Study On The Effects Of Extractant On The Extraction Behavior For Coal Liquefaction Residue And The Separation Of Extraction Products

Direct coal liquefaction can solve the energy situation of my country’s lack of oil resources.However,due to the immature conversion technology,direct coal liquefaction process will produce heavy by-product coal liquefaction residue,which has a great impact on the economic benefits of the entire liquefaction process.At the same time,as a solid waste resource,coal liquefaction residue is also a challenge to the environment.In addition to the unconverted coal,the inherent inorganic matter in the coal and the additional coal liquefaction catalyst,the coal liquefaction residue contains a large amount of coal liquefied pitch rich in polycyclic aromatic hydrocarbons.The solvent extraction method can separate the polycyclic aromatic hydrocarbons and the extracted compounds can be used to prepare high value-added carbon materials.The preparation of these carbon materials have higher requirements for asphaltenes,and the selection of extractants is very important for obtaining these specific asphaltenes.Based on this,different kinds of extractants are selected for soxhlet extraction,to study the influence of the boiling point,polarity,solubility parameters and composition structure of the extractant on the properties of the extract.At the same time,the extracted product is further separated,and the following conclusions are obtained.（1）The closer the solubility parameter and polarity of the extractant to the coal liquefaction residue are,the higher the extraction yield are.When the solubility parameter of the extractant is in the range of 9-10.5,the extraction yield can reach more than 50%,and the range of the solubility parameters of the components in the residue is roughly estimated:The solubility parameter of heavy oil is less than 8,the solubility parameter of asphaltene is between 8 and 10,and the solubility parameter of preasphaltene is greater than 10.When the polarity parameter of the extractant is between 2.5-4.5,the extraction yield can reach more than 50%,and the extract of the more polar extractant mainly contains polycyclic aromatic hydrocarbons and oxygen-containing substances,and almost no aliphatic hydrocarbons.（2）The aliphatic hydrocarbon extractant has only used molecular diffusion to extract the coal liquefaction residue without destroying the original cross-linked structure of the residue,so the extraction yield is only 10%-30%,and most of the extracts are linear alkanes.Due to the principle of similar compatibility and theπ-πinteraction between aromatic rings,the extraction yield of aromatic hydrocarbon extractants can reach 50%-60%,most of the extracts are benzene series and part of polycyclic aromatic hydrocarbons.The heteroatom-containing extractant can break the weaker non-covalent bonds in the oil residue and form new bonds,thereby breaking the cross-linked structure of the residue.So the extraction yield can reach about 50%,and the extracts are mostly polycyclic aromatic hydrocarbons and oxygen-containing substances.At the same time,three pure solvents of benzene,toluene and dimethylbenzene are compounded,and the extraction effect of the simulated coking benzene extractant is basically the same as that of the aromatic hydrocarbon extractant.It is a promising industrial extractant for coal liquefaction residue.（3）Silica gel is used as a stationary phase,petroleum ether,a mixed solution of petroleum ether and carbon disulfide（PE:CS₂=4:1）,a mixed solution of petroleum ether and ethyl acetate（PE:EA=9:1）,ethyl acetate,methanol are used as mobile phase.The n-heptane extract is separated by column chromatography and divided into aliphatic compounds,benzene series compounds,polycyclic aromatic compounds,oxygen atom-containing compounds and other substances.At the same time,some high value-added substances like benzo[ghi]perylene,benzo[e]pyrene,coronene and pyrene can be enriched.