Distinct responses of feedstocks of varied origin in oxidative pyrolysis

Oxidative pyrolysis provides at least the partial energy required for endothermic pyrolysis at the cost of oxidation of gases and organics in volatiles or on the exterior of biochar. Feedstocks of varied origin might have different responses to the oxidative atomsphere, which was researched by conducting oxidative pyrolysis of typical forestry biomass (sawdust), vegetable waste (cabbage), starchy waste (rice), algae (spirulina), and biomass components (cellulose and lignin). The consequences indicated that, regardless of feedstock, oxidation of both organics in volatiles (i.e., carboxylic acids, aldehydes, sugars, and heavy organics) and in biochar took place. This was more evident for cabbage and especially rice (biochar yield: 24.9 % in pyrolysis versus 9.1 % in oxidative pyrolysis), as their organic components were thermally stable and prone to being oxidized, generating higher yields of bio-oil and gases. Oxygenated organics on cabbage- or spirulina-biochar could be retained, while oxygenated species on rice- or cellulose-biochar tended to be further cracked, forming oxygen-deficient biochar. Moreover, oxidative pyrolysis promoted pore development (395.6 m2/g versus 46.9 m2/g in sawdust pyrolysis), enhancing capacity for phenol adsorption. In-situ IR characterization showed the transformation of saturated C=O to COOH/COOR, then to RCOOOR" (acid anhydride), and eventually to CO2, as well as the oxidation of aliphatics to C-O-C in oxidative pyrolysis.