DE19633328A1 - Cyclic, large-scale production of alkylene oxide from olefin - Google Patents

Abstract

Production of an alkylene oxide (A) involves (a) epoxidation of the corresponding olefin with aromatic peroxycarboxylic acid (I) and separation of the resultant aromatic carboxylic acid (II), (b) hydrogenation of (II) to the corresponding aldehyde (III) and (c) oxidation of (III) with oxygen (or gas containing oxygen) to (I), which is re-used for the epoxidation. The novel feature is that (i) (II) and/or (III) lost in the cycle is replaced by compounds obtained by oxidation of the parent alkyl-aromatics, (ii) phenolic by-products in the aldehydes are removed before stage (c) or (iii), if the olefin has 2-6C, it is prepared by dehydrogenation of a corresponding 2-6C hydrocarbon.

Description

The present invention relates to an improved method for Production of alkylene oxides from corresponding olefins by means of aromatic peroxycarboxylic acids.

The epoxidation of olefins with peroxycarboxylic acids, ins especially with m-chloroperoxybenzoic acid, is one for synthesis laboratory method well established by epoxides.

This method is described in detail in the chemical literature wrote, for example by Y. Sawaki in S. Patai (Ed ber), Chem. Hydroxyl, Ether Peroxide Groups, pp. 590-593 (1993) (1).

This is for the production of epoxides on a larger scale Method less suitable, however, because the peroxycarboxylic acid in stoichiometric amounts used and the resulting carbon acid with great effort by reaction with hydrogen peroxide must be regenerated.

From the German patent application 195 05 858.5 (2) a Ver drive to the production of epoxides using aromatic peroxy carboxylic acids in the form of a circulatory process known is particularly suitable for large-scale implementation.

The present invention was based on the object of a method ren for the production of alkylene oxides by epoxidation of oils to provide finen with aromatic peroxycarboxylic acids, the an easy and safe to carry out and economical return management of the resulting carboxylic acid in peroxycarboxylic acid without Allows use of hydrogen peroxide as well as through use of easily and inexpensively accessible starting materials and Utilization of by-products generated a high economy shows.

Accordingly, a process for making epoxides has been made corresponding starting compounds using aromatic peroxy carboxylic acids found in which after epoxidation (Step A) the resulting aromatic carboxylic acids from the Epoxides separated, catalytically in step B to the corresponding aromatic aldehydes hydrogenated and in step C these aldehydes  with oxygen or an oxygen-containing gas mixture the aromatic peroxycarboxylic acids oxidized, which again to Production of epoxides are used, and which thereby is characterized in that occurring losses of aromatic Carboxylic acids and / or aromatic aldehydes in the reaction circuit run through appropriate by oxidizing the underlying Compounds obtainable from alkyl aromatics supplemented.

With this method according to step A, in principle anyone can some olefin can be epoxidized. Preferred are olefins which directly on the double bond no more than one electron wearing substituents. Olefins are particularly preferred without electron-withdrawing substituents on the double bond. At games for good olefins are linear or branched C₂ to C₄₀ olefins, especially C₃ to C₂₄ olefins, or cyclic olefins, such as ethylene, propene, 1-butene, 2-butene, iso butene, 1-pentene, 2-pentene, 1-hexene, 1-heptene, 1-octene, 2,4,4-tri methyl-1-pentene, 2,4,4-trimethyl-2-pentene, 1-nonen, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, C₂₀ olefin, C₂₂ olefin, C₂₄ olefin, C₂₈ olefin or C₃₀ olefin, cyclopropene, Cyclobutene, cyclopentene, cyclohexene, cyclooctene, vinyl alkyl ether such as vinyl methyl ether, vinyl ethyl ether or vinyl butyl ether, Allyl chloride, allyl alcohol, vinyl acetate, vinyl propionate, styrene as well as compounds with several olefinic double bonds such as 1,3-butadiene, isoprene, cyclopentadiene or cyclooctadiene. It olefin mixtures can also be used.

The method according to the invention is particularly suitable for Epoxidation of propene to propylene oxide.

Aromatic peroxycarboxylic acids are particularly suitable Compounds of the general formula I

in which the substituents R¹ to R³ independently of one another for What serstoff, C₁- to C₆-alkyl, C₃- to C₈-cycloalkyl, C₆- bis C₁₄ aryl, C₇ to C₁₂ phenylalkyl, halogen, C₁ to C₆ alkoxy, C₃ to bis C₈-cycloalkoxy, C₆- to C₁₄-aryloxy or C₇- to C₁₂-phenyl are alkoxy and one of the substituents R¹ to R³ also one  mean another peroxycarboxyl group or a carboxyl group can.

In particular, the substituents R¹ to R³ have independently of one another other meaning:

• - hydrogen;
• - C₁ to C₆ alkyl, preferably C₁ to C₄ alkyl such as methyl, Ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec.-butyl, tert-butyl, n-pentyl or n-hexyl, especially methyl or tert-butyl;
• - C₃- to C₈-cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, Cyclohexyl, cycloheptyl or cyclooctyl, especially cyclo pentyl or cyclohexyl or substituted C₃- to C₈-cyclo alkyl, especially 1-methylcyclopentyl or 1-methylcyclo hexyl;
• - C₆ to C₁₄ aryl such as phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl or 9-anthryl, especially phenyl;
• - C₇ to C₁₂ phenylalkyl such as 1-methyl-1-phenylethyl, benzyl, 1-phenylethyl, 2-phenylethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-phenylbutyl, 2-phenylbutyl, 3-phenylbutyl or 4-phenylbutyl, especially 1-methyl-1-phenylethyl;
• - Halogen such as fluorine, chlorine or bromine;
• - C₁ to C₆ alkoxy, C₃ to C₈ cycloalkoxy, C₆ to C₁₄ aryloxy or C₇- to C₁₂-phenylalkoxy, which is at the oxygen atom radicals have the meanings listed above from R¹ to R³ (with the exception of hydrogen);
• - for one of the substituents R¹ to R³ peroxycarboxyl or Carboxyl.

Furthermore, such aromatic peroxycarboxylic acids I before adds one, two or three methyl groups as substituents R¹ to R³ have.

Examples of aromatic peroxycarboxylic acids that can be used are in particular peroxybenzoic acid, 2-methylperoxybenzoic acid (o-peroxytoluic acid), 3-methylperoxybenzoic acid (m-peroxytoluyl acid), 4-methylperoxybenzoic acid (p-peroxytoluic acid), 2,4- and 3,5-dimethylperoxybenzoic acid, 2,4,6-trimethylperoxybenzoic acid, 4-tert-butylperoxybenzoic acid, 2-methyl-4-tert-butylperoxybene  zoic acid, 2,6-dimethyl-4-tert-butylperoxybenzoic acid, 2-, 3- or 4-ethylperoxybenzoic acid, 4- (1-methylcyclohexyl) peroxy benzoic acid, 4- (1-methylcyclopentyl) peroxybenzoic acid, 4-phenyl peroxybenzoic acid, 3-chloroperoxybenzoic acid, 4-methoxy or 4-ethoxyperoxybenzoic acid, 4-methoxy or 4-ethoxy-2,6-dimethyl peroxybenzoic acid, bisperoxyphthalic acid, monoperoxyphthalic acid, Bisperoxy terephthalic acid and monoperoxy terephthalic acid. It can also mixtures of the aromatic peroxycarboxylic acids mentioned be set. O-Peroxytoluylic acid is particularly preferred.

Step A of the method according to the invention is regarding Epoxidation of olefins described in the literature. The Epoxidation is usually carried out as follows:

The aromatic peroxycarboxylic acid, dissolved in a suitable Solvent is reacted with an olefin. The molar ratio of olefin to peroxycarboxylic acid is 0.8: 1 to 100: 1, especially 1: 1 to 20: 1, especially 2: 1 to 8: 1.

The peroxycarboxylic acid solution used can be in a solution isolated medium peroxycarboxylic acid. Prefers however, the solution is used directly in the oxidation step C was prepared (if necessary after a Reini step in which the peroxycarboxylic acid remains in solution).

As an organic solvent for the peroxycarboxylic acids in the Epoxidation can be ketones (e.g. acetone, butanone or tert-butyl methyl ketone), esters (e.g. methyl and ethyl acetate or Methyl benzoate), nitro compounds (e.g. nitromethane or nitro benzene), halogenated hydrocarbons (e.g. di- and trichlor methane, 1,1,1-trichloroethane or chlorobenzene), carbonates (e.g. Dimethyl carbonate), urea derivatives (e.g. tetramethyl urea), inorganic esters or amides (e.g. trimethyl phosphate or hexa methylphosphoric acid triamide), hydrocarbons (e.g. hexane or Heptane) or alkyl aromatics (e.g. benzene, toluene or xylene) and Ethers in which, under the reaction conditions, practically none disturbing and dangerous peroxide formation occurs, for. B. methyl tert-butyl ether or dimethoxymethane can be used. Especially however, the use of the same solution is preferred as in the oxidation in step C. Particularly preferred Solvents for both steps are acetone, methyl acetate and Ethyl acetate.

The epoxidation can be carried out at -20 to 200 ° C, depending for solvent and olefin. When using acetone as Solvents and terminal olefins (such as 1-octene or  Propene) as a substrate are temperatures from 20 to 150 ° C before moves. Temperatures of 50 to 100 ° C. are particularly preferred.

Surprisingly, reacts at the relatively high temperature of 60 ° C or above the olefin to the epoxy much faster than given if necessary, aromatic aldehyde from stage B still available Carboxylic acid.

The separation of the aromatic peroxy in step A. carboxylic acids I created aromatic carboxylic acids from the Oxidation products, especially the alkylene oxides, happen by conventional methods, for example by filtration, extract tion or distillation.

The catalytic hydrogenation of aromatic carboxylic acids in Step B is preferably carried out in the gas phase with hydrogen in Presence of a lanthanide / zirconia catalyst. Such Catalysts are used as hydrogenation catalysts for the transfer tion of aromatic carboxylic acids in the corresponding aldehydes known from DE-A 44 28 994 (3).

Step B of the method according to the invention is expedient carried out as follows:

Hydrogenation of aromatic carboxylic acids with hydrogen in Presence of a catalyst whose catalytically active mass 60 up to 99.9, in particular 80 to 99.9% by weight of zirconium oxide (ZrO₂) and 0.1 to 40, in particular 0.1 to 20% by weight of one or more Elements containing lanthanides are usually found at tempera tures from 200 to 450 ° C, preferably 250 to 400 ° C, in particular 300 to 380 ° C, and pressures of 0.1 to 20 bar, preferably 0.7 up to 5 bar, especially atmospheric pressure (normal pressure) leads. The required temperature and pressure depend on the catalyst activity and the thermal Stability of reactant and product.

Supported catalysts are preferred, preferably Full catalysts of zirconium oxide in cubic, tetragonal or monoclinic phase, preferably in monoclinic phase, with a or several elements from the lanthanide series are doped.

The catalytically active composition preferably contains 90 to 99.9% by weight, in particular 92 to 99% by weight of zirconium oxide and 0.1 to 10 wt .-%, in particular 1 to 8 wt .-%, one or more el elements of the lanthanides, in particular lanthanum, cerium, praseodymium, Neodymium, samarium or europium, but also promethium, Gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytter bium or lutetium, or their mixtures, especially lanthanum as  Lanthanum (III) oxide. The doping is usually done by Soak the zirconium oxide with salt solutions (aqueous or alcoholic lisch) of the lanthanides.

The catalyst can also have additional doping (e.g. chromium, Iron, cobalt, zinc, bismuth, lead, yttrium, hafnium, manganese) in Contain amounts from 0.001 to 10 wt .-%. However, are preferred Catalysts without such additional additives.

For the hydrogenation according to stage B, the in metal-doped zirconium oxide described in EP-A 150 961 (4) Suitable catalysts.

The BET surface area of the zirconium oxide can vary within wide limits ken, but is usually 5 to 150 m² / g, preferably 20 to 150 m² / g, in particular 40 to 120 m² / g.

Such catalysts are known in a known manner, for. B. by Watering preformed carriers such as pellets, balls or strands, Dried and calcined.

With certain types of reactors (e.g. tube bundle reactors) it can be advantageous, the catalysts described as moldings with a streamlined geometry to use in especially to lower the flow resistance and the pressure keep losses low. Such a measure favors especially the heat distribution in the reactor.

The preferred supported catalysts show over a long period of high activity. Deactivated catalysts can be contained by treatment with molecular oxygen tendency gases, e.g. B. air, at temperatures of 350 to 500 ° C brisk kidney.

In general, a catalyst load of 0.01 to is maintained 10, preferably 0.01 to 3 kg of aromatic carboxylic acid per kg Catalyst and hour on.

The hydrogen concentration in the input gas depends on the Carboxylic acid concentration. The molar ratio of hydrogen to aromatic carboxylic acid is usually 2: 1 to 200: 1, be preferably 10: 1 to 100: 1. Ants can also act as a source of hydrogen acid can be used.  

The addition of an inert diluent can also be advantageous be. Usually nitrogen, water or gaseous, compounds which are inert under the reaction conditions, such as coal water substances, aromatics or ethers used.

The reaction can be carried out either continuously in the gas phase Fixed bed reaction with fixed catalyst or as Fluid bed reaction with a swirling and swirling movement Lich catalyst can be carried out. Work is preferred in a fixed bed. The following are suitable as reactor types special tube bundle reactors.

To increase the selectivity, gebil dete by-products, e.g. B. alcohols, in the synthesis cycle be returned.

The mixture from step B containing the aromatic aldehyde is, if necessary after a cleaning step, in step C expediently taken up in a suitable solvent and in the liquid phase with oxygen or an oxygen term gas mixture to the corresponding aromatic percarboxylic acid oxidized. It is preferably carried out at temperatures of -10 ° C to 100 ° C and oxygen partial pressures from 0.001 to 100 bar.

From DE-A 25 15 033 (5) it is known that p-tolylaldehyde in acetone solution with air at 28 ° C and 30 bar without catalyst can oxidize about 80% yield to p-peroxytoluic acid. Such however, high yields are only achieved if they are highly pure p-Toluylaldehyde and anhydrous acetone can be used.

Step C of the method according to the invention is normally carried out as follows:
The concentration of the aromatic aldehyde in the solvent can be 1 to 75% by weight. Concentrations of 5 to 35% by weight, in particular 8 to 20% by weight, are preferred.

Oxygen or the oxygen-containing gas mixture can either the gaseous or as a solution, optionally also under pressure, are reacted with the aromatic aldehyde. Of the Oxygen partial pressure is preferably 0.01 to 30 bar, ins special 0.05 to 5 bar.

The oxidation can be carried out in one or two phases. For the single-phase mode of operation is suitable for reactors in which one Solution of the aromatic aldehyde with a solution of oxygen,  optionally under pressure, can react, e.g. B. Tube reactors, tube bundle reactors or flooded stirred tanks. For The two-phase mode of operation are suitable for reactors that are good Ensure gas / liquid mixing, like bubble columns (with or without dividers or packing), stirred tank (given if arranged with a gassing stirrer and possibly as a cascade net) or trickle reactors.

The reaction temperature is preferably 20 to 80 ° C, ins special 50 to 70 ° C.

The reaction time is chosen so that an aldehyde conversion between 40 and 100% is reached. Reaction times with are preferred which achieve an aldehyde conversion between 60 and 99%. Be reaction times with which an aldehyde is particularly preferred rate between 75 and 95% is reached.

During the oxidation, a stabilizer for the formed can Peroxycarboxylic acid, e.g. B. 8-hydroxyquinoline, dipicolinic acid or 2,6-dihydroxymethylpyridine can be added.

As organic solvents for step C, ketones (e.g. Acetone, butanone or tert-butyl methyl ketone), esters (e.g. Methyl and ethyl acetate or methyl benzoate), nitro compounds (e.g. nitromethane or nitrobenzene), halogenated hydrocarbons substances (e.g. di- and trichloromethane, 1,1,1-trichloroethane or Chlorobenzene), carbonates (e.g. dimethyl carbonate), urea derivatives (e.g. tetramethyl urea), inorganic esters or Amides (e.g. trimethyl phosphate or hexamethyl phosphoric acid tri amide) or alkyl aromatics (e.g. benzene, toluene or xylene) and Ethers in which, under the reaction conditions, practically none disturbing and dangerous peroxide formation occurs, for. B. methyl tert-butyl ether or dimethoxymethane can be used. Before ketones, especially acetone and tert-butyl methylke, are added clay, and esters, especially methyl and ethyl acetate and methyl benzoate.

The aromatic percarboxylic acid can either be isolated (e.g. by precipitation), but also without isolation (i.e. in solution) can be used directly in step A.

It is surprising that o-tolylaldehyde is faster and more selective ver can be oxidized as the isomeric m- and p-tolylaldehydes.

The process described has the advantage that the aromatic Peroxycarboxylic acid after oxidation or epoxidation without Ein hydrogen peroxide is regenerated. The aromatic  Peroxycarboxylic acid only acts as an oxygen carrier and is practically not consumed. The stoichiometry for the whole The procedure in the case of epoxidation is:

Olefin + O₂ + H₂ → alkylene oxide + H₂O.

The statement that the peroxycarboxylic acid circulated practically table is not consumed, however, applies to large-scale technology African implementation of the described method not so. The - if negligible in terms of percentage - by-product education causes with a corresponding large-scale con continuous procedures, seen over a long period of time, a substantial loss (in absolute amounts) of the epoxy dation agent peroxycarboxylic acid. Exactly on this problem the present invention by eliminating these losses in process technically and economically advantageous.

In a preferred embodiment, this supplement is used in such a way that the product mixture, which in the Direct oxidation of the alkyl aromatics occurs without further Separation of the individual oxidation products in the reaction feeds the circuit. This mixture of products usually exists essentially from aromatic benzylic alcohols, aroma aldehydes and aromatic carboxylic acids, the latter make up the bulk.

The direct oxidation of the alkyl aromatics is usually carried out with Oxygen or an oxygen-containing gas mixture, e.g. B. air, performed, it can be in the presence or absence of a ge suitable catalyst and in the presence or absence of ge suitable solvents are made. Such oxidation Processes are described in large numbers in the prior art.

The feeding of the said product mixture from the direct Oxidation of the alkyl aromatics takes place in the reaction cycle expediently after epoxidation of the olefins (Step A) and before the hydrogenation (Step B).

A reaction scheme for epoxidation using the aromatic peroxycarboxylic acids I with addition of losses The epoxidation agent looks like this:

In the case of the use of o-, m- or p-methylperbenzoic acid as Epoxidation agent I goes for example from o-, m- or p-xylene and oxidizes it to a mixture of o-, m- or p-methylbenzyl alcohol, o-, m- or p-methylbenzaldehyde and o-, m- or p-methylbenzoic acid. A selective oxidation to carbon Acid level is general and especially in the example mentioned (because of the risk of oxidation of the second methyl group at zu drastic reaction conditions) difficult and expensive accomplish.

It is the great advantage that, in the sense of the present Er Find a mixture of carboxylic acid, alcohol and aldehyde in the Reaction cycle can use, since yes already in the cycle all components are present.

In a further preferred embodiment, the Working up the aromatic aldehydes obtained in step B. Medium and high-boiling secondary components of the reak partially or completely into the alkylaromatic Oxidation back. Such medium and high-boiling secondary stock Parts can contain aromatic benzylic alcohols, hydrocarbons (e.g. xylenes) or products of side reactions (e.g. phthalides) be.

The present invention also relates to a method for Production of alkylene oxides from the corresponding olefins by means of aromatic peroxycarboxylic acids, in which, after success ter epoxidation of the olefins (step A) the aroma formed  table separates carboxylic acids from the alkylene oxides in step B Catalytically hydrogenated to the corresponding aromatic aldehydes and in step C, these aldehydes with oxygen or an acid substance-containing gas mixture back to the aromatic peroxycarbon acids oxidized, which again for the epoxidation of olefins be set, and which is characterized in that one phenolic by-products contained in the aromatic aldehyde the oxidation removed in step C.

In particular, this removal of phenolic by-product ten in combination with the supplement of Ver loss of aromatic peroxycarboxylic acid as an epoxidation agent performed.

The removal of phenolic by-products is therefore advisable advise because such compounds affect oxidation step C. can be pregnant.

Removal can be done by conventional distillation, crystallization tion or extraction methods take place, but is preferred extraction with aqueous bases such as aqueous sodium or Ka lium carbonate solution or aqueous sodium or potassium hydroxide solution, aqueous Calcium hydroxide or aqueous ammonia.

As phenolic by-products are especially in the case of Use of methyl perbenzoic acids as epoxidation agents To name cresols and / or cresol formates. When extracting with aqueous mineral bases, the cresol formate is split into cresol, so that after acidifying the aqueous mineral base extract nes cresol as an additional valuable product of the process can.

The present invention also relates to a method for Production of alkylene oxides from the corresponding olefins by means of aromatic peroxycarboxylic acids, in which, after success ter epoxidation of the olefins (step A) the aroma formed table separates carboxylic acids from the alkylene oxides in step B Catalytically hydrogenated to the corresponding aromatic aldehydes and in step C, these aldehydes with oxygen or an acid substance-containing gas mixture back to the aromatic peroxycarbon acids oxidized, which again for the epoxidation of olefins be set, and which is characterized in that one in the case of epoxidation of C₂ to C₆ olefins Olefin from a corresponding C₂ to C₆ hydrocarbon Produces dehydration.  

In particular, this generation of C₂ to C₆ olefins by Dehydration in combination with the supplement according to the invention the loss of aromatic peroxycarboxylic acid as an epoxidation agent.

In particular, this generation of olefins is by dehydrogenation important for propene. In addition to dehydrating propane too However, propene are also dehydrogenations from butane to butenes, from Butane or butenes to butadiene, from isobutane to isobutene, from Pentane to pentenes and from cyclohexane to cyclohexene interesting. This dehydration route is one - depending on the host boundary conditions - advantageous alternative to Ge recovery of said olefins by conventional cracking processes.

A particular advantage of the dehydration route described is the possible use of the hydrogen released here the hydrogenation of aromatic aldehydes (and that automatically in the correct amount) according to step B of the reaction described circuit, which is therefore the preferred embodiment is to be emphasized.

Claims (14)

1. A process for the preparation of alkylene oxides from the corresponding olefins by means of aromatic peroxycarboxylic acids, in which, after epoxidation of the olefins (step A), the resulting aromatic carboxylic acids are separated from the alkylene oxides, catalyzed in step B to the corresponding aromatic aldehydes and in step C these aldehydes are oxidized again with oxygen or an oxygen-containing gas mixture to the aromatic peroxycarboxylic acids, which are used again for the epoxidation of olefins, characterized in that losses of aromatic carboxylic acids and / or aromatic aldehydes occurring in the reaction cycle by corresponding oxidation he added the underlying alkyl aromatic compounds. 2. The method according to claim 1, characterized in that one the product mixture, which in the direct oxidation of the Alkyl aromatics are formed without further separation of the individual NEN oxidation products fed into the reaction cycle. 3. The method according to claim 2, characterized in that the Product mixture essentially from aromatic benzylic Alcohols, aromatic aldehydes and aromatic carbon acids. 4. The method according to claims 1 to 3, characterized in net that the oxidation of the alkyl aromatics with oxygen or an oxygen-containing gas mixture. 5. The method according to claims 2 to 4, characterized in net that the product mixture from the direct oxidation the alkylaromatics after epoxidation of the olefins (Step A) and before the hydrogenation (Step B) in the reacti on-cycle. 6. The method according to claims 1 to 5, characterized in net that when working up the obtained in step B. aromatic medium and high-boiling aromatic aldehydes Minor or partial constituents of the reaction mixture constantly leads back into the alkylaromatic oxidation.   7. The method according to claims 1 to 6, characterized in net that phenolic contained in the aromatic aldehyde By-products removed prior to oxidation in step C. 8. Process for the preparation of alkylene oxides from the corre olefins using aromatic peroxycarboxylic acids, in which after epoxidation of the olefins (step A) the resulting aromatic carboxylic acids from the alkylene separates oxides, catalytically in step B to the corresponding hydrogenated the aromatic aldehydes and in step C this Aldehydes with oxygen or an oxygen-containing gas mixed again oxidized to the aromatic peroxycarboxylic acids, which are used again for the epoxidation of olefins the, characterized in that in the aromatic aldehyde phenolic by-products contained according to before oxidation Step C removed. 9. The method according to claim 7 or 8, characterized in that the removal of the phenolic by-products by Ex traction with aqueous bases. 10. The method according to claims 7 to 9, characterized in net that one in the case of using methyl perbenzoic acids as epoxidation agents as phenolic by-products corresponding cresols and / or cresol formates removed. 11. The method according to claims 1 to 10, characterized in net that in the case of the epoxidation of C₂ to C₆ olefins the olefin used from a corresponding C₂ to C₆ hydrocarbon generated by dehydrogenation. 12. Process for the preparation of alkylene oxides from the corre sponding olefins using aromatic peroxycarboxylic acids, in which after epoxidation of the olefins (step A) the resulting aromatic carboxylic acids from the alkylene separates oxides, catalytically in step B to the corresponding hydrogenated the aromatic aldehydes and in step C this Aldehydes with oxygen or an oxygen-containing gas mixed again oxidized to the aromatic peroxycarboxylic acids, which are used again for the epoxidation of olefins the, characterized in that in the case of epoxidia tion of C₂ to C₆ olefins the olefin used from one corresponding C₂ to C₆ hydrocarbon by dehydrogenation generated.   13. The method according to claim 11 or 12, characterized in that one used in the case of the epoxidation of propene Propene generated by dehydration of propane. 14. The method according to claims 11 to 13, characterized in net that one in the dehydrogenation of the hydrocarbon released hydrogen in the hydrogenation of the aromatic Aldehydes used according to step B of the reaction cycle.