Glycerin in Biodiesel by Capillary GC Analysis
Biodiesel is much in the news today as an alternate fuel source that is safe and nontoxic. It is renewable, via farming and recycling, and is biodegradable. It is cleaner burning than petroleum-based gasolines, with virtually no sulfur and with no net carbon load to the atmosphere.
David Witkovic, Quadrex Corporation
Biodiesel is much in the news today as an alternate fuel source that is safe and nontoxic. It is renewable, via farming and recycling, and is biodegradable. It is cleaner burning than petroleum-based gasolines, with virtually no sulfur and with no net carbon load to the atmosphere.
Figure 1
Varieties include soybean oil (90% of all fuel stocks in the U.S.), rapeseed, sunflower, and palm oils, waste vegetable oil (WVO), and animal fats - lard, chicken fat, and yellow grease.
Presently, biodiesel products are used in the retail diesel fuel marketplace. Made from plant oils and animal fats through several chemical pathway mechanisms, transesterification produces fatty acid methyl esters ( F.A.M.E.) with water and glycerin as by-products. The majority of biodiesel has fatty acid methyl esters of carbon lengths from C12–C24, with an average of C18 methyl ester ( F.A.M.E.).
The formal definition of biodiesel according to the National Biodiesel Board: A fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B100 and meeting the requirements of ASTM D6751. (The B designation signifies the % of biofuel in a biodiesel and petroleum diesel blend. For instance, B10 is a 10% biodiesel and 90% petroleum diesel blend.)
ASTM Method D6751 identifies a number of standards that pure biodiesel (B100) must meet before it can serve as fuel or mixed with standard diesel oil as a blend. Such characteristics as flash point, % sulfur, and water and sediment, among others are critical.
One test of biodiesel is the measurement of glycerin content. ASTM recommends Method D6584 to analyze for glycerin in biodiesel fuel by gas chromatography. The method has been developed to insure the quality of the biodiesel fuel. Glycerin is the predominant byproduct of transesterification in free form and bonded mono-, di-, and tri-glycerides. A high glycerin content for a producer means the reaction has not gone to completion or improper amounts were used for the process. High amounts of glycerin and glycerides can leave deposits in fuel tanks, on valves, pistons, and injector nozzles clogging the fuel system.
The Method calls for GC capillary columns that can function at 400 °C or higher. Quadrex offers a 400-5HT-15-0.1F aluminum-clad fused silica column (400-5HT, 5% phenyl methyl silicone/HT, 15 m X 0.23 mm X 0.1 µm film) which satisfies the high temperature requirements of ASTM D6584.
Chromatograms courtesy of James D. Stuart, Emeritus Professor, Analytical and Environmental Chemistry, University of Connecticut, Storrs, CT 06269.
Quadrex Corporation
P.O. Box 3881, Woodbridge, CT 06525
tel. (800)275-7033
Website: www.quadrexcorp.com
