Membranes have gained considerable popularity in aqueous separations, such as potable water treatment, pollution control and various manufacturing processes. But according to David Paulson, director of corporate R&D at Osmonics, very little has been done either in the lab or in industry for separations involving organic solvents. "The one exception is pervaporation," he notes, which involves separating organics by pulling a vacuum on the permeate side of the separator, and essentially vaporizing the permeate to pass through the membrane. Running such processes is tricky, and the usual advantage of membrane-based separations—the reduction of energy consumption by 90-95% relative to distillation—is compromised.
Paulson says that fundamental work needs to be done to evaluate membrane materials, study transport behavior of permeates through a membrane, and engineer processes and process equipment suitable for commercial production. "Here's an example of how the process equipment has to change," he says. "With aqueous separations, there is no fire hazard. You simply open up the equipment to service the membranes and then go back into operation. With many organic solvents, you have to worry about worker exposure and flammability considerations."
Could this be the look of solvent-based separations in the future?
Steve Kloos, project team leader at Osmonics, says that the three types of applications (food processing, pharmaceuticals and petrochemicals) also represent three types of solvent applications. "We're going to be looking at aliphatics like hexane; polar solvents like dimethyl sulfoxide, and the elevated temperature and pressure conditions common in petrochemicals," he notes. Conventional spiral-wound membrane elements will be the first configuration to be evaluated, but other configurations will be studied as well. It may also be possible to use the membranes on fairly viscous materials. In addition, separation processes that involve the use of chemical additives, such as flocculants, to aid an aqueous separation, might be good candidates for organic separations with membranes.
Osmonics, a leading producer of membrane-based separation equipment, will provide membrane and equipment technology. Cargill will provide test applications and knowledge of process conditions. The University of Kentucky, in the person of engineering professor A. Bhattacharyya, will provide transport modeling theory and the Center for Interfacial Engineering at the University of Minnesota will contribute analytical techniques.
Kloos says that although the funding and basic parameters of the project are set, additional assistance from manufacturers with candidate processes will be sought.
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