Bifunctional Ni‐ZSM‐5 Catalysts for the Pyrolysis and Hydropyrolysis of Biomass

Abstract

In this work, we explore pyrolysis options, namely, high pressure, H2, and metal‐loaded ZSM‐5 catalysts, to improve the limited deoxygenation capacity and reduce the excessive production of solids in biomass catalytic fast pyrolysis (CFP). Specifically, we explore the product selectivity of Miscanthus x giganteus CFP in inert or H2‐rich environments, pressures up to 450 psig, and over ZSM‐5 and Ni‐ZSM‐5. We show that higher pressures promote decarboxylation reactions, reduce the yields to liquids, and enhance the formation of solid products. Ni‐ZSM‐5 promotes decarboxylation, dehydration, and methanation reactions. The cofeeding of H2 at high pressures increases the selectivity to monoaromatic hydrocarbons with a parallel enhancement of the yield to saturated products. Solid products are reduced drastically in H2‐rich, high‐pressure experiments, and the CH4 selectivity increases. Based on these experimental findings, we present a reaction scheme that describes the impact of pressure, H2, and Ni on the product selectivity of biomass CFP.

Effect of the catalyst in fluid bed catalytic hydropyrolysis

“…Melligan et al [25,26] have shown that pyrolysis in a H 2 atmosphere at elevated pressure with a Ni-ZSM-5 catalyst significantly decreases the concentration of ethanoic acids in the bio-oil compared to performing the pyrolysis in He. Gamliel et al [27][28][29] investigated the difference between Ni supported on SiO 2 , Al 2 O 3 and ZSM-5 and found that ZSM-5 gave the lowest solid yield, thus the lowest solid yield was obtained with the catalyst with the highest acidity. They ascribed this to an increase in the acid-catalyzed decarbonylation and aromatization of anhydrosugars and furans to stable products prior to secondary polycondensation reactions [27].…”

The effect of ZSM-5 catalyst support in catalytic pyrolysis of biomass and compounds abundant in pyrolysis bio-oils

“…Pyrolysis experiments were performed using a pyrolysis gas chromatography (PyGC, CDS Analytical 5200HP) microsystem, according to experimental protocols presented in Gamliel et al [26]. Biomass and catalyst were physically mixed together in a catalyst to biomass (C/B) ratio of 5:1.…”

Transportation fuels from biomass fast pyrolysis, catalytic hydrodeoxygenation, and catalytic fast hydropyrolysis

“…Milligram scale pyrolysis-GC setups allow for fast pyrolysis of biomass and immediate product analysis [125,[351][352][353][354][355][356]. Catalytic fast hydropyrolysis is achieved by mixing the biomass with a catalyst and applying a flow of H2.…”

“…Using a similar Pyrolysis-GC setup, Gamliel et al [353,354] Fast pyrolysis investigations by Thangalazhy-Gopakumar et al [356] showed minor differences between He and H2 atmospheres, also for catalytic fast pyrolysis, however the H-ZSM-5 catalyst employed had no hydrogenation activity. Using H-ZSM-5 impregnated with Co, Ni, Mo, or Pt as catalysts for catalytic fast hydropyrolysis of pinewood at 27.6 bar improved the hydrocarbon yield compared to using the H-ZSM-5 catalyst [125].…”

“…[355] vs. 5/1 in refs. [353,354]). Performing non-catalytic fast hydropyrolysis at 650 °C and employing a downstream HDO reactor loaded with the Pd-ZSM-5 and operated at 300 or 400 °C increased the yield of cycloalkanes due to the hydrogenation of aromatics.…”