Molecular Simulation And Experimental Study On Microwave Desulfurization Of Coal-like Sulphur Compounds Based On Non-thermal Effect

It is a great enhance for level of clean utilization of coal and a great improve for the ecological environment of China to develop the new theory and technology of desulfurization of coal.As a special energy method,microwave has attracted the attention of experts in the field of coal desulfurization.The Xinyu coal in Shanxi Province was selected as the research object in this paper.Therefore,based on the understanding of sulfur content in coal,dibenzyl sulfide,diphenyl sulfone and dibenzothiophene were selected as model compounds of the sulfur ether,and microwave-water bath control and nonisothermal kinetic experiments were carried out.The characteristics of three compounds and the reaction of dibenzothiophene with peracetic acid were analyzed by quantum chemical calculation.Then the mechanism of microwave desulfurization of coal was explored and the non-thermal effect of microwave desulfurization of coal was revealed.The results are as follows:The molecular properties of three model compounds were calculated and analyzed by Guassin 09 quantum chemical software.The reactive sites,strength of sulfur bonds and the reaction activity were determined.The results show that the order of bond length and dipole moment is diphenyl disulfide > diphenylsulfone > dibenzothiophene,that is,the S of dibenzyl sulfide is the easiest to be removed,but the S of dibenzothiophene is the most difficult to remove.The order of energy gap is diphenyl disulfide < dibenzothiophene < diphenyl sulfone,indicating that the activity of dibenzyl thiophene is best while the activity of dibenzothiophene is worst.The Hirshfeld charge analysis of three molecules shows that,the charge number of S atom in dibenzyl sulfide molecule is negative,it is easy to react,but diphenyl sulfone and dibenzothiophene are not easy to react.The S atom in dibenzyl sulfide and dibenzothiophene is the reactive point of themselves,while the electrophilic active point of benzene sulfone should be on both sides of the benzene ring.The quantum chemical analysis of the reaction of dibenzothiophene with peracetic acid shows that the bond dissociation of dibenzothiophene C-S bond decreases first and then increases with the increase of oxidation degree.That is to say,the thiophene sulfur can oxidized to intermediate product at the first,and then further oxidized to form sulfonate and other products,which is easily easily solubled in water.The thermodynamic analysis of dibenzothiophene molecular oxidation shows that with the reaction,the dibenzothiophene dipole moment increases,the electron energy decreases,and the energy gap changes little,so the polarity of the oxidation product increases.The first step of dibenzothiophene oxidation reaction is difficult,while the second step reaction is relatively easy.The results of microwave-water bath control experiment show that the sulfur removal rate of coal samples and three model compounds increased with the increase of temperature,and the desulphurization rate of test sample after microwave treatment was obviously higher than that after water bath treatment.FTIR,XANES and XPS analysis show that the non-thermal effect of microwave irradiation does not destroy the macromolecular structure of coal,but promotes the reaction of sulfur-containing molecules with peracetic acid by changing the dipole moment,energy gap and density of electron cloud,thus increasing the desulphurization rate.The non-isothermal kinetics study of coal samples and three model compounds show that the boiling point of the desulfurization systems is about 110 degrees.The heating rate of the system increases with the increase of microwave power,and with the change of microwave power,the activation energy and preexponential factors of XinYu coal and three kinds of model compounds have changed correspondingly.It can be concluding that the effect of microwave on coal combined with peracetic acid desulfurization is nonlinear,except for heat effect;there is also a non-thermal effect of microwave,which decreases the activation energy and increases preexponential factor.