Source: http://www.physorg.com/news135927026.html
For Clean Water: Chlorine-tolerant membranes for desalination
PhysOrg.com -- One of the most pressing needs of our time is safe, sustainable access to fresh water. The dominant technology for desalination of water is membrane-based desalination, an energy-efficient, environmentally friendly process. Scientists have now developed a new membrane material that, unlike current polyamide membranes, tolerates chlorinated water.
A team headed by Ho Bum Park (University of Ulsan, South Korea), Benny D. Freeman (University of Texas at Austin, USA), and James E. McGrath (Virginia Polytechnic Institute, Blacksburg, USA) reported in the journal Angewandte Chemie on a membrane that is made of sulfonated copolymers.
Chlorine is the most commonly used biocide in water treatment because it is both inexpensive and very effective in small amounts. The disinfection of water headed into membrane-based desalination facilities is crucial to hinder the growth of biofilms, which reduce efficiency.
Polyamide membranes do not tolerate chlorine. This means that the water must first be treated with chlorine, and then the chlorine must be removed before the water comes into contact with the membrane. Before being fed into the supply network, the water must be chlorinated again. This is a complex, costly procedure.
Membranes made of polysulfone, a sulfur-containing engineering thermoplastic, are being considered as an alternative. They are highly tolerant to chlorine. However, polysufones are hydrophobic and do not allow enough water to pass through them. By attaching additional charged sulfonic acid groups, the researchers hoped to make the polymer more water friendly without affecting its other valuable properties.
Whereas previous efforts focused on modification of the polysulfone after polymerization, the team now took a different route: the simultaneous polymerization of disulfonated monomers (a building block containing two hydrophilic sulfonic acid groups) and another type of monomer led to the formation of a copolymer.
Undesired side-reactions, cross-linking or breaks in the polymer chains do not occur by this method. Most importantly, it is possible to precisely control how many water-friendly, charged sulfonic acid groups are in the polymer chain. This allows the targeted generation of chlorine-resistant membranes whose permeability for water and salts can be tailored to specific applications (e.g., nanofiltration, reverse osmosis).
Chlorine is the most commonly used biocide in water treatment because it is both inexpensive and very effective in small amounts. The disinfection of water headed into membrane-based desalination facilities is crucial to hinder the growth of biofilms, which reduce efficiency.
Polyamide membranes do not tolerate chlorine. This means that the water must first be treated with chlorine, and then the chlorine must be removed before the water comes into contact with the membrane. Before being fed into the supply network, the water must be chlorinated again. This is a complex, costly procedure.
Membranes made of polysulfone, a sulfur-containing engineering thermoplastic, are being considered as an alternative. They are highly tolerant to chlorine. However, polysufones are hydrophobic and do not allow enough water to pass through them. By attaching additional charged sulfonic acid groups, the researchers hoped to make the polymer more water friendly without affecting its other valuable properties.
Whereas previous efforts focused on modification of the polysulfone after polymerization, the team now took a different route: the simultaneous polymerization of disulfonated monomers (a building block containing two hydrophilic sulfonic acid groups) and another type of monomer led to the formation of a copolymer.
Undesired side-reactions, cross-linking or breaks in the polymer chains do not occur by this method. Most importantly, it is possible to precisely control how many water-friendly, charged sulfonic acid groups are in the polymer chain. This allows the targeted generation of chlorine-resistant membranes whose permeability for water and salts can be tailored to specific applications (e.g., nanofiltration, reverse osmosis).
Citation: Benny D. Freeman, Highly Chlorine-Tolerant Polymers for Desalination, Angewandte Chemie International Edition 2007, 46, No. 32, 6019–6024, doi: 10.1002/anie.200800454
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Source: http://www.physorg.com/news135958814.html
New chlorine-tolerant, desalination membrane hopes to boost access to clean water
A chemical engineering professor at The University of Texas at Austin is part of a team that has developed a chlorine-tolerant membrane that should simplify the water desalination process, increasing access to fresh water and possibly reducing greenhouse gases.
"If we make the desalination process more efficient with better membranes, it will be less expensive to desalinate a gallon of water, which will expand the availability of clean water around the world," Professor Benny Freeman says.
The research will be published July 28 in the German Chemical Society's journal Angewandte Chemie.
Freeman worked primarily with James E. McGrath of Virginia Tech University and Ho Bum Park of the University of Ulsan in South Korea for more than three years to develop the chlorine-tolerant membrane made of sulfonated copolymers. A patent has been filed.
Chlorine must be added to water to disinfect it to prevent a biofilm (stemming from biological contaminants in the raw water) from forming on the membrane, which would reduce its performance. It is then de-chlorinated prior to sending it through the currently used polyamide membranes, which don't tolerate chlorinated water.
"It promises to eliminate de-chlorination steps that are required currently to protect membranes from attack by chlorine in water," Freeman says. "We believe that even a small increase in efficiency should result in large cost savings."
The development could also have a direct impact on reducing carbon-dioxide emissions, which contribute to global warming.
"Energy and water are inherently connected," Freeman says. "You need water to generate power (cooling water for electric power generation stations) and generation of pure water requires energy to separate the salt from the water. That energy is often generated from the burning of fossil fuels, which leads inevitably to the generation of carbon dioxide. Therefore, if one can make desalination more energy-efficient by developing better membranes, such as those that we are working on, one could reduce the carbon footprint required to produce pure water."
Freeman says McGrath and his research group developed novel materials based on an entirely different platform of membranes than those used today in desalination membranes. These new materials are extremely tolerant to aqueous chlorine so their performance doesn't deteriorate in the presence of chlorine.
"Basically, Dr. McGrath radically changed the chemical composition of the membranes, relative to what is used commercially, and the new membranes do not have chemical linkages in them that are sensitive to attack by chlorine," says Freeman, who holds the Kenneth A. Kobe Professorship in Chemical Engineering and the Paul D. & Betty Robertson Meek & American Petrofina Foundation Centennial Professorship in Chemical Engineering.
"If we make the desalination process more efficient with better membranes, it will be less expensive to desalinate a gallon of water, which will expand the availability of clean water around the world," Professor Benny Freeman says.
The research will be published July 28 in the German Chemical Society's journal Angewandte Chemie.
Freeman worked primarily with James E. McGrath of Virginia Tech University and Ho Bum Park of the University of Ulsan in South Korea for more than three years to develop the chlorine-tolerant membrane made of sulfonated copolymers. A patent has been filed.
Chlorine must be added to water to disinfect it to prevent a biofilm (stemming from biological contaminants in the raw water) from forming on the membrane, which would reduce its performance. It is then de-chlorinated prior to sending it through the currently used polyamide membranes, which don't tolerate chlorinated water.
"It promises to eliminate de-chlorination steps that are required currently to protect membranes from attack by chlorine in water," Freeman says. "We believe that even a small increase in efficiency should result in large cost savings."
The development could also have a direct impact on reducing carbon-dioxide emissions, which contribute to global warming.
"Energy and water are inherently connected," Freeman says. "You need water to generate power (cooling water for electric power generation stations) and generation of pure water requires energy to separate the salt from the water. That energy is often generated from the burning of fossil fuels, which leads inevitably to the generation of carbon dioxide. Therefore, if one can make desalination more energy-efficient by developing better membranes, such as those that we are working on, one could reduce the carbon footprint required to produce pure water."
Freeman says McGrath and his research group developed novel materials based on an entirely different platform of membranes than those used today in desalination membranes. These new materials are extremely tolerant to aqueous chlorine so their performance doesn't deteriorate in the presence of chlorine.
"Basically, Dr. McGrath radically changed the chemical composition of the membranes, relative to what is used commercially, and the new membranes do not have chemical linkages in them that are sensitive to attack by chlorine," says Freeman, who holds the Kenneth A. Kobe Professorship in Chemical Engineering and the Paul D. & Betty Robertson Meek & American Petrofina Foundation Centennial Professorship in Chemical Engineering.
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