Preparation and performance evaluation of a lignin-based solid acid from acid hydrolysis lignin

A new lignin-based solid acid was prepared by sulfonation of sulfuric acid lignin (a typical acid hydrolysis lignin). The solid acid has been characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), mercury injection apparatus, and elemental analysis. Structural analyses suggest that the material with high thermal and hydrothermal stability is composed of amorphous phenylpropane-based polymers with sulfonic acid groups. Catalytic tests in esterification of acetic acid with ethanol and hydration of 2, 3-dimethyl-2-butene show that the lignin-based solid acid exhibits high catalytic activities in acid-catalyzed reactions, which can be used as a replacement for the conventional solid acid catalysts. This may be attributed to good accessibility of reactants to sulfonic acid groups in the material structure.