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Next Generation Molecular Separations
July 11, 2017

According to information provided by the Georgia Institute of Technology (Georgia Tech), researchers have identified the opportunities they see ahead for scalable membrane materials based on rigid, engineered pore structures. In a paper, “Materials for next-generation molecularly selective synthetic membranes,” published recently in the journal Nature Materials, they say the most promising materials are scalable for use in compact modules and take advantage of entropy at the molecular level to moderate the separation selectivity of membranes.

Photo shows the manufacture of polymer hollow fiber membranes, which are precursors to more advanced carbon molecular sieve hollow fiber membranes. Credit: Rob Felt, Georgia Tech.

Today, chemical separation processes account for as much as 15 percent of the world’s total energy consumption. As part of efforts to significantly reduce that percentage, development of next-generation molecularly-selective synthetic membranes will be among the drivers for more efficient, large-scale separation processes.

“It’s all about energy and carbon dioxide,” noted William Koros, professor and Roberto C. Goizueta Chair in Georgia Tech’s School of Chemical and Biomolecular Engineering. “Chemical separations now consume half as much energy as the entire transportation sector – land, sea and air. Our goal is to assist industry to cut that by a factor of ten, which also means cutting the CO2 emissions. That’s not going to happen right away, but we have shown that the fundamentals of this technology work.”

A membrane is an engineered barrier that controls the sorting of components by selectively allowing molecules of a certain size to pass between the incoming feed stream and an outgoing permeate stream. Because they don’t require large inputs of energy – which usually would come from combustion of fuels – use of these membranes can dramatically reduce both energy consumed and carbon dioxide produced. The membranes are made from advanced polymers, hybrid materials and molecular sieves, with pore sizes tailored for the intended use.

In research supported by the Office of Energy Science of the U.S. Department of Energy (DOE), Prof. Koros’ lab focuses on gas separations, but the article also addresses liquid separation processes. For both applications, he and co-author Chen Zhang point out that to be practical, new materials must be scalable – able to be packed tightly to provide large amounts of surface area inside small modules. That is best done using hollow-fiber membranes produced using advanced versions of processes that were originally developed to make ordinary textile fibers.

“You’ve got to have something that is both high performance and able to be processed on the scale of acres per day,” said Prof. Koros, who is also a Georgia Research Alliance eminent scholar in membrane technology. “Scalability is every bit as important as the capability to do the separation. Exciting materials that are the size of a postage stamp won’t make a contribution.”

The Nature Materials article focused on progress that had been made in the technology and future potential, with highlights on recent advances in Prof. Koros’ lab at Georgia Tech. The goal was to encourage development of new materials and make membrane scientists aware of the most promising paths.

“We want everybody to see this next-generation of materials and understand the processes that help attain the goals of reducing energy consumption and carbon dioxide production,” Prof. Koros emphasized.

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