Biodiesel production from coconut oil in supercritical methanol in the presence of cosolvent

The transesterification of coconut oil with supercritical methanol in the presence of cosolvent was carried out in a batch autoclave for production of biodiesel. The transesterification was found to be catalyzed by the surface of the autoclave. However, the catalytic activity of the autoclave dropped with great extent after a certain period of time. A 1.5 M oxalic acidic solution could be used to wash the surface to restore the catalytic activity of the autoclave. From the measured yields of biodiesel in a period of 20 min, ether was found to be the most effective cosolvent among eight cosolvents tested in this study. The effects of temperature, pressure, molar ratio of methanol to coconut oil, and molar ratio of methanol to cosolvent on methyl esters yield using ether as the cosolvent were examined. A temperature at least 30 °C higher than the critical temperature of methanol is essential for obtaining high biodiesel yield. The yield was also found to increase with increasing pressure, however, the extent of increase was reduced when the pressure was higher than 14 MPa. The most appropriate molar ratios of methanol to coconut oil and to ether were found to be 30/1/3. These molar ratios were observed invariant when CO2 instead of ether was used as the cosolvent.

► Various cosolvents were examined in supercritical methanol transesterification.
► Ether was found to be an effective coslovent in transesterification of coconut oil.
► Temperature above critical point is essential for obtaining high biodiesel yield.
► The 316 stainless steel was found to catalyze the transesterification.