Ton Exchange 383 1.1 lon Exchange processes Processes involving ion exchange resins usually make use of ion interchange with theresin. Examples of these processes are demineralization conversion,purification and concentration. Chromatographic processes with ion exchange resins merely make use of the ionic environment that the resins provide in separating solutes Demineralization is the process in which the salts in the feed stream are removed by passing the stream through a cation exchange column in the hydrogen ion form, followed by an anion exchange column in the hydroxide or"free-base"form. Water is the most common feed stream in demineraliza tion. It may also be necessary to remove the salts from a feed stream before fermentation High metallic ion concentrations and high total salt content in the carbohydrate feed has been found to decrease the yield in citric acid fermentation. 3] These ions can be removed by passing the carbohydrate olution through cation and anion exchange resin beds. The salts required for optimum microorganism activity can be added in the desired concentration prior to fermentation Conversion or metathesis is a process in which salts of acids are converted to the corresponding free acids by reaction with the hydrogen form of a strong acid cation resin. One such example would be the conversion of calcium citrate to citric acid The terms may also be used to describe a process in which the acid salt is converted to a different salt of that acid by interaction with a ion exchang resin regenerated to the desired ionic form Many fermentation products may be purified by adsorbing them on ior exchange resins to separate them from the rest of the fermentation broth Once the resin is loaded, the product is eluted from the column for further purification or crystallization Adsorbing lysine on ion exchange resin is probably the most widely used industrial method of purifying lysine. The fermented broth is adjusted to pH20 with hydrochloric acid and then passed through a column of strong acid cation resin in the NH form. Dilute aqueous ammonia may be used to elute the lysine from the resin, [4 gordienkoll5)has reported that treating the resin with a citrate buffer solution ofpH3 2 and rinsing with distilled water before elution results in an 83-90% yield of lysine, with a purity of 93-96%Ion Exchange 383 1.1 Ion Exchange Processes Processes involving ion exchange resins usually make use of ion interchange with the resin. Examples ofthese processes are demineralization, conversion, purification and concentration. Chromatographic processes with ion exchange resins merely make use of the ionic environment that the resins provide in separating solutes. Demineralization is the process in which the salts in the feed stream are removed by passing the stream through a cation exchange column in the hydrogen ion form, followed by an anion exchange column in the hydroxide or “free-base” form. Water is the most common feed stream in demineraliza￾tion. It may also be necessary to remove the salts from a feed stream before fermentation. High metallic ion concentrations and high total salt content in the carbohydrate feed has been found to decrease the yield in citric acid fermentati~n.[’~] These ions can be removed by passing the carbohydrate solution through cation and anion exchange resin beds. The salts required for optimum microorganism activity can be added in the desired concentration prior to fermentation. Conversion or metathesis is a process in which salts of acids are converted to the corresponding free acids by reaction with the hydrogen form of a strong acid cation resin. One such example would be the conversion of calcium citrate to citric acid. The terms may also be used to describe a process in which the acid salt is converted to a different salt of that acid by interaction with a ion exchange resin regenerated to the desired ionic form. Many fermentation products may be purified by adsorbing them on ion exchange resins to separate them from the rest of the fermentation broth. Once the resin is loaded, the product is eluted from the column for further purification or crystallization. Adsorbing lysine on ion exchange resin is probably the most widely used industrial method of purifying lysine. The fermented broth is adjusted to pH 2.0 with hydrochloric acid and then passed through a column of strong acid cation resin in the NH; form. Dilute aqueous ammonia may be used to elute the lysine from the resin.[14] Gordienko[151 has reported that treating the resin with a citrate buffer solution ofpH 3.2 and rinsing with distilled water before elution results in an 83-90% yield of lysine, with a purity of 93-96%