Supported Structures and Composites for Air Purification Applications

Current individual and collective protection military air purification systems consist of a combination of particulate and gas filtration media. The particulate media is typically a high efficiency particulate air (HEPA) made of glass fibers while the gas filtration material is a packed bed of ASZM-TEDA, a bituminous coal-based activated carbon impregnated with salts of copper, silver, zinc, molybdenum and triethylenediamine.

Current military filters incorporating ASZM-TEDA provide excellent protection against low vapor pressure, physically adsorbing chemical warfare agents (CWA) such as nerve and blister agents and provides reaction for acidic and acid-forming gases such as hydrogen chloride, phosgene, and many other acid forming chemicals. However, there are several shortcomings associated with current filtration media and systems. Specifically, little or no protection is provided against basic and base-forming chemicals such as ammonia and ethylene oxide. Additionally, packed beds, although very efficient in gas removal, present a high breathing encumbrance for the user. Research is moving towards composite filtration media that provides protection against both particulates and toxic chemicals in order to broaden protection capabilities while reducing encumbrance.

Composite filtration materials encompass supported structures and layered or blended beds of varying sorbent functionalities. Filtration systems are moving towards lower capacities in order to broaden protection against a wider range of chemical threats. By developing thin beds of filtration media beds larger surface areas can e configured in order to lower airflow resistance. For these thin bed applications, packed sorbent beds can not be packed effectively to eliminate channeling. The most efficient way of distributing supported beds is to utilize either very small sorbent particles supported by an inert fiber or to utilize electrospun fibers that provide both particulate and gas removal.

Supported structures, or loaded webs, are being developed to evenly distribute entrapped particles and provide an efficiency close to that of a packed bed at a drastically reduced pressure drop. The properties of these materials allow for thin bed configurations, thus different functionalities can be layered in the same footprint as current filters, broadening the protection while reducing the airflow resistance.

High surface area electrospun nanofibers, made from nonwoven viscoelastic fluids, present the possibility of introducing chemical removal functionalities to particulate filtration media. Utilization of nanofibers allows for a higher efficiency in the removal of submicron particles, and a multiplayer assembly method allows for the deposition of chemical functionality on the surface of these fibers. As such, it is possible to add toxic industrial chemical filtration capacity to the particulate media while utilizing ASZM-TEDA in a layered bed approach.

The next generation of military air purification systems will likely employ composite beds, whether they are layered, supported structures, electrospun fibers, or a combination of each. Utilizing these approaches will lead to broader protection and lower encumbrance for the same system footprint for both individual and collective protection applications.

Point of Contact:

Christopher J. Karwacki, Team Leader
CBR Filtration Team
Edgewood Chemical Biological Center
U.S. Army RDECOM
Phone: (410) 436-5704
e-mail: christopher.karwacki@us.army.mil

Gregory W. Peterson, Chemical Engineer
CBR Filtration Team
Edgewood Chemical Biological Center
U.S. Army RDECOM
Phone: (410) 436-9794
e-mail: gregory.w.peterson@us.army.mil

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