DE19647349A1 - Preparation of 1,6-hexan:diol and epsilon-caprolactone from carboxylic acid mixture - Google Patents

Abstract

Preparation of 2,6-hexandiol and iota -caprolactone from a carboxylic acid mixture containing adipic acid, 6-hydroxycaproic acid and small amounts of 1,4-cyclohexandiols. The mixture is obtained as a by-product of the oxidation of cyclohexane into cyclohexanone and cyclohexanol with oxygen or oxygen-containing gases, water extraction, esterification and hydrogenation into hexandiol and cyclisation of 6-hydroxycaproic acid esters into caprolactone. Steps involved are: (a) esterification of the monocarboxylic and dicarboxylic acids in the aqueous reaction mixture with low molecular mass alcohols, (b) excess alcohol and low b.pt. substances are distilled off, (c) a second distillation step separates the mixture into an ester fraction substantially free of 1,4-cyclohexandiols and one containing at least the greater part of the 1,4-cyclohexandiols, (d) at least part of a substantially 6-hydroxycaproic acid ester stream is separated from the ester fraction in a third distillation stage, (e) the ester fraction from (d) from which the 6-hydroxycaproic acid ester was at least partially removed, is hydrogenated catalytically and 1,6-hexandiol is extracted by distillation and (f) the substantially 6-hydroxycaproic acid ester containing stream is heated above 200 deg C at reduced pressure so as to effect cyclisation. Pure iota -caprolactone is recovered by distillation. Preferably water is removed from the carboxylic acid mixture before esterification. Alcohol for esterification is either 1-3C (preferably MeOH) or 4-10C (preferably iso-BuOH or tert.-BuOH) and a variety of distillation, collection and separation arrangements are used depending on the relative b.pts. of the intermediate products involved. A Cu, Co and/or Re based catalyst is used for the hydrogenation step, or one of type CuaAlbZrcMndOx (a > 0, b > 0, c \- 0, d > 0, a > b/2, b > a/4, a > c, a > d and x = a number to balance the formula).

Description

The invention relates to a method for producing 1,6-hexanediol and caprolactone, preferably with at least 99% Purity, particularly practical of 1,4-cyclohexanediols are free from a carboxylic acid mixture which is a by-product of Oxidation of cyclohexane to cyclohexanone / cyclohexanol with acid gases or oxygen-containing gases and water extract tion of the reaction mixture is obtained by esterification and Hydrogenation of a partial stream to hexanediol and cyclization of 6-hydroxycaproic acid esters, with the 1,4-cyclohexanediols either in the fractionation of the esterification mixture or last of Caprolactone are separated. After a modification of the procedure rens of the invention. Refrain from hydrogenation and adipin Acid diester won, the immediate use z. B. can be supplied as a lubricant.

1,6-hexanediol is a sought-after monomer building block that mainly used in the polyester and polyurethane sector becomes. Caprolactone or the polyaddition produced therefrom Polycaprolactones are used to manufacture polyurethanes.

The aqueous solutions of carboxylic acids involved in the oxidation from cyclohexane to cyclohexanol and cyclohexanone (cf.Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., 1987, Vol. A8, P. 49) arise as by-products, hereinafter dicarboxylic acid called solution (DCL), contain (calculated anhydrous in% by weight) generally between 10 and 40% adipic acid, between 10 and 40% 6-hydroxycaproic acid, between 1 and 10% glutaric acid, between 1 and 10% 5-hydroxyvaleric acid, between 1 and 5% 1,2-cyclohexanediols, between 1 and 5% 1,4-cyclohexanediols, between 2 and 10% formic acid and a variety of others Mono- and dicarboxylic acids, esters, oxo and oxa compounds, their Individual levels generally do not exceed 5%. Example be wise acetic acid, propionic acid, butyric acid, valeric acid, Caproic acid, oxalic acid, malonic acid, succinic acid, 4-hydroxy called butyric acid and γ-butyrolactone.

From DE 23 21 101 and DE 12 35 879 it is known that these are aqueous Dicarboxylic acid solutions at temperatures from 120 to 300 ° C and Pressures from 50 to 700 bar in the presence mainly of cobalt holding catalysts to 1,6-hexanediol as the main product hydrogenate. The hydrogenation outputs are preferably distilled worked up. It is also possible with an extremely high style  lations effort not or only incompletely, which in the hydrie Unchanged 1,4-cyclohexanediols of 1,6-hexanediol separate so that the 1,4-cyclohexanediols, which initially were already included in the DCL, with a content of im generally find 2 to 5% by weight in 1,6-hexanediol.

To address this problem are a few approaches known:

In US 3 933 930 the reaction of 1,4-cyclohexanediol in aqueous solutions of adipic acid and 6-hydroxycaproic acid Cyclohexanol, cyclohexane and / or cyclohexene described by the mixture is catalytically prehydrogenated. This method requires the use of two different hydrogenation catalysts, one for the pre-hydrogenation, one for the actual carbon acid hydrogenation and is therefore expensive.

According to DE-OS 20 60 548 very pure 1,6-hexanediol Crystallization won. This process is also very expensive dig and also associated with significant losses in yield.

Another way of obtaining high-purity 1,6-hexane diol consists of pure adipic acid or pure instead of DCL Hydrogenate adipic acid esters (K. Weissermel, H.J. Arpe, Indu Strielle Organic Chemistry, VCH Publishing Association Weinheim, 4th edition, page 263, 1994). Pure adipic acid is however in Very expensive compared to DCL. Furthermore, the carboxylic acid mixture that arises from cyclohexane oxidation, a waste product that also from an environmental point of view of material recycling should be fed.

Caprolactone has so far only been based on industrial scale Cyclohexanone produced by Baeyer-Villiger oxidation. Here explosive per compounds are either used or in ver drive through.

The production of caprolactone from DCL is e.g. B. from DE 16 18 143 has already been described. It is drained DCL thermally reacted with phosphoric acid and a mixture of Dicarboxylic acids, caprolactone and a variety of other components fractionated. The swamp falls z. T. firm and heavy soluble. The caprolactone also has other only 98% purity by distillation.  

Furthermore, 6-hydroxycaproic acid or its is widely described Convert ester to caprolactone (e.g. DE 20 13 525, EP-A 349 861 and literature cited therein).

It was therefore the task, based on DCL, to contain the content to convert tene 6-hydroxycaproic acid into very pure caprolactone and at the same time very pure 1,6-hexanediol or adipic acid ester win from the adipic acid contained in the DCL and thus the disadvantages of the prior art, i. H. either high cost the manufacture or insufficient purity of the products, ver avoid.

This object was achieved with a process for the preparation of 1,6-hexanediol and ε-caprolactone from an adipic acid, 6-hydrocaproic acid and small amounts of 1,4-cyclohexanediols containing carboxylic acid mixture, which as a by-product of. Oxidation of cyclohexane to cyclohexanone / cyclohexanol with oxygen or oxygen-containing gases and water extraction of the reaction mixture is obtained by esterification and hydrogenation of a partial stream to hexanediol and cyclization of 6-hydroxycaproic acid ester to caprolactone, wherein

• a) the mono- and contained in the aqueous reaction mixture Dicarboxylic acids with a low molecular weight alcohol corresponding carboxylic acid esters,
• b) the esterification mixture obtained in a first distilla level of excess alcohol and low boilers liberated,
• c) from the bottom product in a second distillation stage Separation into one of 1,4-cyclohexanediols essentially free ester fraction and at least the greater part of the Fraction containing 1,4-cyclohexanediols,
• d) the ester fraction in a third distillation stage at least partially an essentially 6-hydroxycapron separates stream containing acid esters,
• e) the ester fraction from (d) from the at least partially 6-hydroxycaproic acid ester was removed catalytically hydrogenated and in by distillation of the hydrogenation product in a manner known per se, 1,6-hexanediol wins and  
• f) essentially containing 6-hydroxycaproic acid ester Current at temperatures above 200 ° C at reduced pressure heated, causing 6-hydroxycaproic acid ester to form caprolactone is cyclized and from the cyclization product Distillation of pure ε-caprolactone wins.

After a modification of this procedure, the adipin can Acid esters obtained as such and an immediate Use, e.g. B. supplied as a lubricant, d. H. the Step (s) can be omitted.

It was surprising that in the separation of the ester mixtures, which result from the esterification of the mono- and dicarboxylic acids contained in the DCL, the 1,4-cyclohexanediols, which if so with. Carboxylic acids can be esterified, can be separated so that after hydrogenation and work-up the remaining very low 1,4-cyclohexanediol content in 1,6-hexanediol is no longer of any practical importance. Because of the complicated mixture of substances to be separated, it was surprising that the 1,4-cyclohexanediols or their esters, despite the unfavorable boiling point ratios and azeotropic formation to be feared, were practically completely free of the C ₆ esters used for the hydrogenation to 1,6-hexanediol cut off.

The esterification can be preferred without the addition of catalysts be carried out under the action of catalysts. As low molecular weight alcohols usually come from 1 to 10 carbon atoms, in particular alkanols with 1 to 8 carbon atoms in Consideration. Diols such as butanediol or pentanediol also come in principle. Said caprolactone and adipic acid ester alcohols that are higher than caprolactone are also obtained boil, such as B. 1,6-hexanediol, octadecanol or trimethylol propane into consideration.

The technically preferred ones to be used for the esterification Alcohols are n- or i-butanol and especially methanol.

In the case of esterification with methanol (variant A), this is how it is done before that in the distillation stage (c) an essentially 1,4-cyclohexanediols free carboxylic acid methyl ester fraction on Head of the column and one of the high boilers and the 1,4-cyclohexane bottom fraction containing diols wins and the carboxylic acid methyl ester fraction in the hydrogenation stage (d) catalytically hydrogenated.

If n- or i-butanol is used for the esterification (variant B), in the distillation stage (c) the 1,4-cyclohexanediols separated with the low boilers overhead and you win the  Carboxylic acid butyl ester as a side draw or as containing it Sump with subsequent introduction into the hydrogenation stage (d), or in a further distillation if you win adipic acid esters want.

The method according to the invention, with its variants A ( FIG. 1), B ( FIG. 2), C ( FIG. 3) and D ( FIG. 4), is explained in general as follows (the terms overhead and swamp in each case) mean the deduction above or below the inlet):

option A

As shown in Fig. 1, the dicarboxylic acid solution (DCL), optionally after dewatering, is fed together with a C ₁ to C ₃ alcohol, preferably methanol, into the esterification reactor R ₁ , in which the carboxylic acids are esterified. The esterification mixture obtained then passes into column K ₁ , in which the excess alcohol (ROH), water and low boilers (LS) are distilled off overhead and the ester mixture (EG) is drawn off as a bottom and is fed into column K ₂ . In this column, the EG is fractionated into an ester fraction (EF) essentially free of 1,4-cyclohexanediols and a bottom fraction consisting of high boilers (HS) and cis and trans-1,4-cyclohexanediols (1,4-CHDO). The ester fraction is then passed into a further fractionation column K ₃ , in which the ester fraction is converted into a top product consisting essentially of adipic acid diester (ADSE), preferably dimethyl ester and a bottom product consisting essentially of 6-hydroxycaproic acid ester (HCSE), preferably methyl ester is separated.

The fraction essentially containing adipic acid diester is then hydrogenated in the catalytic hydrogenation R ₂ to 1,6-hexanediol, which is purely distilled in the column K ₄ .

The 6-hydroxycaproic acid ester fraction is subjected to a thermal treatment in the reactor R ₃ above 100 ° C., generally 150 to 350 ° C., preferably 200 to 300 ° C. under reduced pressure, for. B. 900 to 10 mbar, preferably subjected to 300 to 20 mbar; this leads to the cyclization of the ester with formation of ε-caprolactone, which is distilled in column K ₅ .

Variant B

It differs from variant A in that alcohols containing 4 to 10 carbon atoms are used for the esterification. Before preferably one uses n- or i-butanol. This results in a reversal of the fractionation in the distillation column by increasing the boiling points of the esters, ie the ester fraction (EF) is obtained as the bottom product. As shown in Fig. 2, the EF is then again passed into the fracture column K ₃ , in which the adipic acid diester, preferably the -dibutyl ester (ADSE), was now obtained as the bottom product and the 6-hydroxycapronester, preferably -butyl ester, as the top product, both of which were obtained , as described in variant A, be worked up.

Variant C

According to this variant, the distillation of the columns K ₂ and K _{3 is drawn together} to form a distillation stage.

According to FIG. 3, the ester mixture (EG) obtained by esterification with alcohols having 1 to 3 carbon atoms, preferably methanol, is subjected to a fractional distillation and the adipic esters, preferably dimethyl esters, in an upper side draw, and the 6-hydroxycapronester in a lower side draw , preferably methyl ester, and the 1,4-cyclohexanediols obtained as the bottom.

The adipic acid ester and 6-hydroxycaproic acid ester fractions are then worked up as described in FIG. 1.

Variant D

This embodiment corresponds to variant C with the sub decided that for the esterification alcohols including diols 4 to 10 carbon atoms, preferably n- or i-butanol be used. Due to the reversal of the boiling point relations 6-hydroxycaproic acid ester is obtained as the upper side draw lower side deduction adipic acid ester and as the top product 1,4-cyclohexanediols. The further processing of the ester fractions is then carried out as described above.

The method according to the invention is explained in detail below for variant A with reference to FIG. 5. The reaction conditions apply equally to the other variants.

The process steps are broken down into stages, whereby stages 2 , 3 , 4 , 5 , 6 , 7 and 12 , 13 and 14 are essential for the process (stages 5 , 6 , 7, however, only if hexanediol and not adipic acid diesters as such) won) and the levels 3 and 4 as well as 6 and 7 can also be combined. Levels 8 , 9 , 10 and 11 are optional, but may be useful to increase the economics of the process.

The dicarboxylic acid solution (DCL) is generally an aqueous solution with a water content of 20 to 80%. Since an esterification reaction is an equilibrium reaction in which water is formed, it is useful, especially when esterifying with z. B. To remove existing water before the reaction ent, especially if water is not during the esterification reaction, for. B. can not be removed azeotropically. The dewatering tion in stage 1 can, for. B. with a membrane system, or preferably by a distillation apparatus in which at 10 to 250 ° C, preferably 20 to 200 ° C, particularly 30 to 200 ° C and a pressure of 1 to 1500 mbar, preferably 5 to 1100 mbar, particularly preferably 20 to 1000 mbar water overhead and higher monocarboxylic acids, dicarboxylic acids and 1,4-cyclohexanediols are separated off at the bottom. The bottom temperature is preferably chosen so that the bottom product can be drawn off in liquid form. The water content in the bottom of the column can be 0.01 to 10% by weight, preferably 0.01 to 5% by weight, particularly preferably 0.01 to 1% by weight.

The water can be separated so that the water is above is obtained acid-free or can be obtained in the DCL contained lower monocarboxylic acids - essentially ants acid - for the most part distill off with the water, so these do not bind esterification alcohol in the esterification.

Alcohol ROH with 1 to 10 carbon atoms is added to the carboxylic acid stream from stage 1 . Here, methanol, ethanol, propanol or isopropanol or mixtures of the alcohols, but preferably methanol on the one hand or C ₄ and higher alcohols, in particular with 4 to 8 C atoms and preferably n- or i-butanol or also n-pentanol or i -Pentanol on the other hand can be used. The mixing ratio of alcohol to carboxylic acid stream (mass ratio) can be from 0.1 to 30, preferably 0.2 to 20, particularly preferably 0.5 to 10.

This mixture reaches the stage 2 reactor as a melt or solution, in which the carboxylic acids are esterified with the alcohol. The esterification reaction can be carried out at 50 to 400 ° C., preferably 70 to 300 ° C., particularly preferably 90 to 200 ° C. An external pressure can be applied, but the esterification is preferably carried out under the autogenous pressure of the reaction system. A stirred tank or flow tube or several each can be used as the esterification apparatus. The residence time required for the esterification is between 0.3 and 10 hours, preferably 0.5 to 5 hours. The esterification reaction can proceed without the addition of a catalyst, but a catalyst is preferably added to increase the reaction rate. This can be a homogeneous dissolved or a solid catalyst. Examples of homogeneous catalysts are sulfuric acid, phosphoric acid, hydrochloric acid, sulfonic acids such as p-toluenesulfonic acid, heteropolyacids such as tungstophosphoric acid or Lewis acids such as. B. called aluminum, vanadium, titanium, boron compounds. Mine acids, in particular sulfuric acid, are preferred. The weight ratio of homogeneous catalyst to carboxylic acid melt is generally 0.0001 to 0.5, preferably 0.001 to 0.3.

As solid catalysts, acidic or superacid materials, e.g. B. acidic and superacid metal oxides such as SiO ₂ , Al ₂ 9 ₃ , SnO ₂ , ZrO ₂ , layered silicates or zeolites, all of which can be doped with acid residues with mineral acid residues such as sulfate or phosphate, or organic ion exchangers with sulfonic or carboxylic acid groups . The solid catalysts can be arranged as a fixed bed or used as a suspension.

The water formed in the reaction is expediently continuous Lich z. B. removed by a membrane or by distillation.

The completeness of the turnover in the carboxylic acid melt Existing free carboxyl groups are added to those after the reaction measured acid number (mg KOH / g) found. It is deducted Lich the optionally added acid as a catalyst 0.01 to 59, preferably 0.1 to 10. Not all of them have to be in the system existing carboxyl groups as esters of the alcohol used but some can be in the form of dimers or oligo mere esters with the OH end of the hydroxycaproic acid are present.

The esterification mixture is fed in stage 3 , a membrane system or preferably a distillation column. If a dissolved acid was used as the catalyst for the esterification reaction, the esterification mixture is expediently neutralized with a base, 1 to 1.5 base equivalents being added per acid equivalent of the catalyst. As bases are in the. Rule alkali or alkaline earth metal oxides, carbonates, hydroxides or alcoholates, or amines used in bulk or dissolved in the esterification alcohol.

If a column is used in stage 3 , the feed to the column preferably takes place between the top stream and the bottom stream. The excess esterification alcohol ROH, overhead, at pressures of 1 to 1500 mbar, preferably 20 to 1000 mbar, particularly preferably 40 to 800 mbar and temperatures between 0 and 150 ° C., preferably 15 and 90 ° C. and in particular 25 and 75 ° C. Water and corresponding esters of formic acid, acetic acid and propionic acid are withdrawn. This stream can either be burned or preferably processed further in stage 11 .

An ester mixture is obtained as the sump, which mainly consists of the esters of the alcohol used ROH with dicarboxylic acids such as Adipic acid and glutaric acid, hydroxycarboxylic acids such as 6-hydroxy caproic acid and 5-hydroxyvaleric acid, and from oligomers and free or esterified 1,4-cyclohexanediols. It can be useful, a residual content of water and / or alcohol ROH allow up to 4 wt .-% in the ester mixture. The swamp temperatures are 70 to 250 ° C, preferably 80 to 220 ° C, particularly preferred 100 to 190 ° C.

The stream from stage 3 , largely freed of water and esterification alcohol ROH, is fed into stage 4 . This is a distillation column in which the feed between the low-boiling components and the high-boiling components takes place. The column is operated at temperatures from 10 to 300 ° C., preferably 20 to 270 ° C., particularly preferably 30 to 250 ° C. and pressures from 1 to 1000 mbar, preferably 5 to 500 mbar, particularly preferably 10 to 200 mbar.

The top fraction consists predominantly of residual water and residual alcohol ROH, esters of the alcohol ROH with monocarboxylic acids, predominantly C ₃ - to C ₆ -monocarboxylic acid esters with hydroxycarbon acids, such as 6-hydroxycaproic acid, 5-hydroxyvaleric acid, and especially the diesters with dicarboxylic acids such as adipic acid, glutaric acid and succinic acid, 1,2-cyclohexanediols, caprolactone and valerol acetone.

The components mentioned can be separated off overhead or, in a further preferred embodiment, in the column of stage 4 into a top stream which predominantly contains residual water and residual alcohol and the above-mentioned constituents having 3 to 5 carbon atoms and a side stream which predominantly contains the above contains components of the C ₆ esters mentioned, are separated. The stream containing the esters of C ₆ acids, either as a total overhead stream or as a side stream can then, depending on how much caprolactone is to be produced, in the limit case - without caprolactone production - being completely in the hydrogenation (stage 5 ), according to the invention however, part or all of it can be fed into stage 12 .

The high-boiling components of the stream from stage 4 , consisting predominantly of 1,4-cyclohexanediols or their esters, dimeric or oligomeric esters and unspecified z. T. polymeric constituents of the DCL are separated off via the stripping section of the stage 4 column. These can occur together or in such a way that the 1,4-cyclohexanediols are separated predominantly via a side stream of the column in the stripping section and the rest are separated off via the bottom. The 1,4-cyclohexanediols obtained in this way can, for. B. find use as a starting material for active ingredients. The high-boiling components, with or without the 1,4-cyclodiols content, can either be burned or, in a preferred embodiment, go to stage 8 for the so-called transesterification.

Stages 3 and 4 can be combined, especially if only small quantities are processed. For this purpose, the C ₆ ester stream can be obtained, for example, in a batchwise fractional distillation, again without 1,4-cyclohexanediols entering the stream led to the hydrogenation.

The hydrogenation takes place catalytically either in the gas or Liquid phase. In principle, all come as catalysts Hydrogenation of carbonyl groups suitable homogeneous and hetero gene catalysts such as metals, metal oxides, metal compounds or mixtures thereof. Examples of homogeneous Catalysts are in H. Kropf, Houben-Weyl, methods of organization African chemistry, volume IV / 1c, Georg Thieme Verlag Stuttgart, 1980, Pp. 45 to 67, and examples of heterogeneous catalysts are in Houben-Weyl, Methods of Organic Chemistry, Volume IV / 1c, p. 16 to 26.

Catalysts which use one or more of the Elements from subgroups I. and VI. to VIII. of the periods systems of elements, preferably copper, chrome, molybdenum, manganese, Rhenium, ruthenium, cobalt, nickel and palladium, especially preferably contain copper, cobalt or rhenium.

The catalysts can consist solely of the active components or the active components can be applied to supports. Suitable carrier materials are, for. B. Cr ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , ZnO ₂ , BaO and MgO or mixtures thereof.

Catalysts as described in EP 0 552 463 are particularly preferred. These are catalysts that are in the oxidic form the composition

Cu _a Al _b Zr _c Mn _d O _x

have, where a <0, b <0, c ≘ 0, d <0, a <b / 2, b <a / 4, a <c, a <d and x is the number required to maintain electroneutrality per formula unit denoted by oxygen ions. According to EP 0 552 463, these catalysts can be prepared, for example, by precipitation of poorly soluble compounds from solutions which contain the corresponding metal ions in the form of their salts. Suitable salts are, for example, halides, sulfates and nitrates. Suitable agents are all agents which lead to the formation of such insoluble intermediates which can be converted into the oxides by thermal treatment. Particularly suitable intermediate stages are the hydroxides and carbonates or hydrogen carbonates, so that alkali metal carbonates or ammonium carbonate are used as particularly preferred precipitants. The thermal treatment of the intermediates at temperatures between 500 ° C and 1000 ° C is important for the production of the catalysts. The BET surface area of the catalysts is between 10 and 150 m ² / g.

Heterogeneous catalysts are preferably used, which either fixed or used as a suspension. Will the Hydrogenation in the gas phase and over a fixed catalyst are carried out, generally temperatures of 150 to 300 ° C. applied at pressures of 1 to 100 bar, preferably 15 to 70 bar. It is useful to use at least as much hydrogen as hydrogenation medium and carrier gas used that educts, intermediates and Products never become liquid during the reaction. The surplus Sige hydrogen is preferably circulated, with a small part as exhaust gas for the removal of inert such. B. Methane can be removed. A reactor or meh rere reactors are used in series.

The hydrogenation takes place in the liquid phase with a fixed arrangement or suspended catalyst, it is generally at Temperatures between 100 and 350 ° C, preferably 120 and 300 ° C and Pressures from 30 to 350 bar, preferably 40 to 300 bar leads.

The hydrogenation can be carried out in one or more reactors in succession switched reactors are carried out. The hydrogenation in Liquid phase over a fixed bed can be used both in trickle and also carry out swamp driving. After a preferred off In one embodiment, several reactors are used, the first being The majority of the esters are hydrogenated and the reactor first reactor preferably with a liquid circuit for heat dissipation and the subsequent reactor or reactors, preferably without circulation operated to complete sales.  

The hydrogenation can be carried out batchwise, preferably continuously respectively.

The hydrogenation consists essentially of 1,6-hexanediol and the alcohol ROH. Other constituents are, above all, if the entire low-boiling stream from stage 4 was used, 1,5-pentanediol, 1,4-butanediol, 1,2-cyclohexanediols and small amounts of monoalcohols with 1 to 6 carbon atoms and water.

The hydrogenation is in stage 6 , z. B. a membrane system or preferably a distillation column, in the alcohol ROH, which additionally contains the major part of the other low-boiling components and a stream which predominantly contains 1,6-hexanediol in addition to 1,5-pentanediol and the 1,2-cyclohexanediols , on separately. At a pressure of 10 to 1500 mbar, preferably 30 to 1200 mbar, particularly preferably 50 to 1000 mbar, head temperatures of 0 to 120 ° C., preferably 20 to 100 ° C., particularly preferably 30 to 90 ° C. and bottom temperatures of 100 to 270 ° C, preferably 140 to 260 ° C, particularly preferably 160 to 250 ° C. The low-boiling material stream can either be returned directly to the esterification of stage 2 or can reach stage 8 or stage 11 .

The stream of 1,6-hexanediol is purified in stage 7 in a column. 1,5-pentanediol, 1,2-cyclohexanediols and any other low boilers that may be present are removed overhead. If the 1,2-cyclohexanediols and / or 1,5-pentanediol are to be obtained as additional valuable products, they can be separated in a further column. Any existing high boilers are removed from the swamp. 1,6-hexanediol is removed with a purity of at least 99% from a side stream of the column. At pressures of 1 to 1000 bar, preferably 5 to 800 mbar, particularly preferably 20 to 500 mbar, head temperatures of 50 to 200 ° C., preferably 60 to 150 ° C. and bottom temperatures of 130 to 270 ° C., preferably 150 to 250 ° C set.

If only small amounts of 1,6-hexanediol are to be produced, stages 6 and 7 can also be combined in a batchwise fractional distillation.

In order to operate the process according to the invention as economically as possible, it makes sense to recover the esterification alcohol ROH and to use it again and again for the esterification. For this purpose, the stream from stage 3 and / or 6, predominantly containing the alcohol ROH, can be worked up in stage 11 . For this purpose, a column is advantageously used in which components which boil more easily than the alcohol ROH overhead, water and components which boil higher than the alcohol ROH are separated off at the bottom from the alcohol ROH which is obtained in a side stream. The column is advantageously operated at 500 to 5000 mbar, preferably at 800 to 3000 mbar.

According to a further preferred embodiment of the process according to the invention, the high-boiling stream from stage 4 is worked up to increase the overall yield of valuable products, based on the DCL used. For this purpose, the proportion of dimeric and oligomeric esters of adipic acid or hydroxycaproic acid is reacted in step 8 with further amounts of the alcohol ROH, preferably methanol, in the presence of a catalyst. The weight ratio of alcohol ROH and the bottom stream from stage 4 is between 0.1 to 20, preferably 0.5 to 10, particularly preferably 1 to 5. In principle, the catalysts already described for the esterification in stage 2 are suitable. However, Lewis acids are preferably used. Examples include compounds or complexes of aluminum, tin, antimony, zircon or titanium, such as zirconium acetylacetonate or tetraalkyl titanate such as tetraisopropyl titanate, which are used in concentrations of 1 to 10,000 ppm, preferably 50 to 6000 ppm, particularly preferably 100 to 4000 ppm. Titanium compounds are particularly preferred.

The transesterification can be carried out batchwise or continuously, in one Reactor or several reactors, stirrer connected in series boilers or tubular reactors at temperatures between 100 and 300 ° C, preferably 120 to 270 ° C, particularly preferably 140 to 240 ° C and the resulting self-pressures will. The required residence times are 0.5 to 10 hours den, preferably at 1 to 4 hours.

This stream from stage 8 can in the case of esterification with methanol, for. B. back in level 3 . To avoid leveling, especially of 1,4-cyclohexanediols, a partial stream of the high boilers from stage 4 must then be discharged batchwise or continuously. Another possibility is not to return the stream from stage 8 to stage 3 , but rather, analogously to stage 3 , to stage 9 in predominantly alcohol ROH, which can then return to stage 2 , 8 or 11 and a stream of which contains esters to separate.

This ester stream can in principle (with the proviso of avoiding the leveling of 1,4-cyclohexanediols) be returned to stage 4 or is preferably used in a further stage 10 in the esters of C ₆ acids and, in terms of quantity rather insignificantly, in the Esters of C ₅ acids, on the one hand, which are either introduced into stage 4 or directly into stage 5 , and high boilers, on the other hand, which contain 1,4-cyclohexanediols, are separated, whereupon the high boilers are removed.

For the production of caprolactone, the predominantly ester of C ₆ acids containing stream from stage 4 is used. For this purpose, this stream is passed in stage 12 , a distillation column, into a stream containing predominantly adipic acid diester, which contains the 1,2-cyclohexanediols present, and a stream containing predominantly 6-hydroxycaproic acid ester, which contains no 1,2-cyclohexanediols, separated over swamp. The column is operated at pressures of 1 to 500 mbar, preferably 5 to 350 mbar, particularly preferably 10 to 200 mbar and bottom temperatures of 80 to 250 ° C., preferably 100 to 200 ° C., particularly preferably 110 to 180 ° C. The head temperatures are set accordingly.

It is important for a high purity and high yield of caprolactone that the 1,2-cyclohexanediols be separated from the hydroxycaproic acid ester, since these components form azeotropes with one another. In this stage 12, it was not foreseeable that the separation of the 1,2-cyclohexanediols and the hydroxycaproic acid ester would be completely successful, especially if the preferred methyl ester was used as the ester.

To reduce the separation effort, it can be advantageous in step 12 to remove some hy droxycaproic acid ester together with the adipic acid diester. The contents of hydroxycaproic acid ester are advantageously between 0.2 and 7% by weight. Depending on the alcohol component of the ester, this portion of hydroxycaproic acid ester is separated off together with the adipic acid diester via the top (e.g. methyl ester) or via the bottom (e.g. butyl ester).

The bottom stream of stage 12 containing 6-hydroxycaproic acid ester is converted in stage 13 in a manner known per se to either alcohol or caprolactone in the gas or liquid phase. The liquid phase is preferred.

The reaction is preferably carried out without a catalyst or in In the presence of a catalyst. As catalysts acidic or basic catalysts that are homogeneously dissolved are suitable or can be heterogeneous. Examples are alkali and earth alkali metal hydroxides, oxides, carbonates, alkoxylates or carboxylates, acids such as sulfuric or phosphoric acid, organic Acids such as sulfonic acids or mono- or dicarboxylic acids, or Salts of the aforementioned acids, Lewis acids, preferably from the  III. and IV. main group or the I. to VIII. subgroup of Periodic table of the elements.

The same catalysts which are also used in stage 8 are preferably used, since the high-boiling discharge stream in stage 13 contains oligomeric hydroxycaproic acid units which can advantageously be recycled in stage 8 . If a heterogeneous catalyst is used, the catalyst load is usually 0.05 to 5 kg of educt / l catalyst and hour. In the case of homogeneous catalysts, the catalyst is preferably added to the feed stream. The concentration is usually 10 to 10,000 ppm, preferably 50 to 5000 ppm, particularly preferably 100 to 1000 ppm. The reaction is usually carried out at 150 to 400 ° C., preferably 180 to 350 ° C., particularly preferably 190 to 330 ° C. and pressures of 1 to 1020 mbar, preferably 5 to 500 mbar, particularly preferably 10 to 200 mbar.

In some cases the cyclization reaction is advantageous in the presence of high-boiling mono-, di- or polyols such as e.g. B. decanol, undecanol, tridecanol, pentadecanol, octadecanol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexane diols, butylethyl propanediol, neopentyl glycol, triethylene glycol, Carry out tetraethylene glycol, trimethylolpropane or glycerin.

These high-boiling alcohols or polyols are introduced and / or the reaction mixture in concentrations up to 5 wt .-% sets or separately metered z. B. each in concentrations of 1 and 20,000 ppm, preferably 10 to 4,000 ppm, particularly preferred 50 to 2000 ppm.

If the cyclization is carried out in the liquid phase, reaction products, predominantly esterification alcohol ROH and caprolactone, are removed in gaseous form from the reaction mixture. A column attached to the reaction vessel is advantageous, in which unreacted starting material can be kept in the reaction system and the alcohol and caprolactone are taken off overhead. The condensation of the product stream can be carried out in such a way that condensed fractionation is carried out, ie first predominantly caprolactone, then the esterification alcohol. Of course, only the alcohol can be obtained overhead, while caprolactone can be obtained in a side stream. The alcohol stream can advantageously be returned to stage 2 , 8 or 11 . The bottom product of the cyclization can be introduced into stage 8 .

The feed to the reaction vessel can take place without preheating. Who the homogeneous catalysts used, it is advantageous to the Enter feed stream directly into the cyclization sump. Here the catalyst can either feed the feed before the reaction be added, or added directly to the reaction vessel.

However, it is more advantageous to preheat the feed, especially if the catalyst has already been dissolved and a hydroxycaproic acid ester with a C ₁ -C ₅ alcohol component is used. The pre-heating temperature is between 100 and 300 ° C, preferably 130-270 ° C, particularly preferably 150-250 ° C. At these temperatures, the hydroxycaproic acid ester already partially reacts to alcohol, caprolactone and dimeric or oligomeric hydroxycaproic acid esters. This means that only a small amount of hydroxycaproic acid ester, when it gets into the hot reaction vessel, can immediately distill off from the reaction sump. This saves column trays.

Another advantageous option is to use the weighing part of the ester alcohol before working up the Capro to win lactones, especially if this alcohol, like methanol, boils low and would only be condensable as a result. For this, the hydroxycaproate in the presence of a Preheated catalyst as described above, the liberated alcohol is distilled off. This is advantageous at 100-1100 mbar, a pressure range at which the ester alcohol is easily condensable. This is still the case today of the high-boiling alcohols described above possible.

The caprolactone product stream of stage 13 is worked up further in stage 14 . This can be one or more columns. If a column is used, the esterification alcohol which may still be present, as well as other C ₁ to C ₆ low boilers, are removed overhead, pure caprolactone via side stream and, if appropriate, unreacted hydroxycaproic acid ester which is recycled via the bottom.

High-purity caprolactone is obtained if, in stage 14, the low boilers he mentioned are fed in a first column overhead, capro lactone and other high boilers are added to a second column via the bottom, where caprolactone is taken off overhead. If the caprolactone stream to be obtained is only a small amount, caprolactone can be obtained with a column by batchwise fractional distillation.

The distillations are carried out at bottom temperatures of 70 to 250 ° C, preferably 90 to 230 ° C, particularly preferably 100 to 210 ° C and Pressures from 1 to 500 mbar, preferably 5 to 200 mbar, particularly preferably carried out 10 to 150 mbar.

After a further modification of the procedure - in the following Variant E - it is possible, especially smaller quantities of Caprolactone with minimal technical effort after a batch manufacturing process. This is used for the esterification step (a) an alcohol boiling higher than caprolactone and performs the reaction without isolating the adipic acid ester fraction to some extent in a one-pot reaction in the presence of a ver by esterification catalyst, the reactions of the stages (b), (c) and (f) in the same approach, the high-boiling Adipic acid esters remain in the sump and caprolactone remains lat is won.

In this variant E, z. B. alcohols such as Undecanol, tridecanol, pentadecanol, octadecanol, 1,6-hexanediol 1,4-cyclohexanediols, butylethyl propanediol, neopentyl glycol, trie ethylene glycol, tetraethylene glycol, trimethylolpropane or glycerin used. The esterification can be carried out in vacuum at temperatures be carried out in which on the one hand water of reaction, on the other hand, components such as 1,2-cyclohexanediols distill. These can of course only after the Vereste tion are separated by distillation. The esterification discharge will with further catalyst as described above and at 1-200 mbar, preferably 10-50 mbar under distillation conditions heated. Low boilers, e.g. B. the 1,2-cyclohexane diols, are distilled off before caprolactone by cyclization arises in the swamp. The preferred cyclization temperature is between 200 and 300 ° C. The caprolactone is worked up as described above in one or more pure distillations columns.

Yields can be obtained by the process according to the invention 1,6-hexanediol and caprolactone each of over 95%, with pure units of over 99%.

Adipic acid diesters obtained by omitting the hydrogenation stage can be used as a feedstock in the lubricant sector, as a starting material serve for cyclopentanone or as a plasticizer.

The process is illustrated by the following examples explained, but in no way limited.  

Example 1 (variant A) Level 1 : (drainage)

0.1 kg dicarboxylic acid solution / h (adipic acid, 6-hydroxycaproic acid, 1,4-cyclohexanediols, glutaric acid, 5-hydroxyvaleric acid, Formic acid, water) were continuously in a still lationsapparatur (three-vaulted bell-bottom column with outside horizontal oil heating circuit, oil temperature 150 ° C, floor volume each approx. 25 ml, inlet via the bubble cap) with the filler attached body column (approx. 4 theoretical plates, no reflux on Head) distilled. The top product was obtained with 0.045 kg a formic acid content in the water of approx. 3%. In the bottom stream (5.5 kg) the water content was about 0.4%.

Level 2 : (esterification)

5.5 kg of the bottom stream from stage 1 was reacted with 8.3 kg of methanol and 14 g of sulfuric acid. The acid number of the discharge minus sulfuric acid was approx. 10 mg KOH / g.

Level 3

The esterification stream from stage 2 was distilled in a column (1015 mbar, 65 ° C. top temperature, up to 125 ° C. bottom temperature). 7.0 kg were withdrawn overhead. 6.8 kg were obtained as the bottom product.

Stage 4 : (1,4-cyclohexanediol separation)

The bottom stream from stage 3 was fractionally distilled in a 50 cm packed column (1 mbar, head temperature 70-90 ° C., bottom temperature 180 ° C.). The 1,4-cyclohexane diols were found in the sump.

0.6 kg were distilled off as low boilers (1,2-cyclohexanediols, Valerolactone, 5-hydroxyvaleric acid methyl ester, glutaric acid di methyl ester, dimethyl succinate u. a.); than predominantly Dimethyl adipate and methyl 6-hydroxycaproate ent holding fraction was obtained 4.3 kg.

Stage 5 : (hydrogenation of partial stream; alternatively deduction of the C ₆ ester mixture and purifying distillation to obtain methyl adipate)

2.7 kg of C ₆ ester mixture from stage 4 were continuously hydrogenated in a 25 ml reactor over a catalyst (catalyst, 70% by weight, CuO, 25% by weight ZnO, 5% by weight Al ₂ O _3, which was previously activated in a hydrogen stream at 180 ° C, hydrogenation conditions: feed 20 g / h, no circulation, 220 bar, 220 ° C). The ester conversion was 99.5%, the 1,6-hexanediol selectivity was over 99%.

Using another catalyst, the ester fraction was in a two-stage reactor cascade (1st reactor 2.5 l catalyst, trickle mode, 250 bar, product return: inlet = 10: 1, 220-230 ° C; 2nd reactor 0.5 l Catalyst, trickle, straight passage, 260 bar, 220 ° C) contin. hydrated. A catalyst consisting of CuO (60%), Al ₂ O ₃ (30%) and Mn ₂ O ₃ (10%) previously activated at 180 ° C. was used as the catalyst. The feed rate was 1 kg / h. With 99.5% conversion, the hexanediol selectivity was over 99%.

Level 6 and 7 : (hexanediol purification)

2.5 kg of the hydrogenation from stage 5 were fractionally distilled (still with attached 70 cm packed column, reflux ratio 2 ). At 1013 mbar, 0.5 kg of methanol were distilled off and, after applying a vacuum (20 mbar), the 1,2-cyclohexanediols and 1,5-pentane diol predominantly distilled off. Thereafter (bp. 146 ° C) distilled 1,6-hexanediol with a purity of 99.8%.

Level 8

2.9 kg of the bottom discharge from stage 4 were mixed with 3.8 kg of methanol and 3.8 g of tetra-i-propyltitanate and continuously in a 1 m long, 440 ml tubular reactor which was filled with 3 mm V2A rings, implemented. The average residence time was approximately 2 hours.

Level 9

The discharge from stage 8 was fractionally distilled analogously to the apparatus described in stage 3 . At 65 ° C top temperature, 3.5 kg were distilled off (mainly methanol). 2.2 kg remained in the swamp.

Level 10

The bottom from stage 9 was fractionally distilled analogously to stage 4 to a bottom temperature of 160 ° C. 1.3 kg were obtained as the distillate, which can be directly hydrogenated or returned to the 4th stage. (Composition: 52% methyl 6-hydroxycaproate, 31% dimethyl adipate, 5% methyl glutarate, 4% methyl 5-hydroxycaproate and a large number of other, insignificant components).

Level 11

7 kg of the top product of stage 3 were fractionally distilled on a 20 cm packed column at 1015 mbar. 0.8 kg of preliminary fraction were obtained at a head temperature of 59-65 ° C. which, in addition to predominantly methanol, contained C ₁ -C ₄ -monoethyl ester. At a head temperature of 65 ° C., 5.6 kg of methanol with a purity of <99% were obtained. The sump (0.6 kg) consisted mainly of water.

Level 12

Dimethyl ester of predominantly adipic acid was distilled off from 1.6 kg of ester mixture from stage 4 in a 2 l distillation still with attached column (40 cm, 5 mm V2A metal ring packing) and reflux divider (reflux ratio 2, top temperature to 91 ° C., bottom temperature) up to 118 ° C). 0.31 kg of hydroxycaproic acid methyl ester (82% strength, remainder predominantly dimeric hydroxycaproic acid methyl ester, no dimethyl adipate) remained in the sump.

Level 13 : (cyclization)

60 ml of bottom product from stage 12 with the addition of 1000 ppm of tetraisopropyl titanate were placed in a 250 ml distillation still with external heating and a column (70 cm, 5 mm V2A metal ring packing) with reflux divider, heated to 260 ° C. at 40 mbar and 35 ml per hour Bottom product from stage 12 , to which 1000 ppm of tetraisopropyl titanate and 200 ppm of 1,6-hexanediol were added. At a head temperature of 123 to 124 ° C and a reflux ratio of 4 at 25 ° C mainly caprolactone, at -78 ° C methanol was condensed.

Level 14 : (caprolactone purification)

The caprolactone obtained from stage 13 was fractionally distilled at 40 mbar in a 250 ml still with an attached column (70 cm, 5 mm V2A metal ring packing) and reflux divider (reflux ratio 4 ). After essentially valerolactone (bp. 90 to 110 ° C.) had been separated off, caprolactone (bp. 131 ° C.) was obtained in a purity (GC area%) of 99.9%.

Example 2

Analogously to Example 1, stage 13 (cyclization) was operated with a stream containing hydroxycaproic acid of the following composition: 81% methyl hydroxycaproate, 9% dimeric hydroxycaproate, 0.1% dimethyl adipate, and esters of methyl 5-hydroxyvalerate and methyl hydroxycaproate and oligomeric hydroxycaproate. 50 g of 1,6-hexanediol, 30 g of the hydroxycaproate containing methyl ester and 0.1 g of titanate were initially introduced into the 250 ml reaction vessel, the mixture was heated at 40 mbar and continuously contained 30 g / h of ester feed (from 155 ° C. bottom temperature) 1000 ppm titanate) added. At bottom temperatures between 205 and 260 ° C., 1225 g of caprolactone-containing distillate, 336 g of methanol-containing cold trap product and about 100 g of bottom product were obtained within 56 hours. The 100% missing residue is due to methanol losses and the hold-up of the column. After fractional distillation of the caprolactone-containing discharge as in Example 1, caprolactone was obtained with purities between 99 and 99.9%.

Example 3 (variant B)

2400 g of dicarboxylic acid solution according to Example 1, 2400 g of n-butanol and 6 g of sulfuric acid were placed in a reaction vessel 20 cm packed column with water separator as long under back flow heated until no more water passed over (approx. 8 hours). There at the heterogeneous butanol / water distillate became continuous separated in the phase separator, butanol returned and water out smuggled. The acid number of the reaction discharge was minus about 10 mg KOH / g of the sulfuric acid used. After that 2.2 equivalents of NaOH based on the sulfuric acid used sets and then the excess butanol at about 120 mbar up to distilled off a bottom temperature of 120 ° C. The resulting one Residue was distilled on a Sambay evaporator (1419 g) and high boilers separated at 1 mbar and 200 ° C. This distillate was then fractionally distilled over a 75 cm packed column (approx. 5 mbar), 1,4- and 1,2-cyclohexanediols being complete  dig of pre-fractions of hydroxycaproic acid butyl ester fractions, hereinafter referred to as ester mixture, were separated.

119 g of the ester mixture (67% butyl hydroxycaproate, 10% Succinic acid dibutyl ester, 5% glutaric acid dibutyl ester as well a variety of other products) have been distilled flask with 0.05 g of 1,6-hexanediol and 1.2 g of titanate. At 200 mbar / 150-180 ° C bottom temperature was over a 1 m rotating belt column approx. 32 g at a top temperature of 75 ° C predominantly Distilled butanol. After reducing the pressure to 20 mbar and Increasing the bottom temperature to 200-300 ° C distilled at Head temperatures up to 122 ° C from approx. 60 g. 50 g of which were added to one 1 m rotating column column at 20 mbar fractionally distilled and Caprolactone obtained in a purity of 99.7%.

Claims (14)

1. Process for the preparation of 1,6-hexanediol and ε-caprolactone from an adipic acid, 6-hydroxycaproic acid and small amounts of 1,4-cyclohexanediols containing carboxylic acid mixture which is a by-product of the oxidation of cyclohexane to cyclohexane / cyclohexanol with oxygen or oxygen containing gases is obtained by water extraction of the reaction mixture, by esterification and hydrogenation of a partial stream to hexanediol and cyclization of 6-hydroxycaproic acid ester to caprolactone, characterized in that

• a) reacting the mono- and dicarboxylic acids contained in the aqueous reaction mixture with a low molecular weight alcohol to give the corresponding carboxylic acid esters,
• b) the esterification mixture obtained is freed from excess alcohol and low boilers in a first distillation stage,
• c) from the bottom product in a second distillation stage, it is separated into an ester fraction essentially free of 1,4-cyclohexane diols and an fraction containing at least the larger part of the 1,4-cyclohexanediols,
• d) at least partially separating a stream containing essentially 6-hydroxycaproic acid ester from the ester fraction in a third distillation stage,
• e) the ester fraction from (d), from which at least partially 6-hydroxycaproic acid ester has been removed, catalytically hydrogenated and 1,6-hexanediol is obtained by distillation of the hydrogenation product in a manner known per se and
• f) the stream essentially containing 6-hydroxycaproic acid ester is heated to temperatures above 200 ° C. under reduced pressure, as a result of which 6-hydroxycaproic acid ester is cyclized to caprolactone and pure ε-caprolactone is obtained from the cyclization product by distillation.

2. The method according to claim 1, characterized in that one the carboxylic acid mixture is dewatered before the esterification. 3. The method according to claim 1, characterized in that one esterification with alkanols with 1 to 3 carbon atoms carries out. 4. The method according to claim 1, characterized in that esterification with alkanols with 4 to 10 carbon atoms carries out. 5. The method according to claim 1, characterized in that performs the esterification with methanol and in the distilla tion stage (c) essentially of 1,4-cyclohexanediols free carboxylic acid methyl ester fraction at the top of the column and one containing the high boilers and the 1,4-cyclohexanediols Bottom fraction wins and the carboxylic acid methyl ester fraction transferred to the third distillation stage (d). 6. The method according to claim 1, characterized in that one carries out the esterification with n- or i-butanol and in the Distillation stage (c) the 1,4-cyclohexanediols with the Low boilers are removed overhead and the carboxylic acid butyl esters as a side stream or as a sump containing them wins and transferred to the third distillation stage (d). 7. The method according to claim 1, characterized in that one distillation stages (c) and (d) in a single column carries out. 8. The method according to claim 7, characterized in that one in the case of esterification with methanol in an upper side deduction containing an essentially dicarboxylic acid methyl ester fraction, essentially a lower side deduction 6-hydroxycaproic acid methyl ester fraction and as bottom product a fraction containing the 1,4-cyclohexanediols is separated off. 9. The method according to claim 7, characterized in that one in the case of esterification with n- or i-butanol in one above ren side deduction an essentially 6-hydroxycaproic acid fraction containing tylester, a lower side deduction fraction containing essentially dicarboxylic acid butyl ester and the top product is one containing 1,4-cyclohexanediols Faction wins.   10. The method according to claim 1, characterized in that the bottom product of stage (c) is at least partially one reesterification with further addition of the low molecular weight laren alcohol and an esterification catalyst and in a separate distillation stage analogous to (b) and (c) separates or only after separation of the 1,4-cyclohexanediols carries out the re-esterification and the carboxylic acid introduces ester-containing fraction into the hydrogenation stage (d). 11. The method according to claim 1, characterized in that used for hydrogenation catalysts, which are called catalytic main active ingredients copper, cobalt and / or rhenium ent hold. 12. The method according to claim 1, characterized in that catalysts are used for hydrogenation, which have the composition Cu _a Al _b Zr _c Mn _d O _x in the oxidic form, wherein a <0, b <0, c ≧ 0, d <0, a <b / 2, b <a / 4, a <c and a <d applies and x denotes the number of oxygen ions required to maintain electroneutrality per formula unit. 13. Modification of the method according to claim 1, characterized records that the hydrogenation of step (e) is omitted and from the ester fraction of step (d) adipic diester wins. 14. Modification of the method according to claim 1, characterized records that one for a simplified production of Caprolactone for the esterification in step (a) an alcohol used that boils higher than caprolactone and that one the implementation, without isolation of the adipindiester fraction, to some extent in a one-pot reaction in the presence of a Performs esterification catalyst, the reactions stages (b), (c) and (f) take the same approach, and the high-boiling adipic acid diesters remain in the swamp and Caprolactone is obtained as a distillate.