Influence of ionic-liquid incubation temperature on changes in cellulose structure, biomass composition, and enzymatic digestibility
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Varying ionic liquid, 1-ethyl 3-methyl imidazolium acetate, pretreatment incubation temperature on lignocellulosic biomass substrates, corn stover, switchgrass and poplar, can have dramatic effects on the enzymatic digestibility of the resultant regenerated biomass. In order to delineate the chemical and physical changes resulting from the pretreatment process and correlate changes with enzymatic digestibility, X-ray powder and fiber diffraction, 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy, and compositional analysis was completed on poplar, corn stover and switchgrass samples. Optimal pretreatment incubation temperatures were most closely associated with the retention of amorphous substrates upon drying of regenerated biomass. Maximal glucan to glucose conversion for 24 h enzyme hydrolysis was observed for corn stover, switchgrass and poplar at ionic liquid incubation temperatures of 100, 110 and 120 °C, respectively. We hypothesize that effective pretreatment temperatures must attain lignin redistribution and retention of xylan for optimal enzyme digestibility.
KeywordsCellulose structure Ionic liquid pretreatment Mercerization Enzyme digestibility
Research funding was provided by the National Science Foundation grant #0933250, and National Science Foundation GK-12 Program, grant #DGE-0742395. Additional funding for undergraduate research opportunities (KC and GP) as well as access to Argonne National Laboratories Advanced Photon Source was from NSF REU grant 1004921. Use of the Advanced Photon Source, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the US DOE under Contract No. DE-AC02-06CH11357. Assistance in XRD and NMR was provided by Dr. Pannee Burckel, Instrumentation Center, and Dr. Yong Wah Kim, NMR Laboratory, University of Toledo.
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