Abstract
AbstractThe catalytic performance of a set of technical, zeolite ZSM‐5 extruded materials have been studied in a bench scale unit for the ex‐situ Catalytic Fast Pyrolysis (CFP) of lignocellulosic biomass. The set of catalysts include micro‐ and mesoporous materials, with and without ZrO2‐promotion, with different Si/Al ratios and with micro‐ and nanosized zeolite crystals. Mesoporosity, acidity and crystal size play a key role on the overall catalytic performances in terms of activity and selectivity (i. e., in their ability to obtain the highest bio‐oil fraction with the lowest oxygen content), and also importantly, stability. Detailed post‐mortem bulk and micro‐spectroscopic studies of the solid catalysts complement the catalytic testing. The obtained results point towards coke deposits as the main cause for catalyst deactivation. Details of the nature, formation and evolution of these coke deposits revealed essential insights, which serve to evaluate the design of catalysts for the ex‐situ CFP of biomass. In particular the mesoporous catalysts are overall better preserved with increasing time‐on‐stream and deactivate later than their microporous counterparts, which suffer from pore blockage. Likewise, it was seen that ZrO2‐promotion contributed positively in the prevention against deactivation by hard coke spreading, thanks to its enhanced Lewis acidity. The zeolite's crystal size is another important characteristic to combine the different components within catalyst bodies, ensuring the proper interaction between zeolite, promoter and binder. This is illustrated by the nanocrystalline ZrO2/n‐ZSM‐5‐ATP material, which shows the best catalytic performance.
Highlights
In the case of the desilicated ds-ZSM-5-ATP catalyst, a microporous material with additional mesoporosity, the Ar isotherm is between type I to type IIb[31] with a steep H3 hysteresis loop (Figure S2b).[32]
The catalyst performance and stability of the zeolite ZSM-5 based materials in the ex-situ catalytic fast pyrolysis of oak was assessed in a continuous bench scale unit .The tested run times (10–25 min) are long enough to determine the catalyst lifetime, as shown in a preceding work[44] where no substantial deactivation occurred at longer TOS, being the early stages essential to develop the deactivation signs
A series of tailored zeolite ZSM-5-based technical catalysts were tested for ex-situ Catalytic Fast Pyrolysis (CFP) of oak biomass for bio-oil production, comparing and connecting the influence of their respective physical properties with the obtained performance, tips that serve for designing optimal catalyst systems
Summary
But, at the expense of strong acidity-;[10] 2) promotion with ZrO2, anticipated to decrease the amount of strong acid sites and provide bifunctionality, limiting excess cracking to enhance biooil yield;[26] and 3) the interdependence of Si/Al ratio and crystal size, with lower Si/Al ratios typically leading to increased catalyst deactivation rates,[27] while acidity depends on the Si/Al ratio, and on the crystal size.[28] the studied catalyst materials include a micron-sized, standard zeolite ZSM-5 (with a Si/Al ratio of ~ 18); a desilicated version of the former (Si/Al ratio of ~ 9), denoted as ds-ZSM-5, promoted or not with 10 wt % ZrO2; and a nanocrystalline ZSM-5 (Si/Al ratio of ~ 42, n-ZSM-5), ZrO2-promoted.[29] All four samples were extruded with 30 wt % attapulgite as binder. The effect of coke on the textural, acid and structural properties are object of this study
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