Green and simple approach for low-cost bioproducts preparation and CO₂ capture

This study has demonstrated, for the first time, a simple, fast and flexible microwave processing method for the simultaneous preparation of bio-products (bio-oil, bio-gas and biochar) using a methodology that avoids any form of catalyst or chemical activation. The dielectric properties of biomass and physicochemical characterisation such as TGA, elemental and proximate analysis, XRD, SEM/EDX and textural properties, showed that 8 kJ g^-1 of microwave energy can produce superior biochars for applications in CO₂ capture. The maximum CO₂ uptake capacity for biochar produced was 2.5 mmol g^-1 and 2.0 mmol g^-1 at 0 and 25 °C and 1 bar, which and also exhibited high gas selectivity compared with N₂, fast kinetics of adsorption (<10 min) and desirable reusability (>95%) after 20 cycles. GC-MS analysis of generated bio-oil products revealed that higher microwave energies (>8 kJ g^-1) significantly enhanced the amount of bio-oil produced (39%) and specifically the formation of levoglucosan, furfural and phenolics compounds, and bio-gas analysis identified trace levels of H₂ and CH₄. The results from this study confirm a green, inexpensive and efficient approach for biomass valorisation which can easily be embedded within bio-refinery process, and also demonstrates the potential of biochars for post-combustion CO₂ uptake.