Filter Material Types & Filtration Mechanism Research

What is filter material? Filtration refers to the purification process of removing dispersed dust particles from a fluid with a porous medium. During filtration, due to inertial collision, interception, diffusion, sieving, as well as electrostatic force, gravity, and other effects, dust particles suspended in the fluid are deposited on the surface of the porous medium or contained within it. As a porous material, its structure may be fibrous, porous, or a combination of these structures, collectively referred to as filter materials. Filter materials are widely used in almost all situations where dust is generated by human activities, including industrial production, transportation, commercial activities, and daily life.

Filter Material Types

According to the different uses of filter materials, we classify them into three categories, focusing on intake filter materials and exhaust filter materials.

• First category: Intake filter materials, used to filter dust particles in the air. They are further divided into filter materials for creating clean air and those for protecting machinery.
• Second category: Exhaust filter materials, used to filter dust-laden gases emitted by industrial and mining enterprises, protecting the atmosphere from pollution.
• Third category: Liquid filter materials, used to filter impurities from liquids such as water and oil.

Intake Filtration vs Exhaust Filtration

Both intake filtration and exhaust filtration fall under the category of filtration purification technology. They share many similar working principles, with their differences outlined as follows.

Filter Material Types

Woven Filter Material

Fabric is made by interweaving spun fibers in a certain pattern, mainly consisting of plain weave, twill weave, and satin weave.

Non-Woven Filter Material

Non-woven filter material is a type of filter material that forms a fiber web directly without the general spinning and weaving processes. For natural fibers, heat, moisture, pressure, and movement can be used to bond them into felt.

Thermoplastic Molded Filter Material

The filter material is made by hot pressing polymers into single-pore filter elements, then coating them with special materials. Its representative filter material is the corrugated sintered plate, featuring high dust removal efficiency, stable resistance, and long lifespan.

Porous Ceramic Filter Material

Porous ceramic filter material is a filter material made by sintering refractory materials with binders at high temperatures. Its internal structure contains numerous fine pores with controllable pore sizes that are interconnected.

Paper Filter Material

Thin filter materials made using the wet papermaking method are convenient for folding into pleated filter cartridges and high-efficiency filters. They have the characteristics of increasing the filtration area and reducing the footprint and space of dust collectors.

Composite Filter Material

Filter materials made by two or more methods or composed of two or more materials are called composite filter materials. The processing of composite filter materials mainly involves methods such as adhesive bonding and hot-press bonding.

Filtration Mechanism of Filter Material

The filtration mechanism of filter materials can be summarized into five basic types: surface coarse filtration, depth coarse filtration, in-depth filtration, filter cake filtration, and toxic and harmful gas purification filtration.

Surface Coarse Filtration & Depth Coarse Filtration

Surface coarse filtration occurs when particles are larger than the filter pores and cannot pass through. Depth coarse filtration refers to particles entering the deeper part of the filter medium, where they are trapped because the deep flow channel size is smaller than the particle size.

Depth Filtration (Depth Type Filter)

It includes the mechanism of removing particles from fluids, even if the particles may be smaller than the diameter of some points in the filter structure. Most theories related to non-woven filter materials are based on the in-depth filtration effect.

Filter Cake filtration

Dust layer filter cake filtration refers to the process where particles are captured and accumulated into a layer of filter cake on or near the surface of the filter material, participating in the filtration.

Purification and Filtration of Toxic & Harmful Gases

Toxic and harmful gases are gaseous molecular particles that, like air, can penetrate the filter material. However, after special treatment of the conventional filter material fiber layer, they can also be separated, captured, and purified. For example, using nano TiO₂ photocatalytic materials.

Development Trends of Filter Materials

With the continuous expansion of the application fields of filter materials, the trend of replacing other dust removal methods with filtration dust removal methods is closely related to the widespread application of dust removal filter materials, apart from the increasing environmental protection and human health requirements. Currently, the development of dust removal filter materials has the following trends:

• The variety, specifications, and functions of synthetic fiber materials used in exhaust filter materials are continuously expanding, and the processing technology is becoming more advanced and reasonable, indicating a trend of gradually replacing glass fiber materials.
• The comprehensive performance of needle-punched felt filter materials is superior to that of textile filter materials, indicating a trend of gradually replacing textile filter materials.
• Filter materials made from a mixture of various materials are continuously being developed. The blending of different fibers complements each other's strengths and weaknesses, enhancing the comprehensive performance of the filter materials.
• Gradient structure filter materials and membrane-coated filter materials are emerging in an endless stream. The filtration performance of filter materials has evolved from in-depth filtration to surface filtration, providing technical support for efficient purification and the control of respirable dust such as PM₁₀ and even PM_2.5.
• The development and technological maturity of functional filter materials with properties such as high-temperature resistance, corrosion resistance, antistatic, oil and water repellency, hydrolysis resistance, and oxidation resistance have broadened their application fields.
• With the emergence of new materials such as catalyst coatings, nanomaterials, and photocatalysts, as well as the development of new technologies like photocatalysts, filter materials now have dual functions of dust removal and exhaust gas purification, extending their application range to the field of purifying toxic and harmful exhaust gases.
• The application range of filter materials is beginning to expand into all aspects of production and people's lives, becoming essential for production development and improving quality of life.