Porous membranes are provided according to the invention having desirable coefficient of thermal expansion and large surface area, for example at least about 4,000 mm.sup.2. These porous membranes may be made according to an exemplary process employing lithographic patterning of a photoresist followed by development of the photoresist and etching. In one aspect, the etch barrier layer is chosen from a material that does not react with or incorporate metal or other contaminants into the membrane layer.

A composite membrane comprising: a) a porous support; b) a gutter layer; and c) a discriminating layer;
wherein at least 10% of the discriminating layer is intermixed with the gutter layer.

A composite membrane comprising: a) a porous support; b) a gutter layer; and c) a discriminating layer; wherein at least 10% of the discriminating layer is intermixed with the gutter layer.

One method as described herein relates to making a membrane comprising an uncrosslinked high molecular weight polyimide polymer with a small amount of bulky diamine. Also as described herein is a hollow fiber polymer membrane comprising an uncrosslinked high molecular weight polyimide polymer with a small amount of bulky diamine. The polyimide polymers include monomers comprising dianhydride monomers, diamino monomers without carboxylic acid functional groups, and optionally diamino monomers with carboxylic acid functional groups, wherein 2 to 10 mole % of the diamino monomers are bulky diamino compounds and the ratio of diamino monomers with carboxylic acid functional groups to diamino monomers without carboxylic acid functional groups is 0 to 2:3. These uncrosslinked high molecular weight polyimide polymers with a small amount of bulky diamine are useful in forming polymer membranes with high permeance and good selectivity that are useful for the separation of fluid mixtures.

One method as described herein relates to making a membrane comprising an uncrosslinked high molecular weight, monoesterified polyimide polymer with a small amount of bulky diamine. These uncrosslinked high molecular weight, monoesterified polyimide polymers with a small amount of bulky diamine are useful in forming polymer membranes with high permeance and good selectivity that are useful for the separation of fluid mixtures. Also as described herein is a hollow fiber polymer membrane comprising an uncrosslinked high molecular weight, monoesterified polyimide polymer with a small amount of bulky diamine. The small amount of bulky diamine allows for formation of a membrane comprising the uncrosslinked polymer that exhibits high permeance and good selectivity.

A composite membrane comprising: a) a porous support; b) a gutter layer, a portion of which is present within the support and a portion of which is outside of the support; and c) a discriminating layer on the gutter layer; wherein: (i) the portion of the gutter layer outside of the support has an average thickness (GL.sub.e) of 10 nm to 900 nm; and (ii) the portion of the gutter layer present within the support has an average thickness (GL.sub.i) of 10% to 350% of GL.sub.e.

A composite membrane comprising: (a) a porous support; (b) a gutter layer; (c) a discriminating layer having an average thickness of at most 90 nm; and (d) a protective layer having an average thickness 150 nm to 600 nm comprising dialkylsiloxane groups.

The present invention relates to a polyetherimide composite nanofiltration membrane and a preparation method thereof, the method comprises the following steps: (1) dissolving polyetherimide and an additive into an organic solvent, stirring and keeping aside for deaeration to prepare a casting solution, blade coating of the casting solution onto a smooth surface of a nonwoven fabric, and placing under an air atmosphere and then putting into deionized water to obtain a support membrane 1, wherein the surface of the nonwoven fabric coated with the casting solution is referred to as surface A; (2) immersing the surface A of the support membrane 1 into an aqueous solution of m-phenylenediamine, taking out and drying in the air, then immersing the surface A into a solution of 1,2,4,5-benzene tetracarbonyl chloride in n-hexane or cyclohexane, and taking out and drying in the air to obtain a support membrane 2; and (3) immersing the surface A of the support membrane 2 into an aqueous solution of EDC.HCl, then adding NHS into the aqueous solution of EDC.HCl, then adding an aqueous solution of ethylene diamine and keeping aside, and then rinsing with deionized water to obtain a polyetherimide composite nanofiltration membrane. The method of the invention has the advantages of low cost, low energy consumption and low pollution; and also has high rejection towards low-molecular-weight compound, stable performance and a longer lifetime.

Forward osmosis membranes include an active layer and a thin support layer. A bilayer substrate including a removable backing layer may allow forward osmosis membranes with reduced supporting layer thickness to be processed on existing manufacturing lines.

A process for separating a feed gas comprising polar and non-polar gases into a gas mixture enriched in polar gas(es) and a gas mixture depleted in polar gas(es), the process comprising passing the feed gas through a gas separation unit comprising at least two gas-separation modules in order of increasing selectivity for the polar gas(es), wherein the feed gas entering the gas separation unit comprises more than 35 mol % and up to 90 mol % of polar gas(es).