NL8300575A - Polyether poly:ol(s) prodn. - by reacting poly:hydroxy cpd. with alkylene oxide in aq. emulsion and sepg. prod. in fibre bed - Google Patents

Abstract

Polyetherpolyols are made by reacting a polyhydroxy cpd. with one or more alkylene oxides in the presence of an alkaline catalyst, the reaction mixt. being in the form of an aq. emulsion. After the oxyalkylation reaction, the reaction mixt. is neutralised and passed through one or more fibre beds to cause phase separation and the polyol phase is freed from or virtually completely freed from the water present. Pref. the fibre beds are of glass fibre or are made by sintering stainless steel fibres. Each fibre bed is pref. 2-4 cm thick, and two or more fibre beds are combined to form an exchangeable sepn. element. Pref. the reaction mixt. is neutralised with HePO4 the catalyst used for the oxyalkylation is KOH, and after the first phase sepn. the water still present in the polyol phase is largely removed by evapn., the phosphate which crystallises out is filtered off, and the residual water is removed. Prods. are esp. useful for the prodn. of polyurethanes. Process is less time consuming than prior art processes, gives alkali-free polyol, and does not require the use of organic solvents.

Description

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The invention relates to a process for the preparation of polyether polyols by reacting a polyhydraxy compound with one or more alkylene axides in the presence of an alkaline catalyst, wherein the reaction mixture in the form of an aqueous emulsion contains both the water and the alkalis are separated coder using Sen or more fiber beds.

Methods for the effect of polyether polyols using acid neutralization have been known for a long time. Phase separation of the disperse reaction mixture to such an extent that the reaction product can separate effectively from the other constituents takes too much time without taking additional measures. For this reason, it is common practice to extract the reaction mixture with a tan amount of organic solvent, for example hexane or toluene, and then separate the organic phase in which the reaction product is dissolved from the aqueous phase. has the major drawback that the organic solvent has to be removed during the further processing. Another known measure is counter-washing the reaction mixture with an organic solvent. Although a smaller amount of solvent is then required, this method is rather time consuming and technically complicated.

A method is also known in which the alkaline reaction mixture obtained after the above-mentioned axyalkylation reaction (i.e. without prior neutralization) is subjected to the influence of gravity or to another treatment and a partial separation between the polyol and the 8300575 ψ- -'ϊ * - 2 - effect water phase. Although this known method has the advantage that less acid is required in the operation of the polyol, it also has serious drawbacks.

First, in many cases, an amount of organic solvent having the above-mentioned drawback must be added to the mixture obtained after the reaction. Furthermore, even after the addition of such a solvent, the emulsion formed during the reaction must be left to stand for a considerable time under elevated temperature under moderate stirring before the actual phase separation can be effected using a fiber bed or fiber beds. Finally, this method also has the drawback that the polyol phase still contains alkali, so that addition of acid or absorbents is necessary, so that the aforementioned advantage is at least partly nullified and the objections of the above discussed conventional methods.

It has been found that the aforementioned drawbacks are completely or at least largely avoided by carrying out the method described in the preamble of claim 1 in such a way that (a) the mixture obtained after the oxyalkylation reaction is neutralized before it is passed through the fiber bed or fibers beds and to effect a phase separation and (b) completely or almost completely liberates the polyol phase from the water still present therein.

The method according to the invention can suitably be used in the work-up of polyether polyols which, when mixed with water, even in a relatively small amount, do not give a complete hanogenic mixture. This group includes, as far as known, alia polyether polyols which, by reaction with alkylene oxides, such as ethylene oxide, propylene oxide, butylene oxide and mixtures thereof, form polyhydraxy compounds such as, for example, ethylene glycol, propylene glycol, trimethylolpropane, glycerol, diethanolamine and triethanolamine are prepared and used in practice as a starting material for the production of polyurethanes.

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For the neutralization (step a) in the process according to the invention, various acids can be used, for example organic acids such as benzenesulfonic acid, trichloroacetic acid, and formic acid, or inorganic acids such as perchloric acid, nitric acid or sulfuric acid. Carbon dioxide is also suitable in many cases.

Preferably, the aforementioned neutralization uses phosphoric acid.

Many so-called fibers can be used in the method according to the invention, for example synthetic fibers. Very suitable is the embodiment in which the or each fiber bed consists of polyolefin fibers, in the case of fibers consisting of polypropylene. These can be manufactured in different ways, for example by extrusion or by foil splitting.

Glass fibers are also very suitable in many cases. Particular preference is given to the embodiment, in which the or each fiber bed consists of stainless steel fibers. In this category, the fibers commercially available under the trade name "Bekinax" were found to be very effective.

The fibers can be used in the method according to the invention, both in loose form and in processed form, for example as felt in the case of synthetic fibers, and as a fleece in the case of steel fibers. In the latter case, the fiber mats commercially available under the trademark "Bekipor" have been found to be suitable with zander. In general, the fibers to be used in the present process are preferably combined by sintering into a fiber bed.

If desired, it is also possible to use a combination of different types of fiber beds, for example (in order according to the direction of flow) that of synthetic fibers with that of fibers consisting of stainless steel. In many cases it is advantageous to pass the mixture to be separated in phases through one or more filter layers before spreading through beds of metal fibers. If desired, use can be made of particulate filter material or filter candles. A preferably 8300575

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- 4 - Combination used is a glass fiber bed or beds and a stainless steel fiber bed or beds, in the aforementioned or reverse order or alternately.

When using two or more fiber beds, it is preferable for practical reasons to use these fiber beds in the form of an exchangeable separating element, so that the process need not be interrupted in case the fiber beds are insufficiently permeable. In this connection, it should be noted that the life of stainless steel fiber beds when carrying out the present process may be very great under suitable conditions and may be many thousands of hours.

Although the length of the fibers can vary widely, it is generally recommended to use fibers with a length of 8-12 cm, and in particular such randomly laid fibers in the form of flat panels or cylinders. The thickness of the fiber beds to be used can also vary within wide limits, for instance between 1 and 50 cm.

In many cases, fiber beds of 2-4 cm 2o thickness are preferred.

It should also be noted that in most cases good results are obtained by using fibers with gradually larger diameters in the direction of thong. For synthetic fibers, the following diameters are, for example, 2, 15, 50, 200 and 1000 µm, although many other combinations can also be suitable. In many cases it has been found for metal fibers that with diameters of 4, 8, 12 and 22 µm successively, a very efficient phase separation is obtained. In another preferred association, the following diameters are 2, 4, 8 and 22 µm. Insofar as the cross section of the fibers to be used is not round, the term diameter is to be understood to mean that of a circle with the same surface area as that of the aforementioned cross section.

In the method according to the invention, the mixture to be separated in phases can be passed through the fiber beds in a horizontal or vertical direction through 8300575-5. In both cases a, preferably small, pressure drop is used, for example 0.1-1.5 bar.

The embodiments of the present process to be discussed hereinafter, of which step (b) can be accomplished in many ways, will, for the sake of brevity, relate only to the use of potassium hydroxide as a catalyst and phosphorus as a neutralizing agent, but it is clear that the -invention is by no means limited to those aspects.

A preferred embodiment of the process according to the invention comprises axyalkylation with potassium hydroxide as a catalyst, neutralization of the reaction mixture obtained by mixing the net amount of aqueous phosphoric acid required for this purpose and passing the mixture thus obtained through fiber beds of stainless steel fibers. In the phase separation brought about thereby, after separation of the aqueous layer, a polyol layer is obtained in which (primary) phosphate and water are still present. This preferred embodiment is characterized in that in step (b) of the present process the polyol layer is evaporated to such a low water content that the phosphate crystallizes, the mixture is filtered and the filtrate is finally dried in a suitable manner, for example with the aid of a "falling film" evaporator, to obtain the polyether polyol with the purity required for further use, not only in terms of the water but also the potassium content.

In many cases, and especially in oxyalkylation reactions where a low catalyst concentration is used, it is possible and efficient to carry out the phase separation by coalescence in such a way that a phosphate-free polyol layer is obtained. In those cases, which are of course preferred, evaporation of the crystallization of the salt is not necessary. It is only necessary to free the polyol layer from the water still present therein and to obtain the polyether polyol of the desired purity.

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While retaining the inventive concept, the presently requested protection also extends to polyether polyols prepared by the present process and polyurethanes prepared by reacting those polyols with an isocyanate.

The method according to the invention is described by the following

Examples explained.

EXAMPLE 1

To prepare a polyether polyol having a hydroxyl number of 42, glycerol was reacted with propylene-10 oxide and ethylene axide in the presence of KCH as a catalyst.

The product obtained after the alkylalkylation was passed to a neutralization vessel, where it was mixed with an amount of a solution of phosphoric acid in water required for neutralization. The resulting mixture, which contained KH2PO4 at a concentration of 0.65% by weight (based on the polyol), was passed through a separating element composed of stainless steel fibers about 1.5 cm long and consisting of from (in the order of direction of flow) 8 beds of fiber with a diameter of 4 pan, 3 beds of fiber of 8 µm, 3 beds of fiber of 12 µm and 3 beds of fiber of 22 µm. The combined thickness of the beds was 2.5 cm.

After passage and the resulting two-phase separation, the polyol phase was insulated, which was found to contain only 60 mg / kg phosphate, which corresponds to a salt removal quotient of less than 99%.

The polyol phase was then evaporated under vacuum under stirring at a temperature of 120 ° C until the water was completely or almost completely removed, with all the phosphate still present crystallizing out. After filtration thereof, the polyether polyol was obtained as a clear liquid without suspended material and with a water content of only 0.05% m and a potassium content of less than 5 ppn.

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To prepare a polyether polyol having a hydroxyl number of 48, glycerol was reacted with propylene axide and ethylene axide in the presence of KOS as a catalyst.

The mixture obtained after the reaction was neutralized in the manner described in Example 1. The neutralized mixture with a phosphate content of 0.85 wt% (based on polyol) was passed through a candle filter and then through the separating element as described in Example 1, with the proviso that the fibers of the beds to be successively passed through have a diameter of 2, 4, 8 and 22 µm successively.

After passage and separation into layers, a polyol phase was obtained with a phosphate content of only 3 ppm, which corresponds to a salt removal quotient of over 99.9%.

This product was further passed to a "falling film" evaporator to obtain a clear liquid sand suspended material and having a water content of less than 0.05% m and a potassium content of 1 ppm.

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Claims (10)

1. Process for the preparation of polyether polyols by reacting a polyhydroxy compound with one or more alkylene oxides in the presence of an alkaline catalyst, wherein both the water and the alkali are separated from the reaction mixture in the form of an aqueous emulsion using of one or more fiber beds, characterized in that (a) the mixture obtained after the alkylation reaction is neutralized before it is passed through the fiber bed or beds and causes a phase separation and (b) the polyol phase. completely or almost completely freed from the water still present. 2. Method according to canolusion 1, characterized in that the or each fiber bed consists of glass fibers. 3. A method according to claim 1, characterized in that the or each fiber bed consists of sintered fibers of stainless steel. Method according to claims 1-3, characterized in that the or each fiber bed has a thickness of 2-4 cm. Method according to claims 1-4, characterized in that two or more fiber beds are combined to an interchangeable separation moment. Process according to claims 1-5, characterized in that the neutralization in step (a) is carried out with phosphoric acid. 7. Process according to claims 1-6, wherein potassium hydraxide is used as a catalyst and the mixture with phosphoric acid obtained after the OKylalkylation reaction is neutralized before it is passed through the fiber bed or the fiber beds, characterized in that after the phase separation it is first polyol-containing phase removes the water present to a large extent by evaporation, filtering off the phosphate crystallized thereby, and subsequently liberating the polyol from the water still remaining therein. • 8 3.0 0 5 7 5 & .....- - \ \ - 9 - ^ 8. Process according to claims 1-6, wherein potassium hydroxide is used as the catalyst and neutralizes the mixture with phosphoric acid obtained after the oxidation reaction before passing it through the fiber bed or fibers, characterized in that. The phase separation is carried out in such a manner that a phase containing phosphorus-free polyol is obtained, from which the water still remaining therein is subsequently removed. 9. Polyether polyols prepared by the method of claims 1-8. 10. Polyurethanes prepared by reacting a polyether polyol according to claim 9 with an isocyanate. SKKH04 / mf _________ 8300575