Enhanced ion exchange capacity of polyampholytic resins

• Low ion exchange capacities of polyampholytic resins restrict applications.
• A novel process was developed for significantly increasing ion exchange capacity.
• Resin pore expansion produced by thermal decomposition of adsorbed salt.
• Polyampholytic resins might have greater applications for desalination.

Ion exchange (IEX) resins are commonly available as cationic or anionic resins but not as polyampholytic resins. This is probably because sequential acid and base washing cannot produce complete regeneration of polyampholytic resins with chemically attached anionic and cationic groups in close proximity. However, it has recently been shown that these resins can be completely regenerated by washing with concentrated ammonium bicarbonate (AB) solution followed by heating. Even so, the low IEX capacities of polyampholytic resins restrict their commercial applications. Here we report a novel process for increasing the IEX capacity of a typical polyampholytic resin by exposing Ni2+ and Ca2+ saturated resins to concentrated ammonium bicarbonate solutions followed by heating. This process was found to increase the IEX capacity by 4–5 times with a corresponding increase in observable pore size and BET surface area.

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