Research On The Extraction Of Magnetic Ionic Liquids To Remove Ash From Coal Direct Liquefaction Residues

Coal direct liquefaction technology is the process of converting coal into liquid fuels under hydrogen and catalysts. In the process of coal direct liquefaction, coal direct liquefaction residues(CDLR) will be produced, which take up about 30% of crude coal. CDLR is a complex mixture with high ash, carbon and sulfur. Utilization of CDLR reasonably and efficiently, can not only effectively improve the economy of coal liquefaction process, but also maximize the use of limited resources. Solid content of CDLR is derived from unreacted coal, liquefaction residual catalysts and inorganic minerals, while the ash of CDLR is from residual catalysts and other minerals. De-ashing of CDLR helps to reduce the solid content, improve the utilization of liquid content, which is the key to the efficient use of CDLR. Many physical, chemical methods are developed, as de-ashing of CDLR has caused widespread concern in industry and academia.In this paper, with characteristics of low steam pressure, strong dissolving capacity and high stability of ionic liquids, [bmim]Cl, [bPy]Cl, [bmP]Cl, [bmim]FeCl4, [bPy]FeCl4, [bmP]FeCl4 are synthesized as extraction solvents, to separate liquid content from solid content, to remove ash. First of all, these ionic liquids are compared in the performance of extraction and de-ashing effect. They are selected to prove the superiority of magnetic ionic liquids; Secondly, mixing temperature, mixing time, stirring frequency, mass ratio, mixing mode, these five factors are studyed in extraction process. Conditions are optimized to improve extraction performance; Finally, with characterization of CDLR and its extract, the de-ashing effect of ionic liquids is illustrated in the microscopic view. Then the extraction factors affecting de-ashing are explored, to explain the validity of this method.It shows that magnetic ionic liquids are cyclic compounds containing nitrogen atoms. Their structures are similar with the structures of CDLR, having excellent electron donating ability and solubility. What’s more, their magnetic function can make small components from CDLR release directionally to strengthen the uniformity of extraction. When using a magnetic stirrer, the optimal mixing temperature, mixing time, stirring frequency, mass ratio is 50℃, 200r/min,20min,5:1～7:1. The extraction yield of [bmim]FeCl4 is 40%, while the ash content of extract is reduced to 1.9～2.5%; When using ultrasonic oscillation mixing, the extraction yield of [bmim]FeCl4 is 44%, while the ash content of extract is 0.9%, which can remove most of ash. IR analysis and soxhlet extraction analysis of CDLR and its extract also prove that [bmim]FeCl4 is ideal to remove ash from CDLR.