Study On The Reactions Of Catalysts And Hydrocarbons In Coal Hydroliquefaction

Coal hydroliquefaction,termed direct coal liquefaction(DCL)as well,is an important process in coal to liquid(CTL)technology.It has attached much attention in recent years.The coal hydroliquefaction technology is particularly important for China which is short in oil resources but abundant in coal reserves.However,the quality of the oil products from the coal liquefaction technology is not competitive with that from petroleum industry.To improve the competitiveness of coal hydroliquefaction technology,many scientific problems,including the relation between catalytic activity and forms of the catalysts,reaction characteristics of the typical structure in coal,and coking of the oil product during liquefaction and the subsequent process,need to be solved.These problems need to be better understood for optimizing the DCL technology.In the light of of the problems above,this dissertation deals with the reactions of catalysts and hydrocarbons in coal hydroliquefaction.The studies mainly include the following parts:1.Transformation of the catalyst forms and its relation with catalytic activity in tetralin dehydrogenation and coal hydroliquefaction;2.Reacions of the alkylbenzene structures:direct pyrolysis and radical-induced pyrolysis of alkylbenzene;3.Cyclization pathway during the pyrolysis of alkylbenzene;4.Behaviors of coking and radicals of a model heavy oil during thermal reaction.The main results are described in the followings:(1)The catalytic activity of DCL catalysts in tetralin dehydrogenation under nomal pressure is accordant with that in coal liquefaction under high pressure.Therefore a simple and accurate method that using the activity in tetralin dehydrogenation to estimate that in DCL is established.The catalysts in the form of oxides or hydroxides,whether supported on or prysically mixed with a char(simulating the support in coal),undergo sulfidation by H2S initially and then partial reduction by H2.The S content of the catalysts after the reduction stage is proportional to the rate constant and activation energy of tetralin dehydrogenation as well as coal conversion and oil yield in DCL.(2)The pyrolysis of alkylbenzene in the coal liquefaction temperature range can be divided into direct pyrolysis and radical-induced pyrolysis.The latter shows a higher rate constant than the former.The direct pyrolysis can be fitted with first-order kinetic and the radical-induced pyrolysis can be fitted with second-order kinetic.Only one C-C bond(β position of the alkyl chain)dissociates during the direct pyrolysis of n-propylbenzene,n-pentylbenzene and n-hexylbenzene,while more than one C-C bond,other than the β position,dissociate for the direct pyrolysis of n-dodecylbenzene.The radical-induced pyrolysis mainly depends on the number of the radicals.The radical-induced pyrolysis increases the contents of the α-side chain radical intermediate for n-propylbenzene,n-pentylbenzene and n-hexylbenzene,and γ-side chain radical intermediate for n-dodecylbenzene.The long-chain alkane gas or radicals may further crack into short-chain alkanes.(3)The pyrolysis of n-alkylbenzene includes the cyclization of the aliphatic chain.The n-butylbenzene yields the highest naphthalene contents among the linear alkylbenzene pyrolysis.The formation of naphthalene may be related with the δ-side chain radical of butylbenzene whose H in the aliphatic chain is abstracted by the direct pyrolysis radicals.The cyclization ofδ-side chain radical is more favored by isomerism without C-C bond scission than by recombination of radicals.(4)The coke that forms during thermal reaction of a heavy oil(a model of oil product from coal liquefaction or pyrolysis)evolves in the coal liquefaction temperature.The coke can be classified by chlorobenzene insoluble(Cl,hard coke)and toluene insoluble(TI,hard+soft coke).The formation of Cl starts at 440 °C while that of TI starts at 350 °C.The formation of Cl and TI in mass can be fitted by the second-order +autocatalytic kinetics and second-order kinetics,respectively.The soft coke forms initially in the thermal reaction but converts to hard coke at temperatures of and higher than 440 °C.Both hard and soft coke underwent continued cracking and condensation and the hard coke is relatively more condensed in structure than the soft coke.The morphology of soft coke appears to be spherical while that of hard coke appears to be molten layered.(5)Both Cl and Tn contain stable radicals measurable by electron spin resonance(ESR).The formation of these radicals can be fitted by the first-order kinetics for Cl and for TI in the temperature range of 440 °C-500 ℃,and by the second-order kinetics for TI in the temperature range of 350 °C-440 °C.