UCR researchers from the department of chemical engineering have developed a new method to recover fresh water from high-salinity solutions using different processes from analytical electrochemistry. Analytical electrochemistry is the interaction between electricity and chemistry, namely the measurements of electrical quantities, such as current or charge and their relation to chemical parameters. UCR graduate student Alexander Dudchenko, who came up with the new method, was also the lead author on the research paper that was published in “Nature Nanotechnology.” He worked with three other undergraduate students, Chuxiao Chen, Alexis Cardenas and Julianne Rolf, in Assistant Professor David Jassby’s chemical engineering lab, the Water Technologies Group.  

Jassby elaborated more on the technical and analytical aspect of the research in an interview with the Highlander. Brine water is a highly concentrated solution of sodium chloride, much higher than seawater and therefore has to be treated differently from other desalination methods currently used. Seawater is currently treated with the common process of reverse osmosis and brine water is the waste product generated from this process that isolates fresh water from sodium chloride. “However, you can’t really use reverse osmosis for high salinity brines,” explained Jassby, “you have to use thermal methods, meaning you have to heat up the water and essentially distill it, boil it off.”

Most brine waste management utilizes membrane distillation because high-salinity water requires the use of a thermally driven treatment process. “You have a membrane and you heat up your feed or brine. Then you flow it through your membrane module and you collect your water vapor on the other side,” said Jassby when asked to explain membrane distillation. The disadvantage of this process is that it requires the entire feed stream to be heated up, resulting in a high energy intensive proposition required by the high heat necessary to boil brine solutions for the separation of water from sodium chloride. This elevated level of energy corrodes the membrane module and requires high expenses to maintain such energy levels as well as to replace the corroded metal.

Dudchenko was able to identify a way to avoid such a complex process and provide a cost-effective method that “heats up the membrane instead of the entire feed stream. So then, water vapor will form right at that water-vapor interface and the vapor will move across the hydrophobic membrane and you collect it on the other side,” said Jassby.

Jassby clarified that Dudchenko demonstrated this efficiency of his module by “controlling the corrosion of carbon nanotubes under high temperatures.” The professor’s lab specializes in making carbon nanotube polymer composites that are porous and good conductors, which is what Dudchenko used as resistive heaters. Resistive heaters are used to heat up the medium inside the module but the excessive heat they provide, while necessary to reach the boiling point of brine solutions, corrodes the carbon nanotubes or any other material. By using the porous polymer composites instead of standard resistive heaters, Dudchenko was able to better handle the high voltages applied in distillation.

Dudchenko was thus able to prevent the oxidation of carbon nanotubes in ionized water or high-salinity brines, illustrating that porous carbon nanotube polymer composites can be used as self-heating membranes to heat brine solutions and achieve 100 percent fresh water recovery in a single pass.

The current methods of membrane distillation only allow 10 percent of the freshwater to be removed from brine water in a single pass at optimal conditions; effectively extracting the water requires conducting this process over and over again to obtain freshwater. Jassby emphasized that Dudchenko’s method replaced typical heat exchangers that erode in the high temperatures required to desalinate brine water with his self-heating membrane and reduce the heat needed in the process while still recovering 100 percent fresh water.

This research project received funding through grants from the Office of Naval Research, the Department of Energy, the National Science Foundation and the Petroleum Research Fund.