Spectro Scientific

InfraSpec VFA-IR Spectrometer for Biodiesel Blend Measurements


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Simple, yet powerful, filter-based IR spectrometers are ideal for compliance to the new ASTM 7861 test method for accurately measuring biodiesel blend ratios. The Wilks InfraSpec analyzer was the instrument used to develop and validate this method and thus is the industry standard for field measurement of FAME (Fatty Acid Methyl Ester) blend percentages.

Biodiesel is a common fuel commodity that is primarily used as a blending component with diesel fuel. It is important for fuel terminals and distributors as well as regulatory agencies to check the concentration of biodiesel in the diesel fuel in order to make sure it is within the allowable limits. Diesel fuel with too little biodiesel will not meet renewable fuel standards, and fuel with too much biodiesel may cause engine failures.

There is a need for a simple on-site measurement of biodiesel concentration that can be conducted by non-technical users in the field. The most widely accepted methods for analyzing biodiesel in diesel are ASTM D7371 and EN14078, but these methods require an FTIR spectrometer which is expensive, complex and better suited for laboratory use. With Wilks’ InfraSpec analyzers, and the recent passage of ASTM D7861, you can now make these important measurements in the field with rugged, easy-to-use instrumentation that provides answers on the spot rather than waiting for laboratory results.

The InfraSpec VFA-IR Spectrometer for Biodiesel Blend Measurements:

The InfraSpec VFA-IR Spectrometer is a portable infrared analyzer that provides on-site analysis of biodiesel in diesel in less than a minute. Weighing less than 5 lbs. including the rechargeable battery, the system may be on the move for a full shift before requiring a recharge. The InfraSpec VFA-IR is highly reliable and simple to operate, making it ideal where a single, repetitive percent biodiesel in diesel test is needed.

As shown in the schematic, the system uses a patented design consisting of an Attenuated Total Reflection (ATR) sample plate with an electronically modulated source on one end. At the other end of the ATR window is a linear variable filter (LVF) covering a wavelength range of 5.4-10.8 μm (1850-925 cm-1) combined with a 128 pixel detector array. The result is an infrared analyzer that, unlike an FTIR spectrometer, has no moving parts and an insignificant optical air path. This makes for a portable, rugged analyzer suitable for use in a production or field environment. The InfraSpec VFA-IR Spectrometer has a simplified PC interface for non-technically trained personnel as well as complete data and spectral information that can be transmitted to laboratory technicians for review if necessary.

Compliance with ASTM D7861:
The ASTM method D7861 was written in order to give fuel terminals/distributors and regulatory agencies a field test method for measuring biodiesel in diesel. The InfraSpec VFA-IR Spectrometer fully complies with ASTM D7861 and was the primary instrument used to develop the precision statement for the method. There were a total of 27 independently developed samples of varying biodiesel content (1 – 30%) measured on each of twelve spectrometers. The samples contained one of three types of biodiesel (soy, canola, waste vegetable oil) and one of three diesel fuels which differed in aromatic content. The samples were run three times on each instrument and the results sent to an independent, statistician for analysis. The calculated repeatability and reproducibility compared favorably with that of D7371. Differences in the biodiesel type or diesel type had no significant effect on the calculated repeatability and reproducibility. Also, the data showed no significant differences in accuracy between biodiesel types.

Comparison to D7371 and EN14078:
Each sample was measured by an independent laboratory using an FTIR for ASTM D7371 and EN14078 and the InfraSpec VFA-IR Spectrometer. The results from the Infra-Spec VFA-IR Spectrometer show a good correlation to the two FTIR methods with an r2 greater than 0.999.

The InfraSpec VFA-IR Spectrometer is an easy-to-use, rugged, and portable solution for the measurement of biodiesel in diesel. Repeatable results can be obtained in under a minute making the InfraSpec the ideal instrument for on-site measurements. Compliance with ASTM D7861 and high correlation to ASTM D7371 and EN 14078 make the InfraSpec an excellent alternative to more expensive FTIRs.

Benefits include:

  • Compliance with ASTM D7861
  • Compares to ASTM D7371 and EN 14078
  • Suitable for fuel loading areas
  • Results in less than 1 minute
  • Used by fuel terminals, blenders and regulatory agencies

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