ARS | Publication request: Biofuels: The role of biodiesel and improving its performance

Submitted to: Materials Research Society Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 15, 2011
Publication Date: April 25, 2011
Citation: Knothe, G.H. 2011. Biofuels: The role of biodiesel and improving its performance. Proceedings of the Materials Research Society Spring Annual Meeting, San Francisco, CA, April 25-28, 2011.

Technical Abstract: Concerns about the availability and long-term supply of petroleum-derived fuels have caused the search for alternative sources of energy. Liquid fuels will be necessary for some applications for an indefinite period of time. Therefore, defining relevant feedstocks, producing fuels from these feedstocks and the properties of these fuels are critical issues. Fuels powering compression-ignition (diesel) and turbine (jet) engines are among these liquid energy sources. Biodiesel, defined as the mono-alkyl esters of vegetable oils, animal fats or other triacylglycerol-based feedstocks, plays a prominent role in this connection as an alternative to petrodiesel fuels. Important issues facing biodiesel are feedstock supply, as not enough vegetable oil is available to replace the whole petrodiesel market, and the issue of fuel properties, especially cold flow and oxidative stability. The search for additional feedstocks coupled with the food vs fuel issue has increased interest in inedible oils derived from sources, such as used cooking oils, jatropha, and algae. However, biodiesel from these sources, as biodiesel derived from classical sources such as commodity vegetable oils, must meet performance criteria and this is not necessarily the case. Therefore, modifying the composition of biodiesel, i.e., its fatty ester profile, is a critical issue to enhance its use in the marketplace. Esters of specific fatty acids impart improved properties to biodiesel with esters of decanoic and palmitoleic acid displaying favorable properties for enrichment in biodiesel feedstocks. Renewable diesel is another fuel that can be obtained from triacylglycerol-based feedstocks. In its composition, i.e. alkane-type hydrocarbons, it more closely resembles petrodiesel fuel. While biodiesel is obtained from triacylglycerol-based feedstocks via a transesterification reaction using an alcohol in the presence of a catalyst under mild conditions, renewable diesel can be obtained from such feedstocks via a hydrodeoxygenation reaction using hydrogen in the presence of a catalyst under more severe conditions. Biodiesel and renewable diesel are compared regarding their production and properties and it is suggested that each fuel has a role to play in an alternative energy mix based on its properties.