Project story

POREFLON Microfiltration Membrane Module

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04. They set their hopes on field tests, which failed. A new concept had to be introduced to restart the project.

Water treatment was an innovative use of POREFLON. However, project members were not familiar with that field. Even Sumitomo Electric had not tapped into the water treatment market and so the Company had no expertise or relevant information. Taking a sample with him on the road, Morita visited water treatment engineering companies to find out what their needs were.
"Most companies would not listen to me, because the idea of using expensive PTFE for water treatment was not easy for them to accept. Almost all companies were dubious: Why use PTFE when general-purpose polyethylene works fine?"
However, one company became interested in the idea and both parties agreed to conduct field tests. But the results were dismal.
One feature of POREFLON is its high porosity which enables it to have a high permeability to water. To make the water treatment process efficient, it was important for water to be able to pass through the material at a high flow rate. However, in the tests POREFLON clogged up unexpectedly quickly, and the flow rate turned out to be poorer than in a conventional system. Morita's hopes crumbled.

05. Borrowing the Company's wire-making expertise

In the next step, Morita came up with a new concept to make a fresh start.
In the previous prototype, the membrane structure had been uniform throughout the hollow fiber membrane. The drawback to this structure was that the flow rate decreased with decreasing pore size, resulting in a lower porosity. The solution to this problem was to employ a new composite structure, in which an inner hollow fiber membrane with a large pore size and high permeability was integrated with an ultra-thin outer layer made of the same POREFLON with a small pore size. The pore size of the outer POREFLON layer serving as the filter was 0.1 µm. The inner POREFLON layer that served as a support had a pore size of 2 µm and 80% porosity. This structure became known as a PTFE composite hollow fiber membrane, providing both a high flow rate and strength with the minimum compromise. Successive improvements were subsequently made, increasing the flow rate approximately four-fold over the previous product and bringing the cost down by 75% through the use of Sumitomo Electric's original technology developed by the project members.
This technology was made possible through the wire-making expertise of Sumitomo Electric. An electrical wire is made of an inner conductor surrounded by an insulator. This structure is similar to the PTFE composite hollow fiber membrane. At the prototype stage and inspired by the new concept, the project members went to the Industrial Wire & Cable Division to learn how to make an electrical wire. They even borrowed wire-making equipment and produced wires, setting the course for mass production based on this new concept.
"At first, they weren't happy about us contacting them. They must have thought that we amateurs were crazy," smiles Morita. Nonetheless, without his idea and this approach, POREFLON-based water treatment technology would not have advanced. And if Sumitomo Electric had not been an electrical wire manufacturer, this innovation would not have happened.

06. Key person from Korea

Around the time that substantial progress had been made in water treatment technology, a businessman visited the project from a Korean trading company. His aim was to sell POREFLON in Korea. The project members enthusiastically recommended the water treatment technology they were developing. He was persuaded to accept their proposal and began selling the technology in Korea.
"We asked him to pack sample water treatment membrane modules into his car and visit manufacturers throughout Korea." The result produced more positive responses than expected. In fact, sewage treatment had become a national challenge in Korea. Water treatment system manufacturers were developing technology and testing our competitors' membrane modules, none of which could meet the manufacturers' performance requirements. This was when the POREFLON water treatment membrane module was introduced. Water treatment engineering companies became extremely interested in the POREFLON membrane module. Finally Daewoo E&T, a major Korean construction company, made the decision to adopt Sumitomo Electric's POREFLON membrane modules for some sewage treatment plants, including one to be constructed in Sinpyeong.

07. Taking part in a big project—completing membrane module development.

The adopted membrane module needed to meet capacity requirements of approximately 10,000 tons per day for the Sinpyeong and other sewage treatment plants. Needless to say, there was a huge difference in scale between the prototype and the water treatment membrane modules being used there, and it became necessary to optimize a combination between the membrane module and microorganism-based sewage treatment methods. Project members had a huge list of things to be done before implementation in the actual system.
"At first, the flow rate at which our membrane modules could treat sewage fell short of the goal. The cause was in the overall assembly structure, including the arrangement of the hollow fiber membranes. The question was what arrangement of hollow fiber membranes would maximize the treatment capacity? We used a trial-and-error process to explore the most efficient structure."
One major issue in that process was the need to use the actual wastewater discharged in Korea for system evaluation. The project members constructed a sample in Japan, carried it to the actual site for testing, and returned home to Japan with the sample for analysis. This procedure was repeated. As the development deadline drew near, they could not afford to waste time sending equipment using the normal delivery methods. As a result, Morita carried the membrane module onto the airplane in his hand luggage.
"We had deadline and performance requirements that we had to meet at any cost. Under tremendous pressure, I visited Korea almost every week."
Led by Morita, the project members analyzed and improved the membrane module repeatedly. After a period that strengthened them both mentally and physically, a completed POREFLON water treatment membrane module was ready for actual application.

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