Membranes are widely used in a variety of industrial separation processes, but the polymeric materials that make up many membranes are not durable enough to handle extreme conditions, such as processes with low pH or hazardous-metal content. Membrion, Inc. (Seattle, Wash.; www.membrion.com) has developed the Electro-Ceramic Desalination (ECD) process, which uses ceramic membranes for ion separation in extreme environments where polymeric membranes would typically fail. “Ceramic membranes have been in use for decades, but they usually cannot be made with small enough pores to be suitable for ion-transport applications,” explains Greg Newbloom, CEO of Membrion. Taking inspiration from the silica gel packs that are used to remove moisture from packaged foods, and which feature the tiny pores required for molecular transport, the team developed a unique way to shape the silica into membrane sheets instead of spheres. “We work in an amorphous phase with silica, using a sol-gel process to convert liquid materials into gel and then dry them into a solid, which we can then feed into a roll-to-roll process. No one else has really done roll-to-roll manufacturing with ceramics in this way before,” says Newbloom. The company currently operates a pilot membrane-manufacturing facility in Seattle.
Another differentiator in the ECD process is the use of an electric field, rather than pressure, to drive the migration of ions. “The ECD assembly actually consists of two membranes — one selective for cations and one for anions. The electric field helps these ions move across the membrane, and they are then recombined in a concentrated stream. What’s unique about our process is that it targets only ionically charged components,” adds Newbloom. This makes it useful for treating wastewater streams with metal content and high acidity, such as those found in semiconductor manufacturing, which typically would require several separate treatment steps. “The technologies that ECD can replace are not typical membrane units — they’re things like chemical precipitation, or thermal evaporation. In many cases, the most common thing that ECD can replace is simply a facility trucking wastewater offsite and disposing of it elsewhere,” says Newbloom.