Crossflow type filtering operation method using ceramic filter

A filtering operation method for filtering fine crystals contained in an oxidation reaction mother liquor obtained in a terephthalic acid production process by a cross-flow filtration using a ceramic filter while conducting a flowing circulation operation of the oxidation reaction mother liquor,

• the method comprising:
• conducting (I) an operation for filtering the fine crystals;
• and
• conducting (II) a back washing operation with a filtrate while maintaining the flowing circulation operation of the oxidation reaction mother liquor, (II) the back washing operation with the filtrate being conducted under the following conditions:
• (II-A) an operation time that is in the range of from 5 to 180 [s];
• (II-B) a differential pressure between a filtration side and a flow path side that is in the range of from 0.10 to 1.0 [MPa];
• (II-C) a feeding linear velocity of the filtrate that is in the range of from 1.0 to 20 [m/h];
• and
• (II-D) a temperature of the filtrate that is in the range of from “a temperature of the oxidation reaction mother liquor” to “a temperature higher by 35° C. than that of the oxidation reaction mother liquor”.