Process for the preparation of alkyl esters of carboxylic acids, in particular of alkyl esters of fatty acids.

0001Due to the changed raw material situation z. Currently, considerable efforts are being made to use derivatives of natural fats as full or partial replacements for diesel fuels. The esters of fatty acids are of particular importance in this context.

0002The esters of C_6-24-Carboxylic acids with C_1-4In addition, alkanols are an important oleochemical intermediate product which can be further processed into fatty alcohols, fatty acid alkanolamides, alpha-sulfofatty acid alkyl esters etc., but which is also used as a substitute for diesel fuel (see WE Klopfenstein, HS Walker, J. Am. Oil Chem Soc. 60 (8), 1596 (1983) and HJ Harwood, J. Am. Oil Chem, Soc. 61, (2), 315 (1984).

0003Common processes for the production of these esters are based on raw, partially or fully refined fats and / or fatty acids (cf. Bailey, "Industrial Oil and Fat Products", Vol. 2, 4th ed., J. Wiley & Sons, New York, 1982 and J. Baltes "Extraction and Processing of Dietary Fats", P. Parey, Berlin and Hamburg (1975).

0004Common to the known processes under acidic and / or alkaline catalysis is that the reaction products are contaminated to a greater or lesser extent by catalyst components. However, this limits their direct further use to an unacceptable degree.

0005Above all, acidic catalysts are sulfuric acid, phosphoric acid and their derivatives. However, compounds containing S and P in particular are poisons for catalysts which are required for the subsequent conversion of the esters to fatty alcohols and surfactant raw materials (see F. Zymalkowski "Catalytic Hydrogenations", Ferdinand Enke-Verlag, Stuttgart, p. 34 ( 1965).

0006It is also known that the transesterification of fats can be carried out in the presence of halides of boron, aluminum and iron (cf. UP-PS 2 383 601 and SU-PS 255 245). These halides are consumed as a result of hydrolysis. So they have to be continuously updated. The acids formed are not only corrosive, they also contaminate the end product with halogen compounds and thus impair their further processing.

0007Fatty acid-free fats are usually converted into the corresponding esters in the presence of alkaline catalysts such as sodium, potassium hydroxide or sodium methoxide and the desired alcohols. With this procedure, it cannot be avoided that, depending on the metal, the amount of catalyst and the type of process, up to 1,000 ppm alkali metals get into the esters as impurities. If you want to use such esters in the fuel sector, for example, complex cleaning operations are required (cf. "Possible uses of alternative fuels in developing countries", Interdisciplinary Project Consult GmbH (IPC), Frankfurt am Main, (1983), p. 42, G. Vellguth, Fundamentals of Agricultural engineering 32 - (5), (1982) (not suitable for vegetable oils .... ").

0008If crude fats, which in addition to partial glycerides and free glycerol also contain considerable amounts of free fatty acids, are to be largely completely converted into the corresponding esters, the free fatty acids must first be acidified in a preliminary stage, as described above (see US Pat. No. 2 383 601).

0009The process of GB-PS 795 573 provides for crude, fatty acid-containing fats to be converted in one or more stages in the presence of a heterogeneous contact made of zinc silicate. Our own experience shows that the reaction products are contaminated by metallic contaminants (especially zinc soaps) in considerable amounts when using zinc catalysts. This is already visually recognizable. Such a process is out of the question for the production of diesel fuels. Difficulties also arise in the production of tenis raw materials.

0010A considerable disadvantage of the previously known methods is that considerable amounts of glycerol (approx. 5 to 15% of the amount of fat used) inevitably occur. The market for glycerin (cosmetics, humectants, plasticizers, components for polycondensates, surfactants etc.) is overwhelmed in the case of large-scale implementation in view of the huge amounts involved. To avoid economic disadvantages, it is therefore urgently desirable to open up additional uses for glycerol.

0011An object of the present invention was to develop a process for converting glycerides and / or carboxylic acids, in particular fatty acids, which is as universal as possible and which should lead to technically interesting further processing products. The process should provide a catalyst-free product that can be used directly and without restrictions. Another object of the invention was to convert the glycerol which is inevitably obtained into a form in which it can be used expediently.

0012A process has now been found in which carboxylic acid alkyl esters, in particular fatty acid alkyl esters, are obtained free of catalyst components. This process can be applied to all common oleochemical starting products. According to a special process variant, mixtures of fatty acid alkyl esters and glycerol ethers are obtained which are directly suitable as diesel fuel.

0013The present invention relates to the processes according to claims 1 to 12, the use of the products obtained according to claim 13 and the catalyst according to claim 14.

0014Triglycerides, partial glycerides and fatty acids are suitable as starting products for the process according to the invention. It is not necessary that chemically uniform starting products are used, rather mixtures of two or three of the listed types of starting substances are preferably used. These include above all the fats and oils of vegetable or animal origin occurring in nature (see BJ Baltes "Extraction and processing of nutritional fats", P. Parey, Berlin and Hamburg, (1975) or products that are processed by conventional processing methods of fat chemistry, such as. B. Detillation fractionation, refining or crystallization can be obtained from this.

0015Typical representatives of the fats and oils mentioned are e.g. B. coconut oil, palm kernel oil, palm oil, peanut oil, cottonseed oil, soybean oil, sunflower oil, linseed oil, rapeseed oil, lard, beef tallow, herring oil, of course, any mixtures of these fats and oils can be used. The process is particularly advantageous when raw products are used. Raw fats generally contain up to 10% by weight of free fatty acids. In individual cases, however, lots with fatty acid contents of 50 percent by weight and more also occur. Due to the partial hydrolysis of the fat, the proportion of partial glycerides and glycerin can also be very high. Free glycerin and other minor components of raw fats do not interfere with the implementation. It is precisely the fats which are unsuitable for the production of edible fat that are a useful raw material for the process according to the invention.

0016Particularly typical representatives of the starting mixtures which can be used for the production of fatty acid alkyl esters are fully and partially refined fats, raw fats and raw and distilled fatty acids. Fully refined fats are usually produced by alkali refining or by "physical refining" and contain neither free fatty acids nor mucus and odorants. Semi-refined or partially refined fats are obtained if one or more refining stages customary in full refining are omitted. With commercially available partial refinements, e.g. B. dispenses with deodorization, this gives - so-called semi-refinates that are free of mucilage and fatty acids. A particularly economical variant of the process according to the invention is based on crude, unrefined fats which are characterized by the above-mentioned partial refinates, above all by different levels of free fatty acids, the composition of which generally corresponds to the fatty acid pattern of the underlying triglyceride.

0017Fatty acids which are obtained in the steam splitting of fats, the processing of the so-called acid oils, ie by-products of alkali refining or the "physical refining" of raw fats, can also be used according to the invention. It does not matter whether these fatty acids are in undistilled or distilled form. Such fatty acids generally contain 6 to 24 carbon atoms and are mostly linear. They can contain one or more double and / or triple bonds and can be substituted by hydroxyl and methyl groups. Even the acid oils or refining fatty acids obtained during fat refining are a suitable starting material for the process according to the invention.

0018Finally, starting materials accessible from petrochemicals can also be used, provided that their structure corresponds to the carboxylic acids found in nature. These also include carboxylic acids with an odd C number and with a branched carbon chain, which do not generally occur in nature, but which are in the same C number range from 6 to 24 and are chemically very close to the former.

0019The alcohols which can be used to prepare the fatty acid alkyl esters have 1 to 4 carbon atoms. In addition to the primary alcohols methanol, ethanol, propanol-1 and butanol-1, their isomers propanol-2, butanol-2 and tert-butanol and any mixtures of these alcohols can also be used.

0020The alcohols must be used at least in a stoichiometric amount, based on the fatty acid components present in free or bound form, to work with more than stoichiometric amounts of alcohols and e.g. B. to use 2 to 10 times the stoichiometric amount.

0021The catalyst used in the present process contains aluminum oxide, iron II, iron III oxide or any mixture of these oxides. Its surface is at least 10 m²/ g on. Its pore volume is preferably between 0.1 and 0.8 cm / g.

0022The aluminum oxide contacts which can be used for the process can be prepared by processes known per se, e.g. B. made of aluminum hydroxide. This is after peptization with suitable organic or inorganic acids, such as. B. formic, acetic or nitric acid processed to shaped bodies, dried and in one or more stages between 200 and 1000 ° C while passing air, N.₂, other inert gases or water vapor calcined. A particularly suitable method is described in German Patent 10 58 026. A contact made by this process contains between 0.1 and 1% sodium (calculated as Na₂O) and traces of potassium and alkaline earth metals. Contacts with a relatively larger surface area can be obtained by comparatively low caicination temperatures and transfer of inert gases. Smaller surface area contacts are obtained by treating the material with steam at high temperatures. Such contact with a surface of 10 m²/ g and the designation SCS 9 is used in Example 20. The pore volumes are measured in a simple manner by determining the amount of water absorbed by the catalytic converter using the BET method.

0023The iron oxide contact can also be produced by conventional methods known per se. Common starting materials are e.g. B. iron II or II isulfate or nitrate, from which iron in the form of the hydroxide can be precipitated by adding sodium hydroxide, soda, potash or ammonia. The precipitate can, as described in DE-PS 10 58 026, be peptized. After washing the precipitate, the residue is dried and z. B. deformed into tablets. The calcination takes place at 250 to 1000 ° C and provides a contact, which is essentially made of Fe₂O₃ exists, but its effectiveness through shares in Fe₃O₄ is not affected.

0024Aluminum oxide-iron oxide mixed contacts can also be produced by coprecipitation of Al and Fe salts (see Example 24). A cheap starting material is the red mass, a by-product of bauxite production, which mainly contains iron oxide but also small amounts of aluminum oxide. Finally, it is also possible to produce the mixing contacts by mixing finely divided aluminum oxide and iron oxide (cf. Example 23).

0025The contacts can be made using binders such as graphite, zirconium dioxide, titanium dioxide, etc. Also effective are contacts in which the active ingredient on an inert carrier, such as. B. iron, corundum or silicon dioxide is applied (cf. Example 22).

0026The possible contact loads are between 0.05 and 3 1 starting mixture per I contact. If these conditions are observed and the other reaction parameters are observed, sales of fatty acid alkyl esters of more than 95% are achieved. The mechanical and chemical stability of the contact is guaranteed.

0027Various reactor concepts are possible for the practical implementation of the implementation. Carrying out the reaction in a tube filled with catalyst has proven to be particularly simple, in which the ratio between length and diameter is between 10: 1 to 100: 1.

0028The starting materials can be fed in at the beginning of the reaction tube in direct current; however, it is also possible to feed the alcohol in two or more places over the length of the reactor in the manner of a cross-flow procedure.

0029After leaving the reactor, the reaction mixture is expediently first freed from the unreacted alcohol by distillation. When using glycerides and glycerol-containing starting materials, there is a clean separation into an upper carboxylic acid ester phase and a lower glycerol phase, preferably at a slightly elevated temperature (up to about 100 ° C.).

0030There are two variants for the method according to the invention, depending on whether one works at temperatures up to 280 ° C. or above 280 ° C.

0031In the former case (1), the reaction product consists predominantly of fatty acid alkyl esters and glycerol, provided that glycerides are assumed.

0032If only partial and triglycerides, ie fatty acid-free starting products, are used, the most favorable reaction temperatures are between 210 and 280 ° C., preferably between 225 and 260 ° C., and the reaction product contains at most traces of glycerol ether.

0033However, if predominantly fatty acids or analogous carboxylic acids are used, the esterification temperature is preferably between 160 and 200 ° C. The best results are achieved at temperatures between 190 and 210 ° C.

0034In all cases, a higher product quality (lower acid number, lower glycerol content) and an improved conversion are achieved if the reaction is carried out in several stages, preferably in two or three stages. After each stage, the water which has formed in the meantime is preferably distilled off together with the alcohol and the glycerol phase which forms is separated off.

0035Before being used in the next stage, fresh alcohol is added to the only partially converted starting products.

0036A particularly favorable procedure is the 2-stage reaction procedure, the first stage at 215 to 280 ° C, preferably 225 to 260 ° C, and pressures up to 150 bar and the second reaction stage at temperatures of 160 to 210 ° C, preferably between 190 and 210 ° C, and pressure up to 70 bar is carried out. The starting materials should preferably remain in the first stage until a conversion of more than 80% has taken place. The degree of implementation can be determined, for example, by gas chromatographic analysis in the presence of an internal standard.

0037Process variant (11) in which the reaction temperature is above 280 ° C. will be described below. The maximum reaction temperature in this case is 400 ° C, the maximum pressure to be applied is 400 bar. In this case, the reaction mixture does not contain its own glycerol phase. Rather, mono-, di- and trialkyl ethers of glycerol are formed under these conditions, the proportion of fully etherified glycerol derivatives increasing with increasing reaction temperature.

0038The homogeneous ester / ether mixture can be used as such for the dieselification. Possibly to reduce disturbing residual free fatty acid contents, however, it may be appropriate to react the reaction mixture after or before the removal of the excess alkanol and the water formed in the presence of fresh alkanol at a reaction temperature between 160 and 230 ° C., preferably 185 to 215 ° C., a post-reaction in the presence the catalysts that can be used for the main reaction. The reactor volume required for post-reaction is generally 5 to 50% of the total reaction space filled with catalyst.

0039The procedure with post-reaction at reduced temperature can in principle be carried out using the same reactor and the same work-up elements, although additional heating and cooling devices must be fitted which allow two temperature zones to be set in the reactor. The post-reaction can of course also be carried out in a separate reactor, which is connected downstream of the main reactor. Particularly favorable results are achieved if excess alkanol and a small amount of water present are removed before the after-reaction and the residue is re-used in the after-reaction with addition of at least stoichiometric amounts of alcohol, based on the fatty acids present in free or bound form.

0040In all process variants, the iron and / or aluminum content in the reaction product is below 5 ppm.

example 1

0041An upright, externally heated reaction tube made of stainless steel (inner diameter 8 cm, length 200 cm) of 10 I content, which with molded bodies made of aluminum oxide (it is the sales type H 0408, manufacturer: Chemische Werke Hüls AG, D-4370 Marl , see the corresponding leaflet from the catalysts factory Houdry-Hüls GmbH, D-4370 Marl), is continuously charged with 800 g / h raw palm fat and 600 g / h methanol from above. A pressure of 68 bar is established at a reaction temperature of 250 ° C. After leaving the reaction zone, the reaction mixture is continuously broken down into a distillate containing methanol and water and a sump which separates at 60 ° C into an upper palm fatty acid methyl ester phase and a lower glycerol phase using a thin-layer evaporator (210 ° C, 1 bar). The two phases are taken from the separator. The turnover is determined by GC analysis with an internal standard.

Examples 2 to 18

0042These examples are carried out analogously to Example 1. The starting materials, their amounts and the reaction conditions can be found in the table. In cases in which only fatty acids are used (Examples 5, 15), no glycerol phase is obtained during the working up of the reaction mixture by distillation.

Examples 19 to 24

0043Analogously to Example 1, tests are carried out with other catalysts. The amounts of the starting material and the reaction conditions are shown in the table.

0044The type H 0407 catalyst, like the type H 0408, is manufactured by Chemische Werke Hüls AG, D-4370 Marl. The properties of this catalyst can be found in the already mentioned leaflet from the catalyst factory Houdry-Hüls GmbH, D-4370 Marl.

0045The SCS 9 catalyst is manufactured by Rhone-Poulenc. A leaflet entitled "Rhone-Poulenc Specialites, spheralit catalyst carriers, technical documentation 81/1/3" is available from: Rhone-Poulenc Industries, Division Specialites chimiques, F-75 360 Paris, Cedex: 08

Example 25

0046Example 2 is repeated with the exception that the methanol is fed not only at the beginning of the reactor, but in the manner of a cross-flow procedure at three different points in the reactor: 400 g / h at the beginning, 400 g / h after a 70 cm tube length, 400 g / h after 140 cm tube length.

example

26

0047Example 1 is repeated with the exception that the reaction tube is divided into two reactors, each 100 cm in length, and after the first partial reactor work-up is carried out by distillation. While unchanged 800 g / h of crude palm oil are fed into the first partial reactor, the amount of methanol is divided as follows: 400 g / h into the first partial reactor and 200 g / h into the second partial reactor.

0048Working up after the first sub-reactor, like that after the second sub-reactor, is carried out using a thin-film evaporator (210 ° C., 1 bar). The first work-up provides methanol with small amounts of water as the distillate and a mixture of partially converted palm oil (top) and glycerol (bottom) separating into two phases as the bottom. The upper phase of partially converted palm oil is fed to the second partial reactor together with fresh methanol.

0049After leaving the second partial reactor, the reaction mixture is worked up as usual. The glycerol phases from the first and second workup are combined. The water-containing methanol fractions obtained in each case as distillate can be used again in the reaction after appropriate purification. The palm fatty acid methyl ester obtained as the upper sump phase in the second workup is analyzed as usual.

Example 27

0050Example 26 is repeated with the exception that the same weight amount of distilled palm fatty acid is used instead of raw palm oil and a temperature of 200 ° C. is maintained in both partial reactors. In contrast to Example 26, no glycerol is obtained in either work-up step.

Example 28

0051Example 27 is repeated with the exception that the same amount by weight of raw coconut fatty acid is used instead of distilled palm fatty acid.

Example 29

0052Example 28 is repeated with the exception that the FeO: r contact from Example 21 is used instead of the aluminum oxide contact H 0408.

Example 30

0053Example 26 is repeated with the exception that a temperature of only 210 ° C. is maintained in the second partial reactor.

Examples 31 to 34

0054Example 30 is repeated with the exception that instead of raw palm oil, semi-refined palm oil, refined palm oil, raw coconut oil or Taig monoglyceride are used.

Examples 35 to 38

0055Examples 31 to 34 are repeated with the exception that instead of Al₂O₃Contact H 0408 the mixed contact (Al₂O₃ + Fe₂O₃) from Example 23 is used.

Example 39

0056Example 30 is repeated with the exception that a different division of the reaction space into the 1st and 2nd sub-reactors is carried out: the first sub-reactor now accounts for 75% of the total volume (length = 1.5 m) and the second 25% ( Length 0.5 m).

Example 40

0057Example 39 is repeated with the exception that an acid oil based on palm kernel is used instead of raw palm oil. The trial is run for a period of 100 days. Even after 100 days, the same implementation results are obtained as at the beginning.

Example 41

0058Example 39 is repeated with the exception that after the first partial reactor, the reaction mixture is not worked up by distillation.

Example 42

0059Example 41 is repeated with the exception that methanol is added not in two streams (400 g / h and 200 g / h) but in one stream at the beginning of the first partial reactor (600 g / h).

Example 43

0060Example 1 is repeated with the exception that a reaction temperature of 285 ° C. is maintained. There is no glycerol phase.

Examples 44 and 45

0061Example 43 is repeated with semi-refined palm fat or fancy bleachable tallow. There are no glycerine phases.

Example 46

0062Example 41 is repeated with the exception that a temperature of 320 ° C. is maintained in the first partial reactor.

Example 47

0063Example 46 is repeated with the exception that after the 1st partial reactor, the reaction mixture is worked up by distillation, with the methanol / water distillate obtained in this process being discharged. There is no glycerin phase.

Example 48

0064Example 47 is repeated with acid kernel-based acid oil instead of raw palm oil

Examples 49 and 50

0065Example 48 is repeated with the exception that instead of Al₂O₃-Contact H 0408 a Fe₂0₁Contact (example 2) or an Al₂O₃/ Fe₂O₃-Mixing contact (Example 23) is used.<tables id="tabl0001" num="0001"><img file="EP0198243A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0198243A2_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0198243A2_D0003.tif" /></tables><tables id="tabl0004" num="0004"><img file="EP0198243A2_D0004.tif" /></tables><tables id="tabl0005" num="0005"><img file="EP0198243A2_D0005.tif" /></tables><tables id="tabl0006" num="0006"><img file="EP0198243A2_D0006.tif" /></tables><tables id="tabl0007" num="0007"><img file="EP0198243A2_D0007.tif" /></tables><tables id="tabl0008" num="0008"><img file="EP0198243A2_D0008.tif" /></tables><tables id="tabl0009" num="0009"><img file="EP0198243A2_D0009.tif" /></tables><tables id="tabl0010" num="0010"><img file="EP0198243A2_D0010.tif" /></tables><tables id="tabl0011" num="0011"><img file="EP0198243A2_D0011.tif" /></tables><tables id="tabl0012" num="0012"><img file="EP0198243A2_D0012.tif" /></tables>