Chemically activated nanoporous carbon adsorbents from waste plastic for CO2 capture: Breakthrough adsorption study

Abstract

Abstract This paper describes the preparation of O-enriched porous carbonaceous adsorbents derived from low cost, abundantly available polyethylene terephthalate (PET) waste with high carbon content by directly carbonising at different temperatures (500–800 °C) and then chemically activating using variable impregnation ratios of KOH to carbon. The prepared carbon adsorbents were characterized for their textural and surface chemical properties using nitrogen sorption, CHN, FTIR, XRD, SEM, HRTEM, and XPS techniques. Further, to assess their CO2 adsorption-desorption performance under dynamic conditions, breakthrough experiments were conducted in a fixed-bed adsorption set up. Porous carbon obtained at 700 °C with KOH to carbon mass ratio of 3 (Act-3-700) exhibited best textural properties with BET surface area of 1690 m2g-1 and micropore volume of 0.78 cm3 g−1 and showed highest CO2 uptake of 1.31 mmol g−1 at 30 °C and 12.5% CO2 concentration. Four adsorption–desorption cycles establish the adsorbent's remarkable stability and regeneration. Furthermore, fractional order kinetic model explained the CO2 adsorption kinetics and Freundlich isotherm showed superior fit with the adsorption equilibrium data suggesting heterogeneous nature of the adsorbent surface. Negative values of Gibbs free energy ΔG° and adsorption enthalpy ΔH° indicate the spontaneous and exothermic nature of adsorption process.