Effect of oxidative torrefaction on the pyrolysis of Clitocybe maxima stipe: Pyrolysis behaviour, and products' properties

In this study, oxidative torrefaction (OT) was used as the pretreatment process for the pyrolysis of Clitocybe maxima stipe (CMS) which is one kind of typical mushroom wastes, in order to evaluate the influence of OT on pyrolysis behaviour of torrefied CMS and products’ properties. The experimental results demonstrated that OT enhanced the degree of aromatization, and improved the thermal stability of the torrefied CMS compared with inert torrefaction (IT). The biochar (T9-P700) obtained by OT (9% oxygen) coupled pyrolysis (700 °C) had the improved pore structure with the highest specific surface area of 661.61 m2/g, while the obtained liquid products were less acidic with an increased formation of N-containing compounds (up to 19.15%) and phenolic compounds (8.08%). Furthermore, T9-P700 had a higher adsorption efficiency and adsorption capacity (147.31 mg/g) for Pb(Ⅱ). C-O, CO, -COOH, and -OH on the obtained biochar participated in the adsorption process of Pb(Ⅱ), attributing to the adsorption mechanism interpreted as physical adsorption, precipitation, and functional group complexation. Higher oxygen concentrations increased the severity of torrefaction, which facilitated a better pore structure in the CMS biochar generated during the subsequent pyrolysis process and the generation of liquid products with better qualities. Therefore, OT coupled pyrolysis may be an effective way to improve the quality of pyrolysis products. [Display omitted] •OT modified elemental and compositional properties more effectively.•OT increased the Eα and thermal stability of torrfied CMS pyrolysis.•OT coupled pyrolysis biochar had better pore structure and higher SBET.•Liquid products obtained from OT coupled pyrolysis had lower acidity.•OT improved the adsorption performance of CMS biochar for Pb(Ⅱ).