DayalBagh Educational Institute Demineralization or Ion Exchange Process

DayalBagh Educational InstituteDemineralization or Ion Exchange ProcessSubmitted By:-Yashank SrivastavaSubmitted to:-Dr. Sudhir kumar verma1

The Purpose of Ion Exchange.It is the main process used to control the purity and pH of the reactor coolant.Many plants also use this process for feedwater chemistry control and water pretreatment.2DEFINATION Ion ExchangeAny process which results in the reversible exchange of ions contained in a fluid with those contained on a solid without a permanent change in the solid structure.Water is treated with an ion exchange resin.These resins will replace undesirable ions with those which are more acceptable within an aqueous process stream under a specific set of operating conditions.3 The two general types of demineralizer resinsIon exchange demineralizers use microscopic resin beads composed of an insoluble inert structural matrix and a chemically active functional group.

The functional groups are molecules with exchangeable ions such as H+ or OH-, that can be safely released into the system.

Cation resins exchange positively charged functional groups, for undesirable positive ions. With their functional groups in the hydrogen form, R H, R represents the exchange resin and H represents the attached hydrogen ion.

Anion resins exchange negatively charged functional groups for any undesirable negative ion. The hydroxyl ion, OH- (ROH) is commonly used as the functional group in an anion resin.4 Typical Ion Exchange Reaction

5Discription of a typical ion exchange reactionThe cation resin has a higher affinity for Na+ than for H+ and releases the H+ in the exchange reaction. The anion resin has a higher affinity for the Cl- than for the OH-, and releases the OH- in the exchange reaction.The reactions in the previous slide shows a typical demineralizer reaction.In reality, some of the water will leak through the resin allowing some untreated water to reach the reactor system.The greater the ionic charge the greater the affinity of the ion for the resin.Larger ions have a greater affinity than smaller ions.6 pH control utilizing the ion exchange process.pH is the measure of the relative acidity (or alkalinity) of a solution.If a lithium form cation resin is used with a hydroxyl form ion, the effluent will have a high pH and will be strongly basic, due to the exchange of lithium ions (Li+) for cation impurities and hydroxyl ions (OH-) for anion impurities.

Cation exchange resins are classified as:Strong acidIntermediate acidWeak AcidAnion exchange resins are classified as:Strong BaseIntermediate baseIf you have sodium chloride, after the cation is exchanged we have HCl acid remaining in solution. (strong acid)If the cation in solution is magnesium and chloride ions are removed the result is magnesium hydroxide which is a weak base.77 The purpose of a demineralizerDemineralization is the removal of essentially all inorganic salts. In ion exchange demineralization hydrogen cation exchange converts dissolved salts to their corresponding acids, and basic anion exchange removes these acids.PurposeRemoval of ionic substancesReduction of conductivityControl of pH

8Basic DefinitionsRegeneration is the treatment of the resin bed (chemical) to replace impure cations and anions.The spent regenerant containing the undesirable ions is then discarded to the plant wastewater system.Leakage is the very small, almost undetectable amounts of undesirable ions that continuously pass through the demineralizer without being exchanged.

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