Continued Development of Compact Multi-Gas Monitor for Life Support Systems Control in Space

Miniature optic gas sensors (MOGS) based on luminescent materials have shown great potential as alternatives to NIR-based gas sensor systems for the Portable Life Support System (PLSS). The unique capability of MOGS for carbon dioxide and oxygen monitoring under wet conditions has been reported, as has the fast recovery of MOGS humidity sensors after long periods of being wet. Lower volume and power requirements are also potential advantages of MOGS over both traditional and advanced Non-Dispersive Infrared (NDIR) gas sensors, which have shown so far longer life than luminescent sensors. In this paper we present the most recent results in the development and analytical validation of a compact multi-gas sensor unit based on luminescent sensors for the PLSS. Results of extensive testing are presented, including studies conducted at Intelligent Optical Systems laboratories, a United Technology Corporation Aerospace Systems (UTAS) laboratory, and a Johnson Space Center laboratory. The potential of this sensor technology for gas monitoring in PLSSs and other life support systems and the advantages and limitations found through detailed sensor validation are discussed

Continued Development of Compact Multi-Gas Monitor for Life Support Systems Control in Space

Miniature optical gas sensors based on luminescent materials have shown great potential as alternatives to NIR-based gas sensor systems for the Portable Life Support System (PLSS). The unique capability of luminescent sensors for carbon dioxide and oxygen monitoring under wet conditions has been reported, as has the fast recovery of humidity sensors after long periods of being wet. Lower volume and power requirements are also potential advantages over both traditional and advanced non-dispersive infrared (NDIR) gas sensors, which have so far shown longer life than luminescent sensors. In this paper we present the most recent results in the development and analytical validation of a compact multi-gas sensor unit based on luminescent sensors for the PLSS. Results of extensive testing are presented, including studies conducted in Intelligent Optical Systems laboratories, a United Technologies Corporation Aerospace Systems (UTC) laboratory, and a Johnson Space Center laboratory. The potential of this sensor technology for gas monitoring in PLSSs and other life support systems, and the advantages and limitations found through detailed sensor validation are discussed

Electronic considerations in ligand assisted transition metal catalyzed oxidations of alkenes to enones

Ligand assisted transition metal catalysis used in the oxidation of alkenes is an area of research that is always growing. Yet, there is a void in the understanding of how to control the chemoselectivity of reaction. To determine the extent to which the electron density around the transition metal influences selectivity, a series of cobalt salen catalysts, with various electronic densities at the active site, were tested in the oxidation of cyclohexene with t-BuOOH. The changes to the electron density were determined by the Hammett σ-values associated with the substituents at the 5,5'-position on the salen ligand which increases or decreases the partial positive characteristic of the transition metal. When changed from hydrogen to electron withdrawing or donating substituents a reduction in enone chemoselectivity was seen. This also slowed the activity of the catalysts and decreased overall yield

Field Demonstration of CO₂ Leakage Detection in Potable Aquifers with a Pulselike CO₂‑Release Test

This study presents two field pulselike CO₂-release tests to demonstrate CO₂ leakage detection in a shallow aquifer by monitoring groundwater pH, alkalinity, and dissolved inorganic carbon (DIC) using the periodic groundwater sampling method and a fiber-optic CO₂ sensor for real-time in situ monitoring of dissolved CO₂ in groundwater. Measurements of groundwater pH, alkalinity, DIC, and dissolved CO₂ clearly deviated from their background values, showing responses to CO₂ leakage. Dissolved CO₂ observed in the tests was highly sensitive in comparison to groundwater pH, DIC, and alkalinity. Comparison of the pulselike CO₂-release tests to other field tests suggests that pulselike CO₂-release tests can provide reliable assessment of geochemical parameters indicative of CO₂ leakage. Measurements by the fiber-optic CO₂ sensor, showing obvious leakage signals, demonstrated the potential of real-time in situ monitoring of dissolved CO₂ for leakage detection at a geologic carbon sequestration (GCS) site. Results of a two-dimensional reactive transport model reproduced the geochemical measurements and confirmed that the decrease in groundwater pH and the increases in DIC and dissolved CO₂ observed in the pulselike CO₂-release tests were caused by dissolution of CO₂ whereas alkalinity was likely affected by carbonate dissolution