Microporous zirconium silicate and its method of production

Abstract

The present invention relates to novel microporous zirconium silicate compositions having a desired particle size distribution and methods of making those compositions. These compositions have an ideal particle size distribution for use ex vivo, for example in a dialysis exchange cartridge, yet retain many of the desirable properties of prior improved absorbers including high cation exchange capacity. Further, the new zirconium silicate molecular sieve absorbers can be manufactured using a technique that achieves the desired particle size distribution while eliminating the screening step that was previously necessary.

1 . A cation exchange composition comprising a zirconium silicate of formula (I):
   A p M x Zr 1-x Si n Ge y O m   (I)
   
       where
 A is a potassium ion, sodium ion, rubidium ion, cesium ion, calcium ion, magnesium ion, hydronium ion or mixtures thereof, 
 M is at least one framework metal, wherein the framework metal is hafnium (4+), tin (4+), niobium (5+), titanium (4+), cerium (4+), germanium (4+), praseodymium (4+), terbium (4+) or mixtures thereof, 
 “p” has a value from about 1 to about 20, 
 “x” has a value from 0 to less than 1, 
 “n” has a value from about 0 to about 12, 
 “y” has a value from 0 to about 12, 
 “m” has a value from about 3 to about 36 and 1≤n+y≤12, 
 wherein the composition exhibits a volume weighted mean particle size between 5 and 20 microns wherein less than 10% of the particles have a size below 5 microns and less than 10% of the particles have a size above 25 microns, wherein the particle size distribution does not result from a screening or classification process. 
 
     
     
         2 . The cation exchange composition of  claim 1 , wherein the mean particle size is between 10 and 15 microns. 
     
     
         3 . An ion exchange column loaded with exchange media, wherein the exchange media comprises the cation exchange composition of  claim 1 . 
     
     
         4 . The composition of  claim 1 , wherein the potassium exchange capacity is greater than 3.0 meq/g. 
     
     
         5 . The composition of  claim 1 , wherein the potassium exchange capacity is greater than 4.4 meq/g. 
     
     
         6 . The composition of  claim 1 , wherein the potassium exchange capacity is between 3.7 and 4.7 meq/g. 
     
     
         7 . A method for making the composition of  claim 1  comprising:
 providing a reaction mixture comprising sodium silicate and zirconium acetate in a reactor; 
 agitating the reaction mixture with an agitator in the presence of one or more baffle-like structures with an agitation speed within a range of 80 rpm to 350 rpm; and 
 obtaining the cation exchange composition from the reactor. 
 
     
     
         8 . The method of  claim 7 , further comprising a step of contacting the zirconium silicate with a dilute solution of strong acid and/or water. 
     
     
         9 . The method of  claim 7 , further comprising a step of blending different lots of the cation exchange composition to produce a desired particle size distribution. 
     
     
         10 . The method of  claim 7 , wherein the agitation speed is within the range of 120 and 170 rpm. 
     
     
         11 . The method of  claim 10 , wherein the agitation speed is approximately 150 rpm. 
     
     
         12 . The method of  claim 7 , wherein the agitation speed is within the range of 190 and 320 rpm. 
     
     
         13 . The method of  claim 12 , wherein the agitation speed is approximately 307 rpm.