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Activated carbon is a common and effective adsorbent for removal of trace organic compounds from air. Carbon's adsorption capacity for many of these compounds is a strong inverse function of the relative humidity of the air. We have investigated a proposed process for regenerating carbon beds that takes advantage of this effect, in which a reverse flow of high humidity air is used to drive previously adsorbed contaminants out of the bed and into an oxidation system. This paper presents results of our experimental work and its applications to trace contaminant control systems for spacecraft.

The current CO2 removal technology of NASA is very energy intensive and contains many non-optimized subsystems. This paper discusses the concept of a next-generation, membrane-integrated, adsorption processor for CO2 removal and compression in closed-loop air revitalization systems. The membrane module removes water from the feed, passing it directly into the processor's exhaust stream; it replaces the desiccant beds in the current four-bed molecular sieve system, which must be thermally regenerated. Moreover, in the new processor, CO2 is removed and compressed in a single two-stage unit. This processor will use much less power than NASA's current CO2 removal technology and will be capable of maintaining a lower CO2 concentration in the cabin than that can be achieved by the existing CO2 removal systems.

Oxygen loop closure is of high priority for an advanced space station air revitalization system. Closure will require the system's CO2 removal and reduction assemblies to be linked; however, the hardware for these two assemblies that is presently considered for use on the International Space Station (ISS) cannot be connected directly and so an interface device is needed. The interface device must provide an adequate vacuum for the CO2 removal assembly, must provide CO2 at a high enough pressure for the CO2 reduction assembly, and must also store sufficient CO2 to accommodate the difference in operating periods of the two processes. A mechanical vacuum pump/compressor with a buffer tank is one solution to the interface, but has drawbacks particularly in the areas of power consumption and size. A solid-state, adsorption-based compressor design is being developed at NASA Ames Research Center that meets the requirements of the interface device.

Chemical processing of the dusty, low-pressure Martian atmosphere for production of propellants and other consumables will require conditioning and compression of the gases as first steps. A temperature-swing adsorption process can perform these tasks using solid-state hardware and with relatively low power consumption compared to alternative processes. The process can also separate the atmospheric constituents, producing both pressurized CO2 and a buffer gas mixture of nitrogen and argon. We have developed and tested adsorption-based compressors with production levels appropriate for near-term robotic flight experiments, which are needed to demonstrate the basic technologies for ISRU-based human exploration missions. In this talk we describe the characteristics, testing, and performance of these devices. We also discuss scale-up issues associated with meeting the processing demands of sample return and human missions.

This paper offers a concept for a regenerable, low-power system for purifying exhaust from a solid waste processor. The innovations in the concept include the use of a closed-loop regeneration cycle for the adsorber, which prevents contaminants from reaching the breathable air before they are destroyed, and the use of a humidity-swing desorption cycle, which uses less power than a thermal desorption cycle and requires no venting of air and water to space vacuum or planetary atmosphere. The process would also serve well as a trace contaminant control system for the air in the closed environment. A systems-level design is presented that shows how both the exhaust and air purification tasks could be performed by one processor. Data measured with a fixed-bed apparatus demonstrate the effects of the humidity swing on regeneration of the adsorbent.

This paper describes a simple concept for extracting a nitrogen-argon carrier gas mixture from the Martian atmosphere in-situ and compressing the gas to a pressure suitable for use in analytical experiments during exploration missions. Both the separation and compression processes are performed via adsorption. In addition to being a low-mass, low-volume, and virtually solid state unit, the process consumes little or no electrical power. Energy to perform work is taken from the environment using the daily temperature cycle. Such a device would also be a proof-of-concept technology for buffer gas generation for life support application on future human missions to Mars.

Technologies that can be used to extract oxygen and other useful products from the Martian atmosphere for exploration missions will require compression of the low-pressure Martian gas. One technique that appears ideally suited for this application is temperature-swing adsorption, which can produce purified and compressed CO2 in a virtually solid-state process whose energy requirements can be met mainly through the diurnal temperature cycle. This paper focuses on material selection and sensitivity of this adsorption process to variations in Mars surface conditions. Experimental results indicate that, of the zeolite and carbon materials studied, a NaX zeolite is a superior adsorbent in terms of the amount of pressurized gas it can produce per unit mass of sorbent.

Effects of a cabin-level humidity upset on an activated carbon column used for adsorption of trace compounds from air are examined through a series of experiments and computer simulations. Breakthrough curves measured for dichloromethane in the presence of water indicate that a rapid increase in relative humidity can displace large quantities of dichloromethane from the adsorbed phase resulting in effluent streams containing more than 20 times the feed concentration. Additionally, the breakthrough time for organic compounds is reduced significantly at high relative humidity. Numerical simulation results show favorable qualitative agreement with measured breakthrough curves, yet do not consistently predict accurate water or dichloromethane loadings at all experimental conditions.

A finite-difference gas adsorption computer model for CO2, H2O, and N2 on zeolite 5A is discussed. It is part of an effort to predict results, via simulation, of changing a spacecraft CO2 removal system's operational configuration. The mathematical and numerical modeling approach, with emphasis on identification and independent verification of important adsorption physics, is described. The apparatus used to obtain single and multicomponent isotherms, and the subscale packed column bench test used to derive transfer coefficients and verify the model are described. The favorable comparison of simulation and test results show the potential for predictive capability with this modeling approach.

As the durations of manned space missions increase, so will the need for compact and reliable water recycling systems. Optimization of such water-recycling systems involves computer simulation of process elements and subsystems. The operations of water recycling systems are simulated at the Ames Research Center using commercial software called ASPEN-PLUS. Ion exchange is a part of the multifiltration subsystem, used for final polishing of recycled water and in some cases as a complete water treatment. Ion-exchange resins remove hazardous ions from solution by exchanging them with innocuous ions according to selection parameters. The ion-exchange operation is not provided in the ASPEN-PLUS multiprocess simulator package, but FORTRAN-callable modules may be added. Therefore we have adapted a FORTRAN program simulating multicomponent adsorption by ion-exchange resins, for use both as an ASPEN-callable module and as a free-standing simulator of the ion-exchange bed.