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 a key factor in meeting a 10% minimum binding target for biofuel in transportation fuel by 2020, part of the 20% renewable energy target in the overall EU energy mix.

This makes the environmental impact of biodiesel an important consideration. Yet life cycle assessments (LCA) of biodiesel for this purpose have remained questionable, mainly because of methodological problems and because of issues regarding the impacts of land use change and N₂O emissions from fertilizer application.

This study used 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. Looking at 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 was used 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, accounting for 5.35% of total upstream indirect emissions.

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