Study On The Separation Of Cyclopentane And Neohexane Mixture

Cyclopentane and neohexane are very important organic chemicals with high added-value in the petrochemical industry,occupying a considerable proportion of mixed C5 resources.In China,the way of comprehensive utilization of mixed C5 resources is relatively simple and inefficient.Through simple separations,most of the resources are sold as solvent oils or low purity monomer hydrocarbon oils,leading to a huge waste.Therefore,it is one of the most important issues for China's petrochemical industry to carry out the research and innovation of C5 resource separation technology,in order to make rational use of C5 resources.This issue combined with the project of mixed C5 resources separation hosted by Xinjiang Kangjia Investment Co.,Ltd.The research was carried out to separate cyclopentane and neohexane mixture,using extractive distillation technique with new mixed solvents and the hydrate formation method,respectively,which was of important academic and engineering significance.Since cyclopentane and neohexane are a close-boiling and azeotropic system,extractive distillation is an effective way to isolate such a system.In this paper,an optimized COSMO-RS method for predicting infinite dilution activity coefficients of alkanes and cycloalkanes in conventional solvents was established,the relative volatilities of the neohexane-cyclopentane system in the presence of conventional solvents were calculated,and the preferred solvents were screened out.The method of quantum chemistry was used to calculate the interaction between the conventional solvent and cyclopentane/neohexane,which provided a necessary theoretical basis for screening conventional solvents.Similarly,the infinite dilution activity coefficients of cyclopentane/neohexane in 936 kinds of ionic liquids(ILs)were obtained using the COSMO-RS method,respectively,as well as the selectivity of ILs.The relationship between IL structure and selectivity was then studied.The results showed that the selectivity of ILs on the cyclopentane/neohexane system was influenced by the cation and anion type,and the attachment of the functional group on the cation could significantly improve the selectivity of ILs.The microstructures and interactions between IL and cyclopentane/neohexane were studied by quantum chemistry calculation.The difference of interactions between cyclopentane-IL pair and neohexane-IL pair was also revealed at the molecular level.The studies have shown that the interaction between cyclopentane and IL is stronger,and that's why IL can change the relative volatility significantly.Based on the solvent screening,a CP-I dual-cycle vapor-liquid equilibrium still was used to measure vapor-liquid equilibrium(VLE)data for the ternary system of cyclopentane + neohexane + conventional solvent and quaternary system of cyclopentane + neohexane + conventional solvent + IL in different solvent-to-oil ratios at 101.3 kPa.The experimental results showed that the mixed solvents(composed of a conventional solvent and IL)and conventional solvent both could change the relative volatility of the system,and the relative volatility increased with the solvent-to-oil ratio.However,the effect of mixed solvents was obviously better than that of conventional solvent,and the content of IL in mixed solvents was low.Therefore,mixed solvents have the potential to become a new-type solvent for the separation of cyclopentane and neohexane system,which can improve the separation performance.The VLE data were used to regress the binary interaction parameters of the NRTL thermodynamic model,which were then incorporated into the Aspen Plus process simulation software.Two extractive distillation processes using conventional solvent and mixed solvents were studied,respectively.By comparing the design parameters of two processes,the number of theoretical plates and heat load required for the process using mixed solvents were both smaller than that using conventional solvent.The economic analysis showed that the TAC(Total Annual Cost)of the process using mixed solvents was reduced compared with that using the conventional solvent,which further confirmed the superiority of the new mixed solvents in the separation of the cyclopentane-neohexane system.Moreover,there was no need to change the process of conventional solvent in industrial application.The possibility of separating cyclopentane and neohexane mixture via the hydrate formation method was investigated by molecular dynamics simulation.The solubility of cyclopentane and neohexane in the water was studied,respectively,and the reliability of the force field was verified.The influence of temperature on the stability of cyclopentane hydrate was studied.The results showed that cyclopentane hydrate began to decompose at 285 K,which was larger than the experimental value in the literature.The stability of neohexane hydrate at the atmospheric pressure and 280 K was also investigated.Then,the growth behavior of cyclopentane hydrate in the presence of neohexane was studied.The results showed that new cyclopentane hydrate was found to grow at the interface between the cyclopentane solution and hydrate,which was beneficial to the separation of the cyclopentane and neohexane system using the hydrate formation method.Therefore,the molecular dynamics simulation can provide some theoretical guidance from the molecular level.However,the feasibility of this method has to be verified by the experiments.