Energy & Fuels 2009, 23, 2731–2735
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Action Principles of Cosolvent Additives in Ethanol-Diesel Blends: Stability Studies Y. Reyes,*,† D. A. G. Aranda,† L. A. M. Santander,‡ A. Cavado,† and C. R. P. Belchior§ Laborato´rio GREENTEC, Escola de Quı´mica, UniVersidade Federal de Rio de Janeiro, AV. Brigadeiro Trompowsky s/n, Centro de Tecnologia. Bloco E. Sala 211, Ilha do Funda˜o, Rio de Janeiro, Brasil, CEP: 21.949-900, Departamento de Estatı´stica, UniVersidade Federal Fluminense, Rua Mario Santos Braga s/n Praza do Valonguinho-Centro-Nitero´i, Rio de Janeiro, Brasil, CEP: 24.020-110, and Laborato´rio de Ma´quinas Te´rmicas, Departamento de Engenharia NaVal, Escola Polite´cnica, UniVersidade Federal de Rio de Janeiro, AV. Brigadeiro Trompowsky s/n, Centro de Tecnologia, Bloco C. Sala 203, Ilha do Funda˜o, Rio de Janeiro, Brasil, CEP: 21.949-900 ReceiVed December 4, 2008. ReVised Manuscript ReceiVed March 25, 2009
In order to increase the solubility of ethanol in diesel, it is necessary to introduce an additive which improves the solubility in a more stable way, especially in low temperatures and when exposed to the air humidity. Theses additives, which function is to stop the phase separation, act as cosolvents in ethanol-diesel blends. In the present work, the authors present the physical and chemical principles under which the cosolvent material acts. Additionally, they propose and evaluate the additives SPAN80 and AEP-102 as promoters of the blends of diesel fuel with 8% anhydrous ethanol, determinating quantitatively the concentration of water admissible.
1. Introduction In the 1990s, in favor of environmental requirements, the necessity of producing “clean” fuels was imposed internationally, reviving interest in reducing the consumption of diesel fuel by its partial or total substitution for biofuels including alcohol.1 This necessity of reducing diesel fuel consumption is also in agreement with the world tendency to reduce carbon emissions, mitigating the greenhouse effect, in the negotiations of the Kyoto Protocol. Looking forward to accomplishing this objective, it is important to adopt a supportable policy that allow the substitution of diesel fuel for other types of energies in a technically right way, such as the ethanol-diesel blends. However, the explotation of these blends is a topic that is not completely established and requires studies in order to obtain effective performance and a guaranteed conservation of the equipment where the blends are applied, as well as the distribution systems. Some research results prove that although blending alcohol with gasoline introduces some improvements in the fuel such as a significative increasement of the octane number besides environmental benefits, in the case of diesel the advantages are not so clear. In this fuel, as alcohol is added, there are important properties that are sacrificed which are very important such as cetane number, heat of combustion, stability, and lubricity. Therefore, the consumption of theses blends should be supported by an extremely precise formulation.1 In order to add reasonable quantities of ethanol in diesel, it seems to be mandatory to utilizate effective and economic * Corresponding author. Telephone: 55 (21) 2562-7657. Fax: 55 (21) 2562-7567. E-mail address:
[email protected]. † Escola de Quı´mica, Universidade Federal de Rio de Janeiro. ‡ Universidade Federal Fluminense. § Escola Polite ´ cnica. Universidade Federal de Rio de Janeiro. (1) Ahmed, I. Diesel fuel composition. US Patent 6,017,369, January 25, 2000.
additives which maintain the homogeneous blend in storage conditions and restore the quality of ignition and the lubricity of the original diesel fuel.2,3 In particular in this work, the investigation has as an objective: • Propose and evaluate additives that can improve the stability of diesel blends with 8% of anhydrous ethanol, as to measure quantitatively the water concentration in which these additives are going to be soluble. 2. Materials and Methods 2.1. Materials. In the formulation of the studied blends, the following raw materials were used: • Automotive diesel S-500: the quality of commercial diesel fuel S-500 was determined in accordance with the quality specifications of the National Agency for Oil, Natural Gas, and Biofuels (ANP) Resolution No. 15/06.4 • The ethanol used in the tests was limited to essentially anhydrous ethanol in accordance with the 2002 quality specifications of the Brazilian National Petroleum Agency (ANP).4 • Biodiesel produced in the plant of Agropalma in Bele´n-Para´ complies with the quality specification established by ANP Resolution 42. • Sorbitan esters (SPAN 80) commercialized in Brazil by the OXITENO Company. • Soybean methyl esters (AEP-102) produced by the Ecological Company of Mato Grosso (ECOMAT). 2.2. Methods. 2.2.1. Formulation and Characterization of the Base Blends Used in the EValuation of the AdditiVes. The concentration of 8% alcohol was defined as the ideal to blend with diesel, in agreement with the excellent results that were obtained in the studies carried out in 20 urban busses of the metropolitan (2) Ahmed, I. Diesel fuel composition. US Patent 6,306,184, 2003. (3) Glasstone, S. Tratado de Quı´mica-Fı´sica. Universidad de Oklahoma. Instituto Cubano del libro, editorial ciencia y te´cnica, 1972. (4) Ageˆncia Nacional de Petro´leo, Ga´s Natural e Biocombustı´veis-ANP Resolution No. 15, referente a`s especificac¸o˜es dos combustı´Veis automotiVos comercializados em todo o territo´rio brasileiro; July 17, 2006.
10.1021/ef8010492 CCC: $40.75 2009 American Chemical Society Published on Web 04/15/2009
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fleet of Curitiba (Brazil), as a part of the test program realized by the laboratories the Technology Institute of Parana´ (TECPAR), Fuel Technology Institute, Technological Investigations Institute (IPTSP), and National Technology Institute (INT-RJ). The alcohol concentration was optimized taking into account the environmental benefits and the costs and benefits of the program. Investigations conducted by the executive group monitoring alcohol-diesel blends, established by the Brazilian Ministry of Science and Technology in 1999, also confirm these results.5-8 Physical-chemical characterization, either of the diesel fuel or of the formulated mixtures, was realized in the physical-chemical laboratory of the Petroleum Research Center of Cuba (CEINPET), using the established methods in accordance with regulation ANP No. 310.4,9 This laboratory, certified by the ISO/IEC 17025, has quality control procedures implanted to monitor the validity of the analysis as of applying statistic techniques for the revision of the results and methods. 2.2.2. Stability of the blend: AdditiVes. To ensure the stability of the diesel fuel blend with 8% anhydrous ethanol, it is required that a cosolvent is added. In this study, the efficiency of the additive sorbitan monooleate (SPAN 80) proposed by Greentec Laboratory, Federal University of Rio de Janeiro, Brazil, was compared with the additive AEP-102 patented by ECOMAT. In the formulations, the concentrations of additive proposed in the respective patents were considered.10,11 The stability to the separation in the blends was evaluated: • quantitatively, determining the limit concentration of water which promoted the phase separation; the moment when the instant separation of free water occurs is characterized as the separation point.12 The experimental conditions used for stability measurement were the following: • sample total volume: 30 mL. • micropipet of 0.01 mL to the addition of water. • constant temperature (25 °C). • uniform agitation during 1 min after each water addition, and after that, the samples were allowed to rest during 2 min, before making the observation. The limit water concentration was determined in the following blends: • blend 1: diesel fuel S-500 + 2% biodiesel + 8% anhydrous ethanol. • blend 2: diesel fuel S-500 + 2% biodiesel + 8% anhydrous ethanol + 2.6% AEP-102. • blend 3: diesel fuel S-500 + 2% biodiesel + 8% anhydrous ethanol + 0.5% SPAN 80. In the formulated blends, the biodiesel additions were considered taking into account the fact that since 2008 The Brazilian National Oil Agency established the addition of 2% biodiesel to commercial diesel fuel. These studies permitted the selection of the best cosolvent additive supporting this selection with a statistical analysis. (5) Ecolo´gica De Mato Grosso, Industria E Come´rcio Ltda (ECOMAT). Mistura a´lcool-diesel AEP-102. Aspectos so´cio-econoˆmicos e ambientais; 1999. (6) Baccaro, F. E. Considerac¸o˜es sobre o uso de misturas a´lcool-diesel; Instituto de Pesquisas Tecnolo´gicas (IPT). Divisa˜o de Mecaˆnica e Eletricidade. Agrupamento de Motores. Sa˜o Paulo, Fevereiro, 2000. (7) Laurindo, J. C. Misturas a´lcool & diesel em Brasil; Instituto de Tecnologia de Parana´ (TECPAR). Curitiba, May 21, 2002. (8) Projeto Mistura A´lcool-Diesel-AEP 102 (MAD8); Resolution CIMA no. 11, March 2, 1999. Portaria MCT no. 315, July, 15 1999 - GEM. (9) Unio´n Cubapetroleo. Cata´logo de especificaciones, Rama Combustibles; Minbas, Julio 2002. (10) Campi, A. R.; et al. AditiVo para melhorar as propriedades de combustı´Vel automotiVo. Depo´sito de Patente Brasileira PI9903413-1, August 4, 1999. (11) Aranda, D. G. Relato´rio descritiVo da patente de InVenc¸a˜o: AditiVos promotores da mistura etanol-diesel; Escola de Quı´mica, UFRJ, 2004. (12) Almeida, B. I. Influeˆncia do etanol na solubilida de de hidrocarbonetos aroma´ticos presentes no o´leo diesel. Tese doutorado apresentada ao curso de Po´s-Graduac¸a˜o em Quı´mica, Centro de Cieˆncias Fı´sicas e Matema´ticas, Universidade Federal de Santa Catarina, Floriano´polis, 2003.
Reyes et al.
Figure 1. Polarity in cosolvents.
The software used perform the previously mentioned test was MINITAB.
3. Results and Discussion 3.1. Chemical and Physical Principles of Cosolvent Additives. To increase the solubility of the ethanol in diesel, cosolvent agents are usually used to improve the solubility in a more stable way, especially under low temperatures and when exposed to the air moisture. Theses additives should have as basic characteristics the existence of polar and nonpolar groups to foster the simultaneous interaction with diesel and with ethanol.13 Esters of fatty acids of methylic, ethylic, cyclic, or aromatic alcohols are used as pure combustibles and also as additive promoters for alcohol-diesel blends. Ahmed describes in various patents,1,2,14,15 the application of theses compounds as additives to improve the stability of theses blends. Some brazilian patents10,11,16 also recommend additives with a similar composition to increase the stability of the ethanol-diesel blends. According to these patents, addition around 1% to 2% (volume basis) of these additives are typically able to promote a stable blend with up to 15% anhydrous ethanol concentrations. These additives, whose function is to block the phase separation, act as cosolvents in the alcohol-diesel blends. The cosolvents are defined as organic solvents with a good miscibility in polar substances commonly used in liquid formulations to increase the solubility of substances with low polarity increasing the blend chemical stability.17 A structural characteristic which characterizes the cosolvents does not exist; however, Yalkowsky18 made the following observations: • The cosolvent possesses hydrogen donor groups (OH, SH, NH, NH2) and/or groups that accept hydrogen (tN, dNs, dO, dS, sNHs, sOs, sS, sN). • Theses groups interact strongly with the polar substances. • The hydrocarbon chain of the cosolvent, which is joined to these groups, is nonpolar and has affinity with the hydrocarbons present in the diesel fuel. In accordance with the example of Figure 1.3 (13) Verde, R. Tecnologı´a Moderna del Petro´leo en Cuba; Editorial Cientı´fico - Te´cnica: Cidade da Havana, Cuba, 1982. (14) Ahmed, I. Polymeric fuel additiVe and method of making the same, and fuel containing the additiVe. US Patent 6,074,445, June 13, 2000. (15) Ahmed, I. Polymeric fuel additiVe and method of making the same, and fuel containing the additiVe. US Patent 6,183.524. February 6, 2001. (16) Campi, A. R.; et al. Mistura alcoo´lica solu´Vel em o´leo diesel. Depo´sito de Patente Brasileira PI9903414-0. August 4, 1999. (17) Enciclope´dia online. www.tiosam.com/enciclopedia/Diesel (accessed Feb 2008). (18) Yalkowsky, S. H. Solubilization by CosolVents. Solubility and solubilization in aqueous media; American Chemical Society and Oxford University Press: Washington, D.C., and New York, 1999; pp 180-235. (19) Serrano, A. Materiales Modernos -Monografı´a; Escuela Superior Polite´cnia del Litoral: Guayaquil, Ecuador, 2004.
CosolVent AdditiVes in Ethanol-Diesel Blends
Figure 2. Associations by hydrogen bridges between the polar extremity of the cosolvent and the polar molecules of ethanol and water.
Figure 3. Structure of the sorbitan monooleate (SPAN 80).
Taking into account the previous observations, it can be said that the cosolvent effect of theses additives is due to the intermolecular interactions that establishes simultaneously the cosolvent with polar molecules, such as ethanol and water, and with nonpolar molecules, in this case the diesel hydrocarbons, guaranteeing the stability of the blend.3 The polar extremity of the cosolvent establishes associations by hydrogen bridges with theses molecules; Figure 2.3 The oxygen of the cosolvent can establish these associations by hydrogen bridge with (n) polar molecules.3 On the other hand, the hydrocarbon moiety of the cosolvent and the hydrocarbons of diesel attract each other due to van der Waals forces, present in the low polarity molecules. These forces are due to transitory dipoles that are formed in the molecules as a result of the movements of the electrons. At a certain instant, a part of the molecules gets negatively charged; meanwhile, an equivalent positive charge appears on the other region. Under the theory of these intermolecular attraction forces, the solubility between the cosolvent molecules and the hydrocarbons of diesel is sustained.3,20 3.2. Additive Examples. As discussed above, when adding alcohol to diesel fuel, a very important series of properties are affected, such as stability, lubricity, and cetane number. To overcome these problems, the utilization of additives that allow one to use larger concentrations of alcohol in diesel has been studied, seeking the maximization of the environmental benefits, the amplification of the use of alcohol, and the reduction of importing diesel. The fundamental characteristics of several additives that have been patented as cosolvents for anhydrous ethanol-diesel blends are listed next. 3.2.1. SPAN 80.20 The additive is composed by sorbitan esters, specifically sorbitan monooleate, derived from the reaction of sorbitol with fatty acids. Usually, a blend of acid and basic catalysts are employed. Sorbitan esters are commercialized in Brazil by the OXITENO Company, under the commercial name of SPAN 80. In Figure 3, the structure of the SPAN 80 is presented. The previously described ester is a potential promoter of the stability of the ethanol-diesel blend, it increases the solubility (20) Oxiteno. Boletı´n Te´cnico: Alkest SP/Alkest TW. http://www. oxiteno.com.br (accessed Jan 2008).
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of ethanol in diesel fuel. The additive also has the property of increasing the cetane number and the lubricity of the blend.18 Depending on the fatty acids used in the ester synthesis, products with different values of HLB (hydrophilic lypophilic balance) can be obtained.20 The HLB is indicative of the solubility of the esters in aqueous and oily environments. Esters with high HLB values present higher solubility in water or aqueous environments. Lipophilic surfactants exhibit low HLB values. Due to their lipophilic nature, these products are soluble or dispersible in petroleum derivatives. 3.2.2. AEP-102.10,16 AEP-102 additive, produced by the Ecological Company of Mato Grosso (ECOMAT), is a cosolvent for alcohol-diesel blends and allows its homogenization, until certain moisture levels without any recirculation equipment, a simple agitation system is usually enough. The additive is of organic origin and a biodegrable soybean methyl ester which is not flammable, so it can be transported by aircrafts or simply stored in common reservoirs. Typical blend formulation, involves the following: 89.4% diesel fuel, 8% anhydrous ethanol, 2.6% AEP-102. In this blend, the additive guarantees the stability until absorbed water concentrations of 1200 ppm even to temperatures between 0 and 5 °C. This product was evaluated with satisfactory results by the laboratories of the Technology Institute of Parana´ (TECPAR), Combustible Technology Institute, and Institute of Technological Researches of the Sa˜o Paulo State (IPT). The fuel blend is being consumed for several years in fleets and fed vehicles which have covered about 260 000 km in the cities of Curitiba, Cuiaba, and Campo Grande. In these field tests, Om 366 LA engines from Mercedes Benz were used, paying attention to the specification Euro 1 and Conama step 4 which are respectively the international and Brazilian legislations that regulate vehicular emissions.21 3.2.3. OCTIMISE D 7001..22 OCTIMISE D 7001 is commercialized in Brazil by the Quı´mica Fina Company as a representitive of the North-American Company OCTEL. The additive works as a cosolvent in the following blend: • 10% anhydrous ethanol. • 89% diesel fuel. • 0.5% OCTIMISE D 7001 additive. This additive, as well as guaranteeing the stability of the blend, contains compounds that improve the ignition quality and recover the lubricity lost by the fuel with the alcohol addition. The published results22 prove that, under test conditions, neither corrosion nor deterioration are reported in the valves of the inline injection pumps after 1000 h of testing. 3.2.4. Biodiesel..23 A publication of the Clean Technologies Laboratory of the Chemistry Department of the University of Sa˜o Paulo in Ribera˜o Preto (USP/RP) has shown the use of biodiesel, composed by fatty acids esters obtained from renewable biological resources such as vegetable oils and animal fat, as a viable additive to homogenize the alcohol-diesel blends and improve their lubricity and cetane number. Biodiesel is characterized by having properties similar to diesel such as density, viscosity, distillation, carbon residues, (21) Martins, H. Procedimentos para Preparac¸a˜o e Uso de Misturas A´lcool-Diesel, Relato´rio no. 4; Centro de tecnologia canavieira (CTC), July 2005; p 1/10. (22) Quimica Fina. Mistura a´lcool diesel MAD-10, OCTIMISE D 7001; 2005. (23) Dabdoub, M. J. Uso de novos combustı´veis permitira´ a reduc¸a˜o das importac¸o˜es de diesel em no mı´nimo 33%. http://www.dabdoub-labs. com.br (accessed Oct 2006).
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Table 1. Physicochemical Characteristics of the Base Diesel, Anhydrous Ethanol, and the Blends
property
specification ASTM test (resolution diesel diesel S-500 + 8% diesel S-500 + 2% diesel S-500 + 2% method ANP No. 15/06) S-500 AEAC biodiesel biodiesel + 8% AEAC
D 1298 density at 15 °C, kg/m3 copper strip corrosion rating max 3 h at 50 °C D 130 total Sulfur, % m/m D 1266 total acidity, mg KOH/g D 974 D 445 kinematic viscosity at 40 °C, mm2/s color ASTM D 1500 flash point, °C D 93 water anD sediment, % v/v D 96 cetane number D 613 heat of combustion, kcal/kg D 240 conradson carbon residue, % m/m D 189 ash, % m/m D 482 aromatic hydrocarbons, % v/v ultraviolet
0.820-0.865 1 max 0.050 max 2.5-5.5 3.0 max 38 min 0.05 max 42 max 0.050 max 0.0200 max
0.8576 1b 0.026 0.0280 4.6737 1.0 87 0.00 60.50 10100 0.040 0.0070 31.34
0.8556 1b 0.022 0.0272 4.5823 1.0 13 0.0 51.50 9802 0.037 0.0030 29.87
0.8578 1b 0.025 0.0280 4.7000 1.0 87 0.00 59.40 10002 0.040 0.0050 30.26
0.8563 1b 0.020 0.0278 4.6241 1.0 13 0.00 51.50 9786 0.035 0.0026 27.25
79.0 218.0 251.5 262.5 277.0 286.0 296.0 305.5 318.0 335.0 361.0 385.0 387.0 99.0
218.0 242.5 254.5 267.0 277.0 286.0 296.0 306.5 319.0 355.0 362.0 385.0 388.0 99.0
79.0 220.0 252.0 263.0 278.0 286.0 295.5 305.5 318.0 355.0 362.0 385.0 388.0 98.5
physical distillation, °C IBP 5 10 20 30 40 50 60 70 80 90
D 86
95 FBP % vol recovered
217.0 241.5 253.5 267.5 277.0 286.0 295.5 306.5 319.0 335.0 362.0 385.0 388.0 98.0
and content of water and ashes. Biodiesel also has better characteristics than diesel such as higher cetane number, higher flash point, more lubricity, and less sulfur. Besides, there are specific properties of biodiesel such as glyceride content, iodine number, and oxidation stability. 3.3. Formulation and Characterization of the Base Blend Used on the Evaluation of the Additives. In the Petroleum Research Center Laboratories (CEINPET) in Cuba, physical-chemical characterization of the following samples were done: 1. diesel fuel. 2. diesel fuel + 2% biodiesel. 3. diesel fuel + 8% anhydrous ethanol. 4. diesel fuel + 2% biodiesel + 8% anhydrous ethanol. The results are presented in Table 1. Theses samples will be used as the basis of the additives comparative studies. The results in Table 1 indicate that we are working with a Brazilian diesel fuel of low sulfur concentration (500 ppm, according to Brazilian Standard ANP Resolution) and high aromatic hydrocarbon concentration. 3.4. Evaluation and Selection of Cosolvent Additives. The stability of these blends is an aspect that gives rise to doubts as regards the success of a generalized application of the alcohol-diesel blends. As it was explained in item 3.1, the stability should be guaranteed by the addition of a surfactant agent which fosters the solubility in a stable way. Methylic esters of fatty acids have been widely studied and used as promoter additives of alcohol-diesel blends,1,2,14,15 standing out among them the cosolvent additive AEP-102, produced by ECOMAT. The additive, added to the blend in a 2.6% v/v concentration, guarantees the stability of the blend with 8% alcohol up to 1200 ppm of water, a fact that shows good stability in Brazilian storage conditions.10,16 The characteristics of AEP-102 are discussed in section 3.2.2.
Aranda et al.11 describe the catalytic process for the production of sorbitan esters from fatty acids, proposed as promoters of these blends, increasing the solubility of ethanol in diesel, independently of the preliminary addition of the additive in ethanol or in diesel. After the perfect homogenization of the additive in one of the parties (ethanol or diesel), it is proceeded by the addition of the other component. Either the additive dissolution or the final homogenization can be carried out at room temperature (25 °C). There could be introduced some other conventional cetane number promoters if wanted. Sorbitan fatty mono alkyl ester is one of the proposed esters as cosolvent additive of the diesel fuel blended with 8% anhydrous ethanol. Its concentration in the blend was minimized to 0.5% guaranteeing the stability of the blend up to 30 days under Brazilian storage conditions. The characteristics of the SPAN 80 are discussed in section 3.2.1. In this study, we attempt to compare quantitatively the concentration of water solubilized by each of these additives in the 8% ethanol-92% diesel blends. Anhydrous ethanol used in the formulation of the blends presents 7000 ppm of water, in a typical 99.3% ethanol concentration as proposed by the Brazilian standard (ANP Resolution). The data that are related in Table 2 are referred to the concentration of water that the additive is able to solubilize well. This water could be absorbed from the environment due to ethanol being highly hygroscopic or to storage container contamination. These results, under statistical treatment, allow the determination about significant differences in concentration of allowable water by one or the other additive in order to select the best. The studies were made under the experimental conditions described in section 2.2.2. The limit concentration of water was determined in the following samples: • blend 1: diesel fuel + 2% biodiesel + 8% anhydrous ethanol.
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Table 2. Concentration of Allowable Water by the Studied Blends observation number (n)
blend 1 mL
blend 2 mL
blend 3 mL
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
0.03 0.03 0.03 0.02 0.02 0.03 0.03 0.03 0.02 0.03 0.02 0.03 0.03 0.04 0.03 0.03 0.02 0.04 0.03 0.03 0.02 0.02 0.03 0.03 0.03 0.03 0.03 0.02 0.03 0.03 0.02 0.03 0.03 0.03 0.03
0.09 0.10 0.10 0.10 0.11 0.09 0.09 0.10 0.10 0.09 0.10 0.10 0.10 0.10 0.09 0.09 0.09 0.10 0.10 0.10 0.09 0.09 0.10 0.11 0.09 0.10 0.10 0.10 0.09 0.10 0.10 0.10 0.11 0.10 0.10
0.12 0.13 0.13 0.11 0.12 0.12 0.12 0.12 0.11 0.12 0.11 0.12 0.13 0.12 0.12 0.11 0.12 0.13 0.13 0.12 0.12 0.10 0.11 0.12 0.12 0.12 0.13 0.12 0.12 0.12 0.12 0.11 0.12 0.12 0.12
Table 3. Typical Deviation of the Water Concentration Admitted by the Blend, Mean, and Median
mean water concentration (xj) typical deviation of water concentration(s) median water concentration (Me)
blend 1 mL
blend 2 mL
blend 3 mL
0.0280 0.0055 0.0300
0.0977 0.0063 0.1000
0.1194 0.0071 0.1200
• blend 2: diesel fuel + 2% biodiesel + 8% anhydrous ethanol + 2.6% AEP-102. • blend 3: diesel fuel + 2% biodiesel + 8% anhydrous ethanol + 0.5% SPAN 80. One simple observation of the datas allows us to say that the concentration of water that blend 1 admits is significantly lower than that admitted by blends 2 and 3. This can be easily verified by observing the statistics shown in Table 3. In these data, it is also observed that the water concentration admitted by blend 3 with SPAN 80 is higher than that admitted by blend 2 with AEP-102 (see Figure 4). However, to define
Figure 4. Water concentration allowable by the samples studied.
whether this difference is significant, the Wilcoxon nonparametric hypothesis testing was performed,24 which considers as a basic hypothesis the fact that both samples come from the same population (medianblend2 ) medianblend3) against the alternative hypothesis which considers that the samples come from different populations (medianblend2 < medianblend3). The test was highly significant, since the null hypothesis was refused with a significance level close to 0. 4. Conclusions When the addition of higher than 3% anhydrous ethanol concentrations to diesel fuel is necessary, a third element called an additive is needed in the formulation. This additive should improve some fuel properties that are affected by the addition of alcohol, such as stability, lubricity, and injection quality. Most of the additives used to improve the chemical stability of these blends act under the cosolvent principle. This cosolvent effect is owed to the intermolecular interactions that the cosolvent simultaneously establishes with polar molecules such as ethanol and water and with nonpolar molecules, in this case the diesel hydrocarbons, guaranteeing the stability of the blend. In this work, two cosolvent additives patented as AEP-102 and SPAN 80 have been comparatively proposed and evaluated with the objective of increasing the concentration of water solubilized in the diesel fuel blend with 8% anhydrous ethanol. The obtained results permitted the determination that the water content admitted by blend 3 (with SPAN 80) is significatively higher than that admitted by blend 2 (with AEP-102). The sorbitan esters are able to solubilize higher water concentrations than methyl esters. EF8010492 (24) Bland, M. An introduction to Medical Statistics, second ed.; Oxford University Press: New York, 1995.
