- Ionic liquid pretreatment studied on mixed and densified feedstocks.
- Four fuel crops milled into flour or pellets.
- Fermentable sugar yield of 90% achieved.
IN the future, makers of advanced biofuels might blend different feedstock varieties to balance the energy characteristics of the transportation fuel they produce, according to a news release from the Lawrence Berkeley National Laboratory.
A collaborative study by researchers with the U.S. Department of Energy's Joint BioEnergy Institute (JBEI) -- a bioenergy research center led by the Berkeley Lab -- and the Idaho National Laboratory (INL) has shown that an ionic liquid that's effective at pretreating individual biofuel feedstocks is also effective at pretreating multiple feedstocks that have been mixed and densified into a blend.
"Our results show that an ionic liquid pretreatment 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," said Blake Simmons, a chemical engineer who heads JBEI's deconstruction division. "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."
Simmons and colleague Seema Singh, director of JBEI's biomass pretreatment group, led the JBEI/INL study in which four biomass feedstocks -- representing the general classes of plants that are well-suited to serving as fuel crops -- were mixed and milled into either flour or pellets and then were pretreated with 1-ethyl-3-methylimidazolium acetate, the ionic liquid JBEI uses 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.
"Lignocellulosic biorefineries must be able to efficiently process available regional feedstocks at cost-competitive prices year-round, but feedstocks markedly vary from region to region," Singh said. "Also, individual feedstocks within a given region are quite variable, depending on weather conditions, handling, storage and crop variety. Blending and densifying different feedstocks to create a single, uniform feedstock has been proposed as a solution, but not much scientific attention has been paid to the efficiency of converting mixtures of feedstocks into fermentable sugars and fuels."
Produced from the microbial fermentation of sugars in lignocellulosic biomass, advanced biofuels are clean, green and renewable and could displace gasoline, diesel and jet fuel on a gallon-for-gallon basis and be directly dropped into today's engines and infrastructure, according to the news release.
The sugars in lignocellulosic biomass, however, are complex polysaccharides that are deeply embedded within a very recalcitrant material called 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 -- environmentally benign organic salts often used as green chemistry substitutes for volatile organic solvents.
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 affect ionic liquid pretreatment and sugar yield.
The JBEI/INL collaborators mixed switchgrass, lodgepole pine, corn stover and eucalyptus in flour and pellets and, within 24 hours of saccharification, were able to obtain sugar yields of up to 90% for both forms. Pellets, because of their higher energy density, would be the preferred form.
"Our work is the first demonstration that ionic liquid pretreatments can effectively handle mixed and densified feedstocks," Simmons said. "We're continuing the collaboration to next identify the most economical pelletized feedstock mixtures based on targeted regions of the U.S. We'll then determine how efficiently our process can convert these mixtures into fermentable sugars."
The researchers published their results in the journal Biofuels in a paper titled "Impact of Mixed Feedstocks & Feedstock Densification on Ionic Liquid Pretreatment Efficiency." Co-authors, in addition to Simmons and Singh, included JBEI's Jian Shi and Vitalie Stavila and INL's Vicki Thompson and Neal Yancey.