Research On The Stability Of Hydrogen Donor Solvents During Direct Coal Liquefaction

Direct coal liquefaction(DCL)is a clean and efficient utilization technology of coal,which plays a role in supplementing and replacing petroleum resources.It is of great significance to China's energy security.However,an imbalance problem of hydrogen donor solvents(HDSs)occurs and the H-donor capacity of the HDSs is reduced during DCL,which greatly influences the application of DCL.The structure of the HDSs determines the H-donor capacity.Therefore,we used two typical HDSs,tetralin and dihydroanthracene(DHA),as model HDSs.The stability of the HDSs and the influencing factors of the imbalance problem of the HDSs are analyzed via the hydrogenolysis of coal-related model compounds(CRMCs).The main contents and results are shown as follows:(1)The effects of coal model compounds propylbenzene(PB),diphenylethane(DPE)and dibenzyl ether(DBE),hydrogen,iron-based catalysts and non-hydrogen donor components on the behaviors of tetralin were studied via the hydrogenolysis reaction.The results showed that the conversion of tetralin was from 2%to 12.4%under various research conditions.The main derivatives of tetralin are the 1-methylindan and naphthalene,followed by the butylbenzene,decalin,alkyltetralin and heavy products.The three CRMCs promote the conversion of tetralin,and the more the CRMC is used,the more the relative content of the derivative naphthalene.PB promotes the formation of alkyltetralin.The addition of DPE and DBE induces the formation of heavy products in the solvent.The results suggest that the free radicals from three CRMCs can react with tetralyls.In addition,Fe1-xS promotes the dehydrogenation of tetralin significantly,and the relative contents of H-nondonor products are reduced.The effective consumption of the tetralin is enhanced by Fe1-xS.H2 enhanced the hydrogenation and the hydrocracking of the tetralin,which increase the yields of H-nondonor products,and the higher the H2 pressure,the more H-nondonor products are formed,resulting in imbalance of tetralin.The concentration of tetralin was lowered by adding two H-nondonor components,methylnaphthalene and n-dodecane,and it was found that the conversion of tetralin decreased,but the H-donor capacity of the overall solvent also decreased.(2)DHA is represented as a 3-ring hydrogenated aromatic hydrocarbon,and its stability is studied.The hydrogenolysis experiments were carried out to investigate the effects of CRMCs,hydrogen,iron catalysts and H-nondonor components on the structural changes of DHA.It has been found that DHA is very unstable at 425?,and the conversion is up to 86.8%.Different amounts of CRMCs have less effect on the conversion of DHA.The DHA derivatives can be divided into five kinds:two-aromatic-ring substances(TARS),alkyl biphenyl substances(ABS),hydroaromatic substances(HAS),dehydrogenated substances(DHS)and condensed aromatic rings substance(CAS).The higher the amount of three CRMCs,the higher the relative content of DHS formed by DHA,and the distribution of other products is basically unchanged.H2 promotes the formation of TARS and HAS through hydrocracking reaction,while inhibiting the formation of DHS.H2 also slightly increases the yield of ABS,resulting in the imbalance of DHA.Unlike the performance in the tetralin system,the Fe1-XS catalyst has no significant effect on the DHA system.The addition of the H-nondonor components,methylnaphthalene and n-dodecane,reduces the conversion of DHA,and the H-donor capacity of the overall solvent is weakened.