T. J. Mountziaris

The effects of contact time and coking on the catalytic fast pyrolysis of cellulose

The effects of catalyst contact time (WHSV−1) and coking on catalytic fast pyrolysis of cellulose with ZSM-5 were studied in a bubbling fluidized bed reactor. Because coke interferes with catalyst activity, the effect of catalyst contact time was studied at coke loadings known not to deactivate the catalyst. CO and CH4 are favored at low catalyst contact times ( 10000 s). At increased time on stream, the catalyst lost activity due to coking. The majority aromatic-producing activity was lost after site turnovers of 95 (cellulose monomers to Bronsted sites) corresponding to a weight turnover of 2.0 (feed weight to catalyst weight). Accumulated coke deactivates the catalyst by both filling the micropores and blocking the acid sites.

The effects of ZSM-5 mesoporosity and morphology on the catalytic fast pyrolysis of furan

ZSM-5 catalysts with different morphologies were synthesized and evaluated for the catalytic conversion of furan in a fixed bed reactor to provide insights into the rational design of zeolite catalysts for catalytic fast pyrolysis (CFP). The effects of mesoporosity and morphology of ZSM-5 catalysts on the production of aromatics and olefins as well as catalyst deactivation were investigated. The results suggest that increasing mesoporosity and decreasing crystallite size can increase furan conversion and affect selectivity to products. Improved selectivities to benzene, toluene, xylene and olefins were achieved with mesoporous ZSM-5 and 100 nm ZSM-5 compared to 800 nm ZSM-5. Coke formation on zeolite catalysts during the reaction of furan was also largely reduced (up to 65%) by introducing mesoporosity. It was observed that coke is mainly formed and accumulated inside the micropores of ZSM-5 catalysts rather than on the external surface or within the mesopores. Characterization of mass transport in the coked zeolite samples using cyclohexane as a probe molecule suggested that coke blocks micropores, leading to a decrease in micropore volume during the catalyst deactivation process. However, due to the three-dimensional pore structure of ZSM-5, the mass transport properties of mesoporous ZSM-5 do not exhibit an apparent change. Catalyst deactivation was mainly due to the coverage of active sites by coke, rather than the blockage of the transport pathways by coke.