Abstract: A method for separating hydrocarbons and naphthenic acid from an aqueous mixture containing the same by passing the mixture through a spiral wound element to produce a permeate stream and concentrate stream wherein the concentrate stream has a relatively higher concentration of hydrocarbons than the permeate stream, wherein the spiral wound element includes a composite poly amide membrane comprising a porous support and a thin film poly amide layer, wherein the membrane is characterized by having: i) a NaCl rejection and a benzene tetra carboxylic acid rejection of at least 98% when tested with an aqueous solution containing 2000 ppm NaCl and 100 ppm benzene tetra carboxylic acid at 25° C., pH 8 and ImPa (150 psi); and ii) a dissociated carboxylate content of at least 0.3 moles/kg of polyamide at pH 9.5 as measured by Rutherford Backscattering (RBS).