Enzyme-Based Facilitated Transport: Use of Vacuum Induced Sweep for Enhanced CO
The technologies for processing respiratory gases to support humans and plants and to provide material for regeneration of oxygen in Advanced Life Support applications remain far from optimal. Here we report on our ongoing efforts to develop an enzyme-based, hybrid, facilitated transport bioreactor for the efficient capture of CO2 from dilute respiratory gas streams.
In this paper, we examine four different cases with respect to maintaining a driving force for removal of CO2 from respiratory gas. These consist of employing each of the following on the sweep side of the reactor: 1) a relatively high flow rate of an inert sweep gas (in this case argon) at a nominal pressure of 101.3 kPaabs (0 kPa gauge); 2) vacuum at a pressure of 16.3 kPaabs (-85 kPa gauge); 3) a vacuum assisted flow of sweep gas (argon or air) flowing at a rate of 4 sccm (standard cubic centimeters per minute) and a pressure of 16.3 kPaabs and, 4) a vacuum assisted flow of water vapor as the driving force for flow on the sweep side with or without the addition of argon or air as an added sweep gas.
Theoretical calculations show that the flow of an inert sweep gas, the application of a vacuum, and the combined application of vacuum with a small amount of sweep gas (fixed gas and/or water vapor) can result in effective removal of CO2 from respiratory gas, provided the CO2 driving force is maintained. The experimental data are in good agreement with the theoretical results. They show that any condition using a sweep gas can result in effective removal of CO2. Theory also confirms that, as was observed, without an added sweep gas the sweep side pressure of 16.3 kPaabs should not be effective. Furthermore, we calculate that with appropriate combinations of temperature and vacuum pressure it is possible to get effective CO2 removal using water vapor alone as the sweep gas. This strategy results in a situation where it is possible to obtain a dry gas product from the permeate side that is extraordinarily enriched in CO2. This work provides further evidence that our system will be suitable for all NASA applications in low Earth orbit (LEO - ISS, SS and EVA), as well as for long-term expeditions, e.g., to the moon or to Mars.