Abstract: A method for obtaining uniform stream in an adsorption column is disclosed. This method uses an adsorption column having at least one single-flow passage in which the ratio of the inner diameter of the column to the average particle size of a packing to be packed in the adsorption column is at least 20, and comprises classifying the packing to be packed in the adsorption column and packing the fractions of the packing into the adsorption column in the order of particle size. Thus, a desired substance or substances contained in a mixture can be adsorbed and then separated as a uniform stream in an adsorption column.

Abstract: This invention relates to an improved process for recovering highly pure terephthalic acid crystals from a suspension containing terephthalic acid product obtained by the liquid phase oxidation of para-substituted aromatic compounds in the presence of oxidizing catalyst. The improvement comprises bringing said suspension into continuous countercurrent contact with ascending hot acetic acid containing water in a single tower under the conditions of specified temperature, specified ascending rate of the acetic acid containing water and specified residence time of the suspension, to replace the mother liquor of the suspension with said acetic acid, and recovering the mother liquor as an overflow, while recovering terephthalic acid as an underflow in the form of suspension of highly purified crystals and, if necessary, allowing the suspension to stay in a stirring tank.