Biodiesel synthesis in an intensified spinning disk reactor

Abstract

In this paper we describe an innovation for the intensified synthesis of biodiesel, exploiting a two-disk spinning disk reactor. The reactor comprises two flat disks, located coaxially and parallel to each other with a small gap between the disks. The upper disk is located on a rotating shaft while the lower disk is stationary. The feed liquids are introduced coaxially along the center line of each disk, with mixing commencing in the center of the inter-disk gap. The mixed phases flow radially outwards for ejection and coalescence on the inner containment wall of the reactor. Performance results in the reactor for the continuous synthesis of biodiesel from canola oil and methanol in the presence of a sodium hydroxide catalyst are presented. The effects of disk speed, volumetric flowrate, temperature, disk design, and the gap width between the two disks in the reactor were evaluated. The results show potentially a 20–40-fold decrease in residence time for the attainment of equilibrium compared with that determined for a stirred batch reactor used as a “control”. The mathematical modeling of the fluid flow conditions in the reactor is described. This provides further understanding of the potential importance of mixing in determining the reactor performance, pointing to some explanation of the relationship between conversion, flowrate, disk speed and geometry. The inter-disk gap, the reaction temperature, and the surface topology of the disks were the most important factors influencing reactor performance. Surprisingly, reactor performance increased as the inter-disk gap width was reduced. The results of the simulations gave an accurate fit with the experimental reactor performance data using true rate constants which were significantly higher than those reported in the literature. This suggests that some literature data may have not taken full account of mass transfer limitation during experimental determination of rate constants for biodiesel synthesis.