Monounsaturation effects on low temperature fluidity of ester derivatives

Camelina and Crambe crops are potential sources for medium-chain fatty acids (MCFA) from C8 to C14, which represent an important feedstock for specialty oleochemicals. Their oils can also find utilization as lubricants after conversion into esters, if appropriate viscosity is achieved with good fluidity at low temperatures, usually measured as pour point. While MCFA esters might have fluidity problems, cis-double bonds can reduce pour pt. [1] The most abundant fatty acid (FA) in Camelina oil is gondoic (i.e. 11-eicosenoic a.), while Crambe oil contains up to 60 % erucic a. (i.e. 13-docosenoic a.). Initially dibasic esters with MCFA and oleic a. were synthesized, see Fig. 1, using a previously established method [2] with two major types of polyhydric alcohol derivatives: 1) H-containing β-carbon polyol with R=H in Fig. 1 and 2) tertiary β-carbon polyol. Additional branched moieties were also attached as R’ for better fluidity. Kinematic viscosities were measured at 40 °C using Cannon-Fenske method (ASTM D455) and in some cases estimated from structural data. Pour pt. was measured under the same thermal cooling regime as in ASTM D97, just in smaller sample sizes.

Oleates clearly show that higher mol. weight increases viscosity. Since FA moieties were linear, MCFA esters with viscosities over 20 mm²/s could not retain fluidity at -30 °C. However, oleates approached 35 mm²/s viscosity with better pour pt. and showed a remarkable tendency to retain fluidity around -30 °C (with tertiary β-carbon) or -25 °C (when R=H) despite variation of R’ moieties. Further synthesis with gondoic and erucic esters can give even more flexibility in achieving needed viscosities and lead to broader industrial viability of Camelina and Crambe crops.