Catalytic Depolymerization of Alkali Lignin in Sub- and Super-critical Ethanol

The effects of reaction parameters on catalytic depolymerization of alkali lignin in suband super-critical ethanol were investigated using a high pressure autoclave, and the liquid oil and solid char products were characterized. The experimental data indicated that Rh catalysis, controlling reaction conditions at ethanol critical temperature (240 oC) and pressure (7.0 MPa), high ethanol/water ratios (100/0), and the medium reaction time (4 h) enhanced the depolymerization of alkali lignin to liquid oil and decreased the char formation. A gas chromatography/mass spectroscopy (GC/MS) analysis showed that the main compositions of liquid oils were phenols, esters, ketones, and acid compounds, and the supercritical state favored the formation of bio-phenols, but the subcritical state improved the generation of bio-esters. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR) spectra analysis showed that the addition of the Raney/Ni and Rh/C catalysis could inhibit the re-fusion of alkali lignin micron-sized spheres in the supercritical ethanol, which led to an increase in the occurrence of the depolymerization reactions.