Study On Hydrogasification Of Bio-char For Ch₄ And Catalytic Mechanism Of Fe-CaO Catalyst

Natural gas is a high-quality,high-efficiency clean energy source.Driven by the economic transformation and environmental protection requirements,the gap between supply and demand is becoming more and more obvious.The use of resource-rich renewable energy biomass as a raw material to synthesize natural gas technology as a supplement is of great significance for improving our energy independence.Catalytic hydrogasifi-cation of bio-char to methane is a direct,efficient,emission reduction and low production cost synthetic natural gas method.As the core of this technology,catalyst is the current research hot topic.Fe-CaO catalyst has significant economic advantages,but it has the problems of induction time and un-reactive carbon in the application of coal char,which restricts further production applications.It is clear that understanding the cause of the above problems and the working conditions of the process can promote the commissioning of bio-char catalytic hydrogasification for natural gas.Based on above,this paper takes corncob pyrolysis char and Fe-CaQ catalyst as the main research objects,investigates the products distribution law of medium and high temperature pyrolysis in biomass and the optimal conditions for bio-char catalytic hydrogasification to methane.Through the comparison of bio-char and coal char catalytic hydrogasification,the causes of induction time and un-reactive carbon in the application of Fe-CaO catalyst were studied.The following conclusions were obtained:(1)The secondary reaction of volatiles in corncob during high temperature pyrolysis is obvious,and the secondary condensation reaction is more likely to occur than the cracking reaction.The influence of gas phase residence time on the distribution of gas and liquid products is opposite to that of low temperature pyrolysis.(2)The hydrogasification activity of the corncob char decreases with the increase of the final temperature of pyrolysis,and the specific surface area of the micropores increases,but it is difficult to carry out the reaction of hydrogasification to methane by the microporous structure of the char.At 800? and 1.5 MPa hydrogen partial pressure,the bio-char loading with 0.47 wt.%Fe and 0.56 wt.%CaO can show obviously catalytic effect.The optimal ratio of CaO/Fe is about 4.2,when The loading of Fe was 0.95 wt.%,and the loading of CaO was 3.98 wt.%,the yield of methane reached 80%after 473 minutes.(3)Fe-CaO does not exister induction time in the process of catalytic hydrogasification of bio-char to methane,but there is still unreacted carbon.The residual carbon is caused by the catalyst itself.Catalyst agglomeration,sintering and residual ash fusion overlap the active site of the remaining carbon which prevents the carbon from contacting H2,so that the carbon can not be converted.(4)The existence of induction time in Fe-CaO catalyst is related to sulphur in coal char.Sulphur makes the Fe poisoned and inactive.As the hydrogasification goes on,CaO can restore the activity of Fe,and then generate metallic Fe which has high catalytic activity and CaS.