A review on biodiesel production using various heterogeneous nanocatalysts: Operation mechanisms and performances

Abstract

Due to food shortages and increasing fuel prices, scientists are trying to find suitable feedstocks for biodiesel production that do not divert food products to bioenergy. Although many edible oils may be cheaper feedstocks for biodiesel production, they may not be a sustainable source to meet this growing demand. This justifies the need to use non-edible oils, which can be a reliable sustainable oil source for biodiesel production. In this review paper, the effect of several factors was studied on biodiesel production, including different types of nanocatalysts, reusability of nanocatalysts, type of feedstock, and oil content in the feedstock. Also, the reaction mechanism of biodiesel generation using heterogeneous catalysts was thoroughly studied. Moreover, the physical properties of biodiesel produced by various nanocatalysts and its process flow diagram were investigated. The findings reveal that the use of low-cost nanocatalysts such as CaO instead of homogeneous catalysts can reduce the cost of biodiesel generation because the washing step in the biodiesel production process is eliminated. Also, several nanocatalysts like Li/ZnO–Fe3O4, CaO/MgO, SO4/Mg–Al–Fe3O4, nanocrystalline CaO, Sr–Al double oxides, SO4/Mg–Al–Fe3O4, CaO/Al/Fe3O4 and nano-sulfated zirconia have shown significant biodiesel yields (above 98%). Moreover, non-edible oils like jojoba and Schizochytrium sp. microalgae can be used as suitable feedstocks for biodiesel production because they have a high oil content and are not used by humans. In general, nano-catalysts can be suitable alternatives to homogeneous catalysts due to their unique features such as high specific surface area, high reusability, high reactivity, high biodiesel yield, and environmentally friendly.