First, the team carried out salt permeability tests, measuring the amount of salt passing through a membrane in a given amount of time. The less salt found in the filtered water, the better. Freeman and McGrath found that the new membrane performed just as well as many commercial membranes in filtering out water with low to medium salt content. For saltier samples comparable to seawater, the team’s membrane was slightly less permeable.
“We have materials that are competitive today with existing nano filtration and some of the brackish water membranes,” says Freeman. “We are now pushing the chemistry to get further into the seawater area, which is a significant market we’d like to access.”
The researchers also tested the polymer’s chlorine sensitivity. They found that, after exposure to concentrated solutions of chlorine for more than 35 hours, the new membrane suffered little change in composition, compared with commercial polyamide membranes, which were “eaten away by the chlorine.”
Currently, Freeman and his colleagues are further manipulating the polymer composition to try to tune various properties, in hopes of designing a more selective and chlorine-resistant membrane. They are also in talks with a leading manufacturer of desalination membranes, with the goal of bringing the new membrane to market.
“These membranes may represent a reasonable route to commercialization,” says Freeman. “If we’re successful, we’ll have the possibility of basically making these membranes on the same equipment that people use today.”
Eric Hoek, an assistant professor of civil and environmental engineering at the University of California, Los Angeles, works on engineering new desalination membranes at the California Nanosystems Institute. He says that the chlorine-tolerant membrane developed by Freeman’s team may be a promising alternative to today’s industrial counterparts.
“This work is among the most innovative and interesting research on membrane materials in the past decade,” says Hoek. “While the chlorine tolerance exhibited by these membranes is impressive, the basic separation performance is not yet where it needs to be for these materials to be touted as immediate replacements of commercial seawater membrane technology.”