WHAT IS THE BEST USE OF SUGAR CROPS? ENVIRONMENTAL ASSESSMENT OF TWO APPLICATIONS: BIOFUELS VS. BIOPRODUCTS

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1 WHAT IS THE BEST USE OF SUGAR CROPS? ENVIRONMENTAL ASSESSMENT OF TWO APPLICATIONS: BIOFUELS VS. BIOPRODUCTS Sandra M. Belboom (1) and Angélique F. Léonard (1) (1) Chemical engineering Processes and Sustainable Development, University of Liège, Belgium Abstract Agricultural crops became through years a possibility 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 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 for both crops, i.e. sugar cane and sugar beet, with all associated energetic and fertilizer consumptions, the transportation from field to the industrial plant, the sugar crops transformation into hydrate bioethanol and the by-products valorisation. For the biofuel scenario, a dehydration using molecular sieve is added to get anhydrous bioethanol. For the bioethylene scenario, an industrial dehydration is 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 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 category 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. This study shows the importance of assumptions, especially in the agricultural field, on the obtained results. Keywords: Life Cycle Assessment (LCA) Bioethanol Sugar cane Sugar beet Bioethylene 1. INTRODUCTION The decrease of fossil fuels reserves and the consequences on the energy security and supply are both main concerns of our century. Currently, fossils fuels permit to reach 80.3% of the consumed primary energy in the world with 58% of them for the transport sector [1]. In the future, reserves will be empty and other sources are needed to meet the continuously growing energy demand [2] at the world level. Aware of the challenge, the European commission defined the targets meaning the reduction of 20% of greenhouse gases (GHG) emissions and of primary energy use by improving energy efficiency together with the increase of 20% of renewable energy in 2020 [3, 4]. All these objectives are interrelated and rely primarily on the contribution of bioenergy to meet them. Biofuels, produced from biomass, are involved in the strategy to limit the dependence in exports and ensure security of supply especially for the transport sector [5]. The most famous crop for the production of biofuels is sugar cane, as produced in Brazil. This crop is not available in Europe where the production of ethanol is performed with sugar beet or wheat.

2 Biofuels for transportation is the most common application of the bioethanol but the chemical field is also easily accessible. Indeed, bioethanol can be catalytically dehydrated to obtain bioethylene which is a monomer allowing the production of a multitude of plastics. Land, as fossil fuel reserves, is not infinite and should be used for the most environmental-friendly application. Both available applications of bioethanol from sugar crops are analyzed for sugar cane cultivated in Brazil and sugar beet grown in Europe, more specifically in Belgium. Their environmental impacts were assessed using the Life Cycle Assessment methodology and ReCiPe 2008 method [6]. This study is in accordance with the ISO standards [7] and [8] and tends to answer the question: What is the best use of sugar crops?. 2. METHODOLOGY 2.1 Goal definition The aim of this study is to compare both applications of bioethanol from different crops. To achieve this comparison, the modelling of the production of bioethanol from sugar cane and from sugar beet was performed and then further s as the dehydration for biofuel or the catalytic dehydration for bioethylene were added. Direct comparison between biofuel and chemical application is not available; the function is not the same. The comparison was then performed for both scenarios between the bio-based product and its fossil equivalent. 2.2 Scope definition Common boundaries of the systems comprise the cultivation for both crops, i.e. sugar cane and sugar beet, with all associated energetic and fertilizer consumptions, the transportation from field to the industrial plant, the sugar crops transformation into hydrate bioethanol and the co-products valorisation. For the biofuel scenario, a dehydration using molecular sieve is added to get anhydrous bioethanol. For the bioethylene scenario, a catalytic dehydration is added. Figure 1 presents common s for sugar cane and sugar beet scenarios. After the production of hydrous ethanol, two possibilities are available. The scenario relative to biofuel is called (1) and the chemical path is named (2). To compare the environmental impact of the biofuel or the bio-plastic produced from sugar cane or sugar beet, the place where they are used, should be the same and is chosen as Antwerp in Belgium. A further transportation is then added for products from sugar cane. Seeds Fuel Fertilizers Pesticides Emissions Cultivation Transportation Sugar crop Ethanol production plant Catalytic dehydration (2) Hydrous ethanol (1) Molecular sieve dehydration End of life Bioplastics Polymerisation Bioethylene Biofuels Use = end of life Figure 1: Boundaries of the study Functional unit is different for both applications. For biofuels path, the functional unit is similar to the amount of E5 fuel needed to drive 100 km. For the chemical path, the unit is equal to the life cycle of one ton of high density polyethylene (HDPE). 2.3 Life cycle inventory analysis

3 Energy and matter balances were performed for all stages of the life cycle assessment for both crops, using average values from literature. Most variable data are relative to cultivation. Indeed, the amount of fertilizers and emissions due to their application can vary depending on the soil type. Data used for the production of 1000 L of hydrous ethanol are presented in Table 1. Ethanol is only produced from juice; it is assumed that the cultivation of crops is dedicated to the production of alcohol. The yield is t/ha for sugar cane and 73 t/ha for sugar beet. Table 1: Inventory for the production of 1000 L of hydrous ethanol Inputs Unit Sugar cane Sugar beet Inputs Unit Sugar cane Sugar beet Cultivation Bioethanol production Seeds kg 0,00 0,36 Sulphuric acid Kg 9,05 7,40 K 2O kg 0,00 23,97 Lime Kg 8,08 191,50 N kg 8,73 16,85 Electricity kwh -358,30 148,44 P 2O 5 kg 8,05 10,14 Steam MJ 5694,20 Pesticides kg 0,54 0,44 Lime kg 45,13 0,00 Fuel L 5,60 22,52 During the cultivation of crops, carbon dioxide from atmosphere is converted by the plant into biomass. In this study, we consider this gain is completely compensated when taking into account the whole life cycle of the product with the ultimate end of life. For sugar cane cultivation, a part of the needed fertilizers is provided by co-products of bioethanol production as stillage or filter cake. For the transformation of sugar cane into bioethanol, bagasse is used as fuel and an excess amount of electricity is produced. That assumption explained the negative value presented in Table 1. For sugar beet transformation into bioethanol, required energy is provided by fossil fuels. After the production of hydrous ethanol, a further is needed to get anhydrous ethanol and HDPE plastic. To drive 100 km, a consumption of 5 L of petrol was assumed, which is converted into 5.08 L of E5 (petrol with 5% of hydrous ethanol). To produce one ton bio-plastics, litres of hydrous ethanol are required. Consumptions are presented in Table 2. Table 2: Inventory for the production of 1 ton of HDPE and 100 km driven with E5 Inputs Unit Biofuel (5,08 L) Bio-plastic (1000 kg) Hydrous ethanol L Petrol L 4.83 / Energy MJ For products from Brazil, a transportation by trucks and boats is added with a distance of respectively 70 km and 2300 km to reach Antwerp in Belgium. End of life is taken into account for fuel during its use and the ultimate treatment of bio-plastic is assumed to be its incineration. 3. RESULTS Results of this study are presented in Figure 2 and permit to highlight which scenario reaches the most impact in each category; the value is expressed in percentage due to the different unit of each impact category. The graphic on the left represents the chemical application and the E5 biofuel application is shown on the right side. To compare bio- scenarios with a fossil counterpart, the commercial Ecoinvent database is used for the HDPE and the petrol.

4 Figure 2: Results for respectively chemical and biofuel applications Figure 2 shows the environmental gain of bio-scenarios for climate change and fossil fuel depletion categories. Differences between bio and fossil scenarios are higher for the chemical application than for biofuel application where they are not significant, due to the slight part of ethanol present in the fuel. Indeed, only 5% of the consumed fuel is the anhydrous ethanol. The environmental gain for bio-hdpe in the climate change category is about 61% and 48% for respectively sugar cane and sugar beet compared to the fossil HDPE. When taking into account the impact of land use change for sugar cane, assuming that the expansion of its cultivation induced the conversion of grasslands into arable land, gain is completely reversed and the impact of the HDPE from sugar cane is 15% higher than for the fossil HDPE. No land use change impact was used for sugar beet. Indeed, no expansion of the cultivation sector in Belgium is currently occurring. For the fossil fuel depletion category, the gain for sugar cane reaches 77% and 42% for sugar beet. For the biofuel application, the obtained environmental gain is less important and is equivalent for the climate change category, to 1.54% for sugar cane and 1.48% for sugar beet. With the land use change impact, sugar cane gain is reduced to 0.04%. The reduction of fossil fuel consumption is equal to 2.30% for sugar cane and 1.36% for sugar beet. For other categories, bio-product reaches a higher impact than its fossil counterpart. This can be explained by the cultivation with the use of fertilizers which contributes to the acidification and eutrophisation. 4. CONCLUSIONS Use of bio-products permits to reduce the impact in climate change and fossil fuel depletion categories compared to the fossil counterparts. When land use change impact is taken into account, the environmental gain for the climate change category, when using sugar cane, is reduced and can be completely reversed for the chemical application. For other categories, conclusion is less evident and results are often better for fossil products. To reduce these impacts and improve the results of bio-products, the decrease of the amount of fertilizers and the improvement of the crops yield are paths to follow. This study shows the importance of assumptions, especially in the agricultural field, on the obtained results and the need of a common criteria for different application of a same feedstock to be able to answer the question: What is the best use of sugar crops?. REFERENCES [1] Escobar, J.C., et al., Biofuels: Environment, technology and food security. Renewable and Sustainable Energy Reviews. 13(6-7): p [2] Owen, N.A., O.R. Inderwildi, and D.A. King, The status of conventional world oil reserves-- Hype or cause for concern? Energy Policy. 38(8): p [3] Nigam, P.S. and A. Singh, Production of liquid biofuels from renewable resources. Progress in Energy and Combustion Science. In Press, Corrected Proof. [4] European Commission. The EU climate and energy package /02/2011]; Available from: [5] Lindfeldt, E.G., et al., Strategies for a road transport system based on renewable resources - The case of an import-independent Sweden in Applied Energy. 87(6): p

5 [6] Goedkoop, M., et al., ReCiPe A life cycle impact assessment method which comprises harmonised category indicators at the midpoint and the endpoint level, Ruimte en Milieu, Editor [7] ISO, ISO : Management environnemental - Analyse du cycle de vie - Principes et cadre, 2006, ISO. [8] ISO, ISO : Management environnemental - Analyse du cycle de vie - Exigences et lignes directrices, 2006, ISO.