For the biodiesel producer, measurement of Free and Total Glycerin is critical. Analysis is performed in accordance with ASTM D6584. Free glycerin (or glycerol as it is sometimes referred) is the major co-product of the biodiesel production process when the transesterification reaction has proceeded to completion or near-completion. Typically glycerin is separated from the methyl (or ethyl) esters. If inadequate separation of glycerin occurs, the free glycerin component will be detected during the D6584 analysis. If the oil is not well-reacted, evidence of triglycerides will be indicated in the analysis. Additionally, detection of diglycerides and monoglycerides suggests an incomplete reaction.
ASTM D6751 Requirement: a maximum for free glycerin of 0.020% mass and a maximum for total glycerin of 0.240% mass. There is a maximum 0.40% mass Monoglyceride requirement to qualify as a Grade No. 1B biodiesel (a Cold Soak Filtration Time of less than 200 seconds as well as passing results for the remaining ASTM D6751 analyses is required for a No. 1B designation).