Biodiesel is getting a lot of attention these days. Many folks are enamored by the fact that it's not made of dead dinosaurs found under countries with unfriendly leaders, but that doesn't automatically mean it's safe to put in your Cummins, Duramax, or Power Stroke engine. General Electric (makers of everything from light bulbs to Late Night with Conan O'Brien to fuel additives) has put together one of the most comprehensive studies of pure 100 percent biodiesel (B100) and its effects on the modern turbodiesel engines we all love. Here are GE's conclusions based on numerous tests that can't be performed by your local bio-fuel co-op.-The Diesel Power staff
Although biodiesel is not a new fuel, commercialization is increasing as regulations promote the use of green fuels in the marketplace. Fuel system failures and operability problems have been encountered as biodiesel use becomes more widespread. Stability issues include understanding the mechanism of degradation of biodiesel and interactions in petroleum-based fuels, determination of stability that predicts operability, and measurement of the degradation. These issues are reviewed and preventative measures are identified for the mechanisms that may contribute to biodiesel instability. Case studies are included to demonstrate how fuel additives are successfully being used to prevent the operability problems in biodiesel fuel blends.
Managing The Stability Of B100 And Biodiesel Blends Blends of biodiesel are now well-adopted fuels that are gaining market share and popularity. Biodiesel is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats and meeting the requirements of ASTM D-6751 (a standard set by the American Society for Testing and Materials). However, several unique characteristics of biodiesel, also known as fatty acid methyl esters (FAME) or B100, may cause some operability problems. Low-temperature fluidity, water haze, and thermal and oxidation stability are the most significant issues facing the marketers and end users of biodiesel.
Cold Flow Improver technology is evolving, but, because of the composition of B100 and especially soy oil esters, the improvement using additives is limited to a few degrees Fahrenheit. Understanding the chemical makeup of biodiesel and the measurement of the metrics that could impact operability are key to understanding the root causes of instability and are helpful in formulating solutions to overcome stability problems. The work by J. Andrews Waynick of Southwest Research Institute(13) appears to be the most comprehensive and inclusive document on this subject. Now that fuels containing B100 are being used, experiential information and data can be introduced into the analyses of these critical areas.
The variables that have been identified include glycerol content, free fatty acid content, metals, and carbon-carbon double bond types and configurations (degree and level of unsaturation). The manufacturing process is a significant potential source of stability problems, and process controls are the first line of defense to achieve and maintain biodiesel stability. Fuel-blending strategies and fuel additives are now gaining interest to meet market demands for viable fuels containing biodiesel. Fuel additives are successfully being used to improve operability by preventing oxidation and thermal degradation of biodiesel and blends of biodiesel. For clarification, B100 is used in reference to methyl esters and biodiesel blend is used in reference to blends containing petroleum distillate fuels and B100.
The Manufacturing Process, A Critical Success Factor B100 is produced in a batch process by transesterification of methanol with triglycerides, also known as glycerol fatty acids, in the presence of caustic materials. The degree of completion of the reaction to replace the glycerol with an alcohol such as methanol was recognized as important to fuel quality early in the development of biodiesel. The reaction is conducted at elevated temperatures of around 120-150 degrees Fahrenheit to drive the reaction to completion. The mixture is then neutralized with an acid and washed to remove excess methanol, salts, and free glycerol. Effective neutralization is required to remove alkali metals from the oil phase. If washing is not effective, the salts and glycerol may remain in the B100. Minimizing glycerol levels is required to ensure quality B100 production. Maximizing the degree of completion of the esterification reaction minimizes free fatty acids that can contribute to instability. Removal of alkali metal salts from the process and drying is also important to meet the quality standard of a finished B100 product. Process controls and quality testing are required to achieve the quality standards established in ASTM D-6751. These standards are currently being reviewed based on recent problems with biodiesel blends in the marketplace, and modifications may be recommended to prevent potential operability problems in the future with biodiesel products.