In-situ catalytic upgrading of biomass pyrolysis vapor: Using a cascade system of various catalysts in a multi-zone fixed bed reactor

Abstract

The in-situ catalytic upgrading of palm kernel shell (PKS) fast pyrolysis vapors was performed over each individual meso-H-ZSM-5, Ga/meso-HZSM-5 and Cu/SiO2 catalyst or a cascade system of them in a multi-zone fixed bed reactor. The effects of mesoporosity creation into the parent H-ZSM-5 catalyst and also gallium incorporation into mesoporous H-ZSM-5 on the produced bio-oil chemical composition and distribution were studied. Key upgrading reactions for different oxygenated compounds in pyrolysis oil (small oxygenates, lignin derived and sugar derived components), including aldol condensation, alkylation, hydrogenation, aromatization, and deoxygenation were discussed. The catalysts were characterized using SEM, XRF, XRD, N2 adsorption and NH3-TPD methods. Furthermore, the produced bio-oils (catalytic and non-catalytic) were analyzed using GC–MS, FTIR, CHNS/O elemental analyzer and Karl Fischer titration. Production of the upgraded bio-oil with lower content of oxygenated compound was the main objective of this investigation. Among different catalysts, meso-H-ZSM-5 zeolite demonstrated a very good activity in aromatization and deoxygenation during the upgrading of pyrolytic vapors, although it decreased the bio-oil yield (32.6wt.%). The gallium incorporation into the meso-HZSM-5 zeolite increased the bio-oil yield from 32.6wt.% (meso-HZSM-5) to 35.8wt.% (using 1.0wt.% Ga). Furthermore, the aromatics selectivity was enhanced when the appropriate amount of gallium (1.0wt.%) was introduced. A cascade system of various catalysts comprising meso-HZSM-5, Ga (1.0wt.%)/meso-HZSM-5 and Cu (5.0wt.%)/SiO2 indicated the best performance on aromatics formation (15.05wt.%) and bio-oil deoxygenation through small oxygenates, lignin derived phenolics and sugar derived compound conversion, respectively.