Improved lignin pyrolysis over attapulgite-supported solid acid catalysts

Abstract

An efficient process for the pyrolysis of Kraft lignin using attapulgite (ATP) as catalyst was developed in the present work. Compared with the common catalyst carriers of γ-Al2O3, ZSM-5, and diatomite, ATP with rich Lewis acid and Bronsted acid sites gave the lowest residue yield of 33.9% and the highest monomers yield of 7.96% at 500 °C for 1 h. ATP-supported catalyst SZA was optimally selected from the fabricated ATP-supported catalysts (SZA, S2O82−/ATP, Nb2O5/ATP, MgO/ATP, and CaO/ATP), resulting in a residue yield of 16.4% and a monomer yield of 11.5% at the optimized temperature of 600 °C. Moreover, good feedstock adaptability of the selected catalyst was also confirmed. The plausible reaction pathways of lignin degradation by catalytic pyrolysis over ATP-supported catalysts involving demethoxylated phenols and alkylated phenols formation were proposed. In addition, it was also found that the ATP-supported catalyst was effective for the upgrading of bio-oil obtained from lignin liquefaction in a mixture solvent of ethanol/1,4-dioxane/formic acid, which laid a good foundation for the further value-added utilization of bio-oil.