Coconut Shell Activated Carbon Supported Quaternary Ammonium for Continuous Cycloaddition of CO2 and Biogas Upgrading in a Packed Bed

Abstract

Quaternary ammonium was successfully prepared on coconut shell activated carbon (CSAC) granules. The samples were characterized by FT-IR, N2 adsorption–desorption, XPS, TG, and EA. The immobilized quaternary ammonium was thermally stable below 320 °C. The amount of immobilized quaternary ammonium on the CSAC was 0.957 mmol/g. Continuous cycloaddition of CO2 to epichlorohydrin (ECH) was carried out in a packed-bed reactor without using solvent or cocatalyst. When the reaction conditions were 130 °C and 1.4 MPa, the conversion of ECH and the corresponding turnover frequency (TOF) were 43.5% and 64.6 h–1, respectively. The selectivity to epichlorohydrin carbonate (ECHC) reached ∼100%. In biogas upgrading, grafting of quaternary ammonium was demonstrated to enhance CO2 capture capacity of the CSAC. The saturated CO2 capture capacities of the CSAC and the quaternary ammonium functionalized CSAC were 1.82 and 2.40 mmol/g at 20 °C and 0.5 MPa, respectively. The adsorption selectivities of CO2 over CH4 were ∼67% and 85% for the CSAC and the supported quaternary ammonium, respectively. The adsorption heat was 20–30 kJ/mol for the adsorbents. The supported quaternary ammonium also exhibited a relatively stable cyclability in a packed bed.