Utilization, Characterization, and Enzymatic Hydrolysis of Lignocellulosic Substrates for Energy and Materials

The goal of the research presented here is to advance the fundamental and practical field of knowledge related to lignocellulosic biomass utilization in a biochemical conversion platform. This work can be broadly categorized in to three sections: 1) process, financial, and risk modeling of proposed bioenergy production technologies, 2) the inhibitory role of lignin during the enzymatic hydrolysis of cellulose and other biomass polymeric carbohydrates, and 3) exploring processing behavior of lignin and viewing this material as a potential raw material for other products and materials.;The first and second study demonstrate the utility of performing integrated process, financial, and risk modeling of two bioenergy production technologies. The first study examines six different biomasses being processed through a dilute acid pretreatment technology followed by enzymatic hydrolysis and fermentation to produce ethanol. The second study presents a concept termed value prior to combustion which couples an autohydrolysis treatment on biomass with traditional biomass combustion to generate ethanol and electricity. The high level modeling work lays a foundation and emphasizes the practical importance of gaining a better fundamental understanding of enzymatic hydrolysis and lignin utilization for other uses than fuel value.;In the third study, three analytical techniques, x-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectrometry (ToF-SIMS), and a confocal laser scanning microscopy (CLSM) were evaluated for efficacy in measuring lignin distribution across the cell wall of pretreated biomass fibers. Many different substrate features have been studied thoroughly in the literature but little attention has been given to the role of lignin distribution in the biomass matrix. Coupled with the lignin specific fluorochrome, acridine orange, a CLSM can analyze fibers and produce images of lignin distribution across the cell wall. The CLSM technique requires less time in terms of sample preparation and equipment analysis time compared with XPS and ToF-SIMS.;In the fifth study, the CLSM technique identified in the fourth study was further developed by analyzing an array of partially delignified softwood tracheids. The softwood samples were generated using kraft chemistry coupled with extended chlorite, oxygen, or ozone delignification. Chlorite and oxygen delignification primarily remove lignin from the bulk of the cell wall while the ozone treatments are more effective at removing outside surface lignin. Relating lignin distribution to enzymatic hydrolysis performance, the data suggest a slight advantage of removing outside surface lignin but larger gains occur if the treatment removes lignin from the bulk of the cell wall.;In the fifth study, the relationship between fiber dimensional changes and cellulose degree of polymerization with the extent of enzymatic hydrolysis for varying lignin content softwood and hardwood pulps was investigated. The largest changes in fiber length occur during the first 30% of carbohydrate conversion. The data suggest that the presence of high concentrations of lignin in the substrate matrix reduces the rate of fiber cutting but does not completely inhibit this action. A general trend of decreasing number of kinks and average kink angle as a function of carbohydrate conversion was also observed which is consistent with mechanisms proposed in other studies (Clarke et al 2011, Wallace 2006). The degree of polymerization of cellulose in the lignin free samples was measured at different extents of hydrolysis and was found to decrease linearly with carbohydrate conversion.;In the sixth study, the time-temperature-extrusion impact of incorporating various plasticizers with kraft lignin on the rheological behavior of these formulations was examined. The plasticizers have the ability to retard the rate of lignin crosslinking that occurs during an extrusion process. Incorporating a plasticizer can change the rheological behavior of the lignin-plasticizer blend and improve processability in a bench scale extruder.