Reducing CO2 emissions in brewing industry through sustainable valorisation of brewer's spent grain using CO2-assisted pyrolysis

Abstract

The brewing industry confronts significant environmental challenges owing to the substantial CO₂ emissions and high energy consumption during the brewing process. To address these issues, this study proposes a sustainable platform for valorising spent brewer grain (BSG; a byproduct of the brewing industry) to reduce its carbon footprint. CO2 was utilised in the pyrolysis of BSG to enhance energy recovery in the form of pyrolytic gas while reducing carbon emissions. In the initial pyrolysis setup, the reactivity of CO₂ was limited owing to its low reactivity in the temperature range where most BSG-derived volatiles were generated. This limited the capability of CO₂ to enhance the thermal cracking of volatiles, thereby adversely affecting syngas production. To address this limitation, the setup was modified to provide additional thermal energy and incorporate a catalytic process. During catalytic pyrolysis, the presence of a catalyst significantly enhanced syngas production, and substantial CO₂ consumption was observed experimentally. The biosolid generated from catalytic pyrolysis was utilised for CO₂ capture. This dual approach (CO2-catalysed pyrolysis and subsequent CO2-adsorption using biosolids) reduced the net CO₂ emissions associated with brewing. Specifically, the CO₂ emissions for producing 1 L of beer were reduced from 202.7 g in non-catalytic pyrolysis to 11.5 g in the CO₂-catalysed pyrolysis. Additionally, the pyrolytic gases (H2, CO, and CH4) produced through this process is sufficient to satisfy the energy demands of the brewing industry. This would reduce the reliance on fossil fuels. The study demonstrated that valorising BSG through co-catalysed pyrolysis provides a viable and economically feasible pathway for achieving carbon neutrality in the brewing sector. This approach provides a model for sustainable brewing practices by addressing energy recovery and carbon reduction.