Preparation Of New Calcium-based Composite Absorbents By Sol-gel Method And Tar Reforming Investigation

Absorption Enhanced Reforming?AER?gasification technology has the advantages of producing high-purity H₂ syngas and at the same time achieving the pre-combustion capture of greenhouse gas CO₂,which is of great use for improving energy efficiency and coping with the global climate transformation.The key point of this technology is to obtain the calcium-based absorbent which has the advantages of good recycling activity,high mechanical strength and efficient removal of biomass gasification tar.In this investigation,a new method of synthesizing calcium-based composite absorbent based on sol-gel method is proposed.Based on the balance between the cyclic carbonation activity and mechanical strength of the absorbent,the physical and chemical characteristics of the new absorbent are studied,and the parameters are prepared.The influence laws of the physical and chemical properties clearly define the preparation method of the new calcium-based composite absorbent and optimize the preparation parameters.Using the prepared novel calcium-based composite absorbent,the steam distillation reforming experiment of typical tar components,toluene and 1-methylnaphthalene,is carried out to verify the advantages of the new calcium-based composite absorbent relative to the common calcium-based absorbent.The effects of reforming reaction conditions on the removal of tar were also investigated.Optimum reaction conditions are obtained for reference for the popularization and application of this technology.The new calcium-based composite absorbent sol-gel process is mainly divided into two steps:First,the CaO is coupled with the aluminum precursor;then,the obtained solid is mixed with the iron precursor,and the pH of the solution is adjusted by using citric acid.The key preparation parameters of sol-gel method,including calcium precursors and solvents,were studied.It is found that calcium acetate is used as the calcium precursor and citric acid as the solvent to adjust the pH of the solution.The chemical composition of the new calcium-based composite absorbers mainly include CaO,Ca₁₂Al₁₄O₃₃?mayenite?and Ca₂Fe₂O₅?brownmillerite?,and found to contain oxygen free radical chemical structure.In the cyclic"carbonation-calcination"reaction,the activity of the absorption of CO₂ by the novel calcium-based composite absorbent do not show a drastic decrease,which was attributed to the inhibition of CaO sintering by the mayenite.At the same time,the mechanical strength of the novel calcium-based composite absorbers is significantly increased.Compared with convensional CaO,the conversion rate of tar from toluene and1-methylnaphthalene is increased by 75.8%and 62.1%,respectively,and the generation rate of surface area carbon of absorbents is reduced by 57.6%and 64.4%,respectively.In the presence of a novel calcium-based composite absorbent,the main reaction pathways for the toluene and 1-methylnaphthalene rearrangements are dehydrogenation and demethylation,respectively.The reaction conditions have important influences on the tar reforming reaction.Reducing the reaction temperature,the amount of iron loading and H₂O/C molar ratio are not conducive to the removal of tar and inhibit the formation of carbon deposition.The new type of calcium-based composite absorbent obtained better tar reforming effect and the preliminary validation of the feasibility of the new calcium-based composite absorbent to be used in the fluidized bed reaction device is conducted.The optimum conditions for the reforming reaction with the new calcium-based composite absorbent are as follows:the reforming temperature is800?,the loading of iron is 10%and the molar ratio of H₂O/C is 2.