CO2 Control in Space Station and Space Suit by Novel Facilitated Transport Membranes

摘要

For the CO2 control in the space stations and space suits, the adsorption method has been currently used. Recently, CO2 separation using membranes is attracting attention as an alternative technology since it has many advantages over the adsorption method. The membrane separation is a simple continuous system with a low energy consumption and no capacity limit as the CO2 uptake at the feed side of the membrane and the CO2 release at the permeate side occur simultaneously. In order to apply membranes for space uses, the development of novel membranes with extremely high permselectivity of CO2 over O2 and N2 is required for minimizing the O2 and N2 losses. In our previous paper presented at ICES- 2014, we reported novel CO2 selective membranes. The CO2 permeance and CO2/N2 selectivity evaluated by the sweep gas method were favorably compared to those reported so far. In the present work, the membrane performance was mainly measured by the vacuum mode method where the permeate side was evacuated by a vacuum pump at room temperature. A 0.7%-CO2/99.3%-O2 gas mixture was mainly used as a feed gas. The permeate side pressure PS was found to be an important factor, which controls the membrane performance. As Ps increased, both CO2 and O2 permeances increased with the CO2/O2 selectivity higher than 4000. The membrane thickness is also an important factor, and as the thickness increases, the CO2/O2 selectivity increases with very little decrease in the CO2 permeance. At 75% relative humidity and 26.7?C, the highest CO2 permeance was 4.1E-5 mol m~(-2) s~(-1) kPa~(-1) (1.2E-4 Ncm~3 cm~(-2) s~(-1) cmHg~(-1) ). The CO2/N2 selectivity was about 1.9 times the CO2/O2 selectivity. The performance of a membrane module, in which the developed membranes are supposed to be incorporated, was simulated. When the module is applied to the space station, the estimated membrane area was about 21m~2 at the CO2 removal rate of 1kg day~(-1) . In the case of space suit, the area was about 45m~2 at the CO2 removal rate of 93 g h~(-1) . The CO2 concentration recovered from the permeate side of the membrane is higher than 95%, suggesting very small O2 and N2 losses.