The potentialities in the use of bio-chars prepared by steam assisted slow pyrolysis as adsorbents of gases of strategic interest (ca. N2, CO2, CH4) and their mixtures were explored. The bio-chars prepared from Populus nigra wood and cellulose fibers exhibited a narrow microporosity with average pore sizes ranging between 0.55 and 0.6 nm. The micropore volume increased with the pyrolysis temperature, allowing CO2 and CH4 uptakes at room temperature between 1.5-2.5 mmol/g and 0.1-0.5 mmol/g, respectively. These values are in line with those from the literature on biomass derived carbon-based materials exhibiting much higher porous features than those herein reported. As for the separation of CO2/N2 and CO2/CH4 gas mixtures, data showed that the prepared bio-chars exhibited good selectivities for CO2 over both N2 and CH4: between ca. 34 and 119 for a CO2/N2 mixture in typical post-combustion conditions (15/85, v/v) and between 14 and 34 for a CO2/CH4 mixture typical of natural gas upgrading (30/70, v/v).

Refuse-Derived Fuels (RDFs) are segregated forms of wastes obtained by a combined mechanical–biological processing of municipal solid wastes (MSWs). The narrower characteristics, e.g., high calorific value (18–24 MJ/kg), low moisture content (3–6%) and high volatile (77–84%) and carbon (47–56%) contents, make RDFs more suitable than MSWs for thermochemical valorization purposes. As a matter of fact, EU regulations encourage the use of RDF as a source of energy in the frameworks of sustainability and the circular economy. Pyrolysis and gasification are promising thermochemical processes for RDF treatment, since, compared to incineration, they ensure an increase in energy recovery efficiency, a reduction of pollutant emissions and the production of value-added products as chemical platforms or fuels. Despite the growing interest towards RDFs as feedstock, the literature on the thermochemical treatment of RDFs under pyrolysis and gasification conditions still appears to be limited. In this work, results on pyrolysis and gasification tests on a real RDF are reported and coupled with a detailed characterization of the gaseous, condensable and solid products. Pyrolysis tests have been performed in a tubular reactor up to three different final temperatures (550, 650 and 750 °C) while an air gasification test at 850 °C has been performed in a fluidized bed reactor using sand as the bed material. The results of the two thermochemical processes are analyzed in terms of yield, characteristics and quality of the products to highlight how the two thermochemical conversion processes can be used to accomplish waste-to-materials and waste-to-energy targets. The RDF gasification process leads to the production of a syngas with a H₂/CO ratio of 0.51 and a tar concentration of 3.15 g/m³.