Successful Commercialisation Of Reverse Osmosis Technology

The creation of the L-S membrane has brought the dawn of industrial applications of reverse osmosis technology. But to achieve commercial application, it was clear that a crucial engineering problem needed to be solved, and that was the design of the membrane modules.

The L-S membrane invented by Loeb and Soliragin in 1959 was a flat membrane sheet, so early membrane modules were borrowed directly from the plate and frame construction of industrial filtration equipment. Tubular reverse osmosis membranes with diameters between 1 and 3 cm were also subsequently developed by Loeb et al. and applied to the Coringa unit. However, both plate-and-frame and tubular types suffered from complex assembly and small membrane area per unit volume, and so ultimately failed to develop into the mainstream form of commercial reverse osmosis membrane modules.

Around 1965, Dow Chemical and DuPont both invested in the development of hollow fibre reverse osmosis membranes, probably due to their familiarity with the textile industry.

In 1966, H. I. Mahon of Dow Chemical designed the first hollow fibre membrane spinning system and developed a hollow fibre reverse osmosis membrane based on cellulose triacetate material and applied for the first patent (US3228877). They used a concentric capillary spinneret with an outer pore inner diameter of 400 microns, an inner pore outer diameter of 200 microns and an inner pore inner diameter of 100 microns.

In 1971, DuPont patented a polyamide-based hollow fibre RO membrane module (US3567632) and in 1979, another company with a textile background was developing hollow fibre RO modules - TOYOBO in Japan.

Hollow fibre RO modules had a high packing density but did not eventually become the mainstream for RO modules due to the extremely fine filament diameter, uncontrollable hydraulics and the tendency to foul. This is what prompted Dow Chemical to later move to rolled membranes. Toyo Spun, on the other hand, is the only manufacturer to retain a line of cellulose acetate hollow fibre reverse osmosis membranes to this day.

If 1959 was the year of the technological milestone breakthrough in reverse osmosis, 1963 was the year when the seeds of commercial success were sown.

In 1963, the North Star Research Institute in Minneapolis, Minnesota, also conducted research on desalination technology under an OSW grant. 1967 saw the invention of microporous polysulfone support membranes by John E. Cadotte of the North Star Research Institute. In the following years he developed a variety of non-cellulose acetate composite membranes. But his passion for reverse osmosis was not limited to research.

In 1977, Cadotte, together with three others, founded FilmTec, Inc. In 1979, Cadotte applied for the world's first patent for the preparation of reverse osmosis membranes by interfacial polymerisation (US4277344). Interfacial polymerisation allows the support and separation layers of reverse osmosis membranes to be optimised separately in the preparation process, thus further enhancing the performance of the membrane, which is known as a thin layer composite (TFC). Interfacial polymerisation has also become the standard process for the preparation of modern commercial reverse osmosis membranes.

In 1985, after abandoning hollow fibre reverse osmosis membranes, Dow Chemical wholly acquired FilmTec. This is how the famous Dow membrane came to be known. In 2017, Dow Chemical, once sympathetic to hollow fibre reverse osmosis membranes, merged with DuPont.

It was also around 1963 that Donald T. Bray, a 41-year-old veteran of World War II, began working on reverse osmosis membranes. He had joined General Atomics five years earlier and in 1965 Bray applied for the world's first patent (US3417870) for a multi-film rolled reverse osmosis membrane module, which laid the basic structure for what is now the universal rolled reverse osmosis membrane module.

General Atomics' reverse osmosis membrane business later evolved into Fluid Systems, which was acquired by Koch Membrane Systems in 1998, hence the name Koch Membrane.