Lignin is the second most abundant biopolymer on Earth, after cellulose, with a highly complex chemical structure that hinders its possible utilizations. Applications that utilize lignin in different manners are of great interest, due to its inexpensive nature. Present work is based on the notion of converting lignin into different biofuels that have only a few, however important, advantages over lignin as a direct energy source. Matyas Kosa has completed his dissertation regarding lignin conversion under the direction of Professor Art Ragauskas, with the following information from his abstract.

The first part of current work (pyrolysis) details the analysis of lignin from a relatively new lignin isolation process called LignoBoost. It is obtained from the pulp and paper industry via CO2 precipitation of lignin from black liquor (BL). This method is environment friendly, results in lignin with minimal oxidation, eliminates the main bottleneck of the Kraft cycle (recovery boiler capacity), and yet leaves enough lignin in the process stream to recover pulping chemicals and generate energy for the pulp mill. Pyrolysis had converted this lignin into bio-oil with high aliphatic content and low oxidation level, all advantageous for application as liquid fuel.

The second part of this dissertation proved the theory that lignin degradation and lipid accumulation metabolic pathways can be interconnected. Gram-positive Rhodococcus opacus species, DSM 1069 and PD630 were used to evaluate lignin to lipid bioconversion, starting with ethanol organosolv and Kraft lignin. This conversion is a first step in a multistep process towards biodiesel production, which includes transesterification, after lipids are extracted from the cells. Results clearly indicated that the lignin to lipid bioconversion pathway is viable, by cells gaining up to 4% of their weight in lipids, while growing solely on ethanol organosolv lignin as a carbon and energy source. Bench-top (2L) scale fermentation using high extractive content (20%) Kraft lignin and DSM 1069 cell line was even more successful. The lignin loss was approximately 30% within the first 24 hours, while the extractive content of the Kraft lignin only decreased by 3%, indicating that the cell growth (80x weight increase in 24 hours) was mainly supported by lignin.

Experiments with PD630 cell line, using the same Kraft lignin in shake flask fermentations, showed clear indications for the metabolic pathway used in the process, such as degradation of lignin, de-methylation of mono-aromatic units (guaiacol-resembling degradation products) and oxidation of lignin. Overall, Rhodococcus opacus proved to be promising bacteria to be the focal point of lignin to lipid bioconversion research.