低共熔溶剂萃取精馏分离苯/环己烯共沸物研究

Extractive distillation of benzene-cyclohexene azeotrope with deep eutectic solvents

以四丁基溴化铵(TBAB)、氯化胆碱(ChCl)为氢键受体,乙二醇(EG)、乙酰丙酸(LA)为氢键供体合成的TBAB:EG (1:2), TBAB:LA (1:2), ChCl:LA (1:2)三种低共熔溶剂(DES)作为萃取剂,通过萃取精馏分离苯-环己烯共沸体系。实验测量了环己烯-苯-DES三元体系气液相平衡,并对DES组成中氢键供体和氢键受体对分离性能的影响进行探讨。结果表明,DES的分离性能由高到低依次为ChCl:LA (1:2)>TBAB:LA (1:2)>TBAB:EG (1:2);采用NRTL模型关联环己烯-苯-DES三元体系的气液相平衡数据,拟合得到体系二元交互参数;在Aspen Plus V7中针对ChCl:LA (1:2)为溶剂的萃取精馏过程进行建模计算,并将其分离效果与传统溶剂N,N-二甲基乙酰胺(DMAC)进行对比,以DES为溶剂的萃取精馏过程相比于DMAC,回流比由3.8降至0.30,流程整体热负荷减少了16.57%。

High efficiency separation of benzene/cyclohexene azeotropic system at atmospheric pressure is the focus of current research. Extractive distillation is considered to be the most promising method for separation azeotropes. Therefore, it is necessary to screen suitable extractant for extractive distillation. The deep eutectic solvents(DES) formed by the combination of hy drogen bond donor(HBD) and hydrogen bond acceptor(HBA) has a good application prospect in the separation of aromatic/nonaromatic azeotropes. In order to explore the influence of HBA and HBD on the separation performance of benzene/cyclohexene azeotropic system, the three kinds of DES were investigated in this work. The three kinds of DES consisted of HBA [tetrabutylammonium bromide(TBAB), choline chloride(ChCl)] and HBD [ethylene glycol(EG), levulinic acid(LA)] with the mole ratio of 1:2, which were marked as TBAB:EG(1:2), TBAB:LA(1:2), and ChCl:LA(1:2), respectively. The corresponding isobaric vapor-liquid equilibrium(VLE) of cyclohexene-benzene-DES were experimentally determined. The effect of HBA and HBD on separation performance were discussed systematically. By correlating the VLE data with the nonrandom two-liquid(NRTL) model, the binary parameters were fitted. The results showed that the separation performance of the three DES follows the order ChCl:LA(1:2)>TBAB:LA(1:2)>TBAB:EG(1:2). It was indicated that choosing HBA which had the lower steric hindrance effect and HBD which had the weaker polar bond were conducive to form an efficient extractant for benzene/cyclohexene azeotropic system separation. Subsequently, the extractive distillation process used ChCl:LA(1:2) as extractant were designed with Aspen Plus V7 to evaluate the separation energy consumption. For comparison, N,N-dimethylacetamide(DMAC) which is a traditional extractant was evaluated in the same condition. The process simulation results showed that using ChCl:LA(1:2) as extractant,the molar reflux ratio decreased from 3.8 to 0.30 and the total reboiler heat duty reduced 16.57%, compared with those of DMAC used as extractant.