From brewers’ waste to fuel precursors: Catalytic pyrolysis of BSG using CaO and Nb2O5-based catalysts for enhanced hydrocarbon production

Abstract

This study investigates the impact of calcium oxide (CaO) and niobium oxide (Nb₂O₅) catalysts on the analytical pyrolysis of brewer's spent grain (BSG) at temperatures of 550, 650 and 750 °C. The results demonstrate that CaO and Nb₂O₅ based catalysts reduced oxygenated compounds and enhanced the formation of lighter hydrocarbons. At 550 °C, the hydrocarbon relative yield increased from 2.4 % under non-catalytic conditions to 18 % with FeCaO catalyst. The inclusion of iron in the catalysts contributed to improved vapor quality and stability, leading to superior hydrocarbon conversion rates. An increase in hydrocarbon production was observed across all catalysts at various pyrolysis temperatures. Regarding oxygenated compounds, catalytic tests at 650 °C and 750 °C resulted in a slight decrease in oxygenate relative yields, with Nb₂O₅ exhibiting the most significant reduction, dropping from 59 % to 44 % and from 56 % to 40 %, respectively, compared to non-catalytic conditions. Conversely, at 550 °C, the catalyst's impact on oxygenate relative yields was minimal. A comparison between catalytic and non-catalytic tests at 550 °C revealed a reduction in the relative yield of oxygenated compounds with three or more oxygen atoms, from 32 % to below 12 %, while compounds containing one oxygen atom increased from 2 % to 31 % when using FeCaO catalyst. This trend persisted across all catalytic conditions, suggesting partial deoxygenation of oxygenated compounds. Increasing the pyrolysis temperature consistently contributed to deoxygenation across all catalysts. These findings contribute to the advancement of bio-oil production technologies from biomass resources.