Location: Bio-oils Research Unit
Title: A technical evaluation of biodiesel from vegetable oils vs. algae. Will algae-derived biodiesel perform? Author
Submitted to: Green Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 2011
Publication Date: August 17, 2011
Citation: Knothe, G.H. 2011. A technical evaluation of biodiesel from vegetable oils vs. algae. Will algae-derived biodiesel perform? Green Chemistry. 13:3048-3065. Interpretive Summary: Biodiesel is a prominent alternative fuel usually derived from vegetable oils, animal fats or used cooking oils. However, even the combined supply of these feedstocks does not suffice to replace all diesel fuel derived from petroleum. Therefore, a search for additional feedstocks, preferably with high production potential, is ongoing. In this connection, algae have been identified by many researchers as potentially high-yielding feedstock. Nevertheless, the fuel properties of biodiesel derived from all feedstocks depends on their composition. However, a comprehensive analysis of the fuel properties of biodiesel derived from algal oils has been lacking. This work analyzes the composition of algal oils with regard to biodiesel fuel properties. It is discussed that biodiesel derived from many algal oils would exhibit problematic fuel properties, especially in terms of cold flow and oxidative stability. In many cases, these properties would be less favorable for biodiesel derived from algal oils than for biodiesel derived from other feedstocks. A few algal oils likely yielding biodiesel with more favorable properties are identified. Another issue that requires more research is the presence of sulfur and other minor components with potentially problematic properties. Thus the choice of algae for biodiesel production should not only be guided by production aspects but also by the potential properties and performance of the resulting fuel, an aspect that has yet found little to no attention.
Technical Abstract: Biodiesel, one of the most prominent renewable alternative fuels, can be derived from a variety of sources including vegetable oils, animal fats and used cooking oils as well as alternative sources such as algae. While issues such as land-use change, food vs. fuel, feedstock availability, and production potential have influenced the search for the "best" feedstocks, an issue that will ultimately determine the usability of any biodiesel fuel is that of fuel properties. Issues such as cold flow and oxidative stability have been problematic for biodiesel. The fatty acid (FA) profile of a biodiesel fuel is largely identical to that of the feedstock and significantly influences these properties. This article compares biodiesel derived from vegetable oils and biodiesel obtained from algae in light of fuel properties. While the properties of biodiesel fuels derived from vegetable oils are well-known, the properties of biodiesel derived from algal oils have usually not been reported. The FA profiles of many algal oils possess high amounts of saturated and polyunsaturated FAs. Thus, biodiesel fuels derived from algae in many cases likely possess poor fuel properties, i.e., both poor cold flow and low oxidative stability simultaneously. This observation shows that production potential alone does not suffice to judge the suitability of a feedstock for biodiesel use. This article also summarizes how the fuel properties of biodiesel can be improved through modification of the fatty ester content. Algal oils for biodiesel production are probably best produced under tightly controlled conditions since the FA profile of algal oils is very susceptible to changes in these conditions. Algal oils likely yielding biodiesel with the least problematic properties as determined by reported FA profiles are discussed.