System and method for liquid filtration based on a neutral filter material

Abstract

The present invention teaches, that the removal of particles of any charge from liquid stream is possible by mechanisms other than sieving with good flow and low pressure drop. The use of a weakly charged or neutral surface on the one or more filters within a pre-selected pH range is used. Consequently, particles that are much smaller than the filter pore size are captured with high efficiency. The essentially neutral or weakly charged material filter surface in the filtration liquid may be formed through the proper selection of filter material or a surface modification of the base filters(s) to create the essentially neutral or weakly charged surface.

What we claim:  
     
         1 . A filter for liquids comprising one or more porous filters, wherein the one or more filters each have surfaces that are substantially neutral in a selected fluid.  
     
     
         2 . The filter of  claim 1  wherein the fluid is an aqueous fluid and the surface is substantially neutral over a preselected pH range.  
     
     
         3 . The filter of  claim 1  wherein the one or more filters have a Zeta Potential of between about 10 and −10 millivolts in a selected fluid.  
     
     
         4 . The filter of  claim 1  wherein the one or more filters have a Zeta Potential of between about 5 and −5 millivolts in a selected fluid.  
     
     
         5 . A system for filtering fluids comprising a fluid and one or more filters wherein the one or more filters each have surfaces that are substantially neutral in a selected fluid.  
     
     
         6 . The system of  claim 5  wherein the fluid is selected from the group consisting of aqueous fluids, non-aqueous fluids and blends thereof and the one or more filters have a Zeta Potential of between about 5 and −5 millivolts in the selected fluid.  
     
     
         7 . The filter of  claim 1  wherein the one or more filters have a log reduction value (LRV) of at least 3 of particles in the selected fluid.  
     
     
         8 . The filter of  claim 1  wherein the one or more filters have a log reduction value (LRV) of from about 3 to about 20 of particles in the selected fluid.  
     
     
         9 . The filter of  claim 1  wherein the one or more filters have a Zeta Potential of between about 10 and −10 millivolts in the selected fluid and a log reduction value (LRV) of at least 3 of particles in the selected fluid.  
     
     
         10 . The filter of  claim 1  wherein the one or more filters have a Zeta Potential of between about 5 and −5 millivolts in the selected fluid and a log reduction value (LRV) of at least 3 of particles in the selected fluid.  
     
     
         11 . A method of filtration of liquids comprising selecting a fluid containing one or more contaminants to be removed, forming one or more porous filters, said one or more filters having surfaces which are substantially neutral within the selected fluid and passing the fluid through the one or more filters to remove the contaminants.  
     
     
         12 . The filter of  claim 1  wherein the substantially neutral surface is inherent in the nature of the one or more filters.  
     
     
         13 . The filter of  claim 1  wherein the substantially neutral surface is formed by surface modification of the one or more filters.  
     
     
         14 . The filter of  claim 1  wherein the substantially neutral surface is formed by surface modification of the filter and the surface modification is selected from the group consisting of cross linking and grafting of one or more monomers on surfaces of the one or more filters.  
     
     
         15 . The filter of  claim 1  wherein the substantially neutral surface is formed by surface modification of the filter and the surface modification is by application of an energy source on surfaces of the one or more filters.  
     
     
         16 . The filter of  claim 1  wherein the one or more filters are made from a material selected from the group consisting of cellulose, glass, ceramics and metals.  
     
     
         17 . The filter of  claim 1  wherein the one or more filters are made from a material selected from the group consisting of cellulose, regenerated cellulose and nitrocellulose.  
     
     
         18 . The filter of  claim 1  wherein the one or more filters are made from a metal selected from the group consisting of stainless steel, nickel, chromium and alloys and blends thereof.  
     
     
         19 . The filter of  claim 1  wherein the one or more filters are made from a plastic selected from the group consisting of polyolefins; copolymers or terpolymers of polyolefins; PVDF; PTFE resin; PFA; perfluorinated thermoplastic resins; PVC; nylons; polyamides; polysulphones; polyethersulphones; polyarylsulphones; polyphenylsulphones; polyimides; polycarbonates; polyesters; and blends thereof.  
     
     
         20 . The filter of  claim 1  wherein the one or more filters are made from a polyolefin selected from the group consisting of polyethylene, polypropylene and the like.  
     
     
         21 . The filter of  claim 1  wherein the one or more filters are made from an ultrahigh molecular weight polyethylene.  
     
     
         22 . A filter comprising one or more filters each having a surface having an IEP within a selected operating range of pH such that the filter surface either maintains a neutral or weak charge or does not acquire a highly charged surface within the selected pH range.  
     
     
         23 . A filter comprising one or more filters each having a surface having an IEP that matches the pH of the liquid in which it is used.  
     
     
         24 . A filter comprising two or more filters in a composite filter, each with a different IEP.  
     
     
         25 . The filter of  claim 1  wherein the surface of the one or more filters is treated with one or monomers selected from the group consisting of acrylate or acrylamide monomers and methacrylate or acrylamide monomers and blends thereof.  
     
     
         26 . The filter of  claim 1  wherein the surface of the one or more filters is treated with acrylic acid.  
     
     
         27 . The filter of  claim 1  wherein the surface of the one or more filters is treated with acrylic acid, a photoinitiator and a cross linker.  
     
     
         28 . The filter of  claim 1  wherein the surface of the one or more filters is treated with acrylic acid, a photoinitiator and a cross linker, wherein the cross linker is N,N′-methylenebisacrylamide.  
     
     
         29 . The filter of  claim 1  wherein the surface of the one or more filters is treated with N,N′-methylenebisacrylamide.  
     
     
         30 . The filter of  claim 1  wherein the one or more filters have a log reduction value (LRV) of at least 3 of particles of an average diameter that is smaller than the nominal pore size of the filter in the selected fluid.