The effect of branched-chain fatty acid alkyl esters (BCAE) on the cold-flow properties of biodiesel

Authors: Dunn, Robert - Bob; Wyatt, Victor; Wagner, Karen; Ngo, Helen; Hums, Megan

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2019
Publication Date: 6/10/2019
Citation: Dunn, R.O., Wyatt, V.T., Wagner, K., Lew, H.N., Hums, M.E. 2019. The effect of branched-chain fatty acid alkyl esters (BCAE) on the cold-flow properties of biodiesel. Journal of the American Oil Chemists' Society. 96(7):805-823. https://doi.org/10.1002/aocs.12226.
DOI: https://doi.org/10.1002/aocs.12226

Interpretive Summary: This research contributes to the development of new biodiesel cold flow additives from fatty derivatives. Biodiesel is an alternative fuel for compression-ignition engines that is made from animal fat, vegetable oils and waste greases (FOGs). It has cold flow properties that cause it to gel and plug fuel systems at higher temperatures than conventional diesel fuel (petrodiesel). Additives are the most cost-effective means to improve the cold flow properties of biodiesel from FOGs. This study examined new compounds synthesized from oleic acid that can be blended with low quality biodiesel with especially poor cold flow properties. These compounds have specialized chemical structures that modify the temperature where biodiesel begins to form solid particles (the cloud point). The synthesized additives, termed “BCAEs”, were shown to decrease the cloud point and other cold flow properties of biodiesel made from lard, tallow and sewage scum grease. This research will directly benefit scientists and engineers working to develop additives that improve the cold flow properties and other performance factors related to biodiesel.

Technical 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 (v40 = 40°C) and low temperatures (TL) = CP + 5°C (vL). Although the BCAE additives were more effective than SME, relatively large additive concentrations (y[Add]) were needed to decrease CP and PP by more than 2°C. Admixtures with high concentrations of BCAE additive had v40 > 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 y[Add] = 0.50, 2EH-iOL should not exceed y[Add] = 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.