Ionic liquids studied for use in biofuel manufacturing

These fluorescence images of a stem of switchgrass treated with EmimAc ionic liquid shows the section (a) before treatment (b) 20 minutes after treatment (c) 50 minutes after treatment and (d) two hours after treatment when the organized plant cell wall structure has been completely broken down. Photo courtesy of the Lawrence Berkeley National Laboratory

Ionic liquids for biomass pre-treatments can result in a faster biofuel manufacturing process.

Ionic liquids are salts that are liquids rather than crystals at room temperature. Researchers at the Joint BioEnergy Institute (JBEI), a US Department of Energy Bioenergy Research Center led by the Lawrence Berkeley National Laboratory (Berkeley Lab) are studying their use as a pretreatment for biomass for a more efficient conversion into fuels.

Ionic liquids have shown the ability to dissolve lignocelluloses and help hydrolyze the resulting liquid into sugars. However, the best ones have proven too expensive for use on a mass scale.

The new technique developed by the JBEI seeks to better understand how ionic liquids are able to dissolve lignocelluloses in order to find new and more cost-effective varieties for use in biofuel production.
Based on the natural auto-fluorescence of plant cell walls, the technique enables researchers to dynamically track solubilization during an ionic liquid pretreatment of a biomass sample, and to accurately and quickly assess the liquid’s performance without the need of labor-intensive and time-consuming chemical and immunological labeling.

“Working with switchgrass and using the ionic liquid known as EmimAc (1-n-ethyl-3-methylimidazolium acetate), which is currently the most effective known to date in terms of pretreating biomass, we observed a rapid swelling of the secondary plant cell walls within ten minutes of exposure at relatively mild temperatures (120 degrees Celsius),” says Blake Simmons, a chemical engineer who is Vice President of JBEI’s Deconstruction Division and was the principal investigator for this research. “We attributed the swelling to disruption of inter- and intramolecular hydrogen bonding between cellulose fibrils and lignin. The swelling was followed by complete dissolution of biomass over three hours. This is the first study to show the process by which biomass solubilization occurs in an ionic liquid pretreatment using these techniques.”

The EmimAc dissolved the switchgrass biomass into three components: cellulose and hemicellulose sugars, lignin and woody fibers. The subsequent addition of an anti-solvent such as water resulted in the sugars being precipitated out while most of the lignin remained in the solution.

The observations were made using auto-fluorescence, an optical property of biological materials. Living cells contain molecules which fluoresce when excited by the right light. Using auto-fluorescence in combination with a variety of microscopy and spectroscopy techniques, the researchers were able to map and visualize cellulose and lignin in switchgrass and during the pretreatment with EmimAc.
“Our approach can be used to evaluate the deconstruction of lignocellulosics in biomass of different chemical compositions, and also to assist in determining the impact of genetically engineered feedstocks,” Simmons says.

“In comparison to untreated biomass, ionic liquid pretreated biomass produces cellulose that is efficiently hydrolyzed with commercial cellulase cocktail and provides sugar yields over a relatively short time interval,” Simmons says. “We are now in the process of evaluating other ionic liquids to discover the optimal combination of cost and performance.”

The ultimate goal, Simmons says, is to find an ionic liquid that can efficiently pretreat biomass, then scale its use up into a cost-effective process for biorefineries.

The results of this study were reported in the journal Biotechnology and Bioengineering in a paper entitled: “Visualization of Biomass Solubilization and Cellulose Regeneration During Ionic Liquid Pretreatment of Switchgrass.” Co-authoring the paper with Simmons were his JBEI colleague Seema Singh, and Kenneth Vogel of the US Department of Agriculture’s Agricultural Research Service, which is located in Lincoln, NE. Simmons and Singh also hold appointments with Sandia National Laboratories.


- Katrice R. Jalbuena

Sources:

¹ http://newscenter.lbl.gov/press-releases/2009/07/09/nanopillar-solar-cells/
² http://newscenter.lbl.gov/