Linda F. Benedict, Pham-Bugayong, Patrisha, Aita, Giovanna
Patrisha J. Pham-Bugayong and Giovanna M. Aita
Lignocellulosic biomass – which includes agricultural residues such as corn stover and sugarcane bagasse, herbaceous crops such as switchgrass, and both hard and soft woods – is an important source of fermentable sugars and other valuable components. These fermentable sugars can be converted to ethanol, butanol and other value-added chemicals. However, pretreatment is necessary before access to these sugars is possible. There are numerous, well-studied processes in which to treat the biomass without sacrificing fermentable sugar yields. These include treating with acids, water usually in the form of steam and ammonia or other basic ingredients.
For this study LSU AgCenter researchers used bagasse from sweet sorghum and high-fiber sugarcane, also known as energycane, and pretreated with dilute ammonia. After the pretreatment process, the biomass was mixed and converted to specific fermentable sugars. A cocktail of commercially available enzymes was used in various combinations. The results show a mix of monomeric and oligomeric sugars in the sorghum and energycane enzymatic hydrolysate liquor.
The pretreatment and enzymatic hydrolysis processes that soften and break down the biomass generate fermentable sugars but also undesirable nonsugar components, which require removal through detoxification. For this study, the enzyme hydrolysate liquor derived from sorghum and energycane pretreated biomass was characterized for sugar and nonsugar components to aid in the design of an effective detoxification strategy. The researchers explored detoxification strategies successful in obtaining maximum sugar recoveries while nonsugar components were kept at low levels. The successful detoxification strategies include ionic liquids and ion-exchange resins, as evidenced by the removal of most inhibitors. Ionic liquids are salts that are liquid at room temperature and possess several unique properties when compared to regular organic solvents. These properties are useful for separation applications. Ion-exchange resins, on the other hand, are made up of an insoluble matrix of an organic polymer substrate, which is widely used for separation and purification processes as well.
The detoxification strategies chosen were optimized and applied to the enzyme hydrolysates. Results showed that the strategies had no significant effect on monomeric sugar levels while the nonsugar components were minimized. The fermentable monomeric sugars obtained after detoxification can be converted into syrups, which can be stored for future use. This mixed sugar syrup feedstock can be converted to biofuels or introduced into processes to make chemicals. The nonsugar components can be recovered and converted into useful chemicals as well. These detoxification strategies can also be applied to other enzymatic hydrolysate liquors derived from other biomass available in Louisiana.
Patrisha J. Pham-Bugayong is a post-doctoral fellow, and Giovanna M. Aita is an associate professor at the Audubon Sugar Institute, St. Gabriel.
(This article was published in the spring 2015 issue of Louisiana Agriculture Magazine.)