Life cycle assessment of a small-scale methanol production system: A Power-to-Fuel strategy for biogas plants

Power-to-Fuel (PtF) systems use carbon dioxide and hydrogen as feedstock together for renewable fuel production and can hence contribute to climate change mitigation. This study assesses the environmental performance, from cradle to gate, of an innovative PtF system for synthetic methanol production, which integrates a biogas plant based on manure and straw residues as well as a combined heat and power unit. Under this concept, the residual carbon dioxide from biogas production is used for the synthesis of methanol, whereas hydrogen is obtained via wind-based electrolysis. A life cycle assessment (LCA) is carried out here for 1 kg of methanol produced with the integrated system proposed, operated on a small scale. In view of the multi-functionality of the process, the uncertainty in LCA outcomes is assessed by considering different assumptions on co-product credits for both the electricity from cogeneration and the digestate from the anaerobic digestion of organic raw materials. Additionally, a sensitivity analysis is performed to examine the influence of variability in life cycle inventory data on the results. All the analysed scenarios show significant improvements compared with conventional methanol production from fossil resources (with only a few exceptions for acidification and eutrophication). The sensitivity analysis shows that parameters determining the overall energy requirements as well as methane losses from anaerobic digestion in the PtF system greatly influence its environmental performance, and should be carefully considered in process design and upscaling. In spite of the uncertainty inherent in LCA, the system is presented as an interesting option to produce renewable methanol while contributing towards a circular economy, provided that the economic performance is also beneficial relative to the fossil alternative. (C) 2020 Elsevier Ltd. All rights reserved.