Spacecraft Water Regeneration by Catalytic Wet Air Oxidation
NASA Phase I Contract No. NNM05AA29C
The objective of this SBIR Phase I was to determine the feasibility of a class of heterogeneous catalysts for catalytic wet air oxidation (CWAO) of organic compounds for regeneration of spacecraft wastewater. Inclusion of catalysts in wet air oxidation (WAO) systems increases total destruction of organic compounds and reduces the severity of the operating conditions, resulting in a substantial decrease in processing costs and energy expenditure. The technical goals for this project were to achieve high oxidation activity and stability under relevant conditions with minimal leaching of catalysts metals.
A range of catalyst compositions were synthesized, characterized, and evaluated for destruction of organic contaminants under CWAO conditions. Ethanol, acetic acid, amino acids (glycine, aspartic acid, arginine), and saccharides (glucose, lactose, starch) were used as target contaminants for evaluating catalyst performance. In typical experiments, 125 ml of an aqueous contaminant (typically ~500 ppm total organic carbon, TOC) were placed in a reaction vessel with 1.25 g of catalyst, and removal of TOC was measured as a function of time at various temperatures and pressures with continuous stirring and oxygen flow. Selected catalysts were examined for low temperature and pressure activity, lifetime, leaching, and as catalyst grains.
Catalysts evaluated during this project demonstrated high activity for destruction of ethanol, acetic acid, amino acids, and saccharides in water under CWAO conditions. The most active catalysts achieved 50% removal of a 125 ppm acetic acid solution after 4 hours at ambient temperature and pressure. These catalysts were shown not to leach into water after 5 hours at 150°C and 150 psig. Lifetime measurements indicated extended use of the catalysts was possible, and catalysts prepared as grains exhibited minimal activity loss compared to powdered catalysts.
Variation in test conditions (e.g., temperature, pressure, organic contaminant, TOC and oxygen concentrations, solution mixing rate, catalyst quantity, test reactor design, etc.) employed by different laboratories make it difficult to directly compare results from different catalyst systems. However, most of the catalysts developed in this Phase I outperformed commercial 1% Pt/Al2O3 in side-by-side tests. Recent literature reports for precious metal supported mesoporous catalysts showed some activity at room temperature and pressure, though approximately 1.4 kg (2 L) of catalyst would be need to produce enough water for a crew of four for 1 day (220 lbs). The amount of catalyst developed in this Phase I necessary to produce the same amount of water in one day at ambient temperature and pressure would be 0.166 kg (0.1 L), a significant decrease in size considerations for spacecraft applications.
Target NASA application for this technology is a catalytic component for a volatile removal assembly used to purify and recycle spacecraft water. With the initiative for the development of a lunar space station and manned exploration of Mars, NASA must continue to develop life support technology that will allow for more frequent, complex and longer space missions. Spacecrafts are closed environments and inevitably contaminants will accumulate in the air and water systems. Minimization of the crew’s exposure to these contaminants is necessary to prevent the adverse health effects to the crew. The technology to be developed in this program of study will allow for increased contaminant removal at lower pressures and temperatures than current technology. Derivatives of this technology could also be used by NASA for a catalytic air filtration device.