An Automated Test Bed for Rapid Characterization of Sorbent Materials for Siloxane Removal in Contaminated Airstreams

Polydimethylsiloxanes (PDMS) degrade into dimethylsilanediol (DMSD), a soluble compound that affects the performance of several life support systems on the International Space Station (ISS). In industry, PDMS are typically removed using gas purification equipment using commercial sorbents. A bench scale test bed was developed at KSC for evaluating candidate commercial sorbents for the removal of gas phase PDMS using environmental conditions found on ISS (i.e., RH 40% and 23 oC). The test bed consists of four subsystems: 1) a Kin-Tek gas generator to supply a humid gas stream with the desired concentration of siloxanes and volatile organic compounds (VOCs); 2) a sorbent assay tube containing sorbent materials during testing; 3) an environmental monitoring and control system consisting of valves, a heater, and temperature, humidity, and pressure sensors; and 4) an automated gas analysis system to measure pre- and post-sorbent siloxane concentrations using a gas chromatograph and Valco sampling valves. The adsorptive capacity of Chemsorb® 1000, an activated carbon sorbent derived from coconut shell char, for PDMS was tested in this system. The sorbent was challenged with a linear (L2, Hexamethyldisiloxane) and a cyclic (D3, Hexamethylcyclotrisiloxane) siloxane under ISS nominal conditions and adsorptive capacities were determined from breakthrough curves.