Quantum Chemical Study On Mechanism Of Organic Sulfur In Coal During Pyrolysis And Experimental Study On Coal Pyrolysis Desulfurization

With the fast development of society and economy, the problem of environment attracts more and more attention of people. SO2 which is produced during coal combustion is direct related to the issues of acid rain and the destroy of ozonosphere, it becomes the crucial factor that restrict the economic feasibility in the course of coal's exploiting and utilizing process. Considering the sustainable development of resource and environment protection, how to restrain the release of sulfur efficiently in the process of coal thermal processing, realize the utilization of coal cleanly and effectively, which becomes an important issue to people. Based on Quantum Chemistry theory and Organic Chemistry theory, the release mechanism of organic sulfur in coal through pyrolysis is studied in this paper by Quantum Chemistry Calculation, hoping to establish theoretic base for desulfurization of coal through pyrolysis. In this paper four kinds model compounds of organic sulphur are selected to calculate by Quantum Chemistry Calculation. Thiophene is pre-digested rationally, it may release two kinds of thiophene type free radicals through pyrolysis. Two types of free radicals and other model compounds have been investigated using Density Functional Theory (DFT) B3LYP/6-31G(d) by Gaussian 98. Through comparing the Bond Mulliken Population, we find that S-S bond in CH3-S-S-CH₃ and C-S bond in other model compounds are the weakest bond in their system, they will be dissociated first during pyrolysis. The sulfur in non-thiophene will final release in the form of H₂S ; thiophene A free radical is C₂H₂ and (:S) free radical, thiophene B free radical is C₂H₂ and (.SH) free radical. The (:S) free radical or (.SH) free radical is easy to combine with H free radical, release in the form of H2S. The release models of four kinds model compounds of organic sulfur are built. Activation energy of four kinds model compounds of organic sulfur is calculated. Through the results, we can find sequence of thermal stability is that, thiophene B free radical > thiophene A free radical > CH₃-S-CH₃ > phenyl-thiol > CH₃-S-S-CH₃. Pyrolysis experiences are carried out using WuGang coal and three additives as AlCl3, C2H5ONa and CH3COONa. It can be found that AlCl3 is the best additive, decreasing sulfur content in char sharply. C2H5ONa acts in low temperature as 400℃because of its selective oxidation on organic sulfur in coal; in high temperature it can hardly act because of its volatility.