Bio-diesel is the name given to a variety of ester-based oxygenated fuels made from vegetable oils, fats, greases and other sources of triglycerides. Bio-diesel is a clean-burning diesel replacement fuel that can be used in compression ignition (CI) engines and is manufactured from renewable non-petroleum-based sources, including but not limited to, organic fats and oils such as virgin vegetable oil, recycled oil, such as used fryer oil and grease trap materials, and animal fats, such as lard and beef tallow. Non-limiting examples of these feedstocks include soybean oil, peanut oil, coconut oil, palm oil, canola or rapeseed oil, algae oil, jatropha oil, animal fat tallow, waste vegetable grease, and other similar sources.
The basic biodiesel reaction involves a transesterification process to convert triglycerides in the feed stock to methyl esters. The transesterification process typically involves the reaction of a raw oil (source of triglycerides) with methanol or ethanol and an alkaline catalyst such as sodium hydroxide or potassium hydroxide. Excess methanol is typically used to ensure that the process is driven to completion.
The alcohol and catalyst are mixed first and then the alcohol/catalyst mixture is mixed with the raw oil and allowed to react. Once the reactants are thoroughly mixed, the reaction begins and the raw oil begins to separate into methyl ester and glycerin (otherwise known as glycerol). Because the methyl ester is less dense than the glycerin, it floats to the top of the glycerin and may be separated from the glycerin by pumping it off the top or by draining the glycerin off the bottom. A centrifuge or other separation means may also be used to separate the methyl ester from the glycerin by-product. Thereafter, the methyl ester is purified to produce the bio-diesel product.
Bio-diesel is produced in pure form (100% biodiesel or “B100”), but is typically blended with conventional diesel at low levels between about 2% (B2) and about 20% (B20) in the U.S. and may be blended at higher levels in other parts of the world. While B2 biodiesels fuels may be used in conventional diesel engines without modification, higher level blends above approximately B5 (and up to B100) may require special handling and fuel management as well as vehicle modifications such as the use of heaters (especially in colder climates) and different seals/gaskets that come into contact with the fuel. The level of care needed depends on a variety of factors, including, but not limited to the engine, manufacturer, climate conditions, among others.
Bio-diesel has been designated an alternative fuel by the U.S. Department of Energy and the U.S. Department of Transportation, and is registered with the U.S. Environmental Protection Agency as a fuel and fuel additive. It can be used in any diesel engine (when blended with conventional diesel) and is compatible with existing petroleum distribution infrastructure.
Specifications for biodiesel have been implemented in various countries around the world. In the U.S., the specifications have been implemented through the American Society of Testing and Materials (ASTM). The ASTM specification for diesel is ASTM D975 and the ASTM standard for biodiesel is ASTM D6751. It is noted that the standard for biodiesel is as a blendstock for blending into conventional diesel and is not meant to be a specification for B100 alone. It is noted that both No. 1 and No. 2 petroleum diesel fuel (i.e., D1 and D2) may be blended with biodiesel for various reasons, including the need for lower temperature operation.
One of the problems with the conventional transesterification process used to produce bio-diesel is that the reaction produces approximately ten percent glycerin as a byproduct, which must be separated and removed from the methyl ester to produce the biodiesel product. Thus, it would be desirable to utilize a process that produces less glycerin as a byproduct.
Another problem with the conventional transesterification process is that the process must be conducted at elevated temperature (above approximately 130° F.) and elevated pressure (above approximately 20 PSI). Furthermore, the reaction time needed to proceed to completion can also be lengthy. As described for example in U.S. Pat. No. 7,145,026 to Fleisher, the subject matter of which is herein incorporated by reference in its entirety, the transesterification reaction can require many hours to proceed under atmospheric conditions. Fleisher describes a process that operates at a temperature of 80 to 180° C. in order to reduce the reaction time.
However, it is desirable to develop a process that can be conducted under ambient temperature and pressure and that can proceed to completion within a short period of time (i.e., between 10 and 20 minutes) under such ambient conditions.