HOLLOW Fiber Membranes

Japan Continues to Reinforce Its Leadership

By Adrian Wilson, International Correspondent, IFN

Japan remains at the forefront of hollow fiber technology for ultrafiltration (UF) and reverse osmosis (RO) membranes, leading not only in volume production but also in technical refinements, including the development of nanostructured polymer blends and hybrid membranes that integrate adsorptive or catalytic properties.

The strength of Japan’s membrane industry can further be attributed to close collaboration between academia, government, and industry. Organizations like the Tokyo-based Japan Membrane Society (JMS) have fostered knowledge exchange, while national R&D programs have provided consistent funding for membrane science since the 1980s.

Hemodialysis

Japanese researchers and companies were among the first to recognize the potential of these membranes for large-scale applications back in the 1960s. One of the earliest breakthroughs came in the field of hemodialysis — the life-saving treatment for kidney failure that removes waste and extra fluids from the blood and regulates blood pressure.

Toray Industries made a further step forward with the development of hollow fiber membranes made from cellulose acetate for use in dialysis. Toray’s early work was based on refining the phase inversion process and producing fibers with consistent inner diameters and controlled porosity, critical to safe and adequate blood filtration.

At around the same time, Asahi Kasei entered the field and subsequently became a global leader in producing hollow fiber membranes for dialysis machines, ultrafiltration and gas separation. Asahi’s development of polysulfone-based membranes in the 1980s improved the biocompatibility, durability and filtration efficiency of dialysis fibers and is recognized as a key milestone in the field.

Water Purification

Beyond medical use, Japanese companies then began applying hollow fiber membranes to water purification, particularly for municipal and industrial water treatment. Japan’s need for compact, efficient systems — given its limited land and dense urban areas — drove innovation in membrane bioreactors (MBRs) and ultrafiltration modules.

Mitsubishi Rayon (now part of Mitsubishi Chemical Group) played a leading role in advancing hollow fiber membranes for water and wastewater treatment, focusing on PVDF (polyvinylidene fluoride) membranes with excellent chemical and mechanical resistance. PVDF fibers can operate in moderately high-temperature environments and their pore size of around 0.01 µm is ideal for UF applications, allowing excellent removal of microorganisms and fine particles.

Extended Applications

Hollow fiber membranes are also employed in milk protein concentration, wine clarification and juice purification. At the same time, in the field of gas separation, companies including Ube Industries and Kuraray have developed specialized hollow fiber membranes for separating oxygen, nitrogen and carbon dioxide. These are used in applications such as nitrogen blanketing in chemical plants, oxygen enrichment for medical and industrial use and CO2 removal in natural gas processing.

Japanese companies have also been heavily involved in extending the applications for these membranes into applications such as seawater desalination, zero-liquid discharge systems and fuel cells. In the pharmaceutical and biotech industries, they are also employed in cell harvesting, protein concentration and sterile filtration processes in drug manufacturing.

Production

The production of hollow fiber membranes involves a sophisticated polymer spinning process that creates long, flexible fibers with a hollow central core. This process allows for precise control over the membrane’s pore size, structure and filtration performance.

The process begins with the preparation of a polymer solution, consisting of a base polymer, such as polysulfone, polyethersulfone, PVDF or cellulose acetate, dissolved in a suitable solvent like N-methyl-2-pyrrolidone or dimethylacetamide. Additives, such as pore formers or surfactants, are often included to tailor the membrane’s porosity and performance characteristics. The precise composition of this solution has a direct influence on the chemical resistance, q In April this year, mechanical strength and separation efficiency of the final membrane.

The polymer solution is extruded through specially designed spinnerets, which shape the material into its distinctive hollow fiber form. A second fluid, known as the bore fluid, is injected simultaneously through the center of the spinneret to form the inner lumen of the fiber. Depending on the specific manufacturing method, the extruded fiber is either passed directly into a coagulation bath or first exposed to air before coagulation.

In wet spinning, the fiber enters the non-solvent coagulation bath immediately after extrusion, which causes the polymer to solidify and take on a porous structure. In dry-wet spinning, the fiber passes through a short air gap before it hits the bath, allowing some of the solvent to evaporate. This creates an asymmetric membrane structure with a dense, selective outer layer and a more porous inner support layer.

Post Processing

After the fibers are formed, they undergo a series of post-treatment steps, including thorough washing to remove residual solvents and other chemicals, and in some cases, chemical stabilization to improve durability, particularly for cellulose-based membranes. Depending on the intended application, the fibers may also be treated with hydrophilic or hydrophobic coatings or antifouling agents to enhance performance and longevity.

Thousands of individual fibers are then bundled together and secured at both ends using a potting material such as epoxy or polyurethane. These potted bundles are then enclosed in a protective casing to form a complete membrane module. The design of the module determines the direction of flow during operation — either from the inside out, with fluid passing through the hollow core of the fibers, or from the outside in, where fluid flows around the exterior and permeates inward.

These modules have an extremely high surface-to-volume ratio of around 60 square meters and can be operated under moderate pressures of a maximum of 3 bars.

Hybrid UF and RO

The use of a combination of UF and RO membranes to recycle wastewater and industrial effluent is growing. Still, conventional UF membranes are poor at removing the biopolymers commonly found in wastewater. As a result, RO membranes generally have to be cleaned more frequently with chemicals, increasing water production costs and carbon dioxide emissions.

To address this issue, Toray has now developed a high-removal UF membrane that maintains the high water permeability of UF membranes while reducing the RO membrane load to stabilize long-term production of high-quality water in wastewater reuse. This result has been achieved by quantitatively analyzing the formation process of sub-10-nanometer nanopores at the design stage.

Tests have confirmed that Toray’s new UF membrane reduces biopolymer transmission — a prime factor in RO membrane contamination — to less than one-third of the levels of current leading to excellent removal performance, including for sewage and industrial wastewater.

Pilot operations at a sewage plant have linked UF and RO membranes and demonstrated that the high-removal UF membrane maintains water permeability while reducing the decline in RO membrane permeability by one-third.

This advance will reduce the need for RO membrane cleaning in wastewater reuse applications, including for sewage treatment and industrial wastewater recycling in the chemical, steel, textiles, and other sectors. It should also help minimize chemical cleaning, reduce operational problems, and extend RO membrane lifespans, cutting water treatment costs and lowering carbon dioxide emissions from replacing and disposing of RO membranes by more than 30%.

Middle East Demand

The demand for water purification is rising rapidly in the Middle East and in April this year, Toray Membrane Middle East began operations at its new Middle East Water Treatment Technical Center (MEWTEC) in Dammam, Saudi Arabia.

The new facility provides integrated technology services, covering everything from membranes through to full treatment processes, and will cater to the surging water demand in the Middle East, Africa, and neighboring regions.

In July, Toray Membrane Middle East further announced the supply of RO membranes to the new Shuaibah 3 IWP seawater desalination plant in Saudi Arabia. It has a daily potable water

Planova filters are highly regarded for virus removal performance and protein permeability, as cellulose-based hollow fiber filters.

“This new plant reinforces the momentum behind our newly established Life Science business,” says Yusuke Kanazawa, head of the bioprocess division at Asahi Kasei Life Science Corporation. “It demonstrates Asahi’s commitment to making strategic investments while responding to the rising global demand for virus filtration. This project was selected under METI’s Biopharmaceutical Manufacturing Project, which supports the development of the domestic infrastructure critical for vaccine production during public health emergencies. Through this government- production capacity of 600,000 cubic meters. It provides stable supplies of drinking water to Mecca, Jeddah, Taif, and Bahah, where demand has risen as a result of both population growth and inbound tourism.

Asahi Expansion

In July this year, meanwhile, Asahi Kasei Life Science announced plans to construct a new spinning plant in Nobeoka City, Miyazaki, Japan, specifically to expand production of its Planova virus removal filters.

This will be the company’s fourth spinning plant for hollow-fiber cellulose membrane filters and operations, although operations are not scheduled to start until January 2030. The initiative is backed by a grant from Japan’s Ministry of Economy, Trade and Industry (METI).

backed initiative, we are strengthening our supply resilience and enhancing our competitiveness in the global biopharmaceutical market.”

Leadership

Japanese companies have been central to the evolution of hollow fiber membranes, pioneering their use in the medical, industrial, and environmental fields. An emphasis on precision manufacturing, long-term investment in R&D, and an integrated industry structure have ensured the longevity of this leadership.

Adrian Wilson is an international correspondent for International Filtration News . He is a leading journalist covering fiber, filtration, nonwovens and technical textiles. He can be reached at adawilson@gmail.com.