Synthesis of Bis (2-hydroxyethyl) terephthalate (BHET), an intermediate of poly (ethylene terephthalate), from terephthalic acid (TPA) and ethylene oxide(EO) was studied in a high-pressure batch reactor without using solvent. EO was used in excess of stoichiometrical amount to maintain the condition of dispersion of TPA in the reaction system adequate for the reaction to proceed. Triethylamine was used as catalyst throughout this study.
The effects of temperature, EO/TPA mole ratio and catalyst concentration on the conversion on the conversion and yield were experimentally investigated. It appeared that temperature was the most effective vaiable on the yield of BHET. The conversion of TPA increases with an increase in reaction temperature. Optimum range of operating condition which can maximize the yield of BHET were obtained as follows : reaction temperature of 100-110℃, catalyst concentration of 1-2% (vs. TPA wt.%), and EO/TPA mole ratio of 4-6.
The reaction rate was found to be first-order with respect to the catalyst weight, and also it was found that an overall reaction was the first-order heterogeneous reaction with respect to EO concentration. The apparent rate constant was found as follows :
$k_{ES}$ = 1.7, l/ min·$kg_{cat.}$. at 100℃
The plant was scaled up for a production capacity of 132 tons day of BHET, using the optimum conditions obtained, and it's economic feasibility was studied.
