ARTICLE pubs.acs.org/EF
Evaluation of the Oxidation Stability of Biodiesel Produced from Moringa oleifera Oil kos Bereczky,‡ and Mate Z€oldy§ Thomas T. Kivevele,*,† Makame M. Mbarawa,† A †
Department of Mechanical Engineering, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa 00 Department of Energy Engineering, Budapest University of Technology and Economics, Muegyetem rkp. 3-9, H-1111 Budapest, Hungary § DSD Product Development, MOL Hungarian Oil and Gas Public Limited Company, Post Office Box 1, H-2443 Szazhalombatta, Hungary ‡
ABSTRACT: Biodiesel is considered as an alternative fuel to petroleum-based conventional diesel fuel. Dependent upon the raw material, biodiesel can contain more or less unsaturated fatty acids in its composition, which are susceptible to oxidation reactions accelerated by exposure to oxygen and high temperatures. The present study evaluated the oxidative stability of biodiesel produced by methanolysis of Moringa oleifera oil, primarily available on the African continent. The evaluation was conducted by means of the Rancimat instrument, at a temperature of 110 °C, with an air flow of 10 L/h. Moringa oil methyl ester (MOME) displayed an oxidation stability of 5.05 h. Thus, MOME met the oxidative stability requirement in the American Society for Testing and Materials (ASTM) D6751 standard, which prescribes a minimum of 3 h, but did not meet the minimum requirement prescribed in the EN 14214 standard, which is 6 h. Also, this study evaluated the effectiveness of four antioxidants, 1,2,3-trihydroxybenzene [pyrogallol (PY)], 3,4,5-trihydroxybenzoic acid [propyl gallate (PG)], 2-tert-butyl-4-methoxyphenol [butylated hydroxyanisole (BHA)], and 2,6-di-tert-butyl-4-methylphenol [butylated hydroxytoluene (BHT)], on the oxidation stability of MOME. The result showed that the effectiveness of these antioxidants was in the order of PY > PG > BHA > BHT.
’ INTRODUCTION Diesel fuel has been widely used in industry and in automobiles for over a century. As the petroleum prices continue to rise, diesel supply is becoming scarce and unreliable.1 There is a growing concern for a cleaner environment; hence, scientists have invested considerable effort in searching for renewable substitutes for diesel fuel. Biodiesel is a nontoxic, biodegradable, and renewable fuel that can be used in diesel engines and is becoming one of the fastest growing fuels in the global fuel market.1,2 Biodiesel is produced from the transesterification of vegetable oil or animal fat with a simple alcohol in the presence of a catalyst. It is a type of fatty acid ester, which has fuel characteristics similar to mineral diesel. Despite its many advantages, the chemical nature of biodiesel makes it more susceptible to oxidation compared to mineral diesel during long-term storage. The sensitivity to oxidation varies depending upon the raw material, the presence of naturally occurring antioxidants, and the storage conditions, such as exposure to atmospheric oxygen, daylight, contaminants (metals that speed up oxidation), and high temperature.3 The biodiesel stability generally depends upon the fatty acid profile of the parent feedstock. Therefore, biodiesels with high unsaturated fatty acid contents, such as linoleic and linolenic acids, are especially prone to oxidation. The relative oxidation rates for these unsaturated esters are linolenic > linoleic > oleic acids.4 Figure 1 shows the typical oxidation reactions of biodiesel. Oxidation of biodiesel starts with the abstraction (removal) of hydrogen atoms from the “allylic” position next to the double bond to produce a carbon free radical. If diatomic oxygen is present, therefore, the subsequent reaction to form a peroxy r 2011 American Chemical Society
radical is extremely fast. The peroxy free radical is not as reactive as the carbon free radical but is sufficiently reactive to quickly abstract hydrogen from a carbon to form another carbon radical and a hydroperoxide (ROOH). The new carbon free radical can then react with diatomic oxygen to continue the propagation cycle. This chain reaction terminates when two free radicals react with each other to yield stable products, such as aldehydes, shorter chain carboxylic acids, insolubles, gum, and sediments. When biodiesel containing these oxidation products is used in the engine, it impairs the engine performance because of fuel filter plugging, injector fouling, and deposit formation in the engine combustion chamber and various components of the fuel system.5 Several studies related to the stability of biodiesel have been reported in the literature. A number of researchers have investigated the oxidation stability of biodiesel synthesized from most common oils.610 However, increasing the production of biodiesel from conventional sources (soybean, rapeseed, palm, etc.) has placed strain on food production, its price and availability. Therefore, the search for additional regional biodiesel feedstocks is an important objective.11,12 There are few studies reported on oxidation stability of biodiesel from less common or unconventional oils. Sarin et al.11 reported oxidation stability of biodiesel derived from tree-borne non-edible oil seeds, such as Jatropha and karanja, and compared it to biodiesel derived from edible oils, such as palm and sunflower oils. It was found that the trend of the induction period has a direct correlation with the Received: June 10, 2011 Revised: October 19, 2011 Published: October 19, 2011 5416
dx.doi.org/10.1021/ef200855b | Energy Fuels 2011, 25, 5416–5421
Energy & Fuels
ARTICLE
Table 1. Fatty Acid Profile of MOME, COME, and JOME fatty acid composition (wt %) myristic acid methyl ester (C14:0)
0.2
palmitic acid methyl ester (C16:0)
12.7
percentage of saturated fatty acids in the biodiesel. Rashid et al.12 evaluated Moringa oleifera oil as a possible source of biodiesel. The oxidation stability of Moringa oil using the Rancimat test was found to be 15.32 h, which was due to the presence of the antioxidant occurring naturally in the oil and low polyunsaturated fatty acid content. The oxidation stability of Moringa methyl ester (3.61 h) was significantly lower, as compared to the oil itself. The explanation given was that the antioxidants naturally present in M. oleifera oil were either deactivated during the transesterification process and/or removed during the subsequent purification or separation procedures. There were other studies that reported oxidation stability of biodiesel from less common oils, such as karanja,13 tung,14 rubber seed,15 Croton megalocarpus,16 Jatropha curcas,17,18 and Moringa19 oils. M. oleifera is one of the less common biodiesel feedstocks that are available in east Africa, and it has been locally used for making various herbal products for medicinal purposes. Anwar et al.20 report the significance in the nutritional value and the use of M. oleifera in medicinal activities. Indeed, after extraction of a high value of nutrients from Moringa oil (e.g., vitamin A), the oil can eventually be converted to biodiesel without any waste. The most conspicuous property of biodiesel derived from M. oleifera oil is the high cetane numbers of above 60, which are among the highest reported for a biodiesel fuel.12,21 The origin, family, and climatic condition for M. oleifera have been reported in the literature.12,22 However, from previous studies, the influence of antioxidants on the oxidation stability of Moringa methyl ester, as well as thermal stability without and with antioxidants, was not evaluated. The purpose of this study was to evaluate the thermal and oxidation stabilities of Moringa oil methyl ester (MOME) with and without antioxidants and compare it to other biodiesels produced from non-edible oils of African origin, such as C. megalocarpus and Jatropha oils. The production of MOME, Croton oil methyl ester (COME), and Jatropha oil methyl ester (JOME) and the determination of their fuel-related properties were carried out. Thermal and oxidation stabilities without and with antioxidants to produce MOME, COME, and JOME were determined by a Rancimat instrument and thermogravimetric analyzer (TGA), respectively.
’ EXPERIMENTAL SECTION Materials. M. oleifera, C. megalocarpus, and Jatropha oils were purchased from Diligent Tanzania Limited (Arusha, Tanzania), and mineral diesel was purchased from a local filling station in Budapest, Hungary, which was used as the base fuel. Antioxidants, 1,2,3-trihydroxybenzene [pyrogallol (PY)], 3,4,5-trihydroxybenzoic acid [propyl gallate (PG)], 2-tert-butyl-4-methoxyphenol [butylated hydroxyanisole (BHA)], and 2,6-di-tert-butyl-4-methylphenol [butylated hydroxytoluene (BHT)] were from Alfa Aesar, a Johnson Matthey Company, Germany. The chemicals used were analytical reagents, potassium
COME
JOME
5.7
15.7
palmitoleic acid methyl ester (C16:1)
1.1
stearic acid methyl ester (C18:0)
4.9
3.9
6.7
73.0
11.8
39.7
linoleic acid methyl ester (C18:2)
2.5
71.6
36.5
linolenic acid methyl ester (C18:3)
0.8
6.9
0.3
arachidic acid methyl ester (C20:0) eicosenoic acid methyl ester (C20:1)
3.8 0.9 9.6
22.4
oleic acid methyl ester (C18:1)
Figure 1. Typical oxidation reaction of biodiesel.
MOME
0.9
0.2
saturated fatty acids
21.6
monounsaturated fatty acids
75.0
11.8
40.8
polyunsaturated fatty acids
3.3
78.5
36.8
hydroxide (85%) and methanol (99.5%), which were obtained from the chemistry laboratory of the Tshwane University of Technology (Pretoria, South Africa). Biodiesel Synthesis. The free fatty acid (FFA) content of MOME, COME, and JOME was 5, 3.5, and 8.2%, respectively, which was above the 2% recommended for the application of a two-step transesterification process to convert the high FFA oils to their monoesters.23 The acid esterification process followed by the transesterification method was then used to prepare the methyl esters. The former was performed using an acid catalyst (0.5% H2SO4, w/woil) and 6:1 methanol/oil molar ratio.23 After acid esterification, the transesterification was carried out at the following standard conditions: 6:1 methanol/oil molar ratio (mol/ mol), 1.0 wt % potassium hydroxide, 5560 °C reaction temperature, 400 rpm agitation speed, and 60 min reaction time.12 After completion of the reaction, the mixture was transferred to a separating funnel and allowed to cool to room temperature without agitation, leading to the separation of two distinct phases. The upper phase consisted primarily of methyl ester (biodiesel), while the lower phase contained glycerol, excess methanol, and catalyst, with soap formed during the reaction, along with some entrained methyl esters and partial glycerides. The upper phase, i.e., biodiesel, was washed with deionized water at 50 °C repeatedly until the washing water became clear to remove traces of glycerin, unreacted catalyst, and soap formed during the transesterification. The ester was then subjected to heating at 110 °C to remove excess alcohol and moisture. The final product, fatty acid methyl ester (FAME), that is, the biodiesel, formed as a clear, light yellow liquid. Property Determination. The synthesized biodiesel samples were tested for physical and chemical properties and compared to biodiesel standards, such as American Society for Testing and Materials (ASTM) D6751 and EN 14214. Kinematic viscosity was determined using the miniature U-tube and viscometer (TV 4000) as per ASTM D445. The cetane number was determined using a CFR (Waukesha F-5) engine as per ASTM D613. The cloud point and pour point were determined as per ASTM D2500 and D97, respectively. The calorific value of MOME, COME, and JOME was determined by a bomb calorimeter as per ASTM D240. The density of the synthesized biodiesel samples was obtained using a density meter (DA-130N) as per ASTM D941. The acid value of the biodiesel samples was determined as per ASTM D974. The flash point of methyl esters in this study was measured using a PenskyMartens flash point tester (Stanhope-SETA, 34000-0 U) as per ASTM D93. The lubricity was determined using a high-frequency reciprocating rig (HFRR). The measurements were performed as per the ISO 12156 HFRR test method. The fatty acid composition of biodiesel was analyzed using gas chromatographymass spectroscopy (GCMS) (Agilent 6890N). The gas chromatograph was coupled to an inert mass-selective detector 5417
dx.doi.org/10.1021/ef200855b |Energy Fuels 2011, 25, 5416–5421
Energy & Fuels
ARTICLE
Table 2. Fuel Properties of MOME, COME, JOME, and Mineral Diesel methyl esters property
units
MOME
COME
JOME
diesel
density at 15 °C
kg/m
890
879
870
840
viscosity at 40 °C
mm2/s
4.78
4.70
4.35
2.25.3
acid value
mg of KOH/g
0.16
0.2
0.16
flash point
°C
166
160
138
65.5 42.34
3
ASTM D6751
EN 14214 860900
1.96.0
3.55.0
0.5 maximum
0.5 maximum
130 minimum
>101
51
heating value
MJ/kg
38.34
37.24
37.87
lubricity
μm
228
202
224
63
47.5
59.2
54.6
47 minimum
cloud point pour point
°C °C
10 3
4 10
1 2
16 19
report
oxidation stability at 110 °C
h
5.05
2.25
5.5
3 minimum
6 minimum
free glycerol
% mass
0.018
0.019
0.019
0.02 maximum
0.02 maximum
total glycerol
% mass
0.21
0.22
0.20
0.24 maximum
0.25 maximum
cetane number
Figure 3. Chemical structure of the antioxidants.
Figure 2. Oxidation stability of (a) MOME, (b) COME, and (c) JOME with and without antioxidants. (MSD) (Agilent 5973). A total of 1 μL of biodiesel sample was injected using a split ratio (200:1) in an auto sampler at 24.79 psi at an inlet temperature of 250 °C. The gas chromatograph was equipped with a polyethylene glycol column (HP Innowax) of 60 m in length, 250 μm in
inner diameter, and 0.25 μm in film thickness. The oven temperature was kept at 60 °C for the first 10 min, increased at a ramp rate of 4 °C/ min to 220 °C, held for 10 min, and then ramped at 1 °C/min to 250 °C. Helium was used as a carrier gas at a constant flow of 1.2 mL/min. The percentage composition of the individual components was obtained from electronic integration measurements using a flame ionization detection (FID) and reported in Table 1. The oxidation stability of MOME, COME, and JOME with and without different dosages of antioxidants and biodiesel/diesel blends was studied in the Rancimat instrument (model 873, Metrohm, Switzerland). The fuel sample (10 mL) kept at a constant temperature (110 °C) in the Rancimat was induced by passing a stream of purified air at a flow rate of 10 L/h. The vapors released during the oxidation process together with the air are passed through the flask containing distilled water, which contains an electrode for measuring the conductivity. The electrode is connected to a measuring and recording device; it indicates the end of the induction period when the conductivity of water begins to increase rapidly. The acceleration of conductivity is caused by the dissociation of volatile carboxylic acids produced during the oxidation process of biodiesel, and these volatile organic acids are absorbed in the water. When the conductivity of this solution is recorded continuously, an oxidation curve is obtained, whose point of inflection of the first derivative is known as the induction period, and this provides the good parametric value for the oxidation stability. A TA Instruments (TGA 2050 thermogravimetric analyzer) was used for measuring the oxidation stability of biodiesel samples. The measured 5418
dx.doi.org/10.1021/ef200855b |Energy Fuels 2011, 25, 5416–5421
Energy & Fuels
ARTICLE
Figure 4. Thermogravimetry (TG) and differential thermogravimetry (DTG) curves of (a) MOME, (b) COME, and (c) JOME without antioxidants. amount of samples (58 mg) on a partial sealed alumina pan was placed into a platinum pan beam attached to the instrument. Pure oxygen was purged at the rate of 130 mL/min. The temperature was programmed from room temperature to 500 °C at the ramp rate of 10 °C/min. When the oxidation takes place, the removal of secondary oxidation products causes a sudden weight loss of the sample. The onset temperature of oxidation was obtained by the intersection of the extrapolated baseline and the tangent line of the curve obtained by TGA. The onset temperature can be used to indicate the resistance of the biodiesel sample to thermal degradation.
’ RESULTS AND DISCUSSION Fatty Acid Compositions. The fatty acid profiles of MOME, COME, and JOME are summarized in Table 1. Oleic acid methyl ester (73%) is dominant in MOME, which agrees with previous studies.12 Generally, MOME contains a low amount of polyunsaturated FAMEs (3.3%), with 21.6% of saturated FAMEs,
while COME contains a high percentage of polyunsaturated FAMEs (78.5%), with only 9.6% of saturated FAMEs. JOME contains 40.8% monounsaturated FAMEs and 36.8% polyunsaturated FAMEs. JOME possessed 22.4% of saturated FAMEs. Properties of FAMEs. Table 2 summarize important fuel properties of MOME, COME, and JOME. It is clear from the data that most of the properties of MOME determined satisfy the American and European biodiesel standards (ASTM D6751 and EN 14214). Kinematic viscosity of MOME was 4.78 mm2/s at 40 °C, which was slightly higher than that of COME (4.70 mm2/s), JOME (4.35 mm2/s), and mineral diesel, however, within the global biodiesel specifications. MOME showed a significantly higher flash point compared to mineral diesel (roughly 100 °C higher), making it safer in terms of handling, transport, and storage. The acid value of MOME was 0.16 mg of KOH/g, which was less than that specified in the ASTM D6751 standard (0.8 maximum) and EN 14214 (0.5 maximum), slightly lower than COME (0.2 mg of KOH/g), but the same as MOME (0.16 mg of KOH/g). The 5419
dx.doi.org/10.1021/ef200855b |Energy Fuels 2011, 25, 5416–5421
Energy & Fuels
Figure 5. Oxidation onset temperature of methyl esters with PY antioxidant measured with TGA.
density of MOME was 890 kg/m3. This was higher than that of COME (879 kg/m3), JOME (870 kg/m3), and mineral diesel (840 kg/m3) but was within the range specified in EN 14214 standards of 860900 kg/m3. The lower calorific value of MOME was found to be 38.34 MJ/kg, which was lower than that of mineral diesel (42.34 MJ/kg). This possibly resulted from the higher oxygen content in biodiesel. The cetane number (CN) of MOME was 63, the result of which concurred with previous studies,12 which was higher than that of COME (47.5), JOME (59.2), and mineral diesel (54.6). The lubricity of MOME (228 μm) was well within the acceptable limits of 460 and 520 μm, as prescribed in mineral diesel standards EN 590 and ASTM D975, respectively, but higher than that of COME (202 μm) and JOME (224 μm). MOME displayed cloud and pour points of 10 and 3 °C, respectively, while COME displayed remarkably excellent low-temperature flow properties among all methyl esters. This was possibly attributed by lower proportions of saturated fatty acids and a high composition of linoleic and linolenic acid methyl esters (71.6 and 6.9%, respectively).12,24 The total glycerol of MOME (0.21%) was within ASTM (0.24% maximum) and EN (0.25% maximum) limits, lower than that of COME (0.22%), and higher than that of JOME (0.20%). Oxidation Stability of FAMEs with and without Antioxidants. Figure 2a shows the oxidation stability of MOME (5.05 h), as determined by the Rancimat instrument. It fulfilled the minimum requirement of ASTM D6751 (3 h) oxidation stability specifications but did not meet the minimum requirements of EN 14214 (6 h). This was possibly due to the fact that antioxidants naturally present in oils were either deactivated and/or removed by the subsequent purification or separation procedures during the biodiesel production process.12,16 MOME displayed higher oxidation stability than COME (2.25 h) but lower oxidation stability than JOME (5.5 h), as shown in panels b and c of Figure 2, respectively. The JOME displayed high oxidation stability was possibly due to the presence of 22.4% saturated FAMEs and natural occurring antioxidants.25 The lower oxidation stability recorded by COME was possibly due to the presence of a high percentage of methyl linoleate and linolenate, 71.6 and 6.9%, respectively.5 This study evaluated the effectiveness of four antioxidants on the oxidation stability of MOME, COME, and JOME. The antioxidants were selected on the basis of their chemical structure, quality, cost, availability, as well as previous studies on
ARTICLE
biodiesel and vegetable oils used in the food industry.2628 Therefore, the antioxidants used in the present study include 1,2,3-trihydroxybenzene [pyrogallol (PY)], 3,4,5-trihydroxybenzoic acid [propyl gallate (PG)], 2-tert-butyl-4-methoxyphenol [butylated hydroxyanisole (BHA)], and 2,6-di-tert-butyl-4methylphenol [butylated hydroxytoluene (BHT)]. The antioxidants were doped at 200, 500, 700, and 1000 ppm dosage for both methyl esters and tested in the Rancimat to observe their effectiveness. It was found that oxidation stability increased with the increase in the dosage for these antioxidants. Among antioxidants used, PY and PG were found to be more effective than BHA and BHT at all dosages, as depicted in Figure 2. PY and PG displayed an induction period above specified standards at 200 ppm to meet EN 14214 standards of 6 h. PY showed an induction period of 9.94 h, well above limits at 200 ppm, while the induction period for 200 ppm of PG was 7.63 h. BHA and BHT were found to be the least effective antioxidants. A total of 1000 ppm of BHA and BHT was required to meet the EN 14214 oxidation stability specification (6 h) for COME. Overall, the effectiveness of these antioxidants was in the order of PY > PG > BHA > BHT. PY and PG were more effective than BHA and BHT because they possess three OH groups in their aromatic rings, while BHA and BHT have only one OH group in their molecular structure, as shown in Figure 3. The hydroxyl (OH) group of the antioxidant is very active; therefore, the hydrogen is abstracted from OH and donated to the oxidized free radical to inhibit the rate of oxidation in methyl esters. The resulting antioxidant is a stable radical that can react with other fatty acid free radicals and further contribute to oxidation inhibition.29,30 Thermal Stability. Thermal instability is concerned with the increased rate of oxidation at higher temperatures, which, in turn, increases the weight of the molecules because of the formation of insolubles.5,19 TGA determines the temperature at which oxidation reactions take place. This temperature is termed as the oxidation onset temperature.31 Additionally, thermal and oxidation stability reactions are very different. Oxidation stability reactions are generally considered to be peroxidation reactions and perhaps aldol condensation reactions of the peroxidation products. Thermal stability reactions are similar to the Diels Alder reaction, although other high-temperature reactions may also occur.5 Thermal stability results showed a similar trend as oxidation stability results. MOME had an oxidation onset temperature of 237.05 °C, higher than that of COME (211.40 °C) but lower than that of JOME (242.30 °C), as shown in panels a, b, and c of Figure 4, respectively. The onset temperature of oxidation was obtained by the intersection of the extrapolated baseline and the tangent line of the curve obtained by TGA, as shown in Figure 4. The onsets of at least two thermal events are indicated in the first derivative curves. It actually suggests an oxidation event followed by primarily thermal degradation. The maximum degradation rate for both biodiesels occurred at a temperature of about 290310 °C, where the rate of weight decrease increased to the maximum. Slower weight decreases were observed at higher temperatures. Thermal stability and volatility characteristics are important in establishing the ignition quality of fuels and its lubricity properties.19 The effect of the antioxidant was not clearly observed with TGA. There was a slight increase in the onset temperature at a 500 ppm concentration of PY (PY was chosen for thermal stability investigations because it was an effective antioxidant in this study). The onset temperature increased to 242.08, 218.53, and 246.28 °C for MOME, COME, 5420
dx.doi.org/10.1021/ef200855b |Energy Fuels 2011, 25, 5416–5421
Energy & Fuels and JOME, respectively, at 500 ppm of PY. The onset temperature was observed to have decreased at 1000 ppm concentration of PY (241.01, 217.07, and 245.95 °C for MOME, COME, and JOME, respectively), as shown in Figure 5.
’ CONCLUSION Most of the determined fuel-related properties of MOME fulfilled the minimum requirements specified in ASTM D6751 and EN 14214 biodiesel standards. However, the oxidation stability of MOME did not meet the EN 14214 specifications (6 h). Among four antioxidants evaluated in the present study, PY and PG were found to be more effective compared to BHA and BHT. Only 200 ppm of PY and PG was able to satisfy the minimum requirement of oxidation stability, as specified in the ASTM D6751 and EN 14214 biodiesel standards. MOME displayed good thermal stability of 237.05 °C. This study recommends PY and PG to be used for safeguarding biodiesel fuel from the effects of autoxidation during storage. In summary, the biodiesel derived from M. oleifera oil can be used as a partial substitute for mineral diesel. ’ AUTHOR INFORMATION Corresponding Author
*Telephone: +27721276716/+255767120935. Fax: (012) 3825602. E-mail:
[email protected].
’ ACKNOWLEDGMENT This study was conducted at the Budapest University of Technology and Economics, Budapest, Hungary, and was supported by the Hungarian/South African Intergovernmental S&T Cooperation Programme (ZA-17/09). ’ REFERENCES (1) Agarwal, A. K. Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines. Prog. Energy Combust. Sci. 2007, 33 (3), 233–271. (2) Nabi, M. N.; Rahman, M. M.; Akhter, M. S. Biodiesel from cotton seed oil and its effect on engine performance and exhaust emissions. Appl. Therm. Eng. 2009, 29 (1112), 2265–2270. (3) Karavalakis, G.; Stournas, S.; Karonis, D. Evaluation of the oxidation stability of diesel/biodiesel blends. Fuel 2010, 89 (9), 2483–2489. (4) Miyashita, K.; Takagi, T. Study on the oxidative rate and prooxidant activity of free fatty acids. J. Am. Oil Chem. Soc. 1986, 63 (10), 1380–1384. (5) Jain, S.; Sharma, M. P. Stability of biodiesel and its blends: A review. Renewable Sustainable Energy Rev. 2010, 14 (2), 667–678. (6) Dunn, R. Effect of oxidation under accelerated conditions on fuel properties of methyl soyate (biodiesel). J. Am. Oil Chem. Soc. 2002, 79 (9), 915–920. (7) Dunn, R. O. Effect of antioxidants on the oxidative stability of methyl soyate (biodiesel). Fuel Process. Technol. 2005, 86 (10), 1071–1085. (8) Ferrari, R.; Oliveira, V.; Scabio, A. Oxidative stability of biodiesel from soybean oil fatty acid ethyl esters. Sci. Agric. 2005, 62, 291–295. (9) Liang, Y. C.; May, C. Y.; Foon, C. S.; Ngan, M. A.; Hock, C. C.; Basiron, Y. The effect of natural and synthetic antioxidants on the oxidative stability of palm diesel. Fuel 2006, 85 (56), 867–870. (10) Bondioli, P.; Gasparoli, A.; Bella, L. D.; Taghliabue, S.; Toso, G. Biodiesel stability under commercial storage conditions over one year. Eur. J. Lipid Sci. Technol. 2003, 105, 735–741.
ARTICLE
(11) Sarin, R.; Sharma, M.; Sinharay, S.; Malhotra, R. K. Jatrophapalm biodiesel blends: An optimum mix for Asia. Fuel 2007, 86 (1011), 1365–1371. (12) Rashid, U.; Anwar, F.; Moser, B. R.; Knothe, G. Moringa oleifera oil: A possible source of biodiesel. Bioresour. Technol. 2008, 99 (17), 8175–8179. (13) Das, L. M.; Bora, D. K.; Pradhan, S.; Naik, M. K.; Naik, S. N. Long-term storage stability of biodiesel produced from karanja oil. Fuel 2009, 88 (11), 2315–2318. (14) Shang, Q.; Jiang, W.; Lu, H.; Liang, B. Properties of tung oil biodiesel and its blends with 0# diesel. Bioresour. Technol. 2010, 101 (2), 826–828. (15) Ikwuagwu, O. E.; Ononogbu, I. C.; Njoku, O. U. Production of biodiesel using rubber [Hevea brasiliensis (Kunth. Muell.)] seed oil. Ind. Crops Prod. 2000, 12 (1), 57–62. (16) Kivevele, T. T.; Mbarawa, M. M. Comprehensive analysis of fuel properties of biodiesel from Croton megalocarpus oil. Energy Fuels 2010, 24 (11), 6151–6155. (17) Sarin, A.; Arora, R.; Singh, N. P.; Sharma, M.; Malhotra, R. K. Influence of metal contaminants on oxidation stability of Jatropha biodiesel. Energy 2009, 34 (9), 1271–1275. (18) Freire, L.; Bicudo, T.; Rosenhaim, R.; Sinfr^ onio, F.; Botelho, J.; Carvalho Filho, J.; Santos, I.; Fernandes, V.; Antoniosi Filho, N.; Souza, A. Thermal investigation of oil and biodiesel from Jatropha curcas L. J. Therm. Anal. Calorim. 2009, 96 (3), 1029–1033. (19) Sharma, B.; Rashid, U.; Anwar, F.; Erhan, S. Lubricant properties of Moringa oil using thermal and tribological techniques. J. Therm. Anal. Calorim. 2009, 96 (3), 999–1008. (20) Anwar, F.; Latif, S.; Ashraf, M.; Gilani, A. H. Moringa oleifera: A food plant with multiple medicinal uses. Phytother. Res. 2007, 21 (1), 17–25. (21) Kafuku, G.; Lam, M. K.; Kansedo, J.; Lee, K. T.; Mbarawa, M. Heterogeneous catalyzed biodiesel production from Moringa oleifera oil. Fuel Process. Technol. 2010, 91 (11), 1525–1529. (22) Tsaknis., J.; Lalas., S.; Gergis, V.; Dourtoglou, V.; Spiliotis, V. Characterization of Moringa oleifera variety Mbololo seed oil of Kenya. J. Agric. Food Chem. 1999, 47, 4495–4499. (23) Ramadhas, A. S.; Jayaraj, S.; Muraleedharan, C. Biodiesel production from high FFA rubber seed oil. Fuel 2005, 84 (4), 335–340. (24) Knothe, G. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Process. Technol. 2005, 86 (10), 1059–1070. (25) Knothe, G. Some aspects of biodiesel oxidative stability. Fuel Process. Technol. 2007, 88 (7), 669–677. (26) Schober, S.; Mittelbach, M. The impact of antioxidants on biodiesel oxidation stability. Eur. J. Lipid Sci. Technol. 2004, 106, 382–389. (27) Karavalakis, G.; Stournas, S. Impact of antioxidant additives on the oxidation stability of diesel/biodiesel blends. Energy Fuels 2010, 24 (6), 3682–3686. (28) Tang, H.; De Guzman, R. C.; Salley, S. O.; Simon Ng, K. Y. The oxidative stability of biodiesel: Effects of FAME composition and antioxidant. Lipid Technol. 2008, 20, 249–252. (29) Loh, S. K.; Chew, S. M.; Choo, Y. M. Oxidative stability and storage behavior of fatty acid methyl esters derived from used palm oil. J. Am. Oil Chem. Soc. 2006, 83 (11), 947–952. (30) de Guzman, R.; Tang, H.; Salley, S.; Simon, K. Y. Synergistic effects of antioxidants on the oxidative stability of soybean oil- and poultry fat-based biodiesel. J. Am. Oil Chem. Soc. 2009, 86 (5), 459–467. (31) Kivevele, T. T.; Mbarawa, M. M.; Bereczky, A.; Laza, T.; Madarasz, J. Impact of antioxidant additives on the oxidation stability of biodiesel produced from Croton megalocarpus oil. Fuel Process. Technol. 2011, 92, 1244–1248.
5421
dx.doi.org/10.1021/ef200855b |Energy Fuels 2011, 25, 5416–5421
