The nominal pore size is stated in micrometers (µm) and refers to the diameter of particles a membrane is likely to retain to a defined degree of efficiency, at given operating parameters. CoMeTas Nominal pore size is a design pore size based on a formula derived from the Kozeny–Carman equation and the ceramic particle size from which the membrane is made:
R_pore=0.155*R_particle
Through this linear formula, the nominal pore size of the CoMeTas membrane has been determined to be 0.04µm.
This design pore size has then been substantiated through filtration tests, where wide size distribution feed was produced by using silane modified colloidal silica, see Figures 1 and 2. The amorphous silica particles are discrete, spherical and mono-dispersed, and have a slightly negative surface charge. The particle sizes are in the range of 4-100nm. Carbon Black is added in the particle range 30nm-100µm
The filtration was performed in Semi Dead End Mode with a trans-membrane pressure of 0.5bar at 20°C.
Figure 1: poly-modal Feed for retention test, with the resulting permeate particle size distribution.
Figure 2: accumulated size distribution of feed and permeate particle size distributions.
In order to analyze the wide distribution of Feed, a combination of Laser diffraction and Dynamic Light Scattering was used. Given the relatively low cut off value, permeate could only be measured by Dynamic Light Scattering, as the particle size and concentration were well below the capacity of Laser diffraction.