Study On The Preparation And Performance Of The Catalyst For Deoxidization Of Coal Bed Methane

Coal bed methane?CBM?is an unconventional gas,which is mainly composed of methane and found in coal seams.The resources of coal bed methane are abundant in our country,ranking three in thr world,only behind Russia and Canada.The application range of coal bed methane is wide and involves all aspects of production and life.The large-scale using of it can bring enormous economic value.Depending on the amount of methane in the coal bed methane,it can be divided into high methane content gas,medium methane content gas and low methane content gas.The utilization rate of high methane content gas has been reached 100%,while the rate of medium and low methane content gas is low,mainly because the problems about security and economic benefit which caused by the existence of the oxygen to its rational utilization,this is largely a waste of these resources.Therefore,the deoxygenating treatment of coal bed methane has become a hot spot all over the world.Studies show that,the most effective method of removing the oxygen in coal bed methane is the technology of catalytic combustion deoxidization.This method achieves removing effect by consuming a part of methane and oxygen combustion under the condition of poor oxygen and rich methane.Titanium dioxide carrier has become another excellent carrier besides SiO₂ and Al₂O₃,because the adjustability of the surface acidity and the strong interaction which can be produced between active metals.Active components generally use non noble metal oxides.Obviously,the preparation technology of catalysts is closely related to the efficiency of catalytic combustion deoxidation.In this paper,the TiO₂-aerogel carrier was prepared by sol-gel-atmospheric drying method.And then the metal nitrate as a precursor,EDTA as an auxiliary agent,the series of Ni?Cu/Fe?/TiO₂ non-noble-metal supported catalysts were prepared by orthogonal experimental design and impregnation method.The deoxidization performance was tested in the self-built devices.The structure,morphology and reduction properties of the samples were analyzed by XRD,FTIR,H₂-TPR,SEM and N₂ physical adsorption.The results showed that:?1?For the single metal oxide TiO₂ based catalyst,orthogonal analysis was carried out with the deoxygenation efficiency as the index at 500 ^oC.The direct analysis of the orthogonal experiments indicated that the catalyst possessed the highest deoxidization activity under the optimized preparation condition of n?Cu?:n?TiO₂?=30%,pH=7.0,calcination temperature of 400^oC.The deoxidization of the optimal catalyst reached 100%when the reaction temperature was 500 ^oC.It has smaller particle size,smooth surface and loose pore distribution.The influence of preparation parameters on Cu_xO/TiO₂ series catalysts was further investigated,and a better combination of parameters was obtained:n?Cu?:n?TiO₂?=40%,pH=8.0,calcination temperature of 400^oC.Its initial reduction temperature was 188.80 ^oC,hydrogen consumption was 54.46mmol/g.It has the best redox performance in all single metal oxide catalysts.?2?The influence rule of the preparation parameters,the active ingredient:the Cu catalyst is easy to gain the electrons,so the initial reduction temperature is the lowest and the deoxidization performance is the best.The Fe catalyst is easy to form Fe₃Ti₃O₁₀ solid solution,which is not conducive to reduction at lower temperature,resulting in reduced deoxidization performance.Loadings:a lot of metal oxides are prepared by high loading,and more metal oxides will provide more active sites.The catalyst with Cu loading of 40%is well dispersed,and the amount of hydrogen consumed by the first reduction peak is very large,while the hydrogen consumption of other catalysts is concentrated on the second reduction peak.Calcination temperature:the calcination temperature at 400^oC is enough to form the crystalline phase needed for catalytic reaction,and can maintain high specific surface area,so it has better deoxidization performance.The value of pH:metal oxides are obtained by decomposition of nitrate in acid environment.Metal oxides are obtained by dehydration of hydroxides in the middle alkaline environment.The latter is more conducive to the improvement of deoxidization properties.?3?For the double metal oxide TiO₂ based catalyst,orthogonal analysis was carried out with the deoxygenation efficiency as the index at 400 ^oC.The direct analysis of the orthogonal experiments indicated that the catalyst possessed the highest deoxidization activity under the optimized preparation condition of Cu-Ni,mole ratio of 0.1:0.3,pH=7.0,calcination temperature of400 ^oC.The catalyst reached 100%deoxygenation efficiency at 400 ^oC.Its dispersion is more uniform,with smaller pore size and more concentrated pore distribution.The combination of Ni active components and the other metal helps to improve the deoxidization performance,and Ni is the main active center.The composite metal oxide solid solution is easily formed at the lower Ni molar ratio,which is not conducive to the reduction at a lower temperature.The higher hydrogen consumption and lower initial reduction temperature are related to the excellent deoxidization performance.