Properties Of Semicoke Under The Condition Of Optimum Liquefaction Rate In Coal-oil Co-processing

China is a country rich in coal and poor in oil.How to give full play to the advantages of China’s energy structure and realize the clean and efficient utilization of coal energy is a big problem.Coal-oil co-processing technology is one of the technologies for clean utilization of coal,which aims to obtain high liquefaction rate and high quality oil products,and produce a large amount of liquefaction residue,namely semicoke.Therefore,it is of great significance to obtain high quality semicoke and understand the properties of semicoke while ensuring high liquefaction rate.The effects of reaction temperature,reaction time,initial hydrogen pressure and different catalyst additions on liquefaction rate of coal-oil co-processing,distillation range of liquid products and proximate analysis of semicoke were studied using Low quality Ordos coal with high ash and ashless dry basis volatile contentand and coal tar after hydrogenation in an autoclave with self-made coal supported iron based catalyst.The results show that the liquefaction rate first increases and then decreases with the increase of reaction temperature,reaction time and catalyst additions.The content of gasoline fraction in liquid products increased,while the content of high boiling point fraction and vacuum residue decreased.The content of diesel fraction varied with different reaction conditions.The content of volatile and fixed carbon in semicoke decreased gradually,while the relative content of ash increased.The liquefaction rate first increased rapidly and then slowed down with the increase of initial hydrogen pressure.The content of gasoline fraction in liquid products decreased,while the content of high boiling point fraction and vacuum residue increased.The content of diesel fraction is relatively stable.The content of volatile and fixed carbon in semicoke decreased gradually,while the relative content of ash increased.Taking coal liquefaction rate as index,the orthogonal test was carried out by L₉（3⁴）four factors and three levels experimental design,The results show that the optimal liquefaction conditions of Ordos coal were reaction temperature 440℃,initial hydrogen pressure 8 MPa,15%catalyst addition,reaction time 60 min,and the optimal liquefaction rate was 46.7%.Under the optimal liquefaction rate,about 50%of the semicoke with poor properties was formed.The changes of composition,functional groups and microstructure of coal and semicoke were investigated by elemental analysis,proximate analysis,FT-IR,XPS,XRD and SEM.Compared with raw coal,the results show that the H/C and N content of semicoke decreased,S content increased,the volatile and fixed carbon content decreased,the ash content increased,the relative content of methyl and methylene increased,the length of fatty chain was shorter,the degree of branching was lower,the content of ether and phenol compounds increased,self associated OH groups and OH-πhydrogen bond increased,and tightly bound cyclic OH tetramers decreased.C on the surface of coal and semicoke mainly exists in the form of C-C or C-H,and O mainly exists in the form of C-O.The contents of pyridine and thiophene on the surface of semicoke increased,while the contents of protonated pyridine,nitrogen oxide,mercaptan and sulfoxide decreased.In the process of coal-oil co-processing,the condensed aromatic nuclei of raw coal undergo obvious condensation reaction,the arrangement of carbon atoms in organic matter tends to be oriented and regular gradually,and the graphitization structure of semicoke increases.A large number of pores were formed on the surface and inside of semicoke due to the escape of volatiles.The condensation reaction resulted in dense structure and irregular surface arrangement of semicoke.