Study On Separation Of N-Heptane-Thiophene Using Mixed Solvents

The combustion of sulfur compounds in fuel oil has caused serious environmental pollution,which seriously threatens the sustainable development of natural environment.Many countries have put forward stricter requirements on the sulfur content in fuel oil.Extractive desulfurization has the advantages of low energy consumption,simple process,mild conditions,and so on.Single solvent is difficult to take into account the selectivity of the solvent and distribution coefficient of solute,but the mixed solvents can combine the advantages of the two solvents to achieve the best extraction effect.Therefore,this thesis selected the mixed solvents as the extractant,n-heptane as the gasoline model oil,thiophene as the sulfur compounds,the liquid-liquid equilibrium experiment were measured to explore the extraction effect of different mixed solvents and find the best mixed solvent.Compared with ionic liquids,low transition temperature mixtures(LTTMs)have the advantages of simple preparation,environmental friendly and low price.The organic solvents are the most commonly used extractants.Therefore,organic solvents and LTTMs are selected as the research objects in this thesis.First,dimethyl sulfoxide(DMSO),sulfolane(SULF)and N,N-dimethylformamide(DMF)were selected as o extractants.Then three kinds of organic solvents were mixed in pairs according to different mass ratios as the extractant.Finally,LTTMs synthesized by tetrabutylammonium bromide and sulfolane,which had excellent extraction effect in the literature,was selected and mixed with DMSO and DMF respectively in different mass ratio as extractants.The selectivity,partition coefficient and extraction performance index PI were calculated according to the phase equilibrium data,it was found that the extraction effect of the mixed solvent was higher than that of the single solvent.The best extraction effect of the mixed solvents DMSO/DMF(2:1)and DMSO/LTTMs(2:1)were selected.NRTL and UNIQUAC equations are used to correlate phase equilibrium experimental data.The root mean square deviation between the experimental values and simulated values is less than 0.011,which indicates that the model equation can fit the experimental data well.In order to understand the separation mechanism of mixed solvent extraction desulfurization and provide theoretical basis for the selection of mixed solvent,molecular dynamics simulation was used to study the organic solvent-organic solvent mixed system and organic solvent-LTTMs mixed system.Through the analysis of radial distribution function,intermolecular interaction energy,self-diffusion coefficient,it is proved that the interaction energy between DMSO/DMF,DMSO/LTTM1 and thiophene was higher than that of other mixed solvents.Therefore,DMSO/DMF and DMSO/LTTM1 solvent had the best extraction effect,which is the same as the results obtained from phase equilibrium experiment of mixed solvents.In this thesis,through the phase equilibrium experiment of the mixed solvent with nheptane and thiophene system,the best mixed solvent was found.Combined with the molecular dynamics simulation study,the micro-mechanism of the complex solvent extraction desulfurization was revealed.This thesis provides a new way and theoretical basis for fuel oil desulfurization,which has some guiding significance for the research and development of mixed solvent extraction desulfurization.