Process and Apparatus for Continuous Production of Porous Structures

Abstract

A method for producing metal-based micro-porous structures includes continuously feeding a solid green part and a gas flow into a tunnel reactor having an aspect ratio greater than 2, wherein the solid green part has a characteristic diffusion mass transfer dimension less than 1 mm and a gas in the gas flow is substantially free of oxidants, and chemically reacting the gas in the gas flow and the green part under a predetermined temperature profile along a length of the tunnel reactor for a sufficient time to convert the green part into a solid product having pore sizes in a range of 0.3 nm to 5 μm.

1 . A method for producing metal-based micro-porous structures comprising:
 continuously feeding a solid green part and a gas flow into a tunnel reactor having an aspect ratio greater than 2, wherein the solid green part has a characteristic diffusion mass transfer dimension less than 1 mm and a gas in the gas flow is substantially free of oxidants; and   chemically reacting the gas in the gas flow and the green part under a predetermined temperature profile along a length of the tunnel reactor for a sufficient time to convert the green part into a solid product having pore sizes in a range of 0.3 nm to 5 μm.   
     
     
         2 . The method of  claim 1 , wherein the solid green part has a residence time in the tunnel reactor greater than 10 minutes. 
     
     
         3 . The method of  claim 1 , wherein the green part and the gas flow move counter-currently to each other inside the tunnel reactor. 
     
     
         4 . The method of  claim 1 , wherein the predetermined temperature profile comprises increasing a temperature of the green part to a reaction temperature greater than 500° C. for complete conversion of the green part into the solid product and decreasing a temperature of the solid product from the reaction temperature to below 300° C. at an exit of the tunnel reactor. 
     
     
         5 . The method of  claim 1 , wherein:
 the green part comprises a sheet having a thickness less than 500 μm, metal oxide particles less than 5 μm, a pore former, and an organic additive;   the gas in the gas flow comprises hydrogen gas; and   
       wherein chemically reacting the gas in the gas flow and the green part comprises:
  removing the pore former and organic binders; and
 reducing and sintering the metal oxide particles into a porous structure comprising metallic grains. 
 
 
     
     
         6 . The method of  claim 1 , wherein:
 the green part comprises a ceramic coating on a porous metal-based support structure, the porous metal-based support structure having pore sizes in a range of 0.1 to 5 μm; and   the ceramic coating comprises:
 a thickness less than 40 μm; 
 metal oxide or ceramic particles having sizes smaller than the pore sizes of the porous metal-based support structure; 
 organic additives; and 
 sintering promoters. 
   
     
     
         7 . The method of  claim 1 , wherein:
 the green part comprises a carbon-containing coating on a porous metal-based support structure having a pore size in a range of 0.1 to 5 μm;   the carbon-containing coating comprises a thickness less than 40 μm; and   the carbon-containing coating comprises oxygen.   
     
     
         8 . The method of  claim 1 , wherein:
 the green part is a functionalized coating;   the gas in the gas flow comprises a silicon containing compound; and   the functionalized coating comprises a porous metal oxide coating having a pore size less than 0.1 μm and a thickness less than 40 μm.   
     
     
         9 . The method of  claim 8 , wherein the functionalized coating is located on a porous metal-based support structure having a pore size in a range of 0.1 to 5 μm and the silicon containing compound reacts with the functionalized coating to form porous silicon carbide or silica structures. 
     
     
         10 . The method of  claim 1 , wherein:
 the green part comprises a functionalized coating comprising a transition metal catalyst deposited inside pores of a porous metal-based support structure having pore size in a range of 0.1 to 5 μm; and   the gas in the gas flow comprises a carbon precursor gas which reacts to form carbon nanotube-type porous structures inside the pores of the porous metal-based support structure.   
     
     
         11 . A method of forming a porous structure, the method comprising:
 preheating a green part in a preheating section of a furnace having a first temperature profile;   heating the green part in a reaction and sintering section of the furnace having a second temperature profile different than the first temperature profile; and   during the heating of the green part, reacting a reactant gas with the green part to convert the green part into the porous structure.   
     
     
         12 . The method of  claim 11 , further comprising:
 cooling the porous structure in a cooling section of the furnace having a third temperature profile different than the first temperature profile and the second temperature profile.   
     
     
         13 . The method of  claim 12 , wherein the first temperature profile comprises a temperature increase along a first length of the furnace to a temperature in a range from 200° C. to 450° C., the second temperature profile comprises a temperature increase along a second length of the furnace to a temperature in a range from 500° C. to 1300° C., and the third temperature profile comprises a temperature decrease along a third length of the furnace to a temperature below 300° C. 
     
     
         14 . The method of  claim 13 , wherein the temperature increase along the first length of furnace comprises a first rate of change, the temperature increase along the second length of furnace comprises a second rate of change greater than the first rate of change, and the temperature decrease along the third length of furnace comprises a third rate of change greater than the second rate of change. 
     
     
         15 . The method of  claim 11 , wherein the reacting of the reactant gas with the green part comprises:
 reacting the reactant gas with a pore former in the green part to remove the pore former; and   reacting the reactant gas with a metal precursor in the green part to reduce the metal precursor to metallic grains.   
     
     
         16 . The method of  claim 11 , further comprising:
 continuously moving the green part through the furnace, wherein the reacting of the reactant gas with the green part comprises reacting the reactant gas with the green part as the reactant gas flows in the furnace in a direction that is opposite a moving direction of the green part.   
     
     
         17 . The method of  claim 11 , further comprising:
 before the preheating of the green part, supplying the green part to an inlet gas exchange chamber and supplying the inlet gas exchange chamber with an inert gas to remove oxygen from the inlet gas exchange chamber.   
     
     
         18 . The method of  claim 11 , further comprising:
 supplying the porous structure to an outlet gas exchange chamber and supplying the outlet gas exchange chamber with an inert gas to remove the reactant gas from the porous structure.   
     
     
         19 . The method of  claim 11 , further comprising:
 continuously exhausting from the furnace a product gas produced by the reacting of the reactant gas with the green part.   
     
     
         20 . A method of forming a porous structure, the method comprising:
 supplying a green part comprising a metal precursor and a pore former to an inlet gas exchange chamber and supplying the inlet gas exchange chamber with an inert gas to remove oxygen from the inlet gas exchange chamber;   preheating the green part in a preheating section of a furnace having an aspect ratio greater than 2, wherein the preheating section includes a first temperature profile in which a temperature increases along a first length of the furnace to a temperature in a range from 200° C. to 450° C.;   heating the green part in a reaction and sintering section of the furnace having a second temperature profile in which a temperature increases along a second length of the furnace to a temperature in a range from 500° C. to 1300° C.;   during the heating of the green part, reacting a reactant gas with the green part to convert the green part into the porous structure having pore sizes in a range of 0.3 nm to 5 μm, wherein the reacting of the reactant gas with the green part comprises:
 reacting the reactant gas with the pore former in the green part to remove the pore former; and 
 reacting the reactant gas with the metal precursor in the green part to reduce the metal precursor to metallic grains; 
   cooling the porous structure in a cooling section of the furnace having a third temperature profile in which a temperature decreases along a third length of the furnace to a temperature below 300° C.; and   supplying the porous structure to an outlet gas exchange chamber and supplying the outlet gas exchange chamber with an inert gas to remove the reactant gas from the porous structure.