New membrane sets record for separating hydrogen from CO2

BUFFALO, N.Y. – When designing membranes that separate industrial gases, scientists often incorporate structures that attract the gas they want to obtain. This attraction can enhances the membrane’s permeability, and help isolate the desired gas more efficiently.

A study today in Science Advances shows sometimes the opposite can occur – the chemically enhanced membrane can bind too strongly to the intended gas, thus slowing the membrane’s permeability and reducing the separation efficiency.

“It’s very counterintuitive, and it challenges traditional thinking in gas separation science,” says the study’s corresponding author Haiqing Lin, professor of chemical and biological engineering at the University at Buffalo School of Engineering and Applied Sciences.

The study describes these phenomena with carbon dioxide (CO2) and a membrane made of crosslinked polyamines, which are a CO2-attracting polymer. Experiments and simulations show the crosslinked polyamines slowing CO2’s passage through the membrane.

The discovery gave Lin and his collaborators an idea. Since the membrane so effectively stymied CO2’s movement, might it excel at separating hydrogen from CO2? (The two gases are often part of industrial gas separation byproducts, and purified hydrogen is critical for clean energy fuel cells.)

The scientists completed an additional set of experiments and found that the membrane achieved a record-breaking selectivity of 1,800, meaning it allows hydrogen to pass through 1,800 times more easily than CO2.

“Before this work, the best selectivity rates were around 100. So this really sets new benchmark in terms of performance,” says first author Leiqing Hu, a former postdoctoral researcher at UB who is now an assistant professor in the College of Environmental and Resources Sciences at Zhejiang University in China.

In addition to its selectivity, the crosslinked polyamines can be made into industrial thin-film composite membranes, demonstrating its potential for commercialization. It also self-heals, and remains stable under extreme conditions.

“Industrial chemical separations presently require a tremendous amount of energy, up to 15% of global energy consumption,” says co-author Kaihang Shi, assistant professor of chemical and biological engineering at UB. “That’s why membranes like this, due to their energy efficiency and absence of chemical wastes, are critically important to reducing carbon emissions and supporting cleaner industrial processes.”

Additional co-authors include Peihong Zhang, professor of physics in the UB College of Arts and Sciences; present or former UB chemical and biological engineering students Asha Jyothi Gottipalli, Gengyi Zhang, Thien Tran and Narjes Esmaeili; Yifu Ding, professor of mechanical engineering at the University of Colorado at Boulder; and Kieran Fung, process development engineer at Meissner.

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