Esterification of Jatropha Oil with Isopropanol via Ultrasonic Irradiation

The reduction of high acid value (AV) of inedible jatropha oil (JO) by esterification with isopropanol (IPA), which is a common alcohol solvent waste in Taiwan’s high-tech industry, was studied. The decrease of AV is beneficial for the subsequent transesterification to produce JO biodiesel (i.e., biodiesel of fatty acid isopropyl ester (FAIE)). Acid catalyst (H 2 SO 4 ) and a novel mixing/emulsion technique using ultrasound irradiation (UI) were applied to promote and facilitate the esterification process. The results showed that increased IPA/oil molar ratio (M IOE ) can significantly reduce the AV, kinematic viscosity (KV), density (ρ LO ), and water content (M W ) of esterified JO, while also providing the benefit of enhancing the yield (Y F ) of biodiesel of FAIE. For example, with M IOE = 5 at esterification temperature (T E ) = 394.2 K (393.8–394.7 K), a reduction of AV of 99.25% with Y F of 67.15% can be achieved. Free fatty acid (FFA) was reduced from 18.06 wt.% to 0.14 wt.%, indicating 17.92 wt.% out of 18.06 wt.% of FFA was esterified to FAIE. As a result, among the Y F of 67.15%, 49.23% (= 67.15 wt.% deducting 17.92 wt.%) was contributed by the transesterification of triglycerides. By esterification of high FFA-containing raw JO with acid catalyst, one can not only avoid saponification, but also reduce the loading of the subsequent alkali-catalyzed transesterification. Moreover, increasing T E from 394.2 to 454.4 K further reduced AV (from 0.27 to 0.084 mg KOH/g) and M W (from 0.27 to 0.043 wt.%), but, on the other hand, it increased KV (from 14.62 to 25.2 mm 2 /s) and ρ LO (from 901.6 to 913.3 kg/m 3 ), while it decreased Y F (from 67.15 to 25.84%). In sum, IPA was successfully used as a replacement for methanol in the esterification of JO while UI provided mixing/emulsion along with heating resulting from cavitation for the system.