The New Process Of Oxidative Bromination Of Methane To Higher Hydrocarbons

Higher hydrocarbons are obtained in processes of petroleum refinery. It is a clean fuel. Recent years, the majoy process for the conversion of nature gas to liquiud fuels is initial from syngas, which is called Fischer-Tropsch process. But this is an energy consuming process. More than one fourth of natural gas must be burned to generate heat for the steam reforming of natural gas. Here, we developed a non-syngas process to synthesize higher hydrocarbons. In our process, the first step was to convert methane to methyl bromide by the reaction of methane with hydrogen bromide and oxygen, then, higher hydrocarbons were produced by the condensation of methyl bromide in the second step. By this method, methane could be high efficiently converted to higher hydrocarbons.In this paper, we synthesized higher hydrocarbons through two-step method.In the first step oxidative bromination of methane(OBM), methane was converted to bromomethane by reacting methane, oxygen, hydrogen bromide(40wt% in water) over 2.5%Ba2.5%La0.5%Ni0.1%Ru/SiO2 catalyst. The reaction was a strong exothermic reaction. We investigated the effection of oxygen ,hydrogen bromide ,the flux ratio of methane to oxygen and the CO co-feeding on the conversion of methane, the selectivity of CH3Br and CH2Br2, the selectivity of carbon monoxide and carbon dioxide. The results show that the conversion of methane was 26.8%, with the selectivities of CH3Br, CH2Br2, CO and CO2 were 85.0%, 2.0%, 10.1% and 2.9%, respectively under the conditions of 660℃HBr=6.0ml/h, CH4:O2=20ml/min: 5.0ml/min. In a CO co-feeding modle, a methane single pass conversion of 30.4, with the selectivities of CH3Br,CH2Br2,and CO2 were 86.5%,1.7% and 11.8% respectively. Trance of H2 was detected in the products. The gas phase from the first reactor was then directly fed into the second reactor to convert bromomethyl to higher hydrocarbons. We investigated the effection of catalysts, the reaction temperations, the reaction time and the condensities of oxygen on the reaction. We find that when the oxygen was nearly consumed up in the first step, the conversion of bomomethyl was over 98.0% on the catalysts of ZnO/HZSM-5 and MgO/HZSM-5 under the conditions of 240℃,reaction time for 2h or more. The products included alkanes, olefins and aromatics with two to thirteen carbon atoms.In this paper, we also discussed the mechanism of oxidative bromination of methane and condensation of bromomethane. In the research of OBM, the result showed that it was a radical reaction, under the reaction condition, the oxidation of bromomethane and the steaming reforming of bromomethane occured. CH₂Br₂ can be directly recycled back to the reactor and can be converted to CH₃Br. We also presumed the mechanism of condensation reaction of bromomethane. According to several experiments, we tend to believe that the reaction mechanism was similar to the"carbon pool"mechanism. However, we still do not know in detail. The research work is still in progress in this aspect.