Abstract :
[en] Due to the depletion of fossil fuels and the increase of greenhouse gas emissions, solutions are needed to replace petrol based products. As a consequence, the number of biobased products developed using agricultural feedstock is continuously increasing. This study focuses on the carbon footprint of bio-HDPE produced either from Brazilian sugar cane or Belgian sugar beet. The goal of this study is to compare the carbon footprint of bio-HDPE with the fossil one, taking into account the effect of land use change.
Common boundaries of the agricultural systems comprise the cultivation step for both crops, i.e. sugar cane and sugar beet, with all associated energy and fertilizer consumptions, the transportation step from field to the industrial plant, the sugar crops transformation into hydrate bioethanol, the by-products valorisation, the dehydration and polymerization steps and the HDPE incineration as end of life issue. Fossil scenario includes the production of ethylene, its polymerization and its incineration.
When comparing the entire life cycle of bio and fossil HDPE, the GHG emissions are lower for the biobased product which is the willing effect. This result is only valid if no Land Use Change (LUC) or Indirect Land Use Change (ILUC) effect appears. To assess the environmental impact of the deforestation or of the transformation of a pasture into a field, the EC-Guidelines from the European Union were used in order to calculate the CO2 emissions depending on several parameters.
For sugar cane, LUC consists in the transformation of pastures into fields in the region of Sao Paulo in Brazil. Three scenarios can be developed based on different agricultural practices for pasture and field (tillage and fertilizers inputs): the best, the worst and the average. The best case leads to a supplementary environmental gain. The worst and average achieve additional emissions. A payback time, considering the time needed to find again an environmental gain compared to the fossil counterpart, was calculated for the average scenario which is equal to 12 years. The ILUC effect for sugar cane is assumed to be deforestation due to the transformation of forest into pasture induced by the previous LUC effect. The rate of deforestation can vary between 16% or 100% depending on used statistics and leads to a payback time of respectively 26 and 101 years.
For sugar beet, no LUC is considered. Indeed, no land expansion is available in Belgium due to small available areas. In the case of an increase of bioplastics production, Belgium should import sugar beet from neighboring countries which can induce ILUC. In this study, sugar beet is assumed to be provided by the Netherlands on pastures previously transformed into fields. The average scenario implies a payback time of 8 years.
This study permits to highlight the importance of LUC and ILUC especially for energetic crops dedicated to replace fossil products. This effect can reverse expected results and induce long payback times.
