Cloud and Pour Point (property specification):

A fuel property that is particularly important for the low temperature operability of biodiesel fuel is the cloud point defined as the lowest temperature at which wax crystals begin to form in the fuel. Therefore, it is an index of the lowest temperature of the fuel’s usability for certain applications. Operating at temperatures below the cloud point for a biodiesel fuel can result in fuel filter clogging due to the wax crystals. Pour point is the temperature at which the fuel ceases to flow. Therefore, the pour point provides an index of the lowest temperature of the fuel’s utility during cold temperature handling. Cloud point and pour point determinations are also useful information for blending purposes. No ASTM requirement.

Ethanol Purity (quality specification):

Federal and state laws specify the ethanol concentration in gasoline blends. The purity of the fuel ethanol that is to be blended into gasoline must meet the federal and state specifications. This measurement will help the producers and distributors determine if the specifications are being met. ASTM D4806 Requirement: 92.1% minimum ethanol by volume.

Calculated Cetane Index (property specification):

The Cetane number relates to the readiness of the fuel to self-ignite when exposed to the high temperatures and pressure in the diesel engine combustion chamber. The number is also indicative of the relative fuel stability. On-highway diesel fuels in the U.S. are required to have Cetane numbers of 40 or higher. The calculated Cetane index is a useful tool for estimating ASTM Cetane number where a test engine is not available for determining the property. It may be conveniently employed for approximating Cetane number where the quantity of sample is too small for an engine rating. In cases where the Cetane number of a fuel has been initially established, the index is useful as a Cetane number check on subsequent samples of that fuel, provided its source and mode of manufacture remain unchanged. ASTM D6751 Requirement: minimum 47 calculated cetane index.

Karl Fischer Moisture (processing specification):

The content of water in petroleum products plays an important role in predicting quality and performance of the product. If moisture is present in lubricating oils, premature corrosion and wear, diminished lubrication, filter plugging, decreased effectiveness of additives, and bacterial growth may ensue. ASTM D4806 Requirement: 1% maximum water by volume.

Soap and Catalyst (processing specification):

Production of biodiesel using an alkali catalyst always produces some amount of soap. There will be more soap with recycled restaurant waste and animal fats and less with refined vegetable oils. Catalyst and soap tend to concentrate in the glycerol phase; however, some may be found in the biodiesel phase even after the washing process. Determining the presence of soap and catalyst can be useful to know the amount of soap formed, where the catalyst resides, and how effective the washing process is in removing these two compounds. No ASTM requirement.

Free Fatty Acids (processing specification):

The greatest difference among the choice of fats and oils for feedstock is the amount of free fatty acids (FFA) that are associated with the triglycerides. Most vegetable oils have a low percentage of associated free fatty acids, while animal tallows and yellow grease can have as much as 15 percent. Some recovered waste materials can have in excess of 40 percent free fatty acid content. The amount of the FFA content affects the amount and extent of feedstock preparation necessary to use particular reaction chemistry. Early characterization of feedstock can be used to optimize process controls to ensure the correct amount of reagent and catalyst material necessary to support complete production reactions. No ASTM requirement.