Comparative Life Cycle Assessment of Biodiesel Production from

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Comparative Life Cycle Assessment of Biodiesel Production from Cardoon (Cynara cardunculus) and Rapeseed Oil Obtained under Spanish Conditions Javier Dufour,*,†,‡ Jesús Arsuaga,‡ Jovita Moreno,§ Hely Torrealba,‡ and Javier Camacho †

Instituto IMDEA Energía, c/Tulipán s/n 28933 Móstoles, Spain Universidad Rey Juan Carlos, ESCET, Department of Chemical and Energy Technology, c/Tulipán s/n 28933 Móstoles, Spain § Universidad Rey Juan Carlos, ESCET, Department of Chemical and Environmental Technology, c/Tulipán s/n 28933 Móstoles, Spain ‡

ABSTRACT: The high demand of fuels and the problems associated with the resources depletion and environmental effects of its production have motivated the search for alternative sources. An interesting option in Spain is the cultivation of Cynara cardunculus as primary raw material of biodiesel manufacture. In this paper, the environmental feasibility of the value chain form cropping to fuel manufacture is studied for Cynara cardunculus oil (CCB) and compared to rapeseed oil (RSB) through life cycle assessment, according to the ISO Standard 14040 and using the Gabi software v4.3 as calculation tool. The functional unit selected was 1 tonne of biodiesel. The total energy consumption and the energy return on energy investment (EROEI) were calculated from energy balance. The indicators for life cycle assessment corresponding to impact categories in human health, ecosystem quality and resources depletion were estimated by means of Ecoindicator 99 method. Obtained EROEI values (calculated considering only the calorific power of the oil) indicate that the energy balance is more positive for Cynara cardunculus than for rapeseed (EROEI = 1.53 for CCB and 1.20 for RSB). Moreover, biodiesel from cardoon shows lower environmental impacts.

1. INTRODUCTION The energy goals fixed in both Europe and Spain are focused on increasing the biomass as energy source in the midterm.1 In Spain, some traditional oleaginous crops as sunflower, rapeseed, and soybean are used for the extraction of oils dedicated to biodiesel production, a fuel with characteristics similar to conventional diesel from crude oil. This constitutes the first generation biofuels, which are obtained from crops that share alimentary and energy use. Rapeseed is one of the typical raw material for biodiesel production.2,3 Thus, its use has contributed to increase the area allocated to rapeseed cultivation in Spain in recent seasons.4 The rapeseed cultivation is highly recommended in a crop rotation with cereals such as wheat and barley,5−8 and it has been proposed for farms in Navarra and Castilla y León regions, due to the high yields achieved (around 3500 kg/ ha).9,10 The rapeseed is considered a crop with high requirement of P and K fertilizers before planting. Besides, it needs N-fertilizers concentration similar to cereal crops, near 50−60 fertilizer unit/tonne (t) expected. After planting, the N, P, and K fertilization in rapeseed generally is dosed in accordance with soil characteristics and climate conditions, following suggested programs well described in literature.4,11,12 The introduction of rapeseed into European crop rotations has shown favorable results to reduce diseases of grains by means of pest control and the contribution to improve the soil characteristics.8 These conventional raw materials for biofuels have provoked a growing discussion, since they are pointed out as responsible for raising the price of some foods. Several studies have shown © 2013 American Chemical Society

the benefits of using of nonfood crops for energy purposes:13−15 high yields, no competition with alimentary uses, and similar technologies to those employed commonly for first generation biofuels. The cardoon (Cynara cardunculus) is recognized as one of the potential source of biomass for energy purposes in Spain16−18 especially in transport sector.19 The oil can be extracted by means of cold press extraction of the seeds and processed conveniently for biodiesel production, by transesterification of the triglycerides using alcohol in presence of an alkaline catalyst, yielding the methyl or ethylic esters of the fatty acids (biodiesel), depending on the alcohol employed.20,21 The cardoon (Cynara cardunculus) is grown in a perennial cultivation system with an about ten year-old useful life and harvested at the end of the annual plant growth cycle on rainfed conditions. It is well adapted to Mediterranean conditions.19,22−24 Thus, experiments about cardoon biomass production under rainfed conditions in central Spain have proved a productive life of more than 10 years with an average production of 14 t dry biomass/ha year (used in this study).23 The Cynara cardunculus cultivation for industrial use includes an initial period, during the first year, for crop establishment and the subsequent periods of production. The aim of this paper is to determine the environmental feasibility of Cynara cardunculus as primary raw material for second generation biofuels and compare it to first generation Received: May 21, 2013 Revised: July 24, 2013 Published: July 24, 2013 5280

dx.doi.org/10.1021/ef400951f | Energy Fuels 2013, 27, 5280−5286

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(rapeseed-based) ones. A life cycle approach is compulsory to ensure the actual environmental benefits in the whole valuechain of these alternative fuels. Life cycle assessment (LCA) has proven to be a key tool to investigate the real performance and viability of biofuels (see references list). Therefore, this methodology has been used in the development of the research summarized in this paper.

Table 1. Inventory Data for Biodiesel Production from Cynara cardunculus and Rapeseed (per tonne of Produced Biodiesel) stage cultivation

2. EXPERIMENTAL SECTION

a

biomass transportation mechanical separation oil extraction

The systems studied in this work includes cultivation of raw material, crop transportation, manufacturing, and distribution of biodiesel. The functional unit selected is the production of 1 t Cynara cardunculus and rapeseed biodiesel (CCB and RSB, respectively) obtained under Spanish conditions, in order to compare the environmental burdens associated with the flows defined by each stage of the life cycle inventory. The main objective is to determine the most environmental-friendly process and the energy efficient one. 2.1. Systems Description. For Cynara cardunculus the system boundaries have been defined within the stages: cultivation, crop transportation, mechanical separation of seeds, oil extraction, transesterification with methanol, and biodiesel distribution (see Figure 1).

transesterification

distribution

value CSBa

value RSBb

unit

fertilizer pesticides diesel diesel

0.433 0.003 0.065 0.062

0.576 0.020 0.046 0.021

t kg t t

power power hexane steam alcohol (methanol) potassium hidroxide sulphuric acid phosphoric acid steam power water diesel

0.48 1.28

0.09 0.0007 0.43 0.106 0.011

GJ GJ t t t t

0.0046 0.68 0.142 0.025 0.002

t t t GJ t t

flow

0.156 0.0052 0.0056 0.342 0.18 0.002

a

Yield for establishment campaign: 5.6 t biomass/ha; yield for normal campaign: 14 t biomass/ha; percentage of seed in biomass: 10%; seed oil content: 25%. bYield for establishment campaign: 3.5 t biomass/ha; yield for normal campaign: 11 t biomass/ha; percentage of seed in biomass: 35%; seed oil content: 39%.

biodiesel from Cynara cardunculus oil seeds, obtained from the cultivation under rainfed conditions. The system boundaries and the reference flows of the rapeseed biodiesel system have been defined within the stages: cultivation, crop transportation, oil extraction, transesterification with methanol, and biodiesel distribution (see Figure 2). The cultivation subsystem delivers the seeds, which are taken to the oil mill for oil extraction, making unnecessary a mechanical separation stage.

Figure 1. System boundaries and reference flows of the Cynara cardunculus biodiesel.

The system defined for the Cynara cardunculus biodiesel production includes the data set for the first year or the crop establishment, with flows of material and energy according to the suggested values given by literature.13,18,19,22,23 It is assumed that the biomass yield of the crop establishment campaign reaches 40% of the maximum set of 14 t biomass/ha year.25 The cultivation labors starts with basal dressing, with the recommended addition of 1000 kg/ha of 9:18:27 NPK complex fertilizer.17 Only mineral fertilizers are considered in this work. The next step is preparing the land for planting with a couple of passes of ploughing and harrowing. After planting and before crop emergence, it is necessary to provide treatment with a herbicide: 1.5 kg/ha of alachlor and 0.4 kg/ha of linuron.19 Since the second year, the material and energy flows are defined for the maximum biomass yield, taken into account the nutrients needed to replace those extracted by the Cynara cardunculus crop, as well as the field techniques and fuels necessary for harvesting and weed control. It has been determined that each dry cardoon tonne extracts 12.6 kg nitrogen, 3.5 kg of phosphorus, and 20.8 kg of potassium.19 When cardoon plants are fed to a mechanical separation system, seeds represent a 10 wt % of the total biomass.21 Once seeds are separated, they are transported to the extraction plant. A 25 wt % of oil is obtained by cold press.20,23 Methanol is used for transesterification of Cynara cardunculus oil to obtain methyl ester under the following conditions: molar ratio of methanol/oil = 9:1, reaction temperature = 60 °C, reaction time = 120 min using potassium hydroxide catalysts ([KOH] = 0.5 wt % referenced to the total mixture oil-methanol). According to literature, these conditions lead to a yield to methyl ester around 92%.20 Finally, for biodiesel distribution, a distance of 100 km was supposed. Table 1 shows the main materials and energy flows used in each stage defined for the inventory life cycle of the production of

Figure 2. System boundaries and reference flows of the rapeseed biodiesel (RSB).

The rapeseed is cultivated in central Spain, where averages yield of 3845 kg of seeds/ha has been reported for the species adapted to Spanish conditions.9 This value is used in this study for the inventory of the cultivation stage. According to fertilizing recommendations taken from Urbano11 and local fertilizer producers,12 rapeseed cultivation requires 400 kg/ha of 9:18:27 NPK complex fertilizer before planting and 88.2 kg of urea on top dressing. Moreover, rapeseed cultivation has requirements in weed control, through the use of pesticides applied in the early stage of the growth cycle. Thus, it is necessary to provide treatment with herbicides: 5.56 kg propachlor/ha and 6.0 kg metolachlor/ha; fungicide dosage of 16.43 kg maneb/ha, and an insecticides dosage of 2.0 kg carbofuran/ha before flowering.4 5281


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available resources.30 Only nonrenewable resources are evaluated: fossil fuels (MJ surplus) and minerals (MJ surplus). One important aspect dealing with biofuels and energy crops is fields emissions. Eco-indicator 99 uses a methodology based on a soil model (SMART) and a vegetation response model (MOVE) to estimate them.29

The process chain of biodiesel from rapeseed comprises the transport of seeds to the plant, where the oil is extracted through the conventional methodology based on chemical extraction with hexane. This method allows obtaining oil yields about 91%. The unrefined oil is taken to an additional process to eliminate pollutant compounds in order to get a better yield in the posterior biodiesel production.2 The rapeseed oil is transformed by the conventional transesterification of triglicerides with methanol in presence of an alkaline catalyst to obtain methyl ester and glycerol.2 The reaction conditions are taken from literature, using a molar ratio of methanol/oil of 6:1, a temperature of 60 °C, with reaction times of 120 min, and potassium hydroxide as catalysts, with a concentration of 0.5 wt % (referenced to the total mixture oil−methanol). Under these conditions, the reaction yields obtained are about 98%.2 For biodiesel distribution, also a distance of 100 km between manufacturer and consumer was supposed. In summary, the main materials and energy flows used in each stage of the analysis inventory life cycle of the production of biodiesel from rapeseed, cultivated in crop rotation system, are showed in Table 1. 2.2. LCA Tools and Evaluation Methods. Gabi Software 4.3 (PE International) was used as calculation tool. The life cycle inventories defined in database Ecoinvent version 2.0 for transport, field techniques, fertilizers, pesticides, diesel, alcohols, and chemicals were used. The processes incorporated in the database, with different conditions than local (i.e., transport distances and energy mix), were adapted to the local situation. Inventory data were adjusted to the requirements for the production of 1 t of biodiesel. The energy is referred to Spanish conditions with the share of energy sources showed in Table 2.26

3. RESULTS 3.1. Main Inputs. Resources Consumption. The results of the consumption of material resources are shown in Figure 3.

Figure 3. Material resources consumption of the life cycle of 1 t of Cynara cardunculus biodiesel (CCB) and 1 t rapeseed biodiesel (RSB) production.

Table 2. Share of Energy Sources for the Spanish Energy Mix 201026 source

contribution to the energy mix (%)

hard coal heavy fuel oil hydro natural gas nuclear wind others

8.0 1.0 14.0 23.0 21.0 16.0 17.0

Main differences observed between both systems are related to water and carbon dioxide inputs: 5.4 t of water and 9.8 t of CO2 for CCB and 19.6 t of water and 6.8 t of CO2 for RSB. Cultivation of rapeseed in central Spain requires irrigation while the cardoon is a rainfed crop leading to lower water consumption. Since water resources are sometimes limited in several places of central Spain, the lower water consumption is a remarkable result that must be considered to choose energy crops in this region. Regarding carbon dioxide, the amount of seeds (and dry biomass) necessary for the production of 1 t of biodiesel is higher in the case of the cardoon (see Figures 1 and 2). That involves more CO2 fixation during the crop development for obtaining the same quantity of final biofuel. Regarding the nonrenewable resources used (materials and energy) in both processes, they mainly come from the manufacture of agricultural inputs (fertilizers and pesticides), the fuels used for farm and industrial machinery, and the electricity demanded by several operations. It can be observed that RSB system requires more nonrenewable energy resources (indicating a higher energy demand) whereas the consumption of nonrenewable materials is slightly higher for CCB. 3.2. Main Outputs. Emissions. Air emissions (mainly emissions of exhaust gases, carbon dioxide, and other inorganic compounds such as steam) were produced in the overall process, resulting in a flow of 5.4 t/t biodiesel from Cynara cardunculus oil. These emissions are related to the production of fertilizers and pesticides, combustion of fossil fuels for agricultural labors and transportation vehicles, and heat and energy generation for industrial applications. It can be observed that the emissions of fossil carbon dioxide associated with CCB are lower than those corresponding to RSB (1.1 t/t biodiesel and 1.6 t/t biodiesel, respectively; see Figure 4). This is probably related to the higher fertilizer and pesticides amounts demanded for rapeseed cultivation, which involves higher CO2

In addition, the energy return on energy investment (EROEI) parameter was determined. It is defined as the ratio between the energy produced and the total energy consumed (energy input) by the system under consideration.27 This value was calculated using the following expression: EROEI =

Energyoutput Energyinput

(1)

The energy output was estimated with the lower heating values of the biodiesel from both sources (taken from the literature).14,28 The life cycle impact assessment was performed with the Ecoindicator 99 method. In this methodology, the environmental impacts are related to three damage categories: human health, ecosystem quality, and resources depletion. The ecosystem quality damage categories use the Potentially Disappeared Fraction (PDF m2· a), a indicator model expressing the ecosystem damage as a relative difference between the number of species in reference conditions in relation to those resulting from the use of the land during a certain time.29,30 The damage categories assessed are acidification/eutrophication, ecotoxicity, and land conversion. The human health damage categories include: carcinogenic effects, climate change, ozone layer depletion, radiation, respiratory effects (inorganic and organic) expressed by means of DALY (Disability Adjusted Life Years) unit.30 The resources damage categories are defined in Ecoindicator 99 by means of a model based on reducing the concentration of a given resource, leaving future generations with lower concentrations of 5282


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rapeseed requires more nutrients than cardoon. As well, it is more sensitive to weed being necessary higher amounts of herbicides, fungicides, and insecticides.4 Besides, the manufacture of mineral fertilizers involves lower energy consumption that the production of urea31 and whereas cardoon farm uses mainly mineral fertilizers,32 urea is usually employed for rapeseed cultivation,11,12 increasing the energy demand. On the other hand, stages of biomass transportation, oil extraction, and transterification consume more energy by using cardoon. For the production of 1 t of biodiesel, it is necessary much higher amount of cardoon biomass with regards to rapeseed biomass; thus, more energy must be used for transportation and extraction. Likewise, for obtaining Cynara cardunculus oil, the extraction is carried out only by means of mechanical methods, which involve important energy requirements. In the transesterification stage, the variations observed in energy consumption are related to different reaction conditions. Specifically, the higher requirements of methanol for the conversion of cardoon oil in comparison with rapeseed oil (molar ratio methanol/oil = 9 for CCB and 6 for RSB) is the main factor that contributes to the higher energy demand during the transesterifcation stage of CCB system. In conclusion, RSB energy demand is a 45% higher than that corresponding to CCB system indicating a better energy performance for Cynara cardunculus biodiesel. Moreover, the Energy Return on Energy Investment (EROEI) of both systems was calculated by means of eq 1 (which shows the relation between the energy produced and the energy consumed). As expected, the EROEI value of CCB (1.53) is higher than RSB (1.20). Both raw materials lead to positive energy balance (more energy produced than consumed). However, rapeseed biofuel shows a lower value due to higher energy consumption along its processing. Both EROEI values are especially remarkable since they have been estimated without considering the energy use of the rejected parts of the plant during seeds separation and/or oil extraction. It is known that the use of byproducts would raise the energy performance in both cases. Especially interesting are some works,33,34 which have demonstrated the usefulness of the leaves and crop residues for the production of solid fuel for steam boilers (pellets) from Cynara cardunculus biomass. Several alternative scenarios have been also described for using byproducts of rapeseed biodiesel production.3

Figure 4. Emissions of the life cycle of 1 t Cynara cardunculus biodiesel (CCB) and 1 t rapeseed biodiesel (RSB) production.

emissions. Besides, considering inputs previously commented, global CO2 balance would be negative for both processes: −8.7 kg CO2 for CCB and −5.6 for RSB. Therefore, even considering all the production stages necessary for the transformation of biomass into biodiesel, CCB and RSB production processes can be considered as a fossil CO2 sink. However, it must be taken into account that this negative balance will be very different if biodiesel use and/or the utilization of biomass waste are incorporated into system boundaries since, in that case, CO2 fixed during the cultivation will be partially (or totally) returned to air after combustion processes.” Regarding the rest of emissions (inorganic and others), they are slightly higher for CCB system. This kind of emissions mainly includes residual steam and exhaust air coming from electricity production. As detailed, the oil extraction from rapeseed is carried out by chemical extraction whereas, for cardoon, the most usual is to employ only mechanical processes, which involve higher electricity consumption, leading to more residual steam and exhaust air emissions. 3.3. Energy Balance. The total energy consumption for the production of biodiesel from Cynara cardunculus oil was estimated at 23.05 GJ. The same parameter was 33.60 GJ for RSB. The energy resources consumed by each stage of both systems are detailed in Table 3. For rapeseed system, the highest consumption was obtained for the cultivation stage. Actually, this stage involves almost the 80% of the energy requirements of the whole process. It is related to the manufacture of fertilizers and pesticides. As previously described (see Table 1), needs of fertilizers and pesticides are much higher for RSB than for CCB because

4. DISCUSSION 4.1. Damage Categories in Ecosystem Quality. As shown in Figure 5, biodiesel production from rapeseed oil clearly involves higher environmental impacts than from Cynara cardunculus for all the evaluated categories related to the ecosystem quality damage. Among the impact categories, the acidification/eutrophication is the most significant value for both systems. However, for CCB system is 50% lower than for RSB one. This result can be associated with emissions of nitrogen oxides, sulfur oxides, and ammonia from the fertilizers used in the cultivation stage. The better result obtained for CCB is attributed to the lower requirement of N, P, and K fertilizers since the second year of the cultivation. On the other hand, CCB also exhibits a lower ecotoxicity than RSB, getting a reduction around 90%. This result is related to lower emissions of heavy metals and toxic compounds derived from the lower demand of pesticides, weed control substances, and fertilizers. The cultivation of rapeseed demands

Table 3. Energy Consumption in Life Cycle of CCB and RSB Systems (per t Biodiesel Produced) CCB

RSB

stage

GJ

%

GJ

%

cultivation biomass transportation mechanical separation oil extraction transesterification distribution total

6.94 3.14 1.87 3.62 7.37 0.11 23.05

30.1 13.6 8.1 15.7 32.0 0.5 100.0

26.2 1.02

78.1 3.0

0.80 5.43 0.11 33.60

2.4 16.2 0.3 100.0 5283


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51% in comparison to that obtained for rapeseed. As commented, the cultivation stage in the RSB system demands larger amounts of mineral fertilizers to meet the requirements of the crop, which means significant emissions with respiratory effects. The impact assessment for climate change revealed a negative value for the indicators calculated for CCB and RSB due to the fixation of CO2 during the cultivation stage of both crops. It should be noted that these indicators do not include the use of biodiesel and the subsequent emissions are not estimated. In any case, differences observed between both systems are related to the higher amount of biomass needed in the case of CCB and the higher GHG emissions associated with the use of more fertilizers for rapeseed cultivation. In this way, it should be noted that for the quantification of greenhouse effect, not only the CO2 is taken into account but also other emissions as N2O, CO, or CH4 are considered. For agricultural processes, the presence of the N2O is especially relevant since the application of nitrogen-containing nutrients on the field is one of the most important sources of this pollutant, which warms the atmosphere over 300 times more than CO2. Moreover, nitrous oxide is generated as a byproduct during the production of nitric acid, which is used to manufacture commercial fertilizers. Finally, the values estimated for carcinogenic effects, ozone layer depletion, radiation and respiratory effects (organic) categories are less significant than those above commented. However, it is remarkable that all of them are lower for CCB system probably due to the lower toxic emissions coming from the lower use of pesticides and weed control compounds when the cardoon is used. As a conclusion, the production of biodiesel from Cyanara cardunculus oil shows also a better environmental profile considering the effects on human health. 4.3. Damage Categories in Resources Depletion. Resources depletion was estimated for nonrenewable resources (fossil fuels and minerals), as represented in Figure 7.

Figure 5. Ecosystem quality indicators of Cynara cardunculus (CCB) biodiesel and rapeseed biodiesel (RSB) production.

a strict weed control, mainly during the early stages of the plant growth cycle. Land use and conversion category refers to the change in the number of species occurring on the occupied or converted land itself and to the changes on the natural areas outside the occupied or converted area. In this case, the indicator determined for CCB system showed a 30% lower value than RSB system. However, land use and conversion is the third category on relevance in RSB system and less significant in CCB system. The higher nutrient requirements of the rapeseed contributes more to land exhaustion making necessary the conversion of more natural land for agricultural use. Similar results have been reported by Sanz-Requena,35 who evaluated biofuel production processes from rapeseed and other conventional crops. The lower values of indicators for damage categories in ecosystem quality for the CCB system than for RSB one involves a significant lower incidence of environmental burdens, achieving a better environmental performance. 4.2. Damage Categories in Human Health. Results shown in Figure 6 indicate that the most relevant damage category in human health is respiratory effects (inorganic) for both systems, the CCB and RSB. By using cardoon the value of the respiratory effects (inorganic) indicator is reduced down to

Figure 7. Resources depletion indicators of Cynara cardunculus biodiesel (CCB) and rapeseed biodiesel (RSB) production.

The indicator for fossil fuels is the most important value in resource damage assessed for both, the CCB and the RSB systems. CCB showed a favorable result in comparison with the fossil fuel depletion of RSB system, a reduction estimated in 35%. This result is consistent with the energy balance previously analyzed where fabrication of biodiesel coming from rapeseed oil needs 45% more energy than that corresponding to cardoon system.

Figure 6. Human health indicators of Cynara cardunculus biodiesel (CCB) and rapeseed biodiesel (RSB) production. 5284


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(10) Goñi, J.; Irañeta, J.; Sexmili, J. R.; Lafarga, A. La Colza en ́ de Navarra: Navarra, Navarra; Instituto Técnico y de Gestión Agricola Spain, 2008. http://www.navarraagraria.com/n170/arcolz08.pdf (11) Urbano, P. Abonado de las Oleaginosas Herbáceas: Girasol, Colza y Soja. Guiá Práctica de la Fertilización Racional de los Cultivos en España; Ministerio de Ambiente, Medio Rural y Marino: Madrid, 2009; pp 165−171. (12) Guiá del Abonado. Cultivos Tradicionales; Fertiberia: Madrid, 2010. http://www.fertiberia.es/templates/cultivos.aspx?M=237&P= 107&D=108&F=109 (13) Fernández, J.; Curt, M. D. 2nd World Conference and Exhibition on Biomass for Energy; Industry and Climate Protection: Rome, 2004. http://www.cres.gr/bioenergy_chains/files/pdf/Articles/13Rome%20OB6.2.pdf (14) Lapuerta, M.; Armasa, O.; Ballesteros, R.; Fernández, J. Fuel 2005, 84, 773−780. (15) Martínez, C. Análisis de Ciclo de Vida del Cultivo Energético Brassica sp.; Institut de Ciència i Tenologia Ambientals. Universitat Autónoma de Barcelona: Barcelona, 2006; pp 168. (16) Fernández, J.; Curt, M. D. 14th European Biomass Conference on Biomass for Energy; Industry and Climate Protection: Paris, 2005. http://www.cres.gr/bioenergy_chains/files/pdf/Articles/16Paris%20PB1_1.pdf (17) Fernández, J.; Curt, M. D.; Aguado, P. L. Ind. Crops Prod. 2006, 24, 222−229. (18) Angelini, L. G.; Ceccarini, L.; Di Nasso, N.; Bonari, E. Biomass Bioenergy 2009, 33, 810−816. (19) Gominho, J.; Lourenço, A.; Palma, P.; Lourenço, M. E.; Curt, M. D.; Fernández, J.; Pereira, H.. Ind. Crops Prod. 2011, 33, 1−6. (20) Encinar, J. M.; González, J. F.; Rodríguez, J. J.; Tejedor, A. Energy Fuels 2002, 16, 443−450. (21) Pasqualino, J. Cynara cardunculus as an Alternative Crop for Biodiesel Production; Departament of Chemical Engineering. Universitat Rovira i Virgili: Tarragona, 2006; pp 184. (22) Gominho, J.; Fernández, J.; Pereira, H. Ind. Crops Prod. 2001, 13, 1−10. (23) Curt, M. D.; Sánchez, G.; Fernández, J. Biomass Bioenergy 2002, 23, 33−46. (24) Portis, E.; Acquadro, A.; Longo, A. M. G.; Mauro, R.; Mauromicale, G.; Lanteri, S. J. Biotechnol. 2010, 150, 165−166. (25) Balance Energético de la Producción de Pellets a Partir de Cynara ́ cardunculus; Consejeriá de Agricultura y Pesca. Junta de Andalucia: Sevilla, S pain, 2009 . h ttp: //www.j un tadeandalucia.es/ agriculturaypesca/portal/servicios/estadisticas/estudios-e-informes/ desarrollo-rural-sostenible/energeticos/index.html (26) El Sistema Eléctrico Español; Red Eléctrica Española: Madrid, 2010. http://www.ree.es/sistema_electrico/pdf/infosis/Inf_Sis_Elec_ REE_2010.pdf (27) Monti, A.; Fazio, S.; Venturi, G. Eur. J. Agron. 2009, 31, 77−84. (28) Lang, X.; Dalai, A. K.; Bakhshi, N. N.; Reaney, M. J.; Hertz, P. B. Bioresour. Technol. 2001, 80, 53−62. (29) Goedkoop, M.; Spriensma, R. The Eco-Indicator 99. A Damage Oriented Method for Life Cycle Impact Assessment Methodology Report; PRé Consultants B.V.: Amersfoort, 2001. http://www.presustainability.com/download/misc/EI99_annexe_v3.pdf (30) Antón, A.; Castells, F.; Montero, J. I. J. Cleaner Prod. 2007, 15, 432−438. (31) Audesley, E. Harmonisation of Environmental Life Cycle Assessment for Agriculture, Final Report Concert Action AIR3-CT942028; Silsoe Research Institute: Silsoe, 1997. (32) Mantineo, M.; DÁ gosta, G. M.; Cpani, V.; Parabe, C.; Cosentino, S. L. Field Crop. Res. 2009, 114, 204−213. (33) Dahl, J.; Obernberger, I. 2nd World Conference and Exhibition on Biomass for Energy; Industry and Climate Protection: Rome, 2004. http://www.cres.gr/bioenergy_chains/files/pdf/Articles/10Rome%20OE1_1.pdf (34) Danalatos, N.; Tachoulas, G. Production of Solid Biofuel from Cynara cardunculus (Wild Artichoke) Cultivation. US Patent 20100083569, 2010; pp 1−3.

The energy demand is mainly related to the fuel used by agricultural machinery on cultivation labors and processes for manufacturing fertilizers, pesticides, and other agricultural inputs. Besides cultivation stage, oil extraction and refining, as well as transesterification reaction, contribute to increase the consumption of fossil fuels, and thus, the corresponding indicator shown in Figure 7. Finally, mineral depletion is significantly lower than fossil fuel depletion. It is especially important the difference between CCB and RSB, which clearly evidence the influence of the fertilizers production, where minerals as phosphatic rock for Pfertilizers and potash to K-fertilizers are the main raw material to obtain mineral fertilizers. 4.4. Final Remarks. As a conclusion, the comparative life cycle impact assessment of biodiesel obtained from Cynara cardunculus and rape seeds revealed the lower contribution of the CCB process on the consumption of material and energy resources. In this way, the much lower water requirements of cardoon regarding rapeseed is a remarkable factor for locations with water scarcity problems. Moreover, the estimated value of EROEI for both systems indicates that the CCB process has a more positive energy balance (EROEI = 1.53 for CCB and 1.20 for RSB). Regarding climate change, results indicate that the process for Cynara cardunculus (without including biodiesel use and energy generation from waste or byproducts) can be considered a sink for fossil carbon dioxide, because the CO2 fixed by the crop along the cultivation stage (corresponding to biomass growth up to obtaining 43.3 t) is higher than that emitted to air. Concerning all the damage categories evaluated (human health effects, ecosystem quality and resources depletion), the production of biodiesel from Cynara cardunculus oil shows a better environmental performance, being an interesting option for reducing environmental burdens of biofuels production.

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Corresponding Author

*Phone: +34 914888138. Fax: +34 91 4887068. E-mail: javier. [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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