Life Cycle Assessment of Bio-methanol Derived from Various Raw-materials

Abstract

Bio-methanol production from biomass or from carbon dioxide and hydrogen, generated using renewable electricity, are considered to be sustainable routes nowadays. The aim of the present study consists on the environmental evaluation of bio-methanol production using Life Cycle Assessment (LCA) methodology. Two different bio-methanol production processes such as bio-methanol production from an external CO₂ stream and H₂ from water electrolysis, electricity being produced using various sources (i.e. biomass, solar, wind, and hydro or mix electricity) as well as woody biomass gasification for syngas production, syngas being further transformed into bio-methanol, are considered in the current study. The processes were simulated using computer aided design tools (i.e. ChemCAD and Aspen Plus process simulators). The environmental assessment is carried out using GaBi software. The LCA is a cradle-to-gate study with the following system boundaries: a) upstream processes (i.e. biomass, solvent and electricity supply chains, H₂ production, catalysts production and transportation); b) main processes: bio-methanol production through direct gasification and from CO₂ hydrogenation and c) downstream processes: solvent degradation and disposal of wastes. The production of one ton of bio-methanol was considered as functional unit in the present investigation. ReCIPe method was chosen as life cycle impact assessment method. Purities higher than 99% are obtained for the main product. Significant environmental impact categories (i.e. Global Warming Potential, Human Toxicity Potential, Fossil Depletion Potential) are discussed and the influence of various sub-processes is investigated. For instance, the best result in terms of Human Toxicity Potential, 12.30 kg 1,4-DB eq./t_MeOH, was obtained in the case of hydroelectric sources, while the same indicator was at least two times higher for other scenarios. From the environmental point of view, the scenario which relies on hydroelectric power performed better in six out of nine environmental impact categories as compared to other scenarios, being succeeded by the one considering wind power as electricity source.