The carbon footprint of the carbon feedstock CO2

Abstract

Capturing and utilizing CO(2)as carbon feedstock for chemicals, fuels, or polymers is frequently discussed to replace fossil carbon and thereby help mitigate climate change. Emission reductions by Carbon Capture and Utilization (CCU) depend strongly on the choice of the CO(2)source because CO(2)sources differ in CO(2)concentration and the resulting energy demand for capture. From a climate-change perspective, CO(2)should be captured at the CO(2)source with the lowest CO(2)emissions from capture. However, reported carbon footprints differ widely for CO(2)captured, from strongly negative to strongly positive for the same source. The differences are due to methodological ambiguity in the treatment of multifunctionality in current assessment practice. This paper reviews methodological approaches for determining the carbon footprint of captured CO(2)as carbon feedstock, and shows why some approaches lead to suboptimal choices of CO(2)sources and that increased consistency in life cycle assessment (LCA) studies on CCU is needed. Based on strict application of Life Cycle Assessment (LCA) standards and guidelines, it is shown that substitution should be applied to avoid suboptimal choices of CO(2)sources. The resulting methodological recommendations are applied to estimate the carbon footprint of feedstock CO(2)for current CO(2)sources in Europe and for future CO(2)sources in a scenario for a low carbon economy. For all CO(2)sources, the cradle-to-gate footprint of captured CO(2)is negative ranging from -0.95 to -0.59 kg CO(2)eq. per kg of feedstock CO(2)today and from -0.99 to -0.98 kg CO(2)eq. in a low carbon economy. The carbon footprints of different CO(2)sources differ mainly due to their energy demands. The presented assessment method and the carbon footprints of the CO(2)feedstocks CO(2)provide the basis for future assessments of carbon capture and utilization processes.