Palm Oil Methyl Esters As Diesel Substitute

Biodiesel has gained much attention in recent years due to increasing environmental awareness. Biodiesel is produced from renewable plant resources and thus does not contribute to the net increase of carbon dioxide. From 1996 to 2004, the biodiesel production capacity in the European Union (EU) has increased by a factor of four from 591,000 t to a total of 2.355 million t (Bockey, 2002; Bockey, 2004).

Further utilization of biodiesel is anticipated due to the initiative of the respective authorities to promote biodiesel and the high cost of petroleum diesel. For example, by the end of 2005, at least 2% (about 3.1 million t) of fossil fuels will be replaced by biofuels (biodiesel, bioethanol, biogas, biomethanol, etc.) in all EU countries. This minimum target quantity has been set out in the EU commission action plan, and the proportion will be increased annually by 0.75% to reach 5.75% (about 17.5 million t) in the year 2010 (Bockey and Korbitz, 2002; Markolvitz, 2002; Schope and Britschkat, 2002). Biodiesel will take up about 10 million t. This proposal also envisages that by 2020, the proportion of biofuels will be 20% and obligatory blending of 1% of biofuels will be introduced in 2009 (1.75% from 2010 onward). The current trend and legislation will set a momentum for greater biodiesel production and consumption worldwide. Thus, there will be an upward course and new market opportunities for biodiesel.

Methyl esters of vegetable oils have been successfully evaluated as a diesel substitute worldwide (Choo and Ma, 2000; Choo et al., 1997). For example, rapeseed methyl esters in Europe, soybean oil methyl esters in the United States, sunflower oil methyl esters in both Europe and the United States, and palm oil methyl esters in Malaysia. As the choice of vegetable oil depends on the cost of production and reliability of supply, palm oil would be the preferred choice, as it is the highest oil-yielding crop (4 to 5 t/Ha/yr) among all the vegetable oils and the cheapest vegetable oil traded in the world market.

Malaysia has embarked on an extensive biodiesel program since 1982. The biodiesel program includes development of production technology to convert palm oil to palm oil methyl esters (palm diesel), a pilot-plant study of palm diesel production, as well as exhaustive evaluation of palm diesel as a diesel substitute in conventional diesel engines (both stationary engines and exhaustive field trials).

Crude palm oil can be readily converted to their methyl esters. The MPOB/PET-RONAS patented palm diesel technology (Choo et al., 1992) has been successfully demonstrated in a 3000 t/yr pilot plant (Choo et al., 1995; Choo et al., 1997; Choo and Cheah, 2000). The novel aspect of this patented process is the use of solid acid catalysts for the esterification. The resultant of the reaction mixture, which is neutral, is then transesterified in the presence of an alkaline catalyst. The conventional washing stage or neutralization step after the esterification process is obviated, and this is an economic advantage.

Crude palm oil methyl esters (palm diesel) were systematically and exhaustively evaluated as a diesel fuel substitute from 1983 to 1994 (Choo et al., 1995; Choo et al., 2002a). These included laboratory evaluation, stationary engine testing, and field trials on a large number of vehicles, including taxis, trucks, passenger cars, and buses. All of these tests have been successfully completed. It is worth mentioning that the tests also covered field trials with 36 Mercedes Benz engines mounted onto passenger buses running on three types of fuels, namely, 100% petroleum diesel, blends of palm diesel and petroleum diesel (50:50), and 100% palm diesel. Each bus ran for 300,000 km, the expected life of the engines. (Total mileage of the ten buses running on 100% palm diesel was 3.7 million km.) Very promising results have been obtained from the exhaustive field trial. Fuel consumption by volume was comparable with that of the diesel fuel. Differences in engine performance were so

TABLE 14.5

Fuel Characteristics of Malaysian Diesel, Palm Diesel, and Palm Diesel with Low Pour Point

TABLE 14.5

Fuel Characteristics of Malaysian Diesel, Palm Diesel, and Palm Diesel with Low Pour Point


Palm Oil Methyl Esters

Palm Diesel



(Palm Diesel)

with Low Pour Point

Specific gravity




ASTM D1298


@ 23.6oc

@ 15.5oc

Sulfur content (wt%)



< 0.04

IP 242

Viscosity at 40°C (cSt)





Pour point (°C)





Cetane index



NA a


Gross heat of combustion (kJ/kg)




ASTM D 2382

Flash point (°C)





Conradson carbon residue (wt%)




ASTM D 189 a NA: not available.

ASTM D 189 a NA: not available.

small that an operator would not be able to detect it. The exhaust gas was found to be much cleaner, as it contained comparable NO, and less hydrocarbon, CO, and CO2. The very obvious advantage is the absence of black smoke and sulfur dioxide from the exhaust. This is a truly environmentally benign fuel substitute.

Palm diesel has fuel properties that are very similar to those of petroleum diesel (Table 14.5). It also has a higher cetane number (63) than diesel (<40) (Table 14.6). A higher cetane number indicates shorter ignition time-delay characteristics and, generally, a better fuel. Palm diesel can be used directly in unmodified diesel engines, and obviously it can also be used as a diesel improver. Compared with crude palm oil, the palm diesel has very much improved viscosity and volatility properties. It does not contain gummy substances. However, it has a pour point of 15°C, and this has confined its utilization to tropical countries.

In recent years, palm diesel with low pour point (without additives) has been developed to meet seasonal pour-point requirements, for example spring (-10°C), summer (0°C), autumn (-10°C), and winter (-20°C). The MPOB patented technology (Choo et al., 2002b) has overcome the pour-point problem of palm diesel. With the improved pour point, palm diesel can be utilized in temperate countries. Besides having good low-temperature flow characteristics, the palm diesel with low pour point also exhibits comparable fuel properties as petroleum diesel (Table 14.5).

The storage properties of the palm diesel are very good. After storing for more than 6 months in a 50-m3 storage tank, it was found that there was little deterioration in the

TABLE 14.6

Cetane Numbers of Palm Diesel, Petroleum Diesel, and Their Blends


TABLE 14.6

Cetane Numbers of Palm Diesel, Petroleum Diesel, and Their Blends


iyl Esters (%)

Petroleum Diesel (%)

Cetane Number































a Calculated according to ASTM D613.

a Calculated according to ASTM D613.

fuel quality parameters except for the color, which had changed from orange to light yellow. This was due to the breakdown of the high-value colored carotene compounds.

The main benefit derived from such a renewable source of energy is the reduction of emission of greenhouse gases (GHG) such as CO2. The production and consumption of palm diesel has a closed carbon cycle. This closed carbon cycle recycles the carbon dioxide, so there is no net accumulation of carbon dioxide in the atmosphere. Consequently, production of palm diesel, with its lower emissions, is in line with the Clean Development Mechanism (CDM) of the 1997 Kyoto Protocol.

Under the terms of the 1997 Kyoto Protocol (a major international initiative established to reduce the threat of global warming), there is a potential financial gain to transact these GHG benefits to the palm oil industry under the CDM. This mechanism allows emission-reduction projects to be implemented and credits to be awarded to the investing parties. Financial incentives like an attractive carbon-credit scheme should further enhance the economic viability of these renewable fuels.

In 2003, Malaysia consumed 8.91 million t of petroleum diesel (Ministry of Energy, Water and Communication, 2004). The transport sector alone consumed 4.941 million t and generated 19.32 million t of carbon dioxide. The transport sector has also been identified as one of the chief contributors to air pollution, particularly black smoke (due to diesel) and carbon dioxide. If 10% of the diesel (0.4941 million t) were replaced by palm diesel, the industry would be entitled to enjoy 1.932 million t of carbon credit, which amounts to US $19.32 million at a rate of US $10/t of carbon dioxide.

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