Study On Interaction Of H₂-Iron Sulfide Catalyst-Hydrogen Donating Solvent In Hydrogen Environment

Rich of coal,poor in oil and short of gas are Chinese energy conditions,and it is necessary to consolidate the foundation of domestic energy production.The development of coal direct liquefaction technology is not only to ensure national energy security,but also an appropriate measure to actively realize the dual carbon goal strategy.The main problem of the direct coal liquefaction technology is the energy consumption and hydrogen consumption caused by the insufficient hydrogen supply capacity of the circulating solvent.Catalyst is an important way to solve the shortage of solvent hydrogen supply capacity.So far,although there are many studies on catalysts promoting solvent hydrogen supply in the process of direct coal liquefaction,due to the complex system of coal hydrogenation reaction process,there are still disputes on the action mechanism of iron sulfide catalyst,the active center and the hydrogen transfer mechanism of solvent in the hydrogenation process.In order to further understand the hydrogen transfer relationship of solvent-catalyst-H₂and the mechanism of"hydrogen donating"in coal hydrogenation.In this paper,the quantum chemical calculation method is used.Firstly,in order to explore the action mechanism and active center of iron sulfide catalyst,Fe₇S₈ with the best catalytic activity in Fe_1-xS was selected as the catalyst model,and the Fe₇S₈ cell is constructed and optimized.The Fe₇S₈（001）crystal plane was obtained by cutting the Fe₇S₈ crystal cell;Secondly,H₂ was adsorbed on Fe₇S₈（001）crystal surface to explore the effect of catalyst and H₂;Finally,select the appropriate solvent free radical model compound and coal pyrolysis free radical model compound,take hydrogen,hydrogen sulfide and tetralin as hydrogen donors respectively,calculate and compare the hydrogenation reaction energy barrier of solvent free radical and coal pyrolysis free radical,to explore the hydrogen transfer mechanism and the hydrogen transfer relationship of H₂,catalyst and hydrogen supply solvent;Finally,the key factors affecting coal hydrogenation are analyzed and summarized,and the following main results and conclusions are obtained.1.The adsorption of H₂ on two sulfur surfaces without iron vacancies and iron vacancies was analyzed.The results show that vertical adsorption is not conducive to bonding,while horizontal adsorption can bond hydrogen atoms and sulfur atom;hydrogen molecules adsorbed horizontally on the apex of sulfur will dissociate and adsorb on the same sulfur atom.This adsorption method makes the two hydrogen atoms and sulfur atoms generate H₂S,and the generated H₂S tends to be far away from the surface.These H₂S can supply hydrogen to the outside.Iron vacancies affect the bonding of sulfur and hydrogen by affecting the local electron intensity and distribution of the surrounding sulfur atoms,thereby becoming the active center for desorption of H₂S.2.H₂S,H₂ and tetralin can supply hydrogen to solvent free radicals.Compared with H₂ and tetralin,H₂S is easier to supply hydrogen.There is a hydrogen transfer relationship among H₂,catalyst and solvent in the process of direct coal liquefaction.In the process of hydrogen transfer from H₂S and H₂ to solvent,the reaction energy barrier of H₂S and H₂ to solvent radical is greater than that of solvent to coal radical.In this process,solvent hydrogenation is a speed control step.H₂S is easier to supply hydrogen to solvent free radicals than H₂,which indicates that the interaction between H₂ and catalyst to produce H₂S is conducive to solvent free radical hydrogenation.