GB2135322A - A process for purifying at least partially water-soluble polyethers and/or copolymers - Google Patents

Abstract

At least partially water-soluble polyethers and/or copolyethers based on ethylene oxide and/or propylene oxide are purified from a catalyst, comprising ions of alkali metals or undesired admixtures, by acids or acidically reacting substances, e.g. ion exchangers, inorganic or polyhydridic organic acids, preferably trihydrogen phosphoric acid, in an amount of 0.3 to 2.0 mol per one mole of the catalyst.

Description

SPECIFICTION A process for purifying at least partially water-soluble polyothers and/or copolyethers The invention relates to a process for purifying at least partially water-soluble polyethers and/or copolyethers based on ethylene oxide and/or propylene oxide so thatthey could serve as a suitable raw material for producing hydrophilic polyurethanes and other products. Removal of residues of catalysts of polyaddition or copolyaddition, such as hydroxides of alkaline metals, andof products of side reactions of polyether synthesis is mainly a problem.

Forthe production of polyurethanes the required contentof alkali metalsirb polyethers is below 5x1 4 % byveight (5 ppm). 'while the refining of waterinsoluble polyethers, poLyetherdiols or polyether polyolgireparnd, for example, by polyaddition of propyle oxide to diols or polyols, is protected by many patents and certificates of authorship, the refining of water-soluble ethers and copolyethers mainlyfromthe ions of alkali metals is still problematic.Removal of hydroxides ofalkali metalsfrom water-insoluble polyethers-;isthusbased ontheir neutralization with aqueous solutions of sulphuric acid or organic acids, mainly dicarlaaxylic acids (see GB Patents9T6552 and 95839Q) AIEraline catalysts are further adsorbed by magnesium.silicates attempera tures of 80 to 1300C in the presenceofa small amount of water.Silicates are then removed by filtration (US patent4 718). Processes for removing alkaline catalysts from water-insoluble polyols sothat alkaline catalysts are extracted by water are also known, the extraction being accelerated by dissolvirrg polyols in hexane (US Patent 715402) or alkalinecatalysts are neutralized with oleic acid together with allvlbenzene sulphonic acid or with alkyltoluene sulphonic acid (DE PatentApplication 2 737 473). Polyols arefurther refined from alkalies using a suitable solution of potassium hydrogen sulphite at a temperature of 20 to 130"C and pH 6.5 to 7.5. Precipitated salts are filtered off after vacuum removal of water (PL patent 94 408).

Similarly DD Patent71 622 protects removal of alkaline catalyst by means of an aqueous solution of sodium hydrogen sulphate. Also known (DE Patent Application 3016 112) is separation of alkali salts from crude emulsions resulting from neutralization of alkaline catalyst in water-insoluble polyether with sulphuric acid in the presence of 1 to 30 % by weight of water and Oto 30 % by weight of an organic solvent.

The drawback of the above-mentioned processes is mainly thefactthat they are suitable only forthe refining of water-insoluble polyethers. Besides that, when water or aqueous solutions are used a large amount of heat is necessary for distilling the water.

The above-mentioned drawbacks are eliminated or technical problems in the refining of water-soluble polyothers are solved by the process according to this invention.

According to this invention the process for purifying at least partially water-soluble polyethers and/or copolyethers based on ethylene oxide and/or prop ylene oxide from a catalyst comprising ions of alkali metals or undesired admixtures is carried out by refining with acids or acidically reacting compounds, mainly from the group of ion exchangers, inorganic or polyhydridic organic acids, preferably trihydrogen phosphoric acid, in the amount of 0.3 to 2.0, preferably 0.8 to 1.1, mole per one mole of a catalyst, possibly in the presence of a solvent, sorbent or chemical decolourizer, after which removal ofthe insoluble fractions by filtration or centrifugation follows.

High efficiency of removal of alkali metal cations or alkali metalsfrom polyetherorcopolyetheristhe advantage ofthe process for refining of at least partially water-soluble polyothers according to this invention. Thus treated polyother or copolyether contains below 3x10-4 or even 1x1 % % by weight of alkali metals cations and issuitablefor preparing polyurethanes The possibilityofsimultaneous removal of mainly coloured admixtures from polyothers and particularly low power demandsfor refining are further advantages.

The refining process according to this invention does not require any expensive equipment and can be carried out continuously, discontinuously orsemicontinuously.

Bythe practice ofthe process according to this invention further variants can be employed which are suitable for the respective producer or user of polyethers or copolyethersdepending on circumstances.The term "polyether" or "polyether diol or polyether polyol" as used herein is intended to mean products of homopolyaddition of ethylene oxide or propylene oxide, including also polyethylene glycol and polypropylene glycol, and further products of polyaddition of ethylene oxide and propylene oxide to diol orpolyol, ortheir mixtures.The term "copolyether" is intended to mean on the one hand products of copolyaddition of ethylene oxide with propylene oxide, most frequently products of block polyaddition, for example with polyethylene glycol polyaddition of propylene oxide or with polypropylene glycol polyaddition of ethylene oxide. Copolyaddition can start also with other diols or polyols, such as glycerol, trimetolyl propane, pentaerythritol,triethanolamine and similar. The present production of polyethers or copolyethers may take place under the catalytic action of bases mainly hydroxide of alkaline metals or Lewis acids.The catalyst or residues of catalysts can be removed from the produced polyethers or copolyethers for a great number of technically common applications. Atthe sametimethe polyethersshould be liquid attemperatures of up to 1 50"C. If this requirement cannot be simply met it is possible to proceed so that polyother is diluted with a suitable solvent, for example with a lower alcohol. Water can also be employed as a diluent; in that case ions are eliminated by cationic ion exchangers or anionic ion exchangers.

Alcohols, such as methanol or isopropyl alcohol, may be used because these alcohols do not dissolve sodium and potassium salts. Salts of alkali metals can then be easily removed using common separating procedures, such as filtration and centrifugation.

Besidesforthe removal of alcohols from solutions by distillations a substantially smaller amount of heat is necessary than forthe removal of water. Instead of the mentioned solvents also non-reactive solvents or diluents may be used, such as ketone, acetone, methylethylketone, dimethylformamide, if these are employedforpreparing polyurethanes by dissolving technology they need not be removed from polyether.

Production of microporous polyurethane materials can serve as an example.

When inorganic acids are employed, use is made of thefactthatsodium and potasium salts,forexample phosphates, sulphates, carbonates and chlorides, are insoluble in polyethers or polyether diols and the precipitate thus originated can be removed byfiltration or by other separation methods. Forthese reasons it is advantageous to use anhydmus acids and mainly polyhydridic acids, e.g. trihydrogen phosphoric acid which, in addition, is suitable also from the point of view of low corrosion of constructional materials. With the use oftrihydrogen phosphoric aoid over-dosing with the acid does not matter for not only normal but also acid salts of sodium and potassium are insoluble in polyether or copolyether.

Similarly the salts of sulphuric acid do not dissolve in alcohols orin acetone.

When carrying out the process according to this invention preferably a stoichiometric amount of trihydrogen phosphoric acid, possibly with 10 % excess, is added, depending on the amount of employed or present catalyst (sodium or potassium hydroxide) in crude polyether or copolyether. The solution is mixed for approximately 20 minutes, heated to a temperature of 80 to 120"C, at which it is held for 20 to 30 minutes, and then the formed precipitate is filtered off. One can proceed also in such a waythatthe content of alkali in the solution of polyether diol or polyother polyol is determined by acidimetric titration and according to the result the appropriate amount of acid necessary for precipitation is used.

Ifthe polyetherdiol is dark, activated charcoal or chemical decolourizing agent such as sodium sul phite,hypophosphorousacid,orsodium hypochlo- rite, can be added to the solution before sedimentation ofthe alkali. Active charcoal is then filtered off together with the formed salt, preferably potassium phosphate and/or sodium phosphate.

Deionization can be accomplished also by ion exchangers, anionic and/orcationic ion exchangers.

These are employed in the OH(-) orthe H(+) form. For this purpose it is most suitable to use a continuous or semi-continuous devicewherein polyetheror polyether diol, orcopolyether or its solution, is brought through towers filled with ion exchangers.

The towers may be heated to make the polyether less viscous. The most suitable ion exchanger is an anion exchanger-cation exchanger. In addition to catching contingent residues of anions, an anion exchanger has also a decolourizing effect in polyether or copolether. Ions of sodium and potassium are then caught atthe cation exchanger practically quantita tively. Ion exchanger capacity of ion exchangers can be determined or tested by titration with an acid or a hydroxide, and sodium or potassium content is definitively determined in the product usually photo metrically.

Regeneration of ion exchangers is usually made using suitable solutions of acids or hydroxides and washing to neutral reaction with distilledwater,the acid or hydroxide concentration being 3 to 5 % by weight. After removing acids and hydroxides, the ion exchanger is washed with a lower alcohol or acetone to remove moisture.The process can becombined with already mentioned precipitation by acids after removing the sait by filtration.In the cases mentioned sodium and potassium content below tx70-4 % by weight (1 ppm) is reached and long life ofthe ion exchangersintheworking cycle is secured, By the process presented high purity of polyethers or polyether dials and copolyethers BE reached, which are suitable for preparing polyurethanes, at lover energy costs as compared to processes when water is employed.

Further details ofthe process for refining according to this invention are evident from the examples which nevertheless do notincludeallthe possiblecombina tions ofthe invention Example 1 Two columns having an internal diameter of3 cm and a heightof 92 cm jacketed forthe purpose of heating using recirculated heating liquid are filled with ion exchangers. The column I with an anion exchanger (Lewatite S-10) and column II with a cation exchanger (Ostion KS). Thevolume of each ofthe ion exchangers is 500 cm3. Ion exchangers were activated with 1500 cm3 of sodium hydroxide aqueous solution having concentration 5 % by weight or of hydrochloric acid having concentration 3 by weight, with avolume velocity of 3 litres per hour.Aftertransferring into or or H(+) form, the ion exchangers are washed with distilled water by feeding 1.5 volume per one volume of ion exchanger per hourfor7 hours at a temperature of 80"C. After removing residues of hydrochloric acid or sodium hydroxide (determination byfollowing pH value) ion exchangers are washed with 1500 ml of isopropyl alcohol and are used for deionization of crude water-soluble products of polyaddition or copolyaddition of C2 to C4 olefinoxides. The results of the analysis of these products after refining mainly from ions of alkaline metals in ion exchangers in the sequence anion exchanger-cation exchanger are presented in Table 1.The starting crude water-soluble products have atthe sarne time total content of potassium hydroxide and sodium hydroxide 0.20 to 0.30 by weight (thatis 2000to 3000 ppm) is determined by titration.

Considering thatpolyglycols or polyethers having relative molecular mass above 1000 or copolyethers above 1500 are at room temperature too viscouS they deionize in the form of n-butanol or aqueous solution having a concentration 10 to 30 % byweightata temperatureof 80 C. The solvent is evaporated after deionization in a rotary evaporator under reduced pressure. One dm3 of polyether is refined by the cation exchanger so that the content of potassium cations is below 3x10-4 % by weight (below 3 ppm After experiments for preparing polyurethanes with 4,4' - diphenylmethane diisocyanate in nitrogen atmosphere straight polyurethane soluble in organic solvents, such as for example dimethylformamide, are prepared.

TABLE 1

The type of Molar mass Content of Content after deionization crude product (g/mol) ethoxameric (10-4 % by weight; ppm) of polyaddition groups or copolyaddition (Z by weight) Na(+) K(+) polyethylene 650 100 0.2 1.3 glycol polyethylene loec 100 0.0 0.3 glycol polyethylene 1600 ico 0.1 0.65 glycol polypropylene 920 0 0.2 1.1 glycol eopolyether of 990 ' 10 0.1 0.1 0.54 ethylenoxide and propylenoxide copolysther of 1500 42.5 0.0 0.0 0 0.57 ethylenoxide and propylenoxide copolyether of 2340 69.8 0.2 1.6 ethylenoxide and propylenoxide Example2 Copolymer of propylene oxide and ethylene oxide having molar mass 1200 g/mol, content of ethoxameric units 52 % by weight and potassium hydroxide 0.22 % by weight (2200 ppm) is treated by the addition of 0.59 mol of sulphuric acid per 1 mol of potassium hydroxide; 0.39 mol oftrihydrogen phosphoric acid per 1 mol of potassium hydroxide; 1.09 mol of hydrochloric acid per 1 mol of potassium hydroxide; by 1.17 mole of butyric acid and acetic acid each and 0.41 mol of oxalic acid always per 1 mol of potassium hydroxide and by blowing through with carbon dioxide.

After 30 minutes action ofthe acid or individual acids at a temperature of 25 C while stirring the solution or solutions are heated to a temperature of 80 Candafter30 minutesthe precipitateformed is filtered. The precipitate of potassium chloride is filtered best. The others, in descending order are: KCI > K3PO4K2CO3,K2SO4 > K2(CO0)2. When using formic acid and acetic acid the precipitate practically does notform at all.Then the amount of potassium ions is determined by ionoselective electrodes to K(+ in the product: 0.0170 % by weight (170 ppm) with trihydrogen phosphoric acid, 0.0205% by weight (205 ppm) with sulphuric acid,0.0392 by weight (392 ppm) with hydrochloric acid, 0.0070% by weight (70 ppm) with carbon dioxide, 0.0166% by weight (166.5 ppm) with oxalic acid, 0.18to 0.21 % by weight (1850 to 2100 ppm) with formic acid and acetic acid.

The products are, after filtering, deionized using cation exchanger (sulphonazed copolymeric styrene -divinyl benzene bitumen in H(+) fo form). The refining efficiency of the cation exchanger is enhanced four times when hydrochloric acid is used (purifying efficiency 10 dm3) of copolyether per 1 dm3 of cation exchanger) and ten times when trihydrogen phosphoric acid is used.

Example 3 Coplymeric polyether having molar mass 1200 g/mol and content 30 % by weight of ethoxameric units and residues of catalyst of polyaddition in the amount of O.23 by weight, essentially potassium hydroxide with admixture of sodium hydroxide is mixed with various amounts oftrihydrogen phosphoric acid. After addition of tri hydrogen phosphoric acid the polyether is stirred for 10 minutes at room temperature and then 30 minutes at a temperature of 120 C, and is filtered while hot. The content of sodium and potassium ions is determined in the filtrate spectrophotometrically.

The results of the effect of the amount of added trihydrogen phosphoric acid to 500 g samples of copolymeric polyethers having molar mass 1200 g/mol and content of ethoxameric units 30 % by weight and of potassium hydroxide 0.23 % by weight with admixtures of sodium hydroxide are summarized in Table No.2.

TABLE 2

Addition of H3P04 1.0 1.5 2.0 2.5 2.7 2.9 3.1 3.3 (g) Addition of H3P04 0.42 0.63 0.84 1.05 1.13 1.22 1.3 1.38 (mol/nol KOH) After refining:: content of K(+) 190 173 152 3.7 3.0 0.0 0.0 0.0 (10~4 by weight) content of Na(+) 3.3 2.1 1.9 0.0 0.0 0.0 0.0 O.0 % S by weight) pH 9.9 7.7 6.4 4.5 3.8 ~ ~ ~ Tleamountoft?ihydrngen phosphoric acid or other acid needed can be determined by direct titration with an acid at pH below 6.If pH falls below 6.0, calcium carbonate is added to the product (for example in the amount 0.6 % byweight) for neutralization ofthefree acid and is then heated to a temperature of 1 200C while stirring and the solution is then filtered off after approximately 10 minutes. If the water-soluble polyether is dark-coloured before purifying itis advisable to add 1.5 % by weight of active charcoal and after 20 minutes filter off the solution before adding the acid. Filtration of active charcoal can be combined with filtration after neutra lization ofthe base. The solution is decolourized by the process described. Similardecolourizing is achieved by the application of sodium sulphite. In the cases of acid overdosing its excess is removed using an anion exchanger column.

Treatment with the trihydrogen phosphoric acid using one mol of acid per one mol of alkaline catalyst does not require anyfurther purification of polyethers or copolyether by ion exchangers.

Claims (8)

1. A process for purifying at least partially water- soluble polyethers and/or copolyethers based on ethylene oxide and/or propylene oxide from a catalyst comprising alkali metal ions or admixtures whereinthepurification is carried out by acids or acidically reacting substances and the insoluble fractions are removed.

2. A process accordingto Claiin 1, wherein the acids or acidically reacting substances are ion exchangers, inorganic or polyhydric organic acids.

3. A process according to Claim 2, wherein the acid istrihydrogen phosphoricacid.

4. A process according to Claim 2 or3,wherein the acid is in an amount of 0.3 to 2.0 mol per one mole of the catalyst.

5. A process according to Claim 4, wherein the acid is in the amount of 0.8to 1.1 mol per one mole of the catalyst.

6. A process according to any one of Claims 1 to 5, wherein the purification is carried out in the presence of a solvent, sorbent or a chemical decolourizer.

7. A process for purifying at least partiallywatersoluble polyothers and/orcopolyethers based on ethylene oxide and/or propylene oxide from a catalyst substantially as herein described with referenceto Examples 1 to 3.

8. At least partiallywater-soluble polyetherand/ orcopolyother based on ethylene oxide and/or propylene oxide purified from a catalyst according to any one of Claims 1 to 7.