Short communication. Key fuel properties of palm oil alkyl esters. Choo Yuen May
a,*, Yung Chee Lianga,b. , Cheng Sit Foon a,b. ,. Ma Ah Ngan a.
Fuel 84 (2005) 1717–1720 www.fuelfirst.com
Short communication
Key fuel properties of palm oil alkyl esters Choo Yuen Maya,*, Yung Chee Lianga,b, Cheng Sit Foona,b, Ma Ah Ngana, Chuah Cheng Hookb, Yusof Basirona a
Engineering Processing Research Division, Malaysian Palm Oil Board (MPOB), PO Box 10620, 50720 Kualalumpur, Malaysia b Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kualalumpur Received 2 April 2004; received in revised form 14 February 2005; accepted 14 February 2005 Available online 19 March 2005
Abstract Methyl esters of vegetable oils have been successfully evaluated as diesel substitute. In the present study, other alkyl esters, namely ethyl and isopropyl esters of crude palm oil and crude palm stearin were synthesized via chemical transesterification reactions and subsequently evaluated for their fuel properties. Generally, these alkyl esters exhibit higher viscosity (4.4!10K6m2/s–5.2!10K6 m2/s) compared to that of petroleum diesel (4.0!10K6 m2/s). However, compared to petroleum diesel, these alkyl esters exhibit acceptable gross heat of combustion (39–41 MJ/kg). Originated from renewable origin, the low sulfur content in alkyl esters emits much lower SO2. These alkyl esters are much safer than petroleum diesel in terms of safety for storage and transportation as they possess high flash points. They may find applications in the fuel industry besides utilization as oleochemicals. q 2005 Elsevier Ltd. All rights reserved. Keywords: Alkyl esters; Fuel properties; Palm esters
1. Introduction The concept of using vegetable oil as engine fuel dates back to 1895 when Dr Rudolf Diesel developed the first engine running on vegetable oil [1]. In the 1930s and 1940s, vegetable oils were used as fuel from time to time. The high viscosity of vegetable oils compared with petroleumderived fuel had limited its use. Continued use of these fuels led to incomplete combustion, injector and ring coking, and ultimately engine failure. Transesterification of vegetable oil with alkyl alcohols provides significant reduction in viscosity. Alkyl esters of oils and fats, also known as biodiesel, were the end product of the transesterification reaction. Methyl and ethyl soybean esters were tested as renewable fuels for diesel engines and studies showed that these esters could be used as alternative fuels [2]. Fuel properties of tallow and soybean oil esters were also found to be comparable to No. 2 diesel fuel [3]. Emissions testing on soybean oil esters has shown that there * Corresponding author. Tel.: C60 389259592; fax: C60 389262971. E-mail address:
[email protected] (C.Y. May).
0016-2361/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2005.02.010
is a significant reduction on carbon monoxide, particulate and hydrocarbon emissions but higher levels of nitrous oxide emission [4]. Ethyl esters of vegetable oils are proven effective as lubricity enhancers as they showed significant improvement in the wear properties [5]. As early as 1920, palm oil had been experimented as a fuel for diesel engines in Africa. The use of alkyl esters of palm oil as a fuel for diesel engines has been reported and it was concluded that alkyl esters of palm oil were suitable for normal starting and operation [6,7]. The use of methyl esters of refined bleached and deodorized (RBD) palm oil and ethyl esters of palm oil on stationary engines was studied at the National Chemical Laboratories for Industries, Japan and Stazione sperimentale per I Combustibili (SSC), Italy [8,9]. The esters were blended with gas oil and gave satisfactory results. Malaysian Palm Oil Board (MPOB), formerly known as Palm Oil Research Institute of Malaysia (PORIM) has also conducted systematic studies on the production and evaluation of alternative fuel from palm oil and palm oil derivatives [10–12]. In the present study, ethyl and isopropyl esters of crude palm oil (CPO) and crude palm stearin (CPS) were synthesized to study and compare their respective fuel properties with their methyl esters and Malaysian Petroleum Diesel.
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2. Experimental 2.1. Preparation of alkyl esters The acidity of the CPO and CPS used were determined before the reaction. Transesterification reaction was conducted in a two-necked 500 ml flask equipped with a reflux condenser and a magnetic stirrer. Two hundred grams of oil were used and the molar ratio of methanol to oil used was 15.6:1. The reaction mixture was stirred and heated to reflux. After the reaction was completed the ester layer was separated from the glycerol layer, and washed with distilled water until the washing was neutral. In the case of high free fatty acids content, the experiment was carried out using 200 g of the oil, 150 ml of the methanol and a base catalyst (sodium hydroxide or sodium metal). The oil was first neutralized with an appropriate quantity of sodium hydroxide. Using the neutralization steps as described above, methyl, ethyl and isopropyl esters of CPO and CPS were obtained with good yield. 2.2. Fatty acid composition analysis The fatty acid composition of alkyl esters of CPO and CPS synthesized in the present study were analyzed using gas chromatography equipped with a flame ionization detector. 2.3. Laboratory evaluation of alkyl esters as diesel substitute The fuel characteristics of the alkyl esters synthesized were evaluated according to ASTM standard methods as follows: (i) Density at 40 8C (ASTM D4052), (ii) Sulfur content (IP 242), (iii) Viscosity at 40 8C (ASTM D445), (iv) Pour point (ASTM D97), (v) Cloud point (ASTM D2500), (vi) Distillation (ASTM D86), (vii) Gross heat of combustion (ASTM D2382) and (viii) Flash point (ASTM D93).
3. Results and discussion 3.1. Fatty acid composition of palm alkyl esters The typical fatty acid composition of all alkyl esters of CPO and CPS are shown in Table 1. In comparison, palm alkyl esters derived from CPS have a higher content of C16:0 esters but lower in C18:0, C18:1 and C18:2 esters. 3.2. Laboratory evaluation of alkyl esters as diesel substitute Methyl, ethyl and isopropyl esters of CPO and CPS prepared were evaluated for their potential as diesel fuel
Table 1 Typical fatty acid composition of alkyl esters of crude palm oil (CPO) and crude palm stearin (CPS) Fatty acid composition (%)
Alkyl esters of crude palm oil (CPO)
Alkyl esters of crude palm stearin (CPS)
C12 C14 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3
0.3 0.8 44.3 0.2 5.0 39.1 10.1 0.1
0.4 1.9 52.0 – 4.1 32.7 7.9 0.1
based on physical and chemical characteristics. The properties of these esters (Table 2) were found to be comparable with those of petroleum diesel. The densities at 40 8C of methyl, ethyl and isopropyl esters of CPO and CPS were 0.855–0.858 kg/L and, therefore, slightly higher than petroleum diesel, which slightly exceeds 0.820 kg/L. This, however, is not important, as this would only cause a slight increase of fuel consumption. As expected, the sulfur content of these esters are very low; a 0.04 wt% maximum has been determined, as compared with 0.2 wt% presently found in Malaysian petroleum diesel. The exhaust emissions will therefore contain very little SO2. The viscosities at 40 8C of alkyl esters of CPO and CPS were in the range of 4.4!10K6 –5.2!10K6 m2/s, slightly higher than petroleum diesel fuel (4.0!10K6 m2/s). However, they are still in an acceptable range and able to flow under warm weather conditions. The pour points of alkyl esters of CPO and CPS range from 6 to18 8C. Pour point is defined as the lowest temperature that the product still can be poured by gravity. Ethyl and isopropyl esters provide better cold flow properties when compared to methyl esters. Their pour points were lower than that of methyl esters. It was noted that the pour points of alkyl esters of CPS were significantly higher than alkyl esters of CPO. The alkyl esters synthesized in the present study were also evaluated for their cloud points. Cloud point is the temperature at which a cloud of wax crystals first appears in the liquid when it is cooled. Thus, cloud point is usually higher than the pour point of the same product. Alkyl esters of CPO and CPS exhibit cloud points ranging from 7 to 19 8C. As usual, methyl esters of CPS possess a higher cloud point, i.e. 19 8C. The boiling range for all palm alkyl esters prepared in the present study was found to be rather narrow compared to that of petroleum diesel. It was noted that among the alkyl esters of CPO, the isopropyl esters have the widest boiling range, followed by ethyl esters and methyl esters. The same results were observed for the palm alkyl esters of CPS. While in comparison between palm alkyl esters of CPO
C.Y. May et al. / Fuel 84 (2005) 1717–1720
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Table 2 Fuel characteristics of alkyl esters of crude palm oil (CPO) and crude palm stearin CPS) Test conducted
Unit
Crude palm oil (CPO)
Crude palm stearin (CPS)
Malaysian petroleum diesel
Methyl esters
Ethyl esters
Isopropyl esters
Methyl esters
Ethyl esters
Isopropyl esters
Density @ 40 8C (ASTM D 4052) Sulfur content (IP 242) Viscosity @ 40 8C (ASTM D 445) Pour point (ASTM D 97) Cloud point (ASTM D 2500) Distillation (ASTM D86) I.B.P. 10% 20% 50% 90%
kg/L wt% !10K6 m2/s 8C 8C
0.855 !0.04 4.4 15 16
0.857 !0.04 4.7 12 16
0.854 !0.04 5.2 6 7
0.857 !0.04 4.5 18 19
0.858 !0.04 4.8 15 16
0.856 !0.04 5.2 15 16
0.823 0.20 4.0 15 18
8C 8C 8C 8C 8C
313 321 322 325 332
328 336 338 340 350
320 331 332 335 343
330 335 337 340 350
8C mL MJ/kg
345 99.0 39.7
365 99.0 39.7
349 98.5 39.9
362 98.0 39.9
275 314 318 330 Cracked maximum temperature 348 83.0 39.2
228 258 270 298 376
F.B.P. Final recovery Gross heat of combustion (ASTM D 2382) Flash point (ASTM D93)
296 318 322 330 Cracked maximum temperature 355 87.0 40.4
400 – 45.8
8C
178
–
–
165
–
–
80
and CPS, the esters of CPS have a wider boiling range than the esters of CPO. Generally, the boiling curve was significantly flatter than that of petroleum diesel, being about 275–365 8C for palm alkyl esters and about 228– 400 8C for petroleum diesel. This property is unlikely to result in any serious disadvantage, since, the diesel engine is not spark ignited. However, mixtures of palm esters with petroleum diesel exhibit ‘stiffer’ boiling curves and may therefore smoothen the burning characteristics as compared to pure palm diesel fuels. As long as the distillation residue does not exceed 1.5 vol.%, there should be no serious objection from this point of view. In general, the gross heat of combustion of these esters is slightly lower than that of petroleum diesel. The gross heat of combustion (GHC) affects the fuel consumption as long as the same power is considered. The GHC of palm esters is well below that of petroleum diesel, being around 39.7–40.4 MJ/kg compared to 45.8 MJ/kg of Malaysian petroleum diesel. Fuel consumption (expressed in km/kg or km/L) is expected to be 10–12% higher compared with petroleum diesel, for engines running under comparable conditions. The small increase in carbon numbers of the alkyl group of the esters from methyl (CH3–) to ethyl (CH3CH2–) and finally to isopropyl [(CH3)2CH2–] esters does not change the gross heat of combustion significantly. Flash point of methyl esters of CPO and CPS were far greater than that of petroleum diesel fuel. Palm methyl esters exhibit a flash point between 165 and 178 8C, while petroleum diesel has a much lower flash point of 80 8C. In regards to the flash point of methyl ester of palm oil, it was
found that when the methanol content left in the palm diesel product were in excess of 1–2 vol.%, the flash point dropped below the lower limit to 68 8C minimum. Therefore, methanol needs to be removed to less than 1 vol.% in the final product.
4. Conclusions Ethyl and isopropyl esters of CPO and CPS exhibit comparable fuel properties with their methyl esters and Malaysian Petroleum Diesel. Thus, they may find applications in the fuel industry in addition to their utilization as oleochemicals. However, methyl esters may be the preferred choice in terms of the cost, since, methanol is less expensive than ethanol and isopropanol. Besides possessing good fuel properties, the alkyl esters of CPO and CPS have positive environmental impact. Being derived from palm oil, they are environmentfriendly, biodegradable and renewable. Their production and utilization as fuel is also in-line with Clean Development Mechanism (CDM) under the 1997 Kyoto Protocol.
Acknowledgements The authors would like to thank the staff of processing group for their technical assistance.
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