Life cycle assessment of renewable-based hydrocarbon plastics

Licentiate thesis, 2011

Plastics are an important commodity of our daily life. And although their majority is still based on fossil feedstocks, numerous efforts are made to stem the environmental consequences related to their production. One approach is the use of renewable materials (biomass) to produce today’s conventional plastics. Though a considerable part of the development linked to this approach is still in an emerging state, there is a need to assess the environmental impact of these plastics in order to increase knowledge about the environmental advantages and disadvantages of conventional biomass-based plastics. The aims of this thesis are: 1. To investigate the environmental impact of producing conventional plastics from biomass-based monomers - using low density polyethylene (LDPE) as test case. 2. To investigate the potential of using process simulation for life cycle assessments (LCA) of emerging technologies. 3. To develop a framework that facilitates simplified LCAs for the production of conventional, biomass-based plastics from different types of biomass and via different conversion processes. The results for greenhouse gas emissions from LDPE based on sugarcane ethanol are uncertain due to uncertainties in data and methodology for emissions from land use change, in particular from indirect land use change (ILUC). Sugarcane LDPE can be better than the fossil alternative, as was found when using a low estimate for ILUC emissions. However, its potential global warming impact can become similar to that of the fossil LDPE, when using a high estimate for ILUC emissions. For other environmental impacts (acidification, photochemical ozone creation, eutrophication) the fossil and the sugarcane alternative showed similar values, with transport being a key contributor. The LDPE based on sawmill chips ethanol was found to have, at its current state of development, an in general higher environmental impact than the sugarcane and the fossil alternative. The key contributor is off-site enzyme production. For the emerging technology part of the renewable life cycles data is scarce. Process simulation was therefore used to verify and supply data (ethylene production step for both assessments respectively ethanol production step for sawmill chips case). It has been shown to complement the life cycle inventory and with this allowed the assessment of the two biomass cases. The environmental key contributors (dominant life cycle activities) identified in the above work, together with key contributors found during literature screening, were combined to a framework. Its purpose is to enable simplified LCAs, which can be used to guide further investigations. Viewed from the current state, renewable routes for the production of conventional plastics like LDPE will need technical improvements, as well as careful decisions regarding biomass choices. Simplified assessments can support these needs in the way that they enable a comparably fast supply of data, which is needed at the screening stage of a project. Key words: renewable LDPE; LCA and process simulation; simplified LCA for conventional, biomass-based plastics