Study On The Dielectric Properties Of High-sulfur Coal And Transformation Of Sulfur-containing Functional Groups Under Microwave Electric Field

Sulfur is one of the main harmful elements contained in coal.The utilization of high-sulfur coal will lead to the emission of sulfur-containing compound,which not only affects the quality of steel products,but also has a bad impact on the environment.It is of great significance to develop coal clean utilization technology and implement various measures for coal pre-combustion desulfurization.As a novel desulfurization method,microwave irradiation has great potential for the clean utilization of coal.In order to clarify the relationship between microwave parameters and coal sample dielectric responsiveness,and further enhance the microwave desulfurization efficiency,dielectric properties of high sulfur coal,microwave electric field and its influence on sulfur transformation have been studied.The main points of this study are threefold:?1?Dielectric constants and magnetic permeabilities of coal and sulfur-containing model compounds have been determined.Theoretical calculation has been applied to evaluate the electrical and magnetic loss power of coal samples and sulfur-containing model compounds at different microwave frequency.The results show that microwave has an selective heating effect on sulfur-containing model compounds.The reason can be attributed to the higher imaginary part of dielectric constant of sulfur-containing compounds,which produce a stronger dielectric loss effect and generate more heat than coal matrix.The differences in magnetic permeability values of the coal and sulfur-containing model compounds are not large,and magnetic effect of the microwave on the coal is not obvious.The dielectric measurement results indicates the main absorbing mechanism of coal and sulfur-containing compounds is dielectric loss,therefore,the role of microwave electric field is the focus of following sections.?2?The Ansoft HFSS software was used to simulate the electromagnetic field distribution of microwave oven cavity and coal sample under different microwave power.The simulation results show that the microwave electric field is unevenly distributed in coal,and there are regions?hot spots?with large electric field values in the coal sample.The equivalent value of microwave electromagnetic field in the coal sample was obtained through the field calculator of HFSS,and used to calculated the theoretical temperature curve of coal sample under microwave heating.Comparing the theoretical temperature curve with the actual measured temperature curve,it was verified that the software simulation results were reasonable.Referring to the simulation results of microwave electric field,the microwave electric field is defined as 0.01a.u.in the following Materials Studio simulation.?3?The effect of electric field on thiophene?C₄H₄S?,mercaptan?-SH?,disulfide bond?S-S?and sulfuryl?S=O?was investigated using Materials Studio simulation.The LST/QST transition state search indicates that the applied electric field reduced energy barrier of thiophene desulfurization reaction,improved the lnk while reduced the Ea and ?_rH_m.The calculation results suggest that microwave could promote the forward desulfurization reaction.A coal molecular model based on coal Wiser model was established,and Fukui indices,ESP charge,HOMO and LUMO analysis of molecular model were applied.Electric field improved the reactivity of coal molecular model in which-SH is more reactive than S=O and S-S.FTIR analysis has been carried out on coal samples irradiated with different microwave power to obtain the functional group ratio.Through simulation and experimental results,the removal difficulty of three kinds of sulfur functional groups ranks as S=O>S-S>-SH.Microwave electric effect on S=O is limited,which deserves further attention.