Studies On The Relationship Between Retention And Pore Size Of Porous Ceramic Membranes

With the fundamental study on the performances of ceramic microfiltration and ultrafiltration membranes as the background, this paper aimed to establish the relation model between the pore size and the separating performance so as to predict the separating performance of membranes in certain filtrating system by measuring the pore size and pore size distribution.Before establishing the relation model, a very important problem we faced is how to measure the pore size or pore-size distribution exactly. A improved liquid-liquid displacement (LLDP) apparatus was built up, which was modified from"pressure controlled"to"flow controlled", and adjusted the pressure difference by setting the flow of the dosage pump. The minimal adjustable flow of the dosage pump is 0.1ml/min (1.7×10^-9m³/s). Thus the problem that hard to measure the extreme low flow (-10^-9m³/s) was solved. The improved apparatus operated quickly and conveniently.In order to validate the accuracy and reliability of LLDP method, Nuclepore Membranes which were considered as formed by a bunch of parallel cylindrical pores were used. In addition, comparison between gas liquid displacement method and LLDP method was done. The reproducibility of the method was also investigated and the result showed it had good reproducibility when was used to measure the pore size or pore-size distribution of microfiltration and ultrafiltration membranes. After validating the accuracy and reliability of this method, five kinds of membranes which had different nominal pore size were tested.The separating performances of these five membranes were also characterized by solute rejection method by using a series of dextran which had different molecular weight so that the relationship between the pore sizes and the separating property can be established. The experimental results showed that the pore size distributions of membranes from solute rejection method were close to log-normal distribution. Then, by introducing the normal probability and log-normal probability coordinate, the pore-size distribution from LLDP method proved to be a normal probability...