The Catalytic Synthesis Of Higher Hydrocarbon From Methane Via Oxidative Bromination Reaction

Natural gas is considered as clean energy throughout the world. The proportion of natural gas in the world’s primary energy consumption is increasing with the continuous increasing price and the uncertainty supply of petroleum. It is expected that natural gas will replace petroleum as the first energy in2050. Methane is the major component of natural gas with more than80%content. Hence, the chemistry of natural gas is actually the chemistry of methane.The investigation of the dissertation proposed an alternative process for methane utilization to prepare value-added chemicals via non-syngas route. In the process, methane was firstly converted to methyl bromide in the presence of HBr and O2, then the as-synthesized methyl bromide was converted to liquid hydrocarbon and released HBr, which could be recycled in the reaction. Compared with the commercialized energy-consuming syngas route, both of the reactions are exothermic reaction, and no H2O is needed as reactant (contrarily, H2O is produced as by-product). Plants could be constructed at districts with short of water, such as desert or ocean, and stranded reserves, such as associated gas or coal bed gas.The investigation was focued in the following aspects:1) the catalytic performances of both the oxidative bromination of methane and the condensation of methyl bromide,2) the corrosion-resistant materials testing under OBM condition, and3) the HBr removal from product hydrocarbons. The catalytic performance of OBM reaction with CH3Br and CO as target products was also investigated, which could be used in acetic acid synthesis.In the investigation of OBM reaction, the active component, support, and preparation method of the catalysts were explored. Rh/SiO2prepared by sol-gel method showed the best performance. A methane conversion of35.6%with methyl bromide selectivity of more than90%was obtained over0.4Rh/SiO2-900-10. A catalyst lifetime of more than650hours was achieved. By adjusting catalyst specific surface area or manipulating the reaction conditions, different product orientation could be achieved.In order to fit the feedstock demanding in acetic acid synthesis, the catalytic performance of OBM reaction with both CH3Br and CO as target products was also investigated. Over a0.4Rh/SiO2-700-10catalyst with relatively high specific surface area (267.5m2/g), high methane conversion of76.2%with CH3Br and CO equi-selectivity of42.2%was obtained. In this case, the selectivity of CO2was suppressed to5.5%. The thermal stability of catalyst was also improved by optimizing catalyst preparation method.In the higher hydrocarbons synthesis from methyl bromide, product distribution and catalyst deactivation were investigated on2wt%MgO/HZSM-5catalysts with different Si/Al ratios. Catalyst with a Si/Al ratio of360/1had the best performance and the longest lifetime. A methyl bromide conversion of99.0%was maintained within400h. The major products were the C3-C8olefins. The fresh and used catalysts were characterized by XRD, BET, NH3-TPD, TG/DSC, and GC/MS methods. The characterizations showed that the carbon deposition depended on the acid strength of catalyst. The investigation showed that multi-methyl substituted aromatics were primarily formed on strong acid sites, which were responsible for the deactivation of catalyst. The mechanism of methyl bromide to hydrocarbon was also discussed.In the corrosion-resistant material testing, three different reaction conditions were selected:1) the reaction condition,2) the heat-exchange condition, and3) the transportation condition. A series of corrosion-resistant materials were tested under the three conditions by flake hanging experiments.A system for the removing of HBr from hydrocarbons was also designed. In the system, a regeneratable HBr absorbent was used to clear out and recover HBr. The absorbent is MOx/SiO2, which could remove HBr from products to reach a HBr concentration below4.6×10-1mol/L...