GB1028852A - Improvements relating to the preparation of alkali metal salts of terephthalic acid - Google Patents

Abstract

Active carbon used to purify an aqueous solution containing a dialkali metal salt of terephthalic acid produced by the Henkel rearrangement is regenerated by washing with water after separation. The water wash may be preceded by an aqueous alkali wash, preferably 2-20% by wt. conc. Suitable alkalis are caustic potash, caustic soda, sodium and potassium carbonates and bicarbonates and ammonia. Washing is preferably done at 60 DEG F. boiling. The alkali washing and water washing can be repeated, preferably alternately. Powder carbon is preferably treated in stirred suspension. Granular carbon is preferably treated as a fixed or moving bed, circulating the washing liquid through it. The regenerated carbon may be recycled. Example 1 illustrates water washing; Examples 2, 3 and 4 caustic soda and water; and Example 5 repeated caustic soda and water washings.ALSO:An alkali metal salt of terephthalic acid prepared by the Henkel rearrangement is decolorized by contact with active carbon. The carbon is regenerated by water washing, possibly preceded by washing with aqueous alkali, and is reused to decolorize more alkali metal salt. The alkali wash may be done with an alkali metal hydroxide carbonate or bicarbonate or ammonia at an alkali conc. of up to 20% by weight. Alkali and water washing may be repeated. In Example 1, dipotassium phthalate containing 3.5 mol. per cent of cadmium phthalate is heated at 440 DEG C. in a CO2 atmosphere under a pressure of 10 kg./cm.2 for 1 hour. The resulting suspension is filtered, and to 5.0 litres of the filtrate containing 205 gms. of dipotassium terephthalate per litre is added 15 gms. of powdered active carbon containing 50% water. The mixture is stirred at 60 DEG for 1 hour. The regenerated carbon is reacted with a further 5 litres of filtrate as before. In example 3, the filtered dipotassium terephthalate solution is passed through a granular active carbon bed. In Example 4 and 5 dipotassium terephthalate is firstly crystallized from the filtered solution, dissolved in water, and passed through a granular active carbon bed.