March 2021

Texas A&M develops energy-saving HVAC material

The breakthrough is a fast dehumidifying polymer

Texas A&M University announced that researchers in its College of Engineering have developed a polymer with enhanced dehumidification properties. This organic material could help develop more energy-efficient systems with a smaller carbon footprint, considering HVAC systems (which often contain dehumidifiers) guzzle around 76% of the electricity in commercial and residential buildings, the university said in a press release.

Texas A&M University study researched polyimides, an organic material that uses less energy to dry air. Furthermore, the researchers said polyimide-based dehumidifiers can bring down the price of HVAC systems, which currently cost thousands of dollars.

“In this study, we took an existing and rather robust polymer and then improved its dehumidification efficiency,” said Hae-Kwon Jeong, McFerrin Professor in the Artie McFerrin Department of Chemical Engineering. “These polymer-based membranes, we think, will help develop the next generation of HVAC and dehumidifier technologies that are not just more efficient than current systems but also have a smaller carbon footprint.”

The results have been published in the Journal of Membrane Science.

The most commonly available dehumidifiers use refrigerants, which are a source of greenhouse gases, a major culprit for global warming. An alternative is zeolites, Green desiccants that can absorb moisture with their water-attractive or hydrophilic pores. However, zeolite-based dehumidifiers pose challenges of their own.

“Scaling up is a big problem with zeolite membranes,” Jeong said. “First, zeolites are expensive to synthesize. Another issue comes from the mechanical properties of zeolites. They are weak and need really good supporting structures, which are quite expensive, driving up the overall cost.”

Jeong and his team turned to a cost-effective organic material called polyimides that are well-known for their high rigidity and tolerance for heat and chemicals. At the molecular level, the basic unit of these high-performance polymers are repeating, ring-shaped imide groups connected together in long chains. Jeong said the attractive forces between the imides gives the polymer its characteristic strength and thus an advantage over mechanically weak zeolites. But the dehumidification properties of the polyimide material needed enhancement.

The researchers first created a film by carefully applying polyimide molecules on a few nanometers-wide alumina platforms. Next, they put this film in a highly concentrated sodium hydroxide solution, triggering a chemical process called hydrolysis. The reaction caused the imide molecular groups to break and become hydrophilic. When viewed under a high-powered microscope, the researchers uncovered that the hydrolysis reactions lead to the formation of water-attractive percolation channels or highways within the polyimide material.

When Jeong’s team tested their enhanced material for dehumidification, they found that their polyimide membrane was very permeable to water molecules and could be operated continuously without the need for regeneration. Jeong said his team carefully designed their experiments to partial hydrolysis wherein a controlled number of imide groups become hydrophilic.

“The strength of polyimides comes from their intermolecular forces between their chains,” Jeong said. “If too many imides are hydrolyzed, then we are left with weak material. On the other hand, if the hydrolysis is too low, the material won’t be effective at dehumidification.”

Although polyimide membranes have shown great promise in their potential use in dehumidification, Jeong said their performance still lags behind zeolite membranes.

“This is a new approach to improve the property of a polymer for dehumidification and a lot more optimizations need to be done in order to further enhance the performance of this membrane,” Jeong said. “But another key factor for engineering applications is it has to be cheap, especially if you want the technology to be reasonably affordable for homeowners. We are not there yet but are certainly taking strides in that direction.”

Sunghwan Park in the chemical engineering department also contributed to this study. This research was funded by the National Science Foundation and the Qatar National Research Fund.

Source: https://today.tamu.edu/2021/03/29/an-organic-material-for-the-next-generation-of-hvac-technologies/