Filter Media Information
Filter media is material that actively separates solids from a solution and/or binds select materials in a solution. Base fluids may include coolants, corrosive chemicals, gasoline, diesel fuel, hydraulic fluid, lubricants, water, oil, inks, dies, and paints. Filter media can also remove particulates and contaminants from gas or air.
A number of specifications are important to consider when selecting filter media.
- Filtration grade (micron rating, Beta ratio) describes the ability of a fluid filter to remove contaminants by particle size.
- Maximum liquid flow is the highest flow for which the filter is designed.
- Maximum pressure is the largest pressure at which the filter is designed to operate.
Filter media is designed for a variety of performance ranges.
- Micro filtration can remove particles as small as 0.1 to 10 µm.
- Ultra filtration membranes can remove particles in the range of 0.001 to 0.1 µm.
- Nano filtration is a pressure-related process, which separates molecules based on size. It is used mainly in water purification processes such as water softening, de-coloring, and micro-pollutant removal. Nano filtration is also used to remove specific components such as coloring agents.
- Reverse osmosis is a membrane-separation process that uses synthetic membranes to extract purified water from wastewater. These synthetic membranes are permeable to water molecules, but relatively non-permeable to contaminants. Some filtration media is are reusable or disposable. Other products meet requirements from regulatory agencies such as the U.S. Food and Drug Administration (FDA).
Types of Filter Media
A wide range of materials used are used as filtration media, from organic carbon-based substances to synthetic plastics.
Activated carbons are made of a variety of materials, the most common of which are bituminous coal and lignite. They have specific properties that are a function of the material source and the mode of activation. Granular carbons from bituminous coal and lignite are used mainly in wastewater treatment applications. Granulated, activated carbon can also be produced by roasting organic material.
Diatomaceous earth (DE) is a naturally-occurring mineral derived from the microscopic, fossilized remains of marine diatoms. DE has high absorption, low bulk density, and high brightness.
Activated clay is used to remove dissolved contaminants such as acids, oxidation by-products, colors, and surfactants.
Cellulose is made from plant fibers. Because it is a natural material, its fibers are rough in texture and varied in both size and shape. These characteristics create a higher restriction to the flow of fluids compared to synthetic media. Cellulose types include cellulose acetate, nitrocellulose or cellulose nitrate, and regenerated cellulose.
Ceramic materials are made of nonmetallic minerals (such as clay) that have been permanently hardened by firing at high temperatures. Most ceramics resist both heat and chemicals.
Cotton is a highly-efficient filtration media because its fibers are irregularly shaped and have good absorption properties. Cotton filters are often a good choice because they provide increased tenacity under wet conditions.
Glass fibers are completely-incombustible inorganic fibers. They have a high tensile strength in relation to their weight and dimensional stability. Glass fibers do not stretch or shrink, and do not absorb water. Additionally, they resist mildew, deterioration, and decay.
Ion exchange is a process that involves two similar applications of one technology. The first application is water softening, a process that removes ions from water and replaces them with sodium ions and chloride ions. The second application is deionization, a process that removes ions from water and replaces them with H+ and OH- ions which can combine to form water. Ion exchange filters are used in residential applications to reduce hardness or improve the taste of water. They are also used to reduce deposits and scale from water with a high level of hardness. Deionization is often used when extremely pure water is required.
Anion resins come in two types: strong base resins and weak base resins. Strong base resins (SBA) will remove both strong acids and weak acids, while weak base resins (WBA) will remove the strong acids but are not sensitive enough to remove the weak acid contaminants.
Cation resins come in two types: strong acid resins and weak acid resins. Weak acid resins (WAC) have a very large affinity for hydrogen ions while strong acid resins (SAC) have a very low affinity for hydrogen ions.
Mixed resins contain a mixture of both anion and cation resins.
Metal or porous metal filters have a large surface area to trap condensable particles and oil vapor. Products are often corrosion resistant.
Sand filtration is often used to eliminate suspended solids from liquids. Though relatively inexpensive, the filtration media must be changed often.
Nylon is a commonly-used, general-purpose material that comprises several grades of polyamides. Nylon is tough, resistant, and has good pressure ratings. Nylon membranes are compatible with most solvents, both organic and aqueous. Use with strong acids, 70% ethanol, methylene chloride, or dimethylformamide (DMF) is not recommended.
Paper has a porous, semi-permeable nature that makes it a good filter media. Wet strength is an important consideration when selecting a paper filter.
Polyethersulfones (PES) are high-performance polymers that are similar to polycarbonates, but much more heat-resistant. Because PES resists water and steam, it is used to make products that must be sterilized between uses (e.g. cookware, medical instruments).
Polyester is a manufactured product whose fibers are long-chain, synthetic polymers which, by at least 85% per weight, are composed of an ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephthalic units.
Polypropylene (PP) is a thermoplastic material which exhibits excellent cold flow, bi-axial strength, and yield elongation properties. PP is similar to PVC, but can be used in exposed applications because it resists UV, weathering, and ozone.
PTFE is an insoluble compound that exhibits a high degree of chemical resistance and a low coefficient of friction. It is sometimes marketed in proprietary classes of materials, such as Teflon®.
Polyvinylidene fluoride (PVDF) is a melt-processable fluoropolymer that provides better strength and lower creep than other fluoropolymers. PVDF has good wear resistance and excellent chemical resistance, but does not perform well at elevated temperatures. Common brand names include Kynar®.
Polyvinylidene chloride (PVDC) can be made directly from ethylene and chlorine or by the further chlorination of vinyl chloride with the subsequent removal of hydrogen chloride by alkali treatment. Vinylidene chloride is polymerized in suspension or emulsion processes, using free-radical initiators. Because of its low permeability to water vapor and gases, PVDC is ideal for food packaging. Copolymers of vinylidene chloride and other monomers are also marketed.
Polysulfone (PSU) is a thermoplastic polycondensate used in electric connectors. It has high strength, good toughness, good dielectric strength, and dimensional stability. PSU is sold under the trade name Ultrason®.
Hydronomic F: Media filtration process. Video credit: Krones AG via YouTube by CC: SA 4.0
Filter media is designed to remove contaminants from a variety of fluids, including:
- Gasoline / Diesel
- Hydraulic Fluid
- Inks / Dies / Paints
Filter media is used in a wide range of industries, such as:
- Aerospace / Defense
- Engine / Transmission
- Food and Beverage
- Hydrocarbon Processing (Oil & Gas)
- Municipal Water Supply
- Pool and Spa
- Power Generation
- Pulp and Paper
- Semiconductor Processing
- Waste Treatment
ISO 29463-1 – High-efficiency filters and filter media for removing particles in air — Part 1: Classification, performance testing and marking.