Preparation Of Hierarchical Pore ZSM-5 Molecular Sieve And Its Catalytic Performance For The Production Of Aromatics From Biomass

Biomass catalytic fast pyrolysis(CFP)to aromatics is regarded as the most economical route for the preparation of bio-based aromatics.The CFP technology route adopts ZSM-5molecular sieve as a catalyst,but the main factor constraining the industrialization of this route is that the aromatics yield still needs to be further improved,that is,the conversion level of the catalyst needs to be improved.In order to solve the low aromatic carbon yield for cellulose thermal cracking catalyzed by conventional microporous ZSM-5 zeolites of hydrocarbons(with a 32.3% aromatic carbon yield),five different organosilylating reagents(OSA)are used in this study,such as methyltrimethoxysilane(MTS),propyltrimethoxysilane(PTS),octyltrimethoxysilane(OTS),hexadecyltrimethoxysilane(HTS),and octadecyltrimethoxysilane(DTS).Five kinds of hierarchical ZSM-5 molecular sieves were prepared by OSA-assisted synthesis,and the pre-crystallization time was optimized.The hierarchical ZSM-5 molecular sieves catalysts were characterized by XRD,N2 adsorption,SEM and NH3-TPD,and the catalytic performance of hierarchical ZSM-5 to catalyze cellulose thermal cracking to produce aromatics were studied.The relevance between characterization and catalytic performance provides technical support for the development of high-efficient catalytic pyrolysis of biomass to aromatics.Thus the main work of this study are as follows:(1)Five kinds of hierarchical ZSM-5 molecular sieves with mesopores and micropores were prepared using different OSA reagents.The effects of different OSA reagents on the structure of the prepared hierarchical ZSM-5 molecular sieves were investigated.The performance of cellulose thermal cracking reaction catalyzed by hierarchical ZSM-5 was evaluated and the best OSA reagent was selected.The results showed that the hierarchical ZSM-5 sample MZ-3 prepared via OTS had the highest aromatic carbon yield of 37.1%.(2)A series of hierarchical ZSM-5 molecular sieve samples were prepared by using OTS as an OSA reagent with variation of the pre-crystallization time.The influence of pre-crystallization time on the pore structure,mesoporosity,and the amount and the proportion of strong and weak acids of the prepared hierarchical ZSM-5 sieves were investigated.Through the performance evaluation of cellulose-catalyzed thermal cracking reaction,it determined that the best pre-crystallization time was 8 hours,the preparation ofhierarchical ZSM-5 zeolite sample MZ-3-8h,its aromatics carbon yield can increase to 38.6%,6.5% higher than conventional microporous ZSM-5 molecular sieve.(3)Through the relevance study on structural characterization of conventional microporous ZSM-5 molecular sieves and seven hierarchical ZMS-5 molecular sieves and the catalytic performance of catalytic pyrolysis of cellulose to produce aromatics,it determined that the active structure unit in the cellulose catalytic thermal cracking to aromatics reaction is the microporous structure of the MFI framework of the ZSM-5 molecular sieve,and the introduction of mesopores can increase the probability of the cellulose pyrolysis product entering the micropores of the MFI framework structure and further increase the yield of aromatic hydrocarbons.In the cellulose catalytic pyrolysis reaction,the yield of aromatics is mainly determined by the matching of mesoporous and acid sites.For hierarchical ZSM-5molecular sieves,the beneficial structural features for improving the aromatics yield are mesopore volume(Vmeso)between 0.162-0.166 cm3/g,total acid amount between 1.07-1.18mmol/g,and the ratio of strong acid to total acid between 0.65-0.69.