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Methyl esters from vegetable oils with hydroxy fatty acids: Comparison of lesquerella and castor methyl esters

Knothe, Gerhard, Cermak, Steven C., Evangelista, Roque L.
Fuel 2012 v.96 pp. 535
Lesquerella, Ricinus communis, biodiesel, castor oil, esters, glycerol, nuclear magnetic resonance spectroscopy, oxidative stability, ricinoleic acid, sulfur, vegetable oil, viscosity
The search for alternative feedstocks for biodiesel as a partial replacement for petrodiesel has recently extended to castor oil. In this work, the castor oil methyl esters were prepared and their properties determined in comparison to the methyl esters of lesquerella oil, which, in turn, is seen as an alternative to castor oil. Both oils contain high amounts of hydroxy fatty acids, castor oil containing ricinoleic acid, lesquerella oil containing lesquerolic acid as C₂₀ homolog of ricinoleic acid. Lesquerella oil, however, contains higher amounts of conventional C₁₈ fatty acids than castor oil. The methyl esters of lesquerella oil exhibit a higher cetane number (45. 6 vs. 37.55) and lower kinematic viscosity (11.22 vs. 14.82 mm²/s) than the methyl esters of castor oil, both values for lesquerella methyl esters being closer to specifications in biodiesel standards, while oxidative stability of castor methyl esters is higher although this issue appears complex. Both lesquerella and castor oil methyl esters do not meet biodiesel standards requirements in terms of cetane number, kinematic viscosity, and density. Overall, however, lesquerella methyl esters appear to have more favorable fuel properties than castor methyl esters although sulfur content is elevated. Both lesquerella and castor methyl esters have a greater tendency to exceed free glycerol and water specifications in biodiesel standards. The ¹H and ¹³C NMR spectra of lesquerella methyl esters are reported.