Method for purifying compound

Abstract

Provided is a method for purifying a compound capable of providing a high purity compound in high yield and at low cost. The present invention relates to the method for purifying a compound using a purification apparatus, the purification apparatus including: a crystallizing unit including a crystal forming section; and a wash column including a mechanism that forcibly transfers crystals. The crystallizing unit includes N tanks connected in series, wherein N is 2 or greater, a 1st tank is a most downstream tank, a (N)th tank is a most upstream tank, at least the 1st tank is a crystallization tank including a cooling mechanism, and a 2nd and subsequent tanks are each a crystallization tank or a ripening tank. The purification apparatus includes a line that feeds a compound-containing liquid to be purified to at least one of the N tanks. The wash column includes a line that sends a product out; and a line that returns a mother liquor to the crystallizing unit, with the line that returns a mother liquor to the crystallizing unit being connected to at least the (N)th tank. The crystallizing unit includes a line that feeds a slurry from the (N)th tank to the wash column; a line that sends a slurry from a tank among the 1st to (N−1)th tanks to the next upstream tank; and a line that is provided to each of the 1st to (N−1)th tanks and that sends thereto a mother liquor withdrawn from an upstream tank, wherein at least one of the lines that send a slurry from a tank among the 1st to (N−1)th tanks to the next upstream tank is a line that sends a slurry from a tank to the next upstream tank via a solid-liquid separator and that has a line that returns a mother liquor from which crystals are removed in the solid-liquid separator to the tank where the slurry came from, and wherein the line that is provided to each of the 1st to (N−1)th tanks and that sends thereto a mother liquor withdrawn from an upstream tank is a line that directly sends a mother liquor withdrawn from a tank one upstream or a line that sends a mother liquor withdrawn from a tank one upstream via a solid-liquid separator. The purification method includes forming crystals of the compound in the crystallizing unit; discharging at least a portion of a mother liquor to the outside of the purification apparatus; separating a slurry containing the formed crystals into a mother liquor and a slurry having an increased crystal concentration; returning at least a portion of the separated mother liquor to the tank where the slurry came from; mixing a compound-containing liquid to be purified fed to the crystallizing unit with a slurry in the crystallizing unit; sending a slurry in order from any one of the 1st to (N−1)th tanks to the next upstream tank among the N tanks in the crystallizing unit; and feeding at least a portion of a slurry from the crystallizing unit to the wash column; wherein the compound-containing liquid to be purified has a higher purity than the mother liquor discharged to the outside of the purification apparatus, the slurry fed to the wash column contains a mother liquor having a purity A1 of 80 mol % or higher, and a difference between the purity A1 and a purity A2 of the mother liquor discharged, A1-A2, is 5 mol % or more.