WO1998017381A1

WO1998017381A1 - Method for carrying out reactions characterized by an equilibirum

Info

Publication number: WO1998017381A1
Application number: PCT/EP1997/005542
Authority: WO
Inventors: Vincent Simon Ellis
Original assignee: Vincent Simon Ellis
Priority date: 1995-07-10
Filing date: 1997-10-08
Publication date: 1998-04-30
Also published as: DE19643165A1

Abstract

The invention relates to a method for carrying out a chemical reaction characterized by an equilibrium in a reaction system designed as a loop reactor, comprising: a reaction vessel (1), at least one loop connected to the reaction vessel (1) by an outlet and an inlet and provided with devices (3) to pump the reaction fluid, at least one heat exchanger (4), possibly devices (5) feed the reaction fluid into the reaction vessel (1) and a separated gas circuit (8) connected to the gas area in the reaction vessel (1), and separate devices feeding the gas into the gas circuit (8) located just above the fluid reaction mixture and drawing it away from the gas circuit (8) and/or treating the gas circulating in the gas circuit (8). Said method is characterized in that an inert gas is conducted and/or treated in the gas circuit (8), it is fed into the reaction vessel (1) in order to affect the reaction taking place therein which is characterized by an equilibrium, and is drawn off in the gas circuit (8) once the equilibrium of the equilibrium reaction taking place in the reaction vessel (1) has been affected.

Description

Process for performing equilibrium reactions

The present invention relates to a method for carrying out reactions which are characterized by an equilibrium.

Numerous chemical reactions, including reactions that are carried out on an industrial scale, are characterized in that, after a certain time, a chemical equilibrium is established between starting materials and products, which allows the chemical reaction to largely proceed to form the products and thus achieve one for the economical implementation of the reaction prevents important high yield of the desired products.

One tries to counter this problem by trying to influence the equilibrium of a chemical reaction in the desired sense. The basis for this is the well-known law of mass action and the equilibrium constants defined by it and dependent on the reaction conditions. Following the principle of Le Chatelier, the reaction then proceeds in the desired manner and a new equilibrium is established (which is further on the side of the product if the influence is appropriate).

Examples of such equilibrium reactions are the esterification of a carboxylic acid with an alcohol to form an alkyl ester of carboxylic acid and water according to the following reaction equation:

R'CO-OH + R ² OH → R ^ O-OR ² + H, O (1) The equilibrium is shifted to the right (product) side of the reaction by continuously distilling off the water formed in the course of the reaction or by using one of the starting materials (carboxylic acid or alcohol) in excess. In a comparable manner, carboxylic acid alkyl esters can be transesterified in the presence of alcohols with liberation of an alcohol with the alkoxy group primarily bound in the ester:

R ³ CO-OR ⁴ + R ^s OH • * R ³ CO-OR ⁵ + R ⁴ OH (2)

A change in the reaction conditions (temperature, pressure) can also influence the position of the equilibrium. In practice, however, the measures mentioned with the aim of shifting the balance to the product side do not always lead to the desired success. This is regularly due to the fact that a change in the reaction conditions often also leads to the formation of by-products, which is problematic not only in terms of the product yield but also in terms of the purity of the products. The separation of the unwanted by-products from the desired products - especially in large-scale processes - can have a significant impact on economy. The presence of large amounts of starting material, which was used in excess, also leads to problems in connection with the cleaning of the desired product.

Physical equilibria can also play a role in the conduct of chemical reactions.

For example, it is often necessary for certain reactions to be carried out in (for example liquid) media which are free from oxygen or water or moisture and which are physically dissolved in the medium intended for the reaction. In such cases, the vessel containing the medium is usually evacuated and then filled with an inert gas, or the open system is flushed with an inert gas for a certain time. This will expel the unwanted gas or moisture; however, the inert fill gas or purge gas is also lost. In addition, such processes can hardly be carried out economically in plants for the technical management of chemical reactions.

Solution equilibria of chemical substances in solutions also play a role in the technical management of chemical reactions. Following a chemical reaction, undesired by-products or starting materials can be dissolved in the reaction mixture. By-products such as coloring or odorants or low-molecular-weight by-products of a reaction leading to higher-molecular-weight products on a statistical average have to be removed in complex cleaning steps which regularly reduce the product yield as well as unreacted starting materials remaining in the reaction mixture.

The solution equilibria - in this case determined by diffusion - also include the equilibria of dissolving gaseous reactants in liquid reaction systems. In the case of gas-liquid reactions such as hydrogenations, oxidation reactions, nitrilations, phosgenations or alkoxylations with alkylene oxides, the reaction rate, ie the rate at which an equilibrium is as far as possible on the product side, is determined by the amount of in the liquid reaction medium Contact with the dissolved reactant of available gas. In order to achieve practicable reaction rates, the partial pressure of the reaction gas in previous reactions had to be relatively high in order to be able to set a sufficient gas concentration. This not only made it difficult to control the reaction in individual cases, but also regularly required the use of larger amounts of gas than are actually required for the reaction. On the other hand, at the end of the reaction, it could not be prevented that a certain amount of gas had to be removed unreacted, since its partial pressure in the gas space was not sufficient for a complete reaction of the gaseous reactant in the liquid reaction medium in a reasonable reaction time. The latter is particularly unacceptable if the gas is for reasons of protection the environment can not be drained, but must be disposed of laboriously. This also reduced the efficiency of many gas-liquid reactions.

The object of the invention was to remedy the disadvantages of the prior art described above. In particular, a method for carrying out chemical reactions, which are characterized by equilibria, should be provided, in which the intervention in the equilibrium in favor of the desired course of the reaction is possible in a simple and efficient manner and can be carried out by means of the desired shift of the Do not oppose physical or chemical forces to balance.

Another object of the invention was to provide such a method in which the means for shifting the equilibrium can be used as universally as possible. This means that the agent had to be inert against chemical reactions and also be inexpensive and ubiquitously available with a view to the economic management of the process.

Further objects, advantages and features of the method according to the invention result from the following description.

Surprisingly, it has been found that it is possible to carry an inert gas in a separate gas circuit in a process for carrying out chemical reactions which are characterized by an equilibrium, as a result of which it is possible to achieve the objects set.

The invention relates to a method for carrying out a chemical reaction characterized by an equilibrium in a reaction system designed as a loop reactor, comprising a reactor vessel, at least one loop connected to the reactor vessel via an outlet and an inlet, with devices for pumping around of the fluid reaction mixture, at least one heat exchanger, optionally devices for feeding the reaction fluid into the reactor vessel and a separate gas circuit which is connected to the gas space of the reactor vessel located above the fluid reaction mixture, and separate devices for feeding gas into the gas circuit, for extraction of gas from the gas circuit and / or for the treatment of the gas circulating in the gas circuit, the method being characterized in that an inert gas is guided and / or treated in the gas circuit to intervene in the one running in the reactor vessel, characterized by an equilibrium Reaction is fed into the reactor vessel and after intervention in the equilibrium of the equilibrium reaction taking place in the reactor vessel is withdrawn from the reactor vessel into the gas circuit.

In the context of the present invention, the term “equilibrium” is understood to mean both a physical and a chemical equilibrium. Particular examples according to the invention result from the following description, in which the intervention in the equilibrium is an intervention in a physical equilibrium (for example a pure solution equilibrium) or in which on the other hand the intervention in the equilibrium is an intervention in a chemical equilibrium (for example an esterification or transesterification). Sometimes equilibria of both types occur side by side in a reaction system, which can be intervened at the same time or one after the other.

The loop reactor used for the process according to the invention, which encloses the reaction system, is a loop reactor known as such. Such reactors are usually used as closed reaction vessels for carrying out reactions of reactants dissolved in the liquid phase with other reactants dissolved in the liquid phase, including gaseous reactants. An example of such a reaction carried out in a loop reactor is disclosed in EP-A 0 419 419. Such loop reactors usually comprise - as can be seen from FIG. 1 - a reactor vessel 1 in which a considerable part, if not the majority, of the reaction solution is located. This is equipped with devices 7 for heating and / or cooling the reaction material, for example with a jacket for guiding gas or liquid, which can be used for heating or cooling the reaction material, if this is necessary. Connected to the reactor vessel 1 via an outlet 11, 16 and an inlet 12, 17 is at least one loop 2, 22 through which the fluid reaction material can be forcibly guided by means 3, 23 for pumping around. Devices 3, 23 of this type can be pumps, for example. In the loop 2, 22 is usually, in the present case preferred, at least one heat exchanger 4, 24, which in the context of the present invention can have the function of a cooler or the function of a heating device, depending on the reaction which is carried out in the loop reactor . It is also possible that in the case of two loops 2, 22, as shown by way of example in FIG. 2, and - accordingly - two heat exchangers 4 and 24, at least temporarily the function of a cooler and one the function of a heating device.

A device for feeding the circulating reaction fluid into the reactor vessel 1 can be arranged at the inlet of the loop 2, 22 into the reaction vessel 1. This can be done in such a way that the loop 2, 22 at the inlet into the reactor vessel 1 feeds the reaction material into such a device or the inlet itself represents such a device for feeding into the reactor vessel. Examples of this are Venturi tubes or nozzles, jet nozzles or jet suction mixing nozzles, which provide a certain turbulence when the reaction material is fed into the reactor vessel 1 and thus considerably improve the contact between the reaction partners (in particular in the case of gas-liquid reactions).

The loop reactor has a separate gas circuit 8, 28. This is connected to the gas space of the reactor vessel 1 located above the fluid reaction medium and preferably has separate devices for feeding gas into the gas circuit 8, 28, separate devices for withdrawing gas from the gas circuit 8, 28 and / or separate and / or separately switchable or switchable devices for treating the gas circulating in the gas circuit. In preferred embodiments of the invention, this treatment can be an adsorptive treatment, a condensation treatment and a selective chemical (ie a reactive) treatment; Combinations of these are further preferred and can therefore be used with advantage because all conceivable treatment options of your choice are available.

The latter devices are shown in FIGS. 3A to 3D and can, for example (at 8a or 28a in FIGS. 1 and 2), be cartridges or units which can be switched on and off separately and which can be operated with means known per se for removing O ₂ (e.g. with a molecular sieve) or to remove moisture (e.g. with a drying agent such as silica gel ^R ), with an adsorbent such as activated carbon e.g. for the purpose of removing low molecular weight volatile components or also with a carrier which selectively binds reactive components by active chemical reaction and removed or filled with harmless, non-toxic and / or non-environmentally relevant substances. Alternatively, such devices can also be, for example, cartridges or units or units in the form of one or more capacitors, which can be connected in series and can be switched on and off separately, with which components which are carried out with the inert gas from the reaction system into the gas circuit are separated from the inert gas ( if necessary, can be separated individually or in stages). Combinations of such devices (for example a drying cartridge and one or more condenser (s) are also possible according to the invention.

In such a loop reactor, according to the invention, an inert gas is conducted and / or treated in the gas circuit 8, 28, for intervention in the reaction which takes place in the reactor vessel 1 and which is characterized by an equilibrium, is fed into the reactor vessel 1 and after intervention in the equilibrium of the equilibrium in the reactor vessel 1 - deducted weight reaction from the reactor vessel 1 in the gas circuit 8, 28.

A large number of gases can be considered as inert gases. In principle, all gases are suitable which are inert in the special reaction, ie which do not react in an undesirable manner with one of the reaction partners. In the sense of this general definition of inert gas, a gas can be used for a special equilibrium reaction which does not react undesirably with one of the reactants under the given reaction conditions, but which is not inert in other reactions or under other reaction conditions. In order to be as universal as possible, however, nitrogen (N ₂ ), argon (Ar), carbon dioxide (CO ₂ ), water (H ₂ O) and other inert substances which are gaseous under the reaction conditions are preferably used as inert gases. Mixtures of one of the gases mentioned with one or more other inert gases can also be used according to the invention. It is one of the advantages of the invention that in the closed system of the loop reactor it is also possible to use inert gases on an industrial scale which are otherwise out of the question for reasons of cost, since the reaction system only has to be filled once with the desired inert gas and this in the gas circuit 8, 28 and in the gas space above the fluid reaction medium in the circuit and optionally also cleaned and then returned to the circuit. A loss of expensive inert gases can also be avoided. However, nitrogen is particularly preferably used as the inert gas, since it is available ubiquitously, can be obtained inexpensively and is effective in terms of its properties of influencing equilibria.

The inert gas is guided and / or treated in the gas circuit 8, 28. The guidance in the gas circuit 8, 28 can thus serve to condition the inert gas for later intervention in the equilibrium of the reaction taking place in the reaction system. In preferred embodiments of the method according to the invention, such conditioning can be carried out by heating, cooling, freeing the inert gas from undesired components (for example moisture = drying; oxygen or air = removal of acid). material; other gaseous accompanying substances = cleaning) or exposure of the inert gas to the desired gaseous substances. The latter can be advantageous, for example, if the desired gaseous substance is to be introduced into the fluid reaction system for better distribution despite lowering its partial pressure in the system, in order to balance in the sense of improving the contact of the gaseous substance with the other reaction partner (s) to influence. Another advantageous embodiment of the application of a desired gaseous substance to the inert gas lies in the targeted creation of a reductive or oxidative environment during an otherwise non-redox-influenced reaction. This can be desirable, for example, in order to avoid side reactions.

According to the invention, the inert gas from the separate gas circuit 8, 28, in which it is guided and / or treated, is fed into the reactor vessel 1 in order to intervene in the equilibrium prevailing in the reaction medium or to influence the equilibrium in the desired sense. Various forms of intervention or influence are possible, which are explained in detail below. The inert gas can be fed into the gas space above the fluid reaction medium or directly into the fluid reaction medium. In the latter case, the inert gas can, for example, be fed into the reactor vessel 1 via the device 5, 25 for feeding the fluid reaction medium. However, other ways of feeding in are also possible, for example directly into the loop 2, 22 or elsewhere into the circulating reaction material. In individual cases, this is left to the choice of the expert in this field.

In a preferred embodiment of the process according to the invention, the inert gas intervenes in the reaction in the reactor vessel 1 characterized by an equilibrium in such a way that the inert gas dissolves the reaction mixture of gas dissolved therein (or else undesirable low molecular weight constituents which are otherwise only obtained by separate carrier steam distillation can be removed) and cleans this from the reaction mixture discharges. Interfering with the balance

Reaction mixture + gas dissolved therein * ■ »Reaction mixture + gas (t) (3)

leads to the formation of a reaction mixture freed from undesired gaseous components. This can be necessary, for example, when a reaction mixture must not contain oxygen because it interferes with the reaction, directs it in an undesirable direction or impairs one of the components involved in the reaction with regard to its mode of action in the reaction. Such removal of oxygen from the reaction medium is carried out, for example, before the reaction to protect reaction products from oxidative degradation (for example in the condensation of highly unsaturated fatty acids or in the esterification of highly unsaturated compounds), to avoid the formation of low molecular weight by-products (for example in the case of Polymerization reactions) or to protect catalysts against loss of activity (for example to protect phosphorous acid against oxidation to phosphoric acid in the esterification of sorbitol to sorbitan esters). For this purpose, the inert gas, such as nitrogen, which is conducted in the gas circuit 8, 28, is preferably introduced directly into the fluid reaction medium. The inert gas, for example (but not necessarily), passes through the reaction material under high turbulence, for example in the form of a large number of bubbles which are as small as possible, and superimposes the equilibrium (3) with the following equilibrium (4):

dissolved gas + N ₂ → dissolved N ₂ + gas (t) (4)

The gas "displaced" from the solution by nitrogen introduced is discharged with excess nitrogen from the reaction mixture and then from the reaction vessel 1, enters the gas circuit 8, 28 and is separated from the inert gas again in the course of the treatment of the inert gas. The treatment of the inert gas-oxygen mixture in the gas circuit can be carried out according to procedures known to those skilled in the art for such treatment. Such a procedure can - by an game - the treatment of the inert gas-oxygen mixture by means of a molecular sieve that removes the oxygen selectively. This is advantageously (but not necessarily) filled into a cartridge through which the gas mixture flows for treatment. Other procedures are conceivable in the same way to separate the oxygen from the inert gas. The inert gas is then available again for a new cycle of removing oxygen. There are no losses of inert gas. Of course, the oxygen can also be flushed out in an open system without returning the nitrogen back into the circuit. However, this embodiment is less preferred than that previously described.

It is a further embodiment of the same principle to condition the reaction mixture in a step upstream of the actual reaction by deliberately adding small amounts of a reactive gas such that the formation of undesired by-products is prevented in the subsequent reaction. For example, centers (hydroperoxides, peroxides and other intermediates) formed oxidatively before reactions of unsaturated fatty acids can be reduced by pretreatment with H ₂ .

In the same way, the inert gas can be used in the reaction vessel before the start of the reaction to drive off moisture from the reaction mixture intended for the reaction. In the course of this intervention of the inert gas into the solution equilibrium, the inert gas, for example nitrogen, is preferably introduced turbulently into the reaction mixture, as in the case described above, displaces the dissolved water from the reaction mixture and drags it into the gas space above the reaction mixture or into the gas circuit 8 , 28 out. In the gas circuit, the inert gas is then "dried" in a manner known per se, ie the water is separated off. This takes place in the gas circuit in a manner known per se. An example of the drying process, which is particularly preferred when small amounts of water (moisture) are carried out by the inert gas, is to let the moist inert gas flow through a cartridge with a customary drying agent, for example a cartridge with silica gel ^R. . For larger ones Amounts of water are preferred other methods known to those skilled in the art, such as freezing out water in a cooler connected to the gas circuit. After "drying", the inert gas is available for another cycle. There are no losses of inert gas. Of course, even in an open system with nitrogen, the moisture (the water) can be flushed out without returning the nitrogen back into the circuit. However, this embodiment is less preferred than that previously described.

Of course, in the process according to the invention it is possible in the treatment of the gas in the gas circuit, units for condensation, units for adsorption, units for drying, units for reactive reaction of reaction components etc. in any order and combination (but useful for the process) to connect in series. The degree of separation of the components to be separated during treatment in the gas circuit can thus be increased in an advantageous manner, which improves the overall efficiency of the method. It is even more preferred to condensatively remove large amounts of volatile components which have been removed from an equilibrium and are carried into the gas circuit, and then to separate smaller (residual) amounts by adsorption or by chemical reaction.

The same procedure as described above is used when low-molecular impurities which have already formed in the crude starting material and have formed as a result of aging and / or decomposition are to be removed from the reaction system. In the conventional procedure, these have to be laboriously removed by carrier steam distillation. The method on which the present invention is based enables a simpler and gentler removal of such contaminants already in the system in which the subsequent reaction takes place.

Interference of the inert gas in the solution equilibrium also takes place in a further preferred embodiment of the method according to the invention when one with a Equilibrium reaction taking place as a reaction partner is shifted to the side of the products by supplying an excess of gas. After the above reaction (4), the unreacted excess gas can be discharged from the reaction mixture and thus a rapid, efficient and complete purification of excess gaseous reactant can be achieved in the reaction vessel. This plays a role in the industrial field, for example in batch-like processes, in particular in reactions with environmentally relevant, toxic or highly reactive gases. Examples include phosgenations, carbonylation reactions or alkylations. The excess reactants discharged by the inert gas (for example COCl ₂ , CO or RC1) are separated from the inert gas by methods known per se, for example reactively or by adsorption or condensation.

In a further preferred embodiment of the process according to the invention, the inert gas intervenes in the reaction in the reactor vessel 1 characterized by an equilibrium in such a way that the inert gas feeds a gaseous reactant to the reaction mixture. This can lead to positive results in all cases in which gaseous reactants have to be added to a reaction mixture

either accelerating or braking control of the response is desired; or (possibly also with a view to controlling the reaction) a certain, for example low, partial pressure of the gaseous reaction partner is desired; or a balance should be "gently" shifted to the products while avoiding large excesses of a gaseous reactant.

The latter, relatively frequent intervention in an equilibrium is necessary, for example, in chemical reactions which - of course undesirable - only start up after a certain incubation period ("start"). The incubation period is then when the invention The method according to the invention, involving interference in equilibrium, is surprisingly shortened or defused, if not avoided.

Examples of the above-mentioned reactions can all be equilibrium reactions taking place on the reactant side with gas participation, for example hydrogenations, oxidation reactions, alkoxylation reactions, nitrilization, phosgenation, halogenation, alkylation, sulfation, sulfation, etc. In such reactions it may be desirable, by common Entry of the reaction gas with the inert gas to produce better contact between the reaction gas and the reaction partner (s) already dissolved in the reaction mixture, a reaction which is too fast in the case of highly reactive gaseous reaction partners while avoiding side reactions at too high a temperature or too high a concentration of the reaction gas to avoid by "dilution" of the reaction gas, to avoid excessive excess of a reaction gas for economic or reaction-technical reasons or health-endangering or dangerous or expensive reaction gases in d The reaction can only be used at low partial pressures, but no less efficiently. The entry of the reaction gas with the inert gas according to the invention takes these goals into account.

Significant advantages can be achieved in that the thermal, kinetic and thermodynamic parameters of the reaction are improved. In addition, by "diluting" the reaction gas while maintaining the reactivity with respect to the liquid phase, side reactions involving the reaction gas are avoided or largely suppressed. So are u. a. the formation of decomposition products or also condensation or rearrangement reactions (inactivation) can be avoided.

It corresponds to a particularly preferred embodiment of the invention that the gaseous reactant supplied by the inert gas is present in a low partial pressure caused by the end of the reaction. This plays a role, for example, when an equilibrium reaction takes place with the participation of a gaseous reaction partner is not abruptly terminated, but is to come to an end after the supply of the gaseous reactant has ended, with more or less complete reaction of the gas, such as, for example, in the case of alkoxylation reactions. In the prior art, a certain amount of gas (alkylene oxide) regularly remained unconverted in the reaction mixture or in the gas space of the loop reactor if the reaction was not to be allowed to continue uneconomically for a long time. According to the invention, complete reaction can be achieved using an inert gas such as N _2, even if the partial pressure of the gaseous reactant decreases at the end of the reaction, and no reaction gas has to be discharged or pumped off. This not only avoids separate measures to avoid a hazard (safety, health) to the environment (e.g. complex gas scrubbers), but also enables economical process management using resources.

A wide range of applications in terms of influencing equilibrium reactions results in the preferred embodiment according to the invention, in which the inert gas intervenes in the reaction characterized by equilibrium in the reactor vessel 1 in such a way that the inert gas withdraws a volatile reaction partner from the reaction mixture. It is particularly preferred that the volatile reaction partner is withdrawn by the inert gas during the course of the reaction and that the reaction partner withdrawn by the inert gas of the reaction mixture is a product of the reaction characterized by an equilibrium in the course of the reaction. For example, in the esterification reaction represented by equation (1) above, the volatile reaction product water can be removed from the equilibrium by an inert gas. This effectively shifts the balance of the esterification reaction to the product side without thermal stress and without the use of excess educt. The water is simply removed from the reaction mixture and dragged into the gas circuit. There it can be easily separated from the inert gas in a manner known per se, which is then available for a new dewatering cycle. There are no losses of inert gas. In an analogous manner, in the course of the transesterification reaction represented by the above reaction equation (2), the alcohol R ⁴ OH formed as product can be discharged as a volatile product from the reaction mixture and the balance of the transesterification reaction can thus be shifted to the product side if desired. The separation of the alcohol from the inert gas in the course of the treatment of the inert gas in the gas circuit 8, 28 is just as unproblematic (and known per se) as the separation of water after the esterification reaction. In the end, pure inert gas is obtained again for a new cycle.

Also the equilibrium of a directed transesterification according to the reaction equation (5)

R ⁶ CO-OR ⁷ + R ⁸ CO-OR ⁹ ** R ⁶ CO-OR ⁹ (t) + R ⁸ CO-OR ⁷ (5)

can be shifted towards the products during the course of the reaction by adding an inert gas. This is possible in particular if the reaction product R ⁶ CO-OR ⁹ is volatile due to the length of the alkyl chains of the radicals R ⁶ and R ⁹ and can therefore be discharged through the inert gas. Technically, this plays a role in the transesterification of coconut fat to increase its melting point: Here, esters of relatively long-chain fatty acids are reacted with coconut fat and long-chain acyl residues are esterified in the fat. Naturally, shorter-chain fatty acids are released in the form of their esters. The equilibrium of the reaction can be shifted to the product side by driving off the relatively short-chain esters. The inert gas carries the esters of the relatively short-chain fatty acids into the gas cycle, where they are separated off during the treatment of the inert gas. The inert gas is then available for another cycle.

The reaction, which is basically the same, takes place in the transesterification of triglycerides with non-volatile fatty acids or the transesterification of polyalcohols with methyl esters: even in these reactions, the equilibrium can be eliminated when the formed ones are discharged move volatile fatty acids or methanol to the side of the products.

In further preferred embodiments of the process according to the invention, the inert gas engages in a reaction equilibrium with the withdrawal of a volatile reaction partner such that the intervention takes place after the reaction has ended completely and either the reactant withdrawn by the inert gas from the reaction mixture or an reactant used in excess is a reaction characterized by an equilibrium or the reactant withdrawn by the inert gas of the reaction mixture is a product formed in the course of the reaction, the reaction characterized by an equilibrium, or alternatively a reactant is an educt used in excess, the reaction characterized by an equilibrium, and another Product formed in the course of the reaction is the reaction characterized by equilibrium.

An example of the first case (the reactant withdrawn by the inert gas of the reaction mixture is an educt of the reaction used in excess) is the deodorization of the reaction mixture after the conversion of glycerol and, if appropriate, short-chain fatty acid to triglycerides which can be removed under process conditions according to the equation ( 6)

Glycerin + 3 R ¹⁰ CO-OH triglyceride + 3 H ₂ O (6)

Since even small amounts of unreacted, strong-smelling fatty acid lead to a considerable impairment of the smell and taste of the product, it is essential to deodorize the product mixture after the reaction has ended. The relatively volatile fatty acid can be easily expelled from the product mixture by using an inert gas, as a result of which deodorization of the product can be carried out quickly and efficiently on an industrial scale without complex additional steps. Likewise, if an excess of glycerol is used, this excess after the fat has reacted acid can be removed. If necessary, excess educts are returned to the cycle.

Examples of the second case (the reactant withdrawn by the inert gas of the reaction mixture is a product of the reaction characterized by an equilibrium in the course of the reaction) are the esterification which proceeds according to equation (1) above or that which proceeds according to equation (2) above Transesterification: With the aid of a carrier gas such as nitrogen, the desired ester (R'CO-OR ² in the case of reaction (1); R ³ CO-OR ⁵ in the case of reaction (2)), as far as this is volatile, is obtained from the product mixture separated and thus obtain a pure product free of by-products and / or starting materials in one step. During the treatment of the inert gas, the product is completely separated from the inert gas in a manner known per se and, in the end, a pure inert gas suitable for a new separation cycle is obtained again.

Examples of the third case (one reactant is an educt of the reaction characterized by an equilibrium and another is a product of the reaction characterized by an equilibrium formed in the course of the reaction) are the enrichment of products of a certain degree of alkoxylation in the alkoxylation of For example, fatty alcohols and the purification of the triglycerides resulting from the reaction of glycerol and, for example, fatty acid methyl esters: in the alkoxylation, after the reaction has ended, the relatively volatile reactants fatty alcohol (educt) and low-alkoxylated fatty alcohols (products) can be removed from the more alkoxylated by the intervention of an inert gas in the solution equilibrium Fatty alcohols (products) are separated off and the desired products are obtained in relatively high yield and purity. The substances drawn off with the inert gas are easily separated off again in the inert gas treatment step. In a comparable manner, fatty acid methyl esters (educt) used in the production of triglycerides, as well as methanol (product), any partial esters of glycerol (monoesters or diesters) or methyl ether (by-product) formed can be used as more volatile components separate the reaction mixture after completion of the reaction.

In a particularly preferred embodiment of the invention, the principle described above is used in the deodorization of food fats or oils. In the prior art, these were treated in cascades under vacuum (approx. 1.33 mbar) at temperatures up to 270 ° C. in countercurrent against water vapor in order to drive out undesired by-products with a molecular weight below that of the fats or oils. At the same time, color bodies and epoxides or hydroperoxides from chemical bleaching or adsorptive bleaching were also partially decomposed by means of bleaching earth and their subsequent removal. In the process according to the invention, the by-products are eliminated, that is to say bleaching and subsequent deodorization, in the loop reactor by introducing H ₂ with N ₂ and, if appropriate, in the presence of a catalyst and then introducing N ₂ to discharge the by-products into the gas cycle (optionally with addition of water vapor to improve the separation effect). The nitrogen discharges the volatile odorants into the gas cycle, where they are separated from the "entraining gas" in a manner known to those skilled in the art, for example by adsorption using a cartridge containing an adsorbent. Such a deodorization is particularly useful after the hydrogenation of edible fats or oils customary in industry, which can also be carried out with advantage in the loop reactor, the process according to the invention having the advantages indicated in the description. It is particularly advantageous that plants previously used only need to be retrofitted with the gas circuit lying outside the reactor system.

The last-mentioned reactions are - as described - carried out regularly after completion of the reaction, mostly because the educt content is required during the reaction in order not to undesirably shift the equilibrium back towards the educts. However, it is also possible in individual cases to separate the starting materials and / or separate the reaction products formed to be carried out in the course of the method if there are advantages for the position of the equilibrium or for other characteristics of the reaction.

It corresponds to a further embodiment which is preferred within the scope of the method according to the invention to use the inert gas to set a certain gas atmosphere above the reaction mixture and thus also in the reaction mixture and thus to favor the course of reactions. This can be important, for example, in the treatment of natural fats before chemical reactions: reducible centers (epoxy groups; hydroperoxide groups) present in the fat due to storage or transport conditions can be reduced for pretreatment by introducing H ₂ . An inert gas is used as a carrier or medium to intervene in the solution and reaction equilibrium. The efficiency of the reaction is significantly improved, and the subsequent reactions proceed with complete retention of the desired fat product.

The setting of reducing conditions is also desirable in the esterification of sorbitol to sorbitan esters: for this reaction (which proceeds essentially according to equation (1)), catalysts (phosphorous acid and its salts) are selected which have reducing properties in order to ensure the formation of the quality to prevent the coloring by-products which impair the products. If conventional esterification catalysts are used under reducing conditions (H _{2 introduction} into the reaction mixture by means of the inert carrier gas N ₂ ), the formation of by-products, in particular of color-imparting and odor-forming substances, is largely suppressed.

In all of the examples mentioned, the respective equilibrium can be shifted in a simple and efficient manner by the intervention of an inert gas in favor of the desired course of the reaction. The inert gas does not take part in the reaction and can be completely recovered by simple process steps; it is therefore not consumed, which also enables the use of expensive inert gases. No physical or chemical forces are opposed to shifting the respective equilibrium. The GE- Desired reaction products are obtained in high yield and purity. In addition, in catalyzed systems, the amount of catalyst can be drastically reduced, sometimes to 1/10 of the amount used in the prior art, which not only brings about a considerable cost saving in catalyst consumption, but also significantly reduces the problems with separating the catalyst .

The invention is illustrated by the following examples, without being restricted to these.

example 1

Preparation of a caprylic acid-capric acid triglyceride from the corresponding methyl esters

In a loop reactor according to the attached FIG. 1A with a reactor filling volume of 65 liters and with a gas circuit, in which there were switchable units for removing oxygen, for drying, for reacting reactive components and for condensation, and in the liquid circuit there was an optionally switchable filtration unit 6, 40 kg (231 mol) of a caprylic acid methyl ester-capric acid methyl ester mixture (parts by weight C ₈ : C ₁₀ = 1: 1) and 6.07 kg (66 mol) glycerol were introduced. The reactor was then purged and filled with N ₂ and the temperature was then adjusted to 60 ° C.

During a cleaning step lasting 15 minutes, the gas circuit was operated while pumping around the liquid phase with a circulating capacity of about 3.6 m ³ / h, and the drying unit and then the unit for removing oxygen were connected one after the other. The flow velocity at the discharge of the jet suction was around 17 m / s.

After completing the cleaning step, the condensation was unit was switched on while the drying unit and the unit for removing oxygen were switched off after the pretreatment. 0.46 kg of 50% methanol-soluble inertized potassium methylate was added to the reaction mixture as the transesterification catalyst, and the temperature was raised to the reaction temperature of 100.degree.

The transesterification was carried out at 100 ° C. for 30 minutes. During this time, the methanol formed was continuously discharged into the gas circuit and condensed in the condensation unit at 0 ° C.

As soon as no more MeOH was discharged in the course of the reaction, 800 g of crystalline citric acid were fed to the reactor. After circulation for 10 minutes in the reaction mixture, this was removed as K-citrate via the filtration unit which can be connected to the liquid crystal.

The reaction mixture, consisting of the triglyceride formed, excess methyl esters and low molecular weight impurities, unreacted starting materials and by-products formed, was heated to 200.degree. By operating the gas circuit, apart from the desired triglyceride, all other components mentioned, which had a lower molecular weight than the triglyceride, were discharged into the gas circuit and separated from the nitrogen individually by condensation in the condensation unit.

According to a thin-layer chromatographic test, the triglyceride (32 kg) obtained after cooling was free of by-products, in particular of methyl esters, partial glycerides and free fatty acids. Comparative Example 1 and Example 2 Preparation of sorbitan esters under reducing conditions

In the loop reactor described in Example 1, 17.5 kg sorbitol (70% in H ₂ O) and 27.7 kg oleic acid together with 0.3 kg NaOH (50% in H ₂ O) and 0.13 kg crystalline phosphorous Given acid. After purging and inerting with pure nitrogen, the reaction was carried out at 180 ° C. for 1 h and then at 240 ° C. for 2 h. The solution water and the water of reaction were continuously discharged with pure nitrogen into the gas circuit, to which two condensers operated at different temperatures were connected. The exaggerated fatty acid was separated in the first condenser (110 ° C); the water was separated in the second condenser (10 ° C). The fatty acid thus recovered was returned to the reactor 1 hour before the reaction was completed. The sorbitan ester obtained had an OHZ of 205 to 208 and a color of 10 Hess-Ives.

The reaction described above was repeated, with the difference that hydrogen (partial pressure: 0.1 bar) was added to the recycled nitrogen. The sorbitan ester obtained had an OHZ of 205 to 208 and a color of 5 Hess-Ives.

Example 3 and Comparative Example 2

Production of coconut fatty acid dimethylaminopropylamide (removal of oxygen)

33 kg of coconut fat and 18 kg of dimethylaminopropylamine were filled into the loop reactor specified in Example 1. The oxygen was removed from the mixture at 90 ° C. via the gas circuit using nitrogen.

The subsequent conversion to coconut fatty acid dimethylaminopropylamide was carried out at 180 ° C. over a period of 1 h without using the condensation unit. The Raw amide held had a color number well below 100 Hazen.

The reaction described above was repeated, with the modification that the oxygen was not removed from the starting material mixture. The product had a color number of about 500 Hazen.

Example 4 Drying of a Reactant Mixture

In the loop reactor specified in Example 1, 40 kg of C _12/14 fatty alcohol and 24 g of KOH (50% in H ₂ O) were circulated for 30 minutes at a temperature of 140 ° C. under N ₂ circulation. The nitrogen was passed through the condensation unit connected to the gas circuit and then through the drying unit connected in series. The water content before the treatment was 0.1%. The water content was reduced to <0.001% by drying. These low water contents made it possible to drastically reduce the polyethylene glycol content in ethoxylates prepared with this starting material mixture.

Example 5 Preparation of an ethoxylate of a C ^ _/ ^ -fatty alcohol with 2 moles of ethylene oxide

In the loop reactor specified in Example 1, 40 kg of lauryl alcohol / myristyl alcohol were rendered inert. Then 24 g of KOH (50% in H ₂ O) were added. The mixture was dried by circulating under nitrogen as in Example 4. Thereafter, the reaction was carried out while continuously feeding ethylene oxide (8.8 kg in total) while maintaining a reaction temperature of 160 ° C.

The reaction was stopped by stopping the supply of ethylene oxide however, let the ethylene oxide still present in the system react completely. The catalyst was then destroyed by adding acetic acid.

The temperature of the reaction mixture was then raised to 230 ° C. At this temperature, fatty alcohol and simply ethoxylated fatty alcohol were discharged from the reaction mixture over a period of 1 h with the surrounding nitrogen while simultaneously introducing steam into the jet nozzle and separated from the nitrogen with condensation in the condensation unit.

The reaction mixture had prior to separation of the starting materials and by-products have a content of C _{12 / I4} fatty alcohol of 12 wt .-% and a content of mono-ethoxylated adsorption product (ROH + 1 EO) of 10 wt .-%. In contrast, after the starting materials and by-products had been separated off, the content of C _12/14 fatty alcohol was reduced to 3% by weight and the content of simply ethoxylated adduct (ROH + 1 EO) to 7% by weight. This reduction in the lipophilic constituents in the reaction product manifests itself in a significantly improved water solubility.

Claims

claims

1. A method for carrying out a chemical reaction characterized by an equilibrium in a reaction system designed as a loop reactor, comprising a reactor vessel, at least one loop connected to the reactor vessel via in each case one outlet and one inlet each, with devices for pumping around the fluid reaction material, at least one heat exchanger, if appropriate, devices for feeding the reaction fluid into the reactor vessel and a separate gas circuit which is connected to the gas space of the reactor vessel located above the fluid reaction mixture, and separate devices for feeding gas into the gas circuit, for withdrawing gas from the gas circuit and / or for the treatment of the gas circulating in the gas circuit, characterized in that an inert gas is guided and / or treated in the gas circuit to intervene in the Re, which is characterized by an equilibrium, and which takes place in the reactor vessel action is fed into the reactor vessel and, after intervention in the equilibrium of the equilibrium reaction taking place in the reactor vessel, is withdrawn from the reactor vessel into the gas circuit.

2. The method according to claim 1, wherein the inert gas intervenes in the reaction characterized by an equilibrium in the reactor vessel, that the inert gas cleans the reaction mixture of gas dissolved therein and / or of volatiles transported therein and this / this discharges from the reaction mixture .

3. The method according to claim 1 or claim 2, wherein the inert gas frees the reaction mixture located in the reactor vessel from oxygen and / or dries.

4. The method according to claim 1 or claim 2, wherein the inert gas discharges excess reaction gas from the reaction mixture located in the reactor vessel.

5. The method according to claim 1, wherein the inert gas intervenes in the reaction characterized by an equilibrium in the reactor vessel, that the inert gas of the reaction mixture supplies a gaseous reactant.

6. The method according to claim 1, wherein the inert gas engages in the reaction characterized by an equilibrium in the reactor vessel that the inert gas in the reaction mixture improves the contact between gaseous and already dissolved reactants.

7. The method according to claim 6, wherein the gaseous reactant supplied by the inert gas is present in a controlled low partial pressure.

8. The method according to claim 6, wherein the gaseous reactant supplied by the inert gas is present in a low partial pressure caused by the end of the reaction.

9. The method according to claim 1, wherein the inert gas engages in the reaction characterized by an equilibrium in the reactor vessel such that the inert gas withdraws a volatile reactant from the reaction mixture.

10. The method according to claim 9, wherein the withdrawal of the volatile reactant by the inert gas during the course of the reaction or after fully constant reaction takes place and the reactant withdrawn by the inert gas of the reaction mixture is an educt used in excess of the reaction characterized by an equilibrium.

11. The method according to claim 9, wherein the volatile reaction partner is withdrawn by the inert gas during the course of the reaction and the reactant withdrawn by the inert gas of the reaction mixture is a product formed in the course of the reaction and / or a by-product of the reaction characterized by an equilibrium.

12. The method according to claim 9, wherein the volatile reaction partner is withdrawn by the inert gas during the course of the reaction or after the reaction has ended completely and the reactant withdrawn by the inert gas from the reaction mixture is a product and / or by-product formed in the course of the reaction which is a reaction characterized by an equilibrium.

13. The method according to one or more of claims 1 to 12, wherein the inert gas nitrogen (N ₂ ), argon (Ar), CO ₂ , H ₂ O and another inert substance which is gaseous under the reaction conditions or a mixture of one or more inert gases , but is preferably nitrogen.

14. The method according to one or more of claims 1 to 13, wherein the treatment of the inert gas in the gas circuit consists in conditioning the inert gas for intervention in the reaction characterized by an equilibrium.

15. The method according to claim 14, wherein the conditioning of the inert gas in a heating of the inert gas, in a cooling of the inert gas, in one Liberation of the inert gas from unwanted components or exposure to the inert gas with desired gaseous substances.