Evaluation of Bosch-Based Systems Using Non-Traditional Catalysts at Reduced Temperatures

Abstract

Oxygen and water resupply make open loop atmosphere revitalization (AR) systems unfavorable for long-term missions beyond low Earth orbit. Crucial to closing the AR loop are carbon dioxide reduction systems with low mass and volume, minimal power requirements, and minimal consumables. For this purpose, NASA is exploring using Boschbased systems. The Bosch process is favorable over state-of-the-art Sabatier-based processes due to complete loop closure. However, traditional operation of the Bosch required high reaction temperatures, high recycle rates, and significant consumables in the form of catalyst resupply due to carbon fouling. A number of configurations have been proposed for next-generation Bosch systems. First, alternative catalysts (catalysts other than steel wool) can be used in a traditional single-stage Bosch reactor to improve reaction kinetics and increase carbon packing density. Second, the Bosch reactor may be split into separate stages wherein the first reactor stage is dedicated to carbon monoxide and water formation via the reverse water-gas shift reaction and the second reactor stage is dedicated to carbon formation. A series system will enable maximum efficiency of both steps of the Bosch reaction, resulting in optimized operation and maximum carbon formation rate. This paper details the results of testing of both single-stage and two-stage Bosch systems with alternative catalysts at reduced temperatures. These results are compared to a traditional Bosch system operated with a steel wool catalyst.

Performance Evaluation of Staged Bosch Process for CO2 Reduction to Produce Life Support Consumables

“…In comparison to the traditional steel wool catalyst which has been reported to achieve 46% CO conversion at 500°C, 12 the optimum catalyst identified in this study, namely the Co/Microlith was able to achieve CO conversions of 87.0% and 75.4% at 550 o C and 450 o C, respectively at a H 2 to CO ratio of 1.0. Even though the Co/Microlith showed improved CO conversion, the CH 4 selectivity was poor in comparison to the steel wool catalyst.…”

“…This is concurrent with NASA's findings that operating the carbon formation reactor in H 2 lean environment is favorable for carbon formation. 12 The slight decrease in water production shown in Fig. 9(e) is most likely due to the decrease in the hydrogenation and Sabatier reactions due to the decreased partial pressure of H 2 in the feed.…”

“…(4)). The conflicting demands of temperature and space velocity for these reactions make single-stage Bosch reactor optimization highly complicated and less favorable as was suggested by Otsuji et al, 10 and Abney et al, 11,12 among others. Thus, a potential improvement to the process is to split the Bosch chemistry into a series reactor T configuration.…”

“…were operated at a maximum space velocity of ~1-2 L/[hr g-cat] to achieve equilibrium. 12 Thus, the Microlith-based RWGS reactor shows significant size/volume benefits with potential for further improvements. …”

Series Bosch System Development

“…2 In an effort to address these challenges, a new approach to Bosch-based CO 2 reduction has been proposed. 3 In short, this approach seeks to separate the two steps in Bosch-based O 2 recovery such that each step can be optimized for maximum performance and provide alternative options for carbon collection/containment.…”