Advanced Supported Liquid Membranes for Ammonia and Formaldehyde Control in Space Suits

The portable life support system (PLSS) used for extra vehicular activities (EVA) removes carbon dioxide (CO2), controls humidity, and removes potentially harmful trace contaminants. Currently, CO2 and trace contaminants are controlled using sorbent beds contained in one canister, and both beds are regenerated between EVAs. NASA intends to switch CO2 control to the Rapid Cycle Amine (RCA), using beds that are continually regenerated during the EVA. NASA also wants to develop a method to control trace contaminants using beds or sorbents that can be continuously regenerated during the EVA. Recent studies show that ammonia (NH3) and formaldehyde (CH2O) can exceed their spacecraft maximum allowable concentration (SMAC), and therefore a trace contaminant control system must be designed to keep the concentrations of these compounds below their SMAC.

A simple way to remove NH3 and CH2O is with the use of a membrane that allows the contaminants to escape to space but retains oxygen (O2). In this paper, Reaction Systems, Inc. describes the development of supported liquid membranes (SLM) that are effective for NH3 and CH2O removal. An SLM consists of a reactive liquid, supported within a porous membrane; the SLM relies one the chemical reactivity between the liquid and the compound of interest to achieve the high permeance and selectivity. To be effective, the liquid must react reversibly with the contaminant, have extremely low vapor pressure, and have low viscosity to allow diffusion across the membrane to the low-pressure side where the contaminant desorbs. Reaction Systems identified effective liquids for each compound. We showed that the liquids have good reversible uptake capacity for the contaminants and then prepared SLMs with each liquid. Permeance measurements were carried out and show that the SLMs can prevent each contaminant from exceeding their SMAC.