Energy Fuels 2010, 24, 2086–2090 Published on Web 12/30/2009
: DOI:10.1021/ef901295s
Simulated Distillation for Biofuel Analysis Christine Bachler, Sigurd Schober, and Martin Mittelbach* Institute of Chemistry, University of Graz, Austria Received November 4, 2009. Revised Manuscript Received November 26, 2009
Simulated distillation (SimDis) is a gas chromatographic method and has evolved into an indispensable tool in petroleum industries to determine the distillation behavior of different petroleum products and to ensure fuel quality. In contrast to classic physical distillation, SimDis exhibits a range of advantages that include comparatively very small sample amounts and the possibility of automation, which are of great importance in fields of research and in the development of novel fuels. Within this work we could show that SimDis can also be used to characterize not only boiling behaviors of fossil fuels, but also alternative fuels as different kinds of biodiesel. Analysis of different kinds of biodiesel and biodiesel blends, as presented in our work, shows that shorter chain fatty acid methyl esters, as can be found in coconut oil, can significantly change the distillation characteristic to a more favorable distillation curve, which resembles a fossil diesel fuels boiling behavior. The second part of our work shows that there is a good correlation between data obtained using SimDis and conventional distillation, also in case of biodiesel. SimDis therefore can easily be used to classifiy novel biofuels, for example, also bidodiesel made of algae or novel oilseed, regarding boiling characteristics and quality.
engine operability, start of the motors, and in the stage of preheating.10 Recently, the distillation curve is also of main interest in development of diesel fuel surrogates to ensure good engine performance and minimization of pollutants.11,12 For this reason, distillation recoveries at certain temperatures are defined within the European Standard EN 59013 for fossil diesel fuel. Unlike mandatory distillation characteristics for diesel fuel, there is no European standard for distillation behavior of biodiesel. However, the United States prescribe that 90% of a biodiesel or biodiesel blend must be recovered at a maximum temperature of 360 °C according to D 675114 as assurance for the lack of high-boiling compounds. However, by distillation of biodiesel at atmospheric pressure one faces the problem that pyrolysis occurs. This results in an unexpected decrease of the boiling curve, characterized by a decrease of boiling temperature for the last third of the sample, actually characterized by high boiling points.15 To overcome the problem of pyrolysis, distillation can be carried out at reduced pressure as described in ASTM D1160.16 Nevertheless, this method as well as other procedures based on classic physical distillation suffer from poor reproducibility and are time-consuming and laborious.17 Another negative aspect of a physical distillation process is the lack of
Introduction Although biodiesel nowadays is considered an equal alternative to fossil diesel fuel,1 there are not only differences in chemical composition but also in physical properties. The fatty acid composition of the biodiesel, for example, affects some critical parameters such as cetane number, cold flow properties, or oxidation stability2 as well as distillation characteristics, which are of main interest in this study. It is already known that biodiesel basically consists of methyl esters of C16 and C18 fatty acids with similar boiling points.3 Biodiesel therefore exhibits a narrow boiling range around 350 °C with initial boiling points at 300 °C.4 In contrast, fossil diesel additionally contains lower boiling compounds, resulting in a steadily increasing boiling behavior starting at 200 °C. Generally, high-boiling compounds are connected to engine deposits, increase of exhaust gases, and higher cetane numbers,5-7 whereas a high amount of volatile compounds can reduce the flash point of the fuel.8,9 Further, there is a need to ensure a certain boiling behavior of the diesel fuel due to *To whom correspondence should be addressed. E-mail: martin.
[email protected]. Telephone: þ43 316 380-5353. Fax: þ43 316 380 9840. (1) Luque, R.; Herrero-Davila, L.; Campelo, J. M.; Clark, J. H.; Hidalgo, J. M.; Luna, D.; Marinas, J. M.; Romero, A. A. Energy Environ. Sci. 2008, 1, 542–564. (2) Ramos Maria, J.; Fernandez Carmen, M.; Casas, A.; Rodriguez, L.; Perez, A. Bioresour. Technol. 2009, 100, 261–8. (3) Krop, H. B.; van Velzen, M. J. M.; Parsons, J. R.; Govers, H. A. J. J. Am. Oil Chem. Soc. 1997, 74, 309–315. (4) Sarma, A. K.; Konwer, D.; Bordoloi, P. K. Energy Fuels 2005, 19, 656–657. (5) Karonis, D.; Lois, E.; Stournas, S.; Zannikos, F. Energy Fuels 1998, 12, 230–238. (6) Karonis, D.; Lois, E.; Zannikos, F.; Alexandridis, A.; Sarimveis, H. Energy Fuels 2003, 17, 1259–1265. (7) Bajpai, D.; Tyagi, V. K. J. Oleo. Sci. 2006, 55, 487–502. (8) Sjogren, M.; Li, H.; Rannug, U.; Westerholm, R. Fuel 1995, 74, 983–9. (9) Mittelbach M.; Remschmiedt C. Biodiesel: The Comprehensive Handbook; Boersedruck GmbH: Vienna, 2004. r 2009 American Chemical Society
(10) Encinar, J. M.; Gonzalez, J. F.; Rodriguez-Reinares, A. Ind. Eng. Chem. Res. 2005, 44, 5491–5499. (11) Smith, B. L.; Ott, L. S.; Bruno, T. J. Environ. Sci. Technol. 2008, 42, 7682–7689. (12) Semenov, V. G. Chem. Technol. Fuels Oils 2003, 39, 192–196. (13) Kraftstoffe f€ ur Kraftfahrzeuge - Dieselkraftstoff - Anforderungen and Pr€ ufverfahren; Deutsche Fassung EN 590:2009. (14) ASTM D6751 - 09 Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels; American Society for Testing and Materials: West Conshohocken, PA. (15) Wenzel, G.; Lammers, P. S. J. Agric. Food Chem. 1997, 45, 4748– 4752. (16) ASTM D1160 - 06 Standard Test Method for Distillation of Petroleum Products at Reduced Pressure; American Society for Testing and Materials: West Conshohocken, PA. (17) Blomberg, J.; Schoenmakers, P. J.; Brinkman, U. A. T. J. Chromatogr. A. 2002, 972, 137–73.
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Energy Fuels 2010, 24, 2086–2090
: DOI:10.1021/ef901295s
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automation; Although one run takes about 40 min in the case of both methods, simulated and physical, the method of choice would be simulated distillation if a series of samples needs to be analyzed due to high need of manpower for cleaning of the vacuum apparatus after each run and for control of the whole procedure. Further, rather large sample amounts are needed,18 which might be a problem in research and development laboratories, if new kinds of fuels are only available in small volumes. To overcome all those problems, Eggerston et al.19 first proposed to use a gas chromatographic method to simulate a distillation process. Nowadays simulated distillation (SimDis) is a well-established method in petroleum industry where the knowledge of boiling ranges of crudes and various products is important to determine quality and to control or optimize different processes in a refinery. Simulated distillation is based on elution of a series of n-alkanes introduced into a GC system. Equipped with a nonpolar column and by linearly raising the oven temperature, the alkanes separate in order of increasing boiling points. Simply because the boiling points of all n-alkanes are precisely known from literature, a chromatogram received under identical conditions can then be divided into boiling ranges and mimic the physical distillation process. Standardized SimDis methods for fossil diesel fuels compromise ASTM D 288720 or EN 15199-1,21 whereas pure biodiesel or biodiesel blends can be analyzed according to ASTM D 7398,22 generally covering a boiling range from 100 to 615 °C. Although SimDis nowadays is well established, there is hardly any data on biodiesel distillation characteristics available. Sarma et al.4 performed simulated distillation to analyze a biodiesel made of Koroch seed oil, characterized by 95% of the sample distilled between 219 and 372 °C (with IBP and FBP at 219 and 430 °C, respectively). However, a multitude of distillation curves for biodiesel samples still seem to be generated by using classical distillation methods, simply because a vacuum distillation apparatus is not always available. A classic distillation procedure at atmospheric pressure (ASTM D8623), for example, was used to test diesel fuel containing 1 and 5 vol % CME (coconut oil methyl ester), indicating no big differences in boiling behavior in contrast to a pure diesel fuel.24 In this work a comparison of boiling ranges of different biodiesel samples and biodiesel blends, obtained by simulated distillation, will be shown. It has to be mentioned that there is hardly any data available, especially in case of widely used biodiesel blends that can enormously change in fatty acid composition. Diesel blends containing certain amounts of rapeseed oil methyl esters (RME) were measured, because
Table 1. Fatty Acid Composition of RME and CME in Percent, Including Methyl Esters at Least Counting 2% (m/m) fatty acid C8:0 C10:0 C12:0 C14:0 C16:0 C18:0 C18:1 C18:2 C18:3
RME
7.1 2.2 58.4 21.4 7.5
CME 3.5 3.5 46.3 15.8 9.0 15.1 6.1
RME is very popular within the European Union. On the other hand, CME seems to be a promising kind of biodiesel; First, it contains a high amount of lower-boiling point fatty acid methyl esters, similar to palmkernel oil,25 indicating that it exhibits a rather wide distillation curve similar to fossil diesel fuel. Second, it is of major interest in the Philippines and Malaysia, where environmental temperatures are higher and therefore cold temperature problems, for example, fuel filter or injection line blocking,26-28 can be neglected. Although data obtained via simulated distillation are in excellent agreement with actual distillation procedures in the case of petroleum products,18 a comparison of distillation recoveries for a biodiesel sample, as integrated in this work, is of great interest. The reason is based on the nature of biofuels; In contrast to fossil fuels, which consist of hydrocarbons, alternative fuels differ in chemical composition. So, especially in fields of research and development, the amenities of simulated distillation simplify the procedure to obtain distillation characteristics of novel kinds of fuel, for example, made of algae oil or new species of oilseed, where sample amounts are small-sized and fast methods are of great importance. As a consequence of the general trend to create lower-boiling fuels in order to reduce emissions, simulated distillation is an efficient tool for fuel modeling. Experimental Section Specification of the Fossil Diesel Fuel and Biodiesel Samples. Biodiesel, made of rapeseed oil and obtained from BDV (Biodiesel Vienna, Austria), and the coconut oil methyl ester (CME) were prepared according to standard procedures29 and distilled for further purification. Both biodiesel samples were then characterized according to EN 14214.30 The results are shown in Tables 1 and 2. The petroleum diesel fuel is a so-called BP ultimate diesel meeting EN 59013 and contains no FAME. The specification of this diesel fuel is available via the BP homepage.31 Solvents. The carbon disulfide used for dilution of the samples and for preparation of the calibration mixture was purchased from Fluka (puriss. p.a., g99,9%). According to the scope of the method, cyclohexane can also be used as solvent to avoid the use of carbon disulfide in larger volumes.
(18) Schwartz, H. E.; Brownlee, R. G.; Boduszynski, M. M.; Su, F. Anal. Chem. 1987, 59, 1393–401. (19) Eggertsen, F. T.; Groennings, S.; Holst, J. J. Anal. Chem. 1960, 32, 904–9. (20) ASTM D2887 - 08 Standard Test Method for Boiling Range Distribution of Petroleum Fractions by Gas Chromatography; American Society for Testing and Materials: West Conshohocken, PA. (21) Petroleum Products - Determination of boiling range distribution by gas chromatography method - Part 1: Middle distillates and lubricating base oils; German version EN 15199-1:2006; CEN: Brussels, Belgium, 2006. (22) ASTM D7398 - 07 Standard Test Method for Boiling Range Distribution of Fatty Acid Methyl Esters (FAME) in the Boiling Range from 100 to 615C by Gas Chromatography; American Society for Testing and Materials: West Conshohocken, PA. (23) ASTM D86 - 09e1 Standard Test Method for Distillation of Petroleum Products at Atmospheric Pressure; American Society for Testing and Materials: West Conshohocken, PA. (24) National Renewable Energy Laboratory Analysis of CoconutDerived Biodiesel and Conventional Diesel Fuel Samples from the Philippines; 2006;www.nrel.gov/vehiclesandfuels/npbf/pdfs/38643.pdf.
(25) Dale, A. P.; Meara, M. L. J. Sci. Food Agric. 1955, 6, 166–70. (26) Tan, R. R.; Culaba, A. B.; Purvis, M. R. I. Biomass Bioenergy 2004, 26, 579–585. (27) Machacon, H. T. C.; Matsumoto, Y.; Ohkawara, C.; Shiga, S.; Karasawa, T.; Nakamura, H. JSAE Rev. 2001, 22, 349–355. (28) Kalam, M. A.; Husnawan, M.; Masjuki, H. H. Renew. Energy 2003, 28, 2405–2415. (29) Mittelbach, M.; Koncar, M. Process for Preparing Fatty Acid Alkyl Esters. Int. Patent Appl. WO/1995/002661, 1994. (30) Kraftstoffe f€ ur Kraftfahrzeuge - Fetts€aure-Methylester (FAME) f€ ur Dieselmotoren - Anforderungen and Pr€ ufverfahren. (31) BP Global; http://www.bp.com (Accessed July 17, 2009).
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: DOI:10.1021/ef901295s
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C18 acids and by comparison with normal boiling points presented by Yuan et al.,32 the results were meeting our prospects. As a second biodiesel sample we chose CME to demonstrate the benefits of lower boiling point methyl esters on distillation characteristics. The distillation curve of CME is very similar to the fossil diesel fuels boiling curve due to the fact that methyl esters of medium chain fatty acids have a significantly lowered boiling point compared to C18 methyl esters. Notably, the boiling region compromising 40-75% distillation recovery for CME and petroleum-derived diesel fuel is characterized by boiling points with a maximum difference of 10 °C. Further CME exhibits also higher boiling point methyl esters elevating the boiling curve. However, greater parts of the CME seem to boil within a narrow temperature range, resulting in a stairway-like distillation characteristic. Regarding minor distillation recoveries of CME, the boiling curve is evaluated compared to the fossil diesel fuels boiling: At 256 °C only 5% of the CME sample can be vaporized whereas nearly 40% of the fossil diesel fuel is distilled at the same temperature. However, biodiesel made of rapeseed oil does not even start to boil at that temperature and shows a boiling point 76 °C higher than CME and even 136 °C higher than fossil diesel fuel for 5% distillation recovery. At 10% distillation recovery the difference between the boiling temperature of RME and fossil diesel fuel nearly reaches 150 °C. Although the boiling curve of RME stays elevated, CME otherwise also shows decreased boiling regions when compared with the fossil fuel. Having a look at the CME and RME boiling behavior, one can notice that there is an assimilation of the curves at increasing distillation recoveries with maximum value of 94 °C at 10% and a minimum difference of 10 °C at 90% distilled off. Considering the U.S. Standard D 6751, the critical value of 90% distillation recovery at a maximum temperature of 360 °C can also be met. In the course of our investigations, B10 diesel fuel samples, containing 10 % m/m of RME or CME, were analyzed using SimDis to refer to a supposable maximum share for biodiesel within the European Union. B20 diesel fuel samples where generated, as a 20% share is a possible target regarding the US market. Both, B10 and B20 samples show a similar boiling behavior compared to petroleum-derived diesel fuel, which is characterized by a steadily increasing distillation curve (refer Figure 2). Until reaching 40% distillation recovery all of the four samples hardly differ in the boiling behavior. Mainly, the distillation curve of B10 and B20 containing CME (C10, C20) resemble the diesel fuel curve, having a maximum temperature difference of 14 and 18 °C at 30% distilled off. However, great parts of those two samples, approximately 80%, show minimal temperature differences, especially for higher boiling parts. The B10 and B20 samples containing RME (R10, R20) are characterized by higher boiling parts compared to C10, C20, and pure fossil diesel fuel. For R10 and R20 the average temperature difference to fossil diesel fuel is about 15 and 20 °C. Nevertheless, R10 shows extremely decreased boiling points for lower distillation recoveries compared to pure RME. Temperature differences therefore lie between 41 and 139 °C for both samples until reaching the 60% distillation recovery mark. At 90% distilled off the temperature difference for R10 and R20 reaches a minimum value, 5 and 2 °C, respectively. Considering that B20 curves, either RME or CME blends, show similar boiling characteristics, R20 can be preferred to C20 blends
Table 2. Physical and Chemical Properties According to EN 14214 RME ester content [% m/m] density15°C [kg/m3] viscosity40°C [mm2/s] flash point [°C] oxidation stability, 110 °C [h] sulfur content [mg/kg] cetane number water content [mg/kg] total contamination [mg/kg] copper strip corrosion (3 h at 50 °C) acid value [mg KOH/g] iodine value [g/100 g] methanol content [%(m/m)] monoglyceride content [%(m/m)] diglyceride content [%(m/m)] triglyceride content [%(m/m)] free glycerol [%(m/m)] total glycerol [%(m/m)] Group I metals (Na, K) [mg/kg] Group II metals (Ca, Mg) [mg/kg] phosphorus content [mg/kg]
97.4 883 4.51 130 10 6 54 181 9 1 0.31 107 0.09 0.51 0.19 0.01
