Coal Adsorption To Oxygen Molecules Mechanism Research

The coal that stores in the stratum are crushed and form scattered coal when there is an external force acting on them,in the scattered coal it contacts with air oxygen and occurs the oxidizing reaction to emit the quantity of heat,the thermal agglomeration makes the coal body internal temperature increases,finally causes the coal spontaneous combustion.There are three processes that are physical adsorption,chemical adsorption and chemical reaction in the process of coal and oxygen occur oxidation spontaneous combustion.The adsorption of coal and oxygen is the initial process of coal and oxygen chemical reaction,and also is the most important process.There is no one study the coal adsorption to oxygen from the point of microcosmic at home and abroad.Coal is a kind of non-crystal material that has rich pores,so studies the coal and the oxygen adsorption microscopically with the traditional method that used to research crystal material could not be suitable.Coal has huge specific surface area,the definition of chemical structure that formed the coal surface is that the surface structure of coal is an aggregate which is composed of the similar or the same coal molecular structure fragment,and the coal molecular fragment is a part of coal organic macro-molecule,which is composed of the similar or the same benzene ring skeleton and side chain.The definition of coal surface not only solves the problem of coal adsorption to oxygen,but also offers a new method to research non-crystal material adsorption microscopically.The coal has the oxidized spontaneous combustion is start from the coal adsorption to oxygen.The coal and the oxygen has the physical adsorption to emit the quantity of heat,which provides more energies to oxygen molecules thermal motion,thus enable more oxygen molecules to approach the coal surface and occur chemical adsorption with coal molecule,the chemical adsorption emit more quantity of heats to cause the coal spontaneous combustion.The quantum chemistry method can reveal the coal and oxygen adsorption process from the microscopic aspect,obtains the coal oxidation spontaneous combustion original mechanism.Through the quantum chemistry computation,we directly obtains the coal molecule and the oxygen molecule frontal orbit energy,which reflects the capability of coal molecule adsorbing oxygen molecule,as well as each composition atom's contribution to the frontal orbit electron cloud.We can study the chemistry essence of oxygen molecule and coal molecule adsorption by quantum chemistry theory,it is an important fundamental research method to study the coal and oxygen adsorption in the coal oxidation spontaneous combustion process.The thesis studies coal molecule and oxygen molecule physical adsorption and chemical adsorption process under the B3LYP/6-311G level by quantum chemistry density functional theory(DFT).The thesis has promulgated the essence of coal and oxygen adsorption, has established the theory of non-crystal material microscopic adsorption research,and has filled the blank of coal spontaneous combustion research area.Main research content and research results summary as follows:It has defined the coal surface molecule fragment as the coal surface smallest structural unit,researched the adsorption of coal surface to oxygen molecule,thus revealed adsorption mechanism of the coal and the oxygen, well solved the adsorption problem of the coal and the oxygen from the microscopic aspect,established non-crystal microscopic adsorption theory. According to the energy close principle in frontier orbital theory,we can think when forms adsorbed state,it mainly the interaction between C₉H₁₃N HOMO track and O₂ LUMO track,which is the result of the electrons from coal molecule fragment C₉H₁₃N transfer to O₂.The thesis has established physical adsorption models of coal surface to single molecule and to multi-oxygen molecules,and has determined the adsorption position and balanced adsorption distance of each adsorption model.Calculating the adsorption energy of the coal surface to single oxygen molecule and to multi-oxygen molecules show that,the adsorption capacity is proportional to the adsorption energy,and presents linear increasing relation.Besides oxygen it also has studied the coal surface mixture adsorption to nitrogen,methane,steam, carbon monoxide and so on,studied the adsorption of the coal surface to the multi-component gas from the microscopic aspect applying the calculation method of quantum chemistry theory,obtained the adsorption equilibrium geometric configuration,established the mixture adsorption model.Compared the adsorption energy of all kinds of gas to surface molecule fragment, obtained the competitiveness and compatibility of coal surface mixture adsorption to multi-component gas molecules.When the adsorption occurs between the coal surface and each kind of gas in gob area,the compatible order is that:oxygen＞steam＞carbon dioxide＞nitrogen＞carbon monoxide＞methane.The chemistry adsorption energy of oxygen molecule to coal surface -CH₂-NH₂ group and -CH₂-CH₂OH group is increasing with the increase of the number of adsorbed oxygen molecules,which shows quadratic curve relations; the chemistry adsorption energy of oxygen molecule to coal surface-CH₂-CH₃ group is cubic curve relations with the number of adsorbed oxygen molecules.The releasable energy of chemistry adsorption is much bigger than that of physical adsorption,the biggest one is 13.7 times of physical adsorption energy and the smallest is 1.3 times.The releasable average energy of chemistry adsorption is 2.8 times of physical adsorption releasable average energy.The average adsorption energy of physical adsorption to oxygen is 73.31KJ/mol,and the average adsorption energy of chemistry adsorption to oxygen is 205.8KJ/mol.All kinds of coals oxidation spontaneous combustion first occur in side chain groups that contain non-hydrocarbon atoms.The theoretical calculation indicates that,the coal surface mainly concentrates to the multi-oxygen molecules adsorption in the side chain groups as -CH2-NH2,-CH2-SH, -CH2-PH2 and groups with S,P.