TH2682A - A method for producing terephthalic acid through the production of terephthalate-methyl ester from p-xylene and methanol. - Google Patents

Abstract

The method for producing terephthalic acid involves using terephthalic acid dimethyl ester, derived from para-xylene and methanol, by oxidizing the p-x mixture with a derivation of para-toluic acid methyl ester. This derivation is then re-oxidized in the liquid phase under an oxygen atmosphere with a solution of heavy metal compounds acting as a catalyst.

Claims (7)

1. Method for producing terephthalic acid using terephthalic acid dimethyl ester derived from para-xylene and methanol. This is achieved by oxidizing a mixture of p-x and a fraction containing para-toluic acid methyl ester (p-TE), which is then re-oxidized within a liquid layer in an oxygen atmosphere with a solution of heavy metal compounds as a catalyst. This results in the dominant form of para-toluic acid (p-TA) and an oxidation product containing terephthalic acid monomethyl ester (MNT) at temperatures of 140-170°C and pressures of 4-8 bar. Esterification of the oxidation product occurs at temperatures of 220-280°C and pressures of 20-25 bar with liquid methanol, which is pressurized and vaporized to obtain the dominant p-TE and an undistilled ester containing DMT. The resulting fraction is then further processed. The undistilled ester and the methanol-containing vapor fraction are removed during esterification. Distillation separates the undistilled ester into a p-TE fraction and a terephthaladehyde acid methyl ester, which is returned to the undistilled DMT oxidation reaction. The remaining undistilled DMT is hydrolyzed with water, recovering TPA, and the separation of the methanol-aqueous mixture is characteristic in that the methanol-containing vapor and the methanol-aqueous mixture are separated by high-pressure, high-temperature distillation into a methanol-rich top fraction and aqueous bottom fraction. The methanol formed at the top of the distillation column is removed as vapor at high pressure. The esterification reaction of the oxidation products proceeds by compressing the methanol-containing vapor to the required pressure and esterification temperature. 2. The production method described in claim 1 is unique in that the vapor containing methanol used in esterification is produced through purification distillation at pressures of 2 to 20 bar, and specifically 4 to 8 bar. 3. The production method described in claim 1 is unique in that the heat present in the compression of the methanol-containing vapor is used to overheat the methanol-containing vapor to the esterification temperature. 4. The production method described in claim 1 is characterized by a vapor pressure ratio of methanol obtained from compression ranging from 1.2:1 to 15:1, particularly 3:1 to 9:1, and a final temperature reached at the exit point of compression ranging from 150 to 300°C, particularly 220 to 280°C. 5. The production method described in Patent 1 is unique in that the vapors removed from the esterification process are purified and expanded to a pressure of 0.1 to 8 bar in a steam turbine for use in driving a methanol compressor or generator. 6. The production method described in claim number 5 is unique in that the vapor is partially liquefied before entering the turbine, and a portion of the condensed liquid is used for purification of the vapors. 7. The production method described in claim 5 is unique in that vapors are washed away by the water of the production process. (7 claims, 1 illustration)