Preparation of biomass-based activated carbons and their evaluation for biogas upgrading purposes

The use of waste biomass to produce adsorbent materials for the process of biogas upgrading might be a sustainable way to improve the energy matrix and help developing waste disposal technologies. The objective of this study was to prepare and evaluate activated carbons from coconut shell and babassu coconut, a waste biomass highly available at low cost. Both carbon samples were prepared by physical activation with CO2 and characterized by N2 adsorption isotherms at 77 K. The biosorbents produced from babassu and coconut shells presented BET surface areas of 1452 m2/g and 809 m2/g, respectively. Their applicability to upgrade biogas was assessed by experimental evaluation of pure (CO2 and CH4) and mixture (CO2/CH4) adsorption equilibrium data at 293 K and pressures up to 10 bar. The results were used to compare the performance of the samples prepared in this work with a commercial sample. Adsorption capacity for carbon dioxide was similar for both synthesized samples, but the activated carbon from coconut shell presented better properties for CO2/CH4 separation, as its selectivity (4.2 at 1 bar) and working capacity (1.0 mmol/g at 3 bar) are comparable to those of the commercial adsorbent over the low pressure range studied. This indicates that biomass waste is an interesting precursor for the production of activated carbons for biogas upgrading.