Ion Exchange Capacity 1

[JTBorton]

I am very new to Ion Exchange and am having some difficulty understanding the equivilant capacity measurements. I'm seeing things like this:

Total Exchange Capacity, min.
Units: meq/mL
-N(CH3)3 Form: 1.2
-COOH Form: 1.1

Total Exchange Capacity, min.
Units: eq/L
FB(Free Base)Form: 1.3

Total Exchange Capacity, min.
Units: eq/L
H+ Form: 3.8

I understand that eq/L refers to the number of binding sites, but what about all of the different forms? Does it mean it has 3.8 hydrogens available for exchange? What is Free Base form?

-JTBorton
Well, You can try banging your head against the wall, but you just end up with lost-time injuries and damaged equipment. [M. Passman]

 

[bimr]

Total Exchange Capacity is not a parameter that is used in practice. It is something that is only used in resin production.

The percentage of actively used capacity will vary with the ion exchange application. For instance, color removal may only use 10 % of the total capacity.

Total capacity measurement is a laboratory tool to determine if newly manufactured resins meet specifications. It usually falls within a narrow range for any given composition and doesn’t really vary from one manufacturer to another. ‘Good’ resin and ‘bad’ resin generally does not
refer to capacity but to other physical factors related to bead integrity and cleanliness. It must be kept in mind that total capacity is not the same as operating capacity.
One cannot always compare data sheets to determine the proper choice of resin but must rely on knowledge, experience and the help of one’s resin supplier.

Operating capacity is a performance criteria.

The resin manufacturer's have tables that list approximate useful operating capacities and average leakage at various regenerant levels and applications. This tables are what is used to size equipment.

http://www.ffcr.or.jp/zaidan/FFCRHOME.nsf/.../$FILE/D203.pdf

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/IONEX/resins.htm

http://www.wcponline.com/pdf/1105 michaud.pdf

http://www.resintech.com/pdf/PredictingtheOperatingCapacityofStrongAnion.pdf

Resins have the ability to remove ions by sorption in addition to ion exchange reactions. For example, the weak base anion exchanger in the free base form takes up acids without exchanging ions:

R-NH2 + H + CL >>> RNH3 + CL

The phenomenon is actually sorption instead of ion exchange. The weak base anion exchange resin in the free base form can be described as having low apparent capacity and a high sorption capacity for acids. It is more practical to characterize resin capacity by ion exchange capacity.

 

[JTBorton]

Thanks for the help. The literature has been a tremendous asset.

-JTBorton
Well, You can try banging your head against the wall, but you just end up with lost-time injuries and damaged equipment. [M. Passman]