Polyaramide hollow fibers for hydrogen/methane separation — spinning and properties

The Du Pont family of aromatic polyamides is intrinsically superior to other polymers currently commercially used for hydrogen/methane separation. These polyaramides can be easily spun into highly asymmetric hollow fiber membranes. Due to their high glass transition temperature, modulus and yield stress, as compared to other currently commercially-used polymers, the resulting polyaramide hollow fibers exhibit a high collapse pressure and can operate at high temperatures with good retention of permeation properties. For example, at Conoco's Ponca City Refinery, 11-inch diameter, 10-foot long commercial permeators have been in operation for longer than a year purifying a feed stream of 74% hydrogen to 97% hydrogen at a recovery of 76%. Each permeator is capable of processing approximately six million standard cubic feet per day. The number of solvents available for polyaramides is limited, but a proper spin dope formulation can be obtained by using appropriate organic and inorganic additives. Such a spin dope formulation, combined with appropriate control of the spinning process variables, provides sufficient flexibility to control membrane morphology to produce macrovoid-free fibers for high pressure applications with skin thickness of less than 1,000 Angstroms. The solubility characteristics of polyaramides for membrane preparation and the rheology of the spin-dopes will be discussed and the effect of spinning parameters on membrane permeation properties will be illustrated.