Process simulation of two-stage evaporation and crystallization systems for bis(2-hydroxyethyl) terephthalate recovery

Bis(2-hydroxyethyl) Terephthalate (BHET) produced from Polyethylene Terephthalate (PET) waste glycolysis process was purified and compared using two stages evaporation or crystallization processes. ASPEN PLUS equipped with vapor-liquid equilibrium databank together with solubility data was used to simulate these operations. Flash column and mixed product removal crystallizer were used to model two stages evaporation and crystallization process, respectively. First stage evaporation process was run at 90-1 80°C and 130-10,000 Pa while second stage was operated at 120-180°C and 50-250 Pa. The effect of various operating temperatures and pressures on the efficiency of evaporator and product quality were investigated. The optimum condtions for the first and second stage evaporation processes were selected based on the higher Ethylene Glycol (EG) removal with higher BHET recovery and lower heat duty needed. It was found that at higher operating temperature and lower operating pressure the performance of evaporator increased but the heat duty needed also increased whch at the same time reduced the BHET recovery. Crystallization operation was simulated at 5-30°C. The BHET recovery in crystallization process decreased as temperature increased. As a conclusion, less heat duty is required as compared to previous works, higher yield and purity of BHET compared to conventional crystallization process, higher EG removal compared to previous works and conventional process and optimum operating temperatures and pressures are obtained for future scaling up process. © 2012 Asian Network for Scientific Information.