Washing with immiscible liquids - Equilibrium, limitations and opportunities

M. Burisch, U.A. Peuker*, Technical University Bergakademie Freiberg, Germany

The washing of filter cakes represents a central part of material treatment and purification in science, research, and industry. A complete separation from solid, especially regarding fine particles, and fluid phase only through mechanical forces is not possible due to the interaction effects in two-component systems. The displacement washing aims at removing residues or at recovering the target liquid.
Washing is affected by a number of factors such as density, shape, surface, and particle size distribution of the solid material, viscosity and density of the fluid or fluid-solid interactions. Recent literature does not investigate the impact of wetting properties between both phases as separately. When changing the wetting properties of the solid system certain characteristics are considered more important, for example particle size or shape. Especially throughout the flushing of a filter cake the wetting behavior has a great impact on the purification process.

The replacement of the pore liquid with a chemically different washing liquid implies the rewetting of the solid phase. In this step, the physisorption at the pore walls is crucial for the efficiency of the pore fluid discharge with the washing stream. In case of poor wetting between the washing liquid and the solid phase, a sufficient purity cannot be achieved. An idealized particle system with tailored wetting properties offers the opportunity to investigate exclusively the impact of wetting effects. By using different silanes the particles were coated while other granulometric properties remained consistently. The interfacial properties are characterized by means of a converted contact angle measurements in liquid atmosphere and are put in context with the process yield and various parameters. To achieve comparable filter cake structures one solid material is used throughout the analysis.

Due to the immiscibility of the fluids a liquid-liquid phase boundary develops and thus a second liquid is able to replace the fluid. As a result...

Session: L3 - Cake Filtration II - Washing and Multicomponent Separation
Day: 11 October 2016
Time: 14:45 - 16:00 h