Biodiesel Analysis with Mid Infrared - From Feedstock to Fuel

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Courtesy of Spectro Scientific


The biofuels industry is growing rapidly and so is the need for analysis to ensure quality product. The parameters for quality biodiesel require different types of instruments and measurement systems, such as gas chromatographs (GC), titrators, centrifuges, infrared spectrometers... Although claims are out there for the analyzer that will do it all, unfortunately there is no one instrument, or even type of instrument, that can make all the measurements to ensure product quality.

The bottom line is bad product can cause problems in a diesel engine such as filter plugging and injector coking. These problems have made engine manufacturers wary of extending warrantees to high ratios of biofuels. Product quality begins at the production facility and extends to the final burn in the engine. Some of these analyses are for process control or quality verification and can be done with quick and simple verification tests while others require a more complete test according to the ASTM or EN approved methods. Many crucial measurements can be performed by mid-infrared (IR) analysis. These measurements include free fatty acids and water in the incoming feedstock, total glycerin during transesterification in production, to measuring blend ratios (biodiesel in diesel or ethanol in gasoline) and contamination of the finished fuel on the distribution end.

The Production Facility

There are three areas where analysis is useful or necessary in the production of biodiesel, testing incoming feed stock, monitoring the reaction process and verifying the quality of the finished product.

Incoming Feed Stock

Biodiesel is typically made from animal fats or vegetable oils that are chemically reacted with an alcohol (methanol or ethanol) and a catalyst (sodium or potassium hydroxide) to produce an ester or biodiesel. The process is called transesterification. Knowing the amount of Free Fatty Acid (FFA) and water in the incoming feedstock helps the producer to adjust the amount of alcohol and catalyst for a complete reaction. FFA’s in oil react with the alkaline catalyst to form soap and can cause a reduction in yield. Water deactivates the catalyst.

FFA and water measurements are for the producer and do not need to be approved methods. The approved method is a non-aqueous potentiometric acid-base titration to determine the acid number. Moisture is typically measured by Karl Fischer Titration. Both of these analyses can also be done with infrared spectroscopy. Water can be extracted from the biodiesel with acetonitrile and measured in the 6 micron region. Measuring FFA involves adding a weak base to form a salt whose carbonyl absorption band is shifted away from that of the biodiesel ester. Even with sample preparation, either measurement takes under 5 minutes and does not require a skilled technician.

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