Quantum Chemical Simulation And Experimental Study On The Removal Of Organosulfur From Coal By Microwaving

The removal of sulfur from coal, especially the expulsion of organic sulfur, has been a troublesome issue in the clean and efficient utilizations of coal for a long time. Study on the mechanism of desulfurization of coal with assistanceof microwaving has been still difficult to achieve decisive advances, athrough the technology has beenpartly adopted in industrial field already. Quantum chemistry has been introduced in the investigation of coal chemistry with the development of computer science and related theory.Based on quantum chemical method,the organic sulfur in coal has been simplified to several coal-like organosulfur model compounds for the molecular simulation of the removal of organic sulfur from coal. At the same time, we take the external electric field to replace the microwave field, in accordance with the working mechanism of microwave radiation, to analyze thequantum chemistry response of organic sulfur structures in coal to miceowave energy and the effects of microwaving to the reactivity of organic sulfur in coal.Comparing the sulfur compositions of two kinds of high-sulfur coking coalcollected from Shanxi province, Xinyu coal has been selected as the research object in the present thesis. XPS results infer that thiophene, mercapten and thioetherare the dominant existing form of organic sulfur in coal, and the thiophenehas a higher content percentage rather than others.After purification with centrifugationmethod, the low-density coal with high purity of organic sulfur has been chosen as the original material for fractional extraction with multiple accelerate solvents.The determinations of small molecules in the extraction contribute to the design of coal-like organosulfur model compounds. Experiment results tell that the sulfur-containing small molecules in the extraction of Xinyu coal can be identified as dibenzothiophene, dimethyl sulfoxide, 3-Methyldibenzothiophene, 4-Methyldibenzothiophene, 4,6-Dimethyldibenzothiophene, 3-methylbenzenethiol, 4,9-Dimethyl-naphtho[1,2-d]thiophene, diisopropyl sulfiteand4,9-Dimethyl-naphtho[2,3-b]thiophene. Considering the macromolecular structure of coal, benzyl mercaptan, dibenzothiophene, phenyl sulfoxide, dibenzyl sulphideand 3-Methylbenzenethiol have been built as coal-like organosulfur model compounds for later research, in the very end.With the asistence of Gaussain software package, some quantum chemistry properties of coal-like organosulfur model compounds mentioned above have been analyzed. Simultaneously, the influences of electric field in different intensity have been studied. For the geometric configurations of coal-like organosulfur model compounds, most of benzene rings remain relative stable with the change of electric field, while the bond length of most of C-S bonds are prone to stretch.Additionally, the structures around the sulfur atoms show some irregular transformation in configuration, which may be result in the perturbation of sulfur atoms. Population analysis demonstrates that the effects of external electric fields to the distribution of electron around carbon atoms. In different structures, the negativeelectrical charge increases with specificintensity of external electric field, while some specific intensities of electric field are able to impair the density of electron cloudaround carbon atoms. For sulfur atoms, external electric field contributes to the improvement of electronegativity in most of situation.From the vibrational spectrum of organosulfur molecules, we can draw a conclusion that there are designatedelectric fields can enforce and weaken given vibration type of same structure at to the most extent.The removal of sulfur from coal is depended on the development of the desulfurization reaction between organic sulfur and oxidizing agents, after all. That means the study on the mechanism of desulfurization reaction is important to investigation of microwave desulfurization. In this thesis, we take benzyl mercaptan and dibenzothiophene as organic sulfur in coal, to perform the simulation of the reaction process of organic sulfur in coal and H2O2. With the process of the reaction, the transformation of chemicals in reaction system and the energy evolution of system have been recorded. Obviously, the oxidization of the organic sulfur in coal is a multi-step reaction, and entire reaction includes the attack of oxygen atoms to sulfur atoms, the transition of hydrogen and the breakage of O-O bonds. The potential energy profiles illustrate that external electric field reduce the energy barrier of rate-decided step in the oxidization of organic sulfur and the active energy of desulfurization reaction decrease.Taking Xinyu high-sulfur coal as experimental sample, coal desulfurization experiment was carried out.After microwave desulfurization with asistence of H2O2, the ash content and calorific value decline, while the volatile content growing up.Besides, this desulfurization treatment impairs the property of coal to be high-grade feeds in coking industry. Theses chages in the properties of coal attribute to the microwave radiation strengthening the desulfurization reaction.The effects of microwaving to the evolutionof desulfurization reaction are complex. On the one hand, the thermal effect of microwave heating can accelerate the speed of desulfurization reaction indubitably. On the other hand, the microwave own special effect may directly affect the microstructure of organic sulfur in coal, changing the chemical configuration and reaction properties of organosulfur at the root, to promote the removal of organic sulfur from coal.