As the most abundant biopolymers on earth, cellulose and lignin form the building blocks for trees and other plants. For centuries the durable, renewable benefits of wood have helped provide shelter and energy for people across the globe. Using trees such as Loblolly pine and other lignocellulosic biomass like wheat straw and Miscanthus – as renewable, plentiful, non-food and non-petroleum resources – can help reduce dependence on oil products by supplementing traditional gasoline supplies with liquid biofuels.
One of the biggest challenges of converting wood-to-energy is releasing the sugars within the lignin itself. Daniel Yelle, a research forest products technologist at the Forest Products Laboratory says lignin is recalcitrant, meaning it does not break down very easily. Yelle has been working with a team of researchers to unlock the recalcitrant nature of lignin in an effort to improve refinery efficiencies in the production process for advanced biofuels. Their research has been published in the scientific journal Green Chemistry.
Higher plants such as trees, says Yelle, contain cell walls that are rich in lignin and complex sugars – polysaccharides like cellulose. However, cellulose is naturally entrapped in a matrix of lignin. Cellulose is the ideal biopolymer for biofuel production, says Yelle, “because of its simplistic long-chain glucose structure” but the separation of the cellulose from its lignin counterpart typically involves harsh chemical pretreatments. These chemicals may release the cellulose to a certain degree but, says Yelle, “make the remaining lignin even more recalcitrant.” Overcoming pretreatment barriers would help make the biochemical conversion process more efficient and thus more appealing for commercial renewable energy interests.
Yelle and colleagues’ research analyzes lignin following an ionic liquid pretreatment. Ionic liquids, says Yelle, are used to more easily dissolve the lignin that directly surrounds the desired polysaccharides. The non-toxic and recyclable ionic liquid used in this study, says Yelle, was able to more effectively disrupt the lignin, allowing for its extraction in a more native-state, as compared to previous pretreatment strategies. The subsequent use of enzymes to breakdown the polysaccharides into simple sugars is thus more effective. Furthermore, says Yelle, the size of the lignin polymer that is removed can be customized and routed into different product streams and help improve biorefinery economics.
Above, a representation of the ionic liquid pretreatment process for converting biomass to sugars suitable for manufacturing liquid biofuels.