NAMS 2002 Workshop - ICOM 2008

Plenary Lecture III
Friday July 18. 8:00 AM-9:00 AM, Hawai’I Ballroom
The Development of Reverse Osmosis and Nanofiltration through Modern
Times
William E. Mickols (Speaker), DOW Water Solutions, Edina, Minnesota - WEMickols@dow.com
The history of reverse osmosis (RO) began with the discovery of osmotic
pressure. Modern thermodynamics offered the explanation of how theoretical
chemical activity differences could be used to develop a physical pressure
difference. Further developments in stochastic theory showed how either a
physical pressure or a chemical concentration difference could be expressions of
the same effect. The actual proof of using pressure to develop a chemical
gradient was left to Loeb and Sourirajan. Their work on cellulose based
symmetric and asymmetric RO membranes amazed the scientific and popular
world. This mobilized the scientific world to convert their discovery from a
scientific curiosity to a viable method to desalinate water.
The development of RO was driven, in part, by considerations that 80% of the
world’s surface is covered with water too saline to drink. Recently we have found
that 60-80% of the remaining water is too contaminated to drink by World Health
Organization (WHO) standards. Of the remaining 20-30% drinkable water, much
of it is becoming contaminated and will require extensive remediation.
Modified celluloses were initially used to make asymmetric RO membranes.
Charged thermoplastics were also extensively studied. Modern RO membranes
began with asymmetric aromatic polyamides in the hollow fiber form. The recent
explosion in RO began with the development of interfacial synthesis of thin film
composites by John Cadotte at North Star research. Initial development used
polyimine based cross-linked polyamides (NS200). This began the parade of
remarkable high flux, high rejection reverse osmosis membranes.
With the development of interfacial synthesis of two new aromatic polyamides,
the concept of nanofiltration and RO was developed. The FilmTec NF-40
membrane (piperazine and TMC) and FT-30 (meta phenylene diamine and TMC)
launched the modern industry. Over the course of 20 years the water
permeability increased by a factor of eight and the salt permeability dropped by
almost a factor of twenty. Separations that required 400 psi now only require 50
psi and have better rejection. Modification of the surface of FT-30 has also
allowed RO to operate at very low ionic strengths. The altered charged surfaces
changed the ion rejection characteristics at low ionic strength. For high ionic
strength we’ve shown that by designing the membrane to fit the separation, the
efficiency of RO separations can be increased by a factor of over 50%. Modern