Article pubs.acs.org/EF
Effect of Additives in the Reaction Medium on Noncatalytic Ester Production from Used Frying Oil with Supercritical Ethanol Ana Carolina de Araújo Abdala,† Talita Amabile da Silva Colonelli,† Caroline Portilho Trentini,‡ J. Vladimir Oliveira,§ Lúcio Cardozo-Filho,∥ Edson Antonio da Silva,† and Camila da Silva*,†,‡ †
Program of Post-Graduation in Bioenergy, State University of West Paraná (UNIOESTE), Faculdade Street 645, Jardim La Salle, Toledo, Paraná 85903-000, Brazil ‡ Department of Technology, Maringá State University, (UEM), Umuarama, Paraná 87506-370, Brazil § Department of Chemical and Food Engineering, Federal University of Santa Catarina (UFSC), C.P. 476, Florianópolis, Santa Catarina 88040-900, Brazil ∥ Department of Chemical Engineering, Maringa State University (UEM), Av. Colombo 5790, Maringa, Paraná 87020-900, Brazil ABSTRACT: In this study, the noncatalytic production of ethyl esters from used frying oil (UFO) in a continuous process was evaluated under supercritical conditions. Experiments were performed with the objective of evaluating the effect of the addition of water, a co-solvent (n-hexane), and ethyl esters to the reaction medium, applying different temperatures and keeping the oil:ethanol mass ratio (1:1), pressure (20 MPa), and residence time (40 min) fixed. The results demonstrated that the formation of fatty acid ethyl esters (FAEE) is favored at higher temperatures. The addition of 5 wt % water increased the yield, while no significant effect (p > 0.05) was noted with the addition of 10 wt % water. The addition of cosolvent and ethyl esters in the range investigated plays a vital role in maximizing the FAEE yields for most conditions studied. The presence of water and cosolvent reduced the degree of fatty acids decomposition, while the addition of ethyl esters increased this parameter. The effect of the residence time was investigated applying the best conditions observed and good reaction yields (>85 wt %) were achieved under different conditions.
1. INTRODUCTION
nitrogen oxide emissions can be addressed through the proper treatment of the combustion exhausts. This feedstock has high levels of FFA and water, which can compromise the performance achieved in the conventional homogeneous alkali-catalyzed process. To avoid this adverse effect, the used of an alcohol under supercritical conditions can be applied. In this method, the presence of FFA can lead to simultaneous transesterification, hydrolysis, and also esterification10 (and, hence, higher reaction yields11,12). In relation to alcohol, Brazil is one of the largest producers of ethanol in the world, the production technology is well-established and the industrial plants installed have a large capacity. The use of supercritical conditions in the transesterification of vegetable oils provides better solubility between the phases and decreased limitations to mass transfer. Also, the reaction rate increases significantly in the supercritical state and thus the reactions are completed in shorter periods and simpler separation and purification steps are involved.13,14 In addition, it has been shown that the energy consumption associated with the supercritical method is very similar to that of processes involving homogeneous alkaline catalysis.15,16 The transesterification of vegetable oils under supercritical conditions requires operation at elevated temperatures and pressures as well as the use of a high amount of alcohol in order to obtain satisfactory yields. This results in the disadvantage of
In the Brazilian context, soybean oil is the main feedstock used for biodiesel production;1 however, recently, other feedstocks have been considered, because of the fact that the cost of the raw materials represents the highest percentage of the total production cost.2 In this context, the use of waste oil as a raw material for biodiesel production is an interesting alternative, considering its low cost and high availability; it also involves the reuse of a material with high pollution potential.3,4 In Brazil, cooking oil consumption by the population generates ∼3 billion liters of waste oil per year.5 The quality standards for the use of frying oils in Brazil are established by Anvisa,6 which determined that the free fatty acids (FFA) content should not exceed 0.9% and the content of polar compounds should not be greater than 25%. It has been reported that waste oil as a raw material can easily be adapted to biofuel production, since it is appropriate for reuse.7 Ruiz-Méndez et al.8 published useful information regarding the compounds present in used frying oils (UFOs), along with data on the characterization of the biodiesels obtained from them. The same authors reported that, during frying, polymers, dimers, oxidized triacylglycerides, diacylglycerides, and FFA are formed and some of these compounds cannot be converted to alkyl esters. The disadvantages associated with the use of biodiesel include higher emissions of nitrogen oxides, compared with mineral diesel fuel,9 and the use of UFOs can be associated with the emission of nitrogen compounds derived from proteinaceous compounds present in these oils. However, this increase in the © 2014 American Chemical Society
Received: November 15, 2013 Revised: April 22, 2014 Published: April 22, 2014 3122
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
Energy & Fuels
Article
Experimental data were treated applying ANOVA and the Tukey test (p > 0.05). 2.3. Analytical Methods. For the determination of the ethyl esters, triacylglycerides, and intermediates (monoacylglycerides and diacylglycerides), as well as the degree of decomposition, analytical procedures that have been described by Silva et al.31 were used. The samples were injected in triplicate into the gas chromatograph (Agilent, Model GC 7890), equipped with an FID detector and a ZBWAX capillary column (30 m × 0.25 mm × 0.1 μm) for the determination of the ethyl esters and the degree of decomposition or a ZB5 capillary column (25 m × 0.25 mm × 0.1 μm) to determine the triacylglycerides and intermediates. Compounds were quantified following the standard methods UNE-EN 1410333 and UNE-EN 1410534 for esters/decomposition and triacylglycerides/intermediates, respectively. The FAEE yield was then calculated based on the content of ethyl esters in the sample and on the reaction stoichiometry. The convertibility of the UFO was determined using the method described by Gonzalez et al.22 and was found to be 93.1%.
a high processing cost, in addition to the formation of decomposition products. Some alternatives for reducing the operating costs and biodiesel decomposition have been reported, notably the addition of co-solvents17−22 and water10,11,23 to the reaction medium. Some authors have reported that the addition of esters24,25 or recycling of a product partially converted to esters26−28 in the oil−alcohol mixture increases the solubility between the phases involved, leading to an increase in the ester yield. The objective of this study was to investigate the noncatalytic transesterification of UFOs in a continuous process using ethanol under supercritical conditions. To this aim, the effects of temperature and the amounts of water, co-solvent (nhexane), and ethyl esters added were investigated. For the best conditions observed, the effect of the residence time was investigated.
2. MATERIALS AND METHODS
3. RESULTS AND DISCUSSION 3.1. Effect of Temperature and Water Addition. The effect of temperature and water addition on the supercritical transesterification was evaluated varying the temperature from 548 K to 598 K and considering water concentrations of 5 and 10 wt % (in relation to anhydrous ethanol). Figure 1 shows the FAEE yields and the degree of decomposition as a function of the temperature and water concentration. As can be seen in Figure 1a, the FAEE yield increased with temperature for all conditions studied and without water addition ester yields of 34.3 and 45.8 wt % were obtained at 548 and 598 K, respectively. This result indicates that, in this study, the production of esters was favored due to increased reaction rates at higher temperatures. The results obtained in this study were compared with those previously reported for the use of waste oils in biodiesel production under compressed conditions. For reactions carried out with waste cooking oil and methanol, Demirbas et al.35 reported ester yields of 60% and ∼90% at 520 and 560 K, respectively, employing 10 min of reaction and an oil:methanol molar ratio of 1:41. The authors reported that preheating was performed prior to the reaction to remove the moisture present in the oil. Lee et al.36 obtained at ∼4.4 and 96.4 wt % of fatty acid methyl esters (FAME) at 513 and 543 K, respectively, in the transesterification of waste canola oil in batch mode for 45 min using an oil:methanol mass ratio of 1:1. The FFA and water contents of the waste canola oil used were 4.0 wt % and >0.01 wt %, respectively. For reactions with other vegetable oils in continuous mode, Choi et al.37 reported the positive effect of temperature (in the range of 543−623 K) on the FAME yield for transesterification performed in a plug flow reactor at 35 MPa, with a reaction time of 25 min and a palm olein oil:methanol molar ratio of 1:40, with yields of 55% and 80% at 563 and 603 K, respectively. Velez et al.38 reported that in the direct alcoholysis of sunflower oil gums with 50 wt % of ethanol an increase in temperature caused an enhancement in the FAEE yield, obtaining 22.8% and 42.2%, respectively, at 553 and 593 K with 20 min of reaction using a batch reactor. It can be noted from Figure 1a that the addition of 5 wt % water led to improved yields, compared to those obtained with the absence of water, but an increase in the water concentration (10 wt %) did not lead to a statistically significant change in the FAEE yield (p > 0.05). This effect has also been evidenced in other studies published in the literature, for instance, Vieitez et al.39 reported that at 573 K, with a castor oil:ethanol molar ratio
2.1. Materials. The UFO was donated by a restaurant in Maringá (Paraná, Brazil), collected at the time of disposal and subsequently filtered. Ethanol (J.T. Baker, 99.8%) was used as a reagent and nhexane (Vetec, 98.5%) as a cosolvent in the reactions. A chemical (base-catalyzed) method was employed to obtain the soybean fatty acid ethyl esters (FAEE)29 and a content of 97.5 wt % ethyl esters was verified. All other materials employed were purchased from Sigma− Aldrich. The fatty acids profile of the soybean oil, determined by GC analysis, is shown in Table 1. The results for the physicochemical characterization, carried out using the methods of the American Oil Chemists’ Society,30 are summarized in Table 2.
Table 1. Fatty Acid Composition of Used Frying Oil (UFO) Used as the Substrate in the Reactions fatty acid palmitic acid (16:0) palmitoleic acid (16:1n−7) estearic acid (18:0) oleic acid (18:1n−9) linoleic acid (18:2n−6) linolenic acid (18:3n−3)
content (wt %) 15.25 0.95 4.10 33.89 41.51 4.30
± ± ± ± ± ±
0.97 0.11 0.02 0.20 0.21 0.88
Table 2. Physicochemical Characterization of UFO Used as the Substrate in the Reactions parameter
value
acid value (mg KOH/g) saponification value (mg KOH/g) water content (wt %) peroxide value (mequiv/kg) iodine value (g I2/100 g)
3.57 ± 0.4 181.9 ± 2.1 0.03 ± 0.001 8.8 ± 0.4 102.7 ± 1.8
2.2. Apparatus and Experimental Procedure. The experimental apparatus used to perform the reactions was similar to that described elsewhere.31,32 For the tests, duplicate reactions were carried out in a tubular reactor with a packed bed, keeping the oil-to-ethanol mass ratio (1:1), pressure (20 MPa), and residence time (40 min) fixed to evaluate the effect of the process variables. The reactor had a void volume of 60.7 mL and was made of stainless steel tubing (6 m, 316 L 1/4-in. outer diameter (OD) and inner diameter (ID) 3.2 mm HIP) and stainless steel tubing (0.15 m, 304 L 30.5 mm OD and ID 13 mm HIP) packed with glass beads (with a diameter of 4.5 mm adopted after preliminary tests). The experimental procedure adopted for the reactions has been described in detail by Silva et al.31 and Doná et al.32 The residence time was calculated by dividing the void volume of the reactor (mL) by the flow rate of the substrates (mL/min). 3123
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
Energy & Fuels
Article
K (Figure 1b), the decomposition values decreased from 18.6 wt % to 12.10 wt % with the addition of 10 wt % water and to 7.15 wt %, upon decreasing the temperature to 548 K. The degree of decomposition is dependent on the operating conditions and the characteristics of the vegetable oil, as noted by Vieitez et al.12 The UFO had a chemical profile similar to that of soybean oil; however, this raw material is exposed to high temperatures for longer times, which might have induced thermal, oxidative, or hydrolytic reactions,40 reducing its thermal stability and increasing the degree of decomposition when subjected to supercritical conditions. Vieitez et al.11 examined the reaction of soybean oil with supercritical ethanol at 598 K, with an oil:alcohol molar ratio of 1:40, a pressure of 20 MPa, and 42 min of reaction and obtained ∼9 wt % of decomposition without the addition of water and ∼7 wt % with a water concentration of 10 wt %. Regarding the possible products formed during the decomposition of fatty acids, Lee et al.36 reported reactions of glycerol formed with methanol under the reaction conditions commonly used in this method. The results showed that these reactions can affect the ester yield by providing oxygenated compounds such as 3-methoxy-1,2-propanediol, dimethoxymethane, and 2,2-dimethoxypropane. Shin et al.41 reported the formation of hydrocarbons when methyl esters were subjected to treatment with supercritical methanol at temperatures above 648 K and a pressure of 23 MPa, as a result of the pyrolysis of the methyl esters. 3.2. Effect of Co-solvent Addition. The effect of the addition of a co-solvent on the FAEE yield and decomposition of fatty acids was evaluated by adopting co-solvent:oil mass ratios of 5, 10, and 20 wt % (Figure 2). As illustrated in Figure 2a, the addition of n-hexane as a co-solvent in the reaction medium led to an increase in the reaction yields for most conditions investigated. At 598 K, values of 45.8 wt % FAEE yield without co-solvent and ∼73 wt % with a co-solvent:oil mass ratio of 20 wt % were observed. The addition of n-hexane increased the mutual solubility between ethanol and triacylglycerides, decreasing the impediments to mass transfer and increasing the reaction rates. Patil et al.20 reported a positive effect on adding n-hexane in a co-solvent:oil ratio of 0.3 (v/v) in the reaction of camelina oil with supercritical methanol at 563 K, with an oil:methanol molar ratio of 1:25 and reaction time of 40 min. Muppaneni et al.22 studied the ethanolysis of camelina oil with n-hexane as the co-solvent and reported that the addition of a co-solvent can be considered as a promising alternative, allowing a considerable reduction in the operating conditions and maximization of the yields. In fact, these authors showed that the FAEE yield increased by ∼46% with a co-solvent:oil ratio of 0.05 (v/v) at 568 K, a pressure of 10 MPa, an oil:ethanol molar ratio of 1:25, and reaction time of 20 min. Tan et al.21 reported that for transesterification carried out at 633 K, employing an oil:methanol molar ratio of 1:30 and reaction time of 20 min, with n-heptane as the co-solvent, the ester yield increased from 50% to 65% with the addition of n-heptane to methanol at molar ratios of 0.05 and 0.20, respectively. It can be noted from the results in Figure 2b that the addition of n-hexane decreases the degree of decomposition. At 573 K, decomposition values of ∼15.8 wt % and ∼5.2 wt % were obtained with the addition of 0 and 20 wt % of co-solvent, respectively. This effect on the reaction medium, under these conditions, indicates that the transesterification occurs faster
Figure 1. Effect of temperature and water addition at 20 MPa, oil-toethanol mass ratio of 1:1, and 40 min of residence time on the (a) FAEE yield and (b) reaction decomposition. Means followed by same letters (for same temperature) for each column did not differ statistically (p > 0.05).
of 1:40, 52.5 min of reaction and a pressure of 20 MPa, ethyl ester contents of ∼38, 62, and 64 wt % were obtained for 0, 5, and 10 wt % of water in the reaction medium, respectively. Gonzalez et al.23 reported that when 10 wt % of water was added to alcohol an increase in the reaction yield was noted compared to the anhydrous system for the reaction of UFO employing methanol and ethanol under supercritical conditions. However, the authors did not report the yields when 5% of water was added and thus it is not possible to carry out a direct comparison with the results obtained in this study. Kusdiana and Saka10 reported that, when water was present, in addition to transesterification, faster parallel reactions occurred (hat is, the hydrolysis of triacylglycerides and then the esterification of FFAs with the supercritical alcohol). These results indicate that, besides the addition of water increasing the FAEE yield, the use of hydrated ethanol in the process should also be considered, with the objective of improving the biodiesel production costs and the production efficiencies, especially in large-scale industrial processing. Figure 1b illustrates the effect of temperature and water addition on the decomposition of the fatty acids and, according to the results, lower temperatures and higher water contents promoted a decrease in decomposition of the fatty acids. At 598 3124
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
Energy & Fuels
Article
Figure 2. Effect of co-solvent addition at 20 MPa, oil-to-ethanol mass ratio of 1:1, and 40 min of residence time on the (a) FAEE yield and (b) reaction decomposition. Means followed by same letters (for same temperature) for each column did not differ statistically (p > 0.05).
Figure 3. Effect of ethyl esters addition at a pressure of 20 MPa, an oilto-ethanol mass ratio of 1:1, and 40 min of residence time on the (a) FAEE yield and (b) reaction decomposition. Means followed by same letters (for same temperature) for each column did not differ statistically (p > 0.05).
than the degradation, as a result of increased solubility between the oil and ethanol with the addition of the co-solvent. 3.3. Effect of Addition of Ethyl Esters. To investigate the effect of the addition of ethyl esters, assays were performed with 20 and 40 wt % (in relation to oil) and the results are shown in Figure 3. It can be noted that, at 548 K, FAEE yields of 34.3, 55.8, and 64.1 wt % were obtained for 0, 20, and 40 wt % of ethyl esters added to the reaction medium, respectively. At 598 K, increasing the concentration of esters in the reaction mixture caused no significant effect on the FAEE yield (p > 0.05). As expected, the ester yield increased with the addition of esters in the UFO/ethanol reaction mixture, since esters can act as co-solvents, increasing the rate of mass transfer as a result of the increased solubility of the ester/alcohol/triglyceride mixture and thereby increasing the FAEE yield.26 The main benefit associated with using biodiesel as a cosolvent is that no separation stage is required since this is the final product of reaction.25 The addition of ethyl esters to the reaction mixture simulates a reactor with recycling, in which, as in a series system, the products are partially converted in the first step in the reactor and are then mixed with the reaction mixture, increasing the yield of the reaction. According to the experimental results of Granado et al.,24 alcoholysis at low pressure and small amounts of biodiesel in the starting alcohol−triglyceride mixture can provide improved reaction
yields. Silva et al.27 evaluated the effect of adding partially converted oil (∼40 wt % of FAEE) in the supercritical ethanolysis of soybean oil and reported ∼78 and 67 wt % of FAEE content for a reaction time of 25 min in the simulation of a reactor with recycling operated at 573 K, with a pressure of 20 MPa, an oil:ethanol mass ratio of 1:1, and the addition of 20 and 40 wt % of partially converted oil. For the same conditions but without recycling, the reaction provided an ester yield of 40 wt %. Figure 3b illustrates the effect of the addition of ethyl esters on the decomposition of fatty acids. It can be noted that, at lower temperatures, the addition of ethyl esters to the reaction mixture had no significant effect on the decomposition of fatty acids, while at higher temperatures, the results suggest a small decrease in the decomposition rate as the amount of esters is increased, thus indicating that, under these operating conditions, the addition of the esters promotes the reaction. 3.3. Effect of Residence Time. For the conditions that provided the best FAEE yields in Figures 1, 2, and 3 (i.e., addition of 5 wt % water, 20 wt % co-solvent, and 20 wt % ethyl esters), the effect of the residence time was evaluated. Residence times of 20−70 min were considered for the reaction at 573 and 598 K, and the results obtained for the FAEE yield and degree of decomposition are shown in Figure 4. A longer residence time led to a lower yield, accompanied by 3125
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
Energy & Fuels
Article
Figure 4. Effect of residence time at a pressure of 20 MPa and an oil-to-ethanol mass ratio of 1:1 on the (a) FAEE yield and (b) reaction decomposition.
an increase in the decomposition of the fatty acids for reactions conducted at 598 K with the addition of water and co-solvent and at 573 and 598 K with the addition of esters. For example, at 598 K and with water addition, the yield decreased from ∼81.5 wt % at 60 min to ∼78.5 wt % at 70 min, and under these conditions, decomposition levels of ∼18 wt % and ∼20 wt % were observed, respectively. At high temperatures and with long residence times, decomposition of the esters formed may occur and the glycerol formed may react with other constituents of the reaction medium, leading to a decrease in the FAEE yield.41−43 For reactions with the addition of water and co-solvent, residence times of 70 and 60 min provided the best results at 573 and 598 K, respectively, and with the addition of ethyl esters, the best results were obtained for 50 min of reaction. Table 3 shows the contents of triacylglycerides (TGs), diacylglycerides (DGs), and monoacylglycerides (MGs) associated with the conditions that afforded the highest FAEE
Table 3. Content of Triacylglycerides (TGs), Diacylglycerides (DGs), and Monoacylglycerides (MGs) in the Products Obtained at a Pressure of 20 MPa and an Oilto-Ethanol Mass Ratio of 1:1 under Different Conditions conditions
MGs (wt %)
DGs (wt %)
TGs (wt %)
300 K/water addition of 5 wt %/70 min 300 K/co-solvent addition of 20 wt %/70 min 325 K/EE addition of 20 wt %/50 min
0.62 ± 0.09
0.32 ± 0.05
0.41 ± 0.08
0.45 ± 0.10
0.21 ± 0.04
0.25 ± 0.03
0.71 ± 0.13
0.33 ± 0.04
0.62 ± 0.12
yields in Figure 4, to allow for the verification of the completion of the transesterification reaction. These results should be considered together with the convertibility of the UFO used (93.1%) and the degree of decomposition. Mittelbach and Enzelberger40 reported that the formation of oligomers in the 3126
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
Energy & Fuels
Article
Table 4. Comparison of the Results Obtained in This Study with Those Reported in the Literature FAEE (wt %)
reactora
conditions
ethanol
CR
ethanol
CR
ethanol
CR
methanol
BR
UFO-to-ethanol mass ratio of 1:1, 573 K, 20 MPa, 70 min, and 5 wt % of water addition UFO-to-ethanol mass ratio of 1:1, 573 K, 20 MPa, 70 min, and 20 wt % of cosolvent addition UFO-to-ethanol mass ratio of 1:1, 598 K, 20 MPa, 50 min, and 20 wt % of biodiesel addition waste fried oil-to-methanol molar ratio of 1:42, 623 K, and 43 MPa
waste cooking oil waste palm cooking oil waste lard
methanol methanol
BR BR
methanol
BR
waste canola oil waste vegetable oil
methanol methanol
BR BR
waste fried oil
ethanol
CR
oil used frying oil (UFO) used frying oil (UFO) used frying oil (UFO) waste fried oil
a
alcohol
waste cooking oil-to-methanol molar ratio of 1:40, 573 K, 10 MPa, and 30 min waste palm cooking oil-to-methanol molar ratio of 1:40, 623 K, >20 MPa, and 20 min waste lard-to-methanol molar ratio of 1:45, 573 K, 20 MPa, 20 min, and agitation speed of 500 rpm waste canola oil-to-methanol mass ratio of 1:1, 543 K, 10 MPa, and 45 min waste vegetable oil-to-methanol molar ratio of 1:30, 553 K, CO2 reaction pressure of 20 MPa, and 15 min used vegetable oil to ethanol molar ratio of 1:30, 598 K, 15 MPa, ∼46 min, and 5 wt % of water addition
BR = batch reactor; CR = continuous reactor.
■
frying process may play an important role in the ester yields obtained from UFOs. In the transesterification, dimeric and trimeric triacylglycerides in the starting oil were mainly converted into monomeric and dimeric FAMEs. The yields reported herein can be considered satisfactory when compared with the maximum yields reported in the literature for biodiesel production from waste oil under supercritical conditions, as shown in Table 4. Based on the concept of conversion efficiency described by Gonzalez et al.23 and the convertibility of the oil used, the conversion efficiency in this study was >90%. It should be noted that the yields of esters obtained from this feedstock are dependent on the origin of the frying oil, the frying time, and the heating temperature.8,40 Another interesting finding to note is the difference in the reaction yields obtained for the batch and continuous modes. In the former case, the reaction time reported does not consider the time associated with the heating and cooling of the reactor, which does not occur in continuous mode, where the reaction time is computed after the reaction conditions (temperature and pressure) have stabilized. Also, the vigorous agitation usually applied in the batch mode should be taken into account, as this may lead to a more homogeneous reaction medium compared to the continuous mode.32
reference
∼84
this study
∼87
this study
∼83
this study
96.9 ∼80 ∼80 86 ∼96 ∼90 82.2
Kusdiana and Saka10 Patil et al.44 Tan et al.45 Shin et al.46 Lee et al.36 Ghoreishi and Moein47 Gonzalez et al.23
AUTHOR INFORMATION
Corresponding Author
*Tel.: (55) 44-3621 9300. Fax: (55) 44-3621 9326. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors thank CNPq, CAPES and Fundaçaõ Araucária for the financial support and West Paraná State University (UNIOESTE) for the scholarship.
■
REFERENCES
́ (1) Agência Nacional do Petróleo, Gás Natural e Biocombustiveis ́ Brasil, Jan. 9, 2012. Retrieved from http://www.anp. (ANP). Brasilia, gov.br. (2) Robles-Medina, A.; González-Moreno, P. A.; Esteban-Cerdán, L.; Molina-Grima, E. Biotechnol. Adv. 2009, 27, 398−408. (3) Araujo, V. K.; Hamacher, S.; Scavarda, L. F. Bioresour. Technol. 2010, 101, 4415−4422. (4) Yaakob, Z.; Mohammad, M.; Alherbawi, M.; Alam, Z.; Sopian, K. Renew. Sust. Energy Rev. 2013, 18, 184−193. (5) Associação Brasileira das Indústrias de Oléos Vegetais (ABIOVE). Retrieved from http://www.abiove.org.br. (6) Agência Nacional de Vigilância Sanitária (ANVISA). Technical Report 11, Oct. 5, 2004. Retrieved from http://www.anvisa.gov.br. (7) Berrios, M.; Martin, M. A.; Chica, A. F.; Martin, A. Chem. Eng. J. 2010, 160, 473−479. (8) Ruiz-Méndez, M. V.; Marmesat, S.; Liotta, A.; Dobarganes, M. C. Grasas Aceites (Sevilla, Spain) 2008, 59, 45−50. (9) Sharma, Y. C.; Singh, B.; Upadhyay, S. N. Fuel 2008, 87, 2355− 2373. (10) Kusdiana, D.; Saka, S. Bioresour. Technol. 2004, 91, 289−295. (11) Vieitez, I.; Silva, C.; Alkimim, I.; Borges, G. R.; Corazza, F. C.; Oliveira, J. V.; Grompone, M. A.; Jachmanián, I. Energy Fuels 2009, 23, 558−563. (12) Vieitez, I.; Irigaray, B.; Casullo, P.; Pardo, M.; Grompone, M. A.; Jachmanián, I. Energy Fuels 2012, 26, 1946−1951. (13) Kusdiana, D.; Saka, S. Fuel 2001, 80, 225−231. (14) Warabi, Y.; Kusdiana, D.; Saka, S. Bioresour. Technol. 2004, 91, 283−287. (15) Glisic, S.; Skala, D. J. Supercrit. Fluids 2009, 49, 293−301.
4. CONCLUSIONS The reaction of used frying oil (UFO) with supercritical ethanol was investigated in this study, and the results obtained demonstrate that improved fatty acid ethyl ester (FAEE) yields can be attained with UFO. For most of the conditions investigated, the temperature, co-solvent concentration, and biodiesel addition positively affected the FAEE yield (p < 0.05). The addition of 5 wt % water increased the ester yield, but this did not influence the FAEE yield (p > 0.05). A long residence time led to relatively low FAEE yields and a higher degree of decomposition. The results showed that the addition of water and co-solvent led to a decrease in the decomposition of fatty acids, while the opposite scenario was observed with the addition of biodiesel and an increase in the temperature. 3127
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
Energy & Fuels
■
(16) Deshpande, A.; Anitescu, G.; Rice, P. A.; Tavlarides, L. L. Bioresour. Technol. 2010, 101, 1834−1843. (17) Anitescu, G.; Deshpande, A.; Tavlarides, L. L. Energy Fuels 2008, 22, 1391−1399. (18) Imahara, H.; Xin, J.; Saka, S. Fuel 2009, 88, 1329−1332. (19) Wen, D.; Jiang, H.; Zhang, K. Prog. Nat. Sci. 2009, 19, 273−284. (20) Patil, P.; Gude, V. G.; Deng, S. Energy Fuels 2010, 24, 746−751. (21) Tan, K. T.; Lee, K. T.; Mohamed, A. R. J. Supercrit. Fluids 2010, 53, 88−91. (22) Muppaneni, T.; Reddy, H. K.; Patil, P. D.; Dailey, P.; Aday, C.; Deng, S. Appl. Energy 2012, 94, 84−88. (23) Gonzalez, S. L.; Sychoski, M. M.; Navarro-Diaz, H. J.; Vieitez, I.; Jachmanián, I.; Silva, C.; Hense, H.; Oliviera, J. V. Energy Fuels 2013, 27, 5253−5259. (24) Granado, M. L.; Alonso, D. M.; Alba-Rubio, A. C.; Mariscal, R.; Ojeda, M.; Brettes, P. Energy Fuels 2009, 23, 2259−2263. (25) Lam, M. K.; Lee, K. T. Fuel 2010, 89, 3866−3870. (26) Busto, M.; D’Ippolito, S. A.; Yori, J. C.; Iturria, M. E.; Pieck, C. L.; Grau, J. M.; Vera, C. R. Energy Fuels 2006, 20, 2642−2647. (27) Silva, C.; Lima, A. P.; Castilhos, F.; Cardozo Filho, L.; Oliveira, J. V. Biomass Bioenergy 2011, 35, 526−532. (28) Silva, C.; Borges, G.; Castilhos, F.; Oliveira, J. V.; Cardozo Filho, L. Acta Sci. Technol. 2012, 34, 185−192. (29) Vieitez, I.; Silva, C.; Alkimim, I.; Castilhos, F.; Oliveira, J. V.; Grompone, M. A.; Jachmanián, I. J. Supercrit. Fluids 2011, 56, 265− 270. (30) Walker, R. E. Official Methods and Recommended Practices of the American Oil Chemists’ Society, 4th Edition; Champaign−Urbana, IL, 1990. (31) Silva, C.; Castilhos, F.; Oliveira, J. V.; Cardozo Filho, L. Fuel Process. Technol. 2010, 91, 1274−1281. (32) Doná, G.; Cardozo Filho, L.; Silva, C.; Castilhos, F. Fuel Process. Technol. 2013, 106, 605−610. (33) Standard UNE-EN 14103: Determination of Ester and Linolenic Acid Methyl Ester Contents; Asociación Española de Normalización y Certificación, Madrid, Spain, 2003. (34) Standard UNE-EN 14105: Determination of Free and Total Glycerol and Mono-, Di-, Triglyceride Contents; Asociación Española de Normalización y Certificación, Madrid, Spain, 2003. (35) Demirbas, A. Energy Convers. Manage. 2009, 50, 923−927. (36) Lee, S.; Posarac, D.; Ellis, N. Fuel 2012, 91, 229−237. (37) Choi, C.; Kim, J.; Jeong, C.; Kim, H.; Yoo, K. J. Supercrit. Fluids 2011, 58, 365−370. (38) Velez, A.; Soto, G.; Hegel, P.; Mabe, G.; Pereda, S. Fuel 2012, 97, 703−709. (39) Vieitez, I.; Pardo, M. J.; Silva, C.; Bertoldi, C.; Castilhos, F.; Oliveira, J. V.; Grompone, M. A.; Jachmanián, I. J. Supercrit. Fluids 2011, 56, 271−276. (40) Mittelbach, M.; Enzelberger, H. J. Am. Oil Chem. Soc. 1999, 76, 545−550. (41) Shin, H.; Lim, S.; Bae, S.; Oh, S. C. J. Anal. Appl. Pyrolysis 2011, 92, 332−338. (42) Silva, C.; Weschenfelder, T. A.; Rovani, S.; Corazza, F. C.; Corazza, M. L.; Dariva, C.; Oliveira, J. V. Ind. Eng. Chem. Res. 2007, 46, 5304−5309. (43) Olivares-Carrillo, P.; Quesada-Medina, J. J. Supercrit. Fluids 2011, 58, 378−384. (44) Patil, P.; Deng, S.; Rhodes, J. I.; Lammers, P. J. Fuel 2010, 89, 360−364. (45) Tan, K. T.; Lee, K. T.; Mohamed, A. R. Energy 2011, 36, 2085− 2088. (46) Shin, H.; Lee, S.; Ryu, J.; Bae, S. J. Supercrit. Fluids 2012, 61, 134−138. (47) Ghoreishi, S. M.; Moein, P. J. Supercrit. Fluids 2013, 76, 24−31.
Article
NOTE ADDED AFTER ASAP PUBLICATION The title of this paper was modified, and an author name corrected in the version of this article published May 1, 2014. The correct version published May 15, 2014.
3128
dx.doi.org/10.1021/ef402253e | Energy Fuels 2014, 28, 3122−3128
