The role of biogenic waste composition on pyrolysis: Part I – Char properties

The yield and properties of char derived from the co-digested manure and its main macro-components, including organic (cellulose, lignin, and protein) components and an inorganic component (CaCO 3 ), produced at different pyrolysis temperatures (350, 550, and 750 °C) have been studied. Experimental results obtained from a surrogate co-digested manure were compared with the theoretically calculated values to explore potential interactions between these macro-components. The char properties analyzed included elemental analysis, pH, FTIR, XPS, and specific surface area. The effect of pyrolysis temperature on many properties was similar, regardless of the precursor (macro-component). Increasing pyrolysis temperature led to higher C content (>90 wt% for cellulose char at 750 °C), pH (from (∼7 for cellulose at 350 °C to ∼13 for co-digested manure), and specific surface area, observing a marked development of ultramicroporosity and microporosity, especially at the highest pyrolysis temperature studied, 750 °C. An exception was observed for the char derived from proteins due to melting during pyrolysis. By far, the solids from the pyrolysis of cellulose and lignin exhibited the most microporosity development (SS DR ≥ 650 m 2 g -1 ), reaching, at the highest temperature studied, values close to those of physically activated carbons. Pyrolysis of the surrogate co-digested manure revealed the occurrence of Maillard reactions and also showed an interesting interaction involving CaCO 3 . The CaCO 3 thermal decomposition is promoted when it is embedded into the organic matrix, where the CO 2 generated during decomposition favored the Boudouard reaction of C from the organic components. This results in a lower biochar yield, 32 wt% versus 37 wt% (expected value), and a higher development of microporosity in the char. • Char yield, pH, and SSA, show same temperature-trend for any raw material. • CaCO 3 thermal decomposition occurs at lower temperatures in presence of organics. • CO 2 released during CaCO 3 decomposition promotes Boudouard reaction. • Occurrence of Boudouard reaction leads to lower char yield and higher micropore volume. • Cellulose and lignin chars presented similar surface area as physically activated carbon.