Historical Perspectives on Vegetable Oil-Based Diesel Fuels
Biodiesel, defined as the mono-alkyl esters of vegetable oils or animal fats (prepared by transesterification with an alcohol in the presence of a catalyst - Scheme 1), is a promising alternative fuel for use in compression-ignition (diesel) engines and is being produced or used commercially in numerous countries around the world, including the United States, Austria, Czech Republic, France, Germany, Italy, Malaysia, and Sweden.
It is generally known that vegetable oils were tested as diesel fuels well before the energy crises of the 1970's and early 1980's generated renewed interest in alternative fuels, but details on this early, "historic" use are often unclear or presented inconsistently in the literature. Valuable insights on the use of vegetable oils and their derivatives as diesel fuels were achieved during that time, only to be rediscovered beginning in the late 1970's. This article attempts to clarify the history of biodiesel, or, more generally, that of vegetable oil-based diesel fuels and correlate it to "modern" use. Most literature references used here were found through a Chemical Abstracts search or are listed in a publication summarizing literature prior to 1949 on fuels from agricultural sources . After the 1940's, literature on vegetable oil-based diesel fuels is very sparse until the late 1970's. Although discussed later in this article in more detail, three references [2-4] describing the first use of a fuel meeting the current definition of biodiesel are worth close examination.
The Original Demonstration
A relatively common literature statement on the early use of vegetable oils as diesel fuels is that Rudolf Diesel, the inventor of the engine that bears his name, tested 'his' engine on peanut oil at 1900 World's Fair in Paris, the Exposition Universalle. A biography of Diesel by Nitske and Wilson  is often cited as the source. However, on p. 139 of that biography, the statement is made that -
"as the nineteenth century ended, it was obvious that the fate and scope of the internal-combustion engine were dependent on its fuel or fuels. At the Paris exposition of 1900, a Diesel engine, built by the French Otto Company, ran wholly on peanut oil. Apparently none of the onlookers was aware of this. The engine built especially for that type of fuel operated exactly like those powered by other oils."
Unfortunately, the bibliography in that biography  does not clarify where the authors obtained this information, as it does not list the references by Diesel discussed below. Thus, according to that biography, the peanut oil-powered diesel engine at the Paris World Expo was built specifically for using that fuel, a version contradicted by Diesel himself, as discussed below. Furthermore, it is implied but not elaborated that not necessarily Diesel himself conducted the demonstration nor had the idea of using vegetable oils as fuel. This interpretation is corroborated by Diesel's later statements. The idea for using peanut oil appears to have originated instead within the French government, according to Diesel. However, Diesel conducted related tests in later years.
A Chemical Abstracts search yielded references to papers by Diesel in which he reflected on that event in 1900. Two references [6,7] relate to a presentation Diesel made to the Institution of Mechanical Engineers (of Great Britain) in March 1912 (apparently in the last few years of his life, Diesel spent considerable time traveling to promote and discuss his engine according to the biography by Nitske and Wilson). In any case, Diesel states in those papers that -
"At the Paris Exhibition in 1900 there was shown by the Otto Company a small Diesel engine, which, at the request of the French Government, ran on Arachis (earth-nut or pea-nut) oil, and worked so smoothly that only very few people were aware of it. The engine was constructed for using mineral oil, and was then worked on vegetable oil without any alterations being made. The French Government at the time thought of testing the applicability to power production of the Arachide, or ground-nut, which grows in considerable quantities in their African colonies, and which can be easily cultivated there, because in this way the colonies could be supplied with power and industry from their own resources, without being compelled to buy and import coal or liquid fuel.
"This question has not been further developed in France owing to changes in the Ministry, but the author resumed the trials a few months ago. In has been proved that Diesel engines can be worked on earth-nut oil without any difficulty, and the author is in a position to publish, on this occasion for the first time, reliable figures obtained by tests: - Consumption of earth-nut oil, 240 grammes (0.53 lb.) per brake horse-power-hour; calorific power of the oil, 8600 calories (34,124 B.Th.U.) Per kg., thus fully equal to tar oils; hydrogen 11.8 per cent. This oil is almost as effective as the natural mineral oils, and as it can also be used for lubricating oil, the whole work can be carried out with a single kind of oil produced directly on the spot. Thus this engine becomes a really independent engine for the tropics."
Diesel continues that (note the prescient concluding statement) -
"Similar successful experiments have also been made in St. Petersburg with castor oil; and animal oils, such as train-oil, have been used with excellent results. The fact that fat oils from vegetable sources can be used may seem insignificant to-day, but such oils may perhaps become in course of time of the same importance as some natural mineral oils and the tar products are now. Twelve years ago, the latter were not more developed than the fat oils are to-day, and yet how important they have since become. One cannot predict what part these oils will play in the Colonies in the future. In any case, they make it certain that motor-power can still be produced from the heat of the sun, which is always available for agricultural purposes, even when all our natural stores of solid and liquid fuels are exhausted."
Diesel also wrote the book Die Entstehung des Dieselmotors , in which he referred to the use of peanut oil in a diesel engine at the Paris World's Fair in 1900. However, the statements in that book are considerably less detailed than those in the other two references [6,7].
Background and Sources
The background to using vegetable oils to provide the tropical colonies of European countries, especially those in Africa, with a certain degree of energy self-sufficiency can be found in the related literature throughout the 1940's. Palm oil was often considered as source of diesel fuel in the "historic" studies, although the diversity of oils and fats as sources of diesel fuel, an important aspect today again, and striving for energy independence were reflected in other "historic" investigations. Belgium, France and Italy particularly appear to have been interested in vegetable oil fuels at the time, although several German papers were published and reports from other countries also reflect the theme of energy independence.
Vegetable oils were also used as emergency fuels and other purposes during World War II. For example, Brazil prohibited the export of cottonseed oil in order to substitute it for imported diesel fuel . China produced diesel fuel, lubricating oils, "gasoline", and "kerosene", the latter two by a cracking process, from tung and other vegetable oils [10, 11]. However, the exigencies of the war caused hasty installation of cracking plants based on fragmentary data . Researchers in India, prompted by the events in World War II, investigated more than ten vegetable oils for development as a domestic fuel . Work on vegetable oils as diesel fuel ceased in India when petroleum-based diesel fuel became available again plentifully at low cost . The Japanese battleship Yamato reportedly used edible refined soybean oil as bunker fuel .
Once again, energy security perspectives have become a significant driving force for the use of vegetable oil-based diesel fuels, although environmental aspects (mainly reduction of exhaust emissions) play a role at least as important as energy security. For example, in the United States, the Clean Air Act Amendments of 1990 and the Energy Policy Act of 1992 mandate the use of alternative, or "clean," fuels in regulated truck and bus fleets. Amendments to the Energy Policy Act enacted into law in 1998, which provide credits for biodiesel use (also in blends with conventional diesel fuel), are a major reason the use of biodiesel in the United States is increasing significantly.
In modern times, biodiesel is derived or has been reported to be producible from many different sources which include vegetable oils, animal fats, used frying oils, and even soapstock. Generally, the geography of a country determines which vegetable oil is of most interest for biodiesel utilization. Thus, in the United States, soybean oil is considered as a prime feedstock, in Europe it is rapeseed oil (canola oil), and in countries with tropical climate it is palm oil. As alluded to above, different feedstocks were investigated in the "historic" times. These included palm oil, soybean oil, castor oil, and somewhat less common oils such as babassu , as well as non-vegetable sources such as industrial tallow  and even fish oils [17-20].
While some publications on this subject appeared in American journals, apparently little research work was performed in the United States in this area at the time, an exception being an investigation in 1951 at Ohio State University on cottonseed oil and blends thereof with conventional diesel fuel . Walton  summarized results on twenty vegetable oils (castor, grape seed, maize, cameline, pumpkin seed, beechnut, rape, lupin, pea, poppyseed, groundnut, hemp, linseed, chestnut, sunflower seed, palm, olive, soybean, cottonseed and shea butter). He also pointed out  that "at the moment the source of supply of fuels is in a few hands, the operator has little or no control over prices or qualities, and it seems unfortunate that at this date, as with the petrol engine, the engine has to be designed to suit the fuel whereas, strictly speaking, the reverse should obtain - the fuel should be refined to meet the design of an ideal engine." More insights can be gained by consulting the references listed in this article.
Although environmental aspects played virtually no role in promoting the use of vegetable oils as fuel in "historic" times and no emissions studies were conducted, it is still worthwhile to note some allusions to this subject from that time.
"In case further development of vegetable oils as fuel proves practicable, it will simplify the fuel problems of many tropical localities remote from mineral fuel, and where the use of wood entails much extra labor and other difficulties connected with the various heating capacities of the wood's use, to say nothing of the risk of indiscriminate deforestation" .
"It might be advisable to mention at this juncture, that, owing to the altered combustion characteristics, the exhaust with all these oils is invariably quite clean and the characteristic diesel knock is virtually eliminated" .
Observations by other authors included "invisible" or "slightly smoky" exhausts when running an engine on palm oil . Another author also noted clearer exhaust gases . And even in the case of fish oils as diesel fuels, the exhaust was noted to be colorless and practically odorless . The visual observations of yesterday have been confirmed in "modern" times for biodiesel fuel. Numerous recent studies have shown that most exhaust emissions (with the exception of nitrogen oxides; NOx) are reduced when using biodiesel fuel.
The kinematic viscosity of vegetable oils is about an order of magnitude greater than that of conventional, petroleum-derived diesel fuel. High viscosity causes poor atomization of the fuel in the engine's combustion chambers and ultimately results in operational problems such as engine deposits. Since the renewed interest beginning in the late 1970's in vegetable oil-derived fuels, four possible solutions to the problem of high viscosity have been investigated. They are are transesterification, pyrolysis, dilution with conventional petroleum-derived diesel fuel, and micro-emulsification .
Transesterification is currently the most common method and leads to mono-alkyl esters of vegetable oils and fats, now usually called biodiesel when used for fuel purposes. Briefly, it consists of reacting the vegetable oil feedstock with an alcohol, usually methanol, in the presence of a catalyst, usually a base such as sodium or potassium hydroxide, to give the corresponding vegetable oil (Scheme 1). Methyl esters are the most common form, largely due to methanol being the least expensive alcohol. Indeed, the term "biodiesel" usually refers to these esters.
Scheme 1. The transesterification reaction.
Currently, the preferred alcohol is methanol (R = CH3).
The high viscosity of vegetable oils as a major cause of poor fuel atomization resulting in operational problems such as engine deposits was recognized early [24,27-29]. Although engine modifications such as higher injection pressure were considered [27,29], reduction of the high viscosity of vegetable oils was usually achieved by heating of the vegetable oil fuel [24,27]. Often the engine was started on petrodiesel and after a few minutes of operation was then switched to the vegetable oil fuel, although a successful cold-start on high-acidity peanut oil was reported . Advanced injection timing was a technique also employed . Seddon  gives an interesting practical account on a truck that operated successfully on different vegetable oils using preheating of the fuel.
Pyrolysis, cracking or other methods of decomposition of vegetable oils to give fuels of varying nature is an approach that accounts for a significant amount of the literature in "historic" times. Artificial "gasoline," "kerosene," and "diesel" were obtained in China from tung oil  and others . Other oils that have been used in such an approach include work on fish oils [17-19], linseed oil , castor oil , palm oil  and cottonseed oil .
The other approaches, micro-emulsification and dilution with petrodiesel, appear to have found little or no attention during the "historic" times of studies on vegetable oils as diesel fuel. Huguenard  describes the use of blends, while Ilieff  used alcohol (ethanol) for improving the atomization and combustion of highly viscous castor oil.
Various other technical aspects, such as the effects of different kinds of vegetable oils relative to corrosion and lube oil dilution and contamination, have been studied .
The First "Biodiesel"
Walton  recommended that -
"To get the utmost value from vegetable oils as fuel, it is academically necessary to split off the triglycerides and to run on the residual fatty acid. Practical experiments have not yet been carried out with this; the problems are likely to be much more difficult when using free fatty acids than when using the oils straight from the crushing mill. It is obvious that the glycerides have no fuel value and in addition are likely, if anything, to cause an excess of carbon in comparison with gas oil."
Although Walton's statement points in the direction of what is now termed biodiesel by recommending the elimination of glycerol from the fuel, some remarkable work performed in Belgium and its former colony Belgian Congo (after its independence known for a long time as Zaire) deserves more recognition than it has received. Indeed, it appears that Belgian patent 422.877 granted to G. Chavanne (of the University of Brussels) in 1937  constitutes the first report on what is today known as biodiesel. It describes the use of ethyl esters of palm oil (although other oils and methyl esters are mentioned) as diesel fuel. These esters were obtained by acid-catalyzed transesterification of the oil (in present times, base catalysis is preferred). This work has been described in more detail .
Of particular interest is a related extensive report published in 1942 on the production and use of palm oil ethyl ester as fuel (4; note that a single author is listed but it is not quite clear if the bulk of the actual article was written by one or more other authors). That work describes what is probably the first test of an urban bus operating on biodiesel. A bus fueled with palm oil ethyl ester served the commercial passenger line between Brussels and Louvain (Leuven) in the summer of 1938. Performance of the bus operating on that fuel was reported to be satisfactory. It was noted that the viscosity difference between the esters and conventional diesel fuel is considerably less than that between the parent oil and conventional diesel fuel. Also, the author(s) point out that the esters are miscible with other fuels. That work also discusses what is probably the first cetane number testing (the cetane number is a combustion-related diesel fuel quality index) of a biodiesel fuel. On p. 52 of that report, the cetane number of palm oil ethyl ester is reported as approximately 83 (relative to a high-quality standard with CN 70.5 and a low-quality standard of CN 18 and diesel fuels with CNs of 50 and 57.5). Thus, those results agree with "modern" work reporting relatively high cetane numbers for such biodiesel fuels.
In "modern" times, Bruwer et al. reported on the use of methyl esters of sunflower oil to reduce the viscosity of the vegetable oil at several technical conferences in 1980 and 1981 [39-41]. This marks the beginning of the rediscovery and eventual commercialization of biodiesel.
A final thought should be given to the term "biodiesel" itself. A Chemical Abstracts search (using the "SciFinder" search engine with "biodiesel" as key word) yielded the first literature use of the term biodiesel in a Chinese paper published in 1988 . The next paper using that term appears in 1991  and from then on the use of the term "biodiesel" in the literature has expanded exponentially.
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Acknowledgement: This document was first published in Inform, Volume 12, November 2001, pp. 103-1107