Process for high concentration cation exchange metathesis
Provided is a method for high concentration cation exchange metathesis of divalent ions such as calcium with univalent ions such as sodium or potassium. Due to the difference between ionic valences between the exchanged ions, the provided process behavior is strongly dependent upon the selection of resin properties and to total solution normality. A combination of resin properties and solution normality is provided to achieve the cation exchange.
1. A method of resin evaluation, comprising:
(a) loading a known volume of water-washed divalent cation loaded resin with a known activity into a test column;
(b) passing a solution with known concentration of univalent counter ion to be exchanged over the resin for an initial period of time;
(c) repeating steps (a) and (b) for a different period of time than the initial period of time;
(d) calculating the resin conversion X;
(e) calculating a univalent counter ion tau value using the equations:
t
=
τ
Na
(
1
-
3
(
1
-
X
)
2
3
+
2
(
1
-
X
)
)
(
Eq
.
13
)
where
:
τ
Na
=
K
d
C
Na
=
ρ
Ca
R
2
6
bD
e
C
Na
(
Eq
.
14
)
where t is the time it takes to achieve a given resin conversion X, in minutes; ρ Ca is the molar density of divalent cation loaded resin in meq/mL; R is the resin particle radius; D e is the interparticle diffusion coefficient; and C Na is the concentration of univalent counter ion in the feed solution;
(f) loading a known volume of water-washed univalent cation loaded resin with a known activity into a test column;
(g) passing a solution with known concentration of divalent counter ion to be exchanged over the resin for an initial period of time;
(h) repeating steps (f) and (g) for a different period of time than the initial period of time;
(i) calculating the resin conversion X;
(j) calculating a divalent counter ion tau value using the equations:
t
=
τ
Ca
(
1
-
3
(
1
-
X
)
2
3
+
2
(
1
-
X
)
)
where t is the time it takes to achieve a given resin conversion X, in minutes; ρ Na is the molar density of univalent cation loaded resin in meq/mL; R is the resin particle radius;
D e is the interparticle diffusion coefficient; and C Ca is the concentration of divalent counter ion in the feed solution; and
(k) calculating a ratio τ Na /τ Ca .
2. The method of claim 1 , wherein the resin activity for the selected resin is 2.0 eq/L±10 percent where the solution having a univalent counter ion is saturated NaCl.
3. The method of claim 1 , wherein the divalent cation is calcium ion.
4. The method of claim 1 , wherein the univalent counter ion is sodium ion.
5. The method of claim 1 , wherein the resin is completely loaded with the divalent cation in step (a).
6. The method of claim 1 , wherein the resin is completely loaded with univalent cation in step (f).