Process for producing trans-1,4-cyclohexanedicarboxylic acid

A subject for the invention is to obtain trans-1,4-cyclohexanedicarboxylic acid (t-CHDA) in a high concentration by efficiently isomerizing cis-1,4-cyclohexanedicarboxylic acid (c-CHDA) by a simple method. The invention provides: (1) a process for producing t-CHDA which comprises heating crude CHDA to 180° C. or higher in an inert atmosphere and causing the t-CHDA formed by isomerization to precipitate in the molten c-CHDA while holding the crude CHDA at a temperature in the range of not lower than 180° C. and less than the melting point of t-CHDA; (2) a process for producing t-CHDA, wherein crude CHDA which is powdery or granular is heat-treated at a temperature of not lower than the melting point of c-CHDA and lower than the melting point of t-CHDA to thereby isomerize the cis isomer to the trans isomer while maintaining the powdery or granular state; (3) a process for producing t-CHDA, wherein crude CHDA is held at a temperature of not lower than the melting point of c-CHDA and lower than the melting point of t-CHDA in an inert atmosphere while maintaining flowing to thereby obtain powdery or granular t-CHDA; and (4) a process for purifying crude CHDA in which crude CHDA obtained through the step of hydrogenating TPA or the like is heated in an atmosphere of an inert gas to volatilize and remove impurities.