The lignocellulosic biorefinery concept provides an attractive alternative to energy, fuels and chemical production from petroleum-derived and other non-renewable resources. However, the realization of this technology is limited by the economic climate and the technical challenges of maximizing the biorefinery production yield.
This dissertation is an investigation of utilizing targeted Engineered Biomass Deconstruction (EBD), or mechanical refining, to overcome the inherent recalcitrance of the lignocellulosic biomass. This recalcitrant nature is often considered the limiting factor for the commercialization of cellulosic biorefineries – including second generation cellulosic ethanol production facilities – which increases the direct costs for the process inputs of the deconstruction steps. This includes requirements of high temperature and chemical charges during pretreatment and high enzyme dosages during enzymatic hydrolysis unit operations.
First, the effects of mechanical refining on the digestibility lignocellulosic biomass is explored at the laboratory scale. Comparisons of two common laboratory scale refiners, PFI mill and valley beater, confirm improvements in enzymatic hydrolysis with increased mechanical refining severity for all biomass pretreatments; including, kraft (NaOH, Na2S), green liquor (Na2CO3, Na2S), and sodium carbonate (Na2CO3) pretreatments. A maximum in refining improvement is observed, highlighting the ability of EBD to generate the most value for the lignocellulosic biorefinery at moderate pretreatment severities and hydrolysis conditions.
Second, Engineered Biomass Deconstruction is compared at lab, pilot and industrial scales. Using the same industrially sourced sodium carbonate pretreated biomass, similar enzymatic hydrolysis kinetics and their respective improvements with mechanical refining were observed for all mechanical refining scales, with the most similar kinetics being between commercial scale and pilot scale refining. Successful simulation of industrial scale refining allows the use of pilot scale refining for optimization of Engineered Biomass Deconstruction at the pilot scale.
Third, utilizing the same commercial sodium carbonate biomass, the pilot scale mechanical refining conditions were optimized. Close to theoretical maximums in enzymatic hydrolysis conversion were achieved using pilot scale EBD compared to the total carbohydrate conversion of 39% for unrefined hardwood sodium carbonate biomass. Mechanical refining conditions of temperature, plate gap width, and consistency were controlled to optimize the Engineered Biomass Deconstruction process. Optimum conditions for the pilot refiner were found to be to 0.13 mm plate gap width, and 20% biomass consistency, at ambient temperature, which produced a total carbohydrate conversion of 90%.
Following the optimization of EBD conditions, efforts were made to fundamentally understand the reason for the improvement in biomass digestibility with mechanical refining. The motivation of this understanding would facilitate the development and application of engineered biomass deconstruction technologies within the lignocellulosic biorefinery concept. Non-hydrolytic fluorescent recombinant protein probes with carbohydrate binding modules of similar size to commercially available cellulases were used a model for the enzyme adsorption process for the initial stages of enzymatic hydrolysis. Model substrates were used to confirm the selective binding of the fluorescent protein probes to cellulose. Confocal laser scanning microscopy allowed for visualization and quantitative imaging of the fluorescent markers within the lignocellulosic biomass matrix. Relationships between the maximum fluorescent intensities and the different lignocellulosic biomass were observed. The distribution of adsorbed enzymes in the cell wall were altered by the mechanical refining actions of external fibrillation, internal delamination, and cutting. This indicates that improved biomass accessibility to enzymes throughout the lignocellulosic biomass matrix is related to enhanced enzymatic hydrolysis.
This work highlights the effectiveness of Engineered Biomass Deconstruction and its benefits when applied within the lignocellulosic biorefinery concept. Future research should be targeted for further optimization of mechanical refiner operating conditions including specific development of new refiner plate designs for application in a lignocellulosic biorefinery.
|Advisor:||Venditti, Richard A.|
|Commitee:||Jameel, Hasan, Park, Sunkyu, Sheppard, John D.|
|School:||North Carolina State University|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 79/07(E), Dissertation Abstracts International|
|Subjects:||Alternative Energy, Microbiology, Wood sciences|
|Keywords:||Enzvmatic hydrolysis, Woody biomass pretreatment, biochemical conversion, confocal microscopy, enzvme accessibility, mechanical refining|
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