Microwave-Intensified Synthesis of Biodiesel Catalyzed with Graphene Oxide

Biodiesel (BDF), the fatty acid methyl ester (FAME) derived by reaction of alcohol with carbon-neutral plant or vegetable oils, has attracted increased attention recently as an alternative to petroleum diesel. Conventional approach to BDF production employs homogeneous alkali catalysts such as NaOH and KOH, requiring complex and costly purification process. This method also generates enormous amount of wastewater, and its treatment adds up to already high production cost. In this study, the use of functional carbon-based catalyst in combination with microwave irradiation was investigated as an alternative to the conventional method. Oleic acid and rapeseed oil were used as model compounds for free fatty acids and triglycerides, respectively. The graphene oxide catalysts were prepared by the commonly used Hummers’ method, then dried and finely ground. In a typical run, pre-determined amounts of oleic acid or rapeseed oil, methanol and GO were placed in a 100-mL three-necked round flask. The flask was placed inside the microwave apparatus, then microwave power of 200~600 W was irradiated continuously for 1 to 5 min under total reflux. The obtained products were analyzed of its composition by GC-FID. The effects of parameters such as MeOH-to-feedstock ratio, microwave power, irradiation time were then investigated. The maximum conversion of oleic acid to FAME of about 99 % was obtained. The results were then compared to other intensification techniques such as the use of ultrasonic irradiation.