First pilot scale study of basic vs acidic catalysts in biomass pyrolysis: Deoxygenation mechanisms and catalyst deactivation

• Published in: Applied catalysis. B, Environmental Environmental, 2018-12, Vol.238, p.346-357
• Main Authors: Kalogiannis, K.G., Stefanidis, S.D., Karakoulia, S.A., Triantafyllidis, K.S., Yiannoulakis, H., Michailof, C., Lappas, A.A.
• Format: Article
• Language: English
• Subjects: Aldehydes; Aldol condensation; Alkali metals; Base catalysts; Basic oxides; Basicity; Biofuels; Biomass; Biomass catalytic pyrolysis; Carbon dioxide; Catalysis; Catalysts; Condensates; Deactivation; Deoxygenation; Fluidized beds; Ketonization; Magnesite; Magnesium; Magnesium carbonate; Magnesium oxide; Metals; Pyrolysis; Superconductors (materials); Zeolites
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2018.07.016

[Display omitted] •First study of MgO basic catalyst in pilot scale biomass pyrolysis unit.•Deoxygenation, coke production mechanisms on MgO basic sites studied.•MgO catalysts efficient in deoxygenating bio-oil via carbon coupling reactions.•MgO deactivation due to sintering effects, no biomass alkali metal deposition.•Basic catalysis a potentially efficient alternative to expensive acidic zeolites. In order for catalytic biomass pyrolysis to be economically sustainable, low cost and highly efficient catalysts are needed. In a previous work, Magnesium oxide (MgO) basic catalysts produced from natural magnesite (MgCO3) were found to be highly efficient alternatives to zeolitic catalysts which apart from their relatively high cost, they are easily deactivated due to biomass alkali deposition. In order to validate these findings in pilot scale, these natural MgO catalysts were investigated in a circulating fluidized bed pilot scale unit and were compared to a commercially available ZSM-5 catalyst. This is to the best of our knowledge the first attempt to evaluate a basic catalyst in biomass fast pyrolysis in a pilot unit employing commercially relevant process technology. The basic sites of the MgO catalysts enhanced ketonization and aldol condensation reactions, as it was verified by 2DGC-TOFMS analyses of the produced bio-oils. Deoxygenation was achieved mainly via formation of CO2, while H2O yield was substantially reduced in comparison to the ZSM-5 catalyst. As a result, bio-oils richer in hydrogen were obtained by the use of MgOs. However, the MgO catalysts led to a significant increase of the catalytically produced coke compared to ZSM-5. The effect of MgO properties, such as surface area and basicity on product yields and bio-oil composition was elaborated. In contrast to the acidic ZSM-5, no alkali metals were found to deposit on MgO, indicating different deactivation mechanisms between acidic and basic catalysts in biomass fast pyrolysis.