Catalytic depolymerization of organosolv lignin to phenolic monomers and low molecular weight oligomers

The lignin-first strategy provides significant potential for producing value-added phenolics and high-quality biofuels. In this contribution, stepwise extraction and depolymerization of lignin in corncob residue towards the production of phenolic monomers, lignin-derived dimers and trimers was investigated. H2O/n-butanol (4:6, v/v) co-solvent could extract 87.1% of lignin in corncob residue, retaining a high-purity (86.0%) cellulose pulp. Ni/HZSM-5 catalysts with different Ni loadings were prepared and applied for further degradation of organosolv lignin. Over 5% Ni/HZSM-5, the highest yield of phenolic monomer was 19.5% with the selectivity of 66.7% towards 4-ethyl phenols (4-ethyl phenol and 4-ethyl guaiacol) at 300 degrees C, and liquid products with higher heating value (HHV) of 29.2 MJ kg(-1) were obtained. The 5% Ni/HZSM-5 catalyst promoted the cleavage of intramolecular beta-O-4 and C-beta-C-gamma. linkages, resulting in substantially decreased weight-average molecular weight (M-w)/number-average molecular weight (M-n) of the organosolv lignin from 2541/1064 Da to 562/391 Da, which implied the degradation of high-Mw oligomers to dimers and trimers. The catalyst also contributed to the hydrogenation of C-alpha = C-beta bonds in unsaturated intermediates (coniferyl alcohol and coumaryl alcohol). The possible cleavage mechanism for the degradation of lignin-derived oligomers was also proposed.