Experimental Analysis And Molecular Simulation On Desulfuration Of Sulfoether In Coal By Microwave Combined With Oxidizing Agent

Coal microwave desulfurization technology is a new type mild desulfurization and purification method, which has great prospects for development. Most of the research on microwave desulfurization was based on the macro experiment, but the micro mechanism of microwave desulfurization has been rarely studied. Therefore, based on the understanding of sulfur content in coal, phenyl sulfide, dibenzyl sulfide, diphenyl disulfide and dibenzyl disulfide were selected as model compounds of the sulfur ether, and microwave oxidation desulfurization tests of them were carried out. Under the condition of the extra electric field, the molecular characteristics of these four sulfur compounds and their oxidation reaction with acetic acid were researched by quantum chemistry calculation. The main conclusions are as follows:(1) The main types of organic sulfur in selected coal are thiophene and sulfoether. The order of removal effect for these four model compounds by microwave oxidation is: dibenzyl disulfide > diphenyl disulfide > dibenzyl sulfide > phenyl sulfide. Analysis shows that the effect of microwave irradiation time on oxidation desulfurization was the most significant, so it is better to extend the time of microwave irradiation to achieve better desulfurization effect. Sulfoether model compounds are mainly oxidized to the corresponding sulfoxide and sulphone. During the oxidation process, the S-S bond in the disulfur ether were broken to form the sulfur free radicals of high activity, and then the sulfonic acid or sulfuric acid were produced.(2) The sulfur containing bond is longer than that of sulfur free in the model compounds, and the S-S bond is longer than that of C-S. The sulfur atom in the molecule is a electrophilic activity site. With the increase of the degree of oxidation, the bond dissociation energy(BDE) of the sulfur containing bond first decreases and then increases. It is deduced that the proper oxidation of sulfur in coal is beneficial to the fracture of sulfur bond.(3) The path of oxidative reaction of sulfoether is as follows: the sulfur atoms of model compounds are attacked by the oxygen atoms in the oxygen molecule, forming the corresponding sulfoxide, and then further oxidized to the corresponding sulphone. There exist two reaction paths in the reaction of disulfide. The reaction energy barriers of the first step in the oxidative desulfurization reaction are the lowest, and those of the last step are the highest. The analysis results show that the fracture of C-S bond is difficult to occur in phenyl sulfide and dibenzyl sulfide molecule. After oxidized to the corresponding sulfoxide, the S-S bond of disulfide tends to break. After oxidized, the molecular polarity of sulfoether model compounds is enhanced. The results showed that the oxidation products of benzyl sulfide and dibenzyl sulfide are not inclined to react further, while the oxidation products of disulfide ether tend to be further oxidized or occur other reactions. The activation energy of first step is the lowest, its reaction rate is the highest. The reaction rate constants increase exponentially with the increase of temperature.(4) The structure and energy of the transition states and intermediate states in the reaction process and the reaction energy barrier are changed by extra electric field. And the enthalpy change of reaction enthalpy, entropy and Gibbs free energy, the reaction activation energy and rate constant appear to decrease or increase under the difference extra electric field. Under extra appropriate electric field, the reaction activity of the molecule and sulfur atom could be enhanced. And the activation energy of the oxidative desulfurization reaction could be effectively reduced, and the reaction rate would be obviously increased, so that the desulfurization reaction could be accelerated.