Identification of “carbon hot-spots” and quantification of GHG intensities in the biodiesel supply chain using hybrid LCA and structural path analysis

It is expected that biodiesel production in the EU will remain the dominant contributor as part of a 10% minimum binding target for biofuel in transportation fuel by 2020 within the 20% renewable energy target in the overall EU energy mix. Life cycle assessments (LCA) of biodiesel to evaluate its environmental impacts have, however, remained questionable, mainly because of the adoption of a traditional process analysis approach resulting in system boundary truncation and because of issues regarding the impacts of land use change and N2O emissions from fertilizer application. In this study, a hybrid LCA methodology is used to evaluate the life cycle CO2 equivalent emissions of rape methyl ester (RME) biodiesel. The methodology uses input-output analysis to estimate upstream indirect emissions in order to complement traditional process LCA in a hybrid framework. It was estimated that traditional LCA accounted for 2.7 kg CO2-eq per kg of RME or 36.6% of total life cycle emissions of the RME supply chin. Further to the inclusion of upstream indirect impacts in the LCA system (which accounted for 23% of the total life cycle emissions), emissions due to direct land use change (6%) and indirect land use change (16.5%) and N2O emissions from fertilizer applications (17.9%) were also calculated. Structural path analysis is used to decompose upstream indirect emissions paths of the biodiesel supply chain in order to identify, quantify, and rank high carbon emissions paths or ‘hot-spots’ in the biodiesel supply chain. It was shown, for instance, that inputs from the ‘Other Chemical Products’ sector (identified as phosphoric acid, H3PO4) into the biodiesel production process represented the highest carbon emission path (or hot-spot) with 5.35% of total upstream indirect emissions of the RME biodiesel supply chain.

Acquaye A; Wiedmann T; Feng K; Crawford R; Barrett JR; Kuylenstierna J; Duffy A; Koh L; McQueen Mason S (2011) , Environmental Science and Technology, 45, pp.2471-2478.