Investigation On The Characteristics Of Metal-loaded Biochar Gasification And Catalytic Volatile Reforming

Biomass gasification technology can convert low-quality biomass into high-quality synthesis gas under relatively mild conditions.However,the two major problems associated with tar in the gasification process and the difficulty of coke gasification hinder the development and application of biomass gasification technology.Biochar catalyst catalytic tar conversion technology can catalytically crack/reform tar into hydrogen-rich gas products.In addition,biochar catalytic gasification is also an efficient biomass energy conversion and utilization technology.By changing the reaction conditions and adding catalysts,the control of biochar gasification products can be achieved.This article chooses cotton stalk as a typical sample of biomass.The reaction mechanism of the catalytic volatile reforming of the biochar catalyst prepared by metal modification was discussed,and the gasification characteristics of the biochar catalyst itself and the preparation process of catalytic pyrolysis were paid attention to.First,the effects of metal types and nickel loading ratio on the catalytic pyrolysis characteristics of biomass and the catalytic volatile reforming characteristics of metal-modified biochar were investigated in a fixed-bed reactor.The yields of liquid products of cotton stalk pyrolysis after immersion in nickel,iron,and calcium nitrate solutions all decreased,while the yields of solid products increased.Increased gas yield in pyrolysis products of cotton stalk after loading nicke,especially the yield of H₂ and CO.For liquid products,the addition of nickel significantly increases the content of carboxylic acids and reduces the content of phenols.After loading calcium or iron,the content of aromatic hydrocarbons,carboxylic acids,esters and phenols in the liquid product of cotton stalk pyrolysis is significantly reduced,and the content of ketones is increased.The nickel-loaded biochar prepared by pyrolysis at 600℃ has much better catalytic effect on volatile reforming at 600℃ than calcium-loaded biochar and iron-loaded biochar.Increasing the proportion of nickel loading can not only increase the yield and content of H₂ in the product of catalytic pyrolysis of cotton stalk,but also promote the increase of the yield of H₂ in the product of catalytic volatile reforming of nickel-modified biochar.Then,biochar steam gasification experiments were carried out in a fixed bed reactor to explore the effects of carbonization temperature,gasification temperature,metal species and nickel loading on the gasification characteristics of biochar.The increase in the carbon production temperature will make the carbon structure more orderly,which will result in a decrease in the conversion rate of coke and a decrease in the yield of H₂ and CO.From the perspective of gas composition,the increase of gasification temperature is beneficial to increase the CO content in the gas product.In terms of gas yield,when the gasification temperature is lower than 800℃,the yield of each component in the gas product increases slowly with the increase of temperature;when the gasification temperature is higher than800℃,the CO₂ yield decreases slowly.Compared with the catalytic gasification performance of biochar loaded with nickel,iron and calcium,the catalytic gasification reactivity of biochar loaded with nickel can be significantly improved,but the gasification reactivity of biochar will be reduced due to excessive gasification consumption and excessive nickel loading.The presence of iron has a strong promoting effect on the water vapor shift reaction in the process of biochar steam gasification,and the addition of calcium can significantly promote the water gas reaction in the process of biochar steam gasification.Finally,the self-gasification and catalytic biomass gasification characteristics of metal-modified biochar were explored on the fixed-bed reactor.Both the self-gasification and catalytic biomass gasification of biochar modified by loading nickel,iron and calcium have obtained a higher H₂ yield than cotton stalk pyrolysis coke.The addition of nickel is more effective in increasing the yield of H₂ in the gasification products,and the addition of calcium is selective for the formation of CO in the gasification products.Among all the metal-modified biochar prepared at 800℃,the nickel-iron bimetallic biochar has the best self-gasification and catalytic biomass gasification performance.This may be due to the synergy between the extremely high catalytic activity of Ni for the decomposition of tar and the excellent redox ability of adjacent Fe.In addition,the formation of Fe Ni₃ alloy may also serve as an active site for catalytic conversion of tar.Through comparative studies,it can be seen that the nickel-loaded biochar prepared at 600℃ for catalytic volatile reforming at 600℃ achieves better catalytic performance and stability than the nickel-iron bimetallic biochar prepared at 800℃ for catalytic volatile reforming at 800℃.