Using lignocellulosic biomass as a feedstock to produce renewable fuels, chemicals and products implies dealing with heterogeneous materials that have evolved complex protective mechanisms to prevent physical, chemical and microbial degradation of the structural polysaccharides in their cell walls. More efficient organisms and systems that can rapidly breakdown the various polysaccharides present in biomass such as woody and herbaceous biomass are needed to make the cellulosic industry a reality.
Ionic liquids show great promise as a host to biomass fractionation and utilization of each component in the production of fuels and value-added products.
Benefits to Ionic Liquids (ILs):
- Ability to solubilize biomass
- Low volatility
- Environmentally friendly
- “Designer solvent” for green chemistry
To fully exploit the benefits of ILs it is critical, BeST is developing compatible IL-enzymes systems in which the IL is able to effectively solubilize and activate the lignocellulosic biomass, and the cellulolytic enzymes possess high stability and activity.
Organic solvent fractionation of lignocellulosics
Biorefining, the process of converting renewable raw materials into biobased chemicals and fuels, bears many similarities to petrochemical refining. As received, both raw materials are difficult to use, as they are complex mixtures of different, simpler components. Crude oil contains multiple hydrocarbons spanning a wide range of molecular weights and boiling points, while lignocellulosic biomass is a mixture of cellulose, hemicellulose and lignin, along with much smaller amounts of extractable materials and inorganic salts. Thus, crucial to the utility of both feedstocks is an initial separation of the raw material into its simpler constituent parts, affording intermediates more versatile and easily used than the raw material itself. Treatment of biomass with organic solvents frequently meets this requirement. CRC research has developed a separation process using organic solvents that converts biomass into its individual cellulose, hemicellulose and lignin process streams. Each fraction can serve as a starting material for the production of biobased chemicals and fuels. The process being used at the CRC heats biomass with a mixture of methyl isobutyl ketone, ethanol, water and an acid promoter. This mixture selectively dissolves the lignin and hemicellulose leaving the cellulose as an undissolved material that can be washed, fiberized, and further purified. The dissolved solution of lignin and hemicellulose can be further separated into individual components. The process operates with high efficiency: greater than 95% of the components present in the starting feedstock is isolated after fractionation, and, for the lignin and cellulose fractions, in high purity, which is important for their eventual use as chemical building blocks. The cellulose fraction is generally 90-95% pure, and can be further purified using simple bleaching processes with environmentally friendly materials such as hydrogen peroxide. The lignin fraction is normally greater than 95% pure. Importantly, the process works well on multiple feedstocks, including switchgrass, poplar and southern yellow pine – all renewable feedstocks important to developing a biobased economy in the southeastern US.
Catalyst design for lignin conversion
Lignin exists simultaneously as one of the most promising opportunities and greatest challenges for the lignocellulosic biorefinery. Access to this highly abundant renewable carbon source is growing, as pretreatment methodologies, such as the CRC organosolv process, affords lignin as a separate coproduct. Projections suggest that 2nd generation biorefineries may generate over 65 million tons of lignin or as much as 60% more than is needed to satisfy internal energy requirements. However, truly selective lignin transformations remain elusive, and as a result a promising source of renewable carbon generally remains relegated to use as a low-value fuel. Reducing lignin valorization to practice is still fraught with the well-recognized challenges of multiple feedstock sources, structures that change depending on both the source of the lignin and the methods used to isolate it from a lignocellulosic matrix, and a lack of simple, selective transformations tailored for its unique structure. CRC research addresses this problem by investigating new methodology for the selective, catalytic conversion of lignin into high value chemical products. We couple organic synthesis, catalyst design, mechanistic investigation and spectroscopy to develop catalyst systems tailored for the unique structures of lignin. Our focus areas include: Development of metal-Schiff base complexes for lignin oxidation – transformation of organosolv lignin into high value benzoquinones and low molecular weight aromatics