The Cornerstones of Advanced Biofuels

Novel pretreatment technologies are paving the way for the advanced biofuel industry. By Chris Hanson | July 22, 2013 Currently, one of the most common pretreatment methods is accomplished using steam explosion, but further advances and innovations in other pretreatment methods could diversify pretreatment options. In recent months, several breakthroughs and new approaches have been announced, one of which is ionic liquid pretreatments with butadiene sulfone. Some of the newest pretreatment innovations involve the use of ionic liquids to break apart biomass into cellulose, hemicellulose and lignin. Ionic liquids, or liquid salts, are being researched at both the University of Illinois at Urbana-Champaign and the U.S. DOE’s Joint BioEnergy Institute. “Initially, we wanted to find a solvent to actively separate lignin, hemicellulose and cellulose,” adds Hao Feng, associate professor at the University of Illinois. “However, we also found it is probably better to use this as a pretreatment because we can recover it, we can recycle it, and that way we can have that green, sustainable production.” Once pretreatment is complete, the temperature is increased, and the heat breaks down the solvent, forming butadiene and sulfur dioxide. The two gases are then recombined to form the original butadiene sulfone. Halfway across America, the JBEI in California is also developing an ionic liquid pretreatment. Unlike the University of Illinois’ butadiene sulfone method, the institute is utilizing imidazolium chloride with mixed feedstocks. With its pretreatment technology, the institute is able to liberate 95 percent sugar yields from biomass in less than 24 hours, recovering roughly 95 percent of the ionic liquid. Working with Idaho National Laboratory’s feedstock development unit, JBEI tested what Simmons refers to as a “witch’s brew” of feedstocks, comprised of corn stover, switchgrass, eucalyptus and pine biomass. What the researchers unexpectedly discovered was the mixtures performed better in pretreatment than single feedstocks. “Imagine if you had a biorefinery operating with ionic liquid technology that could handle any mixture that’s available regionally, be it yard trimmings, ag residues, tree residues, municipal solid waste,” says Simmons. “That’s pretty remarkable.” Currently, JBEI is working with the industry to commercialize the technology. Simmons hopes sugars produced from ionic liquids will be marketable within three to five years. The biggest steps that need to be taken, he says, are more process engineering and scaling to minimize risks. “We are working with user facilities within the national lab complex, post start-ups and big industry to do that,” he adds. “We are very excited about the future of the process.” Emerging Glycerol Pretreatment Explaining how the pretreatment process works, Simmons says crushed bagasse from a sugar processor is churned with the glycerol in a chamber. Dissolved lignin and glycerol are then pressed out, leaving the cellulose and hemicellulose. “It’s a really simple, easy process using a very cheap substance in glycerol,” he says. Other recent developments, Richards notes, include processes to purify the used glycerol for reuse and to maintain lower costs. Leaf Energy, JBEI and University of Illinois are all using different approaches to create digestible sugars, but all take aim at the same goal. “I think pretreatment is still the most expensive unit operation in biomass-to-biofuel production,” says Feng. “If you could lower the cost, including capital investment and operational costs, I think you could lower the overall cost of production. That’s why it is very important.” Simmons believes the real challenge in biofuel production lies with inexpensive, sugar production from renewable, lignocellulosic feedstocks. He says if people are able to produce those sugars with a production cost lower or equal to corn and sugarcane-derived sugars, that “all things become possible with those sugars in terms of fuels, chemicals and others.” Advanced biofuel, such as cellulosic ethanol, could play a big role in the pressing carbon debates, says Richards. He adds that with lower production costs, decreased enzyme costs and better technologies, cellulosic ethanol “has a very, very big task going forward to help reduce carbon.” Author: Chris Hanson Staff Writer, Biomass Magazine chanson@bbinternational.com 701-738-4970 Taylor Scott International