Alkali-Promoted Activated Alumina Adsorbent

Abstract

An adsorbent for removing CO2 from a gas mixture, the adsorbent comprising alumina and a carbonate compound where the carbonate to alumina IR absorbance intensity ratio is reduced by washing the adsorbent with water. The disclosure also describes a method of making adsorbent particles, process for removing CO2 from a gas mixture using the adsorbent, and an adsorption unit using the adsorbent.

1 . An adsorbent for use in a process to remove CO 2  from a gas mixture containing CO 2 , the adsorbent comprising:
 alumina;   a carbonate compound; and   one or more alkali metals;   wherein the total amount of alkali metals in the adsorbent is from 0.9 weight % to 10 weight %; and   wherein the adsorbent has a carbonate to alumina intensity ratio, R, the carbonate to alumina intensity ratio, R, having a value less than or equal to 0.0150, where the carbonate to alumina intensity ratio is as determined by Fourier Transform infrared (FTIR) spectroscopy of a crushed sample of the adsorbent, wherein the carbonate to alumina intensity ratio is a ratio of a peak absorbance intensity for carbonate, AI carbonate , to a peak absorbance intensity for alumina, AI alumina , (i.e. R=AI carbonate /AI alumina ), each peak absorbance intensity obtained after subtracting a baseline signal intensity, where the peak absorbance intensity for alumina, AI alumina , is observed at an FTIR wavenumber in a range from 420 cm −1  to 520 cm −1 , and the peak absorbance intensity for carbonate, AI carbonate , is observed at an FTIR wavenumber in a range from 1300 cm −1  to 1400 cm −1 .   
     
     
         2 . The adsorbent according to  claim 1  wherein the total amount of alkali metals in the adsorbent is from 1.0 weight % to 8 weight %. 
     
     
         3 . The adsorbent according to  claim 1  wherein the surface area of the adsorbent ranges from 220 m 2 /g to 400 m 2 /g. 
     
     
         4 . The adsorbent according to  claim 1  wherein the amount of alumina in the adsorbent is from 90 to 99 weight %. 
     
     
         5 . The adsorbent according to  claim 1  wherein the alkali metals are Na and/or K. 
     
     
         6 . The adsorbent according to  claim 1  wherein in the adsorbent the amount of carbonate is lower than the amount of carbonate arithmetically necessary for stoichiometrically compensating the charge of the total amount of alkali metals. 
     
     
         7 . The adsorbent according to  claim 1  wherein the value of the carbonate to alumina intensity ratio ranges from 0.003 to 0.0150. 
     
     
         8 . A method for making adsorbent particles for use in a process to remove CO 2  from a gas mixture containing CO 2 , the adsorbent particles comprising alumina, one or more alkali metals, and a carbonate compound, the method comprising:
 washing alumina materials which comprise one or more alkali metals and a carbonate compound with water; and   drying the washed alumina materials to form the adsorbent particles;   wherein the washed and dried adsorbent particles have a carbonate to alumina intensity ratio, R 2 , which is smaller than the carbonate to alumina intensity ratio, R 1 , of the alumina compound which comprises one or more type(s) of alkali metal ions and carbonate ions before washing; and   wherein the carbonate to alumina intensity ratio is as determined by Fourier Transform infrared (FTIR) spectroscopy of a crushed sample of the respective washed and dried adsorbent particles and a crushed sample of the alumina materials which comprises one or more alkali metals and a carbonate compound before washing, wherein the carbonate to alumina intensity ratio is a ratio of a peak absorbance intensity for carbonate, AI carbonate , to a peak absorbance intensity for alumina, AI alumina , (i.e. R=AI carbonate /AI alumina )) each peak absorbance intensity obtained after subtracting a baseline signal intensity, where the peak absorbance intensity for alumina, AI alumina , is observed at an FTIR wavenumber in a range from 420 cm −1  to 520 cm −1 , and the peak absorbance intensity for carbonate, AI carbonate , is observed at an FTIR wavenumber in a range from 1300 cm −1  to 1400 cm −1 .   
     
     
         9 . The method according to  claim 8  wherein the water is deionized water. 
     
     
         10 . The method according to  claim 8  wherein the alumina materials which comprise one or more alkali metals and a carbonate compound are washed sufficiently to produce adsorbent particles having a carbonate to alumina intensity ratio, R 2 , of less than or equal to 0.0150. 
     
     
         11 . The method according to  claim 8  wherein the alumina materials which comprise one or more alkali metals and a carbonate compound are washed with water until the alumina materials have a pH in solution of 9.5 or less thereby forming washed alumina materials, the pH in solution as determined by measuring the pH of an equilibrated 2 liter solution of deionized water containing 100 g of the washed alumina materials. 
     
     
         12 . The method according to  claim 8  wherein the alumina materials which comprises one or more alkali metals and a carbonate compound are washed with water containing less than 100 ppm total dissolved solids. 
     
     
         13 . Adsorbent particles for use in a process to remove CO 2  from a gas mixture containing CO 2  made by a method according to  claim 8 . 
     
     
         14 . A process for removing CO 2  from a gas mixture containing CO 2 , the process comprising:
 passing the gas mixture containing CO 2  into a bed containing the particles according to  claim 13 ; and   withdrawing a CO 2 -depleted gas from the bed.   
     
     
         15 . A process for removing CO 2  from a gas mixture containing CO 2 , the process comprising:
 passing the gas mixture containing CO 2  into a bed containing the adsorbent according to  claim 1 ; and   withdrawing a CO 2 -depleted gas from the bed.   
     
     
         16 . The process according to  claim 15  wherein the gas mixture containing CO 2  has a concentration of CO 2  that ranges from 5 ppmv CO 2  to 1 mole % CO 2 . 
     
     
         17 . The process according to  claim 15  wherein the gas mixture contains oxygen, nitrogen, and water. 
     
     
         18 . The process according to  claim 15  wherein the gas mixture is a feed to a cryogenic air separation unit. 
     
     
         19 . An adsorption unit comprising a bed containing the adsorbent according to  claim 1 . 
     
     
         20 . An adsorption unit comprising a bed containing the adsorbent particles according to  claim 13 .