Benzene purification from thiophene using dimethylformamide as an entrainer in thermally coupled extractive distillation columns

摘要

Thiophene (T) is one of the main sulfur-containing impurities in crude benzene produced by coke production. One effective way to remove the majority of thiophene from crude benzene is extractive distillation (ED) with dimethylformamide (DMF), which has been reported to increase the relative volatility of the benzene-thiophene (B-T) pair from 1.13 to 1.46-1.5 or 1.8-2.18. The aim of this work is to investigate the possibility of increasing the benzene yield from the initial fraction and reducing the ED heat demand of the separation of the B-T mixture with DMF as an entrainer by using an extractive distillation system with partially thermally coupled distillation columns (PTCED). To achieve this goal, both a conventional extractive distillation (CED) and a PTCED system were optimized. The total energy consumption in the column reboilers was selected as the optimization criterion. The same yield of benzene was achieved in the PTCED system at a lower column reboiler heat demand. As the benzene yield was increased, the energy savings of PTCEDS over CED increased. In addition, the production of the thiophene fraction required a significantly smaller reflux ratio in the side section of the PTCED system (1.0-2.28) than in the recovery column of the CED system (7.17-73.13). (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.