Environmental Assessment of Emerging Routes to Biomass Based Chemicals The Case of Ethylene
Abstract: The production of bulk chemicals from biomass instead of fossil resources is perceived as one promising option to decrease society's environmental impact. However, though considerable research and development efforts aim at such production, it might take several more years before biomass based bulk chemicals are fully commercialized. This leaves room for investigating the environmental impact of such production, as well as, identifying improvement options along the related life cycles using environmental assessment tools such as life cycle assessment (LCA). This thesis aims at providing guidance for the development and production of biomass based ethylene, using life cycle assessment as a method of choice. It achieves this by: (1) identifying environmental hot spots along its life cycle and (2) by comparing the environmental impact of a sugarcane, a wood fermentation, and a wood gasification route to ethylene to each other, as well as to a fossil alternative. In addition, the thesis contributes to the methodological development of LCA to better fit the assessment of emerging routes to biomass based products (1) by determining methodological challenges linked to the assessment of products (e.g. biomass based chemicals) produced via emerging technologies; and (2) by identifying application and methodological challenges related to the climate impact assessment of land use and of time lags between CO2 release and uptake from biomass. A number of potential hot spots were revealed for the production of biomass based ethylene. These include e. g. enzyme production and the energy consumption of the ethylene production process and further development such as decreased enzyme and energy consumption is needed. From a global warming perspective, all three biomass routes can outperform the fossil alternative. However, this finding is significantly influenced by the assessment of time lags for biomass CO2 (wood routes), and of emissions from indirect land use change (sugarcane route). Both factors can significantly increase the global warming potential of the biomass routes, making them comparable to the fossil alternative. Therefore, the production of biomass must induce as few changes as possible regarding land use and related decreases in carbon stocks. In addition, consideration needs to given on how to use wood based ethylene to best mitigate potential effects of time lags between CO2 uptake and release from biomass. As regards the other investigated impacts (acidification, eutrophication, and photochemical ozone creation) the biomass routes were found to be in clear need for further development before competing with the fossil route. To ensure the relevance of assessments, two factors were found to be critical: (1) the consideration of the needs and demands of different stakeholders, and (2) the use of process simulation as a means to provide data for emerging technologies. Finally, the climate impact assessment of land use and time lags in CO2 release and uptake was found to encounter a number of methodological and practical issues, including inconsistent modeling for forestry and agricultural and poor data availability. These challenges need to be addressed, in order to consistently assess the impact of land use and time lags.
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