EP1237985A1

EP1237985A1 - Method for working up polyether alcohols

Info

Publication number: EP1237985A1
Application number: EP00979572A
Authority: EP
Inventors: Kathrin Harre; Gerd Hoeppner; Georg Heinrich Grosch; Wolfgang Heider; Eva Baum; Thomas Ostrowski
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1999-11-26
Filing date: 2000-11-16
Publication date: 2002-09-11
Also published as: DE19957105A1; WO2001038421A1; AU1701201A

Abstract

The invention relates to a method for working up polyether alcohols which may be produced by the catalytic addition of alkylene oxides to H-functional starting materials. Said method is characterised in that at least one multi-metal cyanide compound is employed as catalyst and that the catalyst is separated by sedimentation from the polyether alcohol, after the addition of the alkylene oxide.

Description

Process for working up polyether alcohols

description

The invention relates to a process for working up polyether alcohols which have been prepared by addition of alkylene oxides onto H-functional starter substances by means of multimetal cyanide catalysts.

Polyurethanes are manufactured in large quantities. An essential starting product for their production are polyether alcohols. They are usually produced by catalytic addition of lower alkylene oxides, in particular ethylene oxide and propylene oxide, to H-functional starters. Mostly basic metal hydroxides or salts are used as catalysts, the potassium hydroxide being of the greatest practical importance.

In the synthesis of polyether polyols with long chains and hydroxyl numbers from approx. 26 to approx. 60 mg KOH / g, as are used particularly for the production of flexible polyurethane foams, side reactions occur as the chain grows, which leads to disturbances in the chain structure. The resulting by-products are referred to as unsaturated components and lead to an impairment of the properties of the resulting polyurethane materials. In particular, these unsaturated constituents, which have an OH functionality 1, have the following consequences:

Because of their very low molecular weight and thus increase the total volatile content in the polyether polyol and in the polyurethanes produced therefrom, in particular flexible polyurethane foams.

They act as chain terminators in the production of the polyurethane because they delay or reduce the crosslinking of the polyurethane or the build-up of the molecular weight of the polyurethane.

It is therefore technically very desirable to avoid the unsaturated components as much as possible.

One way of producing polyether alcohols with a low content of unsaturated constituents is the use of multimetal cyanide catalysts, also known as DMC catalysts, mostly zinc hexacyanometalates, as alkoxylation catalysts. There are a large number of documents in which ___ the production of polyether alcohols using such catalysts is described. The production of polyether polyols using zinc hexacyanocobaltate is described in DD-A-203 735 and DD-A-203 734. By using multimetal cyanide catalysts, the content of unsaturated constituents in the polyether polyol can be reduced to approx. 0.003 to 0.009 meq / g - in conventional catalysis with potassium hydroxide, about 10 times the amount (approx. 0.03 to 0.08 meq / g) ,

The production of the multimetal cyanide catalysts is also known. These compounds are usually prepared by reacting solutions of metal salts, such as zinc chloride, with solutions of alkali metal or alkaline earth metal cyanometalates, such as potassium hexacyanocobaltate. A water-miscible component containing heteroatoms is generally added to the precipitate suspension formed immediately after the precipitation process. This component can also already be present in one or in both educt solutions. This water-miscible component containing heteroatoms can be, for example, an ether, polyether,

Alcohol, ketone, or a mixture thereof. Such methods are described for example in US 3,278,457, US 3,278,458, US 3,278,459, US 3,427,256, US 3,427,334, US 3,404,109, US 3,829,505, US 3,941,849.

After the polyether alcohols have been produced, the multimetal cyanide catalyst is mostly separated off from the polyether alcohol. Since the multimetal cyanide catalyst is usually present in a very finely divided form in the polyether alcohol, the separation is very difficult.

No. 5,416,241 describes a process for the preparation of polyether alcohols by means of DMC catalysts, in which after the alkylene oxides have been added on, the catalyst is made insoluble by adding alkali compounds and then filtered. In this process, however, the DMC catalyst is destroyed and can therefore no longer be reused.

In the process described in US Pat. No. 5,248,833, the DMC catalyst is precipitated with chelating agents and then filtered. In this process too, the catalyst is inactivated and can no longer be used.

No. 4,877,906 describes a process for the purification of DMC-catalyzed polyether alcohols by treatment with alkali metal compounds, filtration, treatment with phosphorus compounds, renewed filtering and recovery of the so cleaned polyol described. Here, too, the DMC catalyst cannot be reused.

According to US 4721818, the DMC catalyst is rendered poorly soluble by means of alkali metal hydrides and is separated off in this form.

Another method is described in US 5,010,047. Here, the polyether alcohol is dissolved in a non-polar solvent after production, whereby the DMC catalyst fails. The resulting suspension is then filtered using a filter aid. This gives a mixture of DMC catalyst and filter aid which is still catalytically active and which in turn can be used to produce polyether alcohols. However, the concentration of the catalyst in the filter aid is very low, so that a great deal of filter aid is present in the synthesis. With repeated use, more and more filter aids accumulate.

Since DMC catalysts are very expensive to manufacture, it is desirable to use them several times without reducing their catalytic activity and without other substances which impair the activity of the catalysts or the handling of the catalysts or the reaction mixture eg difficult to change due to viscosity change, can be recycled together with the DMC catalysts.

Surprisingly, it has now been found that it is possible to remove the DMC catalyst from the polyether alcohol after the reaction by sedimentation and then to reuse it.

The invention accordingly relates to a process for working up polyether alcohols which have been prepared by means of DMC catalysts, characterized in that, after the reaction, the catalyst is separated from the polyether alcohol by sedimentation, without being chemically changed after the addition of the alkylene oxides has ended becomes.

The preferred embodiment of sedimentation is centrifugation. Surprisingly, it is possible to bring the DMC catalyst content to values below 2 ppm by centrifugation. The catalytic activity of the DMC catalysts is completely retained.

The sedimentation according to the invention is preferably carried out at temperatures in the range between 10 to 200 ° C. It is particularly advantageous to use the process according to the invention to remove those DMC catalysts which are prepared using a hexacyanometalate acid, preferably in the presence of a surfactant. Such DMC catalysts are mostly crystalline and have a monoclinic crystal system. Such catalysts have been described, for example, in EP-A-862 947 and WO 99/16775.

The method can be used particularly advantageously for those polyether alcohols whose molecular weight distribution has a pronounced high-molecular flank with molecular weights above 80,000 daltons. Surprisingly, this very high molecular weight fraction of the polyether alcohol is separated from the polyether alcohol together with the DMC catalyst. It is not necessary to separate this very high molecular weight fraction of the polyether alcohol from the DMC catalyst before reusing it, since this does not impair the catalytic activity and, moreover, the mixture of DMC catalyst and very high molecular weight polyether alcohol is much easier to handle than the pure, powdery catalyst , It is also advantageous if the very high molecular weight fraction is removed from the polyether alcohol, since this can have a very disadvantageous effect in the production of polyurethanes, in particular polyurethane foams.

Surprisingly, this mixture of DMC catalyst and very high molecular weight polyether alcohol can also be used for the production of polyether alcohols whose molecular weight distribution does not have a very high molecular weight flank. It turns out that this mixture of DMC catalyst and very high molecular weight polyether alcohol remains stable and can be separated from the polyether alcohol in this form after the reaction. There is no contamination of the polyether alcohol with the high molecular weight polyether alcohols which have entered the reaction mixture with the DMC catalyst. “Very high molecular weight” here means a molecular weight of more than 80,000 Da, in particular in the range between 80,000 and 1,000,000 Da, preferably between 80,000 and 300,000.

When using the separated DMC catalysts, which were removed together with the very high molecular weight fraction of the polyether alcohol, for the renewed addition of alkylene oxide, it surprisingly shows that the formation of the high molecular weight flank was suppressed. Of course, those polyether alcohols whose molecular weight distribution has no high-molecular flank can also be purified by the process according to the invention. In this case, however, it is necessary to use more energy during sedimentation. Thus, when using centrifuges to carry out the method according to the invention, the speed of the centrifuge can be increased. The optimum conditions for sedimentation can easily be determined for the person skilled in the art by means of comparative experiments.

The DMC catalyst can be freed from adhering polyetherol after separation from the polyether alcohol. This can be done by washing, for example with water or organic solvents. Then it can be converted into a form in which it can be used again as a catalyst for the production of polyether alcohols. This can be done, for example, by emulsification in solvents. The catalyst is worked up in particular when the catalyst is to be used after the separation to produce another polyether alcohol in order to avoid impurities in the product.

However, it is also possible to use it again directly for the production of polyether alcohols without further workup. This process variant is used in particular if the catalyst is to be used after the workup to produce the same polyether alcohol. As explained above, this process variant can also be carried out if the DMC catalyst has been separated from a polyether alcohol, the molar weight distribution of which has a high molecular weight flank.

In the technically customary batchwise production of polyether alcohols, a so-called post-reaction phase is initially connected after the alkylene oxides have been metered in, in which the alkylene oxide still present in the reaction mixture is to react completely. This is usually followed by distillation, in which unreacted monomers and other volatile constituents are to be removed from the reaction mixture. The catalyst can then be separated off according to the invention. The separated catalyst can then, as described, be used for the next batch with or without working up.

Before or after the removal of the catalyst according to the invention, filtration of the polyether alcohol can be carried out to remove coarse mechanical impurities or also larger ones Agglomerates of the DMC catalyst used are carried out.

In the continuous production of polyether alcohols, the end product is separated off continuously or in batches. The stripped-off polyether alcohol is then usually worked up as described above. The separated catalyst can then be added to one of the starting products, preferably the starter substance, which is continuously metered into the reaction mixture. With this procedure, it is usually possible to dispense with working up the separated catalyst.

The work-up process according to the invention surprisingly makes it possible to remove the DMC catalyst from the polyether alcohol almost completely by a simple process which can be easily integrated into existing plants for the production of polyether alcohols, that is to say except for residual zinc and cobalt contents below 10 ppm to remove and then use it again with practically no losses for the production of polyether alcohols. This means that the production of polyether alcohols using DMC catalysts can be carried out much more cost-effectively since much less catalyst has to be provided.

The invention is illustrated by the examples below.

Examples

example 1

2000 ml of strongly acidic ion exchanger (K2431, Bayer) were regenerated with 700 g of sulfuric acid (36% by weight) and washed with water until the process was neutral. A solution of 240 g of potassium hexacyanocobaltate in 700 g of water was then added to the exchange column. The column was then eluted until the outlet was neutral again. The 3085 g of eluate obtained were heated to 40 ° C. and a further 4000 g of water were added. 750 g of Technocell 150 cellulose were then suspended in it. A solution of 267.3 g of Zn (II) acetate was then

Add dihydrate in 600 g of water. Then immediately gave 684 g tert. -Butanol and stirred at 40 ° C for a further 30 min. The solid was then filtered off and washed on the filter with tert-butanol. The solid obtained in this way was dried at 30 ° C. in a vacuum drying cabinet for 16 h. Example 2

7 1 strongly acidic ion exchanger which was in the sodium form (Amberlite 252 Na ^®, Fa. Rohm & Haas) were charged in an exchanger (length, volume 7.7 1). The ion exchanger was then converted into the H form by passing 10% hydrochloric acid at a rate of 2 bed volumes per hour over the exchange column for 9 hours until the Na content in the discharge was less than 1 ppm. The ion exchanger was then washed neutral with water.

The regenerated ion exchanger was now used to produce a substantially alkali-free hexacyanocobaltic acid.

For this purpose, a 0.24 molar solution of potassium hexacyanocobaltate in water was passed over the exchanger at a rate of one bed volume per hour. After 2.5 bed volume, the potassium hexacyanocobaltate solution was changed to water. The 2.5 bed volumes obtained had on average a hexacyanocobaltic acid content of 4.5% by weight and alkali contents of less than 1 ppm.

The hexacyanocobaltic acid solutions used for the further examples were diluted accordingly with water.

2433 g of an aqueous hexacyanocobalta acid solution (cobalt content 6 g / 1, potassium content <1 ppm) were heated to 40 ° C. and with stirring (paddle stirrer, U = 500 min " ¹ ) 120 ml Pluronic PE 6100 (BASF Aktiengesellschaft, Coblock polymer from PO and A solution of 108.8 g of Zn (II) acetate dihydrate in 400 g of water was then added with stirring (blade stirrer, U = 500 min ^-1 ). The suspension was stirred for a further 30 min at 40 ° C. The solid was then filtered off with suction and washed on the filter with tert-butanol.

The moist filter cake was processed with water to form a suspension which had a multimetal cyanide content of 5% by weight.

Example 3

The synthesis was carried out in a cleaned and dried 1 l stirred autoclave. 400 g of polypropylene glycol with a molecular weight of 400 g / mol were added to the stirred tank and intimately mixed with 8.4 g of the catalyst according to Example 2. The boiler Contents were rendered inert with nitrogen and treated in vacuo at 140 ° C. for 1 h.

1 mol of ethylene oxide was then metered in at 140 ° C. and the reaction started. The remaining ethylene oxide was then metered in to a total amount of 440 g. The dosing time was 35 minutes, the maximum pressure was 4.4 bar absolute. The product was worked up by vacuum distillation at 0.1 bar, 110 ° C. The polyol was filtered at 70 ° C at a pressure of 3 bar. The remaining catalyst was depleted by centrifugation in a laboratory centrifuge Universal 30 RF Fa. Hettich at 8000 rpm ^-1 and the polyol by decantation from the catalyst-containing sediment separated.

The resulting polyether alcohol had the following characteristics:

Hydroxyl number: 128 mg KOH / g

Viscosity at 25 ° C: 182 mPas (determined with a capillary viscometer according to Ubbelohde)

Zn / Co content before centrifugation 117/50 ppm; Zn / Co content after centrifugation 5/3 ppm.

Example 4

The synthesis was carried out in a cleaned and dried 1 l stirred autoclave. 400 g of polypropylene glycol with a molecular weight of 400 g / mol were added to the stirred tank and intimately mixed with the catalyst according to Example 1. The contents of the kettle were rendered inert with nitrogen and treated in vacuo at 105 ° C. for 1 h.

1 mol of ethylene oxide was then metered in at 105 ° C. and the reaction started. The remaining ethylene oxide was then metered in to a total amount of 440 g. The dosing time was 1.1 hours, the maximum pressure was 4.1 bar absolute. The product was worked up by vacuum distillation. The catalyst was depleted by centrifugation and the polyol separated from the sediment by decanting. The catalyst residue (the sediment) was not further treated.

The resulting polyether alcohol had the following characteristics:

Hydroxyl number: 127 mg KOH / g

Viscosity at 25 ° C: 146 mPas; (determined with a capillary viscometer according to Ubbelohde)

Zn / Co content in the polyol after filtration: 112 / 46.6 ppm Zn / Co content in the polyol after centrifugation: <1/1 ppm Example 5

The synthesis was carried out in a cleaned and dried 1 l stirred autoclave. 200 g of polypropylene glycol with a molecular weight of 400 g / mol were added to the stirred tank and intimately mixed with the catalyst residue from Example 4. The kettle contents were rendered inert with nitrogen and treated in vacuo at 135 ° C. for 1 h.

1 mol of propylene oxide was then metered in at 130 ° C. and the reaction started. The remaining propylene oxide was then metered in to a total amount of 800 g. The dosing time was 1.8 hours, the maximum pressure was 4.2 bar absolute. The product was worked up by vacuum distillation and centrifugation.

The resulting polyether alcohol had the following characteristics:

Hydroxyl number: 53 mg KOH / g viscosity at 25 ° C: 655 mPa (determined with a capillary viscometer according to Ubbelohde) Zn / Co content: 9.5 / 5 ppm.

Claims

claims

1. Process for working up polyether alcohols which can be prepared by catalytic addition of alkylene oxides

H-functional starter substances, characterized in that at least one multimetal cyanide compound is used as the catalyst and the catalyst is removed from the polyether alcohol by sedimentation after the addition of the alkylene oxides.

2. The method according to claim 1, characterized in that the catalyst is not chemically changed after the addition of the alkylene oxides.

A method according to claim 1, characterized in that the sedimentation is a centrifugation.

4. The method according to claim 1, characterized in that the separated catalyst can be used again as a catalyst for the addition of alkylene oxides to H-functional starter substances.

5. The method according to claim 1, characterized in that the catalyst is crystalline and has a monoclinic crystal system.

6. The method according to claim 1, characterized in that the catalyst was prepared by reacting a metal salt with a hexcyanometalic acid in the presence of a surfactant.