ZnCl2 induced catalytic conversion of softwood lignin to aromatics and hydrocarbons

Selective cleavage of C-O-C bonds in lignin without disrupting the C-C linkages can result in releasing aromatic monomers and dimers that can be subsequently converted into chemicals and fuels. Results from this study showed that both biomass-derived lignin and lignin model compounds were depolymerized in a highly concentrated ZnCl2 solution under relatively mild conditions (120 degrees C-200 degrees C, 4-6 h). Zn2+ ions in highly concentrated ZnCl2 aqueous solutions appeared to selectively coordinate with C-O-C bonds to cause the key linkages of lignin to be much easier to cleave under mild conditions. In a 63 wt% ZnCl2 solution at 200 degrees C for 6 h, nearly half of the softwood technical lignin was converted to oil products, of which the majority were alkylphenols. Results indicated that most of the beta-O-4 and C-methyl-OAr bonds of the lignin model compounds were cleaved under the above reaction conditions, providing a foundation towards understanding lignin depolymerization in a concentrated ZnCl2 solution. Furthermore, by adding Ru/C as a co-catalyst, the phenolic products were further converted into more stable cyclic hydrocarbons via hydrodeoxygenation and coupling reactions.