As a new separation technology, membrane separation is developing vigorously. Microfiltration is one of the most widely used separation methods in the field of modern membrane separation, but there are still many problems to be solved by researchers, and the pollution of microporous filtration media is one of the focus problems. Further understanding of the pollution mechanism of microfiltration media is helpful to realize optimal control in the process of application, so as to improve product quality and reduce investment cost.
At present, microfiltration membrane pollution is mainly divided into physical pollution and chemical pollution. For different filtration systems and different filtration periods, different pollution forms are dominant.
There are two main methods to study the pollution of microfiltration membrane: one is to analyze the experimental data with the existing theory and determine the pollution mechanism according to the degree of conformity; The second is to use instruments to micro analysis the membrane, intuitively determine the location of pollution and pollutant composition, so as to determine the pollution mechanism.
Under the condition of microfiltration, the models commonly used in pollution theory analysis include resistance model and blocking model. In this paper, the resistance model is used to analyze theoretically and experimentally the micro-resistance of microporous media from the Angle of obstruction, and to investigate the pollution status of unfiltered membrane.
Basic theoretical analysis:
The pore size of microfiltration membranes is generally between 0.02 and 1um, and most of them are symmetrical porous membranes. The object of treatment is the suspension system containing micron particles. The intercepting objects of the microfiltration medium are particles with a particle size between 0.1 and 10um, and the separated particles are macromolecules, colloidal particles, proteins and other particles.
The pollution of microfiltration membrane mainly includes the adsorption and plugging of particles, the formation of cake layer and so on. The interception mechanism of microporous filtration membranes varies due to structural differences. The interception mechanism of microporous filtration membranes can be roughly divided into the following types: mechanical interception, that is, screening, physical or adsorption interception, including the influence of adsorption and electrostatic properties, bridging, and internal network interception of network membrane.
Analysis of pollution mechanism:
At the initial stage of filtration, particles with diameters smaller than the membrane pore size enter the membrane pore, and some of them are absorbed into the micropore due to the effect of adsorption force, reducing the effective diameter of the membrane pore. When the adsorption of membrane pore tends to saturation, the particles begin to form cake layer on the surface. With the adsorption of more particles on the membrane surface, the particles began to partially block the membrane pore, and eventually formed a filter cake layer on the membrane surface, and the membrane flux tended to be stable.
The movement of particles in micropores plays a dual role in plugging. On the one hand, the movement of particles makes them migrate, pass through the filter medium, and produce drag force on particles attached to the inner surface of the membrane hole, so that the particles have a tendency to break away. On the other hand, due to the viscous effect of fluid, the movement of other particles will be hindered, and the fluid mechanical resistance will be increased, resulting in the plugging trend.
Post time: 2023-02-22 00:00:00