The Effect of Branched-Chain Fatty Acid Alkyl Esters on the Cold-Flow Properties of Biodiesel |
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Authors: | Robert O. Dunn Victor T. Wyatt Karen Wagner Helen Ngo Megan E. Hums |
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Affiliation: | 1. United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural Research and Utilization, Peoria, IL 61604, USA;2. United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Wyndmoor, PA 19038, USA |
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Abstract: | Biodiesel (fatty acid methyl esters [FAME]) is produced from various fats, oils, and greases (FOG) using catalytic transesterification with methanol. These fuels have poor cold-flow properties depending on the fatty acid (FA) composition of the parent FOG. Improving the cold-flow properties of biodiesel will enhance its prospects for use during cooler months in moderate temperature climates. This work is a study on the use of skeletally branched-chain alkyl esters (BCAE) composed of the isopropyl, n-butyl, and 2-ethylhexyl esters of iso-oleic acid isomers (iPr-iOL, nBu-iOL, and 2EH-iOL). These BCAE additives were tested in blends with linear-FAME (L-FAME) derived from soybean oil (SME), lard (LME), tallow (TME), and sewage scum grease (SGME). Binary L-FAME/SME admixtures were also studied. Admixtures were tested for the effects of the additives on cloud point (CP), pour point (PP), and kinematic viscosities at standard (ν40 = 40 °C) and low temperatures (TL) = CP + 5 °C (νL). Although the BCAE additives were more effective than SME, relatively large additive concentrations (yAdd) were needed to depress CP and PP by more than 2 °C. Admixtures with high concentrations of BCAE additive had ν40 > 6.0 mm2 s−1, the maximum limit in ASTM fuel specification D 6751. While the iPr-iOL and nBu-iOL additives may be blended at concentrations up to yAdd = 0.50, 2EH-iOL should not exceed yAdd = 0.28 in LME, 0.31 in SGME, 0.35 in TME, or 0.41 in SME to avoid driving the admixture out of specification. Some anomalies observed in the results at low yAdd for SGME/BCAE admixtures were speculated to have been affected by the low-temperature rheology of SGME. |
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Keywords: | Admixture Branched-chain alkyl esters Cloud point Kinematic viscosity Additive mass fraction Pour point |
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