The Dielectric Properties of Thiophene Model Compounds: Insights for Microwave Desulfurization of Coking Coal

Abstract

Microwave desulfurization capitalizes on the different dielectric properties of sulfur-containing and sulfur-free components in coal. However, the dielectric properties of thiophene compounds, the predominant sulfur species in coking coal, are not well understood. Herein, the dielectric properties of different thiophene model compounds containing coal-like compositions and structures are investigated under the impact of microwave frequency and temperature. The increases of aromaticity in thiophene compounds suppress their microwave responses to the electric irradiation, as indicated by the decrease of the loss tangent values, while thiophene compounds with polar functional groups exhibit higher microwave reactivity. Additionally, the oxidation of the functional groups in thiophene further increases the ability to absorb and convert the microwave energy to the thermal energy. The dielectric properties of thiophene compounds are also sensitive to the changes in microwave frequency and temperatures. The thiophene compounds exhibit a higher microwave adsorption capacity at the microwave frequency of 915 MHz relative to 2450 MHz, which is opposite to the trends for the penetration depths. Such an observation indicates that the desulfurization of thiophene compounds is more readily achieved at the frequency of 915 MHz. The findings associated with the dielectric properties of different thiophene compounds mark an important step toward optimizing the microwave desulfurization of coal.

Chemical Thermodynamics and Kinetics of Thiophenic Sulfur Removed from Coal by Microwave: A Density Functional Theory Study

“…Therefore, it is considered that the applied electric field can effectively reduce reaction difficulty. By comparing the maximum Eb of the above two reaction paths, it can be concluded that compared with α(a), α(b) is more suitable for H atom migration in the process of removing thiophenic sulfur from coal microwave [43]. Fig.…”

“…Moreover, the ε' values of NTC and LGC are higher than benzothiophene and dibenzothiophene. It is considered that coal can store more electric field energy than sulfur compounds in an alternating electromagnetic field [42][43][44][45]. Fig.…”

“…Fig. 2 (b) exhibits that the ε" values of thiophenic sulfur compounds are higher than coal samples, which indicated that sulfur compounds can better convert electric field energy into heat energy [42][43][44][45]. When microwave frequency reaches 2 GHz, the induced and oriented polarization occurs in the four samples.…”

“…The interaction between dipoles take place, and the microwave energy is converted into heat energy. At this time, the energy storage decreases, and the energy loss increases [42][43][44][45]. There is a peak value of ε" near 9 4 GHz for the four samples, where the microwave frequency reaches the high frequency region above 5…”

Microwave absorption properties and quantum chemistry of organic sulfur compounds in coal

“…Ethyl mercaptan, benzyl mercaptan, furfuryl mercaptan, methyl sulfide, ethyl sulfide, diphenyl sulfide, and difurfuryl sulfide have better microwave absorption properties than 3-methylthiophene, 2-aminothiophene, and benzothiophene. 15,16 The similar organic sulfur compounds also have different microwave absorption properties. The sulfur occurrence environment in coal, such as the length of aliphatic chain, aromaticity, and type of heteroatom, remarkably affects the dielectric properties of thiophene.…”