Spectro Scientific

Biodiesel Analysis With Portable Midinfrared Analyzers

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Courtesy of Spectro Scientific

Biodiesel sales in the U.S. increased from 75 million gallons in 2005 to 250 million gallons in 2006. As ol September 2007, 165 companies arc producing biodiesel and 85 plants are under construction- Along with this rapid growth in production is the iuviI to ensure quality product* Methods fur specifications offinished biodiesel fuels include ASTM D 6751, ON 14214, and DIN 51606. The rest parameters in these methods require difterent types of instruments and measurement systems, such as gas chromatography titrators, centrifuges, and infrared spectrometers. In addition to the various required rests, there are many analyses thar are crucial tor efficient production and consistent product.

Many crucial measurements tan be performed by midinfrared analysis. These measurements include free fatty acids (FFA) and water in the incoming feedstock, total glycerin during rransesrerificarion in production, and measuring the blend ratio of biodiesel in dicsel. Relatively inexpensive filter-based infrared analyzers offer easy-to-use, portable systems to producers, distributors, engine manufacturers, fleet operators, and regulatory agencies that need quick results on site.

The Production Facility
There are two areas in which rapid midinfrared rests are useful or necessary in the production of biodiesel. One is testing the incoming feedstock tor FFA and water. The other is monitoring the total glycerides during the biodiesel reaction process. Production ol biodiesel can In-done as a batch or continuous process. A continuous process is more Suitable to a consistent feedstock. When there are variations in ilie feedstock and its quality, as found with yellow grease and animal fats, a batch process is easier to adjust to accommodate the differences in FFA and water. Pretesting the feedstock and resting the total glycende levels during transestenhcation are crucial to processes producing hiodiesel Irom various feedstocks.

Incoming Feedstock
Biodiesel is typically made from animal tats or vegetable oils that are chemically reacted with an alcohol (methanol or ethauol) and a catalyst (sodium hydroxide or potassium hydroxide) to produce an alkvl methyl esttrr or hiodiesel. The process is called Iransestcrifkal ion. Knowing the amount of FFA and water in rhc incoming feedstock helps the producer to adjust the amount of alcohol and catalyst for a complete reaction. Transesterificatlon can handle up to 4% FFA; thus feedstock oils with a higher FFA content must be pretreated to reduce the FFAs. FFAs in oil react with the alkaline catalyst to form soap. Some of the oil is removed with the soap and results in a lower methyl ester yield. Most refined seed oils are less than 5% FFA, while animal Kits range from 5 lo 50%. Ttdilr I shows some typical feedstocks anil their FFA levels. When waler levels in the feedstock are over 0.5%, the water deactivates the catalyst and inhibits rhe reaction. Yellow grease rends to vary in water content and requires analysis to ensure a complete reaction.

The approved method ior FKA analysis is a nonaqueous potentiometric acid-base titration to determine the acid number. Moisture is typically measured by Karl Fischer titration. Both are time-consuming tc-tv Because FFA and water measurements in feedstock are process control measurements and do nor need CO he approved methods, infrared analysis can he suhstituted as a quick test tor the producer. Water can he extracted from the feedstock with acetonitrile and measured in extract at 6.6 urn (1650 cm '). Measuring FFA involves adding a weak base to lorm a salt whose carKmyl ahsorp-tion hand is shifted away from that of the hiodiesel ester. Even with sample preparation, either measurement by infrared spectroscopy takes under 5 min and does not require a -skilled technician.

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