Optimization of methyl ester production from waste cooking oil in a batch tri-orifice oscillatory baffled reactor

- RSM successfully modeled and optimized biodiesel production in a tri-orifice OBR.
- The reaction yield is only dependent on oscillation frequency and reaction temperature.
- The reaction yield is hardly dependent on the inter-baffle spacing.

Transesterification of vegetable oils is a common route for the production of biodiesel. This reaction is a slow mass transfer limited reaction that has been shown to benefit from process intensification reactors such as the Oscillatory Baffled Reactor (OBR). The use of waste cooking oil as a resource is an attractive alternative to other virgin vegetable oils that will enable the capital costs of biodiesel production to be largely decreased, thereby making biodiesel an affordable and competitive fuel. In this study, optimization of biodiesel, or fatty acid methyl ester (FAME) production from waste cooking oil (WCO) was investigated using a batch OBR (diameter = 0.06 m, height = 0.55 m) with multi-orifice baffles, which have been recommended for scale-up. Response Surface Methodology (RSM) was applied to study the effects and interaction of different operating parameters: oscillation frequency (in the range 2.4-4.9 Hz), inter-baffle spacing (in the range 0.05-0.09 m) and reaction temperature (in the range 40-60 °C). It was found that temperature is the main factor influencing reaction yield and the interaction between temperature and oscillation frequency is non-negligible. Inter-baffle spacing does not, however, have a significant effect on the reaction. This is different from the design recommendations of OBRs in the literature, which were originally developed for single orifice baffles. An optimal reaction yield of 81.9% was obtained with an oscillation frequency of 4.1 Hz and an inter-baffle spacing of 5 cm (i.e. approximately 1.5de) at a temperature of 60 °C. However, similar reaction yields could be obtained for different values of inter-baffle spacing.