Abstract: An aromatic polyimide composite membrane having a satisfactory gas-permeating property and an excellent gas-separating property comprises an aromatic polyimide porous membrane substrate and at least one coating layer which has been prepared (A) by coating at least one surface of the substrate with a dilute dope solution containing 0.01 to 5 parts by weight of a soluble aromatic polyimide and/or polyamic acid dissolved in a solvent which consists essentially of 100 parts by weight of a base component incapable of dissolving therein the substrate in an amount of 3% by weight or more and 0 to 15 parts by weight of an additional component capable of dissolving therein the 5% by weight or more of the aromatic polymeric material and compatible with the base component; and (B) by gradually evaporating the solvent from the coated dilute dope solution layer.

Abstract: A porous aromatic imide polymer membrane usable as a gas or liquid separator or concentrator is prepared by a process comprising the steps of:(1) dissolving 3 to 30% by weight of an aromatic imide polymer which comprises at least 80 molar % of a recurring unit selected from those of the formulae (I) and (II): ##STR1## wherein R represents a divalent aromatic or heterocyclic radical in 70 to 97% by weight of a solvent consisting essentially of a homogeneous mixture of:(A) 100 parts by weight of a base solvent which consists essentially of at least one polar organic compound and is capable of dissolving therein said aromatic imide polymer in a concentration of 5% by weight or more therein and of evaporating at a temperature of from 50.degree. to 400.degree. C.

Abstract: A modified polymeric membrane having an excellent separating property is produced by applying, to a porous polymeric membrane, a volatile treating liquid containing a modifying agent which consists of at least one member selected from:(A) volatile dissolving organic liquids each capable of dissolving therein at least 1% by weight of the porous polymeric membrane at a temperature of 25.degree. C.; and(B) volatile shrinking organic liquids each capable of causing the porous polymeric membrane to shrink at a shrinkage of 3% or more.

Abstract: An aromatic polyimide separating membrane is produced by a process comprising the steps of:forming a thin film of a dope solution containing an aromatic polyamic acid dissolved in a polar organic solvent at a temperature of approximately 100.degree. C. or less;coagulating the thin dope solution film in a coagulating liquid containing at least 60% by volume of at least one member selected from water and lower aliphatic alcohols at a temperature of 60.degree. C. or less;drying the resultant coagulated aromatic polyamic acid membrane; andheating the dried aromatic polyamic acid membrane at a temperature of 100.degree. C. to 300.degree. C. to convert it to an aromatic polyimide membrane.

Abstract: An aromatic polyimide membrane having an excellent gas-separating property comprises (A) a substrate consisting of a porous membrane comprising at least one aromatic polyimide having at least 80 molar % of at least one type of recurring unit of the formula (I): ##STR1## wherein R is a tetravalent aromatic radical and R.sup.1 is a divalent aromatic radical, the porous membrane exhibiting a hydrogen gas permeability (PH.sub.2) of 1.times.10.sup.-5 to 5.times.10.sup.-1 cm.sup.3 /cm.sup.2.sec.cmHg and a ratio of hydrogen gas permeability (PH.sub.2) to carbon monoxide gas permeability (PCO) of 2 to 5; and (B) 50% or more, based on the weight of the porous membrane substrate, of a gas-separating liquid contained in the porous membrane substrate, the gas-separating liquid being substantially incapable of dissolving therein the porous membrane substrate and having a boiling point of 180.degree. C. or more.

Abstract: A porous membrane of an aromatic polyimide having an enhanced permeability of a gas or liquid is produced by a process comprising the steps of(1) preparing a dope solution of 3 to 30% by weight of an aromatic polyimide in a mixed solvent of (A) 100 parts by weight of a base solvent capable of dissolving 5% by weight or more of the polymeric acid and of evaporating at 30.degree. C. to 400.degree. C. and (B) 5 to 150 parts by weight of an additional liquid not capable of dissolving 3% by weight or more of the polyamic acid and capable of evaporating at a smaller evaporating rate than that of the base solvent at the above-mentioned evaporating temperature;(2) forming a thin layer of the dope solution at 0.degree. C. to 120.degree. C.; and(3) heating the dope solution layer at 30.degree. C. to 400.degree. C. so as to evaporate off the mixed solvent and to convert the polyamic acid to the corresponding polyimide.

Abstract: An aromatic polyimide composite membrane having an excellent gas-separating property is produced by a process comprising the steps of: coating at least one surface of a substrate consisting of an aromatic polyimide porous membrane with a solution of 0.05% to 10% by weight of an aromatic polyamic acid in a polar organic solvent, which is not capable of dissolving the polyimide porous membrane, at a temperature not exceeding 140.degree. C.; after a during drying the resultant thin coating layer of the polyamic acid solution, heating the resultant polyamic acid layer at a temperature of 150.degree. C. or more so as to convert the polyamic acid layer to the corresponding polyimide layer.