Impact of ZSM-5 Deactivation on Bio-Oil Quality during Upgrading of Straw Derived Pyrolysis Vapors

Abstract

In this work, we provide detailed information on the change in product distribution and bio-oil 12 quality during extended feeding of biomass derived fast pyrolysis vapors over ZSM-5. The effect 13 of catalyst deactivation by coking on the resulting oil product characteristics was clarified in order 14 to determine when the vapor upgrading should be stopped and the regeneration initiated. Obtaining 15 a stable catalytic fast pyrolysis (CFP) oil while maintaining good energy recovery is important 16 within the context of potential co-processing these oils with petroleum feedstocks via FCC or 17 hydrotreatment of the whole CFP oil. 18 Wheat straw derived fast pyrolysis vapors were upgraded in an ex-situ fixed bed reactor containing 19 a steamed ZSM-5 catalyst at 500 °C. Oils were collected both for runs starting the upgrading over 20

Counteracting Rapid Catalyst Deactivation by Concomitant Temperature Increase during Catalytic Upgrading of Biomass Pyrolysis Vapors Using Solid Acid Catalysts

“…amounted to 74.4 wt%, 15.8 wt%, and 9.8 wt%, respectively. Compositional ash analysis obtained from the same feedstock (particle range 0-1.4 mm) has been reported earlier [27]. The content of N, C, H, S, and O (by difference) of the biomass feedstock on a dry and ash-free basis (daf) was 1.3, 48.2, 5.0, 0.1, and 45.4, respectively.…”

“…Fixed bed reactors are commonly operated using an excess of catalyst. While this ensures high conversion, higher catalyst loadings also lead to higher coke yields [27], which might be attributed to an "over-cracking" and the further reaction of the deoxygenated vapors. As an example, fully deoxygenated products, such as toluene, might encounter other strong acid sites further down the catalytic bed, leading to coke formation.…”

“…In the present work, the focus lies on upgrading biomass-derived fast pyrolysis vapors outside the pyrolysis reactor in a close-coupled catalyst reactor prior to vapor condensation (often termed ex situ catalytic fast pyrolysis). This process configuration can prevent the poisoning of catalytic active sites due to ash species [27][28][29] and allows for the independent temperature control of the pyrolysis and catalytic reactor. Using HZSM-5 as a catalyst, the selectivity of oxygen-free hydrocarbons (HCs) is highest in the initial upgrading phase over a fresh catalyst (at high rates of coke and light gas formation from cracking reactions and thus low organic liquid yield), and then gradually deteriorates due to the incomplete conversion of oxygenates.…”

“…Using HZSM-5 as a catalyst, the selectivity of oxygen-free hydrocarbons (HCs) is highest in the initial upgrading phase over a fresh catalyst (at high rates of coke and light gas formation from cracking reactions and thus low organic liquid yield), and then gradually deteriorates due to the incomplete conversion of oxygenates. The rate and extent of the deactivation of the catalyst by coking is therefore a major issue for its industrial implementation in this application [27,30]. Diebold and Scahill [31] already pointed out over three decades ago that a catalytic reactor, which can maintain a high level of catalytic activity in spite of high coking rates, would be desired.…”

“…The coking problem with zeolites can in principle be addressed by a conventional fluidized catalytic cracking (FCC) arrangement with continuous catalyst regeneration by the oxidation of the coke. However, significant carbon losses to coke and gas occur at the initial upgrading period over a freshly regenerated catalyst [27]. The initially high rate of coke deposition is followed by a much lower rate of coke deposition [30,[32][33][34][35].…”