The goal of this work is to develop a sustainable value chain of carbonaceous adsorbents that can be produced from the solid fibrous digestate (SFD) of biogas plants and further applied in integrated desulfurization-upgrading (CO2/CH4 separation) processes of biogas to yield high-purity biomethane. For this purpose, physical and chemical activation of the SFD-derived BC was optimized to afford micro-mesoporous activated carbons (ACs) of high BET surface area (590-2300 m2g-1) and enhanced pore volume (0.57-1.0 cm3g-1). Gas breakthrough experiments from fixed bed columns of the obtained ACs, using real biogas mixture as feedstock, unveiled that the physical and chemical activation led to different types of ACs, which were sufficient for biogas upgrade and biogas desulfurization, respectively. Performing breakthrough experiments at three temperatures close to ambient, it was possible to define the optimum conditions for enhanced H2S/CO2 separation. It was also concluded that the H2S adsorption capacity was significantly affected by the restriction to gas diffusion. Hence, the best performance was obtained at 50 °C, and the maximum observed in the H2S adsorption capacity vs. the temperature was attributed to the counterbalance between adsorption and diffusion processes.
Keywords: activated carbon; biogas; carbon dioxide; hydrogen sulfide; mesopores; micropores; physical adsorption; solid fibrous digestate.