In this study, Zeolite ANA and CAN are adopted to catalyze transesterification of acidic vegetable oils for biodiesel production. Zeolite ANA and CAN are synthesized via hydrothermal processes by using diatomite as a raw material with an addition of proper alumina at 150 °C and 170°C for a certain duration. Various instruments such as XRD, SEM, FTIR and TPD are employed to characterize these zeolite catalysts. Process variables such as catalyst-to-oil, methanol-to-oil ratio, operation temperature are studied in order to optimize the reaction conditions.
Biodiesel is successfully produced via transesterification by using Zeolite ANA and CAN under appropriate conditions. As a consequence, a high yield above 90% from triolein / soybean oils to biodiesel can be achieved after a period of reaction time. Furthermore, both the spent Zeolite ANA and CAN could be regenerated with Na+-impregnation and exhibited even better catalysis. However, in presence of free fatty acids, such as oleic acid in triglycerides, the yields decrease significantly. Therefore, a two-stage reaction strategy is adopted to process the acidic vegetable oils. (1) Zeolite ANA and CAN in H-form are firstly employed to esterify the oleic acid in feed oil and, subsequently, (2) transesterification of the remaining oils proceeds with the as-prepared zeolite ANA and CAN (in base form). A yield as high as ca. 90% is achieved with soybean oil having 2 wt% oleic acid (3.97 mg KOH / g oil) as the feed oil, zeolite ANA as the catalyst, and the reaction time with 3 h for esterification and 2h for transesterification.