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Game Changing Development

Next Generation Life Support (NGLS): Continuous Electrochemical Gas Separator (CEGS)

Completed Technology Project

Project Introduction

The purpose of this technology development task is to develop a new air purification system based on a liquid membrane, capable of purifying carbon dioxide from air in a far more compact and energy efficient system than what is currently possible. The approach relies on recent advances in supported liquid membranes, which allow the manufacture of mechanically stable, ultra-thin supported liquids that have permeability and selectivity for carbon dioxide over one order of magnitude greater than existing approaches. Most critically, because these membranes use a liquid as an active material, it is possible to electrochemically pump the carbon dioxide, making it viable to build an air purification system that uses no mechanical components such as compressors. Such an innovation has the potential to dramatically improve NASA's capabilities for human missions to Mars and other long-term space habitation applications.

Life support systems on human spacecraft are designed to provide a safe, habitable environment for the astronauts, and one of the most significant challenges is managing acceptable air quality. Carbon dioxide (CO2) is an important trace gas produced by human metabolism that must be actively removed from spacecraft cabin atmosphere. The Carbon Dioxide Removal Assembly (CDRA) currently on board the ISS performs the carbon dioxide (CO2) removal function as part of the on-board Atmosphere Revitalization System (ARS). It is considered the state-of-the-art for manned spacecraft cabins, but has two significant drawbacks: 1. The CDRA requires that air be dried prior to CO2 capture, and this costs energy – in fact, the system uses much energy drying the air than is required for capturing and releasing carbon dioxide. 2. The CDRA works in batch mode, requiring complicated valving and control to switch between sorbing and desorbing beds, while downstream CO2 processing systems can operate on a continuous stream of CO2. This adds unnecessary complexity, as well as a second parasitic energy loss. An ideal system would process CO2 continuously without any need for drying of the air, and without any moving parts. Such a system would require a fraction of the size and weight of the CDRA while dropping the cost of CO2 capture by 5X or more. Such a technology would be enabling for future long term manned flight missions, such as a mission to Mars. This element is developing a new electrochemical membrane technology using patented innovations in electrolyte materials. Technology development began under a Phase I effort funded by the NASA Advanced Innovative Concepts Program. The prior Phase I effort demonstrated the functionality of the basic approach to CO2 separation, demonstrating CO2 removal using only electrical input using a film in a membrane configuration. Membrane synthesis and fabrication techniques were developed that allowed for the successful incorporation and retention of an electrochemically active carrier molecule using composite liquid membrane technology. This allowed for the successful demonstration of a continuous CO2 capture rate at 40% in a single step with no moving parts. A higher capture rate of 80% was demonstrated in a batch mode during this phase.  The work gave promise that highly efficient, low energy separation of CO2 was possible using this technology, with the potential of operational energy savings as high as 80% compared with the state of the art, together with a weight and size footprint that could be as much as 75% smaller. The key enabling technology – composite liquid membrane materials – allow creation of a functional electrochemical membrane in a thin film form factor that enables this technology and application.  This prior work, however, demonstrated CO2 from nitrogen gas only, not humidified air.  It will be a technical challenge to prove the concept in representative cabin atmosphere containing moisture and oxygen. This Element, representing Phase II tasks, will focus on modifying the composite membrane system, evaluating active carrier molecules, ionic liquid solvents and membrane properties to operate the system efficiently in humid air.  Reliability and performance of the system will be evaluated.  Finally, a subscale system for a prototype air purifier will be designed. The effort will include increasing the size of the test cell and demonstrating long-term operation of the membranes under simulated cabin air (oxygen and nitrogen mixture with moisture), consistent with NASA requirements.

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