Every year, chemical producers utilize an enormous amount of energy for separating and refining feedstocks to produce a broad range of products including food, gasoline, and plastics.
In an effort to minimize the amount of energy consumed in chemical separations, scientists at the Georgia Institute of Technology are studying membranes that could separate chemicals without the use of energy-intensive distillation processes.
The vast majority of separations out in the field in a variety of industries are thermally-driven systems such as distillation, and because of that we spend an inordinate amount of energy on these separation processes—something like 10 to 15 percent of the global energy budget is spent on chemical separations.
Ryan Lively, Associate Professor, Georgia Tech School of Chemical & Biomolecular Engineering
Lively added, “Separations that avoid the use of heat and a chemical phase-change are much less energy intense. In practice, using them could produce a 90 percent reduction in energy cost.”
Plastic membranes can already separate some molecules on the basis of size and other differences, for instance, in seawater desalination. However, so far, most membranes have been unable to endure adverse solvent-rich chemical streams while also carrying out demanding separation tasks.
In a study reported in Chemistry of Materials on July 18th, 2019, and sponsored by the Department of Defense and the National Science Foundation, the scientists describe a process for taking a polymer-based membrane and infusing it with a metal oxide network. The ensuing membrane is much more efficient at withstanding adverse chemicals without disintegrating.
After placing the pre-fabricated membrane inside of our reactor, we simply expose it to metal-containing vapors that infuse themselves inside the membrane material. This process is called vapor phase infiltration, and it creates a uniform network of metal oxide throughout the polymer membrane. We call it a ‘hybrid’ membrane.
Mark Losego, Assistant Professor, School of Materials Science and Engineering, Georgia Tech
Apart from being better able to withstand solvents, the chemical separation capabilities of the hybrid membrane also enhanced.
“Some chemicals that need to be separated are very similar in terms of their size, shape and other properties, which makes them even harder to process using membranes,” Lively stated. “These new hybrid membranes are much more selective. They can separate chemicals that are more similar to each other.”
The group of scientists, including graduate students Fengyi Zhang, Emily McGuinness, and Yao Ma, tested the new hybrid membranes using very strong chemicals like dichloromethane, tetrahydrofuran, and chloroform, organic solvents that dissolve the pure polymer membrane within minutes. The hybrid membranes stayed strong for many months during the tests.
In addition, the scientists tested by separating two chemicals very close in size. The hybrid membranes were able to differentiate aromatic molecules that varied in size by as little as 0.2 nm.
“One of the most exciting things about this work was how straightforward this process is from a manufacturing perspective,” stated Losego. “We’re essentially taking pre-made membranes and applying a treatment to them. That’s something that would be very simple to translate to an industrial scale.”
Future study on the membranes will involve determining how to adjust the oxide infusions and make new kinds of hybrid membranes that can separate various other chemicals.