Adapting Life-Cycle Assessment to biofuels: some elements from the first generation case ; Eléments d'adaptation de la méthodologie d'analyse de cycle de vie aux carburants végétaux : cas de la première génération

This thesis aims at giving a better understanding of present Life Cycle Assessment (LCA) results for biofuels in order to identify their potential and breathing spaces from an energy consumption and GreenHouse Gases (GHG) emissions point of view. To this end, LCA methodology and existing studies on first generation biofuels were reviewed; then a sensitivity analysis on methodological and data parameters allowed identifying the roots of the discrepancies of results. Methodological choices appeared to be very crucial elements for final results and recommendations were made for LCA carrying out for biofuels. The close relationship between LCA results and local specificities of production were also underlined. A simplified process simulation was then performed to evaluate the impacts of technological and by-products uses alternatives on LCA results. Energy use of by-products shows the most important potential savings per MJ although its economic profitability is only ensured for high oil prices and reasonable agricultural prices and its GHG savings per used hectares are lower than in the reference cases. Finally LCA methodology was completed by integrating soil quality, especially their role as carbon sinks, within the system boundaries. This led to suggest a more specific temporal framework for comparisons of scenarios and to define a dynamic method of GHG weighting consistent with current uses of Global Warming Potentials and according to their emission year. Application of GHG weighting on two case studies of land-use changes was done and showed the need for assessments of biofuels of defining efficient land use criteria in addition to the GHG savings criteria from Directive 2009/28/CE. ; Cette thèse vise à clarifier le panorama actuel des résultats d'Analyse de Cycle de Vie (ACV) pour les carburants issus de cultures végétales, en vue d'identifier le potentiel et les marges de manœuvre de ces filières, pour la consommation d'énergie et les émissions de Gaz à Effet de Serre (GES). A cette fin, après une analyse ...