Filter retains substances to be separated
During filtration, particles, molecules, viruses, bacteria or other specified undesirable components are separated from a medium using a filter. The medium to be filtered flows through the pores of the filter and the substances to be separated are retained. In addition to solid-liquidseparation (particles are filtered out of a liquid medium), filtration with ceramic membranes can also be used for liquid-liquid separation, where the aim is to remove liquid droplets from a liquid phase. Usually, these droplets are emulsified as is the case, for example, with oil droplets which are often emulsified by surfactants. Liquid-liquid separation is possible in the first place due to emulsified droplets.
Semi-permeable barrier with defined cut-off size
Filtration membranes are semi-permeable barriers with pore sizes that can be designed to retain only the undesirable substances in the medium to be filtered. Depending on the size of the components to be filtered out, the processes are referred to as ultrafiltration (UF), microfiltration (MF) or nanofiltration (NF). atech offers ceramic membranes for microfiltration and ultrafiltration up to a molecular weight cut-off (MWCO) of 1kD. Both are purely physical separation methods in which all components larger than the pores of the membrane are retained.
Microfiltration and ultrafiltration
At atech, we refer to microfiltration when the pores of our membranes are between 0.1 µm and 1.2 µm in size. For ultrafiltration we use pore sizes from 50 nm to 1 kD. Microfiltration and ultrafiltration are purely physical processes for which no chemicals are required. All substances in the medium to be filtered that are larger than the membrane pores are retained by the ceramic membrane, and depending on the pore size used, this is either microfiltration or ultrafiltration.
All our ceramic tubular membranes for microfiltration and ultrafiltration have an asymmetrical structure and consist of a highly porous support body (with relatively large pores of approx. 10 µm), to which several porous layers with different pore sizes are applied. These layers are arranged in such a way that they start with large-pore layers, e.g. for microfiltration, and then layers with increasingly smaller pores are built up for ultrafiltration, thus achieving the asymmetrical structure.
Separation by differential pressure
The separation itself takes place through the differential pressure between the feed side with the medium to be separated and the permeate side, which is the material flow that has been filtered through the separating membrane. Microfiltration and ultrafiltration membranes can be made of both ceramic and organic materials such as polymers. As for the resistance against chemical, thermal and mechanical influences, ceramic membranes are superior to those made of polymers.