CO2 capture by olive pomace biochar: Effect of relative humidity, isosteric heat of adsorption, and a preliminary Life Cycle Assessment investigation

This study investigates the potential of olive pomace biochar, a low-cost agro-industrial byproduct, as an adsorbent for direct air capture (DAC) of CO 2 . The biochar was prepared via gasification and evaluated in terms of adsorption performance, regeneration, humidity influence, thermodynamic behaviour, isosteric heat and life cycle impact. The maximum CO 2 adsorption capacity was 17.68 mg g −1 at 10 °C, with stable performance maintained over five consecutive adsorption–desorption cycles, highlighting its short-term regenerability. The analysis of mass transfer mechanisms during adsorption included the application of an intraparticle diffusion model. The thermodynamic study confirmed the exothermic nature of CO 2 adsorption, with ΔH° values below 20 kJ mol −1 indicating the predominance of physical adsorption. Complementary XPS and FTIR analyses further supported this mechanism, revealing only weak interactions of CO 2 with oxygenated groups and mineral species on the biochar surface. The isosteric heat analysis confirms that once the critical hydration level is reached (humidity ≈18 mmol H 2 O/mol air), further humidity has no significant effect on CO 2 adsorption. The Life Cycle Assessment (LCA) showed that this system is environmentally favorable and achieves carbon-negative performance.