PROCESS FOR CLEANING A MEMBRANE COMPRISING DRYING THE MEMBRANE

Abstract

The invention relates to a process for cleaning a polymer membrane comprising the steps of (A) filtering an aqueous liquid through the polymer membrane; (B) drying the polymer membrane; (C) washing the polymer membrane with water or a chemical washing solution; and (D) continuing the filtering of the aqueous liquid through the polymer membrane.

Claims

1: A process for cleaning a polymer membrane, comprising: (A) filtering an aqueous liquid through the polymer membrane; (B) drying the polymer membrane; (C) washing the polymer membrane with water or a chemical washing solution; and (D) continuing the filtering of the aqueous liquid through the polymer membrane.

2: The process according to claim 1, wherein an amount of liquid in the polymer membrane is reduced at least 3 wt %, during the drying (B).

3: The process according to claim 1, wherein the drying is made at a temperature in the range from 0 to 100° C.

4: The process according to claim 1, wherein the drying is achieved within 1 min to 48 h.

5: The process according to claim 1, wherein the drying is achieved by applying a gas.

6: The process according to claim 5, wherein the gas is applied to a filtration side of the membrane.

7: The process according to claim 5, wherein the gas is inert to the liquid.

8: The process according to claim 1, wherein the drying is achieved by applying vacuum to a filtration side of the membrane.

9: The process according to claim 1, wherein the liquid comprises at least 80 wt % water.

10: The process according to claim 1, wherein the liquid is industrial waste water, sea water, surface water, ground water, process water, drinking water, or liquid food.

11: The process according to claim 1, wherein the chemical washing solution is an aqueous solution comprising an acid, a base, and/or an oxidant.

12: The process according to claim 1, wherein the chemical washing solution comprises an alkaline hydroxide, alkaline earth hydroxide, mineral acid, H.sub.2O.sub.2, ozone, peracid, ClO.sub.2, KMnO.sub.4, chlorate perchlorate or hypochlorite.

13: The process according to claim 1, wherein the polymer membrane is based on polyvinyl pyrolidone, polyvinyl acetates, polyurethanes, cellulose acetates, polyacrylonitriles, polyamides, polyolefines, polyesters, polysulfones, polyethersulfones, polycarbonates, polyether ketones, sulfonated polyether ketones, polyamide sulfones, polyvinylidene fluorides, polyvinylchlorides, polystyrenes, polytetrafluorethylenes, copolymers thereof, and mixtures thereof.

14: The process according to claim 1, wherein the polymer membrane is based on polysulfones, polyethersulfones, copolymers thereof, and mixtures thereof.

Description

EXAMPLE 1

[0101] A commercially available membrane module, type dizzer® XL 60 from inge GmbH (Greifenberg, Germany), has been used for filtration of surface water. The module contained the polyether sulfone based Multibore® 0.9 membranes with 7 capillaries per fibre, 0.9 mm capillary inner diameter and a pore size of about 0.02 μm and the mode of operation was In-to-Out filtration. The module had a membrane area of 60 m.sup.2, a length without end cap of 148.6 cm and an outer diameter of 25.0 cm.

[0102] After operating successfully for many months, some unidentified water constituent fouled the membrane significantly and the permeability was significantly reduced.

[0103] Comparative Cleaning Process:

[0104] The usual chemical cleanings, using NaOH (pH up to 13), NaOCl (up to 500 ppm) and H.sub.2SO.sub.4 (about pH 1) were not able to restore the permeability of the membrane to acceptable levels.

[0105] Inventive Cleaning Process:

[0106] The module was removed from the treatment plant and the three 2 inch module openings (feed top, feed bottom, permeate) were opened, so that the membranes partially dried at room temperature for about 48 h. Next, the membrane was chemically cleaned with an aqueous solution of NaOH (pH up to 13), NaOCl (up to 500 ppm) or H.sub.2SO.sub.4 (about pH 1). When the module was tested, it was found that the permeability had restored close to the levels of a new membrane and it could be used again for the filtration of surface water.