The technique has been developed by researchers at the Joint BioEnergy Institute (JBEI), a US Department of Energy Bioenergy Research Center, led by the Lawrence Berkeley National Laboratory (Berkeley Lab).
Based on the natural auto-fluorescence of plant cell walls, this technique enables researchers for the first time 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 pre-treating biomass, we observed a rapid swelling of the secondary plant cell walls within ten minutes of exposure at relatively mild temperatures (120 degrees Celsius)," said 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 intra-molecular 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 pre-treatment using these techniques," he added.
Simmons said that once the EmimAc had dissolved the switchgrass biomass into its three components - cellulose and hemicellulose sugars, plus lignin, the woody fiber that gives strength and structure to plant cell walls - the subsequent addition of an anti-solvent, such as water, resulted in the sugars being precipitated out while most of the lignin remained in solution, a requirement for recovering the sugars.
This confirmed that the ionic liquid pre-treatment effectively disrupted the recalcitrance of the switchgrass biomass and helped liberate the fermentable sugars.
"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 said.
"We are now in the process of evaluating other ionic liquids to discover the optimal combination of cost and performance," he added.