Process and adsorbent for gas drying

Abstract

An adsorbent and a process are disclosed for drying gases in a pressure swing dryer. The adsorbent comprises a pre-formed alumina particle with a thin layer of colloidal silica disbursed on the surface of the preformed alumina particle. Surprisingly the thin layer of colloidal silica does not interfere with the drying properties of the pre-formed alumina particle, while significantly improving the physical properties of the pre-formed alumina particle

What is claimed is:  
     
         1 . A process for the drying of a compressed gas comprising a gas component and water, said process comprising contacting the compressed gas stream with an adsorbent to adsorb at least a portion of the water to produce a dry compressed gas stream, wherein said selective adsorbent comprises a shaped alumina particle having dispersed thereon a colloidal silica layer.  
     
     
         2 . The process of  claim 1  wherein the adsorbent has an attrition loss of less than 0.04 wt-%.  
     
     
         3 . The process of  claim 1  wherein the silica layer extends less than about 50 microns from the surface of the shaped particle towards the center of the particle.  
     
     
         4 . The process of  claim 1  wherein the adsorbent comprises a rehydration loss of less than about 5 wt-%.  
     
     
         5 . The process of  claim 1  wherein the shaped alumina particle is selected from the group consisting of spherical, an extrudate, a pill, a flake or a monolith.  
     
     
         6 . The process of  claim 1  wherein the gas component is selected from the group consisting of air, nitrogen, light hydrocarbons and mixtures thereof.  
     
     
         7 . The process of  claim 1  wherein the gas component comprises air.  
     
     
         8 . The process of  claim 1  further comprising periodically purging the selective adsorbent to desorb the water.  
     
     
         9 . The process of  claim 1  wherein the contacting of the compressed gas with the adsorbent takes place in a pressure swing adsorption process wherein the adsorbent is depressurized to an effective desorption pressure and purged to desorb the water.  
     
     
         10 . A method for producing an adsorbent for drying compressed gas comprising: 
 a) coating a pre-formed alumina particle with a coating solution comprising colloidal silica to provide a coated pre-formed particle having a narrow layer of colloidal silica disbursed thereon; and    b) drying and activating the coated pre-formed particle to produce the adsorbent.    
     
     
         11 . The method of  claim 10  wherein the pre-formed particle comprises a sphere or an extrudate.  
     
     
         12 . The method of  claim 10  wherein the coating solution also comprises an ion selected from the group consisting of sodium, chloride, hydrogen, and the like.  
     
     
         13 . The method of  claim 10  wherein the coated pre-formed particle is activated at an activation temperature greater than about 400° C. (750° F.).  
     
     
         14 . A shaped particle having a core consisting of a shaped alumina carrier having a colloidal silica layer dispersed on the shaped alumina carrier, at least 60 percent of the colloidal silica being present in a band extending from the surface towards the center and having a width of less than about 50 microns.  
     
     
         15 . The shaped particle of  claim 14  wherein the band of colloidal silica extending from the surface toward the center comprises a width of less than about 20 microns.  
     
     
         16 . The shaped particle of  claim 14  wherein the adsorbent has an attrition loss of less than 0.4 wt-%.  
     
     
         17 . The shaped particle of  claim 14  wherein the adsorbent comprises a rehydration loss of less than about 5 wt-%.  
     
     
         18 . The shaped particle of  claim 14  wherein the shaped alumina particle is selected from the group consisting of a sphere, an extrudate, a pill, a flake or a monolith.  
     
     
         19 . An air brake dryer assembly having a refillable or replaceable cartridge containing the shaped particle of claim  14 .