Method of forming dynamic membrane on stainless steel support

Claim 1

A method of preparing a hyperfiltration member including the steps of: forming a porous stainless steel substrate from powdered stainless steel using suitable particle size, compression and sintering conditions to yield a porous stainless steel substrate having a nominal porosity of from about 2% to about 30% and an absolute particle retention pore rating of from about 0.2 micron to about 20 microns in diameter; flowing through and about and in contact with the porous substrate, an effective amount of an aqueous nitrate solution comprising zirconium nitrate, and also a material selected from the group consisting of soluble sodium nitrate and soluble potassium nitrate to form a solute rejecting membrane of zirconium oxide on said stainless steel substrate; continuing the flow of the aqueous nitrate solution through and about the porous substrate at a flow rate and pressure and for period of time effective to form the zirconium oxide membrane on the porous substrate; adding to the aqueous nitrate solution nitric acid sufficient to lower the pH to between 1.5 to about 2.5; adding to the aqueous nitrate solution polyacrylic acid in the amount of from about 20 to about 100 parts per million; slowly adding to the aqueous nitrate solution sodium hydroxide until the aqueous nitrate solution is neutral to form a zirconium oxide-polyacrylic acid membrane on said substrate; performing all steps in the absence of chlorine or chlorine compounds.

Claim 2

A method of preparing a hyperfiltration member including the steps of: forming a porous stainless steel substrate from powdered stainless steel using suitable particle size, compression and sintering conditions to yield a porous stainless steel substrate having a nominal porosity of from about 2% to about 30% and an absolute particle retention pore rating of from about 0.2 micron to about 20 microns in diameter; flowing through and about and in contact with the porous substrate, an effective amount of an aqueous nitrate solution comprising zirconium nitrate, and also a material selected from the group consisting of soluble sodium nitrate and soluble potassium nitrate to form a solute rejecting membrane of zirconium oxide on said stainless steel substrate; continuing the flow of the aqueous nitrate solution through and about the porous substrate at a flow rate and pressure and for period of time effective to form the zirconium oxide membrane on the porous substrate; adding to the aqueous nitrate solution nitric acid sufficient to lower the pH to between 1.5 to about 2.5; adding to the aqueous nitrate solution polyacrylic acid in the amount of from about 20 to about 100 parts per million; slowly adding to the aqueous nitrate solution sodium hydroxide until the aqueous nitrate solution is neutral to form a zirconium oxide-polyacrylic acid membrane on said substrate; performing all steps in the absence of chlorine or chlorine compounds.

Claim 10

A method of filtering an aqueous solution by forming a membrane on a substrate, comprising the steps of: circulating an aqueous nitrate solution at a pH of about 4 past and through a porous stainless steel tube prepared from sintered, powdered stainless steel, the aqueous nitrate solution containing approximately 0.025 molar sodium nitrate and further containing about 0.04 grams per liter of zirconium nitrate, at a flow rate and pressure and for a period of time effective to form a solute rejecting membrane of zirconium oxide on the stainless steel tube, adding nitric acid sufficient to lower the pH of the aqueous nitrate solution to about 2; adding approximately 50 parts per million of polyacrylic acid to the aqueous nitrate solution; slowly adding sodium hydroxide to the aqueous nitrate solution to bring the pH to neutral to form a zirconium oxide-polyacrylic acid membrane on the stainless steel tube; performing all steps in the absence of chlorine; and filtering the aqueous nitrate solution by flowing it through the stainless steel tube at a throughflow velocity in the range of about 3 to about 5×10 -5 m/sec.

Claim 11

A method of filtering an aqueous solution by forming a membrane on a substrate, comprising the steps of: circulating an aqueous nitrate solution at a pH of about 4 past and through a porous stainless steel tube prepared from sintered, powdered stainless steel, the aqueous nitrate solution containing approximately 0.025 molar sodium nitrate and further containing about 0.04 grams per liter of zirconium nitrate, at a flow rate and pressure and for a period of time effective to form a solute rejecting membrane of zirconium oxide on the stainless steel tube, adding nitric acid sufficient to lower the pH of the aqueous nitrate solution to about 2; adding approximately 50 parts per million of polyacrylic acid to the aqueous nitrate solution; slowly adding sodium hydroxide to the aqueous nitrate solution to bring the pH to neutral to form a zirconium oxide-polyacrylic acid membrane on the stainless steel tube; performing all steps in the absence of chlorine; and filtering the aqueous nitrate solution by flowing it through the stainless steel tube at a throughflow velocity in the range of about 3 to about 5×10 -5 m/sec.