What is the best use of sugar crops? Environmental assessment of two potential applications : biofuels vs. bioproducts

Agricultural crops became through years an attractive option to increase European energy independence. Brazil has taken this opportunity since the seventies by using sugar cane bioethanol as vehicle fuel. The development of biofuels production is more recent in Europe. Due to temperate climates, bioethanol production is mostly based on wheat and sugar beet, this latter being considered as the ‘equivalent’ sugar crop to sugar cane for Europe.
Biofuel is the most common application of bioethanol but its transformation into bioethylene through a dehydration step and then its polymerization into bioplastic can be an alternative as already found in Brazil. This paper will consider both potential uses and compare them using Life Cycle Assessment methodology.
Common boundaries of the systems comprise the cultivation step for both crops, i.e. sugar cane and sugar beet, with all associated energetic and fertilizer consumptions, the transportation step from field to the industrial plant, the sugar crops transformation into hydrate bioethanol, the by-products valorisation and the specific end-of-life. For the biofuel scenario, a dehydration step using molecular sieve is added to get anhydrous bioethanol. For the bioethylene scenario, industrial dehydration and polymerization steps are added.
Direct comparison between both scenarios is not possible due to different products uses. The comparison was then performed for both scenarios between the bio-based product and its fossil equivalent. ReCiPe 2008 method was used at midpoint level to get the environmental impacts.
As expected, the impact of bio-based products in climate change and fossil fuel depletion categories decreases compared to the fossil counterparts. For other categories, difference is less significant and results are often better for fossil products. Land use change impact was implemented to assess its importance. Depending on assumptions, the greenhouse gas emissions from crop implementation on a natural land can counteract the previous mentioned benefits.
To get an idea of the performance of each considered bioethanol use, a single score relative to the amount of sugar cane and sugar beet cultivated on one hectare was calculated using the endpoint level of ReCiPe 2008 methodology. The environmental gain was then evaluated comparing the bio-based product use with the classical one. The highest performance was obtained for the bioplastic scenario based on sugar cane followed by the sugar beet bioplastic. The E5 biofuel based on sugar beet reaches a slightly lower gain. The E85 fuel obtains less gain due to the higher amount of biofuel needed to drive the same distance as using fossil fuel. When taking the land use change into account, the best gain is given by the sugar beet bioplastic.
On the one hand, this study shows the importance of assumptions, especially in the agricultural field, on the obtained results. On the other hand, it points out that considering bioethanol as a chemical intermediate and not a fuel can be better from an environmental point of view.