Comparative life cycle assessment of polyethylene based on sugarcane and crude oil
The goal of this study was to assess the environmental performance of low density polyethylene (LDPE) based on Brazilian sugarcane ethanol and compare it to LDPE based on crude oil and to answer the question if it is environmentally preferable in the production of goods and packaging in Europe. The production routes were compared in a life cycle perspective.
The investigated life cycles start with the cultivation of sugarcane in Brazil and extraction of crude oil in the Middle East, followed by the production of LDPE in Brazil and Europe, respectively. The LDPE was assumed to be used in Europe for both alternatives. A generic waste treatment scenario was applied, incineration, with recovery of the released heat to electricity. The assessment method used was life cycle assessment (LCA) in its two methodological approaches – consequential and attributional LCA. The two approaches were consistently applied in parallel to investigate the impact of methodological choices on the outcome of the LCA.
Use of fossil fuels and release of greenhouse gases were considered to be the two most important types of environmental impact in the study. As may be expected, the use of fossil fuels proved to be much lower for the sugarcane based LDPE.
The results for global warming show that, if effects of land use change are disregarded, the sugar cane route comes out much better than the oil based route. However, there are greenhouse gases released as a consequence of the rapid land use changes taking place in Brazil. It has not been possible to quantify the extent of these emissions with any degree of certainty, but the available data indicate that the effects of land use changes may be significant. The emissions may even be in the order of magnitude to flip the ranking between the oil based and the sugarcane based route to LDPE. But again, the data are too uncertain to allow for any ranking of the alternatives with respect to global warming potential.
What may be said though is that if the feed-stock were to come from some type of biomass that does not imply land use changes, LDPE based on ethanol is probably an environmentally much better alternative than LDPE based on oil.
In summary, polyethylene based on ethanol uses significantly less fossil fuels than the oil based alternative, and has the potential to significantly reduce emissions of greenhouse gases. However, as long as the ethanol is based on sugarcane, the cultivation of which leads to land use changes, there is considerable risk that the positive effect on greenhouse gas emissions is overturned by emissions resulting from land use changes.
The dominance and sensitivity analyses showed that the surrounding technical systems, such as electricity production system and waste management system have a large influence on the results. This was most clearly demonstrated by placing the oil-based route in a Swedish context (oil from North Sea, Swedish electricity production mix). The effect was a dramatically reduced environmental impact, particularly in terms of acidification, eutrophication and photochemical oxidant formation. Shorter transport distances also drastically reduced acidification, and to a lesser extent eutrophication and formation of photooxidants.
The project has revealed extensive knowledge gaps regarding environmental impacts resulting from land use change. Research is needed not only to generate data on the size of the emissions, but also into methodology on how to use such data in LCA.