Process Simulation Of Separation Of Cyclohexane And Benzene

Cyclohexane is an important raw material for industrial production of cyclohexanol,adipic acid and caprolactam which are then used to produce polyamide(nylon-6,6 and nylon 6).The catalytic hydrogenation of benzene to cyclohexane was first proposed in 1980s.Although,the process is simple and the by-products are few,separation of these raw materials is not simple due to the formation of azeotrope between cyclohexane and benzene and their difference in boiling point is only 0.7K.Thus,their separation is difficult by ordinary separation methods.In the chemical industry,they are separated by extraction using organic solvents such as sulfolane but they have low extraction selectivity.Also,they require a large extraction dose which increases the cost of process.These problems are the drive for this work to evaluate the potential of ionic liquids as alternate and green solvents in the benzene-cyclohexane separation process.ILs have strong extraction and separation capability.Due to their unique properties such as wide liquid range,high thermal stability,inflammability and negligible vapor pressure,ILs can be used in separation processes.In this thesis,two separate comparative process simulation study are compared for separation of cyclohexane and benzene using traditional solvent sulfolane and a green ionic liquid 1-butyl-3-methylimidazolium tetrachloroaluminate.Both solvents were simulated in Aspen Plus(V10).By adjusting the number of stages,reflux ratio,distillate rate,solvent flow rate,temperature and stages of azeotrope feed and solvent and other parameters,the feasibility of separating cyclohexane and benzene using these two solvents as extractant were investigated.Results were compared for 450 kg of azeotropic feed with cyclohexane mass fraction 0.86 at temperature 31 OK and pressure 515 kPa.To obtain the cyclohexane mass purity product up to 99.50%and a high benzene recovery of 98.0%,the required number of stages for the column and solvent to feed ratio(S/F)were calculated.The results show that:(1)When sulfolane is used as the extractant,the obtained cyclohexane has a mass purity of 99.56%,benzene recovery of 98.13%,and a total energy consumption of 1.36 GJ/t cyclohexane.When the no.of stages is n=6,the required solvent to feed ratio is 3.(2)When[BMIM][AIC14]is used as the extractant,the obtained cyclohexane has a mass purity of 99.62%,benzene recovery of 99.32%and a total energy consumption of 0.84 GJ/t cyclohexane.When the no.of stages is n=6,the required solvent to feed ratio is 0.4 and negligible loss of IL.(3)By comparing the two separation processes,it is found that the purity and recovery rate of the cyclohexane product obtained by the two separation processes are basically the same which meets the separation requirements.The[BMIM][AlCl4]separation process saves 38.23%energy requirement and 39.33%cost as compared to sulfolane separation process.The research results of this thesis provide a feasible direction for the separation of cyclohexane-benzene azeotrope by IL.To check the feasibility of two solvents,comparison of efficiency,energy,extractant loss and cost analysis is done and IL performs better in every aspect.