Supercritical treatment of organosolv lignin using formic acid as in-situ hydrogen source for production of valued chemicals

Lignin is a heterogeneous biopolymer linked to each lignin monolignols, such as p-coumaryl, coniferyl and sinapyl alcohols. Due to its complexity, however, lignin has been considered as a challenge to overcome for further utilization. It is necessary to develop efficient process to convert lignin to value-added chemicals, not only limiting in primary method such as steam and electricity.

The purpose of this study was to make more homogeneous and low molecular weight lignin. Lignin as a starting material was obtained by organosolv pretreatment which has advantages for producing sulfur free lignin, low molecular weight and narrow polydispersity. Supercritical treatment was used to produce lignin oil fragments. This treatment was conducted in mild conditions at a relatively low temperature and pressure compared to pyrolysis or hydrothermal treatment. It may be effective process for the production of valued chemicals.   

In this study, to find out the optimal condition and yield, formic acid was used as in-situ hydrogen source for producing lignin compounds. The conditions of supercritical treatment were at 350°C for 40min. with limited oxygen. Formic acid was added to solvent in the range of 1-10%. The yield of lignin oil fractions increased depending on the formic acid concentration, while char and gas yield were decreased. The analysis of lignin compounds was measured by chromatography. About 20 kinds of degraded fragment products were identified. The main compounds of lignin oil fragments were syringol, 4-methyl syringol, p-cresol, and guaiacol. The range of the molecular weight of oil fragments was 400 to 600 daltons.