Catalytic fast pyrolysis (CFP) is a promising technology for producing liquid hydrocarbons from lignocellulosic biomass. Rapid coking and catalyst deactivation are significant problems during CFP, and the objective of this work was to determine the role of cellulose and lignin in the deactivation of HZSM-5, a widely applied CFP catalyst. Catalyst deactivation was followed by upgrading successive samples of pine pyrolysis vapors over a single bed of catalyst, and catalysts collected at a cumulative biomass-to-catalyst ratio of 1 were characterized by thermogravimetry, ammonia temperature programmed desorption, and physisorption. Different deactivation mechanisms were found for cellulose and lignin. Coking by cellulose resulted in a rapid decrease of aromatics formation and loss of ZSM-5 acid sites and micropore surface area. In contrast, coking by lignin resulted in fast breakthrough of oxygenated compounds but continued aromatics formation at a relatively constant rate and high retention of micropore surface area. It was concluded that cellulose pyrolysis vapors generate coke as an extension of the aromatization reactions on the active sites whereas deposits by lignin saturate the surface and prevent surface cracking reactions. The catalyst from CFP of pine closely resembled that from CFP of cellulose, suggesting that the decrease in aromatics formation during CFP of biomass is primarily caused by coke generated from cellulose and other polysaccharide components.

Role of cellulose and lignin in catalyst deactivation during catalytic fast pyrolysis over HZSM-5

256th National Meeting (2018)

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