Turning plastic and biomass waste into adsorbents: CO2/CH4 separation and comparison with commercial carbons

Abstract

This work compares two commercial activated carbons (CC1 and CC2) with a novel lab-scale activated carbon (NC) produced from the co-pyrolysis of post-consumer plastic waste and olive cake, followed by physical activation with CO2. The materials were characterized by elemental analysis, proximate analysis, surface area measurements, XRD, and XPS. Elemental and proximate analyses revealed that CC2 possesses the highest carbon content (95.25 %), nitrogen doping (1.62 %), and lowest ash fraction (0.82 %). Textural analysis indicated that CC2 exhibits a high BET surface area (948.55 m2/g) and micropore area (780.84 m2/g), while CC1 showed a negligible surface area (2.82 m2/g), and NC demonstrated a moderate surface area (230.04 m2/g), indicating a poorly developed porous structure in both cases. Dynamic adsorption tests showed that CC2 presented the highest CO2 uptake (up to 2.90 mmol/g) and CO2/CH4 selectivity (2.40 in molar terms under biogas conditions), mainly attributed to its well-developed microporosity that favor physisorption. In contrast, NC showed lower CO2 adsorption (0.80 mmol/g) and higher CH4 uptake (0.93 mmol/g), resulting in poor selectivity (0.96), suggesting the need for further modification, such as surface functionalization or chemical activation. CC1, limited by its almost non-existent porosity, exhibited intermediate performance with comparable CO2 and CH4 uptakes (0.95 and 0.92 mmol/g, respectively) and modest selectivity (1.04), likely influenced by minor chemisorption on mineral impurities. Despite its lower CO2 adsorption capacity and selectivity, NC demonstrates high regeneration efficiency, making it suitable for repeated use in gas separation.