New Controllable Method Of Methane Conversion

In recent years, the continuing shortage of crude oil supply, an increasingly acute contradiction between the supply and demand, the increasing depletion of oil resources have already been an indisputable fact. According to some reports, the world's oil reserves available for human use would last about 30-40 years. As our country is short of oil, the situation of the oil supply is particularly prominent. The available oil reserves are keeping dwindling and we are facing severe challenges in energy and raw material supply. In terms of feedstock resources, it is generally believed that the basic national situation is aboundant in coal, shortage of oil and lack of gas in China.However, from the point of effective use of components, this is not the case. Being similar or same with natural gas in composition, properties, the carbon resources (including natural gas, coal-bed methane, natural gas and methane hydrate), which all have methane as the main component, are extremely rich among all natural resources. Natural gas resources are richer than the oil, which has been estimated to meet the needs of the world for more than 120 years. The main components of coal-bed methane which are similar to nature gas are methane. It is proven that the coal-bed gas buried in the depth of 2000 meters underground are about 240 trillion cubic meters reserve, which is more than twice as much as nature gas. China's coal-bed methane resources are very aboundant, ranking the third in the world; At present, it is internationally recognized that the world's total reserves of gas hydrates on earth are as much 2 to 3 times as the grand sum of all coal, oil and natural gas, which would last more than 1000 years for human use (but it is so pity that the technology has not been put into practice in mining). Marsh gas(being methane as the main component) from biomass are reproducible resources. In addition, compared with oil and coal, they have the advantages of cleanness and high calorific value as an energy. Therefore, such resources are so important that they attract worldwide attention and make nearly all countries in the world to make effort to develop and utilize such resources, which is the best choice in improving the environment and maintaining sustainable developement.However, the biggest obstacle widely to use methane is its thermodynamic stability. The work of the doctoral thesis is aimed at realization of methane conversion through halogenation of methane with higher selectivity around normal pressure at lower temperature by photochemistry; or through thermal reaction of methane by some metals or rare metals promoted HZSM-5 zeolite as catalysts in mixture of methane and ethylene or some low alkanes; by synthesis of a series of iron phosphate supported mesoporous materials as catalysts by a simple one-step synthetic method.The thesis has four parts as follows:Part I Methane Iodination By PhotochemistryIn this part, the methane reactor for the photochemical gas reaction of methane with iodine was designed at first, and iodination reaction of methane by light have been studied. Some results are showed that the available light wavelength must be ultraviolet and the yield of methyl iodide is very low, which makes the process unpractical.Part IIMethane Bromination By PhotochemistryWithout addition of any catalyst, our research in this part focus on high activation of methane with higher selectivity via bromination reaction by photochemical method, since the products (bromomethane and dibromomethane) can be easily converted into methanol and formaldehyde. Through our effort on the choice of light sources, design and manufacture of special reactor, controlling reaction temperature and changing some other factors, an outstanding results is obtained. The products( bromomethane and dibromomethane) are synthesized with high selectivety (8.0% and 85% respectively) and 98% conversion based on bromine at the temperature of 16～140℃around atmosphere pressure. The available light wavelength for methane bromination is visable. The results are better than any other reported in the world.Part IIILow-Temperature Activation of Methane over some metals or rare metalspromoted HZSM-5 zeoliteIn this part, methane conversion in the presence of ethylene has been investigated. It shows that methane can well be activated in the presence of ethylene over rare earth metal or Ce-Mo, or Cr-Mo promoted Zn/HZSM-5 at lower temperature (450℃-520℃) . Especially, methane can be converted to higher hydrocarbons, including aromatic compounds at much lower temperature (723K) over Gd promoted Zn/HZSM-5, and at the same time methane conversion is relatively high (about 37%). In addition, the catalyst (Gd promoted Zn/HZSM-5) has longer life-time than Ga/HZSM-5 does.Part IVDirect Synthesis and Characterization of Mesoporous SBA-15 Loaded FePO₄MaterialsMesoporous SBA-15-loaded FePO₄ materials (FePO₄/SBA-15) have been directly obtained by a simple one-step synthetic method. The investigation results from the X-ray diffraction, transmission electron microscopy, electron spin resonance, ³¹P solid-state MAS-NMR, and N₂ adsorption-desorption analysis indicate that Fe and P are successfully loaded on the mesoporous SBA-15 in the form of FePO₄. From the characterization, the direct synthesized mesoporous FePO₄/SBA-15 materials are revealed the well textural properties and the ordered mesostructures. FePO₄ supported on mesoporous SBA-15 has the uniform dispersion state, even at 70wt% high loading amount. From our experiments, some conclusions are obtained that the catalysis of the direct synthesized mesoporous FePO₄/SBA-15 materials in partial oxidation of methane to formaldehyde is as much 100 times as that of indirect synthesized FePO₄/SB A-15. The catalysis of direct synthesized mesoporous FePO₄/SBA-15 is also better than that of the silica-supported FePO₄.