Enhancement of aromatics production from catalytic pyrolysis of biomass over HZSM-5 modified by chemical liquid deposition

The catalytic pyrolysis of biomass is a promising technology for producing high-quality fuels and value-added chemicals. However, the development of this technology has been hindered by high coke formation and low target product yield. In this study, chemical liquid deposition (CLD) was adopted to improve the catalytic performance of HZSM-5 in the catalytic pyrolysis of biomass. The changes of the characteristics, including crystallographic structure, poroSity and acidity, of the HZSM-5 zeolite after modification were analyzed by XRD, N-2 adsorption-desorption, ETIR and NH3-TPD. The results showed that CLD modification reduced the mesopore volume, pore opening size and the number of external acid sites without changing the micropore structure. PyGC/MS (a pyrolyzer equipped with a gas chromatography-mass spectrometer) and kinetic analysis were used to analyze the catalytic performance of the parent and CLD-modified zeolites. It was found that the production of aromatics increased first and later decreased, reaching optimal levels at a 4% deposition of SiO2, while the selectivity of monoaromatics increased continuously. Additionally, CLD modification raised the energy barriers for the char/coke formation reactions and could inhibit its production. The deposition amount of 4% showed the best char/coke inhibitory effects for catalytic pyrolysis of cellulose, while the char/coke formation decreased continuously with the increase of the deposited amount of SiO2 for catalytic pyrolysis of lignin.