Study On Separation Of Bicyclic Aromaticity Compounds From Fcc Diesel By Ionic Liquids

As a typical inferior oil product,FCC diesel oil has the characteristics of high aromatics content,high sulfur and nitrogen content,and low cetane number,which is the main bottleneck of diesel oil quality upgrading in China.The quality upgrading of FCC diesel oil requires the seperation of a large number of aromaticity compounds from the oil.Hydrogenation is currently the most commonly used method in industry,but this process has the characteristics of high energy consumption,high hydrogen consumption,and harsh operating conditions.Extraction process has simple process and mild operating conditions,making it an important supplement to the hydrogenation process.This work uses ionic liquids as a new type of green solvent systematically studies the separation of bicyclic aromatics and S/N-compounds in FCC diesel from both experimental and theoretical calculations methods.The main work and conclusions of this work are as follows:1.The accuracy of the COSMO-RS model in predicting the thermodynamic and physical properties of ionic liquids was verified by comparing experimental data with calculated values.By considering the selectivity,solubility,viscosity and thermal stability of ionic liquids,[EMIM][NTF₂]was selected as the most appropriate extractant to separate aromaticity compounds from FCC diesel.2.In the aspect of extraction dearomatization of FCC diesel oil,the separation effect of[EMIM][NTF2]and common organic solvents（sulfolane,NMP）on bicyclic aromatics in FCC diesel oil was discussed through liquid-liquid phase equilibrium experiments.The results showed that compared to organic solvents,the selected ionic liquid exhibited higher selectivity for bicyclic aromatics.Further experimental methods were used to investigate the effects of extraction temperature,ionic liquid water content,and ionic liquid regeneration times on extraction efficiency.In addition to experimental exploration,this study uses quantum chemistry calculation methods to study the separation mechanism at the molecular level.It was found that the C-H··πinteraction and hydrogen bonding interaction formed between the extractant and aromatic hydrocarbons are the essential forces that enable the extraction process to proceed.3.In the aspect of extraction desulfurization and denitrification of FCC diesel oil,1-benzothiophene and quinoline were selected as the representatives of bicyclic aromaticity S/N-compounds in FCC diesel.The effects of initial concentration of S/N-compounds,solvent ratio,extraction stages,and the presence of other aromatics on the extraction effect were studied through liquid-liquid equilibrium experiments.The results show that when the solvent ratio is 2:1,the extraction efficiency of quinoline can reach 98.75%after4-stage extraction,and the extraction efficiency of 1-benzothiophene can reach97.31%after 5-stage extraction.The separation mechanism of extractive desulfurization and denitrification was systematically discussed by calculating the free energy of solvent and radial distribution function with Gromacs program.Further combined with quantum chemistry calculation,it was determined that the difference in electrostatic interaction strength between quinoline and benzothiophene and ionic liquid was the fundamental reason for the difference in extraction efficiency of the two systems.