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System for collecting excess carbon dioxide in space cabin is described. System collects carbon dioxide exhaled by human inhabitants and decomposes gas into carbon and water by reaction with hydrogen in presence of catalyst. Diagram of equipment involved in reaction is included.
Life support is a critical function of any crewed space vehicle or habitat. Human life support systems on the International Space Station (ISS) include a number of atmosphere revitalization (AR) technologies to provide breathable air and a comfortable living environment to the crew. The Trace Contaminant Control System removes harmful volatile organic compounds and other trace contaminants from the circulating air. The Carbon Dioxide Removal Assembly (CDRA) removes metabolic carbon dioxide (CO2) and returns air to the cabin. Humidity is kept at comfortable levels by a number of condensing heat exchangers. The Oxygen Generation Assembly (OGA) electrolyzes water to produce oxygen for the crew and hydrogen (H2) as a byproduct. A Sabatier reaction-based CO2 Reduction Assembly (CRA) was launched to the ISS in 2009 and became fully operational in June 2011.The CRA interfaces with both the OGA and CDRA. Carbon dioxide from the CDRA is compressed and stored in tanks until hydrogen is available from OGA water electrolysis. When the OGA is operational and there is CO2 available, the CRA is activated and produces methane and water via the Sabatier reaction shown in Equation 1... One approach to achieve these higher recovery rates builds upon the ISS AR architecture and includes adding a methane post-processor to recover H2 from CRA methane. NASA has been developing the Plasma Pyrolysis Assembly (PPA) to fill the role of a methane post-processor.
Modern seafloor hydrothermal systems are locations where great varieties of geochemistry occur due to the enormous disequilibrium between vent fluids and seawater. The disequilibrium geochemistry has been hypothesized to include reactions to synthesize organic compounds. Despite the incomplete understanding of the carbon budget in hydrothermal systems, the organic geochemistry of these sites has received little attention. Experimental simulations of these environments, however, indicate that organic compounds may have difficulty forming in a purely aqueous environment. On the other hand, thiols, thioesters and disulfides have been implicated as reaction intermediates between CO or CO2 in experiments of carbon reduction in hydrothermal environments, as well as in a variety of biological processes and other abiotic reactions. The reduction of CO2 to thesis, for example, is observed using the FeS-H2S/FeS2 couple to provide the reducing power. We have used recent advances in theoretical geochemistry to estimate the standard partial moral thermodynamic properties and parameters for the revised Helgeson-Kirkham-Flowers equation of state for aqueous straight-chain alkyl thesis. With these data and parameters we have evaluated the role that organic sulfur compounds may play as reaction intermediates during organic compound synthesis. We conclude that organic sulfur compounds may hold the key to the organic chemistry leading to the origin of life in hydrothermal settings. These results may also explain the presence of sulfur in a number of biomolecules present in ancient thermophilic microorganisms.
State‐of‐the‐art life support carbon dioxide (CO2) reduction technology, based on the Sabatier reaction, is theoretically capable of 50% recovery of oxygen from metabolic CO2. This recovery is constrained by the limited availability of reactant hydrogen. Post‐processing of the methane byproduct from the Sabatier reactor results in hydrogen recycle and a subsequent increase in oxygen recovery. For this purpose, a Methane Post‐Processor Assembly containing three sub‐systems has been developed and tested. The assembly includes a Methane Purification Assembly (MePA) to remove residual CO2 and water vapor from the Sabatier product stream, a Plasma Pyrolysis Assembly (PPA) to partially pyrolyze methane into hydrogen and acetylene, and an Acetylene Separation Assembly (ASepA) to purify the hydrogen product for recycle. The results of partially integrated testing of the sub‐systems are reported.
State-of‐the‐art life support carbon dioxide (CO2) reduction technology, based on the Sabatier reaction, is theoretically capable of 50% recovery of oxygen from metabolic CO2. This recovery is constrained by the limited availability of reactant hydrogen. Post‐processing of the methane byproduct from the Sabatier reactor results in hydrogen recycle and a subsequent increase in oxygen recovery. For this purpose, a Methane Post‐Processor Assembly containing three sub‐systems has been developed and tested. The assembly includes a Methane Purification Assembly (MePA) to remove residual CO2 and water vapor from the Sabatier product stream, a Plasma Pyrolysis Assembly (PPA) to partially pyrolyze methane into hydrogen and acetylene, and an Acetylene Separation Assembly (ASepA) to purify the hydrogen product for recycle. The results of partially integrated testing of the sub‐systems are reported
State-of-the-art United States Atmospheric Revitalization carbon dioxide (CO2) reduction is based on the Sabatier reaction process, which recovers approximately 50% of the oxygen (O2) from crew metabolic CO2. Oxygen recovery from carbon dioxide is constrained by the limited availability of reactant hydrogen. Post-processing of methane to recover hydrogen with the Umpqua Research Company Plasma Pyrolysis Assembly (PPA) has the potential to further close the Atmospheric Revitalization oxygen loop. The PPA decomposes methane into hydrogen and hydrocarbons, predominantly acetylene, and a small amount of solid carbon. The hydrogen must then be purified before it can be recycled for additional oxygen recovery. Long duration testing and evaluation of a four crew-member sized PPA and a discussion of hydrogen recycling system architectures are presented.
Oxygen recovery from metabolically-produced carbon dioxide (CO2) is of critical importance for long-duration manned space missions beyond low Earth orbit. On the International Space Station (ISS), oxygen is provided to the crew through electrolysis of water in the Oxygen Generation Assembly (OGA). Prior to 2011, this water was entirely resupplied from Earth. A CO2 Reduction Assembly based on the Sabatier reaction (1) was developed by Hamilton Sundstrand and delivered to ISS in 2010. The unit recovers oxygen by reducing metabolic CO2 with diatomic hydrogen (H2) to produce methane and product water. The water is cleaned by the Water Purification Assembly and recycled to the OGA for continued oxygen production. The methane product is vented overboard.
Hydrothermal environments are locations of varied geochemistry due to the disequilibrium between vent fluids and seawater. The disequilibrium geochemistry has been hypothesized to include reactions to synthesize organic compounds. Observations of the organic geochemistry of hydrothermal vent sites has received little attention. Experimental simulations of these environments, however, indicate that organic compounds may have difficulty forming in a purely aqueous environment. On the other hand, thiols. thioesters and disulfides have been implicated as reaction intermediates between CO or CO2 in experiments of carbon reduction in hydrothermal environments as well as in a variety of biological processes and other abiotic reactions (Wachtershauser, 1990, OLEB 20, 173; Heinen and Lauwers, 1996, OLEB 26, 13 1, Huber and Wachtershauser, 1997, Science 276, 245; Russell et al., 1998, in Thermophiles: The keys to molecular evolution and the origin of life?). The reduction of CO2 to thiols, for example, is observed using the FeS-H2S/FeS2 couple to provide the reducing power (see Schoonen et al., 1999, OLEB 29, 5). In addition, the enzyme involved in final stage of methanogenesis, coenzyme-M, is itself a thiol. Thus, organic sulfur compounds may hold the key to the organic chemistry leading to the origin of life at high temperatures. Understanding the biochemical processes of microorganisms that can live to temperatures at least as high as 113 C (Blochl et al., 1996, Extremophiles 1, 14) requires knowledge of the properties of the chemical reactions involved. In order to assess the role of aqueous organic sulfur compounds in hydrothermal organic geochemistry, we have been attempting to determine their thermodynamic properties. We have culled the literature to obtain the properties of organic sulfur compounds. We are able to calculate a number of essential properties, such as free energies of formation, from solubility data available in the literature together with standard properties of organic sulfur gases. However, a number of the properties for aqueous organic sulfur compounds have not been experimentally determined. Furthermore, most of thermodynamic data that are available are for 25 C and 1 bar. In order to determine reaction properties to temperatures and pressures appropriate to the hydrothermal conditions in which thermophilic organisms actually live, we use equations of state developed by Helgeson and co-workers (Helgeson et al., 1981, AJS 281, 1249). A key piece of information needed to go up in temperature is the partial molal heat capacity, which is one of the properties for which experimental data are unavailable for nearly all organic sulfur compounds. We have used correlation methods to determine the partial molal heat capacities and volumes of many organic solutes. These estimates allow us to asses the role of organic sulfur compounds during the reduction of carbon in hydrothermal settings. We will present these data, along with examples of the thermodynamic properties of reactions involving aqueous organic sulfur compounds.
State-of-the-art life support carbon dioxide (CO2) reduction technology is based on the Sabatier reaction where less than 50% of the oxygen required for the crew is recovered from metabolic CO2. The reaction produces water as the primary product and methane as a byproduct. Oxygen recovery is constrained by the limited availability of reactant hydrogen. This is further exacerbated when Sabatier methane (CH4) is vented as a waste product resulting in a continuous loss of reactant hydrogen. Post-processing methane with the Plasma Pyrolysis Assembly (PPA) to recover hydrogen has the potential to dramatically increase oxygen recovery and thus drastically reduce the logistical challenges associated with oxygen resupply. The PPA decomposes methane into predominantly hydrogen and acetylene. Due to the highly unstable nature of acetylene, a separation system is necessary to purify hydrogen before it is recycled back to the Sabatier reactor. Testing and evaluation of a full-scale Third Generation PPA is reported and investigations into metal hydride hydrogen separation technology is discussed.
The thermodynamics of the FeS-H2S/FeS2 redox couple and a select number of reactions critical to the synthesis of simple carboxylic acids and amino acids have been evaluated as a function of temperature. This thermodynamic evaluation shows that the reducing power of the FeS-H2S/FeS2 redox couple decreases drastically with temperature. By contrast the equilibria describing the reduction of CO2 and the formation of simple carboxylic acids and amino acids require an increasingly higher reducing power with temperature. Given these two opposite trends, the thermodynamic driving force for CO2 reduction and amino acid formation with the FeS-H2S/FeS2 redox couple as reductant diminishes with increasing temperature. An evaluation of the mechanism of CO2 reduction by the FeS-H2S/FeS2 couple suggests that the electron transfer from pyrrhotite to CO2 is hindered by a high activation energy, even though the overall reaction is thermodynamically favorable. By comparison the electron transfer from pyrrhotite to either CS2, CO, or HCOOH are far more facile. This theoretical analysis explains the results of experimental work by Keefe et al. (1995), Heinen and Lauwers (1996) and Huber and Wachtershauser (1997). The implication is that a reaction sequence involving the reduction of CO2 with the FeS-H2S/FeS2 couple as reductant is unlikely to initiate a proposed prebiotic carbon fixation cycle (Wachtershauser, 1988b; 1990b, 1990a, 1992, 1993).
A room-temperature electrocatalytic process that effects the overall chemical reaction CO2 + 2H2O yields CH4 + 2O2 has been investigated as a means of removing carbon dioxide from air and restoring oxygen to the air. The process was originally intended for use in a spacecraft life-support system, in which the methane would be vented to outer space. The process may also have potential utility in terrestrial applications in which either or both of the methane and oxygen produced might be utilized or vented to the atmosphere. A typical cell used to implement the process includes a polymer solid-electrolyte membrane, onto which are deposited cathode and anode films. The cathode film is catalytic for electrolytic reduction of CO2 at low overpotential. The anode film is typically made of platinum. When CO2 is circulated past the cathode, water is circulated past the anode, and a suitable potential is applied, the anode half-cell reaction is 4H2O yields 2O2 + 8H(+) + 8e(-). The H(+) ions travel through the membrane to the cathode, where they participate in the half-cell reaction CO2 + 8H(+) + 8e(-) yields CH4 + 2H2O.
A program was conducted to evaluate and characterize the carbon dioxide-methane (CO2-CH4) decomposition reaction, i.e., CO2 + CH4 = 2C + 2H2O. The primary objective was to determine the feasibility of applying this reaction at low temperatures as a technique for recovering the oxygen (O2) remaining in the CO2 which exits mixed with CH4 from a Sabatier CO2 reduction subsystem (as part of an air revitalization system of a manned spacecraft). A test unit was designed, fabricated, and assembled for characterizing the performance of various catalysts for the reaction and ultraviolet activation of the CH4 and CO2. The reactor included in the test unit was designed to have sufficient capacity to evaluate catalyst charges of up to 76 g (0.17 lb). The test stand contained the necessary instrumentation and controls to obtain the data required to characterize the performance of the catalysts and sensitizers tested: flow control and measurement, temperature control and measurement, product and inlet gas analysis, and pressure measurement. A product assurance program was performed implementing the concepts of quality control and safety into the program effort.
We report results of experiments to measure the C isotope composition of mineral catalyzed organic compounds derived from high temperature and high pressure synthesis. These experiments make use of an innovative pyrolysis technique designed to extract and measure C isotopes. To date, our experiments have focused on the pyrolysis and C isotope ratio measurements of low-molecular weight intermediary hydrocarbons (organic acids and alcohols) and serve as a proof of concept for making C and H isotope measurements on more complicated mixtures of solid-phase hydrocarbons and intermediary products produced during high temperature and high pressure synthesis on mineral-catalyzed surfaces. The impetus for this work stems from recently reported observations of methane detected within the Martian atmosphere [1-4], coupled with evidence showing extensive water-rock interaction during Martian history [5-7]. Methane production on Mars could be the result of synthesis by mineral surface-catalyzed reduction of CO2 and/or CO by Fischer-Tropsch Type (FTT) reactions during serpentization reactions [8,9]. Others have conducted experimental studies to show that FTT reactions are plausible mechanisms for low-molecular weight hydrocarbon formation in hydrothermal systems at mid-ocean ridges [10-12]. Further, recent experiments by Fu et al. [13] focus on examining detailed C isotope measurements of hydrocarbons produced by surface-catalyzed mineral reactions. Work described in this paper details the experimental techniques used to measure intermediary organic reaction products (alcohols and organic acids).
We report results of experiments to measure the H isotope composition of organic acids and alcohols. These experiments make use of a pyroprobe interfaced with a GC and high temperature extraction furnace to make quantitative H isotope measurements. This work compliments our previous work that focused on the extraction and analysis of C isotopes from the same compounds [1]. Together with our carbon isotope analyses our experiments serve as a "proof of concept" for making C and H isotope measurements on more complex mixtures of organic compounds on mineral surfaces in abiotic hydrocarbon formation processes at elevated temperatures and pressures. Our motivation for undertaking this work stems from observations of methane detected within the Martian atmosphere [2-5], coupled with evidence showing extensive water-rock interaction during Mars history [6-8]. Methane production on Mars could be the result of synthesis by mineral surface-catalyzed reduction of CO2 and/or CO by Fischer-Tropsch Type (FTT) reactions during serpentization [9,10]. Others have conducted experimental studies to show that FTT reactions are plausible mechanisms for low-molecular weight hydrocarbon formation in hydrothermal systems at mid-ocean ridges [11-13]. Our H isotope measurements utilize an analytical technique combining Pyrolysis-Gas Chromatograph-Mass Spectrometry-High Temperature Conversion-Isotope Ratio Mass Spectrometry (Py-GC-MS-TC-IRMS). This technique is designed to carry a split of the pyrolyzed GC-separated product to a Thermo DSQII quadrupole mass spectrometer as a means of making qualitative and semi-quantitative compositional measurements of separated organic compounds, therefore both chemical and isotopic measurements can be carried out simultaneously on the same sample.
The detection of methane in the atmosphere of Mars, combined with evidence showing widespread water-rock interaction during martian history, suggests that the production of methane on Mars may be the result of mineral surface-catalyzed CO2 and or CO reduction during Fisher-Tropsch Type (FTT) reactions. A better understanding of these reaction pathways and corresponding C and H isotope fractionations is critical to deciphering the synthesis of organic compounds produced under abiotic hydrothermal conditions. Described here is a technique for the extraction and analysis of both C and H isotopes from alcohols (C1-C4) and organic acids (C1-C6). This work is meant to provide a "proof of concept" for making meaningful isotope measurements on complex mixtures of solid-phase hydrocarbons and other intermediary products produced during high-temperature and high-pressure synthesis on mineral-catalyzed surfaces. These analyses are conducted entirely "on-line" utilizing a CDS model 5000 Pyroprobe connected to a Thermo Trace GC Ultra that is interfaced with a Thermo MAT 253 isotope ratio mass spectrometer operating in continuous flow mode. Also, this technique is designed to carry a split of the GC-separated product to a DSQ II quadrupole mass spectrometer as a means of making semi-quantitative compositional measurements. Therefore, both chemical and isotopic measurements can be carried out on the same sample.
Through the respiration process, humans consume oxygen (O2) while producing carbon dioxide (CO2) and water (H2O) as byproducts. For long term space exploration, CO2 concentration in the atmosphere must be managed to prevent hypercapnia. Moreover, CO2 can be used as a source of oxygen through chemical reduction serving to minimize the amount of oxygen required at launch. Reduction can be achieved through a number of techniques. NASA is currently exploring the Sabatier reaction, the Bosch reaction, and co- electrolysis of CO2 and H2O for this process. Proof-of-concept experiments and prototype units for all three processes have proven capable of returning useful commodities for space exploration. All three techniques have demonstrated the capacity to reduce CO2 in the laboratory, yet there is interest in understanding how all three techniques would perform at a system level within a spacecraft. Consequently, there is an impetus to develop predictive models for these processes that can be readily rescaled and integrated into larger system models. Such analysis tools provide the ability to evaluate each technique on a comparable basis with respect to processing rates. This manuscript describes the current models for the carbon dioxide reduction processes under parallel developmental efforts. Comparison to experimental data is provided were available for verification purposes.
An advanced system for removing CO2 and H2O from cabin air, reducing the CO2, and returning the resulting O2 to the air is less massive than is a prior system that includes two assemblies . one for removal and one for reduction. Also, in this system, unlike in the prior system, there is no need to compress and temporarily store CO2. In this present system, removal and reduction take place within a single assembly, wherein removal is effected by use of an alkali sorbent and reduction is effected using a supply of H2 and Ru catalyst, by means of the Sabatier reaction, which is CO2 + 4H2 CH4 + O2. The assembly contains two fixed-bed reactors operating in alternation: At first, air is blown through the first bed, which absorbs CO2 and H2O. Once the first bed is saturated with CO2 and H2O, the flow of air is diverted through the second bed and the first bed is regenerated by supplying it with H2 for the Sabatier reaction. Initially, the H2 is heated to provide heat for the regeneration reaction, which is endothermic. In the later stages of regeneration, the Sabatier reaction, which is exothermic, supplies the heat for regeneration.
The utilization of CO2 to produce life support consumables, such as O2 and H2O, via the Sabatier reaction is an important aspect of NASA s cabin Atmosphere Revitalization System and In-Situ Resource Utilization architectures for both low-earth orbit and long-term manned space missions. In the current International Space Station (ISS) and other low orbit missions, metabolically-generated CO2 is removed from the cabin air and vented into space, resulting in a net loss of O2. This requires a continuous resupply of O2 via water electrolysis, and thus highlights the need for large water storage capacity. For long-duration space missions, the amount of life support consumables is limited and resupply options are practically nonexistent, thus atmosphere resource management and recycle becomes crucial to significantly reduce necessary O2 and H2O storage. Additionally, the potential use of the Martian CO2-rich atmosphere and Lunar regolith to generate life support consumables and propellant fuels is of interest to NASA. Precision Combustion, Inc. (PCI) has developed a compact, lightweight Microlith(Registered TradeMark)-based Sabatier (CO2 methanation) reactor which demonstrates the capability of achieving high CO2 conversion and near 100% CH4 selectivity at space velocities of 30,000-60,000 hr-1. The combination of the Microlith(Registered TradeMark) substrates and durable, novel catalyst coating permitted efficient Sabatier reactor operation that favors high reactant conversion, high selectivity, and long-term durability. This paper presents the reactor development and performance results at various operating conditions. Additionally, results from 100-hr durability tests and mechanical vibration tests are discussed.