Ion exchange resins

An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of small (0.25–0.5 mm radius) microbeads, usually white or yellowish, fabricated from an organic polymer substrate. The beads are typically porous, providing a large surface area on and inside them. The trapping of ions occurs along with the accompanying release of other ions, and thus the process is called ion exchange. There are multiple types of ion-exchange resin. Most commercial resins are made of polystyrene sulfonate.

Ion-exchange resins are widely used in different separation, purification, and decontamination processes. The most common examples are water softening and water purification. In many cases ion-exchange resins were introduced in such processes as a more flexible alternative to the use of natural or artificial zeolites. Also, ion-exchange resins are highly effective in the biodiesel filtration process.

Most typical ion-exchange resins are based on crosslinked polystyrene. The actual ion-exchanging sites are introduced after polymerisation. Additionally, in the case of polystyrene, crosslinking is introduced by copolymerisation of styrene and a few percent of divinylbenzene (non-crosslinked polymers are soluble in water). Crosslinking decreases ion-exchange capacity of the resin and prolongs the time needed to accomplish the ion-exchange processes but improves the robustness of the resin. Particle size also influences the resin parameters; smaller particles have larger outer surface, but cause larger head loss in the column processes.

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