Selective Degradation of Organosolv Lignin over Noble Metal Catalyst in a Two-Step Process

Dioxane lignin, a typical organosolv lignin, was degraded by supported noble metal catalysts and phosphoric acid by a two-step method at different temperatures. The results showed that under 4 MPa H-2 at 270 degrees C using Rh/C and 1% (w) phosphoric acid as catalysts, the highest total yield of the monomers and dimer was 16.9% after the first step, based on gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analyses. Moreover, the raw products from the first step were analyzed by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), element analysis (EA), and gel permeation chromatography (GPC) to improve the understanding of the chemical transformations involved. The results indicated that the C-O-C bond linkages in the dioxane lignin were cleaved to form lower molecular-weight products, resulting in the degradation of lignin, and the carbonyl and carboxyl groups were partly removed. Oxygen content was reduced dramatically with increasing reaction temperature, from 35% (w) to 21% (w) after reacting at 270 degrees C for 10 h. Based on the analysis results, a reaction pathway for the degradation of lignin was proposed. Finally, the products from the first step could be hydrodeoxygenated to alkanes with carbon numbers in the range of gasoline and diesel with high selectivity catalyzed by Pd/C and phosphoric acid at 250 degrees C.