Ultrasonic Intensification To Produce Diester Biolubricants

Biolubricants synthesized from vegetable oils with oleic acid and 1,3-propanediol possess better cold flow properties and have a smaller environmental footprint than mineral-based lubricants. However, their synthesis is lengthy (>6 h) and requires temperatures above 120 °C. We applied ultrasound (US) to synthesize long-chain diesters (biolubricants): an ultrasonic horn delivered rated powers of 500 and 750 W at a frequency of 20 kHz to a solution of oleic acid and 1,3-propanediol. Amberlyst15-H esterified the acid to the diester biolubricant. US horns with powers of 750 and 500 W increased the reaction rate by factors of 2 and 1.2–1.5, respectively. A temperature of 100 °C is necessary to convert oleic acid to >50%. A partial factorial experimental design confirmed that temperature, US power, and initial molar ratio of reactants affect reaction rate and oleic acid conversion (p-value of <0.05). The 500 W horn is 17% less expensive than the 750 W horn.