Valorization of Lignin: Effective Conversion of Depolymerized Lignin to Oil by Simple Chemical Modifications

Lignin is one of the most promising applicable biomass resources, but its full utilization has yet to be realized, possibly, due to the difficulty in depolymerization and subsequent functionalization. We successfully carried out depolymerization of commercial Kraft lignin with the aid of formic acid and sodium formate to generate a mixture of monomeric and dimeric lignin. The obtained depolymerized lignin was further chemically modified by alkylation and subsequent esterification to afford lignin oil. The obtained lignin oil was thoroughly characterized by proton Nuclear Magnetic Resonance (H-1 NMR) spectroscopy and Fourier Transform Infrared spectroscopy to validate its chemical nature. The properties of the lignin oil, including viscosity, total acid number and thermal properties were well characterized. The lignin oil was blended with commercial engine oil to examine their miscibility, and the result showed that it had good compatibility with some engine oil, rendering it as a potential lubricant or additive for low-end applications in industry.