Porous polyethylene filter membrane with asymmetric pore structure, and related filters and methods

Abstract

Described are liquid-flowable, porous polyethylene filter membranes that include two opposing sides and that have an asymmetric pore structure; filter components and filters that include this type of porous polyethylene filter membrane; methods of making the porous polyethylene filter membranes, filter components, and filters; and methods of using a porous polyethylene filter membrane, filter component, or filter, to filter a fluid such as a liquid chemical to remove unwanted material from the fluid.

1 . A liquid-flowable porous filter membrane comprising polyethylene having two opposed sides and a thickness between the two opposed sides, with pores throughout the thickness, and with the pores having an asymmetric pore structure. 
     
     
         2 . The filter membrane of  claim 1 , wherein the polyethylene has a molecular weight of at least 50,000 grams per mole. 
     
     
         3 . The filter membrane of  claim 1 , comprising smaller pores on a first side and larger pores on a second side, wherein a 1 microliter (1 μL) drop of mineral oil placed on the first side spreads to a diameter of 1 centimeter in a time that is at least 4 times longer than a time for a drop of the mineral oil placed on the second side to spread to a diameter of 1 centimeter. 
     
     
         4 . The filter membrane of  claim 1 , wherein the polyethylene has a density in a range from about 0.94 to about 0.97 gram per cubic centimeter. 
     
     
         5 . The filter membrane of  claim 1 , wherein the polyethylene has a melt index in a range from 0.01 to 0.35 grams per 10 minutes as measured using ASTM D1238-13. 
     
     
         6 . The filter membrane of  claim 1 , comprising smaller pores on a first side and larger pores on a second side and having a mean bubble point in a range from 135 to 185 psi, measured using HFE-7200 liquid fluid at a temperature of 25 degrees Celsius with air flowing from the second side to the first side. 
     
     
         7 . The filter membrane of  claim 1 , having pores on the first side of the membrane that have an average pore size in a range from 0.001 to 0.2 microns. 
     
     
         8 . The filter membrane of  claim 1 , having a retention of at least 95 percent, measured based on a 1 percent monolayer using G25 round polystyrene particles having a nominal diameter of 0.03 microns. 
     
     
         9 . The filter membrane of  claim 1 , having an isopropyl alcohol permeability of at least 50 liters/square meter/hour/bar. 
     
     
         10 . The filter membrane of  claim 1 , wherein the porous filter membrane has a porosity of at least 60 percent. 
     
     
         11 . The membrane of  claim 1 , wherein the porous filter membrane has a thickness in a range from 30 to 200 microns. 
     
     
         12 . The filter membrane of  claim 1 , wherein the filter membrane is prepared by melt casting. 
     
     
         13 . A filter cartridge comprising the membrane of  claim 1 . 
     
     
         14 . A filter comprising the membrane of  claim 1 . 
     
     
         15 . A method of using the filter membrane of  claim 1 , the method comprising passing solvent-containing liquid through the filter membrane. 
     
     
         16 . The method of  claim 15  wherein:
 the liquid comprises: ethyl lactate, gamma-butyrolactone, hexamethyldisilazane, methyl-2-hydroxyisobutyrate, methyl isobutyl carbinol, n-butyl acetate, tetraethyl ammonium hydroxide (TMAH), propylene glycol methyl ether (PGME), propylene glycol methylether acetate (PGMEA), isoamyl acetate, 2-heptanone, or cyclohexanone, 
 the method includes using the filter to remove metal from the liquid. 
 
     
     
         17 . The method of  claim 16 , wherein the filter membrane has a retention of at least 95 percent measured based on a 1 percent monolayer using G25 round polystyrene particles having a nominal diameter of 0.03 microns. 
     
     
         18 . A method of preparing a porous polyethylene film having two opposed sides and a thickness between the two opposed sides, with pores throughout the thickness, and with the pores having an asymmetric pore structure, the method comprising:
 extruding a heated polymer solution comprising polyethylene polymer and solvent, at an extrusion temperature, to form extruded polymer film, and   reducing the temperature of the extruded polymer film to form the cast porous polyethylene film.   
     
     
         19 . The method of  claim 18 , wherein the polymer solution comprises:
 from 15 to 35 weight percent polyethylene polymer, and   from 65 to 85 weight percent solvent,   based on total weight polymer solution.   
     
     
         20 . The method of  claim 18 , wherein the polymer solution comprises:
 from 17 to 25 weight percent polyethylene polymer, and   from 75 to 83 weight percent solvent,   based on total weight polymer solution.   
     
     
         21 . The method of  claim 18 , wherein the solvent comprises a strong solvent in which the polyethylene polymer is soluble, at the extrusion temperature, and a weak solvent in which the polyethylene polymer is less soluble, at the extrusion temperature. 
     
     
         22 . The method of  claim 21 , wherein:
 the strong solvent comprises mineral oil, and   the weak solvent comprises dioctyl phthalate, dibutyl sebacate, or a combination thereof.   
     
     
         23 . The method of  claim 18 , wherein the polyethylene has a molecular weight of at least 50,000 grams per mole. 
     
     
         24 . The method of any of  claim 18 , wherein the cast porous polyethylene film comprising smaller pores on a first side and larger pores on a second side, wherein a 1 microliter (1 μL) drop of mineral oil placed on the first side spreads to a diameter of 1 centimeter in a time that is at least 4 times longer than a time for a drop of the mineral oil placed on the second side to spread to a diameter of 1 centimeter. 
     
     
         25 . The method of  claim 18 , wherein the polyethylene has a density in a range from about 0.94 to about 0.97 gram per cubic centimeter.