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Evaluacion del impacto ambiental del uso de nanoparticulas de alumina como aditivo de mezclas biodiesel/diesel mediante analisis de ciclo de vida.

Environmental impact study by life cycle assessment of the use of alumina nanoparticles as an additive in biodiesel/diesel blends 1. Introduction

Worldwide tendency on the search for new energetic alternatives has promoted the development of biofuels as a possible solution for the depletion of petroleum. At a national level, biodiesel is one of the biofuels that has been on the rise recently. This can be evidenced when comparing the 163.7 thousand tons that were produced in 2009 with the 448.8 thousand tons in 2012 (Fedebiocombustibles, 2012). A growing tendency is expected in the years to come. Biofuels such as biodiesel can be total of partial substitutes of fossil fuels and they can become a new income source for agriculture. However, high environmental and socio-economic impacts in the production of biodiesel are complicated issues being critically discussed in today's sustainability schemes (Consorcio CUE, 2012). Emissions caused by the use of biodiesel and the fact that its performance is lower than the one of petroleum diesel, represent topics that are still under consideration.

It is important to notice that despite the advantages ofbiodiesel, this fuel continues to be used along with fossil fuels, and more specifically with petroleum diesel. Although contaminant emissions caused by fuel combustion are reduced when using biodiesel, they cannot be completely eliminated. In the particular case of soot emissions from incomplete combustion, which worsen the greenhouse effect, they can be reduced in a much easier way than the ones from carbon dioxide by using additives that promote complete combustion (Soutter, 2012).

Fuel additives increase biodiesel competitiveness by improving fuel consumption and reducing greenhouse emissions (Park et al., 2007). Ganesh & Gowrishankar (2011) studied the effect of adding magnalium (Al-Mg) and cobalt oxide (C[O.sub.3][O.sub.4]) nanoparticles to Jatropha biodiesel at a concentration of 100 mg/L. These nano-additives were able to achieve a maximum reduction of 60% of unburned hydrocarbons, 50% of carbon monoxide and 45% of N[O.sub.x] emissions (Ganesh & Gowrishankar, 2011).

It has been found that alumina nanoparticles improve engine performance and reduce exhaust emissions (Kao et al. 2008), but they can also generate environmental problems when expelled through the flue gases. Thus, an assessment on the possible impacts of the release of these nanoadditives to the environment is essential, as much as a comparison between the potential improvements regarding emissions (Soutter, 2012).

Methodological tools dealing with the environmental assessment of biofuels production have already been reported (Consorcio CUE, 2012). Nevertheless, synthesis of nanoparticles has not been integrated to the lifecycle of the fuel that is currently being used in Colombia (B10). Therefore, the present work is performed according to Life Cycle Assessment methodology, and it focuses on the environmental evaluation of such alternative. This allows the identification of opportunities to integrate different development areas to prevent contamination and reduce resource consumption.

2. Methodology

The environmental impact of the use of nanoparticles as additives in diesel/biodiesel blends was assessed by means of a cradle-to-grave methodology. This analysis is based on ISO 14040:2006 regulation (International Organization for Standardization, 2006), which divides Life Cycle Assessment into four stages, as illustrated in Figure 1.

2.1 Quantification of the environmental impacts of the process

The first stage is also known as Life Cycle Inventory (LCI) and itconsists in datacollection and structuration in order to quantify all of the environmental loads that are associated to the functional unit (Castells & Montero, 2004) (International Organization for Standardization, 2006).

In this study the functional unit was defined as the energy that is produced when 1 kg of diesel fuel blend with 10% biodiesel and nanoparticles (A[l.sub.2][O.sub.3]) at 10 and 20 ppm is consumed.

The system under study was subdivided into the following process units: (i) synthesis of alumina nanoparticles; (ii) biodiesel production; (iii) addition of alumina nanoparticles to the biodiesel/diesel blend; and (iv) combustion. Inlets, outlets, products and byproducts were defined for each stage, expressed on the basis of the functional unit.

2.2 Selection of impact categories, indicators and models

Selection of the impact categories that represented the largest contribution to the environmental consequences that are studied in this work was executed in accordance to ISO 14044:2006 regulation (International Organization for Standardization, 2006).

An impact category is defined as a class that represents the environmental consequences caused by processes of product systems. Table 1 summarizes some of the main impact categories in Life Cycle Analysis (Castells & Montero, 2004) (International Organization for Standardization, 2006).

Calculations for these categories were made using the SIMAPRO software, its ECOINVENT database (Goedkoop et al., 2008) and Leiden University's model of Environmental Sciences (CML).

2.3 Impact Assessment of the process

In this stage, the results of the inventory analysis and environmental impact were combined, in order to determine the stage of the LCA study in which the main environmental impacts are generated. This allows the identification of critical stages that could be improved (Castells & Montero, 2004).

3. Results and discussion

3.1 Life cycle inventory

Life cycle inventory of the case study (Figure 2) was performed using mass and energy inputs, products, byproducts, wastes and air, ground and water emissions. All of the data was expressed in terms of the functional unit of reference.

Biodiesel inventory was obtained from the official reports provided by the Ministry of Mines and Energy of Colombia. This information is based on the average biodiesel production process in the northern area of Colombia, from moment the biomass is harvested, up to the refining stage (Consorcio CUE, 2012). In addition, Ecoinvent database of the Simapro software was used to obtain the inventory of diesel.

3.2 Inventory of the nanoparticles synthesis process

Inventory data was extracted from the experimental work performed by Penalosa & Rincon (2014).

They synthetized alumina nanoparticles through the sol-gel method , which consisted on preparing a citric acid and aluminum nitrate solution in distilled water, with a concentration of 0.5 M of each substance. This solution was placed on a thermal plate with magnetic agitation for 2 hours at 60[degrees]C until an amber color was achieved (Penalosa & Rincon, 2014). Then, it was heated at 80[degrees]C for an additional 90 minutes, maintaining the constant agitation. The obtained gel was later taken into an oven at 200[degrees]C in order to eliminate the remaining water content, and it was finally burnt at 1000[degrees]C for 2 hours (Li et al., 2006).

Ecoinvent database was used to obtain the inventory of the chemical reagents (citric acid and aluminum nitrate) that were involved in the synthesis of alumina nanoparticles. In the case of citric acid, a fermentation process using Aspergillus Niger to convert sugar into acid was considered, whereas the reaction between nitric acid and aluminum hydroxide was used for the aluminum nitrate (Eq. 1):

3HN[O.sub.3] + Al[(OH).sub.3] [right arrow] Al[(N[O.sub.3]).sub.3] + 3[H.sub.2]O (1)

Table 2 shows the inlets and outlets of the production of alumina nanoparticles. This information was evaluated during the synthesis process, which allowed the determination of consumption ratios (energy and mass) and emissions per gram of synthesized nanoparticles.

3.3 Inventory for the combustion process of the B10 blend with nanoadditives

Determination of the inventory for the stage of combustion was performed using the Diesels-RK software, developed by the Bauman Moscow State Technical University (BMSTU). The specifications that were used correspond to the diesel engine of a Renault Logan with direct injection, which is one of the most common vehicles in Colombia.

Table 3 presents the inlets of the combustion process for the diesel/biodiesel blend by using a nanoadditive concentration at 10 and 20 ppm. Table 4 shows the combustion emissions of this stage after the generation of mechanical energy for the motor has taken place. The combustion gas analyzer for this engine quantified the emissions of N[O.sub.x], C[O.sub.2], S[O.sub.2] and particulate matter.

3.4 Assessment of the impacts of the synthesis of nanoparticles

Figure 3 shows the environmental impact due to the chemical and biological reagents employed for the synthesis of the nanoparticles, as well as the energy consumption in the equipment, i.e.: agitators and furnaces for drying and calcination of the nanoparticles.

Despite the fact that the energy consumption of the equipment is relatively low, and that this electric energy is supplied by a hydroelectric plant, C[O.sub.2] and methane emissions are generated by the decomposition of organic matter in the ground and vegetation (due to the creation of artificial dams that are used for the conversion of the mechanical energy of the water into electric energy), which intensifies the problematic of global warming (Li & Zhang, 2014). Additionally, aluminum nitrate production generated nitrogen oxides and sulfur oxides emissions. Both of these substances greatly contribute to the stage of acidification, since they are the cause of acid rain (Goedkoop et al., 2008).

In the same way, this analysis proved that production of citric acid generates environmental consequences on human health and aquatic ecosystems. This is due to the fact that during the processing of this organic acid a considerable amount of emissions containing mercury, lead, benzene, arsenic, radium and sulfur compounds are released to the atmosphere. The presence of these compounds in the air and in water bodies can cause harmful effects such as lung cancer (ETH Zurich & EPF Lausanne, 2014). Furthermore, this analysis evidenced a negative impact on the category of abiotic resources. This represents a positive contribution to the environment, since the use of a microorganism to produce citric acid involves savings in resource consumption and shows the beneficial effect that could be achieved by using green chemistry and biological resources when obtaining nanoparticles.

3.5 Assessment on the impacts of the combustion process

The last stage involved the evaluation of the combustion process for the biodiesel/diesel blend (B10) with addition of 10 ppm of alumina nanoparticles. Results of the simulated combustion process using the Diesel-RK software were considered from the corresponding data of the physicochemical properties of the nanoparticle modified blend, which were established both experimentally and using models for the prediction of properties (Benjumea et al., 2008).

Figure 4 shows the characterization of the combustion process of the biodiesel/diesel blend in the presence of alumina nanoparticles. From this figure it was determined that the generation of mechanical energy contributes to the environmental impacts in the stages of acidification, eutrophication and global warming. The emission of combustion gases such as nitrogen oxides, sulfur dioxide and particulate matter is the main reason that causes this phenomenon. Such a release modifies the natural concentration ofthese compounds in the atmosphere, which leads to negative consequences that are caused by a perturbation of the environmental equilibrium.

It is important to note that the use of alumina nanoparticles considerably affects human health, not only because of the fact that it influences the combustion process, but also because of the impact that the synthesis of the nanomaterial exerts on the categories of ground eco-toxicity and depletion of abiotic resources (Figure 4). Regarding the effect of biodiesel on the analyzed life cycle, it is evident that its main influence lies on the eutrophication category that is caused by the agricultural origin of this biofuel, along with the use of fertilizers for the cultivation of biomass. On the other hand, since diesel is the predominant component in the fuel blend, it generated an impact in all of the categories, and especially in the depletion of both abiotic resources and ozone layer. High emissions of contaminant gases to the atmosphere are the cause of this problem, which also accelerates climate change.

3.6 Comparison between combustion at 0, 10 and 20 ppm of alumina nanoparticles

In order to understand the behavior of the combustion stage at an environmental approach, a comparison of the combustion of the blend (B10) with 0, 10 and 20 ppm of alumina nanoparticles was developed (Figure 5). The results show an increasing in most of the impact categories of combustion in the presence of nanoparticles (10 and 20 ppm), due to the fact that N[O.sub.x] emissions increase when compared to combustion without additive. Depletion of abiotic resources and global warming were the only categories that did not exhibited such behavior. This increasing in the NOx emissions can be explained by considering the high content of vegetable oils that compose the biodiesel in the blend. Those organic compounds present large amounts of oxygen in their molecular structure, which facilitates the formation of N[O.sub.x].

In addition, the presence of nanoparticles promotes the increasing of such emissions because of the catalytic activity that the nanomaterial exerts during the reaction between fuel and air at high temperatures (Basha & Anand, 2009).

Combustion with nanoparticles evidenced a decreasing in the emissions of particulate matter, C[O.sub.2] and S[O.sub.2], along with an increasing of N[O.sub.x], according to the results reported by Mehta et al. (2014). They investigated the combustion of diesel with metallic nanoparticles. The increasing of N[O.sub.x] emissions greatly contributed to the acidification, eutrophication and marine eco-toxicity categories. Acidification is a consequence of the release of larger quantities of nitrogen oxide that causes the formation of nitric acid, which in turn gets deposited on the ground and in water bodies by the action of rain. Marine ecosystems, soils, and living organisms that inhabit those places get affected in this way.

A positive environmental impact was observed in this analysis due to the consideration that the citric acid was obtained from biomass, when compared to the others chemical reagents used for the synthesis of the alumina nanoparticles. This suggests that the use of natural origins reagents such as vitamins, sugars, plant extracts, biodegradable polymers and microorganisms, along with the implementation of an eco-friendly process (Iravani, 2011), could reduce the levels of toxicity in the final product and the environmental impact of the byproducts, when compared to the conventional method that was selected (Carma, 2012).

4. Conclusions

The use of citric acid and aluminum nitrate in the sol-gel method for the synthesis of alumina nanoparticles generated environmental impacts on the integrity of ecosystems and human health categories. However, a positive effect on the category of depletion of abiotic resources was observed, since production of citric acid was considered from a fermentation process by Aspergillus Niger, which causes a reduction in resource consumption.

Combustion of the biofuel/fuel blend (B10) in the presence of nanoadditives releases a great amount of nitrogen oxides, which increases the levels of acidification and eutrophication. Nevertheless, the use of nanoparticles causes a reduction in the emissions of C[O.sub.2], S[O.sub.2] and particulate matter (PM), when compared to the combustion of the Colombian commercial blend without additive. The LCA methodological tool proved that even when innovations regarding additives are applied and fossil fuel (diesel) is still being used at a higher proportion, most of the environmental consequences will be influenced by the extraction and refining processes of oil. This fact dismisses the environmental advantages that nanoparticles have when used as catalyzers for the combustion reaction.

Therefore, evaluation of the alumina nanoparticles in higher concentrations that those studied in this paper is recommended for future researches on this topic. Such information would allow determining whether or not the typical emissions from the combustion of fuel blend increase when the concentration of nanoparticles is varied. In the same way, an assessment should be performed on different case scenarios where concentration of the additive and composition of the biofuel in the blend are modified.

Conditions rendering the lowest ecological footprint could be predicted in this way. These complementary analyses may help corroborate if the expected environmental contribution of adding nanoparticles to the fuel blend is proportional to the requirements related to engine performance. Implementation of the nanomaterial as a fuel additive relies on such requirements.

5. Acknowledgements

The authors would like to express their gratitude to the University of Cartagena and the Chemical Engineering Program for allowing the use of the Material Science Laboratory for the synthesis of the nanomaterials. We would also like to give thanks to COLCIENCIAS, and to Andres Penalosa Trujillo, Andy Rincon Ortiz and Mauricio Heras for their support during the development of this project.

6. References

Basha, J. & Anand, R. B. (2009). Performance and emission characteristics of a DI compression ignition engine using carbon nanotubes blended diesel Alexandria Engineering Journal. 53 (2), 259-273.

Benjumea, P., Agudelo, J. & Agudelo, A. (2008). Basic properties of palm oil biodiesel-diesel blends. Fuel 87 (10-11), 2069-2075.

Carma, R. (2012). Greener approach to nanomaterials and their sustainable applications.

Current Opinion in Biotecnology 1 (2), 123-128.

Castells, F. & Montero, J. (2004). Utilizacion del Analisis de Ciclo de Vida en la Evaluacion del Impacto Ambiental del Cultivo Bajo Invernadero Mediterraneo. Tesis de Doctorado para la obtencion del titulo de Doctor en Ingenieria Ambiental. Universidad Politecnica de Catalunya. Barcelona, Espana.

Consorcio CUE (Consorcio Universitario Euroamericano). (2012). Evaluacion del ciclo de vida de la cadena de produccion de biocombustibles en Colombia. Capitulo II: Estudio ACV Impacto ambiental: http://www.fedebiocombustibles.com.

ETH Zurich & EPF Lausanne (2014). Inventory of Citric Acid Production from Aspergillus Niger. Recuperado [4/11/13] desde la base de datos [Ecoinvent] en: http://www.ecoinvent.org/.

Fedebiocombustibles (Federacion Nacional de Biocombustibles de Colombia). (2012). Cifras Informativas del Sector Biocombustibles: Biodiesel de Palma de Aceite. Colombia.

Ganesh, D. & Gowrishankar, G. (2011). Effect of nano-fuel additive on emission reduction in a Biodiesel fuelled CI engine. In Electrical and Control Engineering (ICECE), 2011 International Conference on. Yichang, China p. 3453 - 3459.

Goedkoop, M., Oele, M., Schryver, A. & Vieira, M. (2008) SimaPro Database Manual (en linea). http://www.pre-sustainability.com/download/ manuals/DatabaseManualMethods.pdf.

Iravani, S. (2011). Green synthesis of metal nanoparticles using plants. Green Chem 13, 2638-2650.

Kao, M., Ting, C., Lin, B. & Tsung, T. (2008). Aqueous Aluminum Nanofluid Combustionin Diesel Fuel. Journal of Testing and Evaluation 36 (2), 19428-2959.

Li, J., Pan, Y., Xiang, C., Ge, Q. & Guo, J. (2006). Low temperature synthesis of ultrafine a-Al2O3 powder by a simple aqueous sol-gel process. Ceramics International 32 (5), 587-591.

Li, S. & Zhang, Q. (2014). Partial pressure of CO2 and CO2 emission in a monsoon-driven hydroelectric reservoir (Danjiangkou Reservoir), China. Ecological Engineering. 71, 401-414.

Mehta, R., Chakraborty, M. & Parikh, P. (2014). Nanofuels: Combustion, engine performance and emissions. Fuel, 120, 91-97.

Organizacion Internacional de Normalizacion (2006). Gestion Ambiental: Analisis de Ciclo de Vida. Principios y marco de referencia. Madrid, Espana.

Organizacion Internacional de Normalizacion (2006). Gestion Ambiental: Analisis de Ciclo de Vida. Requisitos y directrices. Madrid, Espana.

Park, B., Martin, P., Harris, C., Guest, R., Whittingham, A., Jenkinson, P. & Handley, J. (2007). Initial in vitro screening approach to investigate the potential health and environmental hazards of Envirox[TM]-a nanoparticulate cerium oxide diesel fuel additive. Journal of Particle and Fibre Toxicology 4 (12), 1-10.

Penalosa, A. & Rincon, A. (2014) Determinacion del efecto del uso de nanoparticulas de alumina en mezcla diesel/biodiesel para mejora de propiedades fisicoquimicas y reduccion de emisiones. Tesis de Pregrado para la obtencion de titulo de Ingeniero Quimico. Facultad de Ingenieria, Universidad de Cartagena, Cartagena, Colombia.

Soutter, W. (2012). Nanoparticles as fuel additives. http://www.azonano.com/article.aspx?ArticleID=3085

Karina A. Ojeda * ([section]), Adriana P. Herrera *, Maria J. Sierra *, Katherine Tamayo *

*Programa de Ingenieria Quimica, Facultad de Ingenieria, Universidad de Cartagena. Cartagena, Colombia.

([section]) kojedad@unicartagena.edu.co, aherrerab2@unicartagena.edu.co, mjsierra319@hotmail.com, kathetamayos@gmail.com

(Recibido: Febrero 2 de 2015 - Aceptado: Abril 14 de 2015)

Caption: Figure 1. Stages of the LCA according to ISO 14040:2006 regulation.

Caption: Figure 2. Representation of the system of study.

Caption: Figure 3. Characterization-production of 1kg of alumina nanoparticles

Caption: Figure 4. Characterization of the combustion-consumption process of 1 kg of fuel (Source: Author's own elaboration using Simapro).

Caption: Figure 5. Comparison between combustion of the B10 blend with 0, 10 and 20 ppm of nanoparticles-Normalization (Source: Author's own elaboration using Simapro).
Table 1. Impact categories

Category                Protection area           Unit

Abiotic resources       Natural resources         kg Sb
depletion (AD)
Global warming          Human health / Natural    kg C[O.sub.2]
(GW 100)                environment
Stratospheric           Human health / Natural    kg CFC-11
ozone depletion         environment
(OD)
Photochemical           Human health / Natural    kg ethylene
oxidant formation       environment / Natural
(PO)                    resources
Acidification           Human health / Natural    kg S[O.sub.2]
                        environment /
(AC)                    Natural resources
Eutrophication          Human health / Natural    kg P[O.sup.
(EU)                    resources                 3-.sub.4]
Human toxicity          Human health              kg 1-4 DCB
(HT)
Freshwater              Natural environment /     kg 1-4 DCB
aquatic eco-toxicity    Natural resources
(FAET)
Marine aquatic          Natural environment /     kg 1-4 DCB
eco-toxicity (MAET)     Natural resources
Terrestrial             Natural environment /     kg 1-4 DCB
eco-toxicity            Natural resources
(TET)

Table 2. Inlets and outlets for the synthesis of alumina nanoparticles.

                                              Unit     Quantity
Outlet (product)

Alumina nanoparticles (A[l.sub.2][O.sub.3])   g        1
Inlet (reagents)
Aluminum nitrate Al[(N[O.sub.3]).sub.3]       g        7.98
Citric acid [C.sub.6][H.sub.8][O.sub.7]       g        4.47
Input (energy consumption)
Stirring and heating at 60 y 80 [grados]C     kWh      5.775
(thermal plate)
Heating at 200[grados]C and 1000[grados]C     kWh      5.92
(furnace)
Air emissions
Water vapor                                   g        253.819

Table 3. Inlet to the combustion system--1 kg of fuel

                              B10/                    B10/
Engine inlet      B10         10 ppm nanoadditives    20 ppm
                                                      nanoadditives

Biodiesel (kg)    0.1153523   0.1153511               0.1153498
Diesel (kg)       0.8846476   0.8846380               0.8846284
NP (g)            0           0.0108133               0.0216264
TOTAL (kg)        1           1                       1

Table 4. Outlet of the combustion system -1 kg of fuel.

Outlet emissions                       B10 /           B10 /
                           B10         10ppm           20ppm
                                       nanoadditives   nanoadditives

Particulate Matter, PM *   0.1518614   0.1489162       0.1406362
C[O.sub.2] *               3177.8327   3159.2435       3139.6619
N[O.sub.x] *               38.324022   40.160220       41.9197695
S[O.sub.2] *               0.0118128   0.0112197       0.01042063

* g/kg of 'consumed fuel
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Title Annotation:INGENIERIA QUIMICA
Author:Ojeda, Karina A.; Herrera, Adriana P.; Sierra, Maria J.; Tamayo, Katherine
Publication:Ingenieria y Competividad
Date:Jun 1, 2015
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