Comparison of infrared biodiesel measurement methods - An overview of ASTM-approved methods and those under consideration

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Courtesy of Spectro Scientific

There are several options for measuring the amount of biodie-sel in diesel fuel. Methods EN 14078 and AS'lTvI D7371 are more amenable to laboratory testing although wailing for an off-site laboratory to perform the test can take several hours to several days. For a driver whose truck has just been loaded for a delivery, any wail is too long. Other options for more simplified on-site testing that will track iht official methods are available for those who need a quick verification check of the blend accuracy.

Official Biodiesel Methods

As biodiesel's presence in rhe marketplace increased over the past 10 years, standards tor verifying die amount of biodiesel blended into diescl fuel were needed. The first standard, which came one in November 2003, was EN 14078, developed by the European Committee for Standardisation (CRN). ASTM International published a method tor biodiesel content in diesel fuel in 2007, method D7371.

Why Infrared?

Both of these methods employ mid infrared (1R) analysis as the measurement technology. Infrared is a common spectroscopic technique used for quantitative and qualitative analysis. In the biodiesel measurement, die fatty acid methyl ester (FAME) has a characteristic absorption at 1745 cm'1 (5.73 micrometers) due to the carbonyl group (see
Figure 1). Both the EN and ASTM methods specify' this wavelength for die blodiesd measurement.

EN14078 Method

EN 14078 uses a transmission sampling ceil typically with a 0.5 mm patfilength cell. The cell is filled with the biodicsel/diesel mix, then the TR light passes directly through die fluid and the amount of light absorbed by the biod-icsel in the sample is measured (see Figure 2). The absorbance increases and decreases with die biodiesel concentration so the 1R absorbance can be correlated with a concentration in percent.

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