Process for producing trans-1,4-cyclohexanedicarboxylic acid
View Patent ↗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.
1. A trans-1,4-cyclohexanedicarboxylic acid composition comprising trans-1,4-cyclohexanedicarboxylic acid in an amount of 90% or higher, wherein
a transmittance of the trans-1,4-cyclohexanedicarboxylic acid composition at 340 nm is 85% or higher when the transmittance is determined by examining an alkali solution, which is prepared by dissolving 1 g of the trans-1,4-cyclohexanedicarboxylic acid composition in 10 mL of 2N KOH solution, with a spectrophotometer using a quartz cell having a thickness of 1 cm; and
the trans-1,4-cyclohexanedicarboxylic acid composition further comprises trans-4-methylcyclohexanecarboxylic acid in an amount ranging from 0.2 to 0.9 wt %.
2. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 1 , further comprising at least one of
a total content of alkali metals and alkaline earth metals of 20 ppm or lower; and
an acid radical content of 25 ppm or lower.
3. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 2 , wherein the acid radical content is a total content of sulfur and chlorine as determined by an emission spectrometry.
4. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 1 , further comprising cis-1,4-cyclohexanedicarboxylic acid, wherein a weight ratio of trans-1,4-cyclohexanedicarboxylic acid to a sum of trans-1,4-cyclohexanedicarboxylic acid and cis-1,4-cyclohexanedicarboxylic acid is 0.8 or higher.
5. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 1 , wherein the trans-1,4-cyclohexanedicarboxylic acid composition further comprises terephthalic acid in an amount of 0.3 wt % or less.
6. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 1 , wherein the transmittance of the trans-1,4-cyclohexanedicarboxylic acid composition at 340 nm is 92.9% or higher.
7. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 1 , wherein the trans-1,4-cyclohexanedicarboxylic acid is in the form of acicular crystals or a mass.
8. The trans-1,4-cyclohexanedicarboxylic acid composition according to claim 1 , wherein the trans-1,4-cyclohexanedicarboxylic acid is in the form of acicular crystals.