EP0000532B1 - Process for the preparation of vinyl oxirane - Google Patents

Description

The present invention relates to an improved process for the continuous production of vinyl oxirane.

Vinyloxirane, the monoepoxide of butadiene, is an important technical intermediate product which, due to its bifunctional character, is widely used in the field of polymers (FC Frostick, B. Phillips and PS Starcher, Journal of Am. Chem. Society, Vol 81, p 3351 (1959)). Vinyloxirane belongs to the class of compounds of epoxy vinyl monomers, which are characterized in that they can be converted into polyethers by reaction of the epoxy ring. These polyethers then contain free vinyl groups suitable for crosslinking or copolymerization with other olefinic compounds. However, it is also possible to polymerize vinyloxirane first on the olefinic double bond of the molecule, so that polymers are then obtained which have epoxy groups in the hydrocarbon chain which can be used for the further reaction.

In accordance with the potential technical importance of vinyloxirane, there has been no lack of attempts in the past to find simple and economical processes for producing vinyloxirane. So far, however, this has not been possible. The difficulties in the production of vinyloxirane consist on the one hand in the reaction of the reaction of butadiene with the epoxidation reagent, and on the other hand in the separation of the reaction mixtures obtained during the reaction and containing vinyloxirane.

Pummerer and Reindel (Chem .berichte 66, 335-339 (1933)) already proposed the use of perbenzoic acid in 1933 for the production of vinyl oxirane from butadiene. However, the yields achieved were only 40-60%.

The production of vinyloxirane using an ethereal solution of this percarboxylic acid containing 3% peracetic acid is also unsatisfactory since the yield is only 50% (Pudovik, Ivanow, Journal of Gen. Chem. Of USSR Vol 26, 3087 (1956) in Engl . translation).

F.C. Frostick et. al., (Journal of Am. Chem. Soc. 81, 3354 (1959)) cannot be achieved. When butadiene was reacted with peracetic acid obtained by oxidation of acetaldehyde in organic solvents, the yield was only 56%.

Peracetic acid obtained by oxidation of acetaldehyde is also described in Japanese Patent No. J 7-4046-284 as a suitable reagent for the production of vinyl oxirane. However, no yields are given.

Processes for the production of vinyloxirane, which use peracetic acid prepared from acetaldehyde for the epoxidation of butadiene, have the fundamental disadvantage that they require acetaldehyde as an auxiliary and that this auxiliary does not leave the process unchanged, so that recycling into the process is practically impossible. In addition, such processes are complex to carry out industrially, since an additional oxidation stage is required. In addition, the oxidation of acetaldehyde or other aldehydes to peracetic acid or percarboxylic acids is a reaction which is difficult to carry out, the safety risks of which are not insignificant in technical application due to the highly explosive aldehyde peracrylates which occur as intermediates (D. Swern, "Organic Peroxides", Vol 1, pp. 353, 354; Wiley-Interscience (1971)).

British Patent 735,974 (Union Carbide Corp.) proposes using acetaldehyde or propionaldehyde monoperacylate for the epoxidation of butadiene to vinyloxirane, likewise obtained by oxidation of the corresponding aldehydes.

The conversion of acetaldehyde monoperacetate in the reaction with butadiene is only 33%. The subsequent distillative processing of such a reaction mixture to obtain vinyloxirane takes place in the presence of the per compound, which precludes industrial use because of the existing risk of explosion.

Even the use of special procedural measures, such as those proposed in German Patent 1,216,306 for carrying out epoxidations, do not bring the desired success in the case of butadiene, as can be seen in Example 3 of this patent, where the epoxidation of butadiene after this Process with peracetic acid only provides a 68% selectivity for vinyl oxirane.

US Pat. No. 3,053,856 describes the reaction of acetonitrile and hydrogen peroxide in the presence of butadiene, vinyloxirane being the main product according to Example XII of this patent. However, since the carboxylic acid amide corresponding to the particular nitrile used is obtained in this process, which is to be regarded as a co-product and either has to be used for a suitable use or has to be converted back into the nitrile by dehydration, there is no technically satisfactory solution to the problem of producing vinyl oxirane.

umgewandelt. Das Kohlenwasserstoffperoxid R-OOH wirkt also als Sauerstoffüberträger, so dass nach Abgabe des Peroxid-Sauerstoffs der entsprechende Alkohol als Koppelprodukt anfällt und häufig als unerwünschtes Nebenprodukt entfernt werden muss. Die technischen Einsatzmöglichkeiten eines solchen Verfahrens sind dementsprechend begrenzt, da nicht in jedem Falle das Nebenprodukt Alkohol verwertet werden kann.The use of alkyl hydroperoxides, such as cumene and tert-butyl hydroperoxide, for the epoxidation of dienes under the catalytic influence of molybdenum or vanadium compounds has been described by Sheng and Zajacek (Journal of Organic Chemistry Vol 35, 6, 1839-1843 (1970) ). Butadiene can be converted into vinyl oxirane using this process with 85% selectivity leads. The alkyl hydroperoxide R-OOH in this reaction, as can be seen from equation (1), in the corresponding alcohol R-OH

converted. The hydrocarbon peroxide R-OOH thus acts as an oxygen carrier, so that after the peroxide oxygen has been released, the corresponding alcohol is obtained as a by-product and often has to be removed as an undesirable by-product. The technical application possibilities of such a process are accordingly limited, since the by-product alcohol cannot be used in every case.

Another process, which is described in Belgian patent 747,316, involves the reaction in the presence of vinyladirane from butadiene and hydrogen peroxide. of a tin-containing catalyst system. In addition to the disadvantage that a solvent, such as n-propanol, is required to carry out the reaction, which in turn can react with vinyloxirane that has already formed, high losses in the product are to be expected, which are due to the fact that the product used Hydrogen peroxide after the reaction with the butadiene-forming water reacts with vinyloxirane with cleavage of the epoxy ring. Furthermore, the separation of the catalyst from the reaction mixture is not an easy task on an industrial scale.

Just as numerous as the proposals that have been made to achieve improvements in the conduct of the epoxidation of butadiene to vinyloxirane have been the efforts made to overcome the problems encountered in the technical implementation of the separation of vinyloxirane-containing mixtures . These problems when working up mixtures which contain vinyloxirane are essentially due to the fact that the epoxy ring in the molecule of vinyloxirane very easily undergoes side reactions, which in some cases leads to considerable losses of vinyloxirane, and thus the economy of a technical process for the preparation of Vinyloxiran is no longer present. There is a particular risk of product loss if the mixtures from which vinyloxirane is to be separated contain acidic components.

This is always the case if vinyloxirane is prepared from butadiene and a percarboxylic acid, since the carboxylic acid corresponding to the percarboxylic acid is then inevitably contained in the reaction mixture.

In British patent specification 852 097 it is proposed for such a reaction mixture for the separation of vinyloxirane and the carboxylic acid to remove the carboxylic acid, for example acetic acid, by firstly dissolving a solution of vinyloxirane and the carboxylic acid in an organic, water-insoluble solvent, such as chlorinated hydrocarbons, and then extracting the solution with water or an aqueous solution of an inert alkali metal salt at temperatures below 15 ° C. This extraction process is complex since it not only requires an additional solvent, but also requires a subsequent separation of the water from the carboxylic acid if the carboxylic acid is to be recovered. Obtaining carboxylic acids from aqueous solutions by distillation is a task that can only be accomplished with considerable effort because of the formation of azeotropic mixtures.

The scope of the measures technically necessary for such an extraction process for the production of vinyloxirane can be found in US Pat. No. 3,019,234. The solution resulting from the addition of the largely water-insoluble solvent containing vinyl oxirane and the carboxylic acid must be extracted below 25 ° C with water or an aqueous solution. The extraction effort is considerable. Example 1 of the above-mentioned patent shows that 10 theoretical extraction stages are required. In addition, work must be carried out at 0 ° C. The problem solution for the lossless separation of vinyloxirane and carboxylic acid given by this process for the production of vinyloxirane is not satisfactory, since there are not insignificant amounts of vinyloxirane in the aqueous phase after extraction.

In French patent specification 1 468 814 it is proposed that the free carboxylic acid obtained in this case after the epoxidation of butanediene - in this case acetic acid - contains reaction mixture which also contains an acetic acid ester as solvent, vinyl oxirane and butadiene, with strong bases, such as alkali or alkaline earth metal hydroxides to neutralize free carboxylic acid, which is thus prevented from reacting with vinyl oxirane. After the neutralization step, the aqueous acetate-containing phase is separated off. In any case, the process according to the above patent provides a saline wastewater, even if the acetate-containing aqueous solution obtained after neutralization of the acetic acid would be worked up after the addition of a strong acid in order to recover the free acetic acid.

It can thus be gathered from the literature on processes for the production of vinyloxirane which has become known that all these processes only disclose approaches for the economical, technical production of vinyloxirane, but in no way a satisfactory description coping with the problems posed by technical requirements and the question of economic viability.

• a) eine 10 bis 45 Gew.-% eines wasserlöslichen, sauren Katalysators und 20 bis 50 Gew.-% Wasserstoffperoxid enthaltende wässrige Lösung mit einer 2 bis 5 Kohlenstoffatomen enthaltenden Carbonsäure im Molverhältnis Wasserstoffperoxid zu Carbonsäure wie 0,5 - 30:1 bei Temperaturen von 10 bis 70°C umsetzt,
• b) das erhaltene Reaktionsgemisch mit einem inerten, organischen Lösungsmittel im Gegenstrom extrahiert,
• c) das im wesentlichen Wasserstoffperoxid und sauren Katalysator enthaltende wässrige Raffinat der Extraktion ganz oder teilweise durch destillative Entfernung von Wasser aufkonzentriert.
• d) das aufkonzentrierte Raffinat, sowie den gegebenenfalls nicht aufkonzentrierten Anteil des Raffinats, unter Wiederherstellung der für die Umsetzung mit der Carbonsäure erforderlichen Konzentrationen an Wasserstoffperoxid und wasserlöslichem sauren Katalysator in die Umsetzungsstufe (a) zurückführt, wobei das zur Wiederherstellung der für die Umsetzung mit der Carbonsäure erforderlichen Wasserstoffperoxidkonzentration benötigte Wasserstoffperoxid dem aufzukonzentrierenden Anteil des Raffinats vor oder nach der destillativen Entfernung von Wasser gemäss (c) zugesetzt wird oder zu dem gegebenenfalls nicht aufkonzentrierten Teil des Raffinats zugegeben wird,
• e) den im wesentlichen Percarbonsäure und Carbonsäure enthaltenden organischen Extrakt mit Wasser oder einer wässrigen Lösung behandelt und
• f) den nunmehr praktisch wasserstoffperoxidfreien, wasserhaltigen, organischen Extrakt einer Azeotropdestillation derart unterwirft, dass der Restgehalt an Wasser im Sumpfprodukt der Azeotropkolonne weniger als 0,5 Gew.-% beträgt,
• g) die nunmehr gewonnene, Percarbonsäure und Carbonsäure enthaltende, organische Lösung mit Butadien im Überschuss bei einem Molverhältnis von Butadien zu Percarbonsäure von 1,5 bis 6:1 bei Temperaturen von 0°C bis 80°C und bei einem Druck von 0,8 bis 20 bar umsetzt, und
• h) das vinyloxiranhaltige Reaktionsgemisch auf destillativem Wege aufarbeitet, wobei reines Vinyloxiran isoliert wird und das überschüssige Butadien, die Carbonsäure und das inerte organische Lösungsmittel wiedergewonnen und ganz oder teilweise in das Verfahren zurückgeführt werden.

In contrast, it has now surprisingly been found that vinyloxirane can be prepared from hydrogen peroxide and butadiene in a technically simple and economically advantageous manner if

• a) an aqueous solution containing 10 to 45% by weight of a water-soluble acidic catalyst and 20 to 50% by weight hydrogen peroxide with a carboxylic acid containing 2 to 5 carbon atoms in a molar ratio of hydrogen peroxide to carboxylic acid such as 0.5-30: 1 at temperatures from 10 to 70 ° C,
• b) the reaction mixture obtained is extracted with an inert, organic solvent in countercurrent,
• c) the aqueous raffinate of the extraction, which essentially contains hydrogen peroxide and acid catalyst, is wholly or partly concentrated by removing water by distillation.
• d) the concentrated raffinate, as well as the possibly not concentrated portion of the raffinate, restoring the concentrations of hydrogen peroxide and water-soluble acidic catalyst required for the reaction with the carboxylic acid in the reaction step (a), the restoration of the reaction for the reaction with the Carbonic acid required hydrogen peroxide concentration required hydrogen peroxide is added to the portion of the raffinate to be concentrated before or after the removal of water by distillation according to (c) or to the portion of the raffinate which may not be concentrated,
• e) the organic extract essentially containing percarboxylic acid and carboxylic acid is treated with water or an aqueous solution and
• f) subjecting the now practically hydrogen peroxide-free, water-containing organic extract to an azeotropic distillation in such a way that the residual water content in the bottom product of the azeotropic column is less than 0.5% by weight,
• g) the now obtained organic solution containing percarboxylic acid and carboxylic acid with butadiene in excess at a molar ratio of butadiene to percarboxylic acid from 1.5 to 6: 1 at temperatures from 0 ° C. to 80 ° C. and at a pressure of 0.8 up to 20 bar, and
• h) the reaction mixture containing vinyloxirane is worked up by distillation, pure vinyloxirane being isolated and the excess butadiene, the carboxylic acid and the inert organic solvent being recovered and fully or partially recycled into the process.

Percarboxylic acids suitable for the process according to the invention are those which are derived from aliphatic carboxylic acids having 2 to 5 carbon atoms, such as acetic acid, propionic acid, n-butyric acid, isobutyric acid and valeric acid or trimethylacetic acid and dimethylpropionic acid. Peracetic acid, perpropionic acid and perisobutyric acid are particularly suitable. Perpropionic acid is particularly suitable.

Die Carbonsäure setzt sich dabei je nach Konzentration an saurem Katalysator, z.B. Schwefelsäure, und Wasserstoffperoxid in Abhängigkeit des Molverhältnisses von Wasserstoffperoxid zu Carbonsäure zu etwa 30 bis 70% zu Percarbonsäure um.In the reaction according to (a) between hydrogen peroxide and the carboxylic acid in the presence of an acid catalyst, an equilibrium is formed between the carboxylic acid and the percarboxylic acid, which can be represented according to the following equation:

Depending on the concentration of acidic catalyst, for example sulfuric acid, and hydrogen peroxide, depending on the molar ratio of hydrogen peroxide to carboxylic acid, about 30 to 70% of the carboxylic acid is converted to percarboxylic acid.

In general, in addition to the 10 to 45% by weight of water-soluble acid catalyst, e.g. Sulfuric acid or methanesulfonic acid, and 20 to 50 wt .-% hydrogen peroxide-containing aqueous solution containing the carboxylic acid in pure, undiluted form. However, it is also possible to use a carboxylic acid containing water, a hydrogen peroxide-containing or an acidic catalyst, in which case the concentration of the aqueous solution must be changed accordingly in order to maintain the ratio of hydrogen peroxide, acidic catalyst, carboxylic acid and water required for the reaction. For example, instead of pure carboxylic acid, a mixture of carboxylic acid and hydrogen peroxide, e.g. use a carboxylic acid containing 20% by weight of hydrogen peroxide. Of course, the hydrogen peroxide content in the aqueous acidic catalyst and hydrogen peroxide feed solution must then be adjusted in accordance with the hydrogen peroxide content in the carboxylic acid, so that the hydrogen peroxide contained in the carboxylic acid and that in the aqueous solution result in a total use of hydrogen peroxide, which corresponds to a content of 20 to 50 wt .-% hydrogen peroxide in the aqueous solution. For example, in such a case where the carboxylic acid to be converted to percarboxylic acid already contains hydrogen peroxide, even the hydrogen peroxide content in the aqueous solution may be less than 20% by weight, e.g. 12 to 19 wt .-%. All conceivable mixing ratios can be used within the stated concentration ratios of catalyst and hydrogen peroxide.

An aqueous solution containing 20 to 43, particularly preferably 23 to 38% by weight of acid catalyst and 22 to 35% by weight of hydrogen peroxide is preferably reacted.

Sulfuric acid is advantageously used as the water-soluble acid catalyst. Other water-soluble acids can also be used are used, for example sulfonic acids such as methane, ethane, propane, butane, isobutanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, trifluoromethane, 1-fluoroethane, perfluoroethane, perfluoropropane or perfluorobutanesulfonic acid; Phosphoric acid, phosphonic acids, such as methane or ethanephosphonic acid, phosphinic acids, or acidic salts, such as sodium bisulfate or potassium bisulfate. Mixtures of water-soluble acids can also be used. Commercial hydrogen peroxide, for example 30 to 90% by weight H ₂ O _{2, is} used as the hydrogen peroxide to prepare the aqueous solution. Of course, hydrogen peroxide, which is obtained as a by-product of other chemical processes or as a recycle stream, is also suitable.

The reaction temperature is generally about 10 to 70 ° C. It is expedient to work at 20-60 ° C. Temperatures below 43 ° C, e.g. Temperatures of 25-43 ° C.

In general, the reaction is carried out until equilibrium is established between the carboxylic acid and the percarboxylic acid. However, it is also possible to terminate the reaction before equilibrium is reached and to obtain the reaction mixture thus obtained for the next process step, i.e. extraction with the inert organic solvent.

The pressure is not important for the reaction of the carboxylic acid with hydrogen peroxide, so that it is possible to work at normal pressure, elevated pressures or even at reduced pressure. In general, it is expedient to implement at pressures below 1.1 bar, e.g. at pressures from 0.8 to 1.1 bar.

The reaction can be carried out in a wide variety of reaction vessels. It is expedient to ensure a steady concentration profile and in particular to avoid so-called dead zones in which parts of the reaction mixture remain for an unreasonably long time. Suitable are, for example, the usual reaction tubes of different diameters and lengths, which are also used as a closed circuit, e.g. can be arranged as loop reactors, and agitator kettle.

The reaction mixture from reaction stage (a) is now fed to countercurrent extraction with the inert organic solvent according to (b). This countercurrent extraction can be carried out in one or more extraction units.

Suitable solvents for the percarboxylic acids are all water-immiscible organic solvents which are inert to the reaction mixture of reaction (a). For example, aromatic hydrocarbons containing 6 to 10 carbon atoms, aliphatic or cycloaliphatic hydrocarbons each containing up to 12 carbon atoms, chlorinated hydrocarbons containing 1 to 10 carbon atoms and 1 to 4 chlorine atoms, and esters of 1 to 5 C atoms have been found to be suitable containing carboxylic acids with straight-chain or branched alcohols in which there are 1 to 8 carbon atoms in the molecule, and ethers which contain 2 to 10 carbon atoms. Examples of suitable solvents are: benzene, toluene, xylene, n-pentane, isooctane, cyclohexane, methylene chloride, chloroform, 1,2-dichloroethane, 1,2-dichloropropane, methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate , Isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate, as well as chlorobenzene and ether. However, it is also possible to use mixtures of the solvents mentioned as solvents for the percarboxylic acid, in which case the components of the mixture are then advantageously chosen so that they have a similar boiling point. Chlorinated hydrocarbons such as methylene chloride, dichloroethane or dichloropropane, aromatic hydrocarbons such as benzene or ether such as diisopropyl ether or mixtures of these solvents are preferably used. Benzene is very particularly preferably used as the solvent for the process according to the invention.

The quantitative ratio of organic solvent to the reaction mixture containing the percarboxylic acid to be extracted is generally 10 to 0.1: 1. However, larger amounts of inert, organic solvent can also be used. The most favorable range in each case of the ratio of the reaction mixture obtained according to (a) to the organic solvent to be used for the extraction according to (b) depends on the particular percarboxylic acid chosen and the extraction properties of the organic solvent and can be easily determined by a person skilled in the art. For the perpropionic acid / benzene system, for example, it is favorable to choose a ratio of 4 to 0.3: 1 of the reaction mixture to be extracted, which was obtained in step (a), and benzene. If the extraction according to (b) is carried out in several extraction units, the amount of organic solvent can vary from unit to unit within the specified limits.

The content of percarboxylic acid in the extract can be varied within wide limits by the amount of extractant and by the number of extraction stages. In general, the procedure is such that an approximately 3 to 40% by weight percarboxylic acid is obtained in the organic solvent. An organic extract containing 5-30% by weight of percarboxylic acid is preferably obtained. Accordingly, the number of extraction stages should be as high as possible. In general, however, an extraction unit with 3 to 10 theoretical extraction stages is sufficient to prepare the solutions with the desired concentration of percarboxylic acids. Of course, it is desirable to obtain the raffinate of extraction stage (b) as free as possible from percarboxylic acid and carboxylic acid. In space However, it is generally sufficient if no more than 0.5% by weight of carboxylic acid and percarboxylic acid remain in the raffinate.

For the process according to the invention, a percarboxylic acid is used, the corresponding carboxylic acid of which has a higher boiling point than the vinyloxirane and an organic solvent which has a boiling point which is either higher than the boiling point of the carboxylic acid corresponding to the percarboxylic acid, or between the boiling point of vinyloxirane and that of Carboxylic acid is. However, it is also possible to choose the solvent so that its boiling point is below the boiling point of vinyloxirane. Of the compounds already listed, an inert organic solvent for the percarboxylic acid is preferably a solvent which boils at normal pressure at least 5 ° C. above the boiling point of vinyloxirane and at least 20 ° C. below the boiling point of the percarboxylic acid. In addition, the selection of the percarboxylic acid or the corresponding carboxylic acid and the solvent for the process according to the invention is advantageously carried out in such a way that no pronounced azeotropes of binary or external type occur within the combination of carboxylic acid / solvent / vinyloxirane.

The temperature during the extraction can be varied within wide limits. In general, temperatures from 10 to 70 ° C. It is expedient to choose the same temperature as in the production of the percarboxylic acid according to (a), so that the other temperatures mentioned for the reaction step (a) are also suitable for the extraction (b). As far as pressure is concerned, work can be carried out at normal pressure, reduced pressure or even at elevated pressures.

The known extraction systems, which enable a multi-stage countercurrent extraction, come into consideration as extraction units.

Suitable are e.g. Mixer-separators, sieve tray extractors, pulsed sieve tray columns or spray columns. However, one-stage or multi-stage centrifugal extractors can also be used.

In addition to the percarboxylic acid and the carboxylic acid, the organic extract also contains small amounts of free hydrogen peroxide, water and traces of the acid used as catalyst, e.g. Sulfuric acid. The raffinate essentially contains the unreacted hydrogen peroxide and the acid catalyst.

This is essentially water, hydrogen peroxide and e.g. In process step (c), sulfuric acid-containing raffinate from the extraction is then reprocessed for the reaction of the carboxylic acid and hydrogen peroxide by concentrating all or part of it in a distillation by removing water. The amount of water to be distilled off from the raffinate stream supplied to this concentration essentially corresponds to both the amount of water which is formed when hydrogen peroxide is reacted with the carboxylic acid according to (a) and the amount of water which is used with the fresh hydrogen peroxide to supplement the amounts used is required, is introduced into the process. The top product of the distillation is water, which can contain small amounts of hydrogen peroxide, percarboxylic acid and carboxylic acid. In general, the distillation is carried out under reduced pressure, e.g. at pressures from 10 to 250 torr, preferably 40 to 150 torr, and at temperatures in the swamp from 40 to 120 ° C, preferably from 60 to 85 ° C. In general, the entire raffinate stream leaving the extraction is also suitable for the concentration if the extraction is carried out in a single extraction unit. However, if the reaction mixture obtained in (a) is extracted in, for example, two extraction units, both the raffinate from the first and the raffinate from the second extraction stage can be fed to the concentration. If the raffinate of the first unit is divided into a larger and a smaller partial stream in an extraction that takes place in two extraction units, each of these portions is in principle suitable for the concentration. In the case of an extraction consisting of two extraction units, in which the raffinate leaving the first unit is divided into a small and a larger partial stream and the smaller portion is fed into the second unit, the raffinate from the second extraction unit is advantageously subjected to the distillation for concentration.

The fresh hydrogen peroxide to supplement the consumed amounts can be added in any concentration. Commercially available, e.g. 30 to 90 wt .-% aqueous hydrogen peroxide, which can be mixed with the usual stabilizers. For example, stabilizers come into consideration, such as those listed in Gmelins “Handbuch der inorganic chemie”, 8th edition, oxygen volume, delivery 7, 1966, on page 2274 and page 2275.

The fresh hydrogen peroxide can be mixed with the raffinate to be concentrated from the extraction according to process step (b) before entering the distillation unit; the two streams can also be fed separately into the distillation unit. It is also possible to add the fresh hydrogen peroxide to the raffinate after concentration. It is also possible to add a portion of the fresh hydrogen peroxide to the raffinate before concentration and to add the remaining amount of the fresh hydrogen peroxide to the raffinate after concentration.

However, one can also enter the fresh hydrogen peroxide directly into the reaction according to (a), or else the extract that does not come to concentration, the extract tion mix. As a distillation unit, it is expedient to use a column provided with a condenser and an evaporator unit.

The known tray columns or packed columns are suitable for distillation. The number of distillation stages is chosen so that the top product contains as little hydrogen peroxide as possible. It is desirable to obtain less than 0.1% by weight of hydrogen peroxide in the condensate. The known evaporators are basically suitable as the evaporator unit. Suitable evaporator units are, for example, in which the residence time of the product is less than 20 minutes, preferably less than 10 minutes. Downflow or thin film evaporators are particularly suitable. Suitable materials for the distillation unit are high-alloy, rustproof stainless steels which essentially contain chromium and nickel in addition to iron, such as a material with the DIN designation 1.4571, which in addition to iron contains 17.5% by weight chromium, 11.5% by weight .-% nickel, 2.25 wt .-% molybdenum, and up to 2 wt .-% manganese, up to 1 wt .-% silicon, up to 0.1 wt .-% carbon and small amounts of titanium, or a material which, in addition to iron, contains 25% by weight chromium, 25% by weight nickel, 2.25% by weight molybdenum and up to 2% by weight manganese, up to 1% by weight silicon, up to 0 , 06 wt .-% carbon and small amounts of titanium and is designated according to DIN with the number 1.4577. Particularly suitable as a material for the destination unit, in particular for the evaporator, zircon, zircon-containing materials and zirconium alloys.

The bottom product of this distillation unit is returned to the reaction stage (a), if necessary with the hydrogen peroxide and catalyst concentrations required for the reaction with the carboxylic acid being restored. Due to this measure of returning the raffinate of the extraction to the reaction step according to (a), whereby it has previously passed all or part of the concentration according to (c), one essentially obtains process steps (a), (b), (c) , and (d) comprehensive cycle of hydrogen peroxide and catalyst. It may be appropriate to use a part, e.g. 0.1 to 6 wt .-% of the circuit stream from time to time or continuously as a side stream from the process. This side stream is advantageously removed at a point in the process where the circulating stream has the lowest possible concentration of hydrogen peroxide and acid catalyst and, if appropriate, of percarboxylic acid and carboxylic acid. The raffinate of the extraction before addition of fresh hydrogen peroxide and before concentration according to (c) is particularly suitable for this side stream withdrawal. This side stream, which is part of the recycle stream, is an aqueous solution essentially containing hydrogen peroxide and acid catalyst, can either be discarded or be worked up in a regeneration stage. A regeneration of this portion of the circulating stream can be carried out, for example, by distilling off the hydrogen peroxide contained therein in vacuo with water vapor, an aqueous solution of the acid catalyst being obtained as the distillation residue. The aqueous solution containing hydrogen peroxide obtained as a distillate can, if appropriate after concentration, be returned to the process. After purification, for example by distillation, the aqueous solution of the acidic catalyst can also be returned to the process. Through this cycle exchange, a corresponding part of the catalyst, e.g. the sulfuric acid, which must be supplemented in the process.

The organic extract which essentially contains the percarboxylic acid and the carboxylic acid and is obtained in process step (b) is treated in process step (e) with water or an aqueous solution. In general, the procedure is such that the organic percarboxylic acid extract is washed with water in one of the customary devices.

It is convenient to use this laundry as an extraction, e.g. as a multi-stage countercurrent extraction, with water, for example in a three-stage extraction unit. Instead of countercurrent extraction, extraction in cocurrent or crosscurrent can of course also be used. When working with several extraction stages, the extraction can also be carried out partly in cocurrent and partly in countercurrent.

It is expedient to use 0.1 to 10% by volume of water or aqueous solution, based on the organic extract. Preferably 0.5 to 7% by volume of water is used. Instead of pure water, it is also possible to use an aqueous solution which is essentially free of hydrogen peroxide and mineral acid. It is expedient to use an aqueous phase which is obtained in the process. For example, the distillate obtained in carrying out process step (d) is suitable. The aqueous phase of the water treatment can be returned to the extraction according to (b) in order to obtain the proportions of percarboxylic acid, carboxylic acid and hydrogen peroxide contained therein for the process.

The known extraction systems are suitable as devices for water treatment according to process stage (e), e.g. Mixer-separators, sieve plate extractors, pulsed sieve plate columns or extraction centrifuges.

After the organic solution of the percarboxylic acid has been treated with water or an aqueous solution according to (e), an essentially hydrogen peroxide and sulfuric acid-free organic solution of the percarboxylic acid is obtained, which is now subjected to the azeotropic distillation according to process step (f), in which contain organic solution water is removed. The water content of the organic solution to be separated is generally 0.5 to 7% by weight. This water content is essentially dependent both on the nature of the organic solvent used in each case and on the selected concentration of percarboxylic acid in the extract obtained in (b).

The entrainer used to remove water from the percarboxylic acid organic solution by azeotropic distillation is generally the inert organic solvent. However, it is also possible to add another suitable entrainer to the organic solution of the percarboxylic acid before entering process step (f) or directly into the distillation unit according to (f) and to use it to carry out the azeotropic distillation.

In process step (f), the amount of distillate is generally chosen such that the residual water content in the bottom product of the azeotrope column is less than 0.5% by weight, preferably less than 0.2% by weight, e.g. 0.05-0.2% by weight. However, it is also possible to reduce the water content to a negligible value. The entrainer which separates out as the organic phase after condensation of the top vapors of the azeotropic column is fed to the column as reflux. The aqueous phase obtained after condensation of the top vapors, which generally contains small amounts of percarboxylic acid, carboxylic acid and hydrogen peroxide, is fed back to the process at a suitable point, for example the extraction according to (e) or (b); however, it can also be removed from the process.

The azeotropic distillation (f) can be carried out under normal or reduced pressure, for example at 200 to 400 torr. The bottom temperature is, for example, 30 to 80 ° C. In general, a bottom temperature of below 70 ° C is sufficient.

The usual columns, for example the known tray or packed columns, are suitable for azeotropic distillation. The usual devices can be used as evaporators. Downflow or thin-film evaporators are particularly suitable.

The organic solution of an essentially water- and hydrogen peroxide-free percarboxylic acid, now obtained as the bottom of the azeotropic distillation, is treated in process step (g) with an excess of butandiene in the molar ratio of butadiene to percarboxylic acid from 1.5 to 6: 1 at temperatures from 0 ° C. to 80 ° C and implemented at a pressure of 0.8 to 20 bar. But you can also work at a pressure of 1 to 10 bar. A suitable pressure range is, for example, pressures from 1.2 to 8 bar. It is preferred to work at a pressure of 1.5 to 5 bar.

The reaction temperature is preferably kept at 10 to 70 ° C. The reaction of butadiene with the organic solution of percarboxylic acid is very particularly preferably carried out at from 20 to 60.degree. In addition to working under isothermal conditions, i.e. Maintaining a uniform temperature in the entire reaction mixture, the reaction can also be carried out with the formation of a so-called temperature gradient, which generally increases with the progress of the reaction. However, the reaction can also be carried out in such a way that a gradient of falling temperature is formed as the reaction proceeds.

The pressure when carrying out process step (g) is expediently chosen such that the reaction mixture is essentially in the liquid phase. With a molar ratio of butadiene to percarboxylic acid of, for example, 2.5: 1 and at a reaction temperature of 40 to 50 ° C., the pressure is, for example, 2 to 3.5 bar.

The molar ratio of butadiene to percarboxylic acid is preferably 1.5 to 4: 1. It is very particularly advantageous to use a molar ratio of 2.0 to 3.0 moles of butadiene per mole of percarboxylic acid.

The devices which are customary for reactions of this type, such as stirred tanks, tubular reactors, loop reactors or loop reactors, can be used to carry out the reaction. In general, a device is used that behaves like a cascade of at least two ideally mixed kettles. It is particularly advantageous to use a reaction system which behaves like a cascade of 4 to 50, preferably 10 to 30, ideally mixed vessels. In the practical implementation of the implementation, e.g. a sequence of several agitator tanks, for example a cascade of 3 to 6 tank reactors.

Technical butadiene is generally used for the reaction in process step (g). It can contain the usual admixtures in technical use, especially n-butenes.

The butadiene can be introduced into the reaction unit in various ways. Butadiene can be used in liquid or gaseous form. The butadiene can also be passed into the reactor unit together with the percarboxylic acid solution. Both feed materials can also be introduced into the reactor separately from one another. It is also possible to pass the butadiene and the percarboxylic acid solution into the reactor unit at various points. When using several reactors connected in cascade, it may be expedient to introduce all of the butadiene into the first reactor. Butadiene can also be divided between the various reactors.

The considerable heat of reaction is dissipated by internal and external coolers. To remove the heat of reaction, the reaction can also be carried out under reflux, ie in boiling reactors. The reaction is conveniently carried out with the most complete possible conversion of the percarboxylic acid men. In general, more than 98% of the percarboxylic acid is converted. It is advisable to convert more than 99% percarboxylic acid. The reaction can be carried out with a particularly high selectivity if it is partially carried out in a reaction tube through which turbulent flow flows and which is connected, for example, to the sequence of agitator vessels. It is particularly favorable to use a reaction tube which is equipped with internals which largely prevent backmixing, for example perforated transverse bottoms. For example, the reaction is first carried out in a few, for example 1 to 3, stirred reaction units connected in series, and the reaction mixture is then passed into a reaction tube to complete the reaction. The reaction tube can be operated under adiabatic conditions; but you can also cool, for example by external cooling, or you can install coolers between individual pipe sections. The dimensioning of a suitable reaction tube depends on the intended throughput. It is essential that the flow rate in the reaction tube is so high that backmixing of the reaction components is essentially excluded. The diameter of the reaction tube can be 0.01 to 10 meters with a length of 1 to 200 meters. You can also operate several pipes in parallel. For example, you can also use tube bundles. If a reaction tube with perforated transverse plates is used, the transverse plates are generally at a distance of 0.1 to 5 m from one another.

When carrying out the reaction between butadiene and the percarboxylic acid (step g) according to the invention, it is possible to achieve vinyloxirane yields of over 95%, based on the percarboxylic acid used. The amount of by-products, e.g. the butene (1) diol (3,4) and its mono- and diester with the carboxylic acid corresponding to the percarboxylic acid is less than 2%, based on vinyl oxirane formed. The amount of polymerized butadiene, based on the total amount of butadiene used in the reaction stage according to (g), is less than 1% by weight.

The reaction mixture is worked up by distillation, pure vinyloxirane being obtained and excess butadiene, the carboxylic acid and the organic solvent being isolated to such a degree of purity that it can be recycled into the process, which may also be only partial. It is useful to separate vinyl oxirane and the carboxylic acid very quickly. A distillation column is used for this purpose, for example, in which vinyloxirane and butadiene, if appropriate together with lower-boiling constituents and part of the solvent, are initially removed overhead and the remaining solvent and the carboxylic acid are obtained as bottom product. After the butadiene has also been separated off by distillation, the overhead product is worked up in a further distillation column in order to obtain pure vinyl oxirane. The organic solvent and the carboxylic acid are recovered from the bottoms of these two distillation columns. The distillation residue of carboxylic acid distillation is the small amount of higher-boiling by-products already mentioned. The organic solvent can basically be recovered quantitatively.

In many cases it can be advantageous to add a stabilizer or a solution of a stabilizer to the reaction mixture leaving process step (g) before entering the first distillation column. However, the reaction mixture can also be worked up by distillation without using a stabilizer. All compounds which are capable of binding oxygen or traces of peroxidic compounds are suitable as stabilizers. These compounds can also contain nitrogen and / or sulfur. Examples include hydroquinone, 4-tert-butyl pyrocatechol, 2,6-di-tert-butyl-4-methylphenol, phenothiazine, N, N-dimethylaniline, tetramethylhydroquinone, N-nitrosodiphenylamine, pyrogallol , 2-methyl-benzothiazole, 6-methoxy-2-amino-benzothiazole, 2,3-dihydroxyquinoxaline and the addition compound of diisobutylene and nitrogen oxide.

An embodiment of the method according to the invention will be explained with reference to Figure 1.

In the first reaction stage (1), an aqueous solution containing 30 to 40% by weight of sulfuric acid and 25 to 35% by weight of hydrogen peroxide and (3) propionic acid in a molar ratio of hydrogen peroxide to propionic acid such as 0.9 are simultaneously added via (2) to 1.2: 1 at a temperature of 25 to 45 ° C. The residence time in the reaction system (1) is 10 to 30 minutes. The reaction mixture, which leaves the reaction system (1) via (4), contains about 26 to 32% by weight of perpropionic acid, 12 to 17% by weight of propionic acid, 17 to 21% by weight of sulfuric acid, 5 to 8% by weight. -% hydrogen peroxide and 2 to 5% by weight Caro's acid. It arrives in an extraction system (5) which consists of a pulsed sieve plate column with 60 to 90 sieve plates and which is charged with benzene with a propionic acid content of less than 0.5% via (6). The raffinate of this extraction, which is removed from the extraction system (5) via (7), contains the unreacted hydrogen peroxide and the sulfuric acid in the reaction system (1). It is passed together with about 50% commercially available aqueous hydrogen peroxide, which is fed in via (9), into the distillation unit (8) consisting of evaporator and column, in which at 40-120 torr and a bottom temperature of 60 to 80 ° C. so much water is taken off overhead that 30 to 40% by weight sulfuric acid and 25 to 35% by weight are used as the bottom product An aqueous solution containing hydrogen peroxide is obtained, which is returned to the reaction system (1) via (2). The water taken overhead in the distillation unit (8) is removed from the process via (10). The amount of water obtained as distillate essentially corresponds to the amount of water contained in the hydrogen peroxide used and formed in the process step according to (a), that is to say in the reaction system (1). A downflow evaporator is used as the evaporator unit of the distillation column (8). The benzene perpropionic acid extract from the extraction system (5) is passed via (11) into the extraction system (12) consisting of 3 mixer separators, where the extract is extracted in countercurrent with water which is fed in via (13). The amount of water is 3 to 6 percent by volume of the benzene solution. The aqueous phase of this extraction unit (12) is returned to the extraction unit (5) via (14).

The water-treated benzene perpropionic acid solution passes through (15) into the distillation unit (16), where an azeotropic dewatering is carried out. The pressure within the distillation system (16) is 100 to 300 torr. The bottom temperature is 50 to 75 ° C. The water content of the benzene perpropionic acid flowing out of the bottom of this column is less than 0.3% by weight. The essentially water and hydrogen peroxide-free benzene perpropionic acid obtained as the bottom of the azeotropic distillation is passed via (17) into the reaction system (18), where the reaction with butadiene in a molar ratio of butadiene to perpropionic acid such as 2 to 4: 1 takes place. The butadiene reaches the reaction system (18) via (19), (20) and (22). The pressure in (18) is 3-5 bar. The reaction system (18) consists of 2 loop reactors connected in series with a downstream retention tube of 10 to 80 m in length. The temperature in the two loop reactors, in which the reactants are mixed by means of a circulation pump, is 20 to 50 ° C. Perpropionic acid is converted to 80 to 95%. The further reaction of the perpropionic acid up to a conversion of 99.8% takes place in the downstream retention tube, which is operated without cooling. The reaction mixture obtained is passed via (23) into an expansion vessel (21) and expanded there. The gas phase obtainable essentially contains butadiene, which is returned to the reaction with perpropionic acid via (22). Vinyloxirane is first separated off from the liquid phase, which passes into the distillation unit (25) via (24), together with butadiene and with part of the benzene by distillation. The stream containing butadiene, vinyloxirane and benzene is fed via (26) to the distillation unit (27), where the further separation of the components takes place and pure vinyloxirane is obtained, which leaves the process via (28). Butadiene is returned to the reaction system (18) via (20). The bottoms from columns (25) and (27) are fed via (29) and (30) to a further distillation unit (31), where benzene is recovered as the top product and returned to the extraction system (5) via (6). The bottom of the benzene recovery column (31), which essentially consists of propionic acid, is fed via (32) to the distillation unit (33), in which propionic acid is distilled off as top product, which is returned to the reaction system (1) via (3). The products boiling higher than propionic acid are obtained as the bottom product of distillation (33) and discharged via (34).

According to the process of the invention, vinyloxirane can be produced in yields of at least 90%, based on the hydrogen peroxide used, and at least 95%, based on the butadiene used.

Example 1 (see also Fig. 2)

Due to the reaction system (1) consisting of a heatable retention tube with fillers and a length of 55 cm and a diameter of 5 cm, 1034 g of a mixture of 415 g (= 5.6 mol) of propionic acid and 619 g are produced per hour during continuous operation an aqueous solution containing 37.8% by weight sulfuric acid and 30.8% by weight hydrogen peroxide (= 5.6 mol H ₂ 0 ₂ ).

• 32,8 Gew.-% freie Schwefelsäure, 29,1 Gew.-% freies Wasserstoffperoxid und 5,8 Gew.-% Carosche Säure. Das Molverhältnis von Wasserstoffperoxid zu Propionsäure beträgt in dem in das Reaktionssystem (1) gelangenden Gemisch 1:1, wobei das in der Caroschen Säure gebundene Wasserstoffperoxid als freies H₂0₂ gerechnet wird.

In the aqueous solution containing hydrogen peroxide and sulfuric acid, some of these components are present as Caro's acid. This part is 5.8% by weight, based on the total amount of the aqueous solution, for which the following composition thus results:

• 32.8% by weight of free sulfuric acid, 29.1% by weight of free hydrogen peroxide and 5.8% by weight of Caro's acid. The molar ratio of hydrogen peroxide to propionic acid in the mixture entering reaction system (1) is 1: 1, the hydrogen peroxide bound in Caro's acid being calculated as free H ₂ 0 ₂ .

Within the reaction system (1), the mixture now consisting of propionic acid, sulfuric acid, hydrogen peroxide, water and Carosic acid is heated to 40 ° C. for about 18 minutes, 59% of the propionic acid being converted to perpropionic acid. After passing through the residence time tube, the average of 28.8% by weight of perpropionic acid, 16.5% by weight of propionic acid, 19.6% by weight of sulfuric acid, 3.47% by weight of Caro's acid, 6.54% by weight. -% hydrogen peroxide and 25.1 water containing product stream (1034 g per hour) cooled to room temperature and passed into a gas separator, where 166 ml of a gas consisting of 87% oxygen and 13% carbon dioxide escape per hour. Then the degassed mixture, after having been combined with the mixture of the two aqueous phases running out of the extraction unit (12), is fed to the extraction system (5). The extraction process is carried out at a temperature of 32 ° C. As an extraction system, a pulsed sieve plate column is used, which is provided with 80 sieve plates, has a length of 4 m and a diameter of 25 mm, and is equipped at the top and bottom with a separating vessel, in which the phases are separated. At the top of the column (5), the product stream obtained after the degassing and with the mixture of the aqueous phases of the extraction system (12) fed in via line (14) is added, which flows through the column from top to bottom as the heavy phase, while on lower end, the benzene serving as extractant, which contains 0.09% by weight of propionic acid and traces of water, is introduced into the column at a rate of 1092 ml per hour (= 961 g / h). From the upper separating vessel, 1585 ml of a benzene solution of perpropionic acid (= 1490 g / h) are drawn off per hour, which in addition to 21.4% by weight of perpropionic acid and 12.6% by weight of propionic acid, 0.97% by weight. -% water, 0.51 wt .-% hydrogen peroxide and traces of sulfuric acid.

The raffinate from the extraction collects as a heavy phase in the lower separating vessel and is continuously removed from there via line (7). This raffinate, which is obtained in an amount of about 587 g per hour, contains on average 34.58% by weight of sulfuric acid, 11.16% by weight of hydrogen peroxide, 6.12% by weight of Caro's acid, and 0.1 % By weight propionic acid and 0.06% by weight perpropionic acid. This raffinate is prepared again for the reaction with propionic acid by adding 195.6 ml of a 50% strength aqueous solution of hydrogen peroxide (= 117 g = 3.44 mol H ₂ O ₂ ) per hour (9) and the mixture thus obtained is concentrated again by distilling off 202 g of water. This concentration process takes place in the distillation unit (8), which consists of a column provided with bubble-cap trays (length = 1 m, diameter = 50 mm), a condenser, a device which allows the reflux ratio to be varied, and a falling film evaporator, which can be heated with the vapors of a boiling liquid and is operated at a pressure of 50 torr. The mixture consisting of the raffinate of the extraction (5) and the aqueous solution of hydrogen peroxide is introduced into the lower part of the column (8). At a bottom temperature of 68-70 ° C, a temperature at the top of the column of 32 ° C, and a reflux ratio of 0.7 (reflux / withdrawal), 202 ml of water distill over per hour. This distillate contains traces of hydrogen peroxide and 0.2% by weight of perpropionic acid and 0.3% by weight of propionic acid. 619 g of an aqueous solution, which in turn contains 32.8% by weight of sulfuric acid, 29.1% by weight of hydrogen peroxide and 5.8% by weight of Caro's acid, are drawn off from the bottom of the column via line (2) per hour . After cooling to room temperature, this mixture is returned to the reaction system (1).

About 4.5 g per hour are discharged as raffinate from the extraction (5) from the circulating stream of hydrogen peroxide and sulfuric acid which forms in this way and which comprises the reaction and extraction system (1) or (5) and the distillation unit (8). The loss of sulfuric acid thus generated in the circuit is supplemented by continuously introducing the same amount of a mixture having the composition of the raffinate of the extraction (5) into the circuit before the distillation unit (8).

The loss of hydrogen peroxide resulting from this cycle exchange is 0.5%, based on the fresh hydrogen peroxide used before the distillation unit (8).

The benzene solution of perpropionic acid removed from the extraction system (5) as a light phase is formed via line (11) to the extraction system (12), which is a three-stage mixer-separator battery, each consisting of a mixing pump with a subsequent separating vessel of about 2 liters is fed in and goes through the system from bottom to top.

In addition to the benzene solution of perpropionic acid, the mixing pump of the lower stage is fed 67 ml of an aqueous solution per hour, which is obtained if the water phase of the top product of the subsequent azeotropic distillation (distillation unit (16)) is added in an amount of 60 ml per hour is obtained and contains 1.48% by weight H ₂ 0 ₂ , 2.43% by weight perpropionic acid and 0.27% propionic acid, mixed with 7 ml deionized water. After passing through the middle mixer-separator arrangement, the benzene solution, which is taken from the lower separating vessel as a light phase, is fed together with 17 ml / h fresh water to the mixing pump belonging to the upper mixer-separator unit. The aqueous phase obtained here after phase separation is passed into the middle extraction stage. The aqueous solutions collecting as a heavy phase in the middle and lower separating vessels are combined and re-introduced into the extraction unit (5) via (14) in such a way that this stream, consisting of an aqueous solution, contains 25.23% by weight. % Perpropionic acid, 6.8% by weight hydrogen peroxide and 22.35% by weight propionic acid, with an amount of 81 ml / h immediately before entering the pulsed sieve tray column (extraction system (5)), with which from the reaction system ( 1) coming product mixes (4) mixes.

From the separating vessel of the extraction system (12) belonging to the upper mixer-separator unit, 1493 g (= 1570 ml) of a benzene solution of perpropionic acid with the composition 20.04 wt. Perpropionic acid, 11.41% by weight of propionic acid, 3.95% by weight of water and 0.2% by weight of hydrogen peroxide are drawn off and introduced into the distillation unit (16) given where the solution is dried azeotropically. Before entering the distillation unit (16), 5 ml of an approximately 3% by weight solution of a stabilizer of the type of the commercially available Na salts of partially esterified polyphosphoric acids in propionic acid are added to the benzene solution of perpropionic acid per hour. The distillation unit (16) is operated at 210 Torr and consists of a thin-film evaporator, a 50 cm long column with 5 bubble-cap trays and a diameter of 50 mm, a condenser and a separator for phase separation of the distillate at the top of the column. The temperature in the bottom of the column is 65 ° C. 60 ml of water and about 915 ml of benzene are obtained as the distillate per hour. The benzene is added to the column as reflux, while the water obtained in the separator, as already described, is introduced as washing water via (35) into the lower stage of the extraction unit (12). As the bottom product of this azeotropic distillation, a quantity of 1438 g per hour gives a 20.71% by weight benzene solution of perpropionic acid, which also contains 12.18% by weight propionic acid and 0.1% by weight water and 0 , 15 wt .-% contains hydrogen peroxide.

The yield of perpropionic acid in the benzene extract thus dried is 96.15% based on the hydrogen peroxide used in the process.

The dried benzene solution of perpropionic acid thus obtained is reacted with excess butadiene in a four-stage cascade (reaction system (18)). The reaction is carried out at a pressure of 2 bar. The butadiene is introduced into the first reactor in gaseous form via lines (22), (20) and (19). The excess of butadiene, based on the perpropionic acid used in the reaction, is a total of 170 mol% (= 482 g of butadiene). The first reactor of this four-stage cascade, which, like the three subsequent reaction vessels, is equipped with a stirring device and has a content of 1600 ml, is at a temperature of 35 ° C., the second, third and fourth reactor at a temperature of 40 ° each C operated.

The perpropionic acid used is converted to 99.8% under these reaction conditions. Behind the fourth reactor, the reaction mixture, which is produced at a rate of 1920 g per hour and on average the composition of 15.62% by weight of butadiene, 11.67% by weight of vinyloxirane, 21.46% by weight of propionic acid and Has 50.08 wt .-% benzene and 0.13 wt .-% water, after cooling to 30 ° C in the separator (21) to normal pressure, a small part of the butadiene (37 g / h) outgassing the (22) is fed back to the reaction system (18). The mixture obtained after the depressurization is now, after it has been mixed with 2.0 g of 4-tert-butylbenzate catechin, fed to a first distillation column (25), where all the vinyloxirane together with the butadiene and part of the benzene decreases as the distillate. This distillate, which contains an average of 32.6% by weight of butadiene, 27.25% by weight of vinyloxirane, 39.9% by weight of benzene and small amounts of water and is obtained at a rate of 822 g per hour, is carried out to the distillation column (27) via (26), where 224 g of a 99.9% vinyl oxirane (product stream 28) and 268 g of butadiene are obtained per hour, which is fed via line (20) into the reaction system (18) . The bottom products of columns (25) and (27) are fed via line (29) and (30) to column (31), where the benzene is recovered as top product at a rate of 961 g / h and then via line (6) is conveyed back into the extraction system (5). The bottom of the column (31) reaches the distillation column (33) via line (32). The top product obtained here is 415 g / h of propionic acid per hour, which are returned to the reaction system (1) via line (3). From the bottom of column (33), 15 g per hour of a mixture of higher-boiling compounds are discharged via (34), which essentially contains butane (1) diol (3,4) mono- and dipropionate .

The yield of vinyloxirane is thus, based on the perpropionic acid used in the reaction system (18), 96.7% or, based on hydrogen peroxide used in the process at (8) via (9), 93%.

Claims (10)

1. Process for the preparation of vinyloxirane from hydrogen peroxide and butadiene, characterised in that

a) an aqueous solution containing 10 to 45% by weight of a watersoluble, acid catalyst and 20 to 50% by weight of hydrogen peroxide is reacted with a carboxylic acid containing 2 to 5 carbon atoms in a molar ratio of hydrogen peroxide to carboxylic acid of 0.5-30:1 at temperatures of 10 to 70°C,

b) the resulting reaction mixture is extracted with an inert, organic solvent, in counter-current,

c) all or some of the aqueous raffinate from the extraction, which essentially contains hydrogen peroxide and acid catalyst, is concentrated by removing the water by distillation,

d) the concentrated raffinate, and the portion of the raffinate which is optionally not concentrated, are recycled into the reaction stage (a), the concentrations of hydrogen peroxide and water - soluble acid catalyst required for the reaction with the carboxylic acid being re-established, and the hydrogen peroxide necessary for re-establishing the hydrogen peroxide concentration required for the reaction with the carboxylic acid being added, before or after the removal of water by distillation according to (c), to the portion of the raffinate to be concentrated or to the portion of the raffinate which is optionally not concentrated,

e) the organic extract, which essentially contains percarboxylic acid and carboxylic acid, is treated with water or an aqueous solution,

f) the water-containing organic extract, which is now virtually free from hydrogen peroxide, is subjected to azeotropic distillation in a manner such that the residual content of water in the bottom product of the azeotropic column is less than 0.5% by weight,

g) the organic solution now obtained, which contains percarboxylic acid and carboxylic acid, is reacted with butadiene in excess at a molar ratio of butadiene to percarboxylic acid of 1.5 to 6:1 at temperatures of 0°C to 80°C and under a pressure of 0.8 to 20 bars, and

h) the vinyloxirane-containing reaction mixture is worked up by a distillative route, pure vinyloxirane being isolated and the excess butadiene, the carboxylic acid and the inert organic solvent being recovered and wholly or partly recycled into the process.

2. Process according to Claim 1, characterised in that an aqueous solution containing 20 to 43% by weight of sulphuric acid and 22 to 35% by weight of hydrogen peroxide is employed in stage (a).

3. Process according to Claim 1 and 2, characterised in that hydrogen peroxide and carboxylic acid are employed in a molar ratio of 0.5 to 1.3 or 3.5 to 25:1 in stage (a).

4. Process according to Claim 1 to 3, characterised in that acetic acid, propionic acid, n-butyric acid or isobutyric acid is reacted as the carboxylic acid in stage (a).

5. Process according to Claim 1 to 4, characterised in that 1,2-dichloropropane, chlorobenzene, toluene, benzene, n-butyl acetate or diisopropyl ether is employed as the inert, organic solvent in stage (b).

6. Process according to Claim 1 to 5, characterised in that the ratio of inert, organic solvent to the reaction mixture, which is obtained according to stage (a) and contains percarboxylic acid of 4 to 0.3:1 is chosen in stage (b).

7. Process according to Claim 1 to 6, characterised in that the removal of water by distillation in stage (c) is carried out under pressures of 40 to 150 mm Hg and at temperatures of 60 to 85°C.

8. Process according to Claim 1 to 7, characterised in that the side stream containing hydrogen peroxide and sulphuric acid is fed to a regenerating stage and the portions of hydrogen peroxide and sulphuric acid recovered are optionally reintroduced into the process.

9. Process according to Claim 1 to 8, characterised in that the reaction in stage (g) is carried out at a molar ratio of butadiene to percarboxylic acid of 1.5 to 4:1.

10. Process according to Claim 1 to 9, characterised in that the organic solvent obtained in stage (h) is recycled into stage (b), the carboxylic acid obtained in stage (h) is recycled into stage (a) and the butadiene obtained in stage (h) is recycled into stage (g).

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