Pyrolytic lignin fractionation from bio-oil

Abstract

This thesis investigated the fractionation of pyrolytic lignin from bio-oil using ethanol-water, acetic acid-water, combined solvent systems, temperature, and mixing time variations. The aim was to investigate how these parameters affected lignin yield, molecular weight distribution, and chemical composition. The resulting fractions were characterized using analytical methods, such as Karl Fischer titration, moisture and ash content analysis, ICP-MS, UV-Vis spectroscopy, and HPLC.

The results showed that the variation in yield values was partly due to water retention in the lignin structure. The addition of ethanol lowered moisture content and led to lower apparent yields. UV-Vis analysis indicated that all the normalized samples had similarly developed aromatic structures, whereas HPLC results demonstrated that they contained similar amounts of pyrolytic lignin, with the main differences in the chromatograms originating from differences in molecular size distribution. The 30 % ethanol-water sample produced the most uniform and highest molecular weight lignin, while the 5 % ethanol-water sample had a more balanced profile. Notably, three samples contained a fourth chromatographic peak, indicating the presence of other molecular compounds.

Overall, the study demonstrates that solvent-based fractionation is an effective method for modifying the properties of pyrolytic lignin. Future studies could explore the reproducibility of the methods tested in this study. They could also evaluate whether higher ethanol concentrations improve the purity and yield of pyrolytic lignin.