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Advanced supported liquid membranes for CO2 control in extravehicular activity applications
Abstract
The development of a new, robust, portable life support system (PLSS) is currently a crucial need for NASA as it continues making advances in space exploration and extends its missions beyond low Earth orbit. The control of carbon dioxide (CO2) produced by astronauts during extravehicular activities (EVAs) is a critical function of the PLSS. Although the metal oxide and lithium hydroxide canisters, currently used to remove CO2, have worked well, they have a finite CO2 absorption capacity. Therefore, the only way to extend mission times with current technology is to make the unit larger or use excessive energy to regenerate, which is undesirable. Therefore, new CO2 control technologies must be developed for EVA applications. Although much recent work has centered on sorbents that can be regenerated during the EVA, this strategy increases the system size, weight, complexity, and power consumption. A much simpler approach is to use a membrane that selectively vents CO2 to space. A membrane is desirable because it is a continuous system with no theoretical capacity limit and it requires no consumables or hardware for switching beds between absorption and regeneration. Unfortunately, conventional gas separation membranes do not have adequate selectivity for use in the PLSS. However, the needed performance could be achieved with a supported liquid membrane (SLM) using a liquid reagent that selectively reacts with CO2 over oxygen (O2). Reaction Systems is developing new liquid compounds that absorb CO2 and have effectively zero vapor pressure, making these compounds ideal candidates for use in a SLM. In this paper, we describe results obtained with two sorbents. The sorbents were first characterized with nuclear magnetic resonance, and then the reversible CO2 uptakes of each were measured. Finally, the liquids were impregnated in porous membranes. Permeance measurements were carried out with both CO2 and O2. While the initial results show that higher permeance and selectivities are needed, they also suggest that SLMs have the potential to control CO2 in an EVA application and identify specific paths towards achieving the needed performance.
... Otherwise, concern for CO toxicity would prevent crew occupancy of the greenhouse. As shown in the figure, the system comprises the following process steps: 1) Capture CO2-laden gas from a simulated Mars atmosphere, 2) remove dust particulates with a two-stage filtration unit, 3) compress the gas flow, 4) selectively permeate 150 g CO2/day through the temperature-controlled SILM to the sweep gas, 5) collect and store the exhaust gases from the process stream, 6) control the CO2-laden sweep gas stream to the greenhouse, 7) plants take up CO2 and produce O2 along with ethylene, 8) a blower circulates the gas flow, 9) condense, separate and collect water vapor from the sweep gas stream leaving the plant growth chamber, 10) remove ethylene and catalytically oxidize carbon monoxide and other volatiles toxic either to plants or the crew, 11) separate excess O2 from the sweep gas flow, and 12) return the sweep gas to the SILM for replenishment of CO2. ...
... In either membrane the concentration of CO2 in the feed gas is lowered depending upon the driving potential for CO2 transport. More recently, it was found that CO2 transport could be facilitated by filling the membrane pores with an ionic liquid [11,12], which are a natural choice given their negligible vapor pressure, chemical stability and high boiling point. The negligible vapor pressure means that fluid will not be lost from the membrane, a common problem with other liquids such as monoethanolamine (MEA). ...
In situ utilization of carbon dioxide (CO2) from the Mars atmosphere provides a critical element for on-surface crop production. The atmosphere management system for the MarsOasis® growth chamber provides CO2, recovers water and oxygen, and removes ethylene to maintain a hospitable atmosphere for the crops. A supported ionic liquid membrane (SILM) can selectively provide CO2 while rejecting carbon monoxide (CO) back to the Mars atmosphere. The SILM comprises an ionic liquid infiltrated into the pores of a thin physical membrane support such as polyethersulfone or nylon. Ionic liquids are most promising for their negligible vapor pressure, low melting points (many remain liquid below 0°C), thermal stability up to 100°C or greater, and solubilities (especially for water and/or acid gases) that depend upon the cation and anion that comprise the IL. The negligible vapor pressure means that fluid will not be lost from the membrane, a common problem with other liquid sorbents. The physical processes of sorption and solution-diffusion through the membrane are enhanced; in part, because the supported liquid membrane can be made much thinner than a purely physical membrane without blowing liquid out of the support or losing it to vaporization. Then, amine-, fluorine-, or nitrile-functionalized groups in the IL can further facilitate the highly selective transport since these compounds chemically interact with CO2 to increase its uptake and rate of diffusion. In this paper we report experiments to characterize a SILM for selective CO2 capture from surrogate atmospheres. Nomenclature A = surface area Ac = acetate bmim = 1-butyl-3-methylimidazolium cm 2 = square centimeters cm Hg = centimeters of mercury CO = carbon monoxide CO2 = carbon dioxide FC = flow control FM = flow meter g = gram IL = ionic liquid mm Hg = millimeters of mercury N2 = nitrogen O2 = oxygen 1 Associate Professor, Smead Aerospace Engineering Sciences, International Conference on Environmental Systems 2 ppm = parts per million P = pressure, permeability P = pressure difference ppCO2 = partial pressure of CO2 Qm = permeance s = second S = selectivity scc = standard cubic centimeters scfm = standard cubic feet per minute SILM = supported ionic liquid membrane slpm = standard liters per minute TC = thermocouple ̇ , = volumetric permeate flow for species i vol% = volume percent V = valve Subscripts i = species i p = permeate x = species x
... 73 It was already discussed that some RTILs have high solubility for CO 2 , which is why there is interest in using them in CO 2 capture and separation systems. [74][75][76] One system design could concentrate CO 2 in an RTIL as part of a CO 2 adsorption system, and then transfer the CO 2 -laden RTIL to an ECRS for reducing the CO 2 present in the RTIL. Using the generic cell presented in Figure 3, a continuous ECRS could be designed where CO 2 is introduced through a gas diffusion electrode as the electrochemical process is driven simultaneously. ...
Improved oxygen (O 2) recovery from carbon dioxide (CO 2) is a recognized capability needed to enable long-term human space exploration. It has applications for environmental control and life support systems (ECLSS) as well as for in-situ resource utilization (ISRU). Past trade studies of technologies for physio-chemical CO 2 reduction processes have included the Sabatier process, the Bosch process, solid oxide co-electrolysis, and carbon formation reactors, but have not made mention of low temperature CO 2 electrolysis. Aqueous, low temperature, electrochemical CO 2 reduction and co-electrolysis processes offer potential advantages for ECLSS and ISRU systems, but they are not yet at sufficient technology readiness levels (TRL) to be considered for use onboard spacecraft. Various research avenues are currently advancing the maturity and performance of these processes, with one attractive prospect being the use of room temperature ionic liquids (RTIL). RTILs are non-volatile solvents with high CO 2 solubility that are generally safer than other liquids used as CO 2 solvents. In an electrochemical cell, RTILs can act as electrolytes with high electrochemical and thermal stability. Recently, RTILs have been seen to act as catalyst promoters that favor selective product formation with lower energy costs compared to conventional low temperature electrochemical CO 2 reduction technologies. Because a variety of human space exploration mission scenarios could benefit from an RTIL-assisted electrochemical reduction system (ECRS), high-level conceptual designs are presented with a qualitative discussion of their potential advantages and challenges. Further, the performance metrics for an ECRS are translated to system-level design parameters (mass, volume, and power). This will allow for a first-order assessment of how an ECRS would fit within ECLSS or ISRU system budgets, and ultimately aid in assessing the feasibility and advancing the TRL of ECRS technologies.
In order to prevent and manage human error, it must be understood how human cognitive functions are linked to failures in short-term sensory processing, long-term memory retrieval, and other error precursors including common cognitive biases. This chapter lays a foundation for understanding human error influenced by internal factors (physiological and mental states) and external factors (environmental, team, and organizational factors) that can negatively impact cognitive functions and error resistance in a challenging and often unpredictable environment.
We report a means for efficient and selective extraction of carbon dioxide (CO(2)) at low to medium concentration from mixed gas streams. CO(2) capture was accomplished by use of a novel enzyme-based, facilitated transport contained liquid membrane (EBCLM) reactor. The parametric studies we report explore both structural and operational parameters of this design. The structural parameters include carbonic anhydrase (CA) concentration, buffer concentration and pH, and liquid membrane thickness. The operational parameters are temperature, humidity of the inlet gas stream, and CO(2) concentration in the feed stream. The data show that this system effectively captures CO(2) over the range 400 ppm to at least 100,000 ppm, at or around ambient temperature and pressure. In a single pass across this homogeneous catalyst design, given a feed of 0.1% CO(2), the selectivity of CO(2) versus N(2) is 1,090 : 1 and CO(2) versus O(2) is 790 :1. CO(2) permeance is 4.71 x 10(-8) molm(-2) Pa(-1) sec(-1). The CLM design results in a system that is very stable even in the presence of dry feed and sweep gases.
Biodegradable polymer/layered silicate nanocomposite membranes were prepared by solution casting method for the application of dehumidification and gas separation. The intercalation and exfoliation of clay in the prepared nanocomposite membranes were confirmed through X-ray diffraction study (XRD). Their thermal and mechanical properties were observed by using Thermo-gravimetric analysis (TGA) and Universal Testing Machine (UTM), respectively. Gas and vapor permeation properties were examined to investigate the effect of the intercalated nanocomposite into membranes. Both gas and vapor permeabilities of the prepared nanocomposite membranes were found to decrease with the increase of clay content. They proved their particular barrier property through intercalation of clay.
This paper reports the results of our continuing efforts to develop glycerol-based immobilized liquid membranes (ILMs) for the selective separation of CO2 from a mixed-gas (CO2, N2) feed having low CO2 concentrations in space-walk and space-cabin atmospheres. The items of specific interest are replacement of the carrier sodium carbonate (studied by Chen et al. (Ind. Eng. Chem. Res. 1999, 38, 3489−3498) by glycine-Na in glycerol, ILM thickness reduction, performance of environmentally benign carriers, e.g., glycine-Na vis-à-vis toxic and volatile carriers, e.g., ethylenediamine. The effects of glycine-Na concentration (range 0−5.0 mol/dm3), CO2 partial pressure (between 0.006 and 0.8 atm), and feed relative humidity (RH; range 40−100%) have been investigated. The sweep gas was always dry helium. As the glycine-Na concentration was increased, N2 permeability decreased, while the CO2 permeability increased drastically at lower glycinate concentrations, leveling off at higher glycinate concentrations. Lower feed stream RHs yielded lower species permeances but greater CO2/N2 selectivities. For a feed RH of 70%, pCO2,f = 0.006 atm, and a glycine-Na concentration of 2.5 mol/dm3, the CO2/N2 separation factor was found to be a very high 5000 in an ILM spanning the whole thickness of a hydrophilized poly(vinylidene fluoride) flat film. ILMs containing both carbonate and glycinate demonstrated high CO2 permeances and high CO2/N2 selectivity. The ILM stability was also tested by a 25-day-long run. Permeances of N2 through glycerol-based membranes and of CO2 through pure glycerol membrane have been estimated and compared with experimentally obtained values.
Separation of carbon dioxide from a humid mixture of CO2−N2 through membranes containing immobilized solutions of Na2CO3−glycerol in porous and hydrophilic poly(vinylidene fluoride) (PVDF) substrate was experimentally studied for use as a venting membrane in space-walk applications. The effects of Na2CO3 concentration, CO2 partial pressure, and feed stream relative humidity (RH) were investigated. The carbonate concentration was in the range of 0−4.0 mol/dm3. The feed gas RH range was 49−100%; the sweep gas was dry helium. CO2 partial pressure (pCO2,f) range was 0.007−0.77 atm. Addition of Na2CO3 increased the CO2 permeability drastically at lower carbonate concentrations; at higher Na2CO3 concentrations, this permeability increase is partly compromised by increased solution viscosity and salting-out effect. N2 permeability coefficient decreased with an increase in Na2CO3 concentration. Very high CO2/N2 selectivities were observed at high Na2CO3 concentrations. Higher CO2/N2 selectivities were observed at lower CO2 partial pressure differentials. Steady-state water content in the hygroscopic immobilized liquid membrane (ILM) increases with an increase in feed stream RH. The water content in the ILM considerably affects its viscosity and the effective concentration of the carriers in the ILM; those factors determine the permeation performances of the ILM. Generally, lower permeances and greater CO2/N2 selectivity values were observed at lower feed stream RHs. When the feed RH = 50.7%, pCO2,f = 0.007 atm and the Na2CO3 concentration was 1.0 mol/dm3; the separation factor α(CO2/N2) observed was 3440. Prolonged runs lasting 14 days showed that the ILM permeation performances were quite stable. The ILMs were also found to be stable when challenged with feed streams of very low RHs.
Glycerol-based liquid membranes immobilized in the pores of hydrophilic microporous hollow fibers have been studied for selective separation of CO2 from a mixed gas (CO2, N2) feed having low concentrations of CO2 characteristic of gases encountered in space walk and space cabin atmosphere. The immobilized liquid membranes (ILMs) investigated consist of sodium carbonate–glycerol or glycine-Na–glycerol solution. Based on the performances of such liquid membranes in flat hydrophilic porous substrates [Chen et al., Ind. Eng. Chem. Res. 38 (1999) 3489; Chen et al., Ind. Eng. Chem. Res. 39 (2000) 2447], hollow fiber-based ILMs were studied at selected CO2 partial pressure differentials (ΔpCO2 range 0.36–0.50 cmHg), relative humidities (RH range 45–100%), as well as carrier concentrations. The sodium carbonate concentration was primarily 1.0 mol/dm3; the glycine-Na concentration was 3.0 mol/dm3. The sweep gas was always dry helium and it flowed on the shell side. Very high CO2/N2 selectivities were observed with porous polysulfone microfiltration membranes as substrate. As in the case of flat film-based ILMs (see references above), feed side RH is an important factor determining the ILM performances. Generally, lower permeances and greater CO2/N2 selectivity values were observed at lower feed stream RHs. When the feed side average RH=60%, pCO2,f=0.005 atm and glycine-Na concentration was 3.0 M, the CO2/N2 separation factor observed was over 5000. Prolonged runs lasting for 300 h showed that the hollow fiber-based ILM permeation performances were stable.
An immobilized film of an aqueous bicarbonate-carbonate solution was developed which was 4100 times more permeable to carbon
dioxide than to oxygen. The carbon dioxide transport was reaction-rate limited, and thus it could be increased by addition
to the film of catalysts for the hydrolysis of carbon dioxide.