FR2890656A1 - Preparing linear monocarboxylic acid esters having 6-26 carbon atoms using a reaction mixture of vegetable/animal oil and aliphatic monoalcohol, useful e.g. as fuel, comprises cross-esterifying and distilling reaction mixture - Google Patents

Abstract

Preparing linear monocarboxylic acid esters having 6-26 carbon atoms using a reaction mixture of neutral/acidic pure or recycled vegetable/animal oil and an aliphatic monoalcohol of low molecular weight, obtained in the presence of a heterogeneous catalyst, the process comprising cross-esterifying and distilling the reaction mixture.

Description

2890656 1

  The present invention relates to a novel process for producing monocarboxylic acid esters from vegetable or animal oils.

  It relates more particularly to a process for producing linear monocarboxylic acid esters of 6 to 26 carbon atoms, by reaction of virgin or recycled vegetable or animal oils, neutral or acidic, with low molecular weight monoalcohols, by example of 1 to 5 carbon atoms, in the presence of a heterogeneous catalyst selected for example from metal oxides and mixtures of oxides capable of forming between them or with alumina combinations of oxides, which combines a single transesterification step and a distillation step of the reaction mixture.

  The fatty acid esters are currently used in many applications as diesel fuels, domestic fuels, ecological solvents, basic compounds for the manufacture of sulfonates of fatty alcohols, amides, ester dimers, etc. In the case of diesel fuel, which is today a major application of fatty acid esters, a number of specifications have been established, the list of which, the limits and the methods are part of the currently applicable EN 14214 (2003) standard. in Europe. The ester must not contain heavy compounds (triglycerides) and diglycerides, for example less than 0.2% by weight, few monoglycerides, for example less than 0.8% by weight, few free fatty acids, which may be corrosive, and little bound and free glycerin, for example less than 0.25% by weight, and not at all strong acids or traces of metals. This implies a precise protocol to obtain the desired purity.

  In the case of domestic fuel oil, it is obvious that all these specifications are not always useful and sometimes even harmful, but the fuel oil and diesel fuel markets are often confused, the fuel oil specifications are similar to those of diesel because in France, domestic fuel can be used in agricultural tractors and construction machinery.

  When an ester is manufactured from oil or fat and monoalcohol, it is automatically formed, depending on the nature of the oil initially engaged, from 10 to 15% by weight of a secondary product, which is the glycerin. 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.

  Also, in the manufacture of fatty-acid methyl esters from refined oils and dry alcohol, whereas catalysts commonly used are simple alkaline derivatives, such as sodium alcoholates, sodium hydroxide or potassium hydroxide, in conditions quite mild (temperature of 50 to 80 C and atmospheric pressure), as can be read in many patents or publications, for example in the JAOCS 61, 343-348 (1984), however, we arrive at a pure product that can be used as a fuel and a glycerine that meets the standards only after many steps.

  If, for example, the most commonly used alkaline catalysts are used, there are traces of alkaline compounds in the glycerin as well as in the ester, which must be removed by washing the ester fraction and drying the latter. this. In the glycerine phase, neutralize the soaps and alcoholates present, filter the salts formed, evaporate the glycerin after removing the water, unless the diluted glycerin is passed on ion exchange resins, before concentrate the glycerine salt free. Finally, it is always necessary to evaporate the excess alcohol and often distil it, avoiding that this evaporation, especially when it is carried out in the ester phase, does not lead to reacting the ester present with partially dissolved glycerine, which lead to the formation of monoglycerides.

  In summary, to obtain the desired specifications for glycerin and ester, it is necessary to resort to so many steps that only large units are able, under these conditions, to be economically profitable.

  Surprisingly, it has now been found that an ester and a high purity glycerin can be economically obtained without having to resort to two transesterification steps, by substituting the second transesterification step by a distillation of the ester mixture. obtained.

  Thus, the invention provides a process for the production of linear monocarboxylic acid esters of 6 to 26 carbon atoms, by reaction of virgin or recycled vegetable or animal oils, neutral or acidic, with low molecular weight monoalcohols. , for example from 1 to 5 carbon atoms, in the presence of a heterogeneous catalyst, characterized in that it combines a single transesterification step and a distillation step of the reaction mixture.

  The reaction aimed primarily in the first step of the process of the invention is a transesterification, carried out according to Scheme I below and possibly a combined esterification and transesterification reaction, the esterification then being carried out according to Scheme II below.

  Scheme I CH 3 (CH 2) 7 CH = CH (CH 2) 7 COO CH 2 CH 2 -OH CH 3 (CH 2) CH = CH (CH 2) 7 COOH CH 3 CHH CH 3 (CH 2) 7 CH = CH (CH 2) 7 CO 2 Embedded image CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2

CH-OH

  In the transesterification step of the process of the invention, by heterogeneous catalyst, is meant any solid catalyst for transesterifying a mixture of triglycerides such as a natural fat (oil or fat) in a mixture of alkyl esters. The heterogeneous catalyst may be chosen more particularly from metal oxides and mixtures of oxides capable of forming between them, and optionally with alumina, combinations of oxides.

  The use of heterogeneous catalysts is not new. However, in no industrial process, it appears that one can economically obtain both an ester and a glycerin of high purity. To produce economically means to obtain a standard ester and a pure glycerin, at a good space velocity or in good times and without tedious purification.

  CH3 (CH2 CH = CH (CH2) 7 COOH + CH2-OH

I

CH-OH I 1

  Among the previous documents which deal with heterogeneous catalysts, mention may be made of European patent EP BO 198 243. The transesterification catalyst, which converts oil and methanol into a methyl ester, is an alumina or a mixture of alumina and ferrous oxide. In the examples, the column used for the fixed bed at a volume of 10 liters and is generally injected with a flow rate of less than 1 liter / hour, which gives a VVH (VVH = volume of oil injected / catalyst volume / hour) less than 0.1. For a 100,000 Van 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% by weight of glycerin, one obtains, even approximatively, this value. Finally, the purity of the esters is quite low, from 93.5 to 98%. What becomes of glycerine 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 therefore does not appear to be economically reasonable.

  British Patent Application GB A 795 573 discloses the use as a catalyst of zinc silicate at temperatures between 250 and 280 C and at a pressure of at least 100 bar (10 MPa) with methanol. In the first step, there appears to be 85% conversion and 100% if glycerine is decanted intermediate way and the reaction is continued. According to the patent EP-B-0 198 243, which cites GB A 795 573, it would be formed with the zinc compounds zinc soaps, which are naturally to proscribe in fuels. This is mainly due, it seems, to the high temperatures that it is necessary to implement in this reaction with this catalyst.

  Since then, a new generation of heterogeneous catalysts make it possible to obtain, from vegetable or animal oils and monoalcohols, esters of high purity and meeting the specifications of the EN 14214 standard and a colorless and sometimes odorless glycerine according to the post treatment used, discoloration on charcoal, activated earth, other adsorbents, etc.). The processes used with these heterogeneous catalysts operate either continuously for example in fixed bed or batchwise. The catalysts consist of a catalytic system based on single or associated metal oxides, deposited or not on an alumina.

  We can cite the patents of the applicant which implement catalysts based on metal oxides and alumina: in particular the patent FR-B-2,752,242, which describes solid and insoluble catalysts from aluminum oxide. zinc and alumina or zinc aluminate, the French patent FR-B-2,838,433, the French patent applications published FR-A-2,855,517, 2,855,518 and 2,855,519 and the French patent applications unpublished deposited on May 3, 2004 under registration numbers EN 04/04 730 ("Process for the transesterification of vegetable or animal oils using heterogeneous catalysts based on zinc, titanium and aluminum") and 04 / 04 731 ("Process for the transesterification of vegetable or animal oils using heterogeneous catalysts based on bismuth, titanium and aluminum").

  All these catalysts are either in the form of powders, beads, extrudates or pellets. However, the combination of alumina in catalytic systems has two favorable effects. The first is to increase the surface often, the second is to create a much more stable compound, especially vis-à-vis conditions in which the metal component of the oxide would tend to form metal soaps.

  Another advantage of oxide catalysts is their ability to catalyze the transesterification of the oil with alcohols heavier than methanol. Thus, it is possible to form ethyl, isopropyl or butyl esters, which are of interest in the field of fuels, because often the pour points of the esters formed with these alcohols are lower than those of the methyl esters, the gain sometimes being of 10 C, which allows starting from more saturated oils.

  Among the metal oxides that can be used in the oxide combinations, there are, in addition to the alumina, the oxides of the group IIA metals such as magnesium, calcium, strontium and barium, of group IIB such as zinc and cadmium, group IIIA such as gallium and indium, group 1118 such as scandium, yttrium, lanthanum, actinium, cerium and thorium, group IVB such as titanium, zirconium and hafnium, group IIIA such as gallium, indium and thallium, group IVA such as germanium, tin and lead, and group VA such as arsenic, antimony and bismuth.

  Their general formulas, for a combination of a single oxide with alumina, is as follows: (M'OX) y (Al 2 O 3) (1-y), (x having a value of 1.2 to 2.6 and y representing the mass ratio of the two oxides having a value of 0.005 to 2).

  For a combination of two metal oxides M 'and M2 between them, optionally in the presence of alumina, there is the general formula [M'aM2b (My [(Al2O3)] (1_y) (where aa has a value of 0.5 at 5, b is 0.5 to 5, c is the number of oxygen atoms which satisfies the valence of metals MI and M2 and has a value of 0.005 to 1).

  The second stage of the process of the invention, the distillation of the reaction mixture resulting from the transesterification step can be carried out batchwise, for example by a flash-type process, or continuously, for example on a thin-film evaporator operating under a vacuum for example between 3 and 15 mmHg, preferably between 3 and 5 mmHg, and at a temperature for example between 185 and 240 C, preferably between 190 and 210 C.

  In the process of the invention, the sequence of the two steps has certain advantages over a conventional heterogeneous process (as described, for example, in US Pat. No. 5,908,946 of the Applicant, cited above). Indeed, we can translate the gain obtained by expressing the annual productivity of manufactured esters reduced to 1 kg of heterogeneous catalyst. For example, for an ester production unit with a capacity of 100,000 Van, would be produced with a single reactor of the order of 4 440 liters of esters per kg of catalyst and half less or 2220 liters for a conventional configuration operating with two transesterification reactors.

  In the case of a conventional homogeneous process operating with sodium methoxide as a catalyst and of the same capacity, only 263 liters of esters per kg of sodium methoxide are obtained, or, compared with the invention, a decrease in productivity. by a factor of 16 brought back to the kg of catalyst.

  The advantages provided by the distillation are numerous: Directly obtained, even if the conversion is not total (greater than or equal to 95% of esters), an ester of high purity can satisfy a diesel fuel use.

  In this case it is possible to use recovery oils (eg fried oils) which contain polymers. These must be eliminated from biodiesel resulting from transesterification.

  Distillation is in this case the only way to purify a mixture of esters containing these polymers.

  On the other hand, it is possible by distilling the ester mixture to concentrate in the bottom of distillation minor products contained in the vegetable oils which can, after purification, be recovered separately.

  There may be mentioned, for example, carotenes, tocopherols, sterols, squalenes, all these compounds being present naturally in certain vegetable oils and in variable amounts depending on the type of oil used.

  After removing the unsaponifiables from the distillation residue, it is advantageous to recycle the methyl ester, mono-, di- and triglyceride mixture to the catalyst reactor so as to increase the yields of the process.

  Among the oils that can be used in the process of the invention, mention may be made of all the common oils, such as palm oils (concretes or oleins), soya, palm kernel, copra, babassu, old or new rapeseed, classical or oleic sunflower, maize, cotton, tallow and lard, peanut, jatropha curcas, castor oil, flax and crambe oils and all oils derived from sunflower or rapeseed, for example by genetic modification or hybridization.

  You can even use frying oils, rendering oils, various animal oils, such as fish oils, seals, and even poultry fat, because esters made from certain alcohols, can earn more than 10 C in pour point.

  Among the oils used, it is also possible to indicate partially modified oils, for example by polymerization or oligomerization.

  The presence of fatty acid in the oils is not a priori detrimental because the oxide-based catalyst systems are also active for esterification and also convert the fatty acids into esters. The limit value for free fatty acids contained in the oils is at an acid number close to 10. The operability of the process under these conditions is close to that defined with a low acid number oil.

  In the case of oils with a very high acid number (for example greater than 10), it is possible to precede with the transesterification reaction an esterification reaction of the free fatty acids present, either by using the same alcohol as the 2890656 8 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 glycerol ester or partially, using the same type of catalyst based on metal oxides, at atmospheric pressure and preferably under a partial vacuum and at temperatures between 180 and 240 C.

  The process of the invention may furthermore comprise a step in which the unsaponifiables naturally present in the starting oil are isolated from the distillation residue, and the mixture obtained, enriched in glycerides, is recycled to the transesterification step. .

  When the oil used is rapeseed oil, these unsaponifiables include sterols, which can be isolated from the distillation residue by a dedicated process, and the glyceride-enriched mixture is recycled to the catalytic reactor to be converted therein. in alkyl esters.

  For other types of oils such as palm oil and olive oil, obtained by extraction, it is the carotenes or squalene that can be recovered and purified.

  With frying oils, which are a very cheap raw material for producing biodiesel, it is the fatty acid polymers that will have to be removed from the reaction mixture so that the ester mixture meets the specifications of EN 14214.

  In the case of a process using a heterogeneous catalyst, the sequencing of the transesterification step with a distillation step of the methyl esters obtained substantially reduces the operating cost of obtaining esters for fuel use.

  The conversion to methyl esters at the outlet of the catalytic reactor may be between 80 and 93% and preferably between 93 and 97% by weight of esters for the distillation stage to produce a distillation foot between 10 and 16. 0/0 by mass, which makes it possible to recycle the unconverted glycerides in a range of between 4 and 8% relative to the feed oil introduced.

  The efficiency of the vacuum distillation should lead to respect the specification in residual glycerides contained in the biodiesel is a maximum of 0.8% by weight of monoglycerides, 0.2% by weight of diglycerides and 0.2% by mass triglycerides.

  The total elimination of unsaponifiables (for example sterols and sterol esters contained in the residue) is advantageously optimized so that it can be recycled without having to deconcentrate part of the distillation residue obtained.

  Finally, the nature of the alcohol involved in the process of the invention plays an important role in the activity of the transesterification reaction. In general, it is possible to use various aliphatic monoalcohols containing, for example, from 1 to 18 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 2-ethylhexyl alcohol or lauric alcohol can also be used. It may be convenient to add to the heavy alcohols a few percent by weight of methyl alcohol, which seems to improve the rate of reaction.

EXAMPLES

  The following examples illustrate the invention, with Example 1 being given for comparison.

  Example 1 (for comparison) This example details the operating conditions of the heterogeneous process using two transesterification steps. These two steps are necessary to reach the degree of purity required of a mixture of esters for fuel use, according to Standard EN 14214.

  The schematic diagram is given in Figure 1.

  In a fixed-bed reactor containing 110 ml of a catalyst consisting of a mixed zinc aluminate oxide, 100 g of rapeseed oil and 100 g of methanol are introduced at 200 ° C. into a V.V.H. 0.5 (relative to the oil).

  At the end of a residence time of about 50 minutes, a mixture consisting of about 97% by weight of methyl esters, 1.2% by weight of monoglycerides, and the balance of 100 consisting of triglycerides, diglycerides, sterols and sterol esters.

  To perform a second catalytic step, it is necessary to remove all or part of the glycerin formed during the first step.

  A flash of the excess methanol is easily obtained by expansion from 200 ° C. to 90 ° C., where at least 75% of the methanol present is removed. A large part of the glycerin is then removed by decantation. The ester phase is then introduced with additional methanol into the second reactor to undergo further conversion.

  During this second stage, the residence time and the excess of methanol are adjusted so as to obtain the monoglyceride specification, which must be less than 0.8% by weight.

  The excess of methanol contained in the ester mixture thus obtained is again removed by evaporation. A second fraction of glycerine, which represents about 10 to 12% of the total glycerin formed during the transesterification reaction, is removed by decantation. The residual methanol is then completely removed by distillation, which constitutes the final step of purification of the ester fraction. The yields obtained in biodiesel are close to 100% theoretical, because in this case, unsaponifiables are contained in biodiesel.

  Example 2 (according to the invention) This example describes the operating conditions using a single transesterification step, and then the distillation under reduced pressure of the manufactured esters, after total evaporation of the excess alcohol and removal of the glycerin formed. In this case, the degree of purity required of the fuel esters is also obtained.

  The schematic diagram is given in Figure 2.

  As in Example 1, in a fixed-bed reactor containing 110 ml of the same catalyst, 100 g of rapeseed oil and 100 g of methanol are introduced at 200 ° C. into a V.V.H. 0.5 (relative to the oil). The composition of the reaction mixture at the end of this residence time is of the order of 97% by weight of methyl esters, 1.2% by weight of monoglycerides and the balance of 100 consisting of residual triglycerides, diglycerides, sterols and sterol esters.

  The next step is to remove all of the excess methanol, and then decant the glycerin formed, and then continue the operation by a distillation step of the methyl ester manufactured leaving a residue consisting of heavy products such as the triglycerides, diglycerides, monoglycerides, sterols and sterol esters, as well as possible fatty acid polymers or other minor components of rapeseed oil.

  A fraction of this residue can be recycled to the feedstock entering the first catalytic reactor, the other fraction is removed in order to deconcentrate the medium into non-transesterifiable heavy products and can be further processed to isolate certain compounds that can be recovered separately.

  After walking for 24 hours, the order of 4800 g of methanol-free ester mixture is collected.

  4000 g of this mixture are distilled on a thin-film evaporator operating under a vacuum of between 3 and 5 mm Hg and at a temperature of between 190 and 210 ° C. The equivalent of 3600 g of distilled esters is collected at the top. whose average composition is close to 99.8% by weight of methyl esters and 0.2% by weight of monoglycerides.

  The composition of the residue obtained is as follows (in% by weight): 20% of methyl esters, 34% of monoglycerides, 21% of diglycerides, 9% of triglycerides and 16% of sterols and esters of sterol fatty acids.

  In the case of rapeseed oil, the sterols can thus be isolated from the distillation residue by a dedicated process, and the glyceride-enriched mixture is recycled to the catalytic reactor to be converted to methyl esters, as illustrated. in the scheme of Example 2.

  In this configuration, the biodiesel yield depends on the efficiency of the sterol recovery step.

Example 3

  The energy consumption of the two processes was simulated on the basis of the two protocols described in Examples 1 and 2 on the basis of an oil flow rate of 100 kg / h.

  Table 1 illustrates the energy consumption expressed in kW of both processes.

  Thermal load Thermal load Total cooling heating consumption (in kW) (in kW) (in kW) Example 1 62.4 9.8 72.2 Example 2 53.9 6.8 60.7 Energy gain (%) - 13.6 - 31.0 - 15.9 The substitution of a second transesterification step by flash distillation under reduced pressure makes it possible to reduce the overall energy consumption by 15.9%.

  To this gain will be added the recovery of the sterols after extraction and purification 5 of the latter.

Claims (11)

  A process for the production of linear monocarboxylic acid esters of 6 to 26 carbon atoms, by reaction of virgin or recycled vegetable or animal oils, neutral or acidic, with at least one aliphatic monohydric alcohol having a low molecular weight, the presence of a heterogeneous catalyst, said process being characterized in that it combines: a single transesterification step and a distillation step of the reaction mixture.   2. Method according to claim 1 characterized in that in the distillation step, the distillation of the reaction mixture from the transesterification step is carried out batchwise, by a flash process, or continuously, on a thin film evaporator operating under a vacuum of between 3 and 15 mm Hg and at a temperature between 185 and 240 C.   3. Method according to claim 1 or 2 characterized in that the starting oil is selected from palm oils (concrete or oleic), palm kernel, copra, babassu, rapeseed old or new, sunflower classic or oleic, corn, cotton, tallow and lard, peanut, jatropha, castor, linseed and cramble oils and sunflower or rapeseed oils obtained by genetic modification or hybridization.   4. Method according to claim 1 or 2 characterized in that the starting oil is selected from frying oils, rendering, fish oils, seals, poultry fat.   5. Method according to claim 1 or 2 characterized in that the starting oil is selected from oils partially modified by polymerization or oligomerization.   6. Process according to claim 1 or 2, characterized in that the starting oil has an acid number close to 10.   7. Process according to Claim 1 or 2, characterized in that, since the starting oil has a very high acid number, the transesterification reaction is preceded by an esterification reaction of the free fatty acids present. either using the same alcohol as used in the transesterification process in the presence of a strong acid such as sulfuric acid or soluble or supported sulfonic acids (Amberlyst type resins 15) or using glycerine to form an ester of total or partial glycerol, using the same type of catalyst based on metal oxides, at atmospheric pressure and preferably under a partial vacuum and at temperatures between 180 and 240 C.   8. Method according to one of claims 1 to 7 characterized in that the aliphatic monohydric alcohol low molecular weight involved contains 1 to 18 carbon atoms.   9. Process according to claim 8, characterized in that said aliphatic monoalcohol is chosen from methyl, ethyl, isopropyl, propyl, butyl, isobutyl, amyl, 2-ethylhexyl and lauric alcohols.   10. Method according to one of claims 1 to 9 characterized in that the heterogeneous catalyst involved in the transesterification step is selected from metal oxides and mixtures of oxides capable of forming between them, and optionally with alumina, combinations of oxides.   11. Method according to one of claims 1 to 10 characterized in that it further comprises a step in which the insaponifiables naturally present in the starting oil are isolated from the distillation residue, and the mixture obtained is recycled. , enriched in glycerides, to the transesterification step.