Civil Engineering Reference
In-Depth Information
groups derived from a weak acid, commonly of the carboxylic or phenolic form. Such
resins are useful only within a fairly narrow pH range.
Functional groups on strong-base exchange resins are usually quaternary ammo-
nium groups, whereas weak-base exchange resins contain either primary, secondary,
and / or tertiary amines as the functional group. The strong-base exchange resins are
useful over a wide pH range, whereas the weak-base exchange resins are effective
only within a fairly narrow pH range.
The active exchange groups associated with each of the different kinds of resins
are listed in Table 18-2, along with their basic structure and dissociation constant. The
TABLE 18-2. Chemical Classification and Performance Parameters of Common
Ion-Exchange Resins
Dissociation
Constant pKa
Classification
Active Groups
Structure
Cation Exchange Resins
Strong acid
Sulfonic
1
R
SO
3
-
H
+
Weak acid
Carboxylic
4-6
R-CH
2
CHCH
2
-R
COO
-
H
+
Phosphonic
2-3
R
PO
3
2-
H
2
+
Phenolic
9-10
R
O
-
H
+
Anion Exchange Resins
Strong base
Type I—quartenary
ammonium
13
R
CH
2
OH
-
(N(CH
3
)
3
)
+
Type II—quartenary
ammonium
13
R
CH
2
(CH
3
)
2
(C
2
H
4
OH) N)
+
OH
-
Weak base
Primary amine
6-9
R
CH
2
NH
2
Secondary amine
7-9
R
CH
2
NRH
Tertiary amine
9-11
R
CH
2
NR
2
Source:
See Reference 2.
