Investigation of the effects of the process and equipment parameters on the separation efficiency of a vibrating plate extractor.

Abstract

In the industrial world where many different types of separation processes are available, liquid-liquid extraction is gaining increasing attention, since it offers many advantages over distillation especially for heat sensitive and azeotropic compounds. Liquid-liquid extraction is an essential separation method that applies to the chemical, petroleum, metallurgy, biotechnology, nuclear and waste management related industries. This separation technique also offers potential means of saving energy, thus making extraction a more economical separation process. The effectiveness of a vibrating plate extractor was previously investigated however limited research was conducted on the effect of tray spacing, solvent-to-feed ratio and agitation level on a vibrating plate extraction column. These parameters affect the hydrodynamics and mass transfer in a vibrating plate extraction column therefore the determination of the optimum process parameters is important in achieving the highest efficiency for the column and this is sought after for a vibrating plate extractor. A toluene-acetone-water system was selected for experimental work to be conducted on the vibrating plate extraction column. This test system for liquid-liquid extraction is a standard system proposed by the European Federation of Chemical Engineering. The research aimed at testing the effect of tray spacing, agitation level (product of amplitude and frequency of vibration), and the ratio of flow rates of the phases on the number of stages in order to optimise the efficiency of a vibrating plate extraction column. For the hydrodynamic experiments the dispersed phase holdup, drop size distribution and Sauter mean diameter were evaluated for varying parameters. For the mass transfer experiments the percentage acetone extracted, number of equilibrium stages, mass transfer coefficient and overall efficiency were determined as well as the dispersed phase holdup, drop size distribution and the Sauter mean diameter for varying parameters. A decrease in the holdup occurred for an increase in the solvent-to-feed ratio and an increase in the agitation level resulted in a decrease in the Sauter mean diameter. Results indicated that lower tray spacing resulted in a higher extraction of acetone. Backmixing in the dispersed phase resulted in higher number of stages.