Lignin-based sulfonated carbon as an efficient biomass catalyst for clean benzylation of benzene ring compounds

Abstract

Low-temperature carbonization–sulfonation two-step process or one-step sulfonation process was employed to draft sodium lignosulfonate (SLS), the primary biological macromolecule ingredient of papermaking black liquor, into lignin-based sulfonated carbon. The two-step lignin-based sulfonated carbon named SLC400,1S was found to be an efficient catalyst for clean Benzyl-alcohol (BA) route Friedel-Crafts (F-C) benzylation of benzene ring compounds. FT-IR, XRD, Raman spectra, XPS, SEM with EDX-mapping, TGA-DSC, acid-base titration, and n-butylamine–acetonitrile titration characterizations demonstrated that the specific two-step process could introduce porous properties and a large number of surface sulfonic, hydroxyl, and carboxyl active groups into the structure of the prepared material, which was found to account for the good catalytic performance for benzylation. Similar to that of hierarchical mesoporous ZSM-5 under optimal conditions, the apparent activation energy for benzylation of paraxylene (PX) with BA over SLC400,1S was estimated to be 119 kJ·mol−1. The common by-product of BA route benzylation, dibenzyl ether (DBE), was almost inhibited because of the extraordinary activity of SLC400,1S and the optimized reaction conditions. A 12-run recycling test demonstrated easy recovery and steady reusability of the above lignin-based sulfonated carbon catalyst.