GB686254A - Improvements in or relating to the manufacture of pentaerythritols - Google Patents

Abstract

Pentaerythritols are made by condensing formaldehyde and acetaldehyde in aqueous solution with a strong alkaline earth base and precipitating and mechanically removing at the end of the condensation part of the alkaline earth metals present in solution, passing the resultant liquor through a bed of cation-exchange material to replace the residual alkaline earth ions by hydrogen ions, and eventually subjecting the thus treated liquor to flash evaporation. "Pentaerythritols" is defined as pentaerythritol in admixture with dipentaerythritol and other polypentaerythritols that accompany it as by-products of the above condensation. Lime is the specified base. Flash evaporation may be effected on hot rolls in vacuo or by spraying into a non-oxidizing gas. Preferably the liquor is concentrated before evaporation. A crop of pentaerythritol may be recovered before the evaporation. Preferably before cation exchange treatment liquor from the condensation is treated with sulphuric acid to precipitate calcium ions which are mechanically removed as the sulphate then with a barium salt, e.g. the carbonate, in an equivalent amount to the excess sulphate present and barium sulphate removed. After cation - exchange treatment any formic acid present may be neutralized with ammonia before concentration and flashing or the liquor may be passed through anion exchange material to reduce or remove residual sulphuric and formic acid. Preferably cation exchange treatment is effected when the liquor is dilute and before pentaerythritols are recovered. Preferably the condensation is effected so that no rise in temperature occurs towards the end of the addition of the reagents. "Zeo-carb" 215 (Registered Trade Mark) and Deacidite E are specified cation and anion exchange materials respectively. On washing the pentaerythritols with cold water they are obtained substantially free from syrupy formaldehyde products. In an example liquor from the condensation is treated with formic acid to dissolve excess lime, steam distilled to recover formaldehyde, sulphuric acid added and calcium sulphate filtered off, barium carbonate added and barium sulphate removed, the filtrate run through "Zeo-carb" 215 and the liquor concentrated to 1/4 of its volume and dried by spray drying into air.