Impact of pyrolysis heating methods on biochars with enhanced CO2/N2 separation and their incorporation in 3D-printed composites

Abstract

N-doped biochars, derived from chitosan sourced from waste crustaceous shells, were produced via microwave-assisted pyrolysis at temperatures ranging from 400 to 800 °C to enhance CO2 and N2 separation. Their performance was compared with biochars from conventional pyrolysis. Microwave-derived biochars exhibited superior CO2 adsorption capacity at 25 °C and 100 kPa (0.78 – 1.56 mmol g−1) compared to conventionally produced ones (0.55 – 1.43 mmol g−1). Increasing the pyrolysis temperature up to 600 °C significantly improved biochar properties, including surface area, pore volume, and CO2 adsorption capacity. Microwave-derived biochar featured enhanced surface area, larger pore volumes, and unique morphologies, requiring, on average, 61 % less preparation time. The higher ultramicroporosity and N-species concentration correlated with superior performance in the biochar produced at 600 °C. In gas mixture experiments (20 % CO2 and 80 % N2) under flow conditions, these biochars showed rapid adsorption/desorption rates due to enhanced macroporosity at samples produced at 600 and 800 °C, facilitating gas diffusion along the ultramicropores. Adsorption heat analysis indicated that the CO2 adsorption is predominantly driven by physisorption, supported by complete sample regeneration when applying N2 flux or increasing the temperature during desorption. The study also explores the feasibility of 3D-printing a composite using the most effective biochar and inorganic polymers sourced from waste, presenting potential benefits for industrial applications.