Solid-Liquid Separation in Bio-Suspension Systems with Compressible Solids and Non- Newtonian / Viscoelastic Fluids Containing Colloidally Dispersed Macromolecules

摘要

Bio-materials are in general compressible due to a structural break down under acting normal and shear forces but also due to gas / air fractions which are entrapped. In solid liquid separation of suspension systems containing solid particles with such properties using pressureand/ or centrifugal filtration techniques the filter-cake permeability is pressure and time dependent. At the same time most of the continuous fluid phases in bio-suspensions contain solved or colloidally dispersed macromolecules which generate non-Newtonian rheological properties like shear-thinning and viscoelasticity. Filtrate flow through compressible filter cakes consisting of bio material particles was carried out in pressure and / or centrifugal fields like applicable in hyperbaric centrifugation processing (superposition of static pressure and centrifugal fields). The filtration process - filter cake structure - filtrate rheology - relationships are described from a theoretical and experimental point of view. For filter cake structure and non-Newtonian filtrate rheology analytics, methods were developed which allow to transfer the measured material data for the interpretation of processing experiments. As shown in detail, the influence of filter cake compressibility and non-Newtonian filtrate flow behavior leads to material related optima in filter cake permeability and mass flow rate at specific static pressure and /or C-value in filtration / centrifugation processing. The developed analytical/experimental methodology provides a basis for pre-calculation of processing optima for filtration processing for complex bio-suspension systems. In the case of dispersed macromolecules in the filtrate its flow behavior in the pore system of the filter cake can additionally depend on the impact of flow forces on the macromolecular structure. If critical shear or elongation stresses or related deformations are exceeded, colloidally dispersed macromolecules can change their structure, thus supporting aggregation. This has a strong impact on the flow through the filter cake but can also influence functional properties of the filtrate. Using dynamic light scattering analysis structural changes of macromolecules in bio-suspension systems were monitored and related to changes in the flow behavior through packed particle beds during filtration processing.