Preparation of fatty acid methyl esters from osage orange (Maclura pomifera) oil and evaluation as biodiesel

Fatty acid methyl esters were prepared in high yield by transesterification of osage orange (Maclura pomifera L.) seed oil. The crude oil was extracted using supercritical CO2 and was initially treated with mineral acid and methanol to lower its content of free fatty acids, thus rendering it amenable to homogeneous, alkali-catalyzed methanolysis. The principle components identified in osage orange methyl esters (OOMEs) were methyl linoleate (76.4%), methyl oleate (11.9%), methyl palmitate (7.0%), and methyl stearate (2.4%). As a result of the high content of methyl linoleate, OOMEs exhibited cetane number (44.9) and induction period (IP; 2.4 h) values below the ranges specified in the biodiesel standards ASTM D6751 and EN 14214. The addition of 500 ppm tert-butylhydroquinone (TBHQ) resulted in a higher IP (6.4 h) compliant with the biodiesel standards. Furthermore, the high content of methyl linoleate resulted in an iodine value (IV; 144 g of I2/100 g) in excess of the maximum limit specified in EN 14214. The acid value (AV), glycerol content, kinematic viscosity, moisture content, phosphorus content, and sulfur content of OOMEs were within the limits prescribed in ASTM D6751 and EN 14214. In addition, data collected for density, lubricity, and energy content were typical for biodiesel fuels. The cold-flow properties of OOMEs were superior to those reported for several other biodiesel fuels. Also investigated were B5 and B20 blends of OOMEs in petrodiesel, which yielded AVs, kinematic viscosities, moisture contents, sulfur contents, lubricities, and densities within the limits prescribed in the petrodiesel standards. The addition of 500 ppm TBHQ to the blends resulted in IPs above the minimum thresholds specified in ASTM D7467 and EN 590. In summary, osage orange seeds provide a low-cost, non-food, high-oil-producing feedstock suitable for production of biodiesel.