The role of biogenic waste composition on pyrolysis: Part II – Char CO2 adsorption capacity

The CO 2 adsorption capacities (AC) of biochars obtained at 350, 550, and 750 °C from the main organic (cellulose, lignin, and protein) and inorganic (CaCO 3 ) macro-components of biogenic waste, as well as from co-digested manure (CDM), have been determined for different CO 2 concentrations (2–83 vol%) at 25 °C and atmospheric pressure. CO 2 adsorption isotherms have been determined using two different experimental methodologies: thermogravimetric and fixed-bed dynamic adsorption tests, yielding similar results. The composition effect has been analyzed by comparing the adsorption performance of the chars derived from individual macro-components and the potential interactions occurring during their co-pyrolysis. Lignin and cellulose-derived chars showed higher CO 2 retention (≈77 mg g biochar −1 ) than those produced from protein (≈40 mg g biochar −1 ). Pyrolyzed CaCO 3 exhibited negligible CO 2 adsorption. For surrogate_CDM chars, prepared at pyrolysis temperatures high enough to decompose CaCO 3 in the organic matrix, experimental results showed a synergistic effect, with AC between 14 % and 47 % higher than theoretical predictions. This decomposition promoted the reverse Boudouard reaction and enhanced char microporosity. However, the improvement was insufficient to offset the dilution effect caused by the high CaCO 3 content. AC results have been discussed based on the biochar textural and chemical properties, with ultramicroporosity being the key factor determining adsorption capacity. The AC of CDM-derived sorbents is similar to that of cellulose-derived, expressed per gram of waste (7–13 mg g waste −1 ). Furthermore, the biochars retained at least 80 % of their initial AC after 3 adsorption-desorption cycles, indicating their potential for stable CO 2 capture. • Thermogravimetric and breakthrough tests provided similar CO 2 adsorption capacities. • Rich lignin wastes poor in proteins are appropriate as precursors for CO 2 adsorbents. • Ultramicroporosity is more important than surface alkalinity for CO 2 retention. • Pyrolyzed CaCO 3 exhibited negligible CO 2 adsorption provoking a dilution effect. • CaCO 3 decomposition in CDM pyrolysis creates a synergistic effect raising CO 2 adsorption.