Extractant Screening Of DES And Its Application In Extractive Distillation For Benzene-Cyclohexene System

The formation of azeotrope makes the separation of benzene and cyclohexene a challenging task.Extractive distillation is widely used in the industry to separate azeotrope systems,and it is considered to be the most promising method for separation of benzene and cyclohexene.Traditional solvents are typically toxic,flammable,volatile and difficult to regenerate,therefore,it is necessary to develop green solvents.In this paper,the deep eutectic solvents(DES)are used as the extractant to carry out an in-depth study on the separation of benzene and cyclohexene by extractive distillation.Eight hydrogen bond acceptor combined with 17 hydrogen bond donor to form 136 DES.The COSMO-RS model was used to calculate the infinite dilution activity coefficient of benzene and cyclohexene in DES.On this basis,a systematic screening method considering various important properties such as selectivity,solubility,viscosity,freezing point,had proposed.Five DES of TBAB:EG(1:2),TBAB:LA(1:2),Chcl:LA(1:2),Chcl:Ur(1:2),Chcl:MA(1:2)were used as entrainers to separate the benzene-cyclohexene mixtures by extractive distillation.The corresponding isobaric vapor-liquid equilibrium(VLE)of ternary mixtures were experimentally determined,and the results show that different DES has different effects on relative volatility,the separation performance can be generally ranked as:Chcl:LA(1:2)≈Chcl:Ur(1:2)>TBAB:LA(1:2)>TBAB:EG(1:2)≈Chcl:MA(1:2).The VLE data were correlated with the nonrandom two-liquid model(NRTL),and the binary parameters were fitted,the RMSD between experimental data and prediction values were both within 2%.The experimental results are consistent with the prediction results of the COSMO-RS screening method,which indicated the high accuracy of the screening method.The extractive distillation process used Chc1:LA(1:2)as entrainer were designed with Aspen plus V11 to evaluated the competitiveness of DES with N.N-dimethylacetamide(DMAC),and the process parameters were optimized with the goal of minimizing total annual cost(TAC).Results show that the extractive distillation process with Chcl:LA(1:2)as entrainer has significant advantages compared with DMAC,the total reboiler heat duty were reduced 16.57%,and TAC were reduced 15.27%.Quantum chemistry calculation method was used to study the separation mechanism of benzene and cyclohexene system by choline-based DES.The intramolecular bonding of DES was analyzed and the hydrogen bond was confirmed as the main driving force during the formation of DES.The significant difference in interaction energy between DES and solute can separate benzene-cyclohexene mixtures selectively.The type and spatial distribution of the interaction force between DES and solute were investigated by RDG analysis,and the results show that Van der Waals interaction was the main force between DES and solute,which further proved by IGM analysis.In addition,the contribution of atoms and atom pair to the intermolecular binding energy was quantitatively calculated.