The influence of particle properties on cake filtration: Surface structure and surface charge

Licentiatavhandling, 2014

Solid-liquid separation is often a key process step when biomass is used as a raw material, and an energy efficient way of achieving solid-liquid separation is through cake filtration. However, many biomaterials present challenges when they are filtrated due to the formation of compressible filter cakes. The particle properties of the solid material have a large influence on the filtration operation, and the effect of particle surfaces increases with decreasing particle size. The aim of this work is to improve understanding of how particle surfaces affect the filtration behaviour of a suspension. The effect of the surface structure of particles, which was modified through mechanical shearing, was studied using microcrystalline cellulose. The effect of the surface charge of particles was investigated using titanium dioxide and the electrostatic particle interactions were controlled through the ionic strength of the suspension. It was found that the surface structure of particles did not significantly affect the solid content of the filter cakes formed, but rather the flow behaviour around individual particles. A rugged particle surface increases the specific surface area that is subjected to drag forces, so the specific filtration resistance of microcrystalline cellulose was found to increase for uneven particle surfaces. The dominating effect of the surface charge of particles was found to be related to the agglomeration of particles. A more porous cake structure was formed from agglomerating titanium dioxide systems, giving an increased compressibility of the filter cake. The filtration resistance decreased in agglomerating systems not only as a result of the more porous cake structure but also due to the agglomeration resulting in particle surfaces less subjected to drag forces.