Optimization of bio-diesel production from oils, cooking oils, microalgae, and castor and jatropha seeds: probing various heating sources and catalysts

The optimization of bio-diesel production depends on numerous parameters such as renewable biological triglyceride sources, type of catalyst and alcohol for the transesterification reaction, molar ratio of oil-alcohol, and heating sources. In this review we will highlight the use of microwave (MW) radiation for bio-diesel production and its advantage over other heating sources, starting with a comparison between the two-stage method consisting of oil extraction (the first step) and bio-diesel production by transesterification (the second step), with a one-stage method that provides direct transesterification of a feed-stock without the extraction step. A comparison will be made for the one and two-stage methods performed under microwave heating, sonication, and reflux using SrO, KOH, and NaOH catalysts for bio-diesel production. The various feed-stocks reviewed in this perspective are triolein, soybean oil, microalgae biomass of Nannochloropsis, and castor and jatropha seeds. The extension of the microwave-heating methodology to continuous-flow processing has been used to scale up the reaction. Moreover, the presented continuous-flow bio-diesel preparation is done via a novel laminar flow reactor-separator. This instrument not only enables to scale up the reaction, but also allows glycerol as a byproduct to phase separate and settle from the reacting flow.