Working Principle of Membrane Filter

A comparatively short definition of membrane filter could be just like this: membrane filter is something to separate and enrich solutes in solution, and separate colloidal suspensions. Let’s know the membrane filtration principle. Hawach provided Cellulose acetate membrane, Hydrophobic PTFE membrane filter, PVDF Filter, and so on. Membrane filter principle construction and working are shown in the following figure.

Principle of membrane filtration

The membrane filter principle is the screening process. The raw material liquid passes through a microporous membrane material to separate specific substances under the action of static pressure difference. Microfiltration is also called a microporous filtration membrane. The principle of membrane filtration uses a membrane with selective permeability as a separation medium. The membrane wall is densely covered with micropores.

The microporous separation process is to use the size selectivity of the membrane for the components to be separated under the action of the fluid pressure difference to retain the particles and macromolecular solutes that can be retained by the membrane pores, while the particles or small molecular solutes that cannot be retained by the die pores through the membrane.

Because of membrane filter principle, the solute is retained by the membrane to achieve the purpose of material separation and concentration. The membrane separation process is a dynamic cross-flow process. The macromolecular solute is blocked by the membrane wall and flows out of the membrane module with the concentrated liquid. The membrane is not easy to be blocked and can be used continuously for a long time. The filtration process can be operated at room temperature and low pressure, with no phase change, high efficiency, and energy-saving.

Microporous filtration membrane is a refined filter material that can retain large solid particles and other particles, microorganisms and some bacteria in the solution, and solvents and small molecular substances. These substances can be separated through the membrane mixture.

nylon membrane filter  hydrophilic ptfe membrane filter membrane2

The filtration mechanism of the microporous membrane is mainly interception. Retention can be divided into the following categories: mechanical retention, adsorption retention, bridging retention, and retention in the network inside the membrane.
1. Mechanical retention: that is, screening. The membrane has the function of retaining impurities such as particles larger than its pore size or its pore size is equivalent.
2. Physical effect or adsorption retention effect: In addition to the screening effect, the influence of other factors should also be considered, including the influence of adsorption and electrical properties.
3. Bridging effect: At the entrance of the hole, particles can also be trapped because of the bridging effect.
4. Network interception of network membrane. This entrapment traps the particles in the interior of the membrane, not on the surface of the membrane.

A membrane filter is to uses the sieving mechanism of the microfiltration membrane, driven by pressure, to trap particles with a diameter between 0.1-1μm, such as suspended solids, bacteria, some viruses, and large-sized colloids. In addition, a membrane with a thickness of less than 100um must have the ability to withstand high pressure, so we should try to make various kinds of pressure-resistant membranes.

Water flow through the membrane is not very fast, so in order to pass the required amount of water, the monomer area of the membrane device should be large, and many thin membrane tubes should be filled in a small space. Tube membranes also need porous materials. Raw water passes through the inner side of the pipe and seepage flows out of the pipe. This kind of membrane filter is commonly used for passengers, but also for externally pressurized ones. The outer diameter of the hollow system is several hundred um, and most fiber tubes are packed in the system.

Do you want to know more about the membrane filter principle construction and working, please click the Principle, Process and Precautions of Microfiltration Membrane.

Click here to know more about PVDF vs PTFE, Membrane Material And Performance Characteristics Of Filter Membrane, Membrane Filtration Applications, What Are Membrane Filters Made Up Of?