Browsing by Author "Rigou, Venetia"
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Item Kinetic and statistical approaches in metabolic networks(2008) Rigou, Venetia; Gonzalez, RamonThe work in the current thesis is focused on the metabolomics field. In general, studies in this area concentrate on obtaining information concerning the metabolites found in a biological sample. Acquiring and analyzing metabolome data provides a better understanding of the bionetwork's mechanisms. The first part of the thesis focalizes on analyzing metabolome data measured from plant systems. The proposed methodology is based on Principal Component Analysis. The primary goal is to reduce the dimensionality of a large dataset while retaining most of the associated information. The aforementioned methodology additionally provides the chance to obtain assay signatures by using metabolite contributions. Its importance relies on the fact that we are able to define the biomarkers in a biological sample and thus, providing a mean to further examine a desirable cellular function. The second part of the thesis introduces the development of a kinetic model, implemented to describe the anaerobic fermentation of glycerol in Escherichia coli. Setting up the overall model required obtaining the parameters from the literature, and determining the kinetic expressions for each enzyme. The results include the acquisition of the metabolite profiles over time, plus their steady-state concentrations. Additionally, Metabolic Control Analysis was applied to the steady-state conditions, in order to obtain an insight of which enzymes can be considered responsible for the control of flux. The accuracy of the outcome could be verified if the computational efforts were combined with experimental work. The results derived from the kinetic modeling of the anaerobic fermentation of glycerol underline the importance of utilizing methodologies that eliminate the need of kinetic data, like metabolic flux analysis, or the incorporation of non-mechanistic methods, like the log-linear approximation.Item Sustainable Production of Biofuels: Plant Optimization and Environmental Impact(2012-09-05) Rigou, Venetia; Zygourakis, Kyriacos; Gonzalez, Ramon; Cox, Kenneth R.; Cohan, Daniel S.Many recent studies on the relative costs and benefits of biofuels have raised the need for a detailed and rigorous analysis of the operations of a biorefinery that is focused on optimization. The current thesis concentrates on the design and optimization of plants for producing biodiesel and ethanol from cellulosic biomass. We have performed numerical simulations combined with systematic parametric analyses to investigate the effect of various parameters on the overall material and energy balances of each biorefinery. The efficiency of the simulated processes was investigated by introducing and/or estimating various metrics in order to select the more beneficial directions for process improvements. Particular emphasis has been paid on heat integration and the design of highly efficient combined heat and power (CHP) units that generate the steam and electricity needed for the purification of biofuels and their co-products. The first part of the thesis is focused on biodiesel production via transesterification of soybean oil with methanol, under alkali-catalyzed conditions. We have analyzed the performance of several reactor configurations in order to improve the conversion of the reversible transesterification reactions. The effect of the oil to alcohol ratio has also been extensively explored. Furthermore, the energy requirements of the simulated process have been rigorously calculated. Since biodiesel facilities can be used either for small-scale, distributed applications or for large-scale production, we have explored whether it is more energy efficient to burn the glycerol-rich stream in a combined heat and power (CHP) plant, or purify the glycerol and use it a feedstock for producing higher-value chemicals with further biotechnological processes. The second part of the thesis focuses on the production of cellulosic ethanol. Having developed the process model, a detailed parametric analysis was carried out to determine how the energy balances and overall efficiency of the biorefinery were influenced by changes in (a) the composition of the biomass feedstock, and (b) the conversion levels of the hydrolysis and fermentation stages. Furthermore, the requirements of the utility section of the ethanol plant were calculated. The utility section included a combined heat and power unit where by-product streams of the production process were utilized for energy generation. The parametric analysis indicated that these streams were in most cases an insufficient fuel source for meeting the energy requirements of the plant and thus, additional fuel was required (biomass, coal, or natural gas). The calculations of this section indicated a significant trade-off between ethanol production and external energy inputs, thus casting some doubt on the ultimate effectiveness of efforts to develop genetically modified energy crops (with high carbohydrate content) in order to maximize fuel production.