Base stable semipermeable membrane and methods thereof

A base stable semipermeable nanofiltration (NF) membrane, wherein said NF membrane is prepared by a process comprising steps of:

• a. providing an ultrafiltration (UF) base support membrane selected from the group consisting of polyethersulfone (PES) and polysulfone (PS);
• said UF base membrane is a non-crosslinked base polymer;
• b. providing a modification solution comprising water soluble partially crosslinked polyethylenimine (PEI) or non-crosslinked PEI;
• c. activating the surface of said UF membrane by subjecting said UF membrane to heating in an aqueous solution containing 0.1% (w/w) of the condensate of cyanuric chloride with sulfanilic acid for 1 hour at a temperature of 70° C.;
• d. forming a first crosslinked layer upon at least a portion of a surface of said UF base support membrane of step (c);
• said forming comprises steps of:
• i. providing said modification solution to comprise 1% (w/w) water soluble partially crosslinked PEI or 1% (w/w) oligomer-polymer mixture of water soluble non-crosslinked PEI (PEI MW 800 and PEI MW 750K at a ratio of 1:1);
• ii. preparing said modification solution to comprise partially crosslinked PEI by admixing an aqueous solution of said condensate of cyanuric chloride with sulfanilic acid within an aqueous solution of said PEI oligomer-polymer mixture at a ratio of said condensate to said PEI being 0.3:1.0, with subsequent heating of said modification solution at 50° C. for 3 hours;
• iii. immersing said UF base support membrane in said prepared 1% (w/w) modification solution to comprise a partially crosslinked PEI, for 18 hours at a room temperature, then subsequent heat-treating said membrane in either modification solution for 1 hour at 50° C. or in prepared 1% (w/w) solution comprising oligomer-polymer mixture of non-crosslinked PEI (PEI MW 800 and PEI MW 750K at a ratio of 1:1) for 1 hour at 90° C.;
• iv. after cooling and washing, contacting said UF base support membrane of step (iii) with aqueous solution comprising 0.1% w/w of the condensate of cyanuric chloride with sulfanilic acid for 1 hour at room temperature;
• and
• v. curing said UF base support membrane of step (iv) in an alkaline solution, pH=11, for 2 hours at 70° C. to complete the formation of the first cross-linked layer upon of said activated UF base support membrane;
• e. forming a second crosslinked layer upon said first layer of said UF base support membrane of step (d) comprising steps of:
• i. providing a modification solution comprising water soluble partially crosslinked PEI prepared according to step (d, ii) and diluted to either concentration of 0.125% (w/w) or 0.125% (w/w) of non-crosslinked PEI, prepared from PEI, MW 750K;
• ii. contacting said UF base support membrane of step (d, v) with an aqueous solution comprising 0.1% w/w of the condensate of cyanuric chloride with sulfanilic acid for 1 hour at room temperature;
• iii. immersing said UF base support membrane of step (ii) in 0.125% (w/w) modification solution for 1 hour at room temperature for partially crosslinked PEI or alternatively at 90° C. for non-crosslinked PEI;
• iv. heat-treatment of said UF base support membrane in alkaline solution, pH=11, for 2-3 hours at 60-90° C.;
• v. cooling and rinsing said UF base support membrane with reverse osmosis (RO) water;
• vi. immersing said UF membrane of step (v) in an aqueous solution comprising 0.1% w/w of the condensate of cyanuric chloride with sulfanilic acid for 1 hour at room temperature;
• and,
• vii. heat-treating in an alkaline solution, pH=11, for 2 hours at 60° C., followed by 2 hours at 90° C. to complete the formation of the second crosslinked layer upon said UF membrane with said first crosslinked layer, said second crosslinked layer is a NF layer;
• f. repeating said step (e) n times for providing NF membrane with n+1 multiple cross-linked layers upon said first layer of said UF base support membrane;
• n is an integer number equals to or greater than 1;
• and,
• g. immersing said base stable semipermeable NF membrane in 20% solution of phosphoric acid in water at a temperature ranging from 70° C. to 90° C. for a period of time ranging from 18 to 24 hours.