The project, led by postdoctoral research associate Tirath Raj and Integrated Bioprocessing Research Laboratory Executive Director Vijay Singh, focused on the critical preprocessing stage that separates plant cell wall components. In most current industrial processes, hydrothermal pretreatment uses high temperature and pressure to break down the recalcitrant plant matrix, freeing cellulose and hemicellulose for fermentation but simultaneously degrading lignin and driving it to condense into a denser, less useful form. This represents a dual loss: energy is consumed to run the harsh process while valuable lignin is partially destroyed or rendered harder to convert into high-value products.
Cellulose consists of long, straight glucose-based fibers that can be readily broken down into sugars and fermented into fatty acids and fuels. Lignin, by contrast, is built from phenolic structural units such as syringyl, guaiacyl, and p-hydroxyphenyl groups. These units are heavily branched and cross-linked, forming a robust, water-resistant network that strengthens plants but resists chemical and biological attack. This complex architecture gives lignin a range of potentially valuable chemical functionalities, yet the same complexity makes it challenging to isolate and upgrade without damaging it.
Singh explained that hydrothermal treatment effectively breaks the "cement" that binds cellulose and hemicellulose, but it also fractures the amorphous polymeric lignin that glues the structure together. As the lignin fragments recombine and condense, they form an even more intractable material that is less accessible for downstream catalytic conversion. As a result, operators pay an energy penalty for running severe conditions and lose some of the original lignin value in the process.
To overcome this limitation, the team turned to natural deep eutectic solvents, or NADES, a class of salt-based liquid mixtures derived from benign components. These solvents are active at or near room temperature, relatively easy to handle, and can be recycled and reused multiple times. By carefully selecting and tuning NADES formulations, Raj and colleagues showed that they could gently loosen lignin from the plant cell wall without collapsing its native structure or forcing it to condense into a more rigid mass.
After pretreatment with NADES, the researchers separated the lignin and characterized its chemical architecture to verify that its original branching and cross-linking patterns were largely preserved. Raj reported that lignins recovered from this process maintained their native structural features, confirming that the solvent system freed lignin without the extensive depolymerization and recombination associated with hydrothermal methods. At the same time, the process yielded more accessible lignin and cleaner cellulose fractions, setting up more efficient conversion pathways.
These higher yields of intact lignin and purer cellulose sugars are precisely what integrated biorefineries require to be both technically and economically viable. High purity lignin can be more readily upgraded via catalytic routes into aromatics and aliphatic chemicals, while specialized yeast strains can ferment the liberated sugars into ethanol, biodiesel, and sustainable aviation fuel. Because the NADES pretreatment operates under milder conditions and allows solvent recovery and reuse as many as five cycles without major performance loss, it also lowers operational costs and environmental impacts compared to hydrothermal treatment.
The work also supports a shared strategic objective across the four U.S. Department of Energy Bioenergy Research Centers, which aim to unlock lignin as a feedstock for diverse bioproducts. While other centers focus on catalytically depolymerizing native lignin and feeding the resulting streams to engineered microorganisms, the Illinois team's contribution lies in delivering lignin that retains its native features, ready for downstream valorization. Singh noted that preserving lignin quality opens the door to a wider portfolio of high-value products generated from the same biomass input.
Another advantage of the NADES-based approach is its flexibility across biomass types. In this study, the researchers applied the method to Miscanthus, a dedicated bioenergy grass, but they emphasized that the process is feedstock agnostic. The same pretreatment framework can be extended to other biofuel crops, agricultural residues, and woody materials, while also preserving oils produced by wild type or engineered plants that can be recovered as additional fuel streams alongside the lignin and sugars.
By enabling gentle, efficient separation of lignin and cellulose with recyclable solvents, the new pretreatment strategy brings integrated biorefineries closer to fully exploiting plant biomass. The researchers envision future facilities capable of processing mixed feedstocks to produce a spectrum of fuels and chemicals, using NADES pretreatment as a foundational step that protects lignin value and boosts the overall energy and economic return of biofuel systems.
Related Links
Carl R. Woese Institute for Genomic Biology
Bio Fuel Technology and Application News
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
