Kinetic And Mechanism Of Shenhua Coal Direct Liquefaction

The aim of this paper is to promote the conversion and oil yield of Shenhua(SH) bituminous coal direct liquefaction.The effects of main factors on SH coal liquefaction were studied;Kinetic models fiting SH coal liquefaction were developed and the mechanism of direct coal liquefaction was investigated;And main approach of promoting SH coal liquefaction was analysed.Main research works and results in this paper are as follows:Kinetic characteristics of SH coal pyrolysis and catalytic pyrolysis were investigated by thermogravimetric analyzer.The results showed that Fe catalyst increases the weight loss of SH coal pyrolysis from 35%to 60%;Activation energy of SH coal pyrolysis and catalytic pyrolysis at the temperature of 300℃—600℃are 135kJ·mol^-1—460kJ·mol^-1 and 150kJ·mol^-1—310kJ·mol^-1,repectively.Catalyst reduce the activation energy of SH coal pyrolysis clearly.An new calculation method of coal pyrolysis fake reaction order distribution curves with temperature or conversion was developed,and the calculation results showed that fake reaction order for pyrolysis and catalytic pyrolysis of SH coal from 200℃to 700℃is 0.2—1.6 and 0.6—1.2,respectively.And it is appropriate comparatively for the regarding SH coal pyrolysis(200℃—700℃) as a serious of first-order reaction.The effect of stirring rate,temperature,H₂ pressure,amount of catalyst loading,ratio of solvent to coal on coal liquefaction were investigated.The results showed that the conversion and oil yield increase with the increasing of temperature in 400℃—460℃and ratio of solvent to coal.The highest oil yield can be obtained with the H₂ original pressure of 8 MPa within the research range(5MPa—10MPa).Oil yield decreases if the amounts of catalyst loading are higher than 2%.Direct liquefaction kinetics of SH coal was studied and kinetic models for heating-up and isothermal stages were developed respectively.In the models,the coal was divided into three parts,easy reactive part,hard reactive part and unreactive part.There were two main reaction approachs of coal liquefaction in heating-up stage,which are coal to preasphaltene & asphaltene and coal to oil & gas.The main reaction approach for isothermal stage is from coal to preasphaltene & asphaltene and then from preasphaltene & asphaltene to oil & gas. Calculation results also showed that the maximal conversion of direct SH coal liquefaction is 7.10%,which is similar to the experimental result(92.61%,430℃,150min).Role of iron-based catalyst and hydrogen transfer mechanism in direct SH coal liquefaction were investigated by using three solvents with different hydrogen donation capability at H₂ or N₂ atmosphere.The results showed that the major role of the catalyst is promoting the formation of activated hydrogen and accelerating the secondary distribution of hydrogen in the whole reaction system including gas,liquid and solid phases.The main sources of activated hydrogen include thermal and catalytic cracking of solvent and H₂,and the major transfer approach of activated hydrogen is from molecular hydrogen to solvent and then from solvent to coal.The solvent acts as a "bridge" role in the hydrogen transfer process.Single and multi-stage liquefaction of SH coal and re-liquefaction of its liquefaction residue were investigated to understand the essential approach of promoting SH coal liquefaction.The experimental results showed that there is positive function of two-stage liquefaction on shortening reaction time at high temperature stage,but little effect on conversion and yield of SH coal liquefaction.The main factor of inhibiting the liquefaction is consumption of activated hydrogen and appearing of polymerization.So the essential approach of increasing oil yield and conversion of SH coal liquefaction is providing enough activated hydrogen to stabilize the free radicals and inhibiting polymerization.