Displacement washing of porous particles

S. Heinisch*, U.A. Peuker, Technical University Bergakademie Freiberg, Germany

Cake filtration is a common process to separate solids from liquids both in the laboratory and in industrial production processes. After the filtration process, the filter cake remains with its pore liquid. Often it is necessary either to clean the bulk material (filter cake) as good as possible or to regain most of the substances that are soluted in the pore liquid. Therefore, a filter cake washing has to be applied right after the filtration. While there has been lot of research to determine the washing behaviour of compact non-porous particles, washing of particles with inner porosity is a challenging task. Examples for those materials are ion exchangers, materials for chromatography or catalyst carriers. The objective of this work is to compare the cleaning of porous particles by washing them with different mass flows.

As a porous particle system, silica gel with a pore diameter of 100 nm was chosen for experiments. Mercury intrusion porosimetry is used to determine the pore size distribution and total pore volume of silica gel particles. For filtration and filter cake washing experiments, first a suspension of silica gel and water containing potassium chloride as a model impurity is prepared. The filtration of the suspension is performed in a pressure filter device. After adding a perforated piston onto the cake, the washing can be performed subsequently with deionized water. Samples of the fluid collected in several intervals are analysed by optical emission spectroscopy to determine the potassium concentration. Washing curves are used to evaluate the washing process. Taking in account porous particles it is assumed that the diffusion stage of the washing curves will give important information about the cleaning effect. The reason for that is that impurities will have to diffuse out of the inner pores of the particles and cannot be washed by displacing the pore liquid with washing liquid only. First results show that ....

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