Study On The Influence Of Modified Red Mud On The Properties Of Straw Catalytic Pyrolysis Products

Biomass catalytic pyrolysis technology is considered one of the effective methods for high-value utilization of straw,and has attracted more and more attention from domestic and foreign researchers.Seeking a low-cost and efficient catalyst is the key to achieving the industrial application of biomass catalytic pyrolysis liquefaction technology.As the waste residue after alumina extraction,red mud（RM）contains various metal elements with catalytic activity,which has a good catalytic effect on biomass pyrolysis.However,RM has strong alkalinity and is easy to sinter.If it is applied to biomass catalytic pyrolysis,it needs to be de-alkalized.Therefore,this article uses RM as the raw material to prepare de-alkalized red mud（ACRM）and nickel loaded de-alkalized red mud（ACRM-x%Ni）catalysts,analyzes their physicochemical properties,and explores the distribution pattern of corn straw products during the catalytic pyrolysis of modified red mud.The main research content and conclusions are as follows:（1）Using citric acid to de-alkalize RM,the effects of p H value and calcination temperature of red mud on Na⁺leaching rate were studied.The highest Na⁺leaching rate is 96.07%when calcined at p H=2,550℃.The characteristic Na peak on ACRM surface almost disappears,the diffraction peak of calcite and sodalite phase weakens,and the content of catalytic elements increases;The polymerization degree of aluminate is reduced,and its structure and properties are more stable;The specific surface area and pore volume significantly increased,and the strength of moderately strong acidic sites significantly increased.（2）Conducted experimental research on ACRM catalytic pyrolysis of corn straw.ACRM promotes a significant increase in phenolic content;Promote the breaking of cellulose glycosidic bond and reduce the sugar content;The enhancement of strong acidic sites promotes glucose dehydration and rearrangement,increases the content of furans,and decreases the content of aldehydes and ketones,with little impact on acids.（3）Analyzed the catalytic characteristics of Ni supported catalysts.The polymerization degree of silicoaluminate on ACRM-x%Ni catalyst is reduced,and it is easier to decompose into oxides;The mesoporous content significantly increased,with ACRM-12%Ni having the highest specific surface area;The actual load of Ni base is basically consistent with the theoretical value,and the load is effective;As the loading amount increases,the catalytic oxide reducibility increases.（4）Explored the influence of ACRM-x%Ni catalyst on the properties of corn straw pyrolysis products.ACRM-x%Ni increases the yield of non condensable gases and increases with the increase of Ni loading.For non condensable gas components,the CO and H₂ contents significantly increase compared to before loading,and decrease with the increase of Ni based loading amount.The CO₂ content gradually increases with the increase of Ni based loading,while the changes in CH₄ and C_nH_m content are relatively small.The H₂,CO,and CH₄ generated by ACRM-12%Ni catalysis have higher combustible gas content and lower CO₂ content.ACRM-x%Ni increased the yield of bio-oil,with the highest yield of 35.97%at ACRM-12%Ni.The relative content of phenols in bio-oil gradually decreases with the increase of Ni loading.ACRM-x%Ni promotes partial hydrogenation of phenol,ketolation reaction,and Piancatelli rearrangement reaction of furfural,which is beneficial for the generation of 1-hydroxy-2-acetone and cyclopentanone,and increases the content of ketones.ACRM-x%Ni enhances furan deoxidation reaction and promotes the generation of benzofurans through lignin pyrolysis;In addition,Ni groups can also promote the decomposition of furan,generating CO,vinyl ketones,etc.The ester content increases,while the changes in alcohol and sugar content are relatively small.After Ni based loading,except for ACRM-12%Ni,the acid content in bio oil slightly decreased.ACRM-12%Ni reduced the number of compounds with lower content in bio oil,and the main components acetic acid,1-hydroxy-2-acetone,and furfural were enriched,which is conducive to the subsequent improvement and application of bio oil.（5）The structural changes and catalytic performance of regenerated catalysts were studied.The pore structure of the regenerated catalyst has deteriorated,but ACRM-12%Ni-r1 still has high catalytic activity and stability.The gas yield,combustible gas content,bio-oil yield,and main component content have relatively small changes,which is conducive to obtaining bio-oil and gas products with relatively stable physical and chemical properties.This provides a stable source of raw materials for subsequent bio-oil upgrading and modification,and is conducive to the development and utilization of bio-oil.This study provides data support and reference for the development of low-cost catalysts,improving pyrolysis efficiency,obtaining stable physicochemical properties of bio-oils,and achieving selective catalytic pyrolysis for the preparation of high value-added chemicals.