Studies On Hydrogen Donateding Ability Of Solvent In Direct Coal Liquefaction

With the increasing scarcity of oil resources and the increasing demand for oil in our country year by year,China's energy supply security issues have received more and more attention.The development of direct coal liquefaction technology is of great significance for solving the shortage of petroleum resources in China and ensuring the safety of China's energy donated.However,the current coal direct liquefaction technology has a series of problems such as low oil yield and condensation and coking,which limits the further development of coal direct liquefaction technology.The core reaction of coal direct liquefaction technology is the matching problem between the "generation rate" of free radical fragments and the "hydrogenation rate"of free radical fragments.Therefore,increasing the hydrogenation rate of free radicals is the key to solving the problems of low oil yield,condensation and coking during the reaction.In the direct coal liquefaction process,the hydrogen-donating solvent has a higher hydrogen-donating activity than hydrogen gas.Therefore,a large amount of hydrogen-donating solvent is applied to the coal direct liquefaction project,which allows the liquefaction process to obtain a higher oil yield.It also reduces the severity of the reaction system,so the hydrogen donating capacity of the solvent is crucial in the direct coal liquefaction process.At present,the evaluation of the hydrogen supply capacity of the hydrogen supply solvent is mostly specific reaction conditions,and not considered to be affected by temperature and coal type.There is no unified evaluation parameters and unified evaluation system to evaluate the hydrogen supply solvent.Therefore,establishing a system to evaluate the hydrogen donating capacity of the solvent through the hydrogen donating parameters of the hydrogen donating solvent(initial hydrogen supply temperature and maximum hydrogen donating amount)is an important breakthrough for promoting the development of coal liquefaction technology.Based on the above analysis,five typical hydrogen-donating solvents and four industrial recycle solvents were selected as the research objects of coal direct liquefaction solvent,and the reaction behavior differences between them and model compounds during the pyrolysis process were investigated.The hydrogen donated kinetic relationships of these solvents were analyzed,then the initial hydrogen donated temperatures and maximum hydrogen donating amount of these solvents were explored.Further more,a method for evaluating the hydrogen donated capacity of coal direct liquefaction solvent was created,and the relationship between the hydrogen donated capacity of coal direct liquefaction solvent and its structure was analyzed.The main conclusions are as follows:(1)When benzyl phenyl ether(BPE)and bibenzyl react with industrial recycle solvents,the amount of free radicals quenched by active hydrogen and the amount of active hydrogen provided by the recycle solvent are consistent.Therefor,the amount of hydrogen supplied by the circulating solvent can be obtained by calculating the amount of free radicals quenched by active hydrogen during the experiment.Cal-O bond breaking temperature in BPE is low,which can be used as a model compound to evaluate the initial hydrogen supply temperature of the solvent during coal liquefaction;while Cal-Cal bond breaking temperature in bibenzyl is high,which can be used as an model compound to evaluate the maximum hydrogen donating of the solvent during coal liquefaction.(2)To evaluate the hydrogen donated capacity of the hydrogen donated solvent(HDS),it is necessary to take the initial hydrogen donated temperature and the maximum hydrogen donating amount of the solvent into account.For these five HDSs of DHA,DHP,THA,THFA,and THN,the initial hydrogen donating temperature of DHA is the lowest at 304.4?,followed by THFA,DHP,and THA,which can be donated at 307.4??310.5? and 320.5?,respectively;the initial hydrogen donating temperature of THN is the highest at 339.4?.The maximum hydrogen donating amount of solvent depends on its molecular structure.The maximum hydrogen donating amount of DHA,DHP,THFA,THA and THN are respectively 11.11 mmol/g,11.11 mmol/g,19.41 mmol/g,25.64 mmol/g and 30.30 mmol/g.(3)The difference in hydrogen donated activity of industrial recycled solvents can be compared by the initial hydrogen donated temperature.The reaction process of the solvents and benzyl BPE can be described by a first-order kinetic relationship;Among them,the initial hydrogen donating temperature of S4 is the highest at 305.2?,followed by S1 and S2,which can be donated at 308.8? and 310.2?,respectively;the initial hydrogen donating temperature of DHA is the lowest at 315.8?.The hydrogen donating activity of the solvent increases as the initial hydrogen donating temperature decreases.(4)The maximum hydrogen donating amount of industrial recycle solvent is the sum of the hydrogen-donated of all hydrogen donating solvents in its components.The reaction with bibenzyl can be described by first-order kinetic relationship.The maximum hydrogen supply of S3 is 35.65 mmol/g,followed by S2 and S1,which can reach 27.25 mmol/g and 22.41 mmol/g,and S4 is the lowest,only 20.16 mmol/g.The result of the reaction between THN and bibenzyl proves that this method for evaluating the maximum hydrogen supply of industrial recycle solvents is reliable.(5)There is a relationship between the hydrogen donating capacity of industrial circulating solvents and its structural parameters.The maximum hydrogen donating amount of recycled solvents decreases with the increase of Hal/Har,and increases with the decrease of Hal/Har;the maximum hydrogen donating amount decreases with the increase of average carbon chain length Cn and increases with the decrease of Cn;the initial hydrogen donating temperature decreases with the increase of W(H?)and increases with the decrease of W(H?).