GB718467A - Improvements in or relating to purification of low boiling tar acids - Google Patents

Abstract

Low-boiling tar acids, i.e. boiling below 230 DEG C., and lower aliphatic carboxylic acids i.e. having a maximum of six carbon atoms, are separated by passing a solution of the tar acids and carboxylic acids in an organic solvent in contact with an anion exchange resin and recovering tar acids substantially free from carboxylic acids from the effluent. The exchange resin initially adsorbs tar acids which are subsequently displaced by the carboxylic acids; the reaction is therefore carried on until more of the tar acids have been added than is necessary to saturate the resin with acids but not longer than is required for the resin to become saturated with carboxylic acids. Suitable solvents are organic polar solvents such as methanol, ethanol, acetone and methyl ethyl ketone, particularly aqueous methanol. The anion exchange resin is preferably one that obtains its activity from quaternary ammonium groups. Basic substances such as tar bases or bases derived from the anion exchange material may be removed from the effluent solution by subsequent passage through a cation exchange resin which preferably derives its exchange capacity from sulphonic acid groups. The anion exchange resin may be regenerated by treatment with a strong acid followed by a strong base, or by treatment with an aqueous solution of a base (e.g. sodium hydroxide) alone. The cation exchange resin may be regenerated by an aqueous methanol solution of a strong acid. The process relates particularly to the removal of butyric acid occurring in amounts of less than 5 per cent in low boiling tar acids. Examples describe the use of an anion exchange resin in (1) the separation of aliphatic acids, acetic, propionic, butyric and valeric, from a mixture of tar acids containing phenol, cresols, xylenols and ethyl phenols; and (2) the separation of o-cresol and butyric acid.