Catalytic Conversion Of Bio-syngas To Enrich Hydrogen And Methane

Natural gas is a clean and efficient energy source,and its demand has continued to grow in recent years.However,the reserves of natural gas are insufficient and unevenly distributed,and are highly dependent on foreign sources.The technology of using renewable biomass to prepare synthetic natural gas（SNG）through gasification-methanation has received extensive attention due to its low pollution,low investment risk and broad market.Aiming at the problems of long process and high energy consumption in the traditional biomass SNG synthesis process of natural gas,and combined with the two major technical problems that the gasification tar is difficult to remove and the methanation process is not mature,the methanation coupled with tar reforming process was studied in this paper,that methanation,tar reforming,WGS and CO₂absorption can Simultaneous react to produce high hydrogen and methane mixed gas with high concentration from bio-syngas by this way.Firstly,a nickel-supported catalyst with tar reforming,methanation and CO₂ absorption activities was designed and prepared.The structure of the catalyst was characterized by XRD and N₂ adsorption in 77K.The CO₂ adsorption performance was tested thermogravimetrically while the methanation performance and tar reforming performance were investigated in a fixed bed reactor.The calcium aluminate cement is used as the forming aid to improve the abrasion resistance of the catalyst,and introduces the inert component Ca₁₂Al₁₄O₃₃,which can resist high temperature.The Mg O from dolomite combines with Ni to form a stable Ni O-Mg O solid solution,which disperses helps maintain the dispersion of Ni in the reaction process.Nickel as the active component of tar reforming and methanation reaction,its optimum loading capacity is 8%.Methanation activity is the highest at 500℃,and the CO₂ conversion and CH₄ selectivity are 66.7% and 85.9%,respectively.Using toluene as the tar model substance,the tar reforming activity of the catalyst is strongest when the reaction temperature was 650℃.Compared with the catalyst 8Ni/Al₂O₃,the catalyst 8Ni/C-Dolomite has higher tar conversion rate and hydrogen yield.It shows that the catalyst can effectively catalyze tar reforming and produce hydrogen.The dolomite component can absorb CO₂ and promote the WGS reaction and reforming reaction,which is conducive to hydrogen production.The H₂ yield of 8Ni/C-dolomite is 5.36mol/mol,which is higher than 8Ni/Al₂O₃.In addition,8Ni/C-dolomite has good CO₂ sorption cycle stability,and the CO₂ sorption rate is stable at about 0.08 g _CO2/g_catafter 8 cycles.The methanation coupled with tar reforming activity of 8Ni/C-dolomite was tested in a free-fall reactor coupled moving bed reactor.When the temperature gradient is 500-700℃,8Ni/C-dolomite can reduce the tar content by 78.7%,and increase the gas yield from0.69Nm³/kg to 1.11Nm³/kg.It can significantly increase the H₂ content,and increase the mixture content of H₂ and CH₄ by 31.6%.Iit is found that the reduction effect of the catalyst was not good in the upper region of the reactor,which may be the reason for the inobvious catalytic effect of the catalyst for methanation reaction.In addition,8Ni/C-dolomite can effectively promote the cracking of PAHs,and can reduce the yield of tar and enrich naphthalene and anthracene at the same time,which the relative contents of the two increase by95.5%and 31.9%,respectively.The catalyst also can completely remove the sulfur component in tar and has good desulfurization performance.