Methods for preparing anisotropic hollow fiber membranes comprising polymer of acrylonitrile and styrene and hollow fiber membranes produced therefrom

A dry, integral anisotropic hollow fiber membrane for the separation of at least one gas of a gaseous mixture comprising a homogeneously-formed, thin, exterior, separating layer on an open, cellular support and comprising polymer of acrylonitrile and styrene in which polymer, acrylonitrile comprises at least about 20 mole percent of said polymer and styrene comprises up to about 60 mole percent of said polymer, wherein a volume majority of the wall of said hollow fiber membrane consists of cells having a mean major dimension of less than about 2 microns and said open, cellular support comprising a substantial absence of macrovoids having a major dimension greater than about 3 microns and a ratio of maximum length to maximum width greater than about 10, said hollow fiber membrane exhibiting a ratio of permeability of at least one of hydrogen, helium and ammonia to the permeability constant of the material of the hollow fiber membrane for said gas of at least about 5.times.10.sup.4 reciprocal centimeters;

• a permeability ratio of (i) the permeability of a lower molecular weight gas divided by the permeability of a higher molecular weight gas to (ii) the square root of the molecular weight of said lower molecular weight gas divided by the square root of the molecular weight of said higher molecular weight gas of at least about 6, wherein said lower molecular weight gas is one of hydrogen and helium and said high molecular weight gas is one of nitrogen, carbon monoxide and carbon dioxide and has a permeability constant in the polymer at least about 10 times less than the permeability constant of said lower molecular weight gas in said material;
• and a collapse pressure of at least about 4(T.sub.S)(t/D).sup.3 wherein T.sub.S is the tensile strength of the polymer, t is the wall thickness and D is the outside diameter of the hollow fiber membrane, said membrane having a permeability for water of less than about 0.05.times.10.sup.-6.