Abstract: A countercurrent washing column adapted to be used in purifying a crude crystalline material with a solvent. A suspension of the crystalline material is fed to the top of the column and flows downwardly therein countercurrent to a washing solvent. A vertically arranged agitator shaft is positioned in the column for axial rotation and carries a plurality of axially spaced paddles. Frusto-conical baffles and guide plates are arranged within the column to cooperate with the paddles to produce radially inward and outward movement of the suspension and solvent as they flow through the column.

Abstract: Crude DMT containing, as impurities mainly dimethyl isophthalate, dimethyl orthophthalate and p-toluic acid methyl ester, is purified with the use of solvents known to be useful for the recrystallization of DMT in such a manner that the crude DMT in molten state is introduced with agitation into the solvent, the temperature of which is maintained above the temperature of that eutectic mixture of DMT and the main impurities associated therewith which has the highest melting point. As soon as the solvent is saturated with DMT, pure DMT crystallizes. The process is preferably carried out continuously and in a special vertical counter-current washing column.