Study On Oxidation Characteristics And Mechanism Of Sulfur In Different Chemical Forms In Coal

Sulfur content in coal is one of the important indices for coal quality analysis,and it plays an important role in coal oxidation process.But the sulfur content in coal is composed of different forms of sulfur.The content and stability of each sulfur form are different.Pyrite sulfur and organic sulfur are considered as the components in coal which are prone to change in quantity.It is necessary to study their oxidation characteristics at room temperature,thus to guide the preparation and storage of special samples with stable quantitative requirements.Therefore,it is significant to study the oxidation characteristics of sulfur forms in coal.This paper starts from the environmental factors that cause the change of sulfur content in coal.Through the analysis of coal quality,the degree of variation caused by different environmental factors was compared,including temperature,oxygen content and environmental humidity.Then the samples with different coalification degree were chosen and oxidized at room temperature for a long time,The functional groups in the samples were analyzed by Fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?.Afterwards,deepening the oxidation of samples by different means,the microscopic changes were analyzed by reflection polarizing microscopy,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,FTIR and XPS,and the variation of functional groups of samples under different oxidation conditions was concluded.At last,based on the variation of organic sulfur in coal under the action of air and oxygen enrichment,the chemical reaction mechanism of thiophene sulfur oxidation was studied by density functional theory?DFT?.This paper draws the following conclusions:?1?Accelerate oxidation by reducing the amount of coal sample and increasing the contact area between sample and air to study the variation of sulfur content in coal with temperature,oxygen content and humidity.And then,monitor the amount of sulfur in coal according to the 50g packing quantity to verify that the law of accelerated oxidation is applicable in the storage process of larger packing quantity samples.The results show that the environmental humidity has the greatest influence on the amount of iron sulfide in coal,and the environmental humidity should be paid attention when preserving samples.Combined with the study of pyrite oxidation,it is shown that moisture in coal plays a key role in promoting the oxidation of pyrite,and the different adsorption order of water and oxygen on the surface of pyrite will affect the species of pyrite slightly oxidized.According to the results of long-term monitoring of sample quantity under two conditions,room temperature storage for 8month and the temperature of 60?storage for 6 month,no matter the degree of coalification,both can satisfy the stability of different sulfur forms measurement in coal in statistics.?2?By comparing the results of chemical analysis and XPS analysis,it shows that the distribution of elements and substances on the surface of coal samples are different from the whole.At the same time,the analysis of XPS results shows that the crushing process promotes the surface oxidation of pyrite,and the oxidation process is accompanied by the loss of inorganic sulfur and the formation of sulfate.The conversion of pyrite by ferrography is between 40%and 80%,and that by sulphur spectrum is about 90%.The conversion varies according to the samples.?3?Coals with different coalification degrees have different oxygen and sulfur functional groups,but their oxidation rules are relatively consistent.The analysis of oxidation at room temperature and enhancement of oxidation shows that the oxidation process is mainly embodied in the oxidation of thiophene to sulfone or sulfoxide.The changes of organic functional groups are mainly reflected in the increase of oxygen-containing functional groups such as hydroxyl,carboxyl and anhydride,the formation of peroxides by ether bonds under the action of oxidants,and the conversion of sulfur-containing heteroatom functional groups from thiophene to sulfone.?4?Compared with the dry oxidation products of inorganic sulfur,the oxidation products in high humidity environment contain Fe_1-xS.The oxidation products of organic sulfur are similar to that of dry air,but the oxidation rate is accelerated to a certain extent and the oxidation degree of samples is deepened.High humidity environment promotes hydroxyl to form self-associating hydrogen bond,which helps to maintain the organic structure of the sample to a certain extent,and alleviates the loss of elements in coal samples caused by oxidation.?5?The theoretical calculation shows that the position of sulfur atom in thiophene structures,a class of the organic sulfur components,is the main attack position of electrophilic reagent?oxygen?.The bond strength of each chemical bond in thiophene structure is similar and bond breaking reaction is not easy to occur.In addition,the oxidation of benzothiophene and dibenzothiophene by oxygen is a spontaneous reaction in thermodynamics.The oxidation products of benzothiophene and dibenzothiophene are sulfite esters,and the activation energies are 62.9 kJ/mol and227.7 kJ/mol,respectively.It shows that the degree of difficulty of oxidation of various organic sulfur components in coal is greatly different.