FR2855518A1 - Transesterification of vegetable or animal oils, useful for preparation of fuels and pure glycerine, involves using heterogeneous catalysts based on zirconium and aluminum - Google Patents

Abstract

Production of fatty acid esters and high purity glycerine involves the reaction of a vegetable or animal oil with a 1 - 18C monoalcohol in the presence of a catalyst comprising zirconium oxide or a mixture of oxides of zirconium and aluminum. The catalyst conforms to the formula (ZrOx)y(Al2O3)1 - y (I); x : 1.5 - 2.2; and y : 0.005 - 1. An independent claim is also included for the products obtained by the above process.

Description

The present invention relates to a new manufacturing process

esters

  of monocarboxylic acids from vegetable or animal oils.

  The reaction which is aimed primarily is a transesterification carried out according to scheme I below and possibly a combined esterification and transesterification reaction, the esterification being carried out according to scheme II below. In these schemes the fatty acid chains are represented by oleic type chains.

  - Diagram I CH3 (CH2) 7 CH = CH (CH2) 7 COOCH2 CH2-OH

I I

  CH 3 (CH 2) 7 CH = CH (CH 2) 7 COOCH 3 H 3 CH 3 (CH 2) 7 CH = CH (CH 2) 7 COO-R + CH-OH II CH 3 (CH 2) 7 CH = CH (CH 2) 7 CO 2 CH 2 CH 2 - OH - Scheme II CH 3 (CH 2) 7 CH = CH (CH 2) 7 COOH + ROH> CH 3 (CH 2) 7 CH = CH (CH 2) 7 COOH + H 2 CH 3 (CH 2) 7 CH = CH (CH 2) 7 COOH + CH 2 OH> CH3 (CH2) 7CH = CH (CH2) 7COO-CH2 + H2O II CH-OH CH-OH

I I

  CH2-OH CH2-OH Fatty esters are currently used in many applications as diesel fuels, domestic fuels, solvents, basic compounds for the manufacture of sulfonates of fatty alcohols, amides, ester dimers, etc. When an ester is made from oil and monoalcohol, from 10 to 15% of a secondary product, glycerine, is formed automatically depending on the nature of the oil initially employed. This glycerine is sold at a high price for a variety of uses, but only when it has a high purity. This is obtained after extensive purification in units specialized in vacuum distillation.

  In the manufacture of fatty acid methyl esters from refined oils and alcohol, whereas simple alkaline derivatives, such as sodium alcoholates, sodium hydroxide or potassium hydroxide, are commonly used as catalysts under the conditions of quite mild (temperature of 50 to 80 C and atmospheric pressure), as can be read in many patents or publications, for example in JAOCS 61, 343-348 (1984), however, a product can not be produced. It can be used as a fuel and a glycerin at 25 standards only after many steps.

  If one takes for example the most used alkaline catalysts, one finds, as well in the glycerin as in the ester, these alkaline compounds, which it is necessary to eliminate by washing and / or by neutralization in the ester fraction, then to dry it. In the glycerine phase, it is necessary to neutralize the soaps and alcoholates present, sometimes to eliminate the formed salts.

  The glycerin thus obtained contains water generally between 5% and 40% by weight. It also contains the salts resulting from the neutralization of the alkaline catalyst, for example sodium chloride when the catalyst is sodium hydroxide or sodium methoxide and when the neutralization is carried out with hydrochloric acid. The concentration of salts in glycerin from these processes is generally in the range of 3% to 6% by weight. Obtaining high purity glycerol from glycerin resulting from these processes therefore imposes purification steps such as distillation under reduced pressure that can sometimes be associated with treatments on exchange resins.

  In summary, most of the commercial ester-making processes quite easily lead to crude products (esters and glycerine), which must, however, be thoroughly purified by various treatments which ultimately add to the cost of processing.

  Surprisingly, it has now surprisingly been possible to obtain, in particular conditions, directly from vegetable or animal oils and monohydric alcohols, esters of these monoalcohols and a glycerine free from sulfuric acid. salts, in any case containing not more than 5 ppm, with a purity of between 95% and 99.9%, most often between 98% and 99.9%, and using as catalysts, either in continuous, for example in fixed bed, or discontinuously, a particular heterogeneous catalytic system.

  The use of heterogeneous catalysts is not new.

  Among the earlier documents which deal with heterogeneous catalysts, mention may be made of the European patent EP-B-0 198 243. The transesterification catalyst, which converts oil and methanol into a methyl ester, is an alumina or a mixture of alumina and alumina. ferrous oxide. In the examples, the column used for the fixed bed has a volume of 10 liters and the oil is generally injected at a rate of less than 1 liter / hour, which gives a VVH (VVH = volume of oil injected / volume of catalyst / hour) less than 0.1. For a 100,000 t / y plant, this would correspond to reactors of at least 150 m3.

  Another problem that seems to arise is that of the amount of glycerin collected, much lower than the theory. In no example where one is supposed to collect 10% of glycerine, one obtains, even approximatively, this value. Finally, the purity of the esters is quite low, from 93.5 to 98%. What becomes of the glycerin that is not recovered is not indicated. In some cases, glycerol ethers are formed, as reported in this patent; in other cases, perhaps it breaks down unless it is eliminated in a first step. The level of performance is therefore quite low. It can be pointed out that at VVH indicated and for contact times of more than 6 hours, conversions of 80% and more can be obtained even without catalyst.

  This patent does not seem to offer a reasonable solution from the economic point of view.

  There are other references in the literature which mention this time zinc oxide, however in esterification reactions of glycerin with a fatty acid [Osman in "Fette Seifen und Anstrichmittel" 331-33 (1968) ]. In this work, about twenty catalysts are compared at 180 ° C in a batch process. There is virtually no difference between zinc chloride, zinc sulphate, zinc powder, barium oxide, calcium oxide, zinc oxide, alumina, thiosalicylic acid, phosphate calcium, potassium bicarbonate, sodium methylate or ethoxide and even lithium hydroxide. All of these salts or oxides give between 32 and 39% monoglyceride yield in a comparative test where excess glycerin is used in relation to the fatty acid.

  US Pat. No. 5,908,946 describes a process that can operate continuously or batchwise and using solid and insoluble catalysts. However, the catalysts used are either zinc oxide or a mixture of zinc oxide and alumina or zinc aluminate.

  The present invention provides a process for producing at least one fatty acid ester of glycerin, both of which products are obtained in a high degree of purity, which process can be defined in a general manner by the fact that the reaction is carried out by reaction of vegetable or animal oils, acidic or neutral, with monoalcohols, for example from 1 to 18 carbon atoms, preferably from 1 to 12 carbon atoms, using at least one catalyst chosen from zirconium oxide and mixtures of zirconium oxide and alumina and having the empirical formula: (ZrOx) y (Al 2 O 3) 1-yx having a value of 1.5 to 2.2 and y, representing the ratio mass of the two oxides, having a value of 0.005 to 1, preferably from 0.005 to 0.995, the conditions of said reaction preferably including a temperature of between 150 and 250 ° C. and a pressure of less than 100 bar and preferably of 10 to 70 bar .

  All catalysts considered are in the form of powder, beads, extrudates or pellets. The use of alumina has two favorable effects. The first is to increase the specific surface of the catalysts because the zirconia in its main crystalline forms (quadratic, monoclinic and cubic) is known to have small specific surfaces. The second is to create a much more stable compound, especially with respect to conditions under which the zirconia compound would tend to form zirconium soaps.

  Another advantage of zirconium catalysts is their ability to catalyze the transesterification of the oil with alcohols heavier than methanol. Thus, ethyl esters and also isopropyl or butyl esters which are of interest outside the fuel domain can be formed.

  A major advantage of these solid catalysts is that they catalyze the transesterification and esterification reactions according to a heterogeneous catalysis process, ie the solid catalyst used on the one hand is not consumed in the reaction and on the other hand, it is never dissolved in the reaction medium but remains in the solid form and will therefore be separated from the liquid reaction medium without loss of catalyst and without pollution of the reaction medium by the presence of catalyst or catalyst residue.

  This is verified in the invention by the absence of traces from the catalyst both in the ester formed and in the glycerin produced.

  The charge of this catalyst is not affected by the transesterification or esterification reaction. Its catalytic activity is preserved after the reaction. This type of catalyst is compatible with use in a continuous industrial process for example fixed bed in which the catalyst load can be used for a very long time without loss of activity.

  The ester and glycerol obtained do not contain impurities from the catalyst. Therefore, no purification treatment will be applied to remove the catalyst or residues thereof, unlike processes using catalysts operating in a homogeneous process where the catalyst or its residues are, after reaction, located in the same phase as the ester and / or glycerin.

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

  The process of the invention is described in more detail below.

  Among the oils that can be used in the process of the invention, mention may be made of all common oils, such as palm, palm kernel, coconut, babassu, old or new rapeseed, sunflower, corn, castor oil and cotton, peanut, flax and crambe oils and all oils derived for example from sunflower or rapeseed by genetic modification or hybridization.

  One can even use cooking oils, various animal oils, such as fish oils, tallow, lard, rendering and even fats.

  Among the oils used, it is also possible to indicate oils partially modified for example by polymerization or oligomerization, for example the "standolies" of linseed oil, sunflower oil and blown vegetable oils.

  The presence of fatty acid in oils is not a priori detrimental, except that there is a risk of saponification. It is possible to precede the transesterification reaction with an esterification reaction, preferably with glycerine, to form, at atmospheric pressure or partial vacuum and at temperatures of 180 to 220 ° C., a glyceride with from fatty acids.

  The nature of the alcohol involved in the process of the invention plays an important role in the activity of transesterification. 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. The most active is methyl alcohol.

  However, ethyl alcohol and isopropyl, propyl, butyl, isobutyl and even amyl alcohols can be used. Heavier alcohols such as ethyl hexyl alcohol or lauric alcohol can also be used. It can be conveniently added to the heavy alcohols methyl alcohol, which seems to facilitate the reaction. On the other hand, when preparing the ethyl ester, 1 to 50%, preferably 1 to 10%, of methyl alcohol may be used to increase the conversion.

  The preparation of zirconia catalysts is known from the prior art. A particular method resulting from the teaching of patent EPB-0 908 232 consists in coprecipitating ZrO (NO 3) 2 and Al (NO 3) 3 at a pH equal to 9.

  Another method inspired by the work of Gao et al. (Top Catal., 6 (1998), 101) consists of coprecipitating ZrOC12 and Al (NO3) 3 with ammonia.

  A preferred method is the precipitation of ZrO (NO 3) 2 by hydrazine, in the presence or absence of Al (NO 3) 3 (for example, the method cited by Ciuparu et al., J. Mater.

Sci. Lett. 19 (2000) 931).

  To produce a catalyst of the formula (ZrO x) y (Al 2 O 3) 1-y (x and y being defined as above), the following sources may be used.

  Zirconium sources include Zr (OR) 4 alkoxides with R = Me, Et, Pr, iPr, Bu, iBu, etc.). It is also possible to use zirconium in the form of inorganic salts (ZrOC12, ZrOSO4, ZrO (NO3) 2, etc.). Similarly, the colloidal forms of zirconium may be used (colloidal, the applicant understands that the size of zirconium oxide or oxyhydroxide particles is between 1 nmn and nm). Finally, the sources of zirconium may be gels resulting from the hydrolysis of the preceding sources, thus obtaining a form of partially hydrated titanium oxide of chemical formula (ZrO2, zH20) with z ranging between 0 and 5. It is also advantageous to use dehydrated, amorphous or crystallized zirconium oxide, which in this latter case has quadratic, monoclinic or cubic crystallographic structures known to those skilled in the art.

  Sources of Alumina The aluminum sources used in the invention may be of the alkoxide form of general formula AI (OR) 3, with R = Me, Et, Pr, iPr, Bu, iBu, etc.) or hydoxides. The inorganic aluminum salts can also be advantageously used, namely chlorides, nitrates, sulfates, etc. Similarly, the aluminum source may be basic, in which case the aluminum is in aluminate form (A102-). The counter-ion can be an alkaline (Li, Na, K, Cs) and more generally any positive counter-ion (NH4 + for example).

  In the case of using an aluminum solid precursor, any alumina compound of the general formula A1203, nH20 may be used. Its specific surface is between 100 and 600 m2 / g. In particular hydrated alumina compounds can be used, such as: hydrargillite, gibbsite, bayerite, boehmite, pseudoboehmite and amorphous or essentially amorphous alumina gels. It is also possible to use the dehydrated forms of these compounds which consist of transition aluminas and which comprise at least one phase taken from the group: rho, khi, eta, kappa, theta, delta, gamma and alpha, which differentiate essentially on the organization of their crystalline structure.

  The catalyst can be advantageously prepared by one of the methods described below.

  The impregnation of at least one soluble salt, an alkoxide, a sol or an alkoxide on a preformed alumina support having a specific surface area of between 20 and 10 600 m2 / g, preferably between 100 and 370 m2 / g. This support may be in the form of powder, beads, extrudates or any other form known to those skilled in the art and for working in fixed bed, bubbling bed or slurry. This support is chosen from the aforementioned sources of aluminas. After various steps known to those skilled in the art, the catalysts are dried between 25 and 150 ° C., preferably between 50 and 120 ° C. and then calcined at temperatures of between 150 and 1000 ° C., preferably between 250 and 600 ° C. .

  The kneading of at least one zirconium compound with a more or less hydrated alumina compound defined above as a solid precursor in the presence of a peptizing agent (mineral acid or organic acid). In a preferred manner, the peptizing agents are nitric and acetic acids. It may also be added to the paste obtained known agents to facilitate the shaping such as methyl cellulose derivatives or any other compounds known to those skilled in the art for this purpose. The product is then shaped by extrusion, then dried at 40 to 150 ° C., preferably at 70 ° to 120 ° C., and then calcined at temperatures of between 300 and 1100 ° C., preferably between 350 and 800 ° C.

  The sol-gel synthesis between a zirconium alkoxide and an aluminum alkoxide, chosen from the sources mentioned above, preferably aluminum sec-butoxide and zirconium n-butoxide. These precursors may be mixed in the presence of a suitable solvent and optionally complexing agent or surfactants.

  Everything can be hydrolyzed to obtain a gel. The gel can be dried between 40 and 140 ° C., preferably between 80 and 130 ° C. and shaped by conventional extrusion techniques with the optional addition of binder, or by resuspension in a suitable liquid to form beads by precipitation "oil-drop">, be pelletized. In all cases, the shaped objects are dried between 40 and 150 C, preferably between 70 and 120 C, and then calcined at temperatures between 300 and 1100 C, preferably between 350 and 800 C.

  Co-precipitation between at least one zirconium salt, zirconium sol or alkoxide and at least one aqueous salt, sol or aluminum alkoxide. The precipitation can take place in the presence of only water or precipitating agents such as an inorganic base (sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, hydrazine, etc.) or organic (urea, etc.) or an acid. inorganic (nitric acid, sulfuric acid, etc.) or organic (formic acid, acetic acid, etc.). The precipitation must take place at a pH of between 4 and 13 as is known to those skilled in the art, more preferably between pH 5 and 9. The co-precipitate is filtered and washed carefully according to the nature of the precursors and agents so as to limit the content of alkaline ions (sodium, potassium, etc.) to less than 0.5% and preferably less than 0.1% by weight relative to the oxides. Likewise, the anion contents (chloride, sulfate, etc.) must be limited to less than 1%, preferably less than 0.3% by weight. The precipitate obtained can be atomized, then shaped by extrusion, pelletizing or resuspension in a suitable solvent to form beads. In all cases, the shaped objects are dried between 40 and 150 C, preferably between 70 and 120 C, and then calcined at temperatures between 300 and 1100 C, preferably between 350 and 800 C.

  Whatever the method of preparation chosen, it is preferable to have at least 10% of zirconium dioxide, preferably 23% of zirconium dioxide and even more preferably 50% of zirconium dioxide. Wherever possible, the zirconium dioxide should be in predominantly amorphous or microcrystallized form, remarkable for the absence on the X-ray diffraction pattern of crystallized forms known to those skilled in the art of zirconium.

  Regarding the texture of the catalyst, it is important to maintain the specific surface area measured by the BET method known to those skilled in the art, and the pore volume to correct values. Thus, the catalyst will generally have a surface area of between 10 and 500 m 2 / g, preferably between 50 and 400 m 2 / g and more preferably between 80 and 300 m 2 / g. Similarly, the pore volume will be between 0.1 cm3 / g and 1.2 cm3 / g, and preferably greater than 0.2 cm3 / g.

  Finally, the porous distribution will be between 0.001 microns and 0.1 microns.

  If the transesterification is carried out in the absence of a catalyst, either in an autoclave or in a fixed bed with inert supports, such as silicon carbide, it is possible to obtain conversions at certain temperatures generally greater than or equal to 250 ° C. which exceed 80%, but at very low VVH and with very long residence times. The thermal reaction therefore exists and it is sometimes difficult to decide between the catalytic effect and the thermal effect, which explains why with simple aluminas high conversions can be obtained. However, the purpose of the method of the invention is to obtain these conversions with reasonable residence times, therefore reasonable VVH.

  The operating conditions used depend clearly on the method chosen. If a batch reaction is used, it can be worked in one or two stages, that is to say carry out a first reaction up to 85% to 95% conversion, cool by evaporating the excess of methanol. , decant the glycerin and finish the reaction by warming again and adding alcohol to obtain a total conversion. One can also aim for a conversion of 98% by working long enough in a single step.

  If you start a continuous reaction, you can work with several autoclaves and decanters. In the first, a conversion is carried out, for example 85%, then decanted by evaporating the alcohol and cooling; in a second reactor, the transesterification reaction is completed by adding a portion of the alcohol which has previously been evaporated. The excess alcohol is finally evaporated in an evaporator and the glycerol and the esters are separated by decantation.

  If a continuous fixed bed process is chosen, it is advantageous to operate at temperatures of 150 to 250 ° C., preferably 170 ° to 210 ° C., at pressures of 30 to 70 bar, if methyl esters are manufactured. , the VVH being preferably between 0.1 and 3, preferably from 0.3 to 2, in the first step and the alcohol / oil weight ratio varying from 25 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.

  If no more than 220 ° C., an ester of the same color as the starting oil and a colorless glycerine after decantation are generally obtained. The ester can be passed through a resin, a soil and / or activated carbon, as well as glycerine.

  The compounds produced are analyzed either by gas chromatography for the esters and glycerin or, more rapidly, by exclusion liquid chromatography for the esters. It is found that the process of the invention, unlike known processes carried out in homogeneous basic catalysis with monoalcohols, produces no or very little sterol esters. Sterol esters, which are heavy products, can cause deposits in the injectors.

  The examples presented below do not limit the invention and serve only to illustrate it.

  Synthesis of catalysts Catalyst 1 A preformed alumina support in the form of beads 1.4 mm in diameter, SBET surface area = 189 m 2 / g and pore volume Vp = 0.6 cm 3 / g is used.

  Catalyst 2 Catalyst 2 is prepared according to the reference Ciuparu (J. Mater Sci Lett 19 (2000) 931). A mixture of zirconyl nitrate with hydrazine is refluxed for 120 h. The gel obtained is filtered, dried and then atomized. The powder obtained is shaped by extrusion. The extrudates are then calcined at 550 ° C. for 4 hours. X-ray diffraction analysis results in amorphous zirconia, no streak characteristic of known crystallographic phases of zirconia being detected. The specific surface area measured by the BET method is 250 m 2 / g. The zirconia content is 100%.

  Catalyst 3 Catalyst 3 is prepared by impregnating zirconium n-butoxide on Catalyst 1. The alumina is calcined at 400 ° C. for 1 hour. 92.7 g of ziconium butoxide is mixed with 64 ml of heptane and then poured slowly over 100 g of alumina. The whole is stirred for 24 hours. The solid obtained is placed in ambient air for 72 h and then dried in an oven. The catalyst is calcined at 500 ° C. for 4 hours. X-ray diffraction analysis shows the presence of crystalline phase, characteristic of the presence of gamma-alumina.

  In addition, a small portion of tetragonal zirconia is detected. The specific surface area measured by the BET method is 193 m2 / g. The content of alumina and zirconia measured by X-ray fluorescence is 84.3% and 14.7% by weight, respectively.

  Catalyst 4 Catalyst 4 is prepared by coprecipitation of zirconyl nitrate and aluminum sulfate to which ammonia is added. The gel obtained is filtered, dried and then atomized. The powder obtained is shaped by extrusion. The extrudates are then calcined at 700 ° C. for 4 hours. X-ray diffraction analysis results in amorphous zirconia, no streak characteristic of known crystallographic phases of zirconia being detected. The specific surface area measured by the BET method is 158 m2 / g. The contents of alumina and zirconia are respectively 15% and 85%.

  Example 1 (Comparative): Reaction in the absence of catalyst In a 100 ml autoclave reactor equipped with a temperature and pressure control system, 2 g of oil composition is detailed in the following table and 25 g of methanol.

  Agitating and rapeseed, including fatty acid glyceride Nature of the fatty chain% by weight Palmitic C16: 0 5 Palmitoleic C16: 1 <0.5 Stearic C18: 0 2 Oleic C18: 1 59 Linoleic C 18: Linoleic C 18: 3 9 Arachid C20: 0 <0.5 Gadoleic C20: 1 1 Behenic C22: 0 <0.5 Erucic C22: 1 <1 The medium is brought to 200 ° C. with stirring. The pressure reaches 32 bar.

  Samples are taken after 2 hours, 5 hours and 7 hours. On each sample, after evaporation of the excess methanol and then removal of the glycerol formed by decantation, the concentration of methyl esters is determined by size exclusion chromatography. It is respectively 18%, 36% and 52%.

  Example 2 (Comparative): Reaction in the Presence of Catalyst 1 In a 100 ml autoclave reactor equipped with a stirring system and a temperature and pressure control, 25 g of rapeseed oil are introduced, the composition of which is detailed in Example 1, 25 g of methanol and 5 g of Catalyst 1. the medium is heated to 200 C with stirring. The pressure reaches 32 bar.

  Samples are taken in the liquid phase after 2 hours, 5 hours and 7 hours of reaction. On each sample, after filtration and evaporation of excess methanol and removal of glycerol formed bydecantation, the concentration of methyl esters is determined by size exclusion chromatography. It is respectively 18%, 35% and 54%. These results are similar to those reported in Example 1 in the absence of catalyst, indicating that the product here referred to as Catalyst 1 consisting solely of alumina has no catalytic effect under the conditions of the experiment.

Example 3

  In a 100 ml autoclave reactor equipped with a stirring system and a temperature and pressure control, 25 g of rapeseed oil, the composition of which is detailed in Example 1, 25 g of methanol are introduced. and 5 g of Catalyst 3. The medium is brought to 200 ° C. with stirring. The pressure reaches 32 bar.

  Samples are taken after 2 hours, 5 hours and 7 hours. On each sample, after filtration and then evaporation of the excess methanol followed by removal of the glycerol formed by decantation, the concentration of methyl esters is determined by steric exclusion chromatography. It is 58%, 83% and 90% respectively.

  The concentration of zirconium in the methyl ester obtained is less than 1 ppm, which confirms the heterogeneous nature of the catalysis.

  This allows the use of the ester obtained as fuel without having to carry out an additional purification treatment of the methyl ester to remove traces of residual catalyst.

  Under the same conditions, the same recycled catalyst leads to a methyl ester concentration of 90% after 7 hours of reaction, which indicates that the catalyst is in no way degraded and that it has retained all its activity. This operation was repeated twice more and led to the same conclusions.

Example 4

  Example 3 is repeated, this time using 16.7 g of methanol instead of 2 g. Samples are taken after 2 hours, 5 hours and 7 hours. On each sample, after filtration and then evaporation of excess methanol followed by removal of the glycerol 5 formed by decantation, the concentration of methyl esters is determined by steric exclusion chromatography. It is respectively 53%, 68% and 83%. The concentration of zirconium in the methyl ester obtained is less than 1 ppm, which confirms the heterogeneous nature of the catalysis.

  Under the same conditions, the same recycled catalyst leads to a concentration of 83% methyl esters after 7 hours of reaction, which indicates that the catalyst is in no way degraded and that it has retained all its activity.

Example 5

  Example 3 is repeated, operating this time at 180 ° C. instead of 200 ° C. The pressure reaches 27 bar.

  Samples are taken after 2 hours, 5 hours and 7 hours. On each sample, after filtration and then evaporation of the excess methanol followed by removal of the glycerol formed by decantation, the concentration of methyl esters is determined by steric exclusion chromatography. It is respectively 38%, 58% and 65%.

  The concentration of zirconium in the methyl ester obtained is less than 1 ppm, which confirms the heterogeneous nature of the catalysis.

  Under the same conditions, the same recycled catalyst leads to a concentration of methyl esters of 65% after 7 hours of reaction, which indicates that the catalyst is in no way degraded and that it has retained all its activity.

Examples 6 to 8

  Methanolysis is carried out in an apparatus comprising a fixed-bed reactor, ie a filled column, of diameter equal to 1.9 cm and of length equal to 120 cm, heated by three shells surrounding the column. Preheating of the oil and methanol is done in the column on 10 cm3 of glass beads and the reaction on 70 cm3 of volume of Catalyst 3. At the outlet of the column was added 20 cm3 of tungsten carbide and 5 cm3 of glass beads. The inverted U-shaped device consists of a tubular reactor, a cooling on the horizontal part and a decanter, which constitutes the second branch. On the upper part of the decanter, a gas purge system makes it possible to regulate the pressure, that is to say to maintain it initially with nitrogen at the desired pressure of 15 to 60 bar. The decanter has at its lower outlet a liquid purge. When the decanter is half full, an automatic valve opens to partially empty the resulting product. Two pumps inject at selected flow rates and at constant pressure the alcohol and the oil in the column and from bottom to top.

  The reaction products are collected after 24 hours of passage with the desired VVH (VVH = volume of oil / volume of catalyst / hour).

  After withdrawing the methanol, glycerol and ester product, generally present in a single phase, the methanol is evaporated and the ester and glycerol are separated by decantation.

  The ester is analyzed by steric exclusion chromatography. The results are therefore those obtained without any final purification, except that which consists of evaporating the excess of methanol and separating the ester from the glycerine by settling, preferably to 50 ° C.

  The following table presents the results obtained after 24 hours of reaction.

  VVH is the volume of oil injected per volume of catalyst per hour. The ratio R is the volume ratio oil / alcohol, denoted H / A. The pressure is the pressure that prevails in the decanter, expressed in bar.

  The composition of the mixture is expressed in% by weight.

  The contact time takes into account the presence of methanol; it is determined by the relation: cm3 of catalyst x 60 (*) time of contact volume in cm3 of the oil + alcohol injected in 1 h (*) 60 = time in minutes.

In the picture:

  - E = esters (also contains sterols) - MG = monoglycerides - DG = diglycerides which do not contain sterol esters, since they do not form under these conditions - TG = triglycerides Methanolysis of rapeseed oil with Catalyst 3 Example T VVH ratio P TG DG MG E t of (OC) H / A (bar) (%) (%) (%) (%) contact vol / vol (min) 6 200 0.5 1 50 0.6 1.9 3.5 94.0 60 7 200 0.5 1.5 50 4.3 3.9 4.6 87.2 72 8 180 0.5 1 50 5.2 5.4 7, 81.5 60 X-ray fluorescence zirconium analysis was performed on the obtained methyl esters and glycerol. The absence of zirconium in these products confirms the heterogeneous nature of the catalysis.

Example 9

  Example 6 is repeated replacing the rapeseed oil used as filler with an ester mixture whose composition is identical to that obtained in Example 6.

  The composition of the ester phase obtained is: - Methyl esters: 99.3% 10 - Monoglycerides: 0.5% - Diglycerides: 0.2% - Triglycerides: undetected This composition is compatible with the specifications required for a fuel ester for diesel motor.

Claims (19)

  A process for producing at least one fatty acid ester and glycerin with a high degree of purity, characterized in that it comprises the reaction of a vegetable or animal oil with an aliphatic monoalcohol containing from 1 to 18 carbon atoms, in the presence of at least one catalyst selected from zirconium oxide and mixtures of zirconium oxide and alumina having the formula: (ZrOx) y (Al 2 O 3) 1 -y, x having a value of 1.5 to 2.2 and y, representing the mass ratio of the two oxides, having a value of 0.005 to 1.   2. Method according to claim 1 characterized in that said aliphatic monoalcohol contains 1 to 12 carbon atoms.   3. Process according to claim 1, characterized in that said aliphatic monoalcohol contains from 1 to 5 carbon atoms.   4. Process according to claim 1 to 3, characterized in that the reaction is carried out at a temperature of between 170 ° C. and 250 ° C. under a pressure of less than 100 bar and with an excess of monoalcohol relative to the oil / alcohol stoichiometry.   5. Process according to claim 1 to 4, characterized in that, in the formula: (ZrOx) y (Al 2 O 3) 1-y, y is a value of 0.005 to 0.995.   6. Method according to claim 1 to 5 characterized in that said catalyst is in the form of powder, extrudates or beads.   7. Method according to one of claims 1 to 6 characterized in that the catalyst has a surface area of 10 to 200 m2 / g, a pore volume of 0.2 to 1.2 cm3 / g and a porous distribution of between 0 , 01 and 0.1 micron.   8. Process according to claim 7, characterized in that the catalyst has a surface area of 50 to 200 m 2 / g and a pore volume greater than 0.3 cm 3 / g.   9. Method according to one of claims 1 to 8 characterized in that the reaction is carried out discontinuously.   10. Method according to one of claims 1 to 9 characterized in that the reaction is carried out continuously, either fixed bed, or with autoclaves and decanters in series.   11. The method of claim 10 characterized in that the reaction is carried out in a fixed bed, at a VVH of 0.1 to 3, preferably 0.3 to 2.   12. Process according to one of Claims 1 to 11, characterized in that the following are carried out successively: an initial transesterification with a conversion of the oil to an ester of at least 80-85%; evaporation of the monoalcohol in excess; - The settling of the glycerin and the ester, said ester being recycled in a second step to undergo transesterification with a portion of the monoalcohol recovered in the first evaporation; - Then a new evaporation of the monoalcohol, the cold decantation and the separation of the glycerin and the ester.   13. Process according to one of Claims 1 to 12, characterized in that the starting oil is an acidic oil and a preliminary glycerolysis operation of the free fatty acid is carried out with a catalyst such as that used for transesterification. at a temperature between 180 and 220 ° C and at a pressure equal to or less than 1 bar.   14. Process according to one of Claims 1 to 13, characterized in that the ester obtained is purified by passage over a resin, a soil and / or activated charcoal.   15. Process according to one of claims 1 to 13, characterized in that the ester obtained is purified, either by distillation or by washing with methanolic glycerin to reduce the monoglyceride content.   16. Method according to one of claims 12 to 15 characterized in that the glycerin obtained after evaporation of the alcohol is purified permanently by passing over a resin, a soil and / or activated carbon. 17. Method according to one of claims 1 to 16 characterized in that, to manufacture the ethyl ester is used ethyl alcohol mixed with a proportion of 1 to 50% methanol.   18. Fuel ester obtained by a method according to one of claims 1 to 17 characterized in that it has a sterol ester content of less than 0.2% and a monoglyceride content of 0.5 to 5% and by the almost total absence of di- and triglycerides.   19. Glycerin obtained by a method according to one of claims 1 to 17 characterized in that it has a purity greater than 99.5%.