| dc.description.abstract | In order to improve mass transfer rate and efficiently employ energy in liquid-liquid contacting processes, especially in biodiesel production through transesterification, two process intensification technologies were addressed based on two different energy sources and were investigated in this dissertation. They include electrostatic liquid spraying based on electric field and a two-disc spinning disc reactor based on high gravity field. Interfacial turbulence plays an important role in electrically enhanced mass transfer. One specific aspect of this work was to investigate interfacial turbulence which can occur at the interface between two phases because of interfacial tension gradients resulting from the change of charge density across droplet surface. Firstly, a Schlieren optical technique was developed and the experimental setup was built for the visualization of electrically induced interfacial phenomena in the ethanol-water-1-decanol system. Two Schlieren cells were designed and fabricated, and were successfully used for the interrogation of interfacial disturbances in pendant droplets and at plane interfaces. The mechanism of interfacial turbulence was further understood by study of these Schlieren images. Additionally, interfacial mass transfer in the ethanol-water-1-decanol system was investigated in the presence of electric fields and mass transfer coefficients were measured from the pendant droplets. Initial results show that a time-dependent nature was presented and mass transfer was intensified by the application of electric fields. As an alternative biofuel, biodiesel is produced through transesterification of vegetable oils, fat and algae lipids and alcohol with the help of acid or base. Transesterification is a liquid-liquid two phase reaction, whose rate is limited by mass transfer between oil and alcohol due to their immiscibility. This work firstly applied electrostatic liquid-liquid contactors to improve biodiesel synthesis. The reaction rate of transesterification of canola oil with sodium methoxide was investigated in the plane interface contactor. A fourfold enhancement was observed at an applied voltage of 10kV DC. A compact electrostatic spraying reactor based on simple tubular geometry with horizontal injection of an electrostatic spray of sodium methoxide was developed to achieve continuous biodiesel production. Preliminary data demonstrate it is a promising technology. A novel two-disc spinning disc reactor was developed as another alternative for biodiesel synthesis. It comprises two flat discs, located coaxially and parallel to each other with a very small gap between the discs. A grooved rotating disc was integrated to increase residence time allowing relatively slow transesterification reaction to be as complete as possible. The reaction performance was investigated widely. The conversion achieved in the reactor was significantly influenced by the size of inter-disc gap, the rotational speed, the canola oil phase flowrate, the surface topography of the rotating disc, and the reaction temperature. The experimental conditions were optimized. Finally, the new reactor was also compared with the stirred tank reactor according to the data of conversion rates and droplet size distribution of the emulsions. | |
