A collaborative study by researchers with the US Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI), a bioenergy research center led by Berkeley Lab, and the Idaho National Laboratory (INL) has shown that an ionic liquid proven to be effective for pre-treating individual biofuel feedstocks is also effective at pre-treating multiple different feedstocks that have been mixed and densified into a blend.
The JBEI/INL study used four biomass feedstocks—switchgrass, lodgepole pine, corn stover and eucalyptus—representing the general classes of plants well-suited to serving as fuel crops, and mixed and milled them into either flour or pellets then pre-treated with 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), the ionic liquid used at JBEI as a benchmark for biomass processing.
The objective was to determine the impact of mixing and densification on the efficiency at which the complex polysaccharides in cellulosic biomass could be converted into fermentable sugars for fuel production. Densification makes transporting the feedstocks easier and less expensive.
Our results show that an ionic liquid pre-treatment can efficiently handle mixed feedstocks that have been milled and densified into pellets, and can generate high yields of fermentable sugars regardless of upstream processing. This indicates that blending and densifying a wide range of feedstocks has significant potential for helping to make biofuels a cost-competitive transportation fuel technology.—Blake Simmons, who heads JBEI’s Deconstruction Division
The sugars in lignocellulosic biomass are complex polysaccharides that are deeply embedded within recalcitrant lignin. To break apart the complex lignocellulose and help hydrolyze the released polysaccharides into sugars that can be fermented by microbes, researchers at JBEI and elsewhere have been studying biomass pretreatments with ionic liquids.
Researchers at INL have been investigating ways to increase the energy densities of biomass feedstocks and make delivery to refineries much more economical. Milling feedstocks into flour or pellets is an effective process for large-scale energy densification, but before this latest study it was unknown as to how densification of single or mixed feedstocks would impact ionic liquid pretreatment and sugar yield.
The JBEI/INL collaboration was able to obtain sugar yields of up to 90% from both flour and pellets. Pellets are the preferred form, due to higher energy density.
The collaboration has published their results in the journal Biofuels.
Jian Shi, Vicki S Thompson, Neal A Yancey, Vitalie Stavila, Blake A Simmons, Seema Singh (2013) Impact of mixed feedstocks and feedstock densification on ionic liquid pretreatment efficiency. Biofuels Vol. 4, No. 1, Pages 63-72 doi: 10.4155/bfs.12.82