SUBSTANCE DEVELOPED AT FAU COULD MAKE BREATHING A BREEZE IN SPACE

At elevated levels, carbon dioxide (CO₂) may act as an asphyxiant by reducing normal oxygen levels in breathing air, resulting in dizziness, difficulty breathing, elevated blood pressure and heart rate, among others. Accordingly, the United States Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit for CO₂  of 5,000 parts per million by volume in air over an eight-hour work shift.

Removing CO₂  requires air revitalization systems, especially in space, to ensure the health and safety of astronauts on long-term exploration missions. One such air revitalization system established by NASA is the Environmental Control and Life Support system, which provides a safe breathing atmosphere for humans in space. To create livable conditions for a human crew in enclosed environments, the CO₂  exhaled during respiration is removed from the cabin air. The technology uses carbon dioxide removal assembly, which consists of two identical sets of in-series desiccant (drying agent) and adsorbent (material that captures CO₂) beds.

The carbon dioxide removal assembly system treats a gaseous mixture of humid air with elevated levels of CO₂, which enters the desiccant bed first where the water vapor is selectively removed. Then, the dried gas enters the adsorbent bed where a molecular crystal material called zeolite-5A removes CO₂. Once the adsorbent beds in the first set are saturated, the gas stream is directed to the second set of beds, while both adsorbent beds in the first set are switched to a regeneration mode at an elevated temperature to recover their adsorption affinity for the subsequent cycle. This system, however, requires numerous adsorption beds and a lot of power consumption to revitalize the air.

There is a need to develop alternative adsorbent materials that can efficiently integrate and intensify the air revitalization process. Researchers from  Florida Atlantic University’s  College of Engineering and Computer Science  could have a promising solution.

In a study, published in the  Chemical Engineering Journal   , researchers investigated and compared the performance of two adsorbent materials: the commercially available zeolite-5A and a white powdery substance they synthesized in their lab called amine-grafted SBA-15 silica, an “aminosilica.”

Although aminosilicas are among the most extensively studied adsorbents for removing CO₂  from different gas streams such as biogas, landfill gas and ambient air, their use for air revitalization applications are different. These differences are what inspired the FAU researchers to develop an adsorbent material designed specifically for air revitalization applications.

For the study, the researchers tested the ability of the aminosilica they synthesized to capture CO₂  from dilute streams, including air revitalization and life support systems in enclosed environments. They systematically studied zeolite-5A and aminosilica by conducting comparative performance metrics, specifically, activation temperature and duration, equilibrium CO₂  uptake, CO₂  adsorption kinetics, regeneration temperature and duration and cyclic stability.

Results showed that the aminosilica material developed at FAU outperformed the zeolite-5A material by requiring lower activation and regeneration temperatures. The aminosilica also required shorter activation and regeneration durations, and achieved faster CO₂  adsorption kinetics. Aminosilica demonstrated 43 percent faster CO₂  adsorption kinetics in the first five minutes of adsorption cycle, lower activation temperature (80 degrees Celsius vs. 180 degrees Celsius), lower regeneration temperature (90 degrees Celsius vs. 200 degrees Celsius), 50 percent shorter activation duration, and 35 percent shorter regeneration duration. The aminosilica also showed stable performance when regenerated in the presence of air at elevated temperatures (8.6 percent CO₂  uptake loss over 100 cycles).

“Findings from our study are significant, because it appears that aminosilica can be used for air revitalization in remote areas where access to other purge gases such as steam or nitrogen is expensive and/or impractical,” said  Masoud Jahandar Lashaki, Ph.D., senior author and an assistant professor, FAU  Department of Civil, Environmental and Geomatics Engineering. “In addition, the use of air as desorption purge gas would drastically reduce the operational costs of the air revitalization process.”

Other co-authors are  Sara Ahsan  and  Ali Ayub; former graduate students in FAU’s Department of Civil, Environmental and Geomatics Engineering; and  Daniel Meeroff, Ph.D., associate chair and professor, FAU Department of Civil, Environmental and Geomatics Engineering.

“There is a great need to enhance carbon capture processes that are economically viable. This important study by our researchers is very promising because all indicators suggest that aminosilica material could be a viable adsorbent for CO₂  removal in air revitalization applications and other dilute streams,” said  Stella Batalama, Ph.D., dean, College of Engineering and Computer Science. “Moreover, it is quite possible that the aminosilica synthesized and tested at FAU could potentially replace the commonly-used zeolite-5A to revitalize air in space and elsewhere.”