Scientists at the Joint BioEnergy Institute are developing a closed-loop biorefinery concept that uses waste lignin as a potential process solvent. They synthesized a new and renewable class of deep eutectic solvents. These solvents when mixed with other liquids and used for biomass pretreatment, release sugar from grassy feedstocks for fuel and chemical production.
The solvents are easy to synthesize due to the wide availability of inexpensive waste lignin. Turning waste into an asset makes these renewable solvents an attractive new approach for biomass conversion into biofuels and products that are less expensive. Further, the deep eutectic solvents offer a sustainable alternative to conventional solvents and ionic liquids.
With the development of commercial production of biofuels and bioproducts, it is anticipated that a significant amount of lignin will be generated annually that needs to be converted into desired bioproducts. Ten lignin-derived phenolic compounds were tested as hydrogen bond donors in varying mixtures with choline chloride to synthesize deep DESs, solvents that when mixed have a lower melting temperature than the individual solvents. After initial screening, the team selected and used four DESs for biomass pretreatment of switch grass. The researchers washed the pretreated biomass to remove potential inhibitory effects on enzymatic hydrolysis and fermentation. A fresh batch of the DES and choline chloride mixture resulted in approximately 87 percent glucose yield, while recycled DES resulted in decreased yields of 78 percent and 70 percent for second and third rounds, respectively. Biomass processes utilizing these renewable DESs could reduce operating costs by achieving a closed-loop biorefinery that generates the solvents needed for biomass pretreatment from the process of biomass conversion itself.
