HZSM-5和MCM-41分子筛催化剂比例对油菜秸秆热解的影响

选取油菜秸秆为原料,利用不同比例均匀混合的HZSM-5/MCM-41进行在线催化热解油菜秸秆制备生物油试验,根据生物油有机相的理化特性、FT-IR、GC-MS分析和催化剂的BET分析结果,研究HZSM-5与MCM-41的混合比例对生物油品质的影响规律.结果表明随着混合催化剂中MCM-41质量分数的增加,生物油有机相产率、密度、运动黏度及O质量分数先减少后增加,C质量分数及高位热值先升高后降低,1,8-二甲基萘、对二甲苯、甲基萘等芳香烃类物质的选择性呈现先增加后减少的变化趋势,生物油有机相中羰基类物质的质量分数先减少后增加,酸性物质持续减少.当HZSM-5与MCM-41以1∶1混合时,生物油产率为18.68％,高位热值高达34.31 MJ/kg,生物油中烃类物质的质量分数为53.83％,羰基类物质的质量分数为6.35％.混合催化剂活性随MCM-41质量分数增加逐渐提高,当MCM-41质量分数超过50％时,混合催化剂的催化活性趋于稳定.

Effects of HZSM-5 and MCM-41mixing ratios on rape straw catalytic pyrolysis

In recent years,the number of fossil fuels is decreasing sharply,and the harmful gases produced by fossil fuel combustion endanger human health and pollute the environment,people are devoted to looking for the alternative fuels of fossil fuels.Biomass energy is a good choice,it is renewable and clean.But the biomass was always burned directly,it is a great waste of biomass sources.In order to reduce the waste of biomass resources and protect the environment,we studied the rapid pyrolysis and catalytic cracking technology to convert the biomass to liquid fuel,which we called the liquid bio-oil.Choosing rape straw as biomass raw materials,HZSM-5 and MCM-41 were used to catalyze the rape straw pyrolysis with different mixing ratios.The experimental instruments include electronic controller,catalytic reactor,pyrolysis reactor,vacuum pump,cold trap,cooling tower,bio-oil collector and connecting pipe.The rape straws were placed in the pyrolysis reactor,the catalysts were replaced in the catalytic reactor,the vacuum pump pressure was controlled at 5kPa and the temperature of the cooling tower was set to-20 ℃.According to the physical and chemical properties,FT-IR and GC-MS analysis results of organic oil and the BET analysis results of catalysts,we studied the effect of HZSM-5 and MCM-41 mixing ratios on the quality of bio-oil.The results showed that with the increase of MCM-41 content,the yield of bio-oil organic phase decreased first and then increased.The density,oxygen content and kinematic viscosity of refined organic oil decreased first and then increased,while carbon content and calorific value increased first and then decreased,when HZSM-5 and MCM-41 were mixed with 1∶1,the higher calorific value was 34.31 MJ/kg.The organic phase of refined oil showed six obvious absorption peaks,respectively,they were the absorption peaks of alcohols or phenols,aromatic compounds,acids and aldehydes,ketones,carboxylates,esters and substituted aromatic compounds.The mass fraction of aromatic hydrocarbon increased first and then decreased,while the mass fraction of carbonyl compounds showed the opposite trend,the mass fraction of acids was continuously reduced.With the increase of MCM-41 content,the catalytic activity and absorption capacity of mixed catalysts improved and tended to be stable when the mass fraction of MCM-41 was 50％.From these analysis results,we can speculate the catalytic cracking reaction mechanism of rape straw on HZSM-5 and MCM-41.Because of the large specific surface area and pore size of mesoporous molecular sieve MCM-41,most of the macromolecules in its pore channels can be decomposed into small molecules such as aldehydes,ketones and other small molecules by decarboxylation,dehydroxylation and ring-opening polymerization in the pore channels.These small molecules re-entered the pores of the microporous molecular sieve HZSM-5,and generated aromatic hydrocarbons,H2O,CO2 and CO through the decarbonylation,aromatization and deoxidation,and then the oxygen content in organic phase decreased,aromatic substances content increased,the acidity reduced,so that the quality of bio-oil was improved.This study could provide the experimental basis and the theoretical basis for the efficient utilization of biomass.