Biodiesel

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Top Catal (2010) 53:714–720 DOI 10.1007/s11244-010-9457-0

ORIGINAL PAPER

Biodiesel: Current Trends and Properties
Gerhard Knothe

Published online: 13 April 2010 Ó GovernmentEmployee: U.S. Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research 2010

Abstract Biodiesel, an alternative to petroleum-derived diesel fuel, is defined asthe mono-alkyl esters of vegetable oils and animal fats. Several current issues affecting biodiesel that are briefly discussed include the role of new feedstocks in meeting increased demand for biodiesel and circumventing the food versus fuel issue, biodiesel production, as well as fuel properties and their improvement. Keywords Biodiesel Á Fatty esters Á Fuel properties Á Algae Á Geneticmodification Á Microbiology Á Vegetable oils

1 Introduction The search for alternative and renewable sources of energy to diminish the dependence on fossil fuels has caused fuels derived from biological sources to be increasingly scrutinized and utilized. Biodiesel [1, 2], defined as the monoalkyl esters of vegetable oils or animal fats [3] and derived from these feedstocks by transesterification, isprobably the most commonly used biofuel as a replacement for petroleum-derived diesel fuel (petrodiesel). Commonly biodiesel has been obtained from commodity vegetable oils such as soybean, rapeseed (canola), palm, and sunflower oils. The observations that such oils can replace only a few percent of the petrodiesel market and that biodiesel from these feedstocks is more expensive than petrodiesel (unlesssubsidized in some form) have resulted

in the search for additional feedstocks. Among the additional feedstocks are animal fats (for example, beef tallow) [4, 5] and used cooking or frying oils [6, 7]. Although these feedstocks have more favorable economics due to lower costs, their supply does not suffice to solve the availability problem. Besides the issues of supply and economics, in recentyears the food versus fuel issue has gained attention, i.e., that a potential source of food (edible vegetable oil) should not be used for fuel purposes due to effects on food prices and land-use change. While this issue is complex, it has provided significant incentive to the search for additional feedstocks not affected by this issue. Some potential feedstocks of interest in this connection arealgae [8–11] and jatropha [12–14]. Regardless of the feedstock, all biodiesel fuels need to meet the specifications in standards such as ASTM D6751 [3] and EN 14214 [15]. Also, some of the technical problems such as poor cold flow and oxidative stability properties can affect biodiesel from any feedstock. Therefore, the issue of fuel composition of biodiesel, i.e. the monoalkyl esters largelycomprising this fuel, is very significant as technical problems may counteract any solutions to the social and economic aspects mentioned above. Therefore, this article briefly summarizes the need for additional biodiesel feedstocks taking aspects of technical viability as expressed by fuel properties into consideration.

2 Discussion 2.1 Sources and Availability

G. Knothe (&) National Center forAgricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 N. University St., Peoria, IL 61604, USA e-mail: gerhard.knothe@ars.usda.gov

The use of vegetable oils as a source of energy to power diesel engines is not a new concept. Indeed, it is almost as old as the diesel engine itself. At the 1900 World

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Top Catal (2010) 53:714–720

715Exposition in Paris, a diesel engine operated on peanut oil as reported by Rudolf Diesel, the inventor of the engine that bears his name, himself [16, 17]. The background was that the French Government at the time was interested in providing its tropical colonies with a local source of energy [16, 17]. The theme of energy independence, especially for the colonies of European countries but also to...
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