5 carbon atoms.

The most active is methyl alcohol. However, ethyl alcohol and isopropyl, propyl, butyl, isobutyl and even amyl alcohols can be envisaged. Heavier alcohols such as ethyl hexyl alcohol or lauric alcohol may also be used. It is advantageously possible to add methyl alcohol to the heavy alcohols, which facilitates the reaction. On the other hand, when preparing the ethyl ester, a mixture of ethyl and methyl alcohol comprising from 1 to 500% by weight, preferably from 1 to 10% by weight, of methyl alcohol may be used in order to increase the conversion.

Operating Conditions of the Transesterification Reaction The process is carried out at temperatures of between 130 ° C. and 220 ° C., at pressures of less than 100 bars with an excess of monoalcohol relative to the stoichiometry of fatty substances / alcohol. Generally, the reaction can be carried out according to different embodiments.

If a batch reaction is used, it can work in one or two stages, that is to say perform a first reaction up to 85% to 95% conversion to esters, cool by evaporating the excess of Alcohol, decant the glycerin and finish the reaction by warming again between 130 ° C and 220 ° C and adding alcohol to obtain a total conversion.

It is also possible to aim for a conversion of 98% to esters by working for a sufficient time in a single step under appropriate conditions, for example by increasing the temperature and / or the alcohol / fat ratio. If you start a continuous reaction, you can work with several autoclaves and decanters. In the first reactor, a partial conversion is generally less than 90% and generally about 85%, then decanted by evaporating the alcohol and cooling; in a second reactor, the transesterification reaction is completed under the conditions mentioned by adding a portion of the alcohol which has previously been evaporated. The excess alcohol is finally evaporated in an evaporator and the glycerine and the esters are separated by decantation. Thus, at the end of these two stages, a biodiesel is obtained that meets the specifications. The conversion level is adjusted to obtain a specification fuel ester and a high purity glycerin, operating in one or two steps.

If a continuous fixed bed process is chosen, it is advantageously possible to work at temperatures of 130 to 220 ° C., preferably 150 to 180 ° C., at pressures of 1 to 7 MPa, the WH being preferably between between 0.1 and 3, preferably from 0.3 to 2, in the first step and the alcohol / oil weight ratio varying from 3/1 to 0.1 / 1. The introduction of the alcohol can be advantageously fractionated. The two-level introduction into the tubular reactor can be carried out as follows: feeding the reactor with the oil and about 2/3 of the alcohol to be used, then introducing the alcohol supplement approximately at level of the upper third of the catalytic bed. The leaching behavior is checked in the present invention by the absence of traces from the catalyst both in the ester formed and in the glycerin produced. The recyclability of the catalyst is evaluated experimentally over time. If it does not exceed 220 ° C, an ester of the same color as the starting oil and a colorless glycerine after decantation are generally obtained.

The compounds produced are analyzed either by gas chromatography for the esters and glycerin or, more rapidly, by exclusion liquid chromatography for the esters. The ester and glycerol obtained do not contain impurities from the catalyst. Therefore, no purification treatment will be applied to remove the catalyst or the residues thereof in contrast to the catalysts operating in a homogeneous process for which the catalyst or its residues are, after reaction, located in the same phase as the ester and / or glycerine. The fuel ester obtained has a monoglyceride content of not more than 0.8% by mass, diglycerides of not more than 0.20% by mass, and triglycerides of not more than 0.2% by weight, glycerin of less than 0.25% by weight.

By this type of process, the final purification is reduced to a minimum, while making it possible to obtain an ester with fuel specifications and a glycerine of purity of between 95 and 99.9% and preferably between 98 and 99.9%.

EXAMPLES The following examples illustrate the invention without limiting its scope, Examples 8 and 9 being given for comparison. All the examples given below were implemented in a closed reactor and therefore correspond to a single step. To obtain a biodiesel that meets the specifications, it would be necessary to proceed to the conclusion of this first step to decantation by evaporating the alcohol and cooling, then complete the transesterification reaction by adding the portion of the evaporated alcohol . The oil used in these examples is rapeseed oil whose fatty acid composition is as follows: Glyceride of fatty acids Nature of the fatty chain ° / U in mass Palmitic C16: 0 5 Palmitoleic C16: 1 <0 , Stearic C18: 0 2 Oleic C18: 1 59 Linoleic C18: 2 21 Linolenic C18: 3 9 Arachidic C20: 0 <0.5 Gadoleic C20: 1 1 Behenic C22: 0 <0.5 Erucic C22: 1 <1 Table 1: Composition of rapeseed oil.

However, any other vegetable or animal oil could give similar results. Example 1: Synthesis of AIPO4

This example illustrates the preparation of AIPO4 by hydrogel: An equimolar mixture of aluminum chloride hexahydrate AIC13,6H2O and H3PO4 acid is first prepared in an ice bath. Propylene oxide (Teb = 35 ° C.) is then added with vigorous stirring in small portions until 3 moles are added per mole of Al. The mixture is then allowed to stand at room temperature until a consistent gel is formed which is washed with isopropanol and then dried and calcined at 650 ° C. The reaction equation is: AICI3 + H3PO4 +3 C3H6O - + AIPO4 + 3 CH (CH3) (OH) CH2Cl

The aluminum phosphates thus prepared have specific surfaces of the order of 250 m 2 / g. The great state of division is accompanied by a very pronounced hygroscopic character. Left in ambient air, the powder can take up to 20% of water in a few days. All the products obtained are white, amorphous X-ray powders. A beginning of crystallization can only be obtained after prolonged heating at high temperature, at 1000 ° C. the tridymite variety is observed.

Example 2 Transesterification of vegetable oils (rapeseed oil) with methanol from a solid catalyst AIPOa at 180 ° C.

25 g of rapeseed oil, 25 g of methanol and 0.5 g of AIPO4 catalyst (Example 1) in powder form are introduced into a closed reactor at ambient temperature. The mass ratio methanol / oil is therefore 1, which corresponds to a molar ratio of 27.5. The reactor is then closed, stirred (200 rpm) and heated to 180 ° C. using a magnetic heating stirrer. The temperature of the reaction medium is stabilized at 180 ° C. after 20 minutes of heating. Pressure is the autogenous pressure of alcohol at working temperature. The monitoring of the reaction is started when the temperature of the reaction medium has reached the set point. Samples are taken regularly to follow the progress of the reaction. After 6 hours of reaction, the stirring is stopped and the reactor is allowed to cool to room temperature. The samples taken and the final effluent are washed with a saturated aqueous solution of NaCl, and after decantation, the upper organic phase is analyzed by gel permeation chromatography (GPC). The following table summarizes the results obtained. Samples (in h) Ob 2 4 6% Triglycerides 73 34 20 12 mass Diglyceridesa 12 11 7 5 in the monoglyceride 2 4 5 6 organic phase 'Methyl esters 13 51 68 77 vegetable oil' determined by GPC bt = 0 when the The reaction medium is at a temperature representing diglycerides and sterols. The conversion of the triglycerides begins while the reaction medium has not reached 180 ° C. (13% of esters at t0). The conversion (estimated to triglycerides, conversion = 1-final (triglycerides) / min, a, e (triglycerides)) is 88% at 6 h. Leaching of the catalyst in the ester and glycerine phase is negligible (the phosphorus and aluminum content, estimated by the inductively coupled plasma (IPC) technique, is less than 10 ppm). Example 3 Transesterification of vegetable oils (rapeseed oil) with ethanol from an AIPO4 solid catalyst at 180 ° C. 20 g of rapeseed oil, 30 g of ethanol and 0.5 g of AIPO4 catalyst (Example 1) in powder form are introduced into a closed reactor at ambient temperature. The ratio molar ratio alcohol / oil is 27.5. The reactor is then closed, stirred (200 rpm) and heated to 180 ° C using a magnetic stirrer heater. The temperature of the reaction medium is stabilized at 180 ° C. after 20 minutes of heating. Pressure is the autogenous pressure of alcohol at working temperature. The monitoring of the reaction is started when the temperature of the reaction medium has reached the set point. Samples are taken regularly to follow the progress of the reaction. After 6 hours of reaction, the stirring is stopped and the reactor is allowed to cool to room temperature. The samples taken and the final effluent are washed with a saturated aqueous solution of NaCl, and after decantation, the upper organic phase is analyzed by gel permeation chromatography (GPC). The following table summarizes the results obtained.

Samples (in h) Ob 2 4 6% Triglycerides 90 55 42 32 mass Diglycerides ° 6 14 14 12 in the monoglyceride 0 4 4 6 organic phase 'Methyl esters 3 27 40 50 of vegetable oil determined by GPC bt = 0 when the reaction medium is at a temperature representing diglycerides and sterols. The conversion of triglycerides begins while the reaction medium has not reached 180 ° C. (3 ° / U of esters at t0). The conversion (estimated to triglycerides, conversion = 1-final (triglycerides) / nitrate (triglycerides)) was 68% at 6 h. The leaching of the catalyst in the ester and glycerine phase is negligible (the phosphorus and aluminum content, estimated by the inductively coupled plasma (IPC) technique, is less than 10 ppm).

Example 4 Transesterification of vegetable oils (rapeseed oil) with methanol from a solid GaPO4 catalyst at 180 ° C. 20 g of rapeseed oil, 30 g of ethanol and 0.5 g of GaPO4 catalyst in powder form are introduced into a closed reactor at ambient temperature. The alcohol / oil molar ratio is 27.5. The reactor is then closed, stirred (200 rpm) and heated to 180 ° C. using a magnetic heating stirrer. The temperature of the reaction medium is stabilized at 180 ° C. after 20 minutes of heating. Pressure is the autogenous pressure of alcohol at working temperature. The monitoring of the reaction is started when the temperature of the reaction medium has reached the set point. Samples are taken regularly to follow the progress of the reaction. After 6 hours of reaction, the stirring is stopped and the reactor is allowed to cool to room temperature. The samples taken and the final effluent are washed with a saturated aqueous solution of NaCl, and after decantation, the upper organic phase is analyzed by gel permeation chromatography (GPC). The following table summarizes the results obtained. Samples (in h) Ob 2 4 6% Triglycerides 89 55 36 27 mass Diglycerides ° 6 13 12 11 in the monoglyceride 0 3 5 5 organic phase 'Methyl esters 5 28 47 57 of vegetable oil determined by GPC bt = 0 when the reaction medium is at a temperature corresponding to the diglycerides and sterols The conversion of the triglycerides begins while the reaction medium has not reached 180 ° C. (5% of esters at t0) The conversion (estimated relative to the triglycerides Conversion = 1-methyl (triglycerides) / min, a, e (triglycerides)) is 73% at 6 hours.

The leaching of the catalyst in the ester and glycerin phase is negligible (the phosphorus and aluminum content, estimated by the inductively coupled plasma (IPC) technique, is less than 10 ppm). Example 8 (comparative): Transesterification of rapeseed oil with methanol in the presence of zinc aluminate (ZnAl-Oa) in powder form at 180 ° C. 25 g of rapeseed oil, 25 g of methanol and 0.5 g of catalyst in powder form are introduced into a closed reactor at ambient temperature. The mass ratio methanol / oil is therefore 1, which corresponds to a molar ratio of 27.5. The reactor is then closed, stirred (200 rpm) and heated to 180 ° C. using a magnetic heating stirrer. The temperature of the reaction medium is stabilized at 180 ° C. after 20 minutes of heating. Pressure is the autogenous pressure of alcohol at working temperature. The monitoring of the reaction is started when the temperature of the reaction medium has reached the set point. Samples are taken regularly to follow the progress of the reaction. After 6 hours of reaction, the stirring is stopped and the reactor allowed to cool to room temperature. The samples taken and the final effluent are washed with a saturated aqueous solution of NaCl, and after decantation, the upper organic phase is analyzed by gel permeation chromatography (GPC). The following table summarizes the results obtained. Samples (in h) Ob 46% by mass Triglycerides 92 44 29 in the phase Diglycerides ° 5 20 18 organic 'Monoglyceride 0 7 9 Esters 3 29 44 methyl 5' vegetable oil determined by GPC bt = 0 when the reaction medium This example clearly shows that the zinc aluminate catalyzes the transesterification reaction much more slowly than a metallophosphate, since in 6 hours, only 44% of esters are obtained instead of 77% of the diglycerides and sterols. % for the metallophosphate AIPO4.

EXAMPLE 9 (Comparative) Transesterification of rapeseed oil with ethanol in the presence of zinc aluminate ZnAl 2 O 4 in the form of a powder at 200 ° C. 21 g of rapeseed oil, 30 g of ethanol and 0.5 g of catalyst in powder form are introduced into a closed reactor at room temperature. The alcohol / oil molar ratio is 27.5. The reactor is then closed, stirred (200 rpm) and heated to 200 ° C. using a magnetic heating stirrer. The temperature of the reaction medium is stabilized at 200 ° C. after 30 minutes of heating. Pressure is the autogenous pressure of alcohol at working temperature. The monitoring of the reaction is started when the temperature of the reaction medium has reached the set point. Samples are taken regularly to follow the progress of the reaction. After 6 hours of reaction, the stirring is stopped and the reactor is allowed to cool to room temperature. The samples taken and the final effluent are washed with a saturated aqueous solution of NaCl, and after decantation, the upper organic phase is analyzed by gel permeation chromatography (GPC). The following table summarizes the results obtained.

Samples (in h) Ob 46% by mass Triglycerides 97 56 36 in the phase Diglycerides ° 1 21 22 organic 'Monoglyceride 0 4 9 Methyl esters 2 18 33 of vegetable oil determined by GPC bt = 0 when the reaction medium is at temperature% representing diglycerides and sterols This example clearly shows that zinc aluminate catalyzes the transesterification reaction with ethanol much more slowly than a metallophosphate, since in 6 hours, only 330% of esters are obtained, 200 ° C, instead of 50% for the metallophosphate AIPO4 with a reaction yet at a lower temperature, at 180 ° C. 16

Claims (10)

REVENDICATIONS1. Process for producing a composition of alcoholic esters of linear monocarboxylic acids of 6 to 26 carbon atoms and of glycerin in which a fatty substance of animal or vegetable origin is reacted with an aliphatic monoalcohol containing from 1 to 18 carbon atoms, in the presence of at least one metallophosphate-based acid-base heterogeneous catalyst having the general formula (1) MPO-YPI3 + 5 (1-y) 1/2, nH2O wherein M is a metal cation at least one element selected from aluminum, gallium or indium, wherein y is such that 3 + 5 (1-y)> 0 n the number of associated water molecules, n possibly being be zero. 2. Method according to claim 1 wherein the catalyst has the following general formula (II): MPO 4, nH 2 O wherein M represents a metal cation of at least one element selected from aluminum, gallium or indium, n the number of associated water molecules, n possibly being zero 3. Method according to one of claims 1 or 2 wherein the metal cation M is selected from aluminum or gallium. 4. Method according to one of the preceding claims wherein the fatty substance 30 of animal or vegetable origin is selected from concrete palm oils or oleins, soybean, palm kernel, copra, babassu, rapeseed old or new , of conventional or oleic sunflower, of maize, of cotton, the oils of peanut, jatropha curcas, castor oil, flax and crambe, all the oils resulting for example from sunflower or rapeseed by genetic modification or hybridization or from algae or micro-algae, cooking oils, various animal oils, such as fish oil, seals, rendering oils, tallow, lard, or fats from sewage treatment and even poultry fat. 5. Method according to one of the preceding claims wherein said aliphatic monoalcohol contains 1 to 12 carbon atoms, preferably 1 to 5 carbon atoms. 6. Method according to one of claims 1 to 5 wherein one operates at temperatures between 130 ° C and 220 ° C at pressures less than 100 bar with an excess of monoalcohol relative to the stoichiometry fat / alcohol . 7. Method according to one of the preceding claims wherein the recation is implemented discontinuously. 8. Method according to one of claims 1 to 6 wherein the reaction is carried out continuously, in a fixed bed or with autoclaves and decanters in series. 9. The method of claim 8 wherein the reaction is carried out in a fixed bed, at temperatures of 130 to 220 ° C, at pressures of 1 to 7 MPa, the VVH between 0.1 and 3, preferably from 0.3 to 2, in the first step and the alcohol / oil weight ratio varying from 3/1 to 0.1 / 1. 10. Method according to one of the preceding claims wherein one operates in one or two stages by adjusting the conversion level to obtain a estercarburant presenatnt a monoglyceride content of u plus 0.8% by weight, in diglycerides with plus 0.2% by mass, triglycerides not exceeding 0.20% by mass, glycerin less than 0.25% by mass and glycerin with a purity of between 95 and 99.90%, and preferably between 98 and 99.9 ° / x.