Composite polyamide membrane with increased carboxylic acid functionality

1. A thin film composite polyamide membrane comprising a porous support and a thin film polyamide layer characterized by having a dissociated carboxylate content of 0.45 moles/kg to 0.556 moles/kg at pH 9.5, and wherein the composite polyamide membrane has a NaCl Passage of less than 1% when tested using an aqueous salt solution (2000 ppm NaCl) at 150 psi, pH 8 and 25° C.

2. The membrane of claim 1 wherein the polyamide layer has an isoelectric point of less than or equal to 3.5.

3. The membrane of claim 1 wherein the polyamide layer forms an outer surface of the membrane without the presence of an additional outer coating.

4. A method for making a composite polyamide membrane including a porous support and a thin film polyamide layer comprising the steps of applying the following monomers to a surface of the porous support and interfacially polymerizing the monomers to form a thin film polyamide layer:

i) a polar solution comprising a polyfunctional amine monomer and

ii) a non-polar solution comprising a polyfunctional amine-reactive monomer comprising at least two moieties selected from: acyl halide, sulfonyl halide and anhydride,

wherein the method is characterized by the non-polar solution further comprising 0.25 wt % to 0.078 wt % of an acid compound comprising at least one carboxylic acid moiety and at least one amine-reactive moiety selected from: acyl halide and anhydride and

wherein the interfacial polymerization is conducted in the presence of a tri-hydrocarbyl phosphate compound provided in a molar ratio of at least 0.5:1 with the polyfunctional amine-reactive monomer.

5. The method of claim 4 wherein the polyfunctional amine-reactive monomer comprises from two to four acyl halide moieties and the acid compound comprises one acyl halide moiety and at least one carboxylic acid moiety.

6. The method of claim 4 wherein the acid compound comprises at least two acyl halide moieties and at least one carboxylic acid moiety.