Membrane purification of Cl 2 gas : II. Permeabilities as function of temperature for Cl 2, O 2, N 2, H 2 and HCl in perfluorinated, glass and carbon molecular sieve membranes

Abstract

Permeabilities ( P) of the gases Cl 2, HCl, O 2, N 2 and H 2 were measured in three different membrane types: two perfluorinated membranes, two pyrolyzed carbon membranes (CMS) and two glass membranes. Some sorption data, and results from durability studies are also reported. The permeability was measured in the low pressure range (1–3 bar) and over a large temperature range (for perfluorinated membranes 25–200°C, for carbon and glass membranes 35–90°C). The functionality of the membranes was compared on the basis of ability to separate (selectivity) the gas pairs Cl 2–O 2 and HCl–H 2 at temperatures preferably above 70°C. The perfluorinated membranes, the glass membranes and the carbon membranes all show good durability over time; the permeabilities and selectivities vary significantly though, with the lowest permeabilities and selectivities for the perfluorinated membranes. All three membranes tested in the current study display different properties for the difficult purification of Cl 2 and HCl in gas mixtures, and are in different ways attractive candidates. The perfluoromembranes showed excellent durability but very low selectivities for the separation of O 2–Cl 2 and is therefore not a candidate for this separation. For HCl–H 2, however, the selectivity was acceptable ( α∼8 at 30°C). The carbon and glass membranes were too porous for separation of HCl–H 2 and showed very low selectivity for this gas pair, while the carbon membranes will, in theory, separate nicely O 2–Cl 2 by retaining Cl 2 almost completely and let O 2 permeate. The CMS membranes became rapidly plugged in the temperature range tested, and this presents a major problem if an efficient regeneration procedure cannot be established. The process temperature should preferably be lifted (above 200°C) where plugging will not be a problem. The surface modified glass membrane showed promising results for the Cl 2–O 2 separation at low temperature ( α∼20 at 30°C). In Part I on Cl 2-purification additional results from two types of poly-dimethyl-siloxane (PDMS) membranes were published. For PDMS, the durability is complex, and the material will only resist degradation under certain conditions. All four membrane materials reported in Parts I and II are part of a comprehensive study on purification of Cl 2 with membranes.