活性炭和HY分子筛复合催化促进生物质热解挥发物转化机理研究

Catalytic conversion of biomass pyrolysis volatiles over composite catalysts of activated carbon and HY zeolite

生物油组成复杂,含氧量较高,制约其高值化利用。本研究以商业活性炭(AC)和HY分子筛为复合催化剂,通过改变催化区的装填方式研究其对稻草和杨木屑两种典型生物质热解挥发物提质的影响规律。结果表明,AC和HY分子筛装填方式影响生物质热解产物分布和生物油组成。在HY与AC按1∶1比例均匀混合(YACM)作用后,生物油产率最低。但YACM方式有利于生物油的脱氧和芳香烃的生成,稻草和杨木屑热解生物油中的芳烃含量在YACM作用下可分别由提质前的13.8%和8.0%提高至56.4%和53.1%。上层HY分子筛和下层AC(YTACL)的催化方式有利于酚类物质生成。对单环芳烃的选择性遵循YTACL>ACTYL>YACM,而对双环芳烃的选择性为YACM>ACTYL>YTACL。分析认为,AC孔径较HY分子筛小,酸性低于分子筛,其活性中心有助于呋喃化合物重排生成环戊酮、2-环戊烯酮、甲基环戊烯酮,后重排形成苯酚,因此,YTACL的装填方式对苯酚、甲酚、甲苯、乙苯、对二甲苯的生成有较好的促进作用。HY分子筛的酸性强,有利于芳构化反应发生,因此,ACTYL装填方式表现出对萘、甲基萘、蒽、芘的生成较高的选择性。该工作为生物油的组成调控以及芳烃和酚类物质的富集等提供重要指导。

Bio-oil has complex compositions and high oxygen content,which restricts its high-value utilization.Commercial activated carbon(AC)and HY zeolite were used as composite catalysts to study their effect on pyrolysis volatiles from rice straw and poplar sawdust by changing the mixing models of two catalysts.The results showed that the loading models of AC and HY zeolite obviously affected the products distribution and bio-oil components.The lowest yield of bio-oil was obtained when HY zeolite and AC were mechanically mixed at a mass ratio of 1:1(YACM).But the loading model of YACM was beneficial to the deoxidation and aromatic hydrocarbon generation.Under the model of YACM,the aromatics content in rice straw and poplar sawdust bio-oil can be increased from 13.8%and 8.0%without catalyst to 56.4%and 53.1%,respectively.However,the layered loading with upper HY zeolite and lower AC(YTACL)was favorable for formation of phenolic compounds.The selectivity to monocyclic and bicyclic aromatic hydrocarbons followed the order of YTACL>ACTYL>YACM,and YACM>ACTYL>YTACL,respectively.Compared with HY zeolite,AC catalyst possessed smaller pore size and fewer acidity,and the active sites of AC were conducive to rearrangement of furan compounds to generate cyclopentanone,2-cyclopentenone and methyl-cyclopentenone,and further rearrangement to form phenol.Therefore,the loading model of YTACL exhibited a promotion effect on the formation of phenol,cresol,toluene,ethylbenzene and p-xylene.The strong acidic sites of HY zeolite were favorable for the aromatization,so the loading model of ACTYL had good selectivity to the formation of naphthalene,methylnaphthalene,anthracene and pyrene.This work will provide a guide for products regulation from biomass pyrolysis and enrich aromatics and phenols in bio-oil.