Study Of Aromatics Extraction Process Based On Ionic Liquid Extractant

Ionic liquid,a new type of green solvent,has attracted much attention as a potential extractant in the separation process.As an ionic type compound in liquid state at room temperature,it is usually composed of organic cations and organic or inorganic anions.It captures many advantages,such as high boiling point,neglectable vapor pressure,wide liquid range,good solubility and designable structure.In order to explore the feasibility of using ionic liquid as extractant for aromatics extraction.The research group has screened out two ionic liquids,1ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([Emim][NTf2])and 1-ethyl-3-methylimidazolium ethylsulfate([Emim][EtSO4]),which can be used as extraction agents and have excellent performance in previous work.In addition,the ternary liquid-liquid extraction experiments of n-hexane+benzene+sulfolane and n-hexane+benzene+ionic liquid were carried out to analyze the ability of the ionic liquid and sulfolane to separate n-hexane and benzene.The improvement of separation performance of complex ionic liquid was observed.It is preliminarily verified that the ionic liquid and its mixture can be used as a potential substitute for sulfolane.Apart from the stage of extraction separation,aromatic extraction process is also very important for the recovery and utilization of extractant.On this basis,the binary vapor-liquid equilibrium data of benzene+ionic liquids([Emim][NTf2],[Emim][EtSO4]and {[Emim][EtSO4]:[Emim][NTf2]=0.5:0.5})were further measured,and the effects of two ionic liquids and their mixtures on the saturated vapor pressure of benzene were analyzed.The NRTL model was used for correlation prediction based on the previously obtained liquid-liquid balance data,and the new binary interaction parameters between the research systems were obtained for process simulation.The structural optimization of n-hexane,benzene,sulfolane,[Emim][NTf2]and[Emim][EtSO4]was carried out by Material Studio,and the interaction forces between molecules and ions were further calculated after the optimization.The results show that the interaction between[Emim]+and benzene is greater than that between sulfolane and benzene,while the interaction between[NTf2]-and benzene is greater than that between[EtSO4]and benzene.Therefore,in vapor-liquid equilibrium,[Emim][NTf2]decreases the saturation vapor pressure of benzene to a greater extent.In liquid-liquid equilibrium,the ionic liquid of[Emim][NTf2]captures higher molar distribution coefficient while one of[Emim[EtSO4]is characterized with higher molar selectivity,compared to the sulfolane solvent that is extensively used for aromatic extraction in industry.Based on the industrial sulfolane aromatics extraction process,a liquidliquid extraction process was designed and optimized for the separation of nhexane and benzene by sulfolane in Aspen Plus.Two different separation processes with ILs extractants are then proposed and designed based on the commercial process with sulfolane extractant.The optimal operating parameters of theoretical stages,the ratio of extractant to hydrocarbon feeding,reflux ratio,feeding stage,etc.for the three processes are determined and the steady-state simulation and the total annual cost(TAC)calculation are performed.Moreover,the carbon dioxide emissions indexes are considered to evaluate the environmental impacts of all processes.The results showed that compared with the sulfolane process,the ionic liquid process significantly reduced energy consumption,annual total cost and CO2 emission(19.6%48.7%,6.3%-27.1%and 17.8%-47.6%,respectively).The results show that ionic liquid extractant and its process are a promising alternative for aromatics separation.