Submitted to: Landbauforschung Voelkenrode
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/17/2003
Publication Date: 9/17/2003
Citation: KNOTHE, G.H. INFLUENCE OF STRUCTURE OF ESTERS OF FATTY ACIDS ON BIODIESEL FUEL PROPERTIES. LANDBAUFORSCHUNG VOELKENRODE. 2003. v.239. pp. 115-124. Interpretive Summary: Biodiesel is an alternative diesel fuel derived from vegetable oils such as soybean oil. It can be used both neat and in blends with conventional, petroleum-derived diesel fuel since biodiesel and conventional diesel fuel are miscible at all blend levels. Biodiesel is a mixture of compounds which can be termed methyl esters of vegetable oils or another term is fatty acid methyl esters. This relates to the fact that biodiesel is usually produced from vegetable oils using another compound called methanol. However, other compounds related to methanol can be used for making biodiesel. This can cause some advantageous changes to the properties of biodiesel, for example better low-temperature properties. Also, the amounts and nature of the different compounds in vegetable oils from which biodiesel is made significantly affect biodiesel properties and performance, such as exhaust emissions and storage stability. This work summarizes the effect of the different materials in biodiesel on important fuel properties and makes recommendations for improved biodiesel. Beyond that, a predictive equation related to how the components of biodiesel fuel ignite in a diesel engine is presented. This research benefits the biodiesel community by pointing out potential improvements to the fuel formation of biodiesel.
Technical Abstract: Biodiesel is becoming a well-established "alternative" diesel fuel derived from vegetable oils or animal fats. This fuel is being produced and used commercially in numerous countries around the world. In almost all cases, the vegetable oil or animal fat is transesterified with methanol to give the corresponding methyl esters. In that form vegetable oils are then used as biodiesel. One of the major factors influencing specific fuel properties of a biodiesel fuel is the fatty acid profile, more specifically, the structure of those fatty acids contained in the oil or fat from which the biodiesel fuel is derived. Structural features influencing fuel properties include chain length and unsaturation. However, since alcohols other than methanol can be used for producing esters of vegetable oils or animal fats, the nature of the ester moiety can also influence fuel properties. The most important fuel properties that are influenced by structural features of both moieties of fatty esters in biodiesel include cetane number which relates to ignition quality and thus ultimately to exhaust emissions, cold flow, oxidative stability and viscosity. This work investigates and evaluates the influence of the various structural features on biodiesel fuel properties and suggests possible routes for improvement of those properties. Predictive equations for cetane numbers of fatty compounds are presented.