DE10258318A1 - High purity 1,6-hexanediol production involves hydroformylating pentenoic acid esters then hydrogenating the product with a chromium-free copper catalyst - Google Patents

Abstract

Production of 1,6-hexanediol of purity at least 99 % comprises hydroformylating 3-, 4- or 2-pentenoic acid alkyl ester with carbon monoxide and hydrogen in presence of rhodium compounds and tertiary organic polyphosphites, hydrogenating in chromium-free mainly copper-containing catalysts; and purifying the resulting diol mixture by fractional distillation. Production of 1,6-hexanediol of purity at least 99 % comprises: (1) hydroformylating 3-, 4- or 2-pentenoic acid alkyl ester with carbon monoxide and hydrogen in presence of rhodium compounds and tertiary organic polyphosphites to a mixture mainly of 5-, 4- and 3-formylvaleric acid esters; (2) hydrogenating the ester mixture in chromium-free mainly copper-containing catalysts; and (3) purifying the resulting diol mixture by fractional distillation.

Description

The present invention relates to a process for the preparation of 1,6-hexanediol, in which 3-, 4- and / or 2-pentenoic with carbon monoxide and hydrogen to mixtures of 5-, 4- and 3-formylvaleric acid esters be hydroformylated, the formylvalerian ester mixture to mixtures from 1,6-hexanediol, 2-methyl-1,5-pentanediol and 2-ethylbutanediol hydrogenated and 1,6-hexanediol by fractional distillation this mixture is obtained in a purity of at least 99%.

It is known to hydroformylate alkenecarboxylic acid esters such as 3-, 4- and 2-pentenoic acid esters with carbon monoxide and hydrogen in the presence of carbonyl complexes of rhodium which have been modified with tertiary organic phosphines or phosphites to give omega-formylvaleric acid esters. So is out for example EP-A 556 681 , Example 1, known to react methyl 3-pentenoate in toluene as solvent at 100 ° C. and 5 bar for 5 hours in the presence of a rhodium carbonyl and a chelate phosphite. The 3-pentenoate conversion is 95.5%. Mixtures are obtained which, in addition to methyl 5-, 4- and 3-formylvalerate, methyl valerate, methyl 2-pentenoate and methyl 4-pentenoate, are obtained.

EP-A 850 213 describes the separation of 5-formylvaleric acid esters from mixtures with the 4- and 3-formylvaleric acid esters by fractional distillation. Formylvaleric acid esters tend to decarbonylate under thermal stress. In order to keep the bottom temperatures as low as possible during the distillation, EP-A 850 213 described conditions are distilled at the lowest possible pressure.

Out EP-A 31 100 Another method for the production of 5-formylvaleric acid esters is known. The European published specification indicates that 5-formylvaleric acid esters are used as starting materials, inter alia for the synthesis of 1,6-hexanediol.

The task was therefore to start from isomer mixtures prepared by hydroformylation of pentenoic esters, consisting of 5-, 4- and 3-formylvalerates, 1,6-hexanediol with preferably high yield and purity and as little cleaning effort as possible manufacture.

• a) 3-, 4- und/oder 2-Pentensäurealkylester mit Kohlenmonoxid und Wasserstoff in Gegenwart von Rhodiumverbindungen und tertiären organischen Polyphosphiten zu Gemischen aus überwiegend 5-, 4- und 3-Formylvaleriansäureestern umsetzt,
• b) das gewonnene Formylvaleriansäureestergemisch in Gegenwart von chromfreien, als Hydrierkomponente überwiegend Kupfer enthaltenden Katalysatoren hydriert und
• c) das so erhaltene Diolgemisch durch fraktionierende Destillation reinigt.

This object is achieved in a process for the preparation of 1,6-hexanediol with a purity of at least 99%, characterized in that

• a) reacting 3-, 4- and / or 2-pentenoic acid alkyl ester with carbon monoxide and hydrogen in the presence of rhodium compounds and tertiary organic polyphosphites to give mixtures of predominantly 5-, 4- and 3-formylvaleric acid esters,
• b) the obtained mixture of formylvalerate esters in the presence of chromium-free catalysts which predominantly contain copper as the hydrogenation component and
• c) the diol mixture thus obtained is purified by fractional distillation.

According to the invention, C ₄ -alkenecarboxylic acid esters, in particular their C ₁ -C ₄ -alkyl esters, are used as starting compounds. The olefinic double bond can be terminal or internal. 4-Pentenoic acid C ₁ -C ₄ alkyl esters and 3-pentenoic acid C ₁ -C ₄ alkyl esters and mixtures thereof have acquired particular industrial importance. For example, ethyl 4-pentenoate, propyl 3-pentenoate, ethyl 2-pentenoate and mixtures thereof are suitable. Methyl 4-pentenoate and methyl 3-pentenoate are particularly preferred.

The C ₄ -alkenecarboxylic esters are reacted with carbon monoxide and hydrogen. As a rule, the gas mixture contains hydrogen: carbon monoxide in a molar ratio of 1:10 to 100: 1, in particular 1: 1 to 40: 1.

The hydroformylation (stage a)) is carried out at a temperature of 30 to 150 ° C in the liquid phase. Advantageous a temperature of 50 to 120 ° C is used. As a rule, one leads the reaction under a pressure of 0.01 to 30 bar, advantageous 1 to 30 bar through. Pressures of have proven particularly successful 1 to 20 bar.

The implementation in Presence of solvents carried out. Suitable solvents are, for example, aromatic hydrocarbons, such as toluene or Xylene, furthermore the ω-formylalkanecarboxylic acid esters obtained in the hydroformylation or high boilers obtained in the hydroformylation.

The hydroformylation is carried out in the presence of Rhodium carbonyl complexes and at least one tertiary organic Polyphosphite with 2 to 6 phosphorus atoms carried out. The concentration of the Rhodium complex catalyst is generally from 10 to 1000 ppm, calculated as rhodium metal, preferably 10 to 500 ppm rhodium and in particular 25 to 350 ppm rhodium.

In general, 2 to 100, preferably 3 to 50, moles of polyphosphite are used per gram of atom of rhodium (this is the sum of the complexed and free polyphosphite). Fresh polyphosphite can be added at any point in the reaction to keep the concentration of free, non-complexed phosphite constant. The rhodium carbonyl polyphosphite complex catalyst can be prepared separately before use. As a rule, however, the catalytically active Complexes formed from a catalyst precursor such as rhodium carbonyl acetylacetonate, rhodium oxide, rhodium carbonyl, rhodium nitrate or rhodium acetate and the polyphosphite ligand in the reaction medium. Rhodium carbonyl acetylacetonate or rhodium acetate is preferably used as the rhodium component, which is reacted with the polyphosphite ligand in the presence of a solvent to form the precursor of the catalytically active complex, which is introduced in the reaction together with excess polyphosphite, in order to reactivate the active, in situ under reaction conditions to form modified rhodium carbonyl complex.

All ternary organic polyphosphites suitable for the hydroformylation of pentene esters can be used as the polyphosphite, for example those from EP-A 556 681 . US 5,710,433 , WO 97/33854, WO 01/21567 and WO 97/8127 known polyphosphites.

Those from are particularly preferred EP-A 556 681 , the disclosure of which is expressly incorporated herein by reference, uses known ternary organic polyphosphites having 2 to 6 phosphorus atoms in the molecule, in each of which a bond on each phosphorus atom via an oxygen bridge to a substituted or unsubstituted at least divalent arylene or bisarylene radical, an alkylene radical, which can contain an oxygen atom in chain, or is bonded to a radical with two isolated aryl radicals via the aryl radicals and has two bonds on each phosphorus atom via an oxygen bridge to a substituted or unsubstituted divalent arylene, bisarylene radical, an alkylene radical or a radical with two isolated Aryl radicals are bonded via the aryl radicals, or two bonds on at least one phosphorus atom are each bonded separately via an oxygen bridge to a monovalent substituted or unsubstituted aryl, bisaryl, alkyl, aralkyl or cycloalkyl radical.

The hydroformylation results predominantly, i.e. usually 90% and more, from 5-, 4- and 3-formyl-valeric acid esters existing mixtures. The hydroformylation discharge turns into rhodium catalyst and polyphosphite, for example by distillation, as the bottom product separated.

The top product may not contain converted cis and trans-2-, cis and trans-3- and 4-pentenoic acid esters, furthermore n-valeric acid esters and 5-, 4-, and 3-formylvaleric acid esters.

With large amounts of unconverted alkyl pentenoates can this from the formylvalerate mixture separated, for small quantities, i.e. not more than 2 to 5% by weight, these are in the formylvaleric acid ester mixture leave and with the subsequent Hydrogenation converted into n-pentanol, which can be easily separated from 1,6-hexanediol is. Also valeric acid esters can either from the formylvalerate mixture separated or left in a mixture. They also result in the hydrogenation of n-pentanol. The separation of the unconverted pentenoic is preferably carried out by distillation.

Separated pentenoate mixtures can, if appropriate after isomerization to 3- and 4-pentenoate esters, be returned to the hydroformylation stage. Methods for isomerization are, for example, from EP-A 269 043 and EP-A 126 349 known.

The hydrogenation is catalytic either in the gas or liquid phase. In principle, all come as catalysts for the hydrogenation of carbonyl groups suitable homogeneous and heterogeneous catalysts such as metals, Metal oxides, metal compounds or mixtures thereof into consideration. examples for homogeneous catalysts are described in H. Kropf, Houben-Weyl, Methods of Organic Chemistry, Volume IV / 1 c, Georg Thieme Verlag Stuttgart, 1980, pp. 45 to 67, and are examples of heterogeneous catalysts in Houben-Weyl, Methods of Organic Chemistry, Volume IV / 1 c, p. 16 to 26.

Catalysts are preferably used, which one or more of the elements from subgroups I. and VI. to VIII. of the Periodic Table of the Elements, preferably copper, Chromium, molybdenum, manganese, Rhenium, ruthenium, cobalt, nickel and palladium, particularly preferred 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 example, Cr ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , ZrO ₂ , ZnO, BaO and MgO or mixtures thereof.

In particular, the catalyst copper oxide as the main catalytically active component. This is on an oxidic carrier applied. A suitable carrier material is aluminum oxide, the use of which according to one embodiment of the present invention is preferred. According to another embodiment In the present invention, it is preferred as the carrier material a combination of aluminum oxide and zinc oxide in a weight ratio of 20 : 1 to 1:20, preferably 5: 1 to 1: 5 to use. The amount copper oxide is <80 Wt .-%. Preferred catalyst compositions have <70% by weight copper oxide and> 30 wt% carrier, especially preferred catalysts 10 to 65 wt .-% copper oxide and 35 to 90% by weight carrier on.

Hydrogenation catalysts as described in EP-A 552 463 are described. These are catalysts in the oxidic form of 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 and a> d and x is the number required to maintain electroneutrality per formula unit designated by oxygen ions. The preparation of these catalysts can, for example, according to the information from EP-A 552 463 by precipitating sparingly soluble compound solutions from solutions which contain the corresponding metal ions in the form of their salts.

In detail, e.g. B. Catalysts of the compositions of about 60 wt .-% CuO, 30 wt .-% Al ₂ O ₃ and 10 wt .-% Mn ₂ O ₃ are considered.

Optionally, the hydrogenation catalysts used according to the invention, which are Cr-free, one or more further metals or a compound thereof, preferably an oxide, from groups 1 to 14 (IA to VIIIA and IB to IVB of the old IUPAC nomenclature) of the periodic table of the Contain elements. If such a further oxide is used, TiO ₂ , ZrO ₂ , SiO ₂ and / or MgO is preferably used.

The catalysts used can also contain an auxiliary in an amount of 0 to 10 wt .-%. Under Aids are understood to be organic and inorganic substances that for improved processing during catalyst production and / or an increase contribute to the mechanical strength of the shaped catalyst bodies. Such tools are known to the person skilled in the art; Examples include graphite, stearic acid, silica gel and copper powder.

The catalysts can be prepared by methods known to those skilled in the art. Methods in which the copper oxide is finely divided and intimately mixed with the other constituents are preferred; precipitation reactions are particularly preferred. Precursor compounds dissolved in a solvent are precipitated with a precipitant in the presence of further soluble metal compounds or metal compounds suspended in the solvent, filtered off, washed, dried and optionally calcined. At this point, I would like to once again expressly refer to the disclosure of the EP-A 552 463 directed.

These starting materials can according to known methods for the moldings processed, for example extruding, tableting or by agglomeration processes, optionally with the addition of auxiliaries.

Alternatively, catalysts according to the invention can be used for example, by applying the active component to one carrier are produced, for example by soaking or vapor deposition. Farther can catalysts of the invention Deforming a heterogeneous mixture of active component or precursor compound of these with a carrier component or forerunner of which can be obtained.

In the hydrogenation according to the invention the catalyst is used in a reduced, activated form. The activation takes place with reducing gases, preferably hydrogen or hydrogen / inert gas mixtures, either before or after Installation in the reactor in which the process according to the invention is carried out. If the catalyst was installed in the reactor in oxidic form, so the activation can be done with the Hydrogenation according to the invention as well during start-up, i.e. in situ. The separate activation Before starting up the system, it is generally done with reducing Gases, preferably hydrogen or hydrogen / inert gas mixtures at elevated temperatures, preferably between 100 and 300 ° C. With the so-called in-situ activation it is activated by contact when the system is started up with hydrogen at elevated Temperature.

The catalysts are used as shaped articles. Examples include strands, ribbed, other extrudate forms, tablets, rings, balls and grit.

The BET surface area of the copper catalysts in the oxidic state is 10 to 400 m ² / g, preferably 15 to 200 m ² / g, in particular 20 to 150 m ² / g. The copper surface (N ₂ O decomposition) of the reduced catalyst in the installed state is> 0.2 m ² / g, preferably> 1 m ² / g, in particular> 2 m ² / g.

The catalysts used in the invention generally have a sufficient service life. In the case, that the activity and / or selectivity the catalyst should nevertheless decrease over the course of its operating time, this can be regenerated by measures known to the person skilled in the art. This counts preferably a reductive treatment of the catalyst in a hydrogen stream with increased Temperature. If necessary, the reductive treatment can be an oxidative precede. Here, the catalyst bed with a molecular Gas mixture containing oxygen, for example air, at elevated temperature flows through. There is also the possibility the catalyst with a suitable solvent, for example Wash methanol, THF or gamma-butyrolactone and then in to dry a gas stream.

Heterogeneous catalysts are preferably used, which are either fixed, as a fluidized bed or as a suspension be used. If the hydrogenation is in the gas phase and over solid arranged catalyst are carried out in general Temperatures from 150 to 300 ° C when you press 1 to 80 bar applied. At least as much hydrogen is used used as a hydrogenating agent and carrier gas, that starting materials, intermediates and products never become liquid during the reaction.

If the hydrogenation takes place in the liquid phase fixed or suspended catalyst, it is in the generally at temperatures between 100 and 350 ° C, preferred 120 and 300 ° C and press from 30 to 350 bar, preferably 40 to 300 bar.

The hydrogenation can be carried out without or with the addition of a solvent. Alcohols, ethers, hydrocarbons such as for example methanol, i-propanol, ethanol, dioxane, tetrahydrofuran, n-pentane in question. 5 to 70%, preferably 10 to 60%, particularly preferably 15 to 50% solutions of the isomer mixtures of formylvalerate are possible. It is particularly preferred to use the alcohol as solvent, which is also released during the hydrogenation of the ester groups.

The hydrogenation can be done in a reactor or several reactors connected in series. The hydrogenation in liquid phase over a Fixed bed can be carried out in both trickle and swamp mode. To a preferred embodiment one uses several reactors, the predominant one in the first reactor Part of the ester is hydrogenated and the first reactor preferably with Liquid circuit for heat dissipation and the subsequent reactor or reactors preferably without circulation to completion of sales are operated.

The hydrogenation can be carried out batchwise, preferably take place continuously.

The catalyst load is 0.01 to 1, preferably 0.05 to 0.8, particularly preferably 0.1 to 0.5 kg of C ₆ diester / l catalyst to be hydrogenated for 1 hour.

The hydrogen / educt molar ratio is also a parameter that has an important impact on profitability of the method according to the invention Has. A low hydrogen / starting material ratio is desirable from an economic point of view. The The lower limit is 5, but generally higher hydrogen / educt molar ratios from 20 to 400 can be applied.

To the used according to the invention Hydrogen / reactant molar ratios part of the hydrogen is circulated. To this end, the cycle gas compressors known to those skilled in the art are generally used on. The amount of hydrogen chemically consumed by the hydrogenation will be added. In a preferred embodiment part of the circulating gas is discharged to create inert compounds to remove. The one in a circle Hydrogen can also be used for evaporation, if necessary after preheating of the educt stream can be used.

Together with the hydrogen cycle gas all products in a circle, the one while cooling of the gas stream emerging from the hydrogenation reactor not or not Completely condense. The cooling temperature is 0 to 60 ° C, preferably 20 to 45 ° C.

Sales based on the total of the diol-forming 5-, 4- and 3-formylvaleric acid esters is over 95%, especially about 98%.

The hydrogenation discharge consists essentially of 1,6-hexanediol and the alcohol corresponding to the ester group. On Another important ingredient is 2-methyl-1,5-pentanediol.

The hydrogenation is carried out by fractional distillation cleaned in one or more columns.

By the method according to the invention high 1,6-hexanediol yields combined with a purity of the hexanediol from above 99% achieved. It was not foreseeable that 2-methyl-1,5-pentanediol as an isomer of 1,6-hexanediol with reasonable effort would separate to let.

Example 1:

• a) Hydroformylation The hydroformylation was carried out in accordance with EP-A 556 681 , Example 1, carried out. The hydroformylation output was worked up by distillation. Toluene unreacted methyl pentenoate and methyl valerate were initially separated from the methyl formylvalerate / isomeric mixture. The methyl formyl isomer mixture of isomer was distilled off from the remaining residue. It consisted of 85% methyl 5-, 9% 4- and 6% 3-formylvalerate.
• b) Hydrogenation of methyl formylvalerate mixture In a batch autoclave experiment, 150 g of a 30% by weight methanolic methyl formylvalerate solution were prepared from the formyl ester isomer mixture obtained in a) in the presence of 20 g copper catalyst (55% CuO, 35% Al ₂ O ₃ , 10 Mn ₂ O ₃ ) hydrogenated at 210 ° C / 240 bar hydrogen for 6 hours. The oxidation catalyst was activated before hydrogenation with hydrogen at 200 ° C./300 bar. According to gas chromatographic analysis (internal standard: diethylene glycol dimethyl ether), the 1,6-hexanediol yield was 92% (based on the 5-formylvaleric acid methyl ester contained). According to gas chromatographic analysis (area percent in the following "area%"), the crude hydrogenation output contained 84 area% 1,6-hexanediol, 10 area% 2-methyl-1,5-pentanediol and 6 area% 2-ethyl 1,4-butanediol.
• c) distillation of the hydrogenation discharge The distillation of the Hydrogen discharge, from which methanol was largely removed, on one Belt conveyor column (max. 160 ° C / 1 mbar) gave 1,6-hexanediol with a purity of 99.4%, which is only about 1000 ppm 2-methyl-1,5-pentanediol and about 300 ppm 2-ethyl-1,4-butanediol contained.

Claims (5)

Process for the preparation of 1,6-hexanediol with a purity of at least 99%, characterized in that a) alkyl 3-, 4- and / or 2-pentenoate with carbon monoxide and hydrogen in the presence of Rho converts dium compounds and tertiary, organic polyphosphites to mixtures of predominantly 5-, 4- and 3-formylvalerate esters, b) hydrogenates the obtained formylvalerate ester mixture in the presence of chromium-free catalysts, predominantly containing copper as hydrogenation component, and c) purifies the diol mixture thus obtained by fractional distillation. A method according to claim 1, characterized in that from the formylvaleric acid ester mixture obtained in step a) is separated before the hydrogenation of unreacted alkyl pentenoate. Method according to one of claims 1 or 2, characterized in that the hydrogenation over a catalyst which in the oxidic form the composition Cu _a Al _b Zr _c Mn _d O _x has, where a> 0, b> 0, c ≥ 0, d> 0, a> b / 2, b> a / 4, a> c and a> d and x is the number required to maintain electroneutrality per formula unit designated by oxygen ions. Method according to one of claims 1 to 3, characterized in that that the hydroformylation step a) at 30 to 150 ° C and pressures of 0.01 to 30 bar becomes. Method according to one of claims 1 to 5, characterized in that that the hydrogenation is carried out at 100 to 350 ° C and pressures of 30 to 350 bar.