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While biodiesel is a potential alternative to diesel produced from fossil fuels, there are still barriers towards the creation of high efficiency biodiesel. The quality and performance of biodiesels are considerably influenced by their fatty acid methyl ester (FAME) content.
Fourier transform infrared (FT-IR) spectroscopy using the Pearl™ liquid transmission unit from Specac offers a fast, accurate, and easy method to establish the FAME content of biodiesel.
Global awareness of the depletion of fossil fuels and their environment has led to a search for suitable alternatives. Biodiesel, which is considered a sustainable alternative to fossil fuels, is made from cooking oil, animal fats and/or plant oils. Biodiesel is also believed to be a ‘carbon neutral’ fuel as the CO2 generated during combustion is balanced by the CO2 consumed by the plants used to produce biodiesel as they grow.
Biodiesel provides various other benefits over conventional fuels including high biodegradability, low sulfur content, low toxicity, and reduced carbon black emissions. Although biodiesel has these advantages, its uptake remains limited. Factors contributing to the limited uptake and utilization of biodiesel are: feed stock availability, governmental policy, the long-term stability of biodiesel fuels, and conversion efficiencies.
FAME Content Affects Fuel Performance
Transesterification is the process by which animal fats and plant oils are converted into biodiesel. It involves a reaction between an alcohol and the lipids in the oils to form fatty acid esters. Generally, methanol is the preferred alcohol for transesterification, as this gives the maximum conversion to biodiesel.
When the oils react with methanol, a mixture of different fatty acid methyl esters (FAME) is formed. Other fatty acid esters, including FAME, have physical characteristics that are similar to fossil fuel diesel than the oils they are produced from. Yet, there are some properties of biodiesel that can be more challenging than fossil fuel diesel; gelling at low temperatures, poor long-term stability, and foaming are all major issues encountered with FAME mixtures.
The quality and performance of diesel fuels depends on the FAME content, so all commercial diesel fuels must meet strict specifications regarding their FAME contents. For instance, EN 590 specifies that the FAME content of diesel fuel sold in Europe may not exceed 7%. It is required that biodiesel blends also meet specific standards, including containing specific FAME concentrations. Hence, measuring the FAME content of diesel fuels is a vital part of the quality control process. Reliable and accurate techniques to measure FAME content are therefore important for quality control purposes.
Measuring Biodiesel FAME Content
Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance spectroscopy, and chromatography are some of the various analytical methods by which FAME content can be assessed. FT-IR spectroscopy is certainly the most practical option for measuring the FAME content of biodiesels as it offers rapid, quantitative measurements with relatively low-cost instrumentation, little sample preparation, and simple procedures.
FT-IR spectroscopy involves transmission of infrared light through a diesel sample to be analyzed. As the light passes through the sample, light is absorbed at specific wavelengths by the molecules present in the fuel based on their chemical structure. FAME molecules absorb infrared at 1745 cm-1 because of their ester carbonyl bonds. For diesel fuels in which FAME molecules are not present, there is no infrared absorption at this wavelength. Therefore, it is possible to calculate the FAME content by measuring the absorption at 1745 cm-1.
The two standard test methods for measuring FAME in diesel blends using FT-IR are EN 14078 and ASTM D7371. In EN 14078, the fuel sample has to be diluted in hexane but involves a comparatively simple calibration procedure and offers greater sensitivity than ASTM D7371. In ASTM D7371, the measurement is conducted on a neat fuel sample. While this method requires less sample preparation and provides quick analysis, it demands a more complex calibration procedure, and the method is not suitable for quantifying FAME levels below 1%.
Irrespective of the method selected for FAME content measurement, reliable and accurate equipment must be used for analysis. Performing FT-IR measurements on viscous liquids, such as diesel samples, using conventional liquid cells can be lengthy and difficult. Using a liquid sample holder designed for viscous liquids, for example, the Pearl™ from Specac, makes FAME analysis more straightforward and easier than using traditional FT-IR equipment.
Specac’s Pearl™ is a user-friendly and robust liquid transmission accessory that is specifically designed to enable simple and repeatable FT-IR analysis of viscous liquid samples, like diesel fuels. The design of the Pearl™ also enables rapid and easy sampling and cleaning between samples. The Pearl™ minimizes the difficulty of FAME analysis, eventually saving time and money.
To sum up, FAME content analysis plays a significant role in quality control for biodiesel blends and diesel fuels. FT-IR provides the most straight-forward method of FAME analysis. The use of Specac’s Pearl™ liquid transmission accessory can make analysis even easier, increasing accuracy and speed, while cutting cost.
References and Further Reading
- ‘Biodiesel: an Alternative to Conventional Fuel’ D. Huang, H. Zhou, L. Lin, Energy Procedia, 2012.
- ‘Overview of the challenges in the production of biodiesel’ M. Meira, C. M. Quintella. M. O. Ribeiro. R. G. Silva. K. Guimarães, Biomass Conversion and Biorefinery, 2015.
- ‘Biodiesel Blends’ http://www.etipbioenergy.eu/images/fame-fact-sheet.pdf
- ‘Fuel Stability Problems Challenge FAME Biodiesel’ https://breakingenergy.com/2014/07/30/fuel-stability-problems-challenge-fame-biodiesel/
- ‘ASTM D7371 - 14 Standard Test Method for Determination of Biodiesel (Fatty Acid Methyl Esters) Content in Diesel Fuel Oil Using Mid Infrared Spectroscopy (FTIR-ATR-PLS Method)’ https://www.astm.org/Standards/D7371.htm
- ‘ASTM D7467 - 17 Standard Specification for Diesel Fuel Oil, Biodiesel Blend (B6 to B20)’ https://www.astm.org/Standards/D7467.htm
- EN 14078 Liquid petroleum products - Determination of fatty acid methyl ester (FAME) content in middle distillates - Infrared spectrometry method https://www.en-standard.eu/csn-en-14078-liquid-petroleum-products-determination-of-fatty-acid-methyl-ester-fame-content-in-middle-distillates-infrared-spectrometry-method/
- ‘Pearl | Liquid FTIR Accessory’ https://www.specac.com/en/products/ftir-acc/transmission/liquid/pearl
This information has been sourced, reviewed and adapted from materials provided by Specac.
For more information on this source, please visit Specac.