Study On Macerals And Recycle Solvent Hydrotreatment In The Shendong Coal Liquefaction Process

The long-running results of Shenhua direct coal liquefaction demonstration plant (DP) show that the high inertinite content in Shendong coal and poor hydrogen-donating ability of recycle solvent is the main factors which influence the oil yield. Therefore, Shendong coal with different macerals and recycle solvent were focused in this dissertation. The mechanism on effects of coal macerals and recycle solvents on the liquefaction process and oil yield of Shendong coal was studied by the liquefaction experiment in the Shenhua 0.18 t/day direct coal liquefaction bench support unit (a continuous device) and 0.5 L stirring autoclave. The research can provide the theoretical and experimental basis for improving the oil yield of Shendong coal hydroliquefaction.The results of the Shendong coal with different macerals hydroliquefaction showed that the coal conversion increased with an increase in the reaction temperature from 440℃ to 465℃. The oil yield of coal with low inertinite content improved gradually with increasing reaction temperature. However, the oil yield of coal with high inertinite content firstly increased and then decreased. The suitable hydroliquefaction reaction temperature of Shendong coal was 455℃～460℃. Improving the reaction pressure was beneficial to the inertinite hydroliquefaction. When the recycle donor solvent from Shenhua DP was used as the coal liquefaction solvent, the conversion and oil yield of the vitrinite from Shendong coal were higher than the inertinite from the same coal in the same hydroliquefaction reaction conditions obviously. The types of monoaromatics were main aromatic structure in vitrinite macrostructure. The macrosturcture of vitrinite collapsed after pyrolysis and hydrogented reation basically. The types of tricyclic aromatics and tetracyclic aromatics were main aromatic structure in inertinite macrostructure. The main aromatic structure of inertinite in shendong coal was connected by naphthenic rings. The naphthenic rings were relatively broken with difficulty, but could be broken in the coal liquefaction process. The chemical structure of the inertinite from Shendong coal caused that shendong coal could be hydroliquefied mainly. The hydroliquefaction reaction pathway of Shendong coal inertinite was different from that of Shendong coal vitrinite. When the inertinite cracked further during pyrolysis, the extent of inertinite decomposition eventually reached the same level as that for the vitrinite. The hydroliquefaction of inertinite need more active hydrogen at higher temperature than that of vitrinite. However, the higher reaction temperature intensified the cracking reaction and the oil yield could be declined. The excellent solvent could improve the oil yield greatly and weaken the effect of inertinite content in Shendong coal on the hydroliquefaction oil yield. The hydrogen-donating ability of coal liquefaction solvent and the matching ability between Shendong coal and solvent were the key factors to determine the oil yield of Shendong coal, especially coal with high inertinite content. When the inertinite content of Shendong coal was less than 51%, the oil yield and coal conversion had little change. Hence improving the hydrogen-donating ability of the recycle solvent could dramatically increase the oil yield of Shenhua DP.The results of Shendong coal hydroliquefaction with solvents of different hydrocarbon compositions further suggested that hydrocarbon compositions of solvent determined the hydrogen-donating ability of solvent and the oil yield of coal hydroliquefaction. The hydroliquefaction solvent both had the hdyrogen-donating ability and dissolving capacity. The aromatic compounds with naphthenic rings, phenanthrenes and anthracenes in the coal liquefaction process behaved well at the oil yield of Shendong coal hydroliquefaction. The high content of ployaromatics with little naphthenic rings in the Shenhua DP recycle solvent was the main cause of decreasing the solvent hydrogen-donating ability. In the same conditions of Shenhua DP solvent hydrotreatment, the content of ploycyclic aromatics in the recycle solvent had little change, meanwhile, the oil yield and coal conversion of Shendong coal hydroliquefaction reached maximum when the recycle solvent hydrogenation reaction temperature reached 380℃. However, improving the solvent hydrogenation reaction temperature further, the oil yield of Shendong coal hydroliquefaction decreased because the thermodynamic equilibrium of ploycyclic aromatics hydrogenation caused the ploycyclic aromatics content in the recycle solvent even had increasing trend. The ployaromatics hydrogenation reaction was promoted by increasing the reaction pressure, reducing the liquid hourly space velocity and recycle solvent fraction only used as the hydrogenation feed in the recycle solvent hydrotreatment. Meanwhile, the oil yield and coal conversion were improved further in the coal liquefaction process.The studies on the variation of coal-oil slurry viscosity indicated the solvent hydrocarbon compositons and coal macerals structure determined the difference in the adsorption and swelling of coal caused the slurry viscosity change. The viscosity of slurries increased greatly with an increase in the inertinite content in Shendong coal. The sequence of slurry viscosity was the inertinite concentrate> raw coal> vitrinite concentrate at a low coal concentration. At a high coal concentration, the solvent swelling of coal changed the slurry viscosity and the sequence of coal-oil slurry viscosity was the inertinite concentrate> raw coal> vitrinite concentrate. The solvents with more heavy fraction as well as the solvent hydrogenated at the higher reaction temperatue caused that the slurry viscosity increased at the low temperature and decreased at the high temperature. The relation equations of viscosity-temperature and viscosity-coal concentration of slurry were established respectively.