Modelling of a vibrating-plate extraction column.

Abstract

Liquid extraction, sometimes called solvent extraction, is the separation of the constituents of a liquid solution by contact with another insoluble liquid. It belongs to the class of countercurrent diffusional separation processes, where it ranks second in importance to distillation. There are many different types of columns that are available for liquid-liquid extraction and the reciprocating column (RPC) and vibrating plate column (VPE) are two types of mechanically aided columns. This research aims at developing a mathematical model for the prediction of NTUIHETS and the mass transfer coefficient, k-ox for the VPE based on the agitation level of the plates (af- the product of frequency and amplitude of the plate motion), the plate spacing and the flow rates which will allow for the simplification in the design of this type of column. There is a lot of research that has gone into the development of mechanically aided extraction columns but it is limited when it comes to the RPC and VPE and most of this research is devoted to the RPC. The system chosen is the acetone-toluene-water system with the acetone in toluene forming the feed that is dispersed in the column as it moves upward while the water moves as a continuous phase down the column. Experiments were conducted to evaluate the hydrodynamics of the droplets moving up the column (in terms of drop sizes, size distribution and dispersed phase holdup) and to evaluate the mass transfer that occurs (in order to evaluate NTU, HTU and k-ox) as well as the effect of mass transfer on the hydrodynamics of the system while varying the agitation levels and spacing of the plates in the column. Successful models were developed using some of the experimental data and these correlations were verified with additional data.