Catalyst Optimization And Reaction Rate Description Of Lignite Direct Coal Liquefaction

Direct coal liquefaction(DCL)is a clean coal technology that directly transforms coal into liquid fuel.In order to increase the content of high value-added products of the liquefaction,it is necessary to solve the problem of mismatch between cracking and hydrogenation rate in the process.Therefore,it is very important to describe the cracking and hydrogenation rate accurately and quantitatively.Based on above problems,the preparation of Fe₇S₈ catalysts were optimized firstly.The Fe₇S₈ of monoclinic and hexagonal were prepared respectively,and the corresponding relationship between their catalytic activity and structures was investigated.Then,three model compounds,dibenzyl disulfide,diphenylethane,diphenylmethane were selected according to the covalent bond type in coal.Based on the results of cracking and hydrogenation of three model compounds,the reaction rate constant of cracking and hydrogenation of diphenylethane were achieved by data fitting.Finally,the cracking and hydrogenation rates of coal in DCL were described.The conclusion is as follows:(1)Two Fe₇S₈ with different crystal structure were prepared by roasting and solvothermal methods.The conversion and oil yield of Fe₇S₈-R prepared by solvothermal were 20.3%and 3.0%,showing better performance than Fe₇S₈-B prepared by roasting.The conversion and oil yield of Fe₇S₈-R prepared at 180°C by solvothermal method were 92.8%and 75.3%,which is the best preparation temperature.Fe₇S₈ not only promotes the production of hydrogen free radicals,but also makes oxygen migrate to oil,preasphaltene and asphaltene;(2)Combined with TG-DTA,XRD and Raman analysis,the change of the hexagonal Fe₇S₈-R with increasing temperature was studied.The decomposition of Fe₇S₈ at 350-550°C resulted in the loss of sulfur,which indicated the lost of sulfur occurred in the process of liquefaction.XRD and in-situ Raman analysis showed that the catalyst was transformed to Fe_1-xS,which is the active component of liquefaction;(3)The cracking and hydrogenation reactions of dibenzyl disulfide,diphenylethane and diphenylmethane with Fe₇S₈-R were conducted at different atmosphere and solvents.The experimental results of three model compound showed that at same temperature the cracking of dibenzyldisulfide was easiest and the cracking of diphenylmethane was the most difficult.In the liquefaction of diphenylethane.The cracking rate of diphenylethane is higher than its hydrogenation rate,and the promoting of Fe₇S₈ catalyst on cracking and hydrogenation rate is not obvious under different atmospheres and solvents;(4)The reaction rate constants of coal direct liquefaction were calculated under different atmosphere and solvents.Results showed that the rate of cracking and hydrogenation of PAA was the fastest,and the cracking and hydrogenation to oil,gas and PAA are slower.The cracking and hydrogenation of coal are promoted by addition of hydrogen donator solvent solvents and hydrogen,in which the promoting to the cracking and hydrogenation from coal to oil and gas is the most obviously.The goal of catalyst design is to increase the concentration of hydrogen radicals in the liquefaction,which may accordingly increase the hydrogenation rate of free radical fragments produced during the cracking reaction of coal.