Composite Nanoporous Metal Membrane

Abstract

A composite nanoporous metal membrane, a method of making same, and a method of using same to filter supercritical CO 2 are provided. The method of making generally includes a) providing a sintered coarse porous layer; b) applying to an outer face of the coarse porous layer second metal particles; c) sintering to form a structure comprising coarse and intermediate layers; d) applying a suspension of third metal particles; e) drying the suspension of third particles; f) pressing the dried layer of third particles; and g) sintering to form a composite nanoporous metal membrane. The composite nanoporous metal membrane generally includes: a) a sintered coarse layer; b) an intermediate layer comprising first metal particles and second metal particles joined in a sintered structure which is sintered to the coarse layer; and c) a fine layer comprising third metal particles joined in a sintered structure which is sintered to the intermediate layer.

We claim: 
     
         1 . A method of making a composite nanoporous metal membrane comprising:
 a) providing a coarse porous layer comprising first particles comprising a first metal or alloy in metallic state, the first particles having an average diameter of 50-200 micrometers and a first sintering temperature, wherein the first particles of the coarse layer are joined in a sintered structure;   b) applying to an outer face of the coarse porous layer second particles comprising a second metal or alloy in metallic state to form a first intermediate structure, the second particles having an average diameter of 1-5 micrometers and a second sintering temperature;   c) sintering the first intermediate structure at a temperature less than the first sintering temperature to form a second intermediate structure comprising coarse and intermediate layers;   d) applying to the second intermediate structure a suspension of third particles comprising a third metal or alloy in metallic state, the third particles having an average diameter of 50-150 nanometers and a third sintering temperature;   e) drying the suspension of third particles to form a third particle layer borne on the second intermediate structure;   f) pressing the third particle layer borne on the second intermediate structure together with the second intermediate structure to form a third intermediate structure; and   g) sintering the third intermediate structure at a temperature less than the second sintering temperature to form a composite nanoporous metal membrane.   
     
     
         2 . The method according to  claim 1 , wherein the second particles having an average diameter of 1-4 micrometers. 
     
     
         3 . The method according to  claim 1 , wherein step f) comprises uniform orthogonal compression of the third particle layer. 
     
     
         4 . The method according to  claim 1 , wherein the suspension of third particles is a suspension in a solvent system of one or more alcohols and/or water. 
     
     
         5 . The method according to  claim 1 , wherein the suspension of third particles is a suspension in a solvent system having a surface tension of less than 30.0 millinewtons per meter at 20° C. 
     
     
         6 . The method according to  claim 1 , wherein the composite nanoporous metal membrane has a bubble point of 207 kPa (30 PSI) or greater as measured by the IPA Bubble Point Test Method and an air permeability of 0.200 slpm/cm 2  or greater as measured by the Air Permeability Test Method. 
     
     
         7 . The method according to  claim 1 , wherein the composite nanoporous metal membrane has a bubble point of 380 kPa (55 PSI) or greater as measured by the IPA Bubble Point Test Method. 
     
     
         8 . The method according to  claim 1 , wherein the composite nanoporous metal membrane comprises pores capable of passing liquids or supercritical fluids. 
     
     
         9 . The method according to  claim 1 , wherein the first, second, and third metals are independently selected from the group consisting of stainless steel and nickel. 
     
     
         10 . A composite nanoporous metal membrane comprising:
 a) a coarse layer comprising first particles comprising a first metal or alloy in metallic state, the first particles having an average diameter of 50-200 micrometers, wherein the first particles of the coarse layer are joined in a sintered structure;   b) an intermediate layer comprising first particles and second particles comprising a second metal or alloy in metallic state, the second particles having an average diameter of 1-5 micrometers, wherein the first and second particles of the intermediate layer are joined in a sintered structure which is sintered to the coarse layer; and   c) a fine layer comprising third particles comprising a third metal or alloy in metallic state, the third particles having an average diameter of 50-150 nanometers, wherein the third particles of the fine layer are joined in a sintered structure which is sintered to the intermediate layer.   
     
     
         11 . The composite nanoporous metal membrane according to  claim 10 , wherein the composite nanoporous metal membrane has a bubble point of 207 kPa (30 PSI) or greater as measured by the IPA Bubble Point Test Method and an air permeability of 0.200 slpm/cm 2  or greater as measured by the Air Permeability Test Method. 
     
     
         12 . The composite nanoporous metal membrane according to  claim 10 , having a bubble point of 380 kPa (55 PSI) or greater as measured by the IPA Bubble Point Test Method. 
     
     
         13 . The composite nanoporous metal membrane according to  claim 10 , wherein the composite nanoporous metal membrane comprises pores capable of passing liquids or supercritical fluids. 
     
     
         14 . The composite nanoporous metal membrane according to  claim 10 , wherein the first, second, and third metals are independently selected from the group consisting of stainless steel and nickel. 
     
     
         15 . The composite nanoporous metal membrane according to  claim 10 , wherein the fine layer has a thickness of 50-250 micrometers. 
     
     
         16 . A method of filtering supercritical CO 2  comprising the step of passing supercritical CO 2  through the composite nanoporous metal membrane according to  claim 10 . 
     
     
         17 . The method according to  claim 16 , wherein the step of passing supercritical CO 2  through the composite nanoporous metal membrane can occur at pressure drop across the composite nanoporous metal membrane of greater than 2.5 MPa without degradation of the composite nanoporous metal membrane. 
     
     
         18 . A filter comprising the composite nanoporous metal membrane according to  claim 10  mounted in a filter housing. 
     
     
         19 . The filter according to  claim 18 , wherein the filter housing comprises metal and the fine layer of the composite nanoporous metal membrane is welded to the filter housing.