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

Experiments at various Sb₂O₃ concentrations were made in a pilot plant and the effect of Sb₂O₃ 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 Sb₂O₃ on reaction rate constant (k_i) can be expressed as follows.

• k₁ = (3.75 × 10⁻⁴Sb + 1.0) × 1.5657 × 10⁹exp(−19,640/RT)

• k₂ = (4.75 × 10⁻⁴Sb + 1.0) × 1.5515 × 10⁸exp(−18,140/RT)

• k₃ = (6.25 × 10⁻⁴Sb + 1.0) × 3.5165 × 10⁹exp(−22,310/RT)

• k₄ = (4.50 × 10⁻⁴Sb + 1.0) × 6.7640 × 10⁷exp(−18,380/RT)

• k₅ = (3.50 × 10⁻⁴Sb + 1.0) × 7.7069 × exp(−2810/RT)

• k₆ = (1.75 × 10⁻⁴Sb + 1.0) × 6.2595 × 10⁶exp(−14.960/RT)

• k₇ = (3.75 × 10⁻⁴Sb + 1.0) × 2.0583 × 10¹⁵exp(−42,520/RT)

Simulation of esterification with these reaction rate constants at various Sb₂O₃ concentrations was made and the following results were obtained.

• 1

  Sb₂O₃ accelerates the esterification reaction between TPA and EG.

• 2

  Sb₂O₃ accelerates the main reaction and its effects on side reactions are minor. The higher the addition rate of Sb₂O₃, the lower the carboxyl end-group concentration (AV) and diethylene glycol content (DEG).

• 3

  The comparison between simulation with potassium titanium oxyoxalate (PTO) in the previous report and with Sb₂O₃ in the present report shows that the acceleration of polycondensation reaction by Sb₂O₃ is higher. DEG formation rate is lower with PTO than Sb₂O₃.