Biodiesel is a promising alternative to diesel produced from fossil fuels, however barriers still exist towards the creation of high efficiency biodiesel. The fatty acid methyl ester (FAME) content of biodiesels significantly affects their quality and performance. Fourier transform infrared (FTIR) spectroscopy using the Pearl™ liquid transmission unit from Specac provides a quick, easy, and accurate method of determining the FAME content of biodiesel.
Biodiesel, made from cooking oil, animal fats and/or plant oils, is considered a sustainable alternative to fossil fuels. In addition, biodiesel is considered a ‘carbon neutral’ fuel as the CO2 produced during combustion is balanced by the CO2 consumed by the plants used to make biodiesel as they grow.
Biodiesel offers several other advantages over traditional fuels including reduced carbon black emissions, low toxicity, low sulfur content, and high biodegradability. Despite these advantages, biodiesels uptake remains limited. Governmental policy, feed stock availability, conversion efficiencies, and the long-term stability of biodiesel fuels all contribute to the limited uptake and utilization of biodiesel.
FAME Content Affects Fuel Performance
Animal fats and plant oils are converted to biodiesel using a process called transesterification, which involves reacting the lipids in the oils with an alcohol to form fatty acid esters. Typically, methanol is the alcohol of choice for transesterification, as this gives the greatest conversion to biodiesel.
Reacting the oils with methanol results in the formation of a mixture of different fatty acid methyl esters (FAME). FAME and other fatty acid esters have physical characteristics that are more similar to fossil fuel diesel than the oils they are produced from. However, some of the properties of biodiesel can be more problematic than fossil fuel diesel; foaming, poor long-term stability, and gelling at low temperatures are all significant problems encountered with FAME mixtures.
FAME content influences the quality and performance of diesel fuels, so all commercial diesel fuels must meet strict specifications regarding their FAME contents. For example, EN 590 specifies that diesel fuel sold in Europe may contain up to 7% FAME at the most. Biodiesel blends must meet also meet specific standards, including containing specific FAME concentrations. Measuring the FAME content of diesel fuels is, therefore, an important part of the quality control process. Accurate and reliable methods of measuring FAME content are therefore essential for quality control purposes.
Measuring Biodiesel FAME Content
FAME content can be measured with a number of analytical methods including chromatography, nuclear magnetic resonance spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. FTIR spectroscopy is by far the most practical option for measuring the FAME content of biodiesels as it provides quick, quantitative measurements with simple procedures, little sample preparation, and relatively low-cost instrumentation.
FTIR spectroscopy involves transmitting infrared light through a sample of the diesel to be analyzed. As the light passes through the sample, the molecules present in the fuel absorb light at specific wavelengths depending on their chemical structure. FAME molecules absorb infrared at 1745 cm-1 due to their ester carbonyl bonds. For diesel fuels that do not contain FAME molecules, there is no infrared absorption at this wavelength. Therefore, by measuring the absorption at 1745 cm-1, the FAME content of the fuel can be calculated.
There are two standard test methods for quantifying FAME in diesel blends using FTIR: ASTM D7371 and EN 14078. EN 14078 requires the fuel sample to be diluted in hexane but involves a comparatively simple calibration procedure and provides greater sensitivity than ASTM D7371. ASTM D7371 involves conducting the measurement on a neat fuel sample, so requires less sample preparation and provides rapid analysis, but a more complex calibration procedure is needed, and the method is not suitable for measuring FAME levels below 1%.
Regardless of the method selected for FAME content measurement, it is essential to use reliable and accurate equipment for analysis. Conducting FTIR measurements on viscous liquids, such as diesel samples, using traditional liquid cells can challenging and time-consuming. Using a liquid sample holder designed for viscous liquids, such as the Pearl™ from Specac, makes FAME analysis easier and more straightforward than using conventional FTIR equipment.
The Pearl™ from Specac is a liquid transmission accessory that is robust and easy to use. It is specifically designed to make conducting FTIR analysis on viscous liquid samples, like diesel fuels, simple and repeatable. The design of the Pearl™ allows for fast and easy sampling and cleaning between samples. The Pearl reduces the difficulty of FAME analysis, ultimately saving time and money.
In conclusion, FAME content analysis is an important step in quality control for diesel fuels and biodiesel blends. FTIR offers the most straight-forward method of FAME analysis. Using a liquid transmission accessory like the Pearl from Specac™ can make analysis even easier, increasing speed and accuracy, while reducing cost.