Bis(2-hydroxyethyl) terephthalate(BHET), an intermediate of poly(ethylene terephthalate) preparation, was synthesized directly from terephthalic acid(TPA) and ethylene oxide(EO) under various conditions. Efficiency of different catalyst systems including triethylamine, metal halides, and their complexes was investigated.
All the reactions were carried out in an pressure reactor using acetone as a solvent. When triethylamine/ferric chloride complex was used as a catalyst, the reaction gave high yield of BHET at 85℃. However higher temperature(110℃) was required for triethyamine alone. Under the following reaction conditions; the temperature 100℃, EO/TPA ratio(in mole) 2.47, reaction time 6hrs, the reaction conversion was 99%. This product contained 93.2% BHET, the rest being a mixture of diethylene glycol terephthalates.
Formation of undesirable terephthalates of diethylene glycol and higher molecular weight polymers of EO were found to be most sensitive to reaction temperature. With triethylamine as a catalyst, significant amount of waxy by-product was formed at the temperature higher than 115℃. At higher temperature, the formation of waxy polymers was observed even with smaller EO/TPA ratios(＜2.0).
