Study On Extraction And Separation Of Benzene-heptane By Low Transition Temperature Mixtures(LTTMs)

Separation of mixtures of aliphatic hydrocarbons(C4 to C10)and aromatic hydrocarbons(benzene,toluene,ethylbenzene and xylene)is one of the difficulties in the petrochemical industry because some aromatic hydrocarbons and can form an azeotrope within a certain concentration range.Liquid-liquid extraction is a common method for separating aromatic hydrocarbons and aliphatic hydrocarbon mixtures,but conventional solvents often have the disadvantage of large recovery energy consumption in the solvent recovery process of liquid-liquid extraction.Therefore,it is the key to solve this problem to find a new type of solvent with low energy consumption and high selectivity and high solubility.In this paper,benzene and n-heptane are used as the system to be separated,and suitable substances are selected from 41 hydrogen bond donors and 13 hydrogen bond acceptors,and low transition temperature mixture(LTTMs)is prepared as an extractant.The activity coefficients of LTTMs were predicted by COSMO-SAC model,and their selectivity,solubility and performance index were calculated.According to these three indexes,the best extractant was sulfolane + tetrabutylammonium bromide.Another extractant,triethylene glycol and tetrabutylammonium bromide,with a lower performance index was also selected.The effects of different temperature(30℃,40℃ and 50℃)and the ratio of hydrogen bond donor to hydrogen bond acceptor(3:1 and 5:1)on the extraction performance of LTTMs were investigated by liquid-liquid equilibrium experiments.The experimental data were correlated by Othmer-Tobias equation.The linear correlation coefficient R2 of the experimental data was greater than 0.985,indicating that the experimental data quality was higher.And the activity coefficient model NRTL is used to correlate the experimental data to obtain the binary interaction parameters between the components.The root mean square deviation between the experimental value and the model simulation value is less than 0.012,which indicates that the NTRL model can fit the experimental data well.The experimental results show that the performance of sulfolane + tetrabutylammonium bromide is better than that of triethylene glycol and tetrabutylammonium bromide,which is consistent with the prediction of COSMO-SAC model.The extraction performance of LTTMs is best when the temperature is 30 ° C and the ratio of hydrogen bond donor to hydrogen bond acceptor is 5:1.Finally,the extraction process of benzene-n-heptane was simulated by Aspen plus software,and the operating conditions were optimized.At the same time,the process of the traditional solvent sulfolane as an extractant was simulated,and the total annual cost of the two extraction processes was compared and analyzed.Compared to conventional solvents,the total annual cost of LTTMs as an extractant is reduced by 25.6%.Through the above research,sulfolane + tetrabutylammonium bromide is an excellent solvent for the extraction and separation of benzene and n-heptane,providing basic data for the separation of aliphatic and aromatic hydrocarbon mixtures in the petrochemical industry.