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Energy & Fuels 2008, 22, 4274–4280
New Class of Acetal Derived from Glycerin as a Biodiesel Fuel Component Eva Garcı´a,* Miriam Laca, Elena Pe´rez, Angel Garrido, and Julia´n Peinado Research and DeVelopment Department, Intertek, Alda Rekalde, 27, 5th Floor, Bilbao, Bizkaia 48009, Spain ReceiVed June 18, 2008. ReVised Manuscript ReceiVed August 6, 2008
The biodiesel production increase in the last few years has led to an overproduction of glycerin, the main byproduct of this industry. To avoid a glut in the glycerin market, many researchers are exploring new uses for this product. One of the most promising research areas is the use of glycerin-based additives to improve biodiesel properties. In this context, this paper presents the results of the study of a new oxygenate synthesized from crude glycerin as a biodiesel additive. The obtained results reveal that new acetal (2,2-dimethyl-1,3dioxolan-4-yl)methyl acetate not only improves biodiesel viscosity but also meets the requirements established by diesel and biodiesel fuels by the European and American Standards (EN 14214 and ASTM D6751, respectively) for other important parameters, such as flash point and oxidation stability, that have not been studied before with previous acetals. The comparison study between this new acetal and the known additive glycerol triacetate (triacetin) demonstrates that this new compound can compete with other biodiesel additives. Moreover, along this work, new synthetic methodology of triacetin has been designed using new reaction conditions, which avoid high temperatures and the presence of catalysts.
1. Introduction With the new energy legislation implemented in Europe,1 the global production of biodiesel has dramatically increased in the last few years. Other countries, such as Canada, Australia, U.S.A., and Japan, have also adopted policies that will mean higher biofuels production over the next decade.2 As a result, a large surplus of glycerin is formed as a byproduct (10% in weight), which has significantly impacted the glycerol market, resulting in a decline in glycerin pricing.3 Because of the economic viability of biodiesel and oleochemical industries being closely linked to glycerin, the deterioration of glycerin prices negatively affects the cost of materials derived from these industries. Although glycerin has many commercial uses, these markets are generally considered mature, making it difficult to absorb the extra glycerin surpluses. The increasing abundance of glycerin, its renewability, and attractive pricing make this product an appealing platform chemical to derive a family of commercially valued compounds. To this end, to convert glycerin into high volume value-added products, new chemistry is being developed.4-6 Despite the increase of biodiesel production, the demand of this biofuel has not been as expected; the relatively high price * To whom correspondence should be addressed. Telephone: 34946361730. Fax: 34946361880. E-mail:
[email protected]. (1) Directive 2003/30 EC of the European Parliament and Council of May 8, 2003 on the Promotion of the Use of Biofuels or Other Renewable Fuels for Transportation. Official Journal of the European Union, May 2003. (2) Mabee, W. E. Policy options to support biofuel production. AdVances in Biochemical Engineering/Biotechnology; Springer: New York, 2007; Vol. 108, pp 329-357. (3) Glycerine market research. Market report of Merchant Research and Consulting, Ltd., Birmingham, U.K., March, 2008. (4) Bondioli, P. Ital. J. Agron. 2003, 7, 129–135. (5) Pachauri, N.; He, B. ASABE Annual Meeting Presentation, 2006; Paper 066223. (6) Pagliaro, M.; Ciriminna, R.; Kimura, H.; Rossi, M.; Della Pina, C. Angew. Chem., Int. Ed. 2007, 46, 4434–4440.
of biodiesel compared to diesel fuel derived from petroleum is one of the main obstacles to its complete commercial acceptance. However, the most important barriers to its expansion are their inferior properties at low temperature7,8 and lower oxidation stability.9,10 This situation has prompted an intensive search for new additives derived from glycerol for this biofuel. This approach not only revalorizes this byproduct but also increases the fuel yield in the overall biodiesel process. Initial studies proposed glycerin ethers as low-temperature property improvers. For example, Noureddini11,12 etherified glycerin using isobutylene; in this way, he obtained new oxygenate compounds that, mixed with biodiesel, decreased its viscosity and cloud point (CP). This class of compounds has been also proven as additives to reduce particulate matter emission in diesel and biodiesel fuels.13-15 Other authors have focused their work in the preparation of other derivatives, such as glycerin carbonates16,17 or acetals.18-20 Delgado and coworkers18 described the use of glycerin acetals to reduce the (7) Peterson, C. L. Trans. Am. Soc. Agic. Eng. 1986, 29, 1413–1422. (8) Dunn, R.; Bagby, M. O. J. Am. Oil Chem. Soc. 1995, 72, 895–903. (9) Lacoste, F.; Bondioli, P.; Mittelbach, M.; Blassnegger, J.; Brehemer, T.; Fro¨hlich, A.; Dufrenoy, B.; Fischer, J. Stability of biodiesel. Project in the 5th Framework Programme: Quality of Life and Management of Living Resources Key Action Sustainable Agriculture, Fisheries and Foresty. Supported by the European Comission, Wieselburg, Austria, Aug 2003. (10) McCormick, R. L.; Alleman, T. L.; Ratcliff, M.; Moens, L.; Lawrence, R. Survey of the quality and stability of biodiesel and biodiesel blends in the United States in 2004. Technical Report of NREL/TP 54038836, Oct 2005. (11) Noureddini, H.; Dailey, W. R.; Hunt, B. A. Chemical and Biomolecular Engineering Research and Publications, 1998. (12) Noureddini, H. U.S. Patent 6,015,440, 2001. (13) Kesling, H. S.; Karas, L. J.; Liotta, F. J. U.S. Patent 5,308,365, 1994. (14) Kije´nski, J.; Jamro´z, M. E.; Tecza, W. Jarosz Appl. Pol. Patent 959, 2004. (15) Olah, G. A. U.S. Patent 5,520,710, 1996. (16) Delfort, B.; Duran, I.; Jaecker, A.; Lacome, T.; Montagne, X.; Paille, F. U.S. Patent 7,097,674, 2006.
10.1021/ef800477m CCC: $40.75 2008 American Chemical Society Published on Web 09/10/2008
Acetal from Glycerin as a Biodiesel Fuel Component Scheme 1. (a) Synthesis of Acetal 1 from Glycerin and Acetone and (b) Acylation of the OH Group and Synthesis of Acetal 2 and Triacetin 3
pour point (PP) and the viscosity of methyl or ethyl esters of fatty acids. This type of compounds has also been used to reduce diesel fuel particulate emissions.20 Likewise, glycerin has also been esterified with acetic acid or transesterified with methyl acetate to yield triacetin.18,21-23 This product has also been used in biodiesel formulation, resulting in a final fuel having enhanced low-temperature and viscosity properties. None of these previous studies mention other important parameters, such as flash point or oxidation stability. The aim of this work is to study a new type of oxygenated compound as an additive in diesel and biodiesel blends. We will demonstrate that a slight modification of known acetal 1 (see Scheme 1) converts it into a better alternative that, besides improving viscosity, meets the specifications contained in EN 1421424 and ASTM D675125 Standards for other important parameters, such as flash point or oxidation stability. 2. Experimental Section 2.1. Materials and Synthetic Procedures. Glycerin crude and biodiesel used in the present work were provided by Bionor, a biodiesel production plant in the Basque Country (Spain). Standard diesel fuel per EN 590 available in the laboratory was used for biodiesel mixtures. This fuel was obtained from different Spanish petrol stations (Repsol, Cepsa, Shell, and BP) that usually send their products to the Intertek laboratory to be analyzed. The rest of the reagents used for the synthesis reactions were purchased from Sigma-Aldrich and Fluka (P.O. Box 278, Tres Cantos 28760, Madrid) and Panreac (Castellar del Valle`s 08211, Barcelona) in Spain. Acetal (2,2-dimethyl-1,3-dioxolan-4-yl)methanol 1 was synthesized by adapting the patent published by Bruchmann et al.27 This (17) Fabbri, D.; Bevoni, V.; Notari, M.; Rivetti, F. Fuel 2007, 86, 690– 697. (18) Delgado, J. U.S. Patent 0,167,681, 2003. (19) Miller, D.; Peereboom, L.; Kolah, A. K.; Asthana, N. S. U.S. Patent 0,199,970, 2006. (20) Delfort, B.; Duran, I.; Jaecker, A.; Lacome, T.; Montagne, X.; Paille, F. U.S. Patent 6,890,364, 2005. (21) Wessendorf, R. Petrochemia 1995, 48, 138–143. (22) Delfort, B.; Hilion, G.; Durand, I. FR Patent 2,866,654, 2004. (23) Melero, J. A.; van Grieken, R.; Morales, G.; Paniagua, M. Energy Fuels 2007, 21, 1782–1791. (24) European Standard EN 14214. Automotive fuels. Fatty acid methylesters (FAME) for diesel engines. Requirements and test methods, 2003. (25) American Society for Testing and Materials (ASTM) Standard D6751. Standard specification for biodiesel fuel blend stock (B100) for middle distillate fuels. (26) European Standard EN 590. Automotive fuels. Diesel. Requirements and test methods, 2004. (27) Bruchmann, B.; Haberle, K.; Gruner, H.; Hirn, M. U.S. Patent 5,917,059, 1999.
Energy & Fuels, Vol. 22, No. 6, 2008 4275 involved mixing glycerin (200 mL, 2.74 mol) and acetone (Panreac, 99.5%) (603.5 mL, 8.22 mol) with p-toluenesulfonic acid monohydrate (Aldrich, g98.5%) (0.1 mol % based on glycerin) (reaction a in Scheme 1). The reaction mixture was heated to reflux for 16 h. As the wet acetone was distilled, more dry acetone was simultaneously introduced in the reactor, keeping the level of the liquid in the reactor constant. Finally, the reaction was stopped by adding Na2CO3 (0.2 mol % based on glycerin) to neutralize the reaction medium. The formed salts were eliminated by filtration, and the solvents were removed in a rotary evaporator under reduced pressure. Acetal (2,2-dimethyl-1,3-dioxolan-4-yl)methyl acetate 2 was obtained by reacting 1 (195 g, 1.5133 mol) with acetic anhydride (Panreac, 99%) (380 mL, 3.026 mol) in triethylamine (Aldrich, g99%) (420 mL, 3.026 mol) solution at room temperature for 4 h. Then, the reaction mixture was dissolved in ethyl acetate (Panreac, 99.5%) washed with a saturated solution of NaHCO3, water, and brine and dried over anhydrous MgSO4, and the solvent was evaporated in the rotary evaporator. Traces of water and acetic acid were eliminated from the mixture by vacuum distillation. The reaction yielded a mixture of acetal 2 and triacetin 3 that could not be separated by flash chromatography or different distillation techniques (reaction b in Scheme 1). The average share of triacetin in this mixture was determined by nuclear magnetic resonance (NMR) spectroscopy. The integration of signals in 1H NMR spectra indicated that the ratio 2/3 was 1.6:1 (Figure 1). Triacetin 3 was obtained pure from crude glycerin and acetic anhydride following the same procedure described above (Scheme 2). 2.2. Acetal Characterization. Reaction progress and acetal identification was followed by gas chromatography, using a HP 5890 series II equipped with a flame ionization detector (FID). As an example, Figure 2 shows the reaction monitoring of glycerol when mixed with acetone to produce acetal 1 (Figure 2). The structures of compounds 1, 2, and 3 were determined by mass spectrometry (MS) on a Shimadzu GCMS-QP2010 (Figure 3) and Fourier transform infrared (FTIR) spectrometry on a Shimadzu 8400S (Figure 4). A more detailed description of the analysis methods and product characterization can be found in the Supporting Information. 2.3. Preparation of Samples. After acetal 1 was synthesized, this was added in a 5% concentration (v/v) to a 1:1 mixture of fatty acid methyl esters (FAME)/diesel and to a FAME sample (B100). The corresponding samples without acetal addition were prepared simultaneously. The study of acetal 2 and triacetin 3 was carried out with B20 and B100 samples. Each compound was added in 5, 10, and 15% concentration (v/v). At the same time, samples of B20 and B100 with no addition were prepared. 2.4. Analytical Methods. B50 and B20 samples were analyzed according to procedures enclosed in EN 590 Standard:26 kinematic viscosity (40 °C) according to EN ISO 3104, density (15 °C) according to EN ISO 12185, oxidation stability according to EN ISO 12205, flash point according to EN ISO 3679, and cold filter plugging point (CFPP) according to EN 116. B100 samples were analyzed according to procedures listed in EN 14214 Standard.24 The tests were similar to those enumerated above, except for the oxidation stability test, where the Rancimat method was used (EN 14112). Moreover, acidity of these samples was studied following the EN 14104 test method.
3. Results and Discussion Acetal 1 was obtained in very good yield (90%), and no further purification was needed after solvent elimination. The first purpose was to study the effect of this compound on FAME properties when blended with conventional diesel fuel and when it was pure. For preliminary studies, acetal 1 was added to a B50 blend and to B100 in a 5% volume concentration. Table 1 shows the results for the first parameters
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Figure 1. 1H NMR spectra of the mixture of acetal 2/triacetin 3 (1.6:1 ratio).
Figure 2. Synthesis monitorization of acetal 1 by gas chromatography: (A) 5 h of reaction time, (B) 10 h of reaction time, and (C) 16 h of reaction time. Scheme 2. Synthesis Reaction of Triacetin 3 from Crude Glycerin and Acetic Anhydride
studied. These data reveal that acetal 1 slightly enhanced viscosity as published before,18 but we did not observe any change in the CFPP. The study of density in the B50 blend revealed that, even before adding acetal 1, this parameter value was above the maximum limit established by EN 59026 specifications for FAME-diesel fuel blends (845 kg/m3). The addition of acetal 1 slightly increased the value of this parameter.
With these results, we decided to follow the study with other blends with less biodiesel content. On the other hand, the density value of FAME, despite the increase observed, was between the established limits in EN 14214 Standard (860-900 kg/m3). The results obtained in oxidation stability and flash point tests are remarkable. Both samples, B50 and B100 presented a flash point lower than the minimum required by European regulations,24,26 55 °C (EN 590) and 120 °C (EN 14214), respectively. Likewise, the total amount of insolubles obtained when the B50 sample was submitted to oxidation stability test conditions28 greatly exceeded the maximum permitted (164 versus 25 g/m3). Analysis of sediments encountered in the filter revealed that the main compound was glycerol, which means that acetal 1 (28) European Test Standard EN ISO 12205. Petroleum products. Determination of the oxidation stability of middle-distillate fuels, 1995.
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Figure 3. Mass spectra of acetal 1, acetal 2, and triacetin 3.
had suffered hydrolysis under test conditions (95 °C and O2 bubbling at a rate of 3 L/h for 16 h). Stability studies performed with this compound showed that acetal 1 was stable while it was pure, but when mixed with FAME, it was hydrolyzed at temperatures over 90 °C. Thus, traces of acid or water present in FAME must have caused the hydrolysis of this compound. Moreover, the OH group gives hygroscopic character to the acetal 1, which can lead to water absorbance. This functionality also explains the marked drop in flash point, which is too low for these samples to be accepted in the European market. With these results in hand, we stopped the tests with acetal 1 and proceeded to modify its structure, introducing an acyl group to the OH (see Scheme 1). Without any free OH in the medium, we hoped to avoid the low stability and low flash point observed before. The acylation of the hydroxyl group of the acetal 1 was initially carried out with acetic anhydride and DMAP as a
catalyst, following the general procedure described by Kazlauskas et al.29 Later on, this method was slightly modified because we found that the use of catalyst DMAP was unnecessary. Despite several attempts to optimize reaction conditions, we could not avoid the formation of the byproduct glycerol triacetate 3, formed by the hydrolysis of acetal 1 and esterification of the resulting glycerol at the reaction conditions (see Scheme 1). Thus, we decided to study the effect of the obtained mixture 2-3 in biodiesel parameters knowing that the 2/3 molar ratio was 1.6:1. The obtained results were compared to the results of adding similar amounts of pure triacetin 3. This compound was successfully synthesized from glycerol as described in the previous section (see Scheme 2). In this stage, it is remarkable that we performed the acylation of OH groups with no catalyst. Previous work in the literature (29) Mezzetti, A.; Keith, C.; Kazlauskas, R. J. Tetrahedron: Asymmetry 2003, 14, 3917–3924.
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Figure 4. FTIR spectra of of acetal 1, acetal 2, and triacetin 3.
describes this reaction by using acetic acid23 or methyl acetate,30 and in most cases, even when acetic anhydride is used, a catalyst is employed.31-34 We proved that acylation of glycerin could (30) Delfort, B.; Hillion, G.; Durand, I. FR Patent 2,866,654, 2004. (31) Bartoli, G.; Bosco, M.; Dalpozzo, R.; Marcantoni, E.; Massaccesi, M.; Sambri, L. Eur. J. Org. Chem. 2003, 4611–4617.
be achieved at room temperature in 4 h with an excess of acetic anhydride (4 mol/mol of glycerin) and no catalyst. Before preparing samples for the study, several tests of solubility were performed. It is known that acetal 1 and triacetin 3 are soluble in FAME,18,20 but there were no precedents about acetal 2. We found that the acetal 2/triacetin mixture was
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Table 1. Changes in Parameters of B100 and B50 When 5% of Acetal 1 Is Added UNE EN 14112 oxidation stability (h)
samplesa B100 B100 + 5% Ac 1 B50 B50 + 5% Ac 1 a
EN ISO 12205 oxidation stability (g/m3)
EN ISO 12185 density at 15 °C (kg/m3)
EN ISO 3104 viscosity at 40 °C (mm2/s)
EN ISO 3679 flash point (°C)
UNE 116 CFPP (°C)
3 164
885.2 889.3 863.5 868.2
4.609 4.464 3.699 3.65
159 40.5 76 37
-4 -4 -12 -12
5.3 5.3
Ac 1 ) acetal 1.
Table 2. Effect of Acetal 2/Triacetin Mixture and Pure Triacetin Addition to B20 Fuel Properties
samplesa B20 B20 B20 B20 B20 B20 B20 a
EN ISO 12205 oxidation stability (g/m3)
EN ISO 12185 density at 15 °C (kg/m3)
EN ISO 3104 viscosity at 40 °C (mm2/s)
EN ISO 3679 flash point (°C)
EN 116 CFPP (°C)
3
