Energy Fuels 2010, 24, 6151–6155 Published on Web 10/21/2010
: DOI:10.1021/ef100880g
Comprehensive Analysis of Fuel Properties of Biodiesel from Croton megalocarpus Oil Thomas T. Kivevele* and Makame M. Mbarawa Department of Mechanical Engineering, Tshwane University of Technology, Private Bag X680, Pretoria 0001, South Africa Received July 9, 2010. Revised Manuscript Received October 7, 2010
Of late, much emphasis has been placed on searching for alternative fuels and significant investigations have been carried out regarding the production of biodiesel, especially from non-edible vegetable oils, with a view to minimize the dependence upon liquid hydrocarbon fuels, reduce emissions, and boost the rural economy. In this paper, the properties of Croton megalocarpus oil methyl ester (COME) from C. megalocarpus seed oil (non-edible) were investigated to determine their suitability for use as a petrodiesel substitute. C. megalocarpus seed oil was found to contain free fatty acids (FFAs) of 1.73%, which was below the 2% recommended for the application of the one-step base-catalyzed transesterification method. The transesterification process was carried out at the following optimized conditions: methanol/oil molar ratio (mol/mol), 6:1; potassium hydroxide, 1.0 wt %; reaction temperature, 50 °C; agitation speed, 500 rpm; and reaction time, 60 min. COME obtained was analyzed by gas chromatography (GC) to determine the methyl ester yield. COME offered the maximum methyl ester yield of 89.6%. The fuel-related properties of COME, cold filter plugging point (CFPP), cloud point (CP), kinematic viscosity, lubricity, oxidative stability, cetane number, flash point, acid value, density, calorific value, and free and total glycerol, were determined and discussed in light of biodiesel standards, such as ASTM D6751 and EN 14214. The most remarkable feature of COME was the CFPP and CP, which were -11 and -6 °C, respectively. The good cold flow properties of COME demonstrate its operational viability during the cold season. Tribological results showed that the lubrication ability of COME was better than that of conventional diesel fuel. However, COME did not fulfill the oxidative stability requirements of ASTM D6751 and EN 14214.
oils or animal fats, is well-positioned to replace mineral diesel.2-8 Biodiesel is a biodegradable, nontoxic biofuel, which possesses inherent lubricity. It reduces most regulated exhaust emissions and has a relatively high flash point in comparison to petroleum-based diesel, making it safer in transportation, storage, and handling. In addition, it reduces the dependence upon imported fossil fuels, which continue to decrease in availability and affordability.8 Most of the studies have been directed toward the production of biodiesel from vegetable oils that are edible than non-edible oils because the former possess low free fatty acids, making it easy during the transesterification process. Transesterification is a chemical reaction in which vegetable oils and animal fats are reacted with alcohol in the presence of a catalyst. The end products of the reaction are fatty acid alkyl ester (biodiesel) and glycerin. Thus, soybean oil is the largest source of vegetable oil in the United States, while rapeseed (canola) and sunflower oils are the largest source in Europe. Similarly, palm oil in southeast Asia (mainly Malaysia and Indonesia) and coconut oil in the
Introduction The world’s fossil fuels are being depleted because of an increase in demand, while the supply is limited. In 2005, studies carried out predicted that the present reserves of fuels used in internal combustion (IC) engines, including diesel, would be exhausted within 40 years if consumed at an increasing rate, estimated to be of the order of 3% per annum.1,2 Also, fossil fuels are currently the dominant global source of CO2 emissions, and their combustion poses a stronger threat to a clean environment. Hence, to solve the energy and environmental concerns, renewable energies with a lower environmental pollution impact must be considered. Presently, several new and renewable energies are been emphasized, and biomass energy is among them. Biomass energy, which includes liquid biofuels, is a promising alternative source of energy with low environmental pollution to replace petroleum-based fuels. Some of the well-known liquid biofuels are ethanol for gasoline engines and biodiesel for compression ignition (CI) or diesel engines. Biodiesel, known as monoalkyl esters of long-chain fatty acids derived from renewable lipid feedstock, such as vegetable
(4) Demirbas, A. Biodiesel fuels from vegetable oils via catalytic and non-catalytic supercritical alcohol transesterifications and other methods: A survey. Energy Convers. Manage. 2003, 44 (13), 2093–2109. ~ez, E. E.; Castillo, (5) Escobar, J. C.; Lora, E. S.; Venturini, O. J.; Yan E. F.; Almazan, O. Biofuels: Environment, technology and food security. Renewable Sustainable Energy Rev. 2009, 13 (6-7), 1275–1287. (6) Berrios, M.; Skelton, R. L. Comparison of purification methods for biodiesel. Chem. Eng. J. 2008, 144 (3), 459–465. (7) Dunn, R. O. Effect of temperature on the oil stability index (OSI) of biodiesel. Energy Fuels 2008, 22 (1), 657–662. (8) Rashid, U.; Anwar, F.; Moser, B. R.; Knothe, G. Moringa oleifera oil: A possible source of biodiesel. Bioresour. Technol. 2008, 99 (17), 8175–8179.
*To whom correspondence should be addressed. Telephone: (012) 382-5177. Fax: (012) 382-5602. E-mail:
[email protected]. (1) Nabi, M. N.; Akhter, M. S.; Zaglul Shahadat, M. M. Improvement of engine emissions with conventional diesel fuel and dieselbiodiesel blends. Bioresour. Technol. 2006, 97 (3), 372–378. (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 (11-12), 2265–2270. (3) Moser, B. Comparative oxidative stability of fatty acid alkyl esters by accelerated methods. J. Am. Oil Chem. Soc. 2009, 86 (7), 699–706. r 2010 American Chemical Society
6151
pubs.acs.org/EF
Energy Fuels 2010, 24, 6151–6155
: DOI:10.1021/ef100880g
Kivevele and Mbarawa 8
Philippines are the largest source of vegetable oil. However, increasing the production of biodiesel from edible oils places a strain on the production of food, its prices, and availability, because of the tension in growing food versus producing fuel. Hence, the search for additional regional biodiesel that is not obtained from this feedstock is an important objective.9-11 One of the possible alternative oil crops for biodiesel production is non-edible Croton megalocarpus, primarily available on the African continent. C. megalocarpus is a pioneer species, grown in cleared parts of natural forests, forest margins, or as a canopy tree. It is about 15-35 m high. Its fruit turn from green to grayish brown as they mature. Each fruit contains three ellipsoid-ovoid or oblong-ellipsoid seeds, 1.2-2.0 cm long and 0.85-1.4 cm wide. Seeds are white when immature and grayish brown when mature. The non-edible C. megalocarpus plant can be grown in areas with mean annual rainfall of 800-1600 mm, mean annual temperature of 11-26 °C, and altitude of 1300-220 m.12 The productive life span of the plant is more than 40 years. C. megalocarpus oil is a transparent liquid and brownish in color. There is a limited amount of literature on the production of biodiesel from nonedible C. megalocarpus oil. Kafuku and Mbarawa11 produced biodiesel from C. megalocarpus oil and investigated its process of optimization. It was found that C. megalocarpus seeds contain approximately 32% by weight of oil, and its acid profile showed higher linoleic acid (72.7%). The most remarkable feature of C. megalocarpus oil biodiesel was its cold flow properties; it yielded a cloud point (CP) and pour point of -4 and -9 °C, respectively. These superior flow properties of C. megalocarpus oil methyl ester (COME) point to the viability of using it in cold regions. In their study, the impact of blending COME with mineral diesel on fuel-related proprieties was not investigated. It is important to know the basic properties of biodiesel-diesel blends. Some of these properties are required as input data for predictive and diagnostic engine combustion models. Additionally, it is necessary to know if the fuel resulting from the blending process meets the standard specification for diesel fuels. The purpose of the present study was to investigate the suitability of biodiesel produced from C. megalocarpus oil for use as a petrodiesel substitute. The production of COME was carried out using optimized conditions. The important fuel properties of COME were determined and compared to the international biodiesel standards (ASTM D6751 and EN 14214). The effects of blending COME with mineral diesel on the fuel-related properties were also investigated.
(99.5%), propyl-2-ol, and phenolphthalein powder, which were obtained from the chemistry laboratory, Tshwane University of Technology (Pretoria, South Africa). Preparation of COME. The free fatty acid (FFA) content of C. megalocarpus seed oil was analyzed by a simple laboratory titration method using a standard potassium hydroxide solution and phenolphthalein indicator.13 The latter was prepared by dissolving 1 g of phenolphthalein powder in 100 mL of propyl2-ol. It was found to contain FFAs of 1.73%, a proportion that was below the 2% recommended for the application of the onestep base-catalyzed transesterification method.14,15 The methanolysis of C. megalocarpus oil was conducted by a standard procedure employing a 6:1 methanol/oil molar ratio (mol/mol) for 60 min at 50 °C reaction temperature with 1.0 wt % potassium hydroxide as the catalyst and 500 rpm agitation speed.11 The measured amount of C. megalocarpus oil was dehydrated by heating to 110 °C and allowed to cool to room temperature. The amount of oil was weighed and placed in a beaker equipped with a magnetic stirrer and thermometer. The oil was then heated under agitation to the desired temperature on a heating plate. The amount of catalyst (KOH) was poured into a beaker containing a measured amount of methanol and allowed to mix for a while at room temperature. After the oil temperature reached the desired point, the prepared catalyst-methanol solution was added to the oil, taking this moment as the starting time of the reaction; thereafter, the mixture was stirred for 60 min at 50 °C. After completion of the reaction process, 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 COME, while the lower phase contained glycerol, excess methanol and catalyst, soap formed during the reaction, some entrained COME, and partial glycerides. The upper phase, i.e., methyl ester (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 water. The final product (biodiesel) formed as a clear, light yellow liquid. Blend Preparation. There are different techniques for blending biodiesel with mineral diesel (D2), such as splash blending, in-tank blending, and in-line blending. In the present study, splash blending was used because it is an effective and efficient technique and is widely employed. Measured amounts of COME and mineral diesel were splash-blended in a 300 mL beaker under continuous stirring to ensure uniform mixing. The blends were based on mass. Those prepared were B80 (80% biodiesel and 20% mineral diesel), B50 (50% biodiesel and 50% mineral diesel), and B20 (20% biodiesel and 80% mineral diesel). In addition, B100 (pure biodiesel) and petroleum-based diesel were also evaluated. Analytical Methods. The analysis of biodiesel products was carried out by Varian gas chromatography (GC) (model CP3400) equipped with an auto-sampler (model CP3800). The HT-5 polysiloxane-coated column with a length of 30 m, inner diameter of 0.3 mm, and film thickness of 0.53 μm was used. The oven temperature was kept at 90 °C for 1 min, increased at 15 °C/ min up to 230 °C, held for 2 min, and then ramped at 50 °C/min up to 380 °C, whereafter it was held for 2 min. The injector temperature was started at 90 °C and ramped up to 380 °C at a rate of 50 °C/min, while the detector temperature was maintained at 380 °C throughout the reaction. The weighed mass of
Experimental Section Materials. C. megalocarpus oil was purchased from Diligent Tanzania Limited (Arusha, Tanzania), and mineral diesel was purchased from a local filling station in Pretoria, South Africa, which was used for making blends with C. megalocarpus biodiesel and as the base fuel for comparison. The chemicals used were analytical reagents: potassium hydroxide (85%), methanol (9) Baka, J.; Roland-Holst, D. Food or fuel? What European farmers can contribute to Europe’s transport energy requirements and the Doha Round. Energy Policy 2009, 37 (7), 2505–2513. (10) Srinivasan, S. The food v. fuel debate: A nuanced view of incentive structures. Renewable Energy 2009, 34 (4), 950–954. (11) Kafuku, G.; Mbarawa, M. Biodiesel production from Croton megalocarpus oil and its process optimization. Fuel 2010, 89 (9), 2556– 2560. (12) Aliyu, B.; Agnew, B.; Douglas, S. Croton megalocarpus (Musine) seeds as a potential source of bio-diesel. Biomass Bioenergy 2010, 34 (10), 1495–1499.
(13) Knothe, G.; Van Gerpen, J. H.; Krahl, J. The Biodiesel Handbook; American Oil Chemists' Society (AOCS) Press: Champaign, IL, 2005. (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) Ramadhas, A. S.; Jayaraj, S.; Muraleedharan, C. Biodiesel production from high FFA rubber seed oil. Fuel 2005, 84 (4), 335–340.
6152
Energy Fuels 2010, 24, 6151–6155
: DOI:10.1021/ef100880g
Kivevele and Mbarawa
Table 1. Fatty Acid Profile of C. megalocarpus Oil and Other Properties fatty acid composition (wt %) myristic (C14:0) palmitic (C16:0) palmitoleic (C16:1) stearic (C18:0) oleic (C18:1) linoleic (C18:2) linolenic (C18:3) arachidic (C20:0) eicosenoic (C20:1) eicosadienoic (C20:2) behenic (C22:0) kinematic viscosity (mm2/s) acid value (mg of KOH/g) FFAs (%) lubricity (μm) oxidation stability (h) specific gravity
C20:1) and 11% of saturated fatty acids (C14:0, C16:0, and C18:0). Also, the properties of C. megalocarpus oil were determined before it was converted to COME, as shown in Table 1. C. megalocarpus oil indicated excellent antiwear (201 μm), which was within the maximum acceptable limit of 460 μm, as prescribed in standards EN 590 and South African standards SANS 342. The oxidation stability of C. megalocarpus oil was 3.12 h. COME Yield. The optimized conditions used in the transesterification of C. megalocarpus oil offered the maximum methyl ester yield of 89.6%. The methyl ester yield is the weight percentage of methyl ester relative to the weight of oil at the start (weight of ester/weight of oil), which can also be determined by multiplying the biodiesel product yield by the ester content in the biodiesel product. The biodiesel product yield is defined as the weight percentage of the product (transesterified oil) relative to the weight of oil at the start (weight of product/weight of oil), and the ester content is defined as the weight percentage of methyl esters in the transesterified oil (weight of ester/weight of product). Properties of COME. The properties of COME are summarized in Table 2. Most of them met the minimum requirements of ASTM 6751 and EN 14214 biodiesel standards. Kinematic viscosity of COME was 4.78 mm2/s, which was much higher than that of mineral diesel (2.45 mm2/s) at 40 °C. COME recorded a higher flash point than that of mineral diesel, which was above 100 °C, making it safer with regard to handling, transport, and storage. The acid value of COME was 0.20 mg of KOH/g less than that specified in ASTM D6751 (0.8 max) and EN 14214 (0.5 max). The density of COME was 883 kg/m3 greater than 840 kg/m3 of mineral diesel but was within the range specified in the EN 14214 standard of 860-900 kg/m3; hence, a higher density for biodiesel results in the delivery of a slightly greater mass of fuel in a CI engine. However, biodiesels possess lower energy content on both a volumetric and mass basis. Therefore, although the injection system delivers a larger mass of biodiesel, the actual energy delivered is less than for mineral diesel.16 The heat value of COME was 37.24 MJ/kg, lower than 42.34 MJ/kg of mineral diesel. This resulted from the higher oxygen content in COME.17,18 The cetane number (CN) of COME was 47.52, meeting the ASTM D6751 standard (47 min) but lower than 54.60 of mineral diesel. Generally, it is understood that biodiesel has a higher cetane number than conventional diesel, but the cetane number of diesel fuel used in this study was higher than that of COME, an indication that it was likely to have a cetane-numberenhancing additive in it, known as cetane improvers. The total glycerol of COME (0.22%) was within ASTM (0.24% max) and EN (0.25% max) limits. The effects of mineral diesel on kinematic viscosity, flash point, density, and heating value of COME were investigated and are summarized in Table 2. It was observed that blending COME with mineral diesel offered a number of advantages. Its kinematic viscosity decreased from 4.78 to 2.97 mm2/s at 40 °C, while similar trends were observed with respect to
C. megalocarpus oil 0.1 7.2 3.7 13.7 69.0 4.6 1.5 0.1 52.5 3.46 1.73 201 3.12 0.921
the sample decanted into a clean reaction vial of 4 mL was dissolved with hexane and further made up to 2 mL before injecting 0.5 μL onto GC. Calibration standards were prepared from a methyl ester solution of a known concentration, after which these standards were used to plot a calibration curve that was used in the determination of methyl esters. Kinematic viscosity was obtained using the Miniature U-Tube and viscometer (TV 4000) as per ASTM D445. The cetane number was determined using A Waukesha CFR F-5 engine as per standard ASTM D613. The cold filter plugging point (CFPP) and CP were determined as per ASTM D6371 and ASTM D2500, respectively. The calorific value of COME, mineral diesel, and blends was determined by a bomb calorimeter as per ASTM D240. Oxidative stability measurements were carried out with a Rancimat equipment model 743 using the standard EN 14112. The density of COME, mineral diesel, and blends was obtained using a DA-130N density meter as per ASTM D941. The flash points in the present study were measured using a Pensky-Martens Stanhope-SETA multi-flash point tester (model 34000-0 U) as per ASTM D93. All measurements were carried out 3 times for each sample, and the results were averaged. In addition, the free and total glycerol in COME was measured as per ASTM 6584. The lubricity of COME and blends was investigated using a high-frequency reciprocating rig (HFRR). Measurements were performed as per the ISO 12156 HFRR test method. This used a ball and disk immersed in the sample to be tested. The conditions employed during the HFRR test were as follows: fluid temperature, 60 °C; frequency, 50 Hz; test duration, 75 min; length of the stroke, 1 mm; bath surface area, 6 cm2; and applied load, 200 g. The diameter of the wear scar left on the ball was measured under a microscope. This value was reported as the HFRR test result. The average wear scar diameter (μm) of each replicates was determined by calculating the average of the x- and y-axis wear scar lengths. Both x- and y-axis, average, and corrected wear scars are presented. The corrected wear scar diameter is a measure of the lubricity of the fluid.
Results and Discussion Fatty Acid Profile of C. megalocarpus Oil. The fatty acid profile of C. megalocarpus oil results agrees with prior literature on C. megalocarpus oil.11 As indicated in Table 1, linoleic acid (69.0%) is the predominant fatty acid in C. megalocarpus oil, followed by oleic acid (13.7%). Saturated fatty acids, palmitic and stearic acids, constituted 7.2 and 3.7%, respectively. Generally, C. megalocarpus oil possesses a high amount (73.7%) of polyunsaturated fatty acids (C18:2, C18:3, and C20:2), followed by 15.2% of monounsaturated fatty acids (C18:1 and
(16) Alptekin, E.; Canakci, M. Determination of the density and the viscosities of biodiesel-diesel fuel blends. Renewable Energy 2008, 33 (12), 2623–2630. (17) Lapuerta, M.; Armas, O.; Rodrı´ guez-Fernandez, J. Effect of biodiesel fuels on diesel engine emissions. Prog. Energy Combust. Sci. 2008, 34 (2), 198–223. (18) Naik, M.; Meher, L. C.; Naik, S. N.; Das, L. M. Production of biodiesel from high free fatty acid Karanja (Pongamia pinnata) oil. Biomass Bioenergy 2008, 32 (4), 354–357.
6153
Energy Fuels 2010, 24, 6151–6155
: DOI:10.1021/ef100880g
Kivevele and Mbarawa
Table 2. Properties of COME in Comparison to Mineral Diesel, Blends, and Standards property kinematic viscosity (mm /s, at 40 °C) cetane number CP (°C) CFPP (°C) oxidative stability (h) acid value (mg of KOH/g) calorific value (MJ/kg) density at 15 °C (kg/m3) flash point (°C) free glycerol % (m/m) total glycerol % (m/m) 2
D2
COME (B100)
B80
B50
B20
ASTM D6751
2.45 54.60 -16 -18
4.78 47.52 -6 -11 2.88 0.20 37.24 883 192 0.019 0.22
4.32
3.66
2.97
-11 2.52
-12 2.32
-13 2.25
38.30 874 154
39.87 862 115
41.28 849 90
1.9-6.0 47 min reporta reporta 3 min 0.80 max c
42.34 840 65.5
EN 14214 3.5-5.0 51 min variableb 6 min 0.50 max d 860- 900 120 min 0.02 max 0.25 max
130 min 0.02 max 0.24 max
a Not specified. The CFPP/CP of biodiesel is generally higher than petroleum-based diesel fuel and should be taken into consideration when blending. Dependent upon the location and time of year. South Africa: -4 °C max winter and þ3 °C max summer, as prescribed in South African standards (SANS 1935:2004). c Not specified. d Not specified. The minimum of 35 MJ/kg was prescribed in EN 14213 (biodiesel for heating purposes). b
Table 3. HFRR Lubricity Data of COME and Its Blends with Mineral Diesel at 60 °C COME/diesel blend
x wear scar ( μm)
y wear scar ( μm)
average wear scar ( μm)
corrected wear scar ( μm)
film (%)
friction
B100 B80 B50 B20
250 290 320 310
210 190 290 260
230 240 303 285
224 232 297 280
91 92 91 94
0.101 0.107 0.108 0.121
density, which decreased from 883 to 849 kg/m3, and the flash point, from 192 to 90 °C, when blended with 80% mineral diesel. The caloric value was improved from 37.24 to 41.28 MJ/kg after blending with 80% mineral diesel fuel. Therefore, blending COME with mineral diesel sharply improved the properties of COME to acceptable ranges, which would improve the atomization process during combustion in CI engines. Oxidation Stability. The oxidation stability of pure COME (B100) was 2.88 h lower than that of virgin C. megalocarpus oil, as shown in Tables 2 and 1, respectively. Thus, COME did not meet the international oxidative stability requirements, which prescribe a minimum of 3 h for the ASTM D6751 standard and 6 h for the EN 14214 standard. This was due to the presence of a high percentage of linoleic acid (C18:2) of about 69.0% and nearly 5% linolenic acid (C18:3), which are prone to oxidative degradability. Also, the antioxidants naturally present in oils were either deactivated and/or removed by the subsequent purification or separation procedures during the biodiesel production process, contributing to the lower oxidation stability of COME.8 Moreover, blending biodiesel with mineral diesel accelerates its oxidative degradability. This phenomenon was mainly attributed to the low amount or absence of sulfur and aromatic compounds in the mineral diesel fuel. Sulfur compounds may act as natural oxidation inhibitors in the fuel, and their presence usually slows the aging of the fuel and prevents the formation of acids and sludge.19 From the test results, it was observed that B20 exhibited the lowest oxidation stability (2.25 h), followed by B50 (2.32 h), while the oxidation stability of B80 was 2.52 h. Therefore, a dosage of tocopherols or synthesis antioxidants is required to increase the stability of COME and its blends. Low-Temperature Flow Properties. One of the major problems associated with the use of biodiesel is its poor lowtemperature flow property, which is characterized by the CP and CFPP. The former and latter are the temperatures at which a liquid fuel becomes cloudy because of the formation
of crystals and solidification of saturates.20-22 The CP and CFPP are higher for biodiesel than for mineral diesel, indicating that biodiesel tends to gel at higher temperatures than mineral diesel, causing engine problems, such as poor fuel atomization, incomplete combustion, and the depositing of carbon on the injectors. The high CP and CFPP values of biodiesel can be explained by the high amounts of the saturated fatty acid alkyl esters, because the unsaturated fatty acid alkyl esters have lower melting points than the saturated fatty acid alkyl esters.23 A remarkable feature of COME was its good low-temperature flow properties, as depicted in Table 2, with CP and CFPP being -6 and -11 °C, respectively. This was attributed to lower proportions of saturated fatty acids and a high composition of linoleic acid (69.0%) and linolenic acid (5%). The effects of blending with mineral diesel on the CFPP of COME were also investigated in this study. From the experiment, it was observed that pure COME recorded a higher CFPP than the blends. The pure COME (B100) displayed a promisingly low CFPP of about -11 °C, which was improved to -13 °C when blended with 80% mineral diesel fuel. This result indicated that the cold flow properties of COME were improved by blending with mineral diesel to levels that are comparable to the conventional diesel fuel, a finding that concurred with previous studies.24-26 (20) Dunn, R.; Bagby, M. Low-temperature properties of triglyceridebased diesel fuels: Transesterified methyl esters and petroleum middle distillate/ester blends. J. Am. Oil Chem. Soc. 1995, 72 (8), 895–904. (21) Dunn, R.; Shockley, M.; Bagby, M. Improving the low-temperature properties of alternative diesel fuels: Vegetable oil-derived methyl esters. J. Am. Oil Chem. Soc. 1996, 73 (12), 1719–1728. (22) Srivastava, A.; Prasad, R. Triglycerides-based diesel fuels. Renewable Sustainable Energy Rev. 2000, 4 (2), 111–133. (23) Knothe, G. Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters. Fuel Process. Technol. 2005, 86 (10), 1059–1070. (24) Tang, H.; Salley, S. O.; Ng, K. Y. S. Fuel properties and precipitate formation at low temperature in soy-, cottonseed-, and poultry fat-based biodiesel blends. Fuel 2008, 87 (13-14), 3006–3017. (25) Bhale, P. V.; Deshpande, N. V.; Thombre, S. B. Improving the low temperature properties of biodiesel fuel. Renewable Energy 2009, 34 (3), 794–800.
(19) Karavalakis, G.; Stournas, S.; Karonis, D. Evaluation of the oxidation stability of diesel/biodiesel blends. Fuel 2010, 89 (9), 2483– 2489.
6154
Energy Fuels 2010, 24, 6151–6155
: DOI:10.1021/ef100880g
Kivevele and Mbarawa
Lubricity. The results of HFRR testing on COME and its blends are as depicted in Table 3. It was observed that all of the blends showed wear scar diameters well within the acceptable limits of 460 and 520 μm, as prescribed in petrodiesel standards EN 590 and ASTM D975, respectively. Lubricity is not specified in the ASTM and EN biodiesel standards; the petrodiesel standards are used instead. In the present study, the smaller the wear scar diameters, the better the lubricity. The pure COME showed excellent antiwear (224 μm), better than all of the blends. It was observed that lubricity was improved as the amount of biodiesel in the blend increased, except for B50, which was 297 μm higher than 280 μm for B20. This possibly resulted from the unstable friction process, which was lubricated by B50 during the performance of the HFRR test. The average friction coefficient of B100 was 0.101, which was lower than those of 0.107, 0.108, and 0.121 for B80, B50, and B20, respectively. This result indicated that B100 possessed better antifriction properties than other blends. The good lubricity properties provided by COME and COME/mineral diesel were possibly the result of the high percentage of unsaturates in COME (linoleic and oleic acids, 69.0 and 13.7%, respectively), which agrees with previous studies.27,28 In addition, the presence of oxygenated moieties possible attributed to the good lubricity of COME.29 On the basis of various investigations, it was realized that biodiesel can be used as a lubricity enhancer in low-sulfur mineral diesel. Even such a small amount of biodiesel can significantly enhance the lubricity of the diesel.29,30 Whereas the 634 μm ball wear scar of mineral diesel, which was used in
this study, improved its lubricity significantly to 232, 297, and 280 μm when blended with 80, 50, and 20% of COME, respectively, all values were within specified standards, as shown in Table 3. Conclusion The following conclusions can be deduced from the results: (1) Most of the properties of COME fulfilled the minimum requirements specified in the ASTM D6751 and EN 14214 biodiesel standards. (2) The most remarkable feature exhibited by COME was that of excellent low-temperature properties, CP and CFPP, of -6 and -11 °C, respectively. Also, blending COME with 80% mineral diesel improved the CFPP to -13 °C, while the kinematic viscosity of COME was also within specified standards. These superior flow properties of COME point to the viability of using it in cold regions. (3) The oxidation stability of COME was 2.88 h, which did not meet the minimum requirement described in ASTM D6751 (3 h) and EN 14214 (6 h) biodiesel standards. This was due to the presence of large amounts of unsaturated fatty acids in COME, producing a high level of reactivity when it is placed in contact with air/oxygen. Moreover, blending biodiesel with mineral diesel accelerates its oxidative degradability; therefore, a dosage of tocopherols or synthesis antioxidants is required to increase the stability of COME and its blends. (4) COME displayed good antiwear and antifriction properties compared to mineral diesel, while blending COME with mineral diesel improved the lubricity of the latter. (5) Overall, C. megalocarpus oil was established as a promising non-edible feedstock for biodiesel production, while its methyl ester would appear to be a proper substitute for petroleum-based diesel fuel.
(26) Sarin, A.; Arora, R.; Singh, N. P.; Sarin, R.; Malhotra, R. K.; Kundu, K. Effect of blends of palm-Jatropha-Pongamia biodiesels on cloud point and pour point. Energy 2009, 34 (11), 2016–2021. (27) Geller, D. P.; Goodrum, J. W. Effects of specific fatty acid methyl esters on diesel fuel lubricity. Fuel 2004, 83 (17-18), 2351–2356. (28) 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. (29) Knothe, G. H.; Steidley, K. R. Lubricity of components of biodiesel and petrodiesel. The origin of biodiesel lubricity. Energy Fuels 2005, 19 (3), 1192–1200.
Acknowledgment. This study was conducted at Tshwane University of Technology, South Africa, and was supported by the South Africa/India Research Cooperation Programme (Grant UID 69823). (30) Hu, J.; Du, Z.; Li, C.; Min, E. Study on the lubrication properties of biodiesel as fuel lubricity enhancers. Fuel 2005, 84 (12-13), 1601– 1606.
6155
