Reduction of CO2 captured in basic solutions with biomass as reducing agent and metallic catalysts†

Abstract

CO₂ capture and utilization technologies can make an important contribution to the decarbonization of industry. However, capture processes entail significant economic and energy costs, mainly associated with the purification, compression and transport of CO₂. These costs would be reduced if captured CO₂ could be transformed in situ into useful products, avoiding purification, compression and transport costs. This work presents a hydrothermal process in which CO₂ absorbed in aqueous solutions as bicarbonate is reduced with biomass waste to give formic acid as a joint product of the biomass and CO₂ transformation, and acetic and lactic acids as byproducts from the decomposition of the biomass. Several biomass materials are applied as reductants: softwood, sugarcane bagasse, sugar beet, cork, pine needles, vermicompost and pure cellulose as reference material. Moreover, different catalysts are tested to improve conversion yield: Pd(5%)/C and Pd(10%)/C, Ru(5%)/C and activated carbon. The best results (18% formic acid yield) are obtained using pure cellulose as biomass and Pd(5%)/C catalyst. The next best results are obtained with the biomasses with the highest cellulose content, such as wood (11%) and sugarcane bagasse (9%). Experiments performed with labelled H¹³CO₃⁻ as carbon source at 300 °C using the Pd(5%)/C catalyst demonstrate that over 70% of the produced formic acid is formed from the inorganic bicarbonate carbon source. These high yields of conversion using renewable biomass as reductant can contribute to improve the technical and economic feasibility of CO₂ capture technology.