Process Intensification On The Separation Of Benzene And Thiophene By Extractive Distillation

Benzene is a very important raw material in organic chemical industry. As the developing of coking industry in China, the coking benzene will become an important source of pure benzene. Because the boiling point of thiophene is close to benzene in coking benzene, ordinary distillation is difficult to meet the requirements of separation. Extractive distillation is applicable for the separation of mixtures with close boiling points. In this study, according to the way of experiment and the method of process simulation, a mixture of organic solvent and ionic liquid (IL) was proposed as the entrainer for the separation of benzene and thiophene by extractive distillation.First of all, the COSMO-RS model was used for the selection of ILs. Because suitable extractant makes separation process easy, the selection of extraction agent for extractive distillation is important. The COSMO-RS model was used for the selection of 45 ILs from the viewpoint of selectivity and solvent capacity. Results show that, the selectivity and solubility of ILs is contradictory, that is, the IL with the highest selectivity does not always possess the lowest capacity. To comprehensively consider the selectivity, dissolving capacity, thermal stability, chemical stability and price of ionic liquid, [EMIM]+[BF4]- might be a suitable IL as organic solvents (NMP and DMF) additive.Then, we get the vapor-liquid equilibrium (VLE) according to experiment. Results show that, the addition of IL did not obviously improve the relative volatility of benzene to thiophene; however, the content of organic solvent in the vapor phase could be significantly reduced using the combination of organic solvent and [EMIM]+[BF4]- in comparison to the pure organic solvent. Moreover, the UNIFAC model was extended and the corresponding interaction parameters were obtained by correlating VLE equilibrium data obtained in this work. The predicted results by UNIFAC model basically agree well with experimental data, which indicates that the UNIFAC model is reliable and accurate.Once more, we take the UNIFAC interaction parameters into the Aspen plus software to make process simulation. The comparison between DMF and DMF+IL has been summarized. The addition of [EMIM]+[BF4]- can significantly reduce the content of organic solvent in the vapor phase. And an further purify the benzene product obtained at the top of extractive distillation column. Meanwhile, the reduction of volatile loss of organic solvent can simplify the subsequent recovery system and save the amount of entrainer. Moreover, we compare extractive distillation process of two columns with extractive distillation process of one column. As results shown, extractive distillation process with one column can reach the same effect. And extractive distillation process with one column can not only save equipment investment, but also can reduce energy consumption.Finally, traditional extractive distillation process with six columns is replaced by retrofitted extractive distillation process with four columns. The comparison of the simulation results between the different extractive distillation processes indicates that the improved process, which make extraction distillation tower and solvent recovery tower into one tower by heat integration, saves two solvent recovery towers. Meanwhile, the condenser and reboiler heat duty is reduced by 6.41% and 6.41%, respectively. This not only saves equipment, but also reduces the energy consumption. Moreover, this accords with environmental protection requirements of energy conservation and emissions reduction now.