Carbon molecular sieve (cms) hollow fiber membranes and preparation thereof from pre-oxidized polyimides

Abstract

Prepare a carbon molecular sieve membrane from a polyimide (e.g., a 6FDA / BPDA-DAM polyimide) that has a glass transition temperature of at least 400 DEG C and includes a bridged phenyl compound for separation of hydrogen and ethylene from one another whether present as a pure mixture of hydrogen and ethylene or as components of a cracked gas. Preparation comprises two sequential steps a) and b). In step a), place a membrane fabricated from defect-free fibers of the polyimide in contact with an oxygen-containing atmosphere under conditions of time and temperature sufficient to produce a pre-oxidized and pre-carbonized polymeric membrane that is insoluble in hot (110 DEG C) n-methylpyrolidone and at least substantially free of substructure collapse. In step b) pyrolyze the pre-oxidized and pre-carbonized membrane in the presence of a purge gas under conditions of time and temperature sufficient to yield a carbon molecular sieve membrane that has at least one of a hydrogen permeance and a hydrogen / ethylene selectivity greater than that of a carbon molecular sieve membrane prepared from the same membrane using only pyrolysis as in step b).

Description

technical field [0001] This application claims the benefit of US Provisional Application No. 62 / 054,427, filed September 24, 2014. [0002] The present invention generally relates to carbon molecular sieve (CMS) hollow fiber membranes, their preparation starting from preoxidized polyimides, and their use in the separation of gases, especially hydrogen from cracked gases CMS (H 2 )the use of. Background technique [0003] During pyrolysis, multiple asymmetric polymer fibers undergo some degree of collapse of the porous substructure, which in turn leads to an increase in separation layer (CMS) thickness and a consequent decrease in permeability. Commercially available polymer Matrimid TM (BTDA-DAPI, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and 5(6)-amino-1-(4'-aminophenyl)-1,3,3 The condensation product of '-trimethylindane (DAPI), its glass transition temperature (T g ) is 305 degrees Celsius (°C)) at or above its T g Examples of polyimides that undergo c...

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Problems solved by technology

[0003] During pyrolysis, multiple asymmetric polymer fibers undergo some degree of collapse of the porous substructure, which in turn leads to increased separation layer (CMS) thickness and a consequent decrease in permeability

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