Modelling filtration processes from local filtration properties: The effect of surface properties on microcrystalline cellulose

- Compressible cake filtration was modelled using local filtration properties.
- The influence of structure and charge of particles surfaces was described.
- Charged particle surfaces increased the surface area subjected to drag.

The influence of structure and charge of particles surfaces on the cake filtration behaviour of microcrystalline cellulose was investigated. The local filtration properties were evaluated experimentally and used to model the overall filtration behaviour. At suspension conditions where the microcrystalline cellulose particles are charged, a large pressure drop was observed close to the filter medium, thereby indicating that a rate-limiting skin layer was formed. Measurements of the local solidosity of the filter cake indicated that a secondary filter cake, with a negligible filtration resistance, formed above the rate-limiting skin layer. This behaviour was not observed when the surface roughness of the particles was increased or when the surface charge of the particles was neutralised by making a change to the pH of the suspension. The filtration behaviour of particles with these surface properties was instead dominated by the formation of a compressible filter cake. Local filtration properties of compressible filter cakes determined experimentally were used to successfully model the overall filtration behaviour. The filtration model used an empirical relationship to describe the pressure dependence of the local solidosity of the filter cake along with a cell model to describe the relationship between the solidosity and the permeability of the filter cake.