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

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.