Types of hollow fibre membranes and their applications

Hollow fibre membranes are membranes that are fibre-like in shape and self-supporting. Hollow fibre membranes are made from polysulfone and dimethylacetamide, which are processed into fibrous filaments with a hollow inner cavity, and then divided by a highly permeable polymer, which has selective permeation characteristics. As water vapour, hydrogen, ammonia and carbon dioxide permeate more quickly, while methane, nitrogen, argon, oxygen and carbon monoxide permeate more slowly, this separates the fast permeating from the slow permeating. The outer diameter of the hollow fibres is usually 500 to 600 pum and the inner diameter 200 to 300 pum, made into 3 to 6 metre bundles in a high pressure resistant metal housing, one end of the bundle is sealed and the other end is bonded together with a specially formulated epoxy resin.

During the sieving process, the operating pressure is generally 0.7-7 kPa and the raw material is passed through a filter material under a static pressure difference. The filter material can be divided into various types, such as folded cartridges, meltblown cartridges, bag filters, microfiltration membranes, etc. Through microporous filter membranes made of cellulose or polymer materials, the uniform pore size is used to trap particles and bacteria in the water so that they cannot pass through the membrane and be removed.

It is the physical structure of the membrane, the shape and size of the pores, that determines the effectiveness of the membrane. There are currently more than a dozen specifications for microporous membranes, with pore sizes ranging from 0.1 to 75 μm and membrane thicknesses of 120 to 150&μm.

Types

Mixed cellulose ester microporous membranes; nitrocellulose membranes; polyvinylidene fluoride membranes; cellulose acetate membranes; regenerated cellulose membranes; polyamide membranes; polytetrafluoroethylene membranes and polyvinyl chloride membranes. The technology is often used for the further filtration of high-purity water used in the electronics industry, semiconductors, large-scale integrated circuit production, etc.

Technical applications

Ultrafiltration is a membrane separation process based on the principle of sieving and driven by pressure, with a filtration precision in the range of 0.005-0.01 μm. It can effectively remove particles, colloids, bacteria, heat sources and high molecular organic substances from water. It can be widely used for the separation, concentration and purification of substances.

In the early days, industrial ultrafiltration was used for wastewater and sewage treatment. With the development of ultrafiltration technology over the past thirty years, the application areas of ultrafiltration membrane technology are now very wide, mainly including food industry, beverage industry, dairy industry, biological fermentation, biopharmaceuticals, pharmaceutical chemicals, biological preparations, Chinese pharmaceutical preparations, clinical medicine, printing and dyeing wastewater, food industry wastewater treatment, resource recovery and environmental engineering, etc. Raw water flows under pressure in the outer or inner chamber of the hollow fibres, which constitute the outer and inner pressure hollow ultrafiltration membranes respectively. Ultrafiltration is a dynamic filtration process in which the retained material can be removed with the concentrate without blocking the membrane surface and can be operated continuously for a long period of time.

Ultrafiltration membranes are divided into plate and frame (plate type), hollow fibre type, nano-membrane table ultrafiltration membrane, tube type, roll type and other structures according to the structure type. Among them, hollow fibre ultrafiltration membrane is the most mature and advanced form of ultrafiltration technology. The outer diameter of the hollow fibre is 0.4-2.0mm and the inner diameter is 0.3-1.4mm. The wall of the hollow fibre is covered with micro-pores and the pore size is expressed in terms of the molecular weight of the material to be retained, which can be in the range of several thousand to several hundred thousand.

The ultrafiltration process has no phase transformation, operates at room temperature, and is particularly suitable for the separation of heat-sensitive substances, and has good resistance to temperature, acid and alkali and oxidation.