Molten alkali carbonates pyrolysis of digestate for phenolic productions

Abstract

Molten alkali carbonates (MC) pyrolysis technology is proposed to dispose digestate waste and convert it into high value-added phenolics in this work. The results showed that temperature strongly affected phenolic production by promoting the depolymerization of lignin, while particle size had less influence on phenolic productions owing to the catalysis and dynamic diffusion of alkali metal ions. Meanwhile, the effect of mass ratio between sample and molten carbonates was investigated by a series of differentiated proportions from 5 to 25%. The optimum reaction conditions were 10% of mass ratio in a particle size from 0.6 to 0.85 mm at 450 °C, with the maximum phenolics yield of 67.08% in organic. In sum, 5.6 g of phenolics and 0.96 g of guaiacols were generated from 100 g of digestate. Compared with conventional pyrolysis method, the methoxyl group in liquid product could be efficiently removed at atmosphere in molten carbonates. Additionally, thermogravimetric analysis further demonstrated that alkali metal ions (Li+, Na+ and K+) promoted the primary degradation of lignin and secondary monomolecular dissociation reactions of methoxyphenol.