Tannin treatment for non-porous semipermeable membranes

Claim 2

A PROCESS FOR SEPARATING SOLVENT FROM AN AQUOUS MIXTURE CONTAINING A SOLUTE OTHER THAN AQUEOUS TANNING EXTRACTS, COMPRISING CONTACTING A NONPOROUS SEMIPERMEABLE MEMBRANE SELECTED FROM A. A CELLULOSE ACETATE POLYMER OF THE GENERAL FORMULA:

Claim 3

The process of claim 1 wherein the aqueous mixture contains at least one inorganic salt and the membrane is contacted with the mixture at an applied pressure greater than the osmotic pressure of the mixture.

Claim 4

The process of claim 1 wherein the reduction in salt passage is at least 50%.

Claim 5

The process of claim 1 wherein the semipermeable membrane is treated with a solution of hydrolyzable tannin at a pH of about 1.5 to about 6.0 and a temperature of between about 0*C. and about 100*C. for from about 30 seconds to several days, the concentration of tannin in said solution being at least 2 parts per million.

Claim 6

The process of claim 4 wherein the semipermeable membrane is treated with a solution of hydrolyzable tannin at a pressure of at least 100 pounds per square inch.

Claim 7

The process of claim 4 wherein the semipermeable membrane is treated with a solution of hydrolyzable tannin at a pH of about 2.0 to about 5.0.

Claim 8

The process of claim 6 wherein the solution of hydrolyzable tannin contains between about 0.1 and about 2 weight percent of citric acid.

Claim 9

The process of claim 6 wherein the semipermeable membrane is treated with a solution of hydrolyzable tannin at a pressure of at least 100 pounds per square inch and a temperature between about 10*C. and about 90*C. for from about 2 minutes to about 24 hours, the concentration of tannin in said solution being at least 10 parts per million.

Claim 10

The process of claim 1 wherein the semipermeable membrane is asymmetric in structure.

Claim 11

The process of claim 9 wherein the semipermeable membrane is treated on its more permselective side with a solution of hydrolyzable tannin at a pH of from about 1.5 to about 6, a temperature of from about 0*C. to about 100*C., and a pressure of at least 100 pounds per square inch for from about one second to several days, the concentration of tannin in said solution being at least 2 parts per million.

Claim 12

The process of claim 9 wherein the semipermeable membrane is treated with a solution of hydrolyzable tannin at a pH between 2 and 4, a temperature between 20*C. and 40*C., and a pressure of at least 250 pounds per square inch for from 2 minutes to about 5 hours, the concentration of tannin in said solution being between about 20 parts per million and about 2 percent.

Claim 13

The process of claim 1 wherein the membrane is composed essentially of a linear aromatic synthetic polymer containing between about 0.1 and about 5 sulfonic acid moieties per 1,000 grams of dry polymer.

Claim 14

A process for separating solvent from an aqueous mixture containing a solute other than aqueous tanning extracts, comprising contacting a non-porous semipermeable membrane with said mixture under permselective separation conditions, said membrane having been treated with a solution of a hydrolyzable tannin in an amount and under conditions which result in an initial reduction in solute passage through the membrane of at least 10%, wherein the semipermeable membrane is a cellulose acetate polymer of the general formula

Claim 15

A process for separating solvent from an aqueous mixture containing a solute other than aqueous tanning extracts, comprising contacting a non-porous semipermeable membrane with said mixture under permselective separation conditions, said membrane having been treated with a solution of a hydrolyzable tannin in an amount and under conditions which result in an initial reduction in solute passage through the membrane of at least 10%, wherein the semipermeable membrane is a cellulose acetate polymer of the general formula

Claim 16

The process of claim 13 wherein the membrane is treated with a solution of hydrolyzable tannin at pH of about 2 to 4, at a temperature of between about 20*C. and about 90*C., and for from about 2 minutes to about 24 hours, the concentration of tannin in said solution being at least 10 parts per million.

Claim 17

A process for separating solvent from an aqueous mixture containing a solute other than aqueous tanning extracts, comprising contacting a non-porous semipermeable membrane consisting essentially of sulfonated poly(arylene ether sulfone) with said mixture under permselective separation conditions, said membrane having been treated with a solution of a hydrolyzable tannin in an amount and under conditions which result in an initial reduction in solute passage through the membrane of at least 10%.

Claim 18

A process for separating solvent from an aqueous mixture containing a solute other than aqueous tanning extracts, comprising contacting a non-porous semipermeable membrane consisting essentially of sulfonated poly(arylene ether sulfone) with said mixture under permselective separation conditions, said membrane having been treated with a solution of a hydrolyzable tannin in an amount and under conditions which result in an initial reduction in solute passage through the membrane of at least 10%.

Claim 19

A process for separating solvent from an aqueous mixture containing a solute other than aqueous tanning extracts, comprising contacting a non-porous semipermeable membrane consistinG essentially of sulfonated poly(phenylene ether) with said mixture under permselective separation conditions, said membrane having been treated with a solution of a hydrolyzable tannin in an amount and under conditions which result in an initial reduction in solute passage through the membrane of at least 10%.

Claim 20

A process for separating solvent from an aqueous mixture containing a solute other than aqueous tanning extracts, comprising contacting a non-porous semipermeable membrane consistinG essentially of sulfonated poly(phenylene ether) with said mixture under permselective separation conditions, said membrane having been treated with a solution of a hydrolyzable tannin in an amount and under conditions which result in an initial reduction in solute passage through the membrane of at least 10%.