Activated char from the co-pyrolysis of polystyrene and olive stone mixtures for the adsorption of CO2

Abstract

Yogurt plastic containers made of polystyrene (PS), olive stone, and mixtures of both have been converted into activated carbon materials transforming them firstly into char via pyrolysis and secondly with activation using either KOH or H2SO4. The pyrolysis of the olive stone gave a higher yield of material than the plastic PS. However, the activation of the PS char with KOH was more effective, reaching surface areas of 508 vs 194 m2 g−1 of the corresponding prepared with olive stone. The prepared materials were tested as CO2 adsorbent in thermobalance and fixed-be column assays. The materials activated with H2SO4 slightly enhanced the adsorption ability of the original char but were far from the performance obtained with KOH activation. The CO2 isotherms showed high synergy of CO2 uptake and selectivity when using activated chars prepared with the char from the mixture of raw materials, specially at a 1:1 mass ratio. The isosteric heat of adsorption values were those expected for a physisorption process. Further experiments in a fixed-bed column were also studied at atmospheric pressure at different inlet CO2 concentrations (10–50%). The CO2 retention increased as the partial CO2 pressure rose. Besides, a very similar performance of the material prepared with plastic and olive stones was obtained at 50%, i.e. 220 and 197 mg g−1 respectively. At low CO2 concentrations, the materials enriched with plastic displayed better performance than those prepared with olive stone. Cycles of adsorption-desorption were carried out in the column to assess the stability of the materials. The curves obtained did not display any substantial change, demonstrating the lack of adsorption retention.