Selective CO₂ Separation from CO₂−N₂ Mixtures by Immobilized Carbonate−Glycerol Membranes

Abstract

Separation of carbon dioxide from a humid mixture of CO2−N2 through membranes containing immobilized solutions of Na2CO3−glycerol in porous and hydrophilic poly(vinylidene fluoride) (PVDF) substrate was experimentally studied for use as a venting membrane in space-walk applications. The effects of Na2CO3 concentration, CO2 partial pressure, and feed stream relative humidity (RH) were investigated. The carbonate concentration was in the range of 0−4.0 mol/dm3. The feed gas RH range was 49−100%; the sweep gas was dry helium. CO2 partial pressure (p CO 2 ,f) range was 0.007−0.77 atm. Addition of Na2CO3 increased the CO2 permeability drastically at lower carbonate concentrations; at higher Na2CO3 concentrations, this permeability increase is partly compromised by increased solution viscosity and salting-out effect. N2 permeability coefficient decreased with an increase in Na2CO3 concentration. Very high CO2/N2 selectivities were observed at high Na2CO3 concentrations. Higher CO2/N2 selectivities were observed at lower CO2 partial pressure differentials. Steady-state water content in the hygroscopic immobilized liquid membrane (ILM) increases with an increase in feed stream RH. The water content in the ILM considerably affects its viscosity and the effective concentration of the carriers in the ILM; those factors determine the permeation performances of the ILM. Generally, lower permeances and greater CO2/N2 selectivity values were observed at lower feed stream RHs. When the feed RH = 50.7%, p CO 2 ,f = 0.007 atm and the Na2CO3 concentration was 1.0 mol/dm3; the separation factor α(CO2/N2) observed was 3440. Prolonged runs lasting 14 days showed that the ILM permeation performances were quite stable. The ILMs were also found to be stable when challenged with feed streams of very low RHs.

Particularities of Membrane Gas Separation Under Unsteady State Conditions

“…are the only volatile species; a negligible change in the liquid phase volume during absorption of volatile components; concentration of volatile components in molecular form in the membrane and the liquid phase obeying Henry's law. The approach of CO 2 interaction with aqueous potassium carbonate can be found in numerous studies (Cents et al, 2005;Chen et al, 1999;Danckwerts & Sharma, 1966;Dindore et al, 2005;Lee et al, 2001;Morales-Cabrera et al, 2005;Otto & Quinn, 1971;Pohorecki & Kucharski, 1991;Suchdeo & Schultz 1974;Ward & Robb, 1967 Theoretical and experimental dependencies are almost identical for the LM with distilled water (Fig. 18) and the time of unsteady CO 2 transfer is about 30 seconds.…”

Post-Combustion Decarbonisation Processes

“…Finally, selectivity is reduced by a reduction in membrane thickness. Recent development work has focused on the following technological options: -Amine containing membranes (Teramoto et al, 1996); -Potassium carbonate containing polymer gel membranes (Okabe et al, 2003); -Potassium carbonate-glycerol containing membranes (Chen et al, 1999); -Dendrimer containing membranes (Kovalli and Sirkar, 2001); -Poly-electrolyte membranes (Quinn and Laciak, 1997).…”

A Review of Carbon Dioxide Selective Membranes: A Topical Report

“…Low-volatility and hygroscopic liquids such as poly(ethylene glycol) (PEG) were used as the component in the ILM fluid to alleviate the drying problem. Chen et al [199][200][201] performed separation of CO 2 from a humid mixture of CO 2 -N 2 through ILMs containing immobilized solutions of sodium carbonate/sodium glycinate-glycerol in porous and hydrophilic hollow fiber supports. They carried out separations from gas mixtures containing very low CO 2 concentrations, particularly for space-walk applications.…”