Presidential Green Chemistry Challenge: 1999 Greener Reaction Conditions Award
The Development and Commercialization of ULTIMER®: The First of a New Family of Water-Soluble Polymer Dispersions
Innovation and Benefits: The Nalco Company developed a novel way to synthesize the polymers used to treat water in a variety of industrial and municipal operations. Nalco now manufactures these polymers in water, replacing the traditional water-in-oil mixtures and preventing the release of organic solvents and other chemicals into the environment.
Summary of Technology: High-molecular-weight polyacrylamides are commonly used as process aids and water treatment agents in various industrial and municipal operations. Annually, at least 200 million pounds of water-soluble, acrylamide-based polymers are used to condition and purify water. These water-soluble polymers assist in removing suspended solids and contaminants and effecting separations. Traditionally, these polymers are produced as water-in-oil emulsions. Emulsions are prepared by combining the monomer, water, and a hydrocarbon oil–surfactant mixture in approximately equal parts. Although the oil and surfactant are required for processing, they do not contribute to the performance of the polymer. Consequently, approximately 90 million pounds of oil and surfactant are released to the environment each year. Nalco has developed a new technology that permits production of the polymers as stable colloids in water, eliminating the introduction of oil and surfactants into the environment.
The Nalco process uses a homogeneous dispersion polymerization technique. The water-soluble monomers are dissolved in an aqueous salt solution of ammonium sulfate then polymerized using a water-soluble, free-radical initiator. A low-molecular-weight dispersant polymer is added to prevent aggregation of the growing polymer chains. For end-use applications, the dispersion is simply added to water, thereby diluting the salt and allowing the polymer to dissolve into a clear, homogeneous, polymer solution. This technology has been successfully demonstrated with cationic copolymers of acrylamide, anionic copolymers of acrylamide, and non-ionic polymers.
Development of water-based dispersion polymers provides three important environmental benefits. First, the new process eliminates the use of hydrocarbon solvents and surfactants required in the manufacture of emulsion polymers. Dispersion polymers produce no VOCs (volatile organic compounds) and exhibit lower biological oxygen demand (BOD) and chemical oxygen demand (COD) than do emulsion polymers. Second, the salt used, ammonium sulfate, is a waste byproduct from another industrial process, the production of caprolactam. Caprolactam is the precursor in the manufacture of nylon; 2.5–4.5 million pounds of ammonium sulfate are produced for every million pounds of caprolactam, providing a ready supply of feedstock. Finally, dispersion polymers eliminate the need for costly equipment and inverter surfactants needed for mixing emulsion polymers. This technological advantage will make wastewater treatment more affordable for small- and medium-sized operations.
Nalco's dispersion polymers contain the same active polymer component as traditional emulsion polymers without employing oil and surfactant carrier systems. The polymers are produced as stable colloids in water, retaining ease and safety of handling while eliminating the release of oil and surfactants into the environment. By adopting this new technology, Nalco has conserved over one million pounds of hydrocarbon solvent and surfactants since 1997 on two polymers alone. In 1998, the water-based dispersions used 3.2 million pounds of ammonium sulfate, a byproduct from caprolactam synthesis that would otherwise be treated as waste. Additional environmental benefits will be realized as the dispersion polymerization process is extended to the manufacture of other polymers.
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