What is Ion exchange resin regeneration?
Over the course of one or more service cycles, an Ion exchange resin will become exhausted, meaning that it can no longer facilitate ion exchange reactions. This happens when contaminant ions have bound to nearly all available active sites on the resin matrix. Put simply, regeneration is a process where anionic or cationic functional groups are restored to the spent resin matrix. This is accomplished through the application of a chemical regenerant solution, though the exact process and regenerants used will depend upon several process factors.
Types of Ion exchange resin regeneration processes
Ion exchange resin systems typically take the form of columns that contain one or more varieties of resin. During a service cycle, a stream is directed into the IX column where it reacts with the resin. The regeneration cycle may be one of two types, depending on the path that the regenerant solution takes. These include:
Co-flow regeneration (CFR). In CFR, the regenerant solution follows the same path as the solution to be treated, which is usually top to bottom in an ion exchange column. CFR is not typically used when large flows require treatment or higher quality is needed, for strong acid cation (SAC) and strong base anion (SBA) resin beds since excessive quantities of regenerant solution would be required to uniformly regenerate the resin. Without full regeneration, the resin may leak contaminant ions into the treated stream on the next service run.
Reverse flow regeneration (RFR). Also known as counterflow regeneration, RFR involves injection of the regenerant solution in the opposite direction of the service flow. This can mean an upflow loading/downflow regeneration or downflow loading/upflow regeneration cycle. In either case, the regenerant solution contacts the less exhausted resin layers first, making the regeneration process more efficient. As a result, RFR requires less regenerant solution and results in less contaminant leakage, though it is important to note that RFR only functions effectively if the resin layers stay in place throughout regeneration. Therefore, RFR should be used only with packed bed ion exchange columns, or if some type of retention device is used to prevent the resin from moving within the column.