Experimental And Quantum Chemical Simulation Of Microwave Assisted Removal Of Organic Sulfur From Coal By Urea Peroxide

The removal of sulfur components in coal,especially the removal of organic sulfur in coal,has long been a difficult problem for clean and efficient utilization of coal.Although microwave-assisted coal desulfurization technology has been applied in some practical production,the research on the mechanism of microwave-assisted desulfurization has not made key progress.With the development of computer technology and related theories,quantum chemical calculation methods are widely used in coal chemistry.Because the structure of coal is extremely complex and the migration processes of different forms of sulfur are intertwined,it is difficult to accurately clarify the fracture essence of chemical bonds and the migration laws of sulfur.It is very difficult to directly study the migration law of sulfur in coal.Based on this,relying on the quantum chemical method,this paper simplifies the organic sulfur in coal into several kinds of coal organic sulfur model compounds.At the same time,based on the principle of microwave action,the microwave field is simplified into an electric field.The quantum chemical response of the organic sulfur structure in coal to microwave energy and the effect of microwave field on the reactivity of organic sulfur are studied.This work takes the microwave oxidation removal of organic sulfur in high sulfur coking coal as the research object.The experiments show that the removal efficiency of organic sulfur in coal is different under different microwave power.The removal rates of organic sulfur corresponding to microwave power 600W,800W and 1000W are 45.79%,55.14%and67.29%respectively,and 28.97%under traditional heating mode.FT-IR analysis of coal samples before and after desulfurization is carried out.On the basis of full understanding of sulfur structure in high sulfur coal,Combined with the macromolecular structure theory of coal,benzyl mercaptan,dibenzyl sulfide and dibenzyl disulfide are selected as model compounds representing the form of organic sulfur in coal.Relying on the corresponding quantum chemical calculation software and the principle of microwave heating,the microwave removal of organic sulfur in coal is quantitatively calculated by using electric field instead of microwave field,so as to determine the reaction active sites of molecules and the strength of sulfur-containing bonds,Calculate the change law of quantum chemical properties of molecules with or without external electric field(0 10 20 50 100 200*10^-3au).Through the calculation and analysis of molecular quantum chemical properties,it is concluded that the C-S bond and S-S bond increase in varying degrees and tend to break.In a few cases,the benzene ring is deformed and bent,and the molecular structure is folded.From the perspective of energy gap,the electric field makes the molecule in an unstable state and improves the reaction activity.The stability is benzylmercaptan>dibenzyl sulfide>dibenzyl disulfide.From Mulliken’s charge distribution,the activity of C atom connected with S atom is also large.For S atom,the response of its charge to electric field is obvious.With the increase of electric field,the overall trend of charge increases.Therefore,S atom will be the center of electrophilic attack.From the perspective of molecular vibration form,the difference of different structures in molecules will lead to a certain electric field strength,which can strengthen a molecular vibration form and weaken a molecular vibration form.This may be the essence of microwave selectivity in experimental desulfurization or the explanation of non thermal effect.By guessing the possible reaction path between sulfur-containing model compound and urea peroxide,the calculation method adopts density functional B3LYP,the solvent model selects PCM implicit solvent model,the base group adopts 6-31G（d）,the combination of qst1 and TS is used to find the reaction transition state,and the frequency calculation is used to ensure that there is and only one virtual frequency in the transition state system.The correctness of the transition state is verified by the intrinsic reaction coordinate IRC.Finally,the reactants,intermediates The single point energy of transition state and product is calculated,and the relative energy change and reaction potential barrier of each reaction are obtained.Among them,benzyl mercaptan is divided into four steps to generate sulfonic acid group,and dibenzyl sulfide is divided into two steps to generate corresponding sulfoxide and sulfone.Dibenzyl disulfide is divided into four steps,but there are two oxidation paths a and B.from the perspective of reaction energy barrier,the reaction tends to occur B reaction to generate corresponding sulfoxide and sulfones.Through the analysis of the experimental and calculation results,it is concluded that microwave has thermal effect and non thermal effect.The thermal effect is to increase the system temperature,and the non thermal effect is that microwave acts directly on molecules.The peroxy group in urea peroxide attacks the S atom to generate SO₂ gas after cracking,which escapes.Because there is not enough active hydrogen source in the reaction system,it is speculated that the main gas generated is SO₂,while H₂S is less,Therefore,the main sulfur migration path is to generate SO₂ to escape or generate soluble substances to be dissolved in the solution and removed by filtration.