Continuous biodiesel production using canola oil and supercritical methanol with the aid of CaO/carbon nanotube catalyst

Abstract

A catalyst can improve the rate of supercritical transesterification, thereby reducing the construction costs of the reactor. Although calcium oxide (CaO) is an effective catalyst, it has low stability and requires a support structure. Multiwall carbon nanotubes (MWCNTs) have high porosity, large specific surface area, and high tensile strength, and could serve as support structures. Therefore, this study elucidated the effectiveness of a CaO-impregnated MWCNT catalyst in accelerating the supercritical transesterification process. A 40 wt% of CaO was the optimal concentration for impregnation onto CNTs for transesterification in supercritical methanol under the following conditions: 300 °C, 20 MPa, methanol to oil molar ratio of 40:1, WHSV of 100 h⁻¹. The fatty acid methyl esters yield of the supercritical methanol transesterification process reached 1.0 under these conditions; additionally, the yield was maintained for 6 h. The reaction was well described by the first-order reaction rate of the homogeneous and heterogeneous reactions.