RU2454399C2 - Method of producing alpha-hydroxy carboxylic acids - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to an improved continuous method of producing esters of alpha-hydroxy carboxylic acids, in which an amide of alpha-hydroxy carboxylic acid reacts with alcohol as the starting components in the presence of a catalyst to obtain a mixture of products containing esters of alpha-hydroxy carboxylic acids, ammonia, unreacted amide of alpha-hydroxy carboxylic acid, as well as alcohol and a catalyst, in which a) streams of starting components containing amide of alpha-hydroxy carboxylic acid, alcohol and catalyst as the starting components are fed into a high-pressure reactor; b) the streams of starting components react with each other in the high-pressure reactor at pressure from 1 bar to 100 bar; c) the mixture of products obtained at step b), which contains esters of alpha-hydroxy carboxylic acids, unreacted amide of alpha-hydroxy carboxylic acid and catalyst, is removed from the high-pressure reactor; and d) alcohol and ammonia content in the mixture of products is reduced, where ammonia is removed by distillation under pressure which is constantly kept higher than 1 bar without recourse to additional cleaning agents. The continuous method is especially expedient when used on an industrial scale.

EFFECT: improved continuous method of producing esters of alpha-hydroxy carboxylic acids.

30 cl, 12 ex, 2 tbl, 2 dwg

Description

The present invention relates to a method for producing alpha-hydroxycarboxylic acid esters on an industrial scale. In particular, the invention relates to a process for the preparation of alpha-hydroxycarboxylic acid esters according to the preamble of claim 1.

Esters of alpha-hydroxycarboxylic acids are valuable intermediates in the industrial synthesis of acrylic acid esters and methacrylic acid esters, hereinafter referred to as alkyl (meth) acrylates. Alkyl (meth) acrylates, in turn, find their main application in the production of polymers and copolymers with other compounds suitable for polymerization.

An overview of the most widely known processes for the preparation of (meth) acrylic acid esters can be found in the literature, for example: Weissermel, Arre "Industrielle organische Chemie", VCH, Weinheim 1994, 4. Auflage, S.305 ff or Kirk Othmer "Encyclopedia of Chemical Technology" 3. Ausgabe, Vol. 15, Seite 357.

If the task is to synthesize methacrylic acid esters, then the central intermediate in their preparation as alpha-hydroxycarboxylic acid ester is 2-hydroxyisobutyric acid methyl ester (= HIBSM).

Obtaining an ester of alpha-hydroxycarboxylic acids by reacting an alcohol with an amide of alpha-hydroxycarboxylic acid is described, for example, in the publication of German patent application DE-A-2454497. This publication describes the use of lead compounds to catalyze a reaction. At the same time, a continuous process is mentioned, however, without specifying a technical solution that allows to obtain products with high efficiency.

In addition, a method for producing alpha-hydroxycarboxylic acid esters is described in German patent application DE-A-2528524. Various catalysts are used, including but not limited to lanthanum compounds. Although DE-A-2528524 also mentions that the described methods are suitable for continuous implementation, this publication also does not provide a satisfactory solution to the problems that arise.

A corresponding category of the method is known from European patent EP 0 945 423. It describes a method for producing alpha-hydroxycarboxylic acid esters, comprising the steps of reacting the liquid amine with the presence of a catalyst in the presence of a catalyst and maintaining the concentration of ammonia in the reaction solution. at the level of 0.1 wt.% or lower, for which the resulting ammonia is discharged in the form of gas into the gas phase.

To remove ammonia from the reaction solution in the form of a gas in the gas phase, it is removed from the reaction solution by distillation. For this, the reaction solution is heated to boiling and / or bubbles of a “cleaning gas” are passed through the reaction solution, i.e. inert gas.

The disadvantages of the method described in publication EP 0945423 for producing esters of alpha-hydroxycarboxylic acids by decomposition of the corresponding amides of alpha-hydroxycarboxylic acid under the influence of alcohols (hereinafter - alcoholysis) can be represented in the form of the following disadvantages.

i. The simple removal of ammonia by distillation according to the process variant described in EP 0945423 is characterized by low efficiency. The implementation of this proposal requires an extremely efficient separation column and, therefore, overcoming special technical difficulties.

ii. If an inert cleaning gas is additionally or exclusively used, then the ammonia removal efficiency does increase, however, this is due to another component of the process, the processing of which requires additional efforts.

iii. If alpha-hydroxybutyric acid amide and methanol are used as starting components, under the conditions described in patent EP 0945423, separation of the ammonia formed and residual methanol is only possible with difficulty.

The almost constant need to use an inert gas to remove ammonia and the associated work with another stream of substances (separation of the cleaning gas and ammonia) makes the proposed method relatively uninteresting from an economic point of view, which is also reflected in the fact that the technical implementation of the published method is absent until so far.

In view of the state of the art, the object of the present invention was to provide a process for producing alpha-hydroxycarboxylic acid esters, which can be easily and inexpensively implemented.

Another objective of the invention was to develop a method in which it is possible to obtain esters of alpha-hydroxycarboxylic acids with very high selectivity.

Furthermore, an object of the present invention was to provide a process for producing alpha-hydroxycarboxylic acid esters in which no by-products are obtained at all, or only minor amounts of by-products are obtained. At the same time, it is necessary to obtain a product with the highest yield possible and, in general, with a low energy consumption.

This problem and other tasks, not specified separately, but unconditionally following from the problems connected with each other described in the introductory part, are solved by the method with all the features of paragraph 1 of the claims. Preferred variants of the method according to the invention are protected in dependent clauses with reference to clause 1 and based on it.

Accordingly, an object of the present invention is a continuous method for producing alpha-hydroxycarboxylic acid esters, in which the alpha-hydroxycarboxylic acid amide is reacted with alcohol (starting components) in the presence of a catalyst, to obtain a product mixture that contains alpha-hydroxycarboxylic acid esters, ammonia, which has not passed an alpha-hydroxycarboxylic acid amide reaction, as well as an alcohol and a catalyst; moreover, the method is characterized in that the flows of the starting components, including alpha-hydroxycarboxylic acid amide, alcohol and a catalyst, are fed to the pressurized reactor; in a reactor under pressure from 1 bar to 100 bar, the reaction of the streams of the starting components between themselves; and in the mixture of products, the alcohol and ammonia content is reduced, and the ammonia is removed by distillation under pressure, which is constantly maintained at a level above 1 bar, without resorting to additional cleaning agents.

By using the methods of the invention, the following advantages can be achieved, inter alia.

- Ammonia obtained by the reaction according to the invention can, unexpectedly, at relatively low cost, be easily separated from alcohol, for example methanol, which is used for alcoholysis or methanolysis of alpha-hydroxycarboxylic acid amide. This is possible, although alcohol (methanol) and ammonia in dissolved form under normal conditions only separate with difficulty.

- In the separation of ammonia is already released in a very pure form, and thus, it can be used again in various processes without further purification. Alcohol is also obtained in such a way that its quality is suitable for use in the process and it can, for example, be used again in the production process.

- In this case, the method according to the invention dispenses with the use of auxiliary means for separating ammonia, in the first place there is no need to use inert gases as means for purifying ammonia. Accordingly, when using the method according to the invention, no significant additional inert gas flow is obtained, which would, in turn, be separated from ammonia.

- Using the process according to the invention, alpha-hydroxycarboxylic acid esters are obtained in high yield and purity. In particular, this is significant in comparison with the methods described in European application EP-A-0945423, in the implementation of which amides of α-hydroxycarboxylic acids, while maintaining the current concentration of ammonia at a very low level, are decomposed under the influence of alcohols to esters of alpha-hydroxycarboxylic acids. It was unexpectedly found that the use of high pressure in combination with conventional distillation / distillation not only dispenses with additional inert gas purification measures, but also makes a higher concentration of ammonia in the liquid phase acceptable, while not reducing overall high selectivity.

- At the same time, the scale of formation of by-products is unusually low. In addition, especially given the higher selectivity, it is possible to achieve an increase in turnover.

- The method described in the present invention, in addition, has an extremely low tendency to form by-products.

- Further, the method according to the invention can be implemented with low cost, especially low energy demand. In this case, the catalysts used for alcoholysis of amide alpha-hydroxycarboxylic acid can be used for a long time without lowering selectivity or activity. Thus, the resource of the catalysts is high.

- Finally, the method according to the invention has special advantages when implemented on an industrial scale.

When implementing the method according to the invention, alpha-hydroxycarboxylic acid esters are synthesized by reaction between starting materials such as alpha-hydroxycarboxylic acid amide and alcohol in the presence of a catalyst.

Suitable for use in the reaction of the invention amides of alpha-hydroxycarboxylic acid are usually all those amides of carboxylic acids that contain at least one hydroxy group in the alpha position to the amide group of the carboxylic acid.

In turn, carboxylic acid amides are well known to those skilled in the art. Typically, these include compounds with groups of the formula —CONR′R ″ ″, where R ′ and R ″ independently represent hydrogen or a group containing from 1 to 30 carbon atoms, including, in particular, 1-20 preferably 1-10, and in particular 1-5 carbon atoms. The carboxylic acid amide may include 1, 2, 3, 4 or more groups of the formula —CONR′R ″ ″ -. These include, in particular, compounds of the formula R (—CONR′R ″) _n , in which the remainder R represents a group containing from 1 to 30 carbon atoms, including, in particular, 1-20, preferably 1 -10, in particular 1-5, and particularly preferably 2-3 carbon atoms, R 'and R''have the above meaning, and n is an integer in the range from 1 to 10, preferably 1-4, and particularly preferably 1 or 2.

The expression "group containing from 1 to 30 carbon atoms" refers to residues of organic compounds with 1-30 carbon atoms. In addition to aromatic and heteroaromatic groups, it means aliphatic and heteroaliphatic groups, such as, for example, alkyl, cycloalkyl, alkoxy groups, cycloalkoxy groups, cycloalkylthio groups and alkenyl groups. Moreover, these groups can be branched or unbranched.

According to the invention, aromatic groups are understood to mean residues of mononuclear or multicore aromatic compounds having preferably 6-20, in particular 6 to 12 carbon atoms.

Heteroaromatic groups mean aryl residues in which at least one CH group is substituted with N and / or at least two adjacent CH groups are substituted with S, NH or O.

Preferred aromatic or heteroaromatic groups according to the invention start with benzene, naphthalene, biphenyl, diphenylether, diphenylmethane, diphenyl dimethyl methane, bisphenone, diphenyl sulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole, pyrazadi 2,5-diphenyl-1,3,4-oxadiazole, 1,3,4-thiadiazole, 1,3,4-triazole, 2,5-diphenyl-1,3,4-triazole, 1,2,5 -triphenyl-1,3,4-triazole, 1,2,4-oxadiazole, 1,2,4-thiadiazole, 1,2,4-triazole, 1,2,3-triazole, 1,2,3,4 -tetrazole, benzo [b] thiophene, benzo [b] furan, Indol, benzo [s] thiophene, benzo [s] furan, isoindole, benzoxazo l, benzothiazole, benzimidazole, benzisooxazole, benzisothiazole, benzopyrazole, benzothiadiazole, benzotriazole, dibenzofuran, dibenzothiophene, carbazole, pyridine, bipyridine, pyrazine, pyrazole, pyrimidine, pyridazine, 1,3,5-tri-azaz, 1,3,5-triazaz, 1,3,5-triazaz 1,2,4,5-triazine, tetrazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, 1,8-naphthyridine, 1,5-naphthyridine, 1,6-naphthyridine, 1,7-naphthyridine, phthalazine, pyridopyrimidine, purine, pteridine or quinolysine, 4H-quinolizine, diphenylether, anthracene, benzopyrrole, benzooxathiadiazole, benzooxadiazole, benzopyridine, benzopyrazine, benzopyraz idin, benzopyrimidine, benzotriazine, indolysin, pyridopyridine, imidazopyridine, pyrazinopyrimidine, carbazole, aciridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridin, phenanthroline and phenanthrene, which may also be substituted.

Preferred alkyl groups include methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, 2-methylpropyl, tert-butyl, pentyl, 2-methylbutyl, 1,1-dimethylpropyl, hexyl, heptyl, octyl, 1,1 , 3,3-tetramethylbutyl, nonyl, 1-decyl, 2-decyl, undecyl, dodecyl, pentadecyl and eicosyl groups.

Preferred cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl groups, which optionally contain branched or unbranched alkyl substituents.

Preferred alkenyl groups include vinyl, allyl, 2-methyl-2-propene, 2-butenyl, 2-pentenyl, 2-decenyl and 2-eicosenyl groups.

Preferred heteroaliphatic groups include the aforementioned preferred alkyl and cycloalkyl radicals in which at least one carbon unit is substituted with O, S, or with an NR ⁸ or NR ⁸ R ⁹ group, and R ⁸ and R ^{9 are} independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, or an aryl group.

According to the invention, it is particularly preferred that the carboxylic acid amides have branched or unbranched alkyl groups or alkoxy groups with 1 to 20 carbon atoms, preferably 1 to 12, suitably having from 1 to 6, in particular from 1 to 4 carbon atoms, and cycloalkyl groups or cycloalkyloxy groups with 3-20 carbon atoms, preferably with 5-6 carbon atoms.

The residue R may contain substituents. Preferred substituents include halogens, in particular fluorine, chlorine, bromine, as well as alkoxy radicals and hydroxyl radicals.

Amides of alpha-hydroxycarboxylic acid in the implementation of the method according to the invention can be used individually or in the form of a mixture of two, or three, or more amides of alpha-hydroxycarboxylic acid. Particularly preferred alpha-hydroxycarboxylic acid amides include alpha-hydroxyisobutyric acid amide and alpha-hydroxyisopropionic acid amide.

In addition, in one embodiment of the method according to the invention, of particular interest is the use of such amides of alpha-hydroxycarboxylic acid, which are obtained by cyanohydrin synthesis from ketones or aldehydes and hydrocyanic acid. In this case, at the first stage, a carbonyl compound, for example, a ketone, in particular acetone, or an aldehyde, for example, acetic aldehyde, propanal, butanal, is reacted with hydrocyanic acid to give the corresponding cyanohydrin. It is particularly preferable to carry out the reaction of acetone and / or acetaldehyde, usually using a small amount of alkali or amine as a catalyst. In the next step, the cyanohydrin thus obtained is reacted with water to produce alpha-hydroxycarboxylic acid amide.

This reaction is usually carried out in the presence of a catalyst. For this purpose, in particular, manganese oxide catalysts can be used, which are described, for example, in European patent applications EP-A-0945429, EP-A-0561614, as well as EP-A-0545697. Moreover, manganese oxide can be used in the form of manganese dioxide obtained by treating manganese sulfate with potassium permanganate in an acidic medium (cf. Biochem.J., 50 S.43 (1951) and J.Chem.Soc., 1953, S.2189, 1953) or by electrolytic oxidation of manganese sulfate in an aqueous solution. In general, the catalyst is repeatedly used in the form of a powder or granulate with an appropriate grain size. In this case, in particular, it is possible to use the so-called slurry (slurry) reactors or reactors with a solid layer, which can also be operated as a bulk layer and which are also described in European application EP-A-956898. In addition, the hydrolysis reaction can be catalyzed by enzymes. Suitable enzymes include, but are not limited to, nitrile hydratase. This reaction is described as an example in Screening, Characterization and Application of Cyanide-resistant Nitrile Hydratases Eng. Life Sci. 2004, 4, No.6. In addition, the hydrolysis reaction can be catalyzed by acids, in particular sulfuric acid. This is presented, inter alia, in JP Hei 4-193845.

Alcohols that are successfully applicable in the implementation of the method according to the invention include all alcohols known to the person skilled in the art, as well as precursor compounds of alcohols which, at the indicated pressure and temperature, can react with alpha-hydroxycarboxylic acid amides by alcoholysis. Preferably, the α-hydroxycarboxylic acid amide production reaction is carried out by alcoholysis with alcohol, which includes 1-10 carbon atoms, particularly preferably 1 to 5 carbon atoms. Preferred alcohols include methanol, ethanol, propanol, butanol, in particular n-butanol and 2-methyl-1-propanol, pentanol, hexanol, heptanol, 2-ethylhexanol, octanol, nonanol and decanol. It is particularly preferable to use methanol and / or ethanol as the alcohol, wherein methanol is extremely suitable. It is also fundamentally possible to use precursors of alcohols. For example, alkyl formates can be used. Particularly advantageous is the use of methyl formate or a mixture of methanol and carbon monoxide.

The reaction between an alpha-hydroxycarboxylic acid amide and an alcohol in the framework of the invention is carried out in a pressure reactor. Under such, in principle, mean the reaction space, allowing to maintain high pressure during the reaction. In this context, increased pressure means a pressure in excess of atmospheric, i.e., in particular, above 1 bar. In the framework of the invention, the pressure can range from values in excess of 1 bar to values not exceeding 100 bar. From the foregoing, it inevitably follows that both during the alcoholysis reaction of the alpha-hydroxycarboxylic acid amide according to the invention, and during the separation (removal) of ammonia from the product mixture, the pressure exceeds atmospheric or is greater than 1 bar. In particular, this means that the ammonia formed during the reaction is isolated from the mixture by distillation under a pressure exceeding 1 bar, and for the distillation removal of ammonia, auxiliary means, for example, a cleaning gas, are not used at all.

In the mixture of products within the framework of the invention, the concentration of not only ammonia, but also the alcohol that has not undergone the reaction, is reduced. It is in the case when methanol is used for alcoholysis, as a result, a mixture of products is obtained containing ammonia and methanol are components that are very difficult to separate from each other. In the simplest case, to reduce the concentration of ammonia and alcohol in the mixture of products (depletion of the mixture), both of these components are removed from the mixture of products directly as a mixture of substances. Then these substances are subjected to separation operations, for example rectification. On the other hand, within the framework of the invention, it is also possible to isolate both components - alcohol (methanol) and ammonia - at one stage from a mixture of products and also separate both components - ammonia and alcohol (methanol) from each other.

In a preferred embodiment of the method according to the invention, it may be particularly appropriate that the stages of the chemical reaction and the removal of ammonia / alcohol from the product mixture are spatially separated from each other and carried out in various devices. For this purpose, it is possible, for example, to provide one or more reactors operating under pressure, and to connect them to a distillation column of high pressure. In this case, we are talking about one or more reactors, which are located on a separate site outside the distillation / reaction column.

In the broadest sense, a continuous process for producing alpha-hydroxycarboxylic acid esters in which the reaction of alpha-hydroxycarboxylic acid amide with alcohol (starting components) is carried out in the presence of a catalyst, to obtain a mixture of products that contains alpha-hydroxycarboxylic acid esters of ammonia that has not undergone the reaction alpha hydroxycarboxylic acid amide, characterized in that

a) streams of the starting components, including alpha-hydroxycarboxylic acid amide, alcohol and a catalyst, are fed to a pressure reactor;

b) in a pressure reactor, the streams of the starting components are reacted with each other under pressure ranging from a value of more than 1 bar to 100 bar;

c) the product mixture obtained in step b) comprising a mixture of alpha-hydroxycarboxylic acid esters, an unreacted alpha-hydroxycarboxylic acid amide and a catalyst is withdrawn from the reactor; and

d) reduce the concentration of alcohol and ammonia in the product mixture, and the ammonia is removed by distillation under pressure, which constantly exceeds 1 bar.

In accordance with the foregoing, a particularly expedient embodiment of the method provides that

b1) the reaction of the starting components with each other in a pressure reactor is carried out under pressure ranging from 5 bar to 70 bar;

b2) the pressure obtained in step b1) of the product mixture is reduced to a value less than the pressure in the pressure reactor, and above 1 bar;

c1) obtained in step b2) the mixture of products under reduced pressure is fed to a distillation column;

c2) through the head of the distillation column, ammonia and alcohol are removed by distillation, and the pressure in the distillation column is maintained in the range from values exceeding 1 bar to values not exceeding 10 bar; and

d1) obtained in step c2) a mixture of products with a reduced concentration of ammonia and alcohol, containing alpha-hydroxycarboxylic acid esters, an un-reacted alpha-hydroxycarboxylic acid amide and catalyst, is withdrawn from the column.

According to this variant of the method, the chemical reaction of the starting components and the removal of ammonia / alcohol take place in two different units, spatially separated from each other. In other words, the reactor (reaction space) and the separator for separating ammonia / alcohol from the product mixture are separated. This has the advantage that various pressure ranges can be used for the reaction of the starting materials and subsequent separation of ammonia / alcohol. Due to the separation of the method into a reaction step in the reactor with a pressure higher than that at the separation step in the pressure column, both stages are carried out at increased pressure, i.e. above 1 bar, it is possible - in a way that was not easy to foresee - in addition to the previously agreed advantages in the first embodiment of the method according to the invention, to again significantly improve the separating effect and increase the separation efficiency of the ammonia-alcohol mixture.

These quality indicators can be further improved by repeating the reaction once or repeatedly in a pressure reactor with a mixture of products, the ammonia and alcohol content of which is reduced in the lower part of the separation (distillation) column, the reaction stage being carried out in a series of pressure reactors connected in series.

Accordingly, a process variant which is characterized in that

e) the pressure in the mixture removed in step d1) is increased to a value in the range from 5 to 70 bar;

f) a mixture in which the pressure is thus increased according to step e) is fed to a further pressurized reactor and reacted again; and

g) steps b2), c1), c2) and d1) are repeated according to the above listing.

Therefore, it is especially advisable to extract a mixture in which the concentration of ammonia and alcohol is low (lean mixture) from a level above the bottom of the first distillation column, increase the pressure in it to a level higher than that in the distillation column, then feed it to a second pressure reactor, from where , after repeated reaction under the influence of suspended pressure and temperature, obtain a mixture of products that has passed the reaction twice, remove pressure from the latter to a value lower than in the second reactor pressure, and greater than 1 bar, and then return it to the first distillation column below the plate from which the high pressure reactor was supplied, but above the lower part of the first distillation column, where ammonia and alcohol are re-separated by distillation through the head of the column with obtaining a mixture in which the concentration of ammonia and alcohol is twice reduced.

This stage of the process can be repeated an arbitrary number of times; for example, three or four repetitions are especially useful. Thus, a method is preferred which is characterized in that the reaction in the high pressure reactor, depressurization of the mixture undergoing conversion, feeding to the first distillation column, lowering the concentration of ammonia and alcohol in the first distillation column, selecting the lean mixture, increasing the pressure in the lean mixture and feeding it to yet another pressurized reactor is repeated many times, moreover, in the lower part of the distillation column after n series-connected pressurized reactors, a mixture of oduktov, n-fold depleted ammonia and alcohol (with a reduced concentration of ammonia and an alcohol). Moreover, n can be a positive integer. Preferably, n is in the range of 2 to 10.

In an expedient variant of the method, it is provided that the steps mentioned above and previously specified from e) to g) are repeated many times.

Particular process variants include conversion and depletion four times using four series-connected pressure reactors to produce a product mixture four times depleted in ammonia and alcohol. This variant of the method, therefore, is characterized in that steps e) to g) are repeated at least two more times, so that the interaction takes place in a total of at least four pressure reactors connected one after another.

In this regard, it is obvious for a specialist that at each stage of the interaction there is a sufficient amount of alcohol. Therefore, it is advisable to reduce the concentration of alcohol in the mixture of products only partially. On the other hand, alcohol can be separately supplied for each specific stage of interaction.

For the above variant of the method, various temperature ranges in the column and reactor turned out to be especially expedient.

According to the method variant described above, the interaction in step c) can be carried out at a higher pressure than the distillation of ammonia in step d). It is advisable that the pressure difference is at least 10 bar, particularly preferably at least 40 bar, and very preferably at least 50 bar.

Thus, the temperature in the high-pressure distillation column is generally and preferably in the range of from about 50 ° C to about 160 ° C. The exact temperature is usually set using a boiling system depending on the available pressure.

Preferably, the temperature in the reactor is in the range of about 120 ° C-240 ° C. It is especially advisable to reduce the temperature from the reactor to the reactor, for example, with an interval ranging from 3-15 ° C, preferably 4-10 ° C, and it is extremely advisable with a step of 5 ° C. This positively affects the selectivity of the reaction.

Another measure aimed at increasing selectivity may consist in reducing the volume of each subsequent reactor compared to the previous one. With a decrease in reactor volume with increasing turnover, an improvement in selectivity is also obtained. It is advisable that the reduction in reactor volume is in the range from 1% to 50%, particularly preferably from 2% to 20%, and very preferably from 5% to 10%, in each case, relative to the volume of the larger reactor.

Various activities aimed at increasing selectivity can be combined with special benefits. Thus, the specialist is able to optimize selectivity by simple means by varying pressure, temperature and residence time. It is especially advisable that the conversion takes place at a temperature in the range from 200 to 220 ° C, and it is possible to optimize the residence time. Due to the separation of ammonia from the reaction mixture, the conversion can be repeated many times, and in this way it is possible to organize a particularly expedient variant of the reaction, i.e. with high selectivity at low costs.

As already mentioned above, it is advisable to extract a mixture of products intended for output from the distillation column of high pressure at certain points of the column. In this case, for orientation, the distance between the output point and the lower part of the column (cube) is used as a relative position. In the framework of the invention, it is especially advisable to act so that the mixture of products in which the pressure is reduced, according to step c1), after each new interaction in the high-pressure reactor is introduced into the distillation column closer to its lower part compared to the place of introduction in the previous step c1).

This variant of the method may have the advantage that the interaction in step b) is carried out at a pressure in the range from 20 bar to 90 bar, particularly preferably from 40 bar to 80 bar, and very preferably from 50 bar to 70 bar.

The ammonia distillation according to step d) is expediently carried out under a pressure in the range from 1.2 bar to 10 bar, particularly preferably from 1.5 bar to 3 bar.

In addition to the described embodiment, in which the reaction of alpha-hydroxycarboxylic acid amide with alcohol is carried out separately from the removal of ammonia formed in this case, inter alia, in two spatially separated but connected devices, it may be preferable to carry out an interaction step and a removal step in another modification of the method in the same device. The high-pressure reactor and the high-pressure distillation column are then realized in the same device, combining them.

In accordance with this particular embodiment of the invention, it includes a continuous process for producing alpha-hydroxycarboxylic acid esters, in which the alpha-hydroxycarboxylic acid amide is reacted with alcohol (starting components) in the presence of a catalyst to produce a product mixture that contains alpha- hydroxycarboxylic acids, ammonia, non-reacted alpha-hydroxycarboxylic acid amide; moreover, the method is characterized in that

a ') streams of the starting components, including alpha-hydroxycarboxylic acid amide, alcohol and a catalyst, are fed to a pressure reactor;

b ') in the reactor of high pressure carry out the reaction of the streams of the starting components with each other under pressure, in the range from more than 1 bar to 100 bar;

c ') reduce the concentration of alcohol and ammonia in the mixture of products, and the ammonia is removed by distillation under a pressure that constantly exceeds 1 bar, without resorting to additional cleaning agents; and

d ') obtained in step c') a mixture of products depleted in respect of ammonia and alcohol, including alpha-hydroxycarboxylic acid esters, non-reacted alpha-hydroxycarboxylic acid amide and catalyst, is withdrawn from the reactor.

The pressure range that must be maintained in the previously described embodiment according to the invention, preferably in the reaction distillation column operating as a reactor, can be varied within wide limits. Moreover, a preferred embodiment of the invention implies that steps a ') to c') are carried out simultaneously in a reaction-distillation column under a pressure ranging from 2 bar to 50 bar, preferably from 5 bar to 40 bar. Particularly appropriate is the method, characterized in that the steps from a ') to c') are carried out simultaneously in a reaction-distillation column under pressure ranging from 10 bar to 30 bar.

In a preferred embodiment of the method according to the invention, the reaction of the starting components is carried out in a reaction distillation column designed as a high pressure column, and the ammonia formed during the reaction is continuously removed by distillation through the head of the column. This leads to the unexpected effect that ammonia can be easily separated and obtained as a high-purity product without pressure reduction. In addition, of particular interest is the option in which ammonia is removed by distillation through the head of the column under pressure, and alcohol is removed from the column through the bottom or using a side stream. Due to the appropriately planned separation efficiency of the reaction distillation column, it is thus possible to achieve a direct separation of ammonia and alcohol.

The temperature during the interaction according to the invention can be varied within wide limits, and in general, with increasing temperature, the reaction rate increases. The upper temperature limit is generally given by the boiling point of the alcohol used. Preferably, the reaction temperature is in the range from 40-300 ° C, particularly preferably from 120-240 ° C, and very preferably from 180 ° C to 220 ° C.

It may be advantageous for the invention that no more than 10 wt.%, Preferably no more than 5 wt.%, And particularly preferably no more than 1 wt.% Of the alcohol in the reaction phase is removed from the reaction system through the gas phase. This measure allows the reaction to be carried out with a significant reduction in costs. Moreover, the reaction system has the advantage that the pressure in it is constantly maintained at a level above 1 bar. The composition of the reaction system, in particular, may include sections of the system in which the interaction takes place, and zones of the system in which ammonia is separated from products and alcohol, in particular distillation columns. Accordingly, the separation of ammonia and alcohol can preferably take place with very high efficiency under a pressure in excess of 1 bar, particularly preferably in excess of 1.5 bar. In this case, it may be especially advisable to remove from the reaction system by distillation together with ammonia not more than 10 wt.% Alcohol relative to the amount fed during the stay.

It is advisable that the residence time is from 30 seconds to 2 hours, particularly preferably from 1 to 30 minutes, and very preferably from 2 to 15 minutes. These data relate preferably to the reactor volume. In the case of using several reactors, the calculation is carried out using the sum of the volumes of high pressure reactors, not taking into account the volume of distillation devices. When using reactive distillation columns, residence times are calculated according to the volume of the reactive distillation column.

In one embodiment, any multi-stage high pressure distillation column that preferably has two or more stages (cascades) of separation can be used in the present invention. As the number of separation steps in the present invention, the number of plates in a plate column or the number of theoretical plates in the case of a packaged column or a filled column is indicated.

Examples of multi-stage distillation columns with plates include those with cap, perforated, tunnel, valve, slotted, perforated-slotted plates, perforated-cap plates, nozzle, centrifugal plates, examples of multi-stage distillation columns with ring rings with fillers , Pall rings, Burl saddles, saddles, and to examples of multi-stage distillation columns with bags, such as Mellapak (Sulzer), Rombopak (Kühni), Montz-Pak (Montz), and pa Keta with catalyst pockets, for example, Kata-Pak.

It is also possible to use a distillation column combining plate regions, filler regions or packet regions.

A mixture of products in which the concentration of ammonia is reduced contains, inter alia, the desired alpha-hydroxycarboxylic acid ester. In a suitable embodiment of the method for further isolation and purification of ether, it is possible to withdraw a mixture of products with a reduced concentration of ammonia through the lower part of the distillation column and feed it to another, second distillation column, where, obtaining a mixture in which both the concentration of ammonia and alcohol are reduced , the alcohol is removed by distillation through the head of the column and is preferably returned to the reactor.

To further isolate and obtain an alpha-hydroxycarboxylic acid ester from a mixture with a reduced concentration of ammonia and alcohol, in this case, a method is preferred in which a mixture with a reduced concentration of ammonia and alcohol is discharged through the bottom of another distillation column and fed to another, next distillation column, in which the alpha-hydroxycarboxylic acid ester is removed by distillation through the head of the column, and the mixture thus obtained with a reduced concentration of alpha-hydroxycarboxylic carboxylic esters Lot, ammonia and alcohol, if necessary - after further purification steps - is recycled to the reactor. The product obtained in the head of the column — alpha-hydroxycarboxylic acid ester — is of high purity, and it is extremely advantageous, for example, to submit it to further reaction steps to obtain alkyl (meth) acrylates.

It is advisable that the distillation apparatus contains, as already described, at least one zone, referred to as a reactor, in which at least one catalyst is provided. This reactor may, as said, preferably be located inside a distillation column.

It turned out that in the framework of the invention for the described method is acceptable a wide range of quantitative ratios of the starting components. Thus, alcoholysis can be carried out with a relatively significant excess or deficiency of alcohol relative to alpha-hydroxycarboxylic acid amide. Particularly preferred are processes in which the reaction of the starting components is carried out at a molar ratio of alcohol to amide of alpha-hydroxycarboxylic acid in the range from 1: 3 to 20: 1. A ratio of from 1: 2 to 15: 1 is particularly advisable, and even more appropriate is from 1: 1 to 10: 1.

In addition, methods are preferred which are characterized in that hydroxyisobutyramide is used as the alpha-hydroxycarboxylic acid amide and methanol is used as the alcohol.

The reaction according to the invention is carried out in the presence of a catalyst. The reaction can be accelerated, for example, by basic catalysts. These include homogeneous as well as heterogeneous catalysts.

Of particular interest for the implementation of the method according to the invention is the use of lanthanide compounds as catalysts, the waterproof compounds of lanthanides being particularly preferred. The use of this type of homogeneous catalysts in the method according to the invention is new, it gives unexpectedly favorable results. The expression "waterproof" means that in the presence of water, the catalyst retains its catalytic properties. Accordingly, the reaction according to the invention can be carried out in the presence of water in amounts of up to 2 wt.% Without the catalytic ability of the catalyst being significantly affected. In this sense, the expression “substantially” means that the rate and / or selectivity of the reaction is reduced by at most 50% compared with the reaction in the absence of water.

By lanthanide compounds are meant compounds of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Td, Dy, Ho, Er, Tm, Yb and / or Lu. It is preferable to use a lanthanide compound including lanthanum.

It is advisable that the lanthanide compound has a solubility in water of at least 1 g / l, preferably at least 10 g / l at 25 ° C.

Preferred lanthanide compounds are salts, the oxidation state of which is preferably 3.

Particularly preferred water resistant lanthanide compounds are La (NO ₃ ) ₃ and / or LaCl ₃ . These compounds can be added to the reaction mixture as salts or synthesized in situ.

Other homogeneous catalysts that can be successfully used in the present invention include alkali metal alkoxides and organo-metal compounds of titanium, tin and aluminum. It is preferable to use titanium alcoholate or tin alcoholate, such as tetraisopropyl oxide-titanium or tetrabutyl oxide-tin.

A particular embodiment of the process involves the use as a catalyst of a soluble metal complex compound containing titanium and / or tin, and alpha-hydroxycarboxylic acid amide.

Another particular embodiment of the method according to the invention provides that metal trifluoromethanesulfonate is used as a catalyst. Preferably, trifluoromethanesulfonate of a metal selected from the group consisting of elements of groups 1, 2, 3, 4, 11, 12, 13 and 14 of the Periodic system is used. Among them, metal trifluoromethanesulfonates are preferably used in which the metal is one or more lanthanides.

In addition to the preferred variants of homogeneous catalysis, in certain circumstances it is also advisable to use a method using heterogeneous catalysts. Catalysts that can be used successfully include, but are not limited to, magnesium oxide, calcium oxide, and also basic ion exchangers and the like.

Thus, for example, process variants may be preferred in which the catalyst is an insoluble metal oxide containing at least one element selected from the group consisting of Sb, Sc, V, La, Ce, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Co, Ni, Cu, Al, Si, Sn, Pb and Bi.

Alternatively, process variants may be preferred in which an insoluble metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, Cu, is used as a catalyst. Ga, In, Bi, and Te.

Ammonia released during alcoholysis in the framework of the method according to the invention can, for example, be easily returned to the general process for the production of alkyl (meth) acrylates. Possible, for example, the reaction of ammonia with methanol with the formation of hydrocyanic acid. This is described, for example, in European patent application EP-A-0941984. In addition, hydrocyanic acid can be obtained from ammonia and methane using the BMA method or the Andrusov method, these methods being described in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition on CD-ROM, with the keyword "Inorganic Cyano Compounds". Ammonia can also be returned in the process of ammoxidation, such as, for example, the industrial synthesis of acrylonitrile from ammonia, oxygen and propene. The synthesis of acrylonitrile is described (keyword Sohio-Prozess) in the Indsutrial Organic Chemistry K. Weisermehl and H.-J. Arre on p. 307 ff.

The general process flow of the first embodiment according to the invention is illustrated with reference to FIG.

According to a particularly preferred embodiment, alcoholysis, preferably methanolysis, can be carried out in the combination of a high pressure distillation column and several high pressure reactors shown in FIG. Hydroxyisocarboxylic acid amide, for example hydroxyisobutyramide, is fed via line (1) together with methanol through line (2) and a mixture of methanol and catalyst through line (3) through line (4) to the first high pressure reactor (R -one). Under the above reaction conditions, a reaction mixture is formed in the reactor (R-1) from a hydroxyisocarboxylic acid ester of ammonia, unreacted hydroxyisocarboxylic acid amide and methanol, a catalyst, as well as traces of a by-product. At this mixture, after it leaves the reactor (R-1), the pressure is reduced, bringing it to lower values, and it is sent to the first high-pressure column (K-1) through pipeline (5). It is advisable that the column was equipped with bags. There, ammonia with a part of methanol is separated from the reaction mixture and obtained in the head of the column as a distillate. The higher boiling components, hydroxyisocarboxylic acid ester, by-product and unreacted hydroxyisobutyramide together with the remaining methanol are again withdrawn from the column, compressed, to the pressure corresponding to that in the reactor, and fed to the second reactor (R-2). The reaction is preferably carried out in 4 reactors connected in series (R-1 to R-4). The product mixture leaving the bottom of the column (K-1) consists of a hydroxyisocarboxylic acid ester, traces of a by-product and hydroxyisobutyramide. Through the pipeline (9) it is sent to a distiller (K-2). There, a hydroxyisocarboxylic acid ester is obtained in the form of a distillate, and it is withdrawn through a pipeline (10). The mixture of hydroxyisobutyramide and catalyst is withdrawn from the column (K-2) through a cube and partially returned via pipelines (12) and (4) to the first high pressure reactor (R-1). Part of the stream (11) is fed to a thin-layer evaporator (D-1). It makes it possible to remove the mixture from amide, a high-boiling by-product and a catalyst through a pipeline (13).

The mixture of ammonia and methanol obtained in the column (K-1) as a distillate is compressed and piped (14) to another column (K-3). There, ammonia, which is obtained in its pure part from the column head, is separated from methanol, which is returned via pipelines (15) and (4) to the first high-pressure reactor (R-1).

Reaction conditions in the column and 4 outside reactors Temperature [° C] 120-240 The pressure in the reactor [bar] 5-70 Column pressure [bar] 1-10 n _CH3OH : n _amide 1: 3 - 20: 1

The overall process flow of the second embodiment according to the invention is illustrated with reference to FIG. 2.

As an example, alcoholysis, preferably methanolysis, can be carried out in the installation shown in Figure 1. Hydroxyisocarboxylic acid amide, for example hydroxyisobutyramide, is fed via line (1) along with methanol through line (2) and a mixture of methanol and catalyst through line (3) to a reaction distillation column (K-1). The column is designed as a high pressure column and is preferably equipped with trays. Under the above reaction conditions, a reaction mixture of hydroxyisocarboxylic acid ester and ammonia, unreacted hydroxyisocarboxylic acid amide and methanol, a catalyst, and also traces of a by-product is formed on the plates of the column. Ammonia is obtained in the form of a distillate and discharged through a pipeline (7). The higher boiling components, hydroxyisocarboxylic acid ester, by-product and unreacted starting components hydroxyisobutyramide and methanol leave the bottom of the column. Through a pipe (6) this mixture is sent to another distiller (K-2). Methanol is obtained in this column as a distillate, which can be returned to the column (K-1) via pipelines (9) and (5). The mixture obtained in the cube from the hydroxyisocarboxylic acid ester, by-product and hydroxyisobutyramide is sent via line (8) to the distiller (K-3). There, a hydroxyisocarboxylic acid ester is obtained in the form of a distillate, and it is withdrawn through a pipeline (10). The mixture of hydroxyisobutyramide and catalyst is withdrawn from the column through a cube and partially returned via pipelines (12), (4) and (5) to the column (K-1). Part of the stream (11) is fed to a thin-layer evaporator (D-1). It makes it possible to remove the mixture from amide, a high-boiling by-product and a catalyst through a pipeline (13).

Reaction conditions in a high pressure reaction distillation column Temperature [° C] 120-240 Column pressure [bar] 2-40, preferably 5-30 n _CH3OH : n _amide 1: 3-20: 1

Below is a more detailed explanation of the present invention based on examples.

Example 1

157 g / h of a mixture of methanol with a catalyst with a catalyst fraction of 0.8 wt.%, And 35 g / were supplied to a laboratory experimental setup consisting of batchers of initial components and a continuous reactor-boiler with a stirrer. h alpha hydroxyisobutyramide. The reaction was carried out using La (NO ₃ ) ₃ as a catalyst. The resulting mixture of products was analyzed by gas chromatography. The molar selectivity for methyl ester of alpha-hydroxyisobutyramide relative to alpha-hydroxyisobutyramide was 98.7%, and an ammonia concentration of 0.7 wt.% Was obtained in the product mixture.

Examples 2-7

Table 1 shows other examples implemented in the specified experimental setup with a molar ratio of the starting components MeOH: HIBA equal to 14: 1, but with different values of the reaction temperature and duration of stay.

Table 1 Example Reaction temperature [° C] Stay time [min] Alpha hydroxyisobutyric acid methyl ester selectivity [%] wt.% [NH ₃ ] 2 200 5 95 0.356 3 220 5 98 0.588 four 180 10 92 0.154 5 200 10 94 0.285 6 200 thirty 89 0.611 7 220 thirty 89 0.791

From table 1 it is obvious that the selectivity to HIBSM (methyl ester of α-hydroxyisobutyric acid) depends not only on the concentration of ammonia in the reaction mixture in the reactor, but also on such technical parameters of the reaction as the length of stay and temperature, and thus on the exact carrying out the reaction.

Example 8

A mixture of methanol with a catalyst with a catalyst fraction of 1.0 wt.% And alpha-hydroxyisobutyramide in a molar ratio of 7: 1 was continuously fed into the indicated laboratory experimental unit during the experiment lasting 48 hours. The conversion of alpha-hydroxyisobutyric acid (HIBSM) and ammonia to methyl ester was effective at a pressure of 75 bar and at a reaction temperature of 220 ° C, with a residence time of 5 minutes. The reaction was carried out using La (NO ₃ ) ₃ as a catalyst. The resulting mixture of products was analyzed by gas chromatography. The molar selectivity for methyl ester of alpha-hydroxyisobutyramide relative to alpha-hydroxyisobutyramide was 99%, and in the mixture of products an ammonia concentration of 0.63 wt.% Was obtained.

Examples 9-12

A mixture of methanol with a catalyst with a catalyst fraction of 0.9 wt.% And alpha-hydroxyisobutyramide in a molar ratio of 10: 1 was continuously fed into the indicated laboratory experimental unit during the experiment lasting 48 hours. The conversion of alpha-hydroxyisobutyric acid (HIBSM) and ammonia to methyl ester was effective at a pressure of 75 bar and at a reaction temperature of 200 and 220 ° C, and the residence time was 5 or 10 minutes. The resulting product mixture was analyzed by gas chromatography. The values of molar selectivity for methyl ester of alpha-hydroxyisobutyramide relative to alpha-hydroxyisobutyramide and the concentration of ammonia in the mixture of products are shown in table 2.

table 2 Example Reaction temperature [° C] Stay time [min] Hydroxyisobutyric Acid Methyl Selectivity [%] wt.% [NH ₃ ] 9 200 5 97 0.429 10 220 5 98 0.73 eleven 200 10 98 0.544 12 220 10 96 0.889

Claims (30)

1. A continuous method for producing alpha-hydroxycarboxylic acid esters, in which the alpha-hydroxycarboxylic acid amide is reacted with an alcohol as starting components in the presence of a catalyst to produce a product mixture that contains alpha-hydroxycarboxylic acid esters, ammonia, unreacted alpha-amide hydroxycarboxylic acid, as well as alcohol and a catalyst, characterized in that
a) streams of the starting components, including alpha-hydroxycarboxylic acid amide, alcohol and a catalyst, are fed to a pressure reactor;
b) in an overpressure reactor under pressure from 1 bar to 100 bar, the streams of the starting components interact with each other;
c) the product mixture obtained in step b), including alpha-hydroxycarboxylic acid esters, unreacted alpha-hydroxycarboxylic acid amide and a catalyst, is withdrawn from the pressure reactor; and
d) in the mixture of products reduce the content; alcohol and ammonia, and ammonia is removed by distillation under pressure, which is constantly maintained at a level above 1 bar, without resorting to additional cleaning agents. 2. The continuous method according to claim 1, characterized in that b1) the interaction of the starting components with each other in a pressure reactor is carried out under pressure ranging from 5 bar to 70 bar;
b2) the pressure obtained in step b1) of the product mixture is reduced to a value less than the pressure in the pressure reactor, and above 1 bar;
c1) obtained in step b2) the mixture of products under reduced pressure is fed to a distillation column;
c2) through the head of the distillation column, ammonia and alcohol are removed by distillation, and the pressure in the distillation column is maintained in the range from values exceeding 1 bar to values not exceeding 10 bar; and
d1) obtained in step c2) a mixture of products with a reduced concentration of ammonia and alcohol, containing alpha-hydroxycarboxylic acid esters, unreacted alpha-hydroxycarboxylic acid amide and catalyst, is withdrawn from the column. 3. The continuous method according to claim 2, characterized in that
e) the pressure in the product displayed in step d1) is increased to a value in the range from 5 to 70 bar;
f) a mixture in which the pressure is thus increased according to step e) is fed for reaction to another pressurized reactor and reacted again; and
g) steps b2), c1), c2) and d1) are repeated according to claim 2. 4. The continuous method according to claim 3, characterized in that the steps from e) to g) are repeated many times. 5. The continuous method according to claim 4, characterized in that steps e) to g) are repeated at least twice more, so that the interaction is carried out in a total of at least four pressure reactors connected one after another. 6. The continuous method according to claim 3, characterized in that the mixture of products in which the pressure is reduced, according to step c1), after each new interaction in the high-pressure reactor, is introduced into the distillation column closer to its cube compared to the place of introduction at the previous stage with one). 7. The continuous method according to claim 3, characterized in that the temperature in each subsequent reactor is reduced compared to the previous one. 8. The continuous method according to claim 7, characterized in that the temperature reduction is in the range from 3 to 15 ° C. 9. The continuous method according to claim 3, characterized in that the volume of each subsequent reactor is reduced compared to the previous one. 10. The continuous method according to claim 9, characterized in that the decrease in reactor volume is in the range from 2% to 20%, in each case, relative to the volume of a larger reactor. 11. The continuous method according to claim 1, characterized in that the interaction of step c) is carried out at a higher pressure than the distillation of ammonia in step d). 12. The continuous method according to claim 11, characterized in that the pressure drop is at least 40 bar. 13. The continuous method according to claim 1, characterized in that the distillation of ammonia in step d) is carried out under a pressure in the range from 1.5 bar to 3 bar. 14. The continuous method according to claim 1, characterized in that the interaction of the starting components according to step b) is carried out under pressure in the range from 50 to 70 bar. 15. The continuous method according to claim 1, characterized in that the interaction of the starting components is carried out at a molar ratio of alcohol to alpha-hydroxycarboxylic acid amide in the range from 1: 3 to 20: 1. 16. The continuous method according to claim 1, characterized in that the use of α-hydroxyisobutyric acid amide and / or α-hydroxyisopropionic acid amide. 17. The continuous method according to claim 15, characterized in that hydroxyisobutyramide is used as the alpha-hydroxycarboxylic acid amide, and methanol is used as the alcohol. 18. The continuous method according to one of claims 1 to 17, characterized in that the interaction is carried out at a temperature in the range of 120-240 ° C. 19. The continuous method according to one of claims 1 to 17, characterized in that the residence time during the interaction of the starting components is in the range from 1 to 30 minutes. 20. The continuous method according to claim 19, characterized in that the residence time is in the range from 2 to 15 minutes 21. The continuous method according to one of claims 1 to 17, characterized in that not more than 10% by weight of alcohol is removed from the reaction system by distillation together with ammonia relative to the amount fed during the stay. 22. The continuous method according to one of claims 1 to 17, characterized in that the interaction is catalyzed by at least one lanthanide compound. 23. The continuous method according to item 22, wherein the lanthanide compound is a salt. 24. The continuous method according to item 22, wherein the lanthanide compound includes lanthanum. 25. The continuous method according to one of claims 1 to 17, characterized in that the catalyst used is a soluble metal complex compound containing titanium and / or tin, and alpha-hydroxycarboxylic acid amide. 26. The continuous method according to one of claims 1 to 17, characterized in that metal trifluoromethanesulfonate is used as a catalyst. 27. The continuous method according to p. 26, characterized in that the use of trifluoromethanesulfonate metal selected from the group comprising elements of groups 1, 2, 3, 4, 11, 12, 13 and 14 of the Periodic system. 28. The continuous method according to claim 27, characterized in that metal trifluoromethanesulfonates are used in which the metal is one or more lanthanides. 29. The continuous method according to one of claims 1 to 17, characterized in that the catalyst is an insoluble metal oxide containing at least one element selected from the group consisting of Sb, Sc, V, La, Ce, Ti, Zr , Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Fe, Co, Ni, Cu, Al, Si, Sn, Pb and Bi. 30. The continuous method according to one of claims 1 to 17, characterized in that the catalyst is an insoluble metal selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, Cu, Ga, In, Bi, and Te.

Images