化学工程与工艺专业英语Unit15ReadingIonExchange

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1、Unit15ReadingIonExchangeIonexchangestandsasaunitoperationinitsownright,oftensharingtheorywithadsorptionorchromatographybuthavingitsownspecialareasofapplication.Itsoldestandmostenduringapplicationisfortreatment,tosoftenordemineralizewaterbeforeindustrialuse,torecovercomponentsfromanaqueou

2、seffluentbeforeitisdischargedorrecirculated.Ionexchangecanbemanufacturedwhichcatalyzespec讦icreac廿onsorwhicharesuitabletouseforchromatographicseparations.离子交换本身作为一个单元操作，常与吸附或色谱法有相同的理论，但离子交换在自己的特殊领域有着很多应用。它的最古老和最持久的应用是治疗，在工业使用前软化或生产去离子水,在废水排放或循环前将其处理。离子交换可以制造催化特定反应催化剂或适合用于色谱分离。Inthepresent

3、consent,theexchangeisthatofequivalentnumbersofsimilarlychargedions,betweenanimmobilephase,whichmaybeacrystallatticeoragel,andaliquidsurrounclingtheimmobilephase・Iftheexchangingionscarryapositivecharge,theionexchangeistermedcationic,and,ifanegativecharge,anionic.Therateatwhichionsdiffuseb

4、etweenexchangerandliquidisdeterminednotonlybytheconcentrationdifferencesinthetwophases,butalsobythenecessityofmaintainingelectroneutralityinbothphase・现阶段主流的观点是，离子交换是固定相之间同等数量的类似的带电离子的交换，这个固定相可能是晶格、凝胶或周围液体。如果交换离子带正电荷，称为阳离子交换；如果交换离子带负电荷,则称为阴离子交换。交换器和液体之间的离子扩散的速度不仅取决于两个固定相的离子浓度，还取决去两个固定相保持电

5、中性的必要性。IonexchangeprocessfunctionbyreplacingundesirableionsofaliquidwithionssuchasH+or0H・fromasolidmaterialinwhichtheionsaresufficientlymobile,usuallysomesyntheticresin.Eventuallytheresinbecomesexhaustedandmayberegeneratedbycontactwithasmallamountofsolutionwithahighcontentofthedesiredion

6、.Resinscanbetailoredtohaveselectiveaffinitiesforparticularkindsofions.离子交换的运作过程是用合成树脂中移动性较好氢离子和氢氧根离子取代液体中不希望存在的某些离子。最终，这些树脂达到交换饱和状态，并可以通过与少量高浓度离子的接触再生。树脂可以制作成对某些离子有选择性的亲和力。Commercialcolumnsrangefromupto6mdiaandbedheightsfrom1to6m,mostcommonly1~3m.Freeboardof50%~100%isprovidedtoaccommodat

7、ebedexpansionwhenregenerantflowisupward・Theliquidmustbedistributedandwithdrawnun讦ormlyoverthecrosssection.Perforatedspidersaresuitable・Theusualsupportforthebedofresinisabedofgravelorlayersofceramicballsofgradedsizes,ballssometimesareplacedontopofthebedtoaidindistributiono