Catalytic Fast Pyrolysis (CFP) is a promising emerging technology for converting biomass to transportation fuels and chemicals. There is ample literature on catalysts that can be used to achieve effective deoxygenation of pyrolysis vapors, but little exists on the compositions and combustion kinetics of cokes that deactivate these catalysts. In this presentation, we compare catalytic coke formed on a HZSM-5 catalyst used in an FCC-type pilot-scale unit with coke formed on a Pt./TiO2 catalyst used in a packed bed reactor (PBR). Figure 1 shows a highly idealized schematic of the two CFP routes. The routes are both ex-situ: a thermal pyrolyzer produces pyrolates which are catalytically upgraded in a second reactor. The upgrading route shown on the bottom represents the “TCPDU R3” pilot-plant system at NREL. This system is based on the FCC process, and uses an HZSM-5 based catalyst with a particle size typical for FCC. Coked catalyst is obtained from the stripper outlet, and regenerated catalyst is obtained from the regenerator outlet. Also shown on the top is an alternate route being investigated at smaller scale. This unit, known as the “2FBR” uses a 1.37” diameter PBR containing 100 grams of Pt/TiO2 catalyst in the form of 0.5 mm spheres. Typically, the reactor is operated in a cyclical fashion. Coked catalyst is obtained by dissecting the bed after stripping but before regeneration. Regenerated catalyst is obtained after the regeneration is complete. Because of the high biomass to catalyst ratio (B:C) at the end of the pyrolysis runs, the Pt/TiO2 catalyst has very high levels of coke (20-25% of catalyst mass), whereas the HZSM-5 coke is much lower (&lt; 1%), typical for the FCC process. The two cokes were characterized by various means. Combustion kinetic parameters were determined using detailed FEM modeling of the regeneration process for the Pt/TiO2 coke, and approximate mixed-flow kinetic equations for the ZSM-5 coke.

Composition and combustion kinetics of catalytic fast pyrolysis (CFP) coke

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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