Effect of diantimony trioxide on direct esterification between terephthalic acid and ethylene glycol

Experiments at various Sb 2 O 3 concentrations were made in a pilot plant and the effect of Sb 2 O 3 on continuous esterification between terephthalic acid (TPA) and ethylene glycol (EG) was obtained. Reaction rate constants of the previously reported reaction scheme were determined to fit with the experimental data obtained. It was found that the effect of Sb 2 O 3 on reaction rate constant ( k i ) can be expressed as follows. k 1 = (3.75 × 10 −4 Sb + 1.0) × 1.5657 × 10 9 exp(−19,640/RT) k 2 = (4.75 × 10 −4 Sb + 1.0) × 1.5515 × 10 8 exp(−18,140/RT) k 3 = (6.25 × 10 −4 Sb + 1.0) × 3.5165 × 10 9 exp(−22,310/RT) k 4 = (4.50 × 10 −4 Sb + 1.0) × 6.7640 × 10 7 exp(−18,380/RT) k 5 = (3.50 × 10 −4 Sb + 1.0) × 7.7069 × exp(−2810/RT) k 6 = (1.75 × 10 −4 Sb + 1.0) × 6.2595 × 10 6 exp(−14.960/RT) k 7 = (3.75 × 10 −4 Sb + 1.0) × 2.0583 × 10 15 exp(−42,520/RT) Simulation of esterification with these reaction rate constants at various Sb 2 O 3 concentrations was made and the following results were obtained. Sb 2 O 3 accelerates the esterification reaction between TPA and EG. Sb 2 O 3 accelerates the main reaction and its effects on side reactions are minor. The higher the addition rate of Sb 2 O 3 , the lower the carboxyl end‐group concentration (AV) and diethylene glycol content (DEG). The comparison between simulation with potassium titanium oxyoxalate (PTO) in the previous report and with Sb 2 O 3 in the present report shows that the acceleration of polycondensation reaction by Sb 2 O 3 is higher. DEG formation rate is lower with PTO than Sb 2 O 3 .