Kinetics Of Shengli Lignite Direct Liquefaction

Direct coal liquefaction (DCL) is a strategic technology to relieve the shortage of oil and to ensure the energy security in China. In this paper, the experiments were carried out in an autoclave apparatus to investigate the effects of main factors on direct liquefaction of Shengli lignite and the liquefaction kinetics.TG/DTG curves shown that Shengli lignite exhibits its major decomposition range between 250 and 600℃and the maximum rate of weight loss exists at about 430℃. The weight loss is about 45wt% at 900℃.The effects of stirring rate, temperature, H₂ pressure, amount of catalyst loading, ratio of solvent to coal on coal liquefaction behaviors were investigated using the autoclave. The results showed that the conversion and oil yield increase with the increase of temperature in 385-460℃. H₂ atmosphere is one of the key fators to DCL and the highest oil yield can be obtained with the initial H₂ pressure of 10MPa within the research range of 3 to 10MPa. Conversion and oil yield increase with the amount of catalyst loaded. Nano-Fe and S have significantly positive effect on the liquefaction process, and the increase of S added is helpful for conversion of middle product to oil with the same Fe loaded. The tirring rate and ratio of solvent to coal had slightly effect on the liquefaction behaviors of Shengli lignite. The main gas products of DCL are CO₂, CH₄, N₂, CO at H₂ atmosphere.Based on the results of DCL, the DCL kinetics model at isothermal stage (430℃) was developed and the kinetics parameters were also calculated. In the model, the coal was divided into three parts, easy reactive part, hard reactive part and unreactive part. The results show that the adjusted model was perfectly consistent with the experimental data and can commendably depict the isothermal DCL process of Shengli lignite. Two main reaction approachs exist in heating-up stage of coal liquefaction, one is coal to preasphaltene and asphaltene, and anothere is coal to oil and gas. The main reaction route at isothermal stage is from coal to preasphaltene and asphaltene and then from preasphaltene and asphaltene to oil and gas. It is indicated that the reaction of preasphaltene and asphaltene to oil and gas is the rate-dominated step at the isothermal stage in DCL of Shengli lignite.