Method of cleaning membranes

Abstract

The present invention relates a method for cleaning polymeric microfiltration membranes and membrane units, and to compositions useful in such methods.

1 . A method of cleaning a porous polymeric membrane contaminated with a contaminant, the method comprising the step of: 
 contacting the contaminant with a composition comprising a sulfite reducing agent and a solvent, wherein the sulfite reducing agent is soluble in the solvent, and wherein the solvent is compatible with the porous polymeric membrane.    
   
   
       2 . The method according to  claim 1 , wherein the contaminant comprises a metal oxide or a metal hydroxide.  
   
   
       3 . The method according to  claim 1 , wherein the contaminant comprises an organic compound.  
   
   
       4 . The method according to  claim 1 , wherein the solvent comprises water.  
   
   
       5 . The method according to  claim 1 , wherein the sulfite reducing agent is selected from the group consisting of sodium metabisulfite, sodium hydrosulfite, sodium sulfite, potassium metabisulfite, potassium hydrosulfite, potassium sulfite, and mixtures thereof.  
   
   
       6 . The method according to  claim 1 , further comprising the step of: 
 reducing a valence state of an atom of the contaminant to a lower valence state, whereby the contaminant is solublized and removed from the membrane.    
   
   
       7 . The method according to  claim 1 , wherein the composition further comprises an enhancing agent.  
   
   
       8 . The method according to  claim 7 , wherein the enhancing agent is selected from the group consisting of inorganic acids, organic acids, and mixtures thereof.  
   
   
       9 . The method according to  claim 7 , wherein the enhancing agent comprises citric acid.  
   
   
       10 . The method according to  claim 1 , wherein the solvent comprises water and the sulfite reducing agent is selected from the group consisting of sodium metabisulfite, sodium hydrosulfite, and mixtures thereof.  
   
   
       11 . The method according to  claim 10 , wherein the sulfite reducing agent comprises from about 0.1 wt. % to about 5 wt. % of a component selected from the group consisting of sodium metabisulfite, sodium hydrosulfite, and mixtures thereof.  
   
   
       12 . The method according to  claim 10 , wherein the sulfite reducing agent comprises from about 0.5 wt. % to about 2 wt. % of a component selected from the group consisting of sodium metabisulfite, sodium hydrosulfite, and mixtures thereof.  
   
   
       13 . A method according to  claim 10 , wherein the composition comprises from about 0.5 wt. % to about 1.5 wt. % sodium metabisulfite and from about 0.5 wt. % to about 1.5 wt. % sodium hydrosulfite.  
   
   
       14 . The method according to  claim 1 , wherein the membrane comprises a hollow fiber microfiltration membrane or a hollow fiber ultrafiltration membrane.  
   
   
       15 . The method according to  claim 1 , wherein the membrane comprises a flat microfiltration membrane or a flat ultrafiltration membrane.  
   
   
       16 . The method according to  claim 1 , wherein the membrane comprises a polyvinylidene fluoride polymer.  
   
   
       17 . A composition for cleaning a porous polymeric membrane contaminated with a contaminant, the composition comprising a sulfite reducing agent, an enhancing agent and a solvent, wherein the sulfite reducing agent is soluble in the solvent, and wherein the solvent is compatible with the membrane.  
   
   
       18 . The composition according to  claim 17 , wherein the contaminant comprises a metal oxide or a metal hydroxide.  
   
   
       19 . The composition according to  claim 17 , wherein the contaminant is ferric floc.  
   
   
       20 . The composition according to  claim 17 , wherein the sulfite reducing agent is selected from the group consisting of sodium metabisulfite, sodium hydrosulfite, sodium sulfite, potassium metabisulfite, potassium hydrosulfite, potassium sulfite, and mixtures thereof.  
   
   
       21 . The composition according to  claim 17 , wherein the sulfite reducing agent comprises sodium metabisulfite and sodium hydrosulfite.  
   
   
       22 . The composition according to  claim 17 , further comprising an enhancing agent.  
   
   
       23 . The composition according to  claim 22 , wherein the enhancing agent comprises an inorganic acid or an organic acid.  
   
   
       24 . The composition according to  claim 23 , wherein the organic acid comprises citric acid.  
   
   
       25 . The composition according to  claim 17 , wherein the sulfite reducing agent comprises from about 20 wt. % to about 60 wt. % sodium metabisulfite, wherein the sulfite reducing agent is capable of dilution to a working concentration of from about 0.5 wt. % to about 2 wt. % of sulfite reducing agent in a solubilized form.  
   
   
       26 . The composition according to  claim 17 , wherein the sulfite reducing agent comprises from about 0.5 wt. % to about 2 wt. % sodium metabisulfite.  
   
   
       27 . The composition according to  claim 17 , wherein the sulfite reducing agent comprises from about 20 wt. % to about 65 wt. % sodium hydrosulfite, and wherein the sulfite reducing agent is capable of dilution to a working concentration of about 0.5 wt. % to about 2 wt. % soluble sulfite reducing agent present in solubilized form.  
   
   
       28 . The composition according to  claim 17 , wherein the sulfite reducing agent comprises from about 0.5 wt. % to about 2 wt. % sodium hydrosulfite.  
   
   
       29 . The composition according to  claim 17 , comprising from about 20 wt. % to about 65 wt. % sodium metabisulfite and from about 20 wt. % to about 65 wt. % sodium hydrosulfite, wherein the sodium metabisulfite and sodium hydrosulfite are capable of dilution to a working concentration of from about 0.5 wt. % to about 2 wt. % sulfite reducing agent in solubilized form.  
   
   
       30 . The composition according to  claim 17 , comprising from about 0.5 wt. % to about 2 wt. % sodium metabisulfite and sodium hydrosulfite.