EP0654528A1 - Process for the production of fatty acid methyl esters from a natural oil or fat, fatty acid methyl esters so obtained, and their use - Google Patents

Abstract

Process for the production of fatty acid methyl esters from a natural oil or fat by transesterification with methanol in the presence of a catalyst, in which a catalyst based on an organotitanate, in particular tetrabutyl orthotitanate, is used as catalyst, methyl esters so obtained and their use as fuel.

Description

The present invention relates to a process for the manufacture of methyl esters of fatty acids from a natural fat or oil by transesterification with methanol in the presence of a catalyst.

Methyl esters derived from natural oil or fat have become important in the oleochemical industry as fuels or as raw materials for the manufacture of several derivatives, such as fatty alcohols or fatty alkanolamides. These methyl esters can be produced by esterification of fatty acids, but the conventional process used to manufacture these methyl esters is catalytic transesterification or methanolysis of the triglycerides, that is to say an ester substitution, with an excess of methanol. During the transesterification which is carried out according to the following reaction scheme:
oil or fat + methanol → methyl esters + glycerol
the glycerol molecule in the triglyceride is replaced by three methanol molecules. The manufacture of methyl esters by transesterification is described in "Manufacture of Fatty Alcohols Based on Natural Fats and Oils" by UR Kreutze, JAOCS, vol. 61, No. 2 (February 1984), pages 343-345 and in "CEH Marketing Research Report - Detergent Alcohols" by RF Modler et al., 1990, Chemical Economics Handbook, SRI International.

In these known processes, a good yield of fatty acid esters is obtained by the use of an alkaline catalyst, such as sodium or potassium hydroxide in solution in methyl alcohol or sodium methylate.

• le catalyseur alcalin est très corrosif et le milieu de réaction étant donné son pH élevé (de l'ordre de 8 à 10) donne également des sous-produits très corrosifs; l'équipement utilisé pour le procédé doit par conséquent être en acier inoxydable;
• une étape supplémentaire de neutralisation des acides gras libre contenus dans l'huile ou la graisse avec séparation du savon ainsi formé est nécessaire;
• une étape supplémentaire de raffinage des eaux glycérineuses et de séparation du sel est également nécessaire;
• les rendements de la récupération du méthanol en excès et du glycérol sont faibles.

The use of an alkaline catalyst however has several drawbacks:

• the alkaline catalyst is very corrosive and the reaction medium, given its high pH (of the order of 8 to 10), also gives very corrosive by-products; the equipment used for the process must therefore be made of stainless steel;
• an additional step of neutralizing the free fatty acids contained in the oil or fat with separation of the soap thus formed is necessary;
• an additional step of refining glycerol waters and separating the salt is also necessary;
• the yields of recovery of excess methanol and of glycerol are low.

One of the essential aims of the present invention consists in remedying the aforementioned drawbacks of existing methods and in providing an industrially and economically valid method making it possible to obtain methyl esters in high yield and which does not in particular require the neutralization of fatty acids and which does not use or give corrosive products.

To this end, the process according to the invention consists in using, as catalyst, an organotitanate-based catalyst.

Advantageously, the organotitanate is chosen from the group comprising tetraalkyl orthotitanates, monomeric and polymeric cresyl titanates, titanium lactate, stearic titanate, 2-ethylhexyl titanate, n-butyl titanate polymer, titanium acetylacetonate, triethanolamine titanate and octylene glycol titanate and mixtures of two or more of these two substances.

According to an advantageous embodiment of the invention, a tetraalkyl orthotitanate containing from 1 to 5 carbon atoms is used as organotitanate, the tetrabutyl orthotitanate being particularly suitable in this regard.

According to a particularly advantageous embodiment of the invention, the catalyst comprises zinc acetylacetonate, the amount by weight of zinc acetylacetonate being from 2 to 5% and preferably 3% relative to the titanium of the catalyst.

According to an advantageous embodiment of the invention, the oil or the fat, the methanol and the catalyst are mixed before being subjected to transesterification.

According to a particularly advantageous embodiment of the invention, the transesterification is carried out at a pressure of 35 to 60 bars, preferably from 45 to 55 bars and at a temperature of 150 to 300 ° C, preferably from 200 to 250 ° C, a pressure between 48 and 50 bars and a temperature between 222 and 227 ° C proving to be particularly advantageous.

The present invention also relates to the methyl esters of fatty acids as thus obtained and their use as fuels in mixture or not with other fuels.

Other details and particularities of the invention will emerge from the description given below by way of nonlimiting example or from some particular forms of the invention.

The present invention therefore relates to a process for the production of methyl esters of acids. fat from a natural oil or fat by transesterification with methanol in the presence of a catalyst, which consists in using, as catalyst, a catalyst comprising one or more organotitanates. Among the organotitanates which may be suitable for this purpose, mention will be made in particular of tetraalkyl orthotitanates, in particular tetraalkyl orthotitanates containing from 1 to 5 carbon atoms, cresyl titanates monomer and polymer, titanium lactate, stearic titanate, titanate 2-ethylhexyl, polymeric n-butyl titanate, titanium acetylacetonate, triethanolamine titanate and octylene glycol titanate. C₁-C₅ tetraalkyl orthotitanates are particularly advantageous; examples of these are especially tetraethyl, tetrapropyl, tetraisopropyl, tetrabutyl and tetraisobutyl orthotitanates. Tetrabutyl orthotitanate is the preferred organotitanate as a catalyst. The catalyst can also comprise a small amount of zinc acetylacetonate, which increases the activity of the organotitanate, the amount by weight of zinc acetylacetonate of the catalyst being from 2 to 5% and preferably from 3% relative to the titanium.

According to the invention, the oil or the fat, the methanol and the catalyst are mixed before being introduced into the transesterification reactor with the aim, on the one hand, of obtaining a fine dispersion of the catalyst in the reaction mass. and, on the other hand, to protect the catalyst from too long a presence with the hydroxyl radicals of methanol. This preliminary mixing, when one is carried out, and the transesterification are generally carried out at a pressure of 35 to 60 bars and at a temperature of 150 to 300 ° C., a pressure of 45 to 55 bars and a temperature from 200 to 250 ° C being preferable. Particularly advantageous results are obtained, however, with a pressure between 48 and 50 bars and a temperature between 222 and 227 ° C. The oil or fat and methanol are generally maintained in the presence of the organotitanate catalyst for approximately 0.5 to 4 hours, and preferably for 2 to 3 hours. A good reaction yield is obtained when the amount by weight of catalyst per tonne of oil or fat is between 0.5 and 1.5 kg and preferably when it is of the order of 1.3 kg. To obtain fatty acid methyl esters from a natural oil or fat by transesterification, the fat or oil must be mixed with an excess of methanol which corresponds to 1-3 times the stoichiometric quantity necessary to replace the glycerol. bound in fat or oil.

The oil or fat to be mixed with methanol can contain free acidity, i.e. a free fatty acid content of up to 5% and therefore should not normally be neutralized. However, since the orthotitanate catalyst requires an oil or fat with a low water and phosphorus content, the oil or fat will therefore have to be pretreated before its possible preliminary mixing with methanol and the catalyst and the reaction. transesterification. According to the invention, the pretreatment of oil or fat comprises two stages, namely acid degumming to reduce its phosphorus content to 50 ppm or less and dry pretreatment followed by filtration, for example on land bleaching, to reduce humidity to about 0.01% and phosphorus content to 15 ppm or less. It should be noted that most vegetable oils, such as rapeseed oil, have a moisture content of 0.3 to 0.5% and contain 1 to 2% of gums (phospholipids). The crude oil or fat should therefore be subjected to the aforementioned two-stage pretreatment, i.e. the acid degumming stage and in the drying step combined with filtration. During the degumming step, the phosphorus content will be reduced for example to 25-50 ppm and during the drying and filtration step, the humidity will be reduced for example to 0.01% and the content of phosphorus will be further reduced, for example to 10-15 ppm. It is understood that when using degummed oil, only the drying step will be necessary.

By natural oil or fat, it is understood in the context of the present invention an oil or fat having a linear chain of fatty acids. Vegetable oils are all usable, in particular rapeseed oil, palm oil and palm kernel oil. Animal fats are also all usable.

The preheated liquid mixture comprising the oil or fat to be treated, methanol, of a purity of at least 99% _, advantageously 99.5% and the catalyst is preferably introduced continuously by a high pressure pump into the reactor. It crosses the transesterification zone maintained at the specified temperature and pressure. During the transesterification reaction, the catalyst is consumed and finally removed as a residue. It will be noted, in this regard, that it is not necessary for the oil or the fat, the methanol and the catalyst to be mixed before introduction into the reactor. The mixing can take place partly or completely in the reactor. The oil and the catalyst can be mixed and this mixture can be introduced into the reactor at the same time as methanol, or else the three components can be introduced simultaneously into the reactor and be mixed there.

After the reaction, the duration of which is of the order of 0.5 to 4 hours and preferably 2 to 3 hours, the product leaving the reactor is then subjected instantaneous evaporation in a first separator where the excess methanol is evaporated. This evaporated methanol is recycled after condensation and distillation and reused in transesterification. The mixture is then transferred to a second separator which removes the last traces of methanol. The mixture of methyl esters and glycerol is introduced into a decanter. The upper phase consists of methyl esters and the lower phase consists of glycerol. Glycerol does not require any refining and it can be directly concentrated from 40-50% to 82-88%. Pharmacopoeial grade glycerol is obtained by distillation of the concentrated product. The glycerol present in the methyl esters is separated by washing against the current with demineralized water. If necessary, the methyl esters are distilled. The purity of the methyl esters before distillation is greater than 95%.

If the methyl esters obtained according to the process of the invention are used as fuel in mixture with other fuels, for example at a rate of 50/50 with diesel, they must not be distilled but only dried to a moisture content less than 0.05%. If they are used as 100% fuel or as a raw material for oleochemical derivatives, they must be distilled to a purity higher than 98.5%. These fatty acid methyl esters can also be converted by hydrogenation in the presence of a copper chromite catalyst to fatty alcohols. Conversion to alkanolamides, sulfonated esters or other derivatives is possible by known conventional reactions.

The few examples which follow make it possible to illustrate the invention without however constituting a limitation to it.

Example 1

1000 kg of palm oil and / or palm kernel oil are mixed with 300 kg of methanol and 1.5 kg of tetraisobutyl orthotitanate, at a pressure of 50 bars and a temperature of 220 ° C. and then transferred to a reactor also maintained under a pressure of 50 bars and at a temperature of 220 ° C. The mixture in the reactor is subjected to a liquid hourly space velocity (LHSV) of 4-6 m / hour and is maintained there for 2.5 hours. The product leaving the reactor is subjected to instant evaporation, separation and decantation. The methyl esters obtained have a purity of more than 95%.

Example 2

Crude rapeseed oil obtained by pressure and solvent extraction containing less than 4% of free fatty acids, a humidity of 0.5% _, 2% of gums and 1% of solid matter, is degummed and dried. 1000 kg of this oil are then mixed with 300 kg of methanol and 1.5 kg of tetraisopropyl orthotitanate and treated under the same conditions as those of Example 1. The methyl esters obtained also have a purity of more than 95% .

Example 3

Example 1 is repeated, but with rapeseed oil in place of palm and / or palm kernel oil. Similar results are obtained.

Example 4

1000 kg of palm, palm kernel or rapeseed oil are mixed with 300 kg of methanol and 1.5 kg of tetraisobutyl orthotitanate containing 3% by weight of zinc acetylacetonate (relative to titanium) and then we proceed under the same conditions as those illustrated in Example 1. Methyl esters are also obtained with a purity of more than 95%.

In addition to the advantages which have already been mentioned previously, the process for preparing methyl esters according to the invention is extremely simple and economical to carry out. The crude oil or fat should only be degummed and dried and does not require, as in conventional processes, a step of removing fatty acids by chemical means (alkaline neutralization) or by physical means (steam entrainment). The crude glycerol obtained contains very few non-volatile products and does not require either chemical refining or separation of the soaps before concentration. The crude methyl esters obtained also have a very high purity. As already stated, taking into account that the catalyst is not alkaline and is not corrosive and that no corrosive by-product is formed, the reactor and the accessories can be constructed essentially of mild steel and, for example, partially in ordinary SS 304 stainless steel. Besides the fact that the process can be applied continuously, the consumption of catalyst is also very low and will have little influence on the purity of the final products and on the operating costs of the process.

It should be understood that the present invention is in no way limited to the above embodiments and that many modifications can be made thereto without departing from the scope of this patent.

Claims (22)

Process for the production of methyl esters of fatty acids from a natural oil or fat by transesterification with methanol in the presence of a catalyst, characterized in that a catalyst based on a catalyst is used organotitanate. Process according to Claim 1, characterized in that the organotitanate is chosen from the group comprising tetraalkyl orthotitanates, monomeric and polymeric cresyl titanates, titanium lactate, stearic titanate, 2-ethylhexyl titanate, titanate n-butyl polymer, titanium acetylacetonate, triethanolamine titanate, octylene glycol titanate and mixtures of two or more of these substances. Process according to Claim 2, characterized in that a tetraalkyl orthotitanate containing from 1 to 5 carbon atoms is used as the organotitanate. Process according to claim 3, characterized in that the tetraalkyl orthotitanate is tetrabutyl orthotitanate. Process according to any one of Claims 1 to 4, characterized in that the catalyst comprises zinc acetylacetonate. Process according to Claim 5, characterized in that the quantity by weight of zinc acetylacetonate in the catalyst is 2 to 5% relative to the titanium. Process according to Claim 6, characterized in that the quantity by weight of zinc acetylacetonate is 3%. Process according to any one of Claims 1 to 7, characterized in that the oil or the grease, methanol and catalyst are mixed together before being subjected to transesterification. Process according to any one of Claims 1 to 8, characterized in that the transesterification is carried out at a pressure of 35 to 60 bars and at a temperature of 150 to 300 ° C. Process according to Claim 9, characterized in that the transesterification is carried out at a pressure of 45 to 55 bars and at a temperature of 200 to 250 ° C. Process according to Claim 10, characterized in that the pressure is between 48 and 50 bar and the temperature between 222 and 227 ° C. Process according to any one of Claims 9 to 11, characterized in that the duration of the transesterification is from 0.5 to 4 hours. Process according to Claim 12, characterized in that the transesterification lasts 2 to 3 hours. Process according to any one of Claims 1 to 13, characterized in that the quantity by weight of catalyst used per tonne of oil or fat is between 0.5 and 1.5 kg. Process according to Claim 14, characterized in that the quantity by weight of catalyst used per tonne of oil or fat is of the order of 1.3 kg. Process according to any one of Claims 1 to 15, characterized in that the quantity by weight of methanol used is from 1 to 3 times the stoichiometric quantity necessary to replace the glycerol bound in the oil or the fat. Process according to any one of Claims 1 to 16, characterized in that the oil or the fat used has a free acidity not exceeding 5%. Process according to Claim 17, characterized in that the oil or the fat is, before transesterification, degummed and then dried. Process according to claim 18, characterized in that degumming makes it possible to reduce the phosphorus content to 50 ppm or less. Process according to either of Claims 18 and 19, characterized in that the drying, followed by filtration, makes it possible to reduce the moisture content to 0.01% or less and the phosphorus content to 15 ppm or less. Methyl esters of fatty acids, as obtained by the process according to any one of Claims 1 to 20. Use of the fatty acid methyl esters according to Claim 21 and / or as obtained according to any one of Claims 1 to 20, as fuels, whether or not mixed with other fuels.