CausticinBrine,

EffectonOperation&Monitoring

JSG,ZhangjiagangSite,PRChina

中華人民共和國張家港BrianBrandreth14th-20thOctober20092009年10月14日至29日CellChemistry

電池化學Basics基本原理Electrolysis,inthiscase,isthesplittingofachemicalcompoundusinganelectriccurrent.電解，定義是這樣的，通過導入電流來對化合物進行快速分解IntheChlor-alkaliprocesssodiumchloridesolution(brine)isseparatedintochlorinegas,sodiumhydroxidesolution(causticsoda)andhydrogengas.在氯堿綜合過程中，氯化鈉溶液分解成氯氣，氫氧化鈉溶液（苛性鈉）和氫氣Toensuretheprocessoperatesefficientlygivinghighqualityproducts,itisessentialthatwekeepverytightcontrolofalloperatingparametersandimpuritiesinthefeedliquors.為確保高效操作運行，產(chǎn)出優(yōu)質(zhì)產(chǎn)品，嚴格控制生產(chǎn)過程中所有因素和進液時的雜質(zhì)量顯得很重要。Wemustalsotakeextremecarewhenhandlingmembranesinthatanyfaultsintroducedinthemembranewillallowmorecausticbackmigrationwhenitisinoperation.在操作離子膜時，我們同樣也必須極度小心。因為一點小的缺陷操作都將會導致運行期間離子膜有更多苛性鈉的反遷移BasicPrinciples基本原理Na+Cl-OH-FeedsandProductsAnode陽極Cathode陰極Membrane隔離物HydrogenGas氫氣ChlorineGas氯氣StrongCaustic強堿WeakCaustic弱堿WeakBrine稀鹽水StrongBrine濃鹽水Strongbrineisfedtoanodecompartment濃鹽水注入陽極室Chlorideionselectrolysedonanodetoproducechlorinegas處于陽極的氯離子電解產(chǎn)生氯氣Sodiumionsandwaterfromthebrinepassthroughthemembranedrivenbytheelectricfield.鹽水中的鈉離子和水在電場作用下透過離子膜Unreactedchlorideionsleaveasweakordepletedbrine未反應的氯離子隨稀鹽水或廢鹽水離開Weakcausticfedintocathodecompartments弱堿注入陰極室Waterelectrolysedatthecathodetoformhydrogengasandhydroxylions處于陰極的水電解形成氫氣和氫氧根離子Sodiumionsandhydroxylionsformthecausticproduct鈉離子和氫氧根離子生成苛性鈉Exitcausticstrengthiscontrolledbycontrollingfeedcausticstrength出口堿濃度是通過進口堿濃度來控制的TheAnodeorAnolyteCompartmentChemistry

陽極及其電解液室化學反應TheAnodeorAnolyteCompartmentReactionse-Cl2Cl--ClNa+HO2Na+HO2Anode陽極Cathode陰極TheAnode陽極Electricallyconductivetitaniummetalbase金屬鈦是導電基Electro-catalyticcoating電解反應涂層: MainlyRuO2&TiO2mixture主要是RuO2和二氧化鈦的混合物 Hastocatalysethechlorinereaction(havelowoverpotential)氯的催化加快反應（低超電勢） MinimiseOxygenproduction降低氧氣產(chǎn)生 Longlife&durableagainstfeedimpuritiesMn,F,heavymetals壽命長，可以阻止雜質(zhì)，錳，氟及重金屬的滲入PrincipalReaction主要反應2Cl-(aqueous)在水中→

Cl2(gas)氣體+2e

SideReactions副反應Cl2(gas)氣體→

Cl2(dissolved)溶解Cl2(dissolved)溶解

+H2O→H+

+Cl-

+HOClHOCl→H++OCl-TheAnodeorAnolyteCompartmentReactionsBrineFeedBrineExitO2inCl2H2NaClO3(recycledchlorate)（循環(huán)氯酸鹽）HOCl&NaClO3OH-BackMigratione-TheFormationofChlorate氯酸鹽的形成Formedbyachemicalorelectrochemicalroute.通過化學或電氣化學的方式形成Bothroutesinvolvedissolvedchlorineandhypochlorite兩種途徑都涉及到氯和次氯酸鹽的溶解OverallChemistry總化學反應Cl-

+3H2O→

ClO-3+6H++6e-FormationofOxygen氧氣的形成2H2O→

O2(gas)

+4H++4e-TheCathodeorCatholyteCompartmentChemistry陰極及其電解液室化學反應TheCathodeorCatholyteCompartmentReactionsNa+HO2CausticFeed28-32%w/wNaOHCausticExit

30-33%w/wNaOHH2HO2H+OH-H+e-TheCathode陽極Electricallyconductivenickelmetalbase導電鎳金屬Electro-catalyticpreciousmetalcoating Hastocatalysethewaterreduction(havelowoverpotential) Bestabletoreversecurrents(shorting)andhypoattack.PrincipalReaction基本反應2H2O+2e-

→H2(gas)+2OH-

Hydroxideionscombinewithsodiumionscomingthroughthemembranetoformcausticsoda氫氧離子與通過離子膜的鈉離子結合，形成酸性鈉LookingattheAnodeReactions

請看陽極反應AnodeReactions陽極反應SideReactions副反應Cl2(gas)→Cl2(dissolved)Cl2(dissolved)+H2O→H+

+Cl-

+HOClHOCl→H++OCl-TheproductionofHypochlorousAcidanditsdissociationintoprotonsisthesourceoftheacidityintheanolytecompartment.次氯酸的產(chǎn)生及其進一步分離成質(zhì)子根源在于陽極電解液室呈酸性ThehypochloriteionproducedondissociationcombineswithNa+intheanolytetoproducesodiumhypochlorite.分離產(chǎn)生的次氯酸鹽離子和陽極電解液中的鈉離子結合，產(chǎn)生次氯酸鈉ThebackmigrationofhydroxylsfromthecatholytecompartmentthroughthemembraneisthepHadjusterandinfluencestheexitbrinepH.透過離子膜從陰極室反遷移過來的氫氧根可通過PH來調(diào)節(jié)，否則會影響出口淡鹽水PHWenotedpreviously:我們先前的例子BackMigrationofCausticintotheAnodeAllmembranesallowbackmigrationofcaustic,theCationselectivityisnot100%effectiveinanymembrane.所有膜都允許燒堿往回遷移，任何膜的陽離子選擇性不是100％有效。Thereisalwaysasmallbackmigrationofcausticacrossthemembrane,infactthepHprofileacrossamembranealwaysshowsahighpHrightuptotheboundarywiththebrine.總有一部分燒堿會透過膜往回遷移，事實上在膜與鹽水的交界，鹽水的PH比出口鹽水顯示的PH要高Brineimpurities,suchasSulphates,andIodates,Silicates,Barium,Calcium,Aluminiumallcombinetoreducetheeffectivenessofthecarboxyliclayersabilitytorejecthydroxylionsanditisnormalthatduringthemembranelifethebackmigrationofcausticincreasesovertime.鹽水雜質(zhì)，如硫酸鹽，碘，硅酸鹽，鋇，鈣，鋁所有這些都將造成離子膜羧基酸降低氫氧離子返遷移的能力，這是正常的，在離子膜運行一段時間后，燒堿的遷移量會出現(xiàn)上升Howeverthisrateofbackmigrationisfargreaterifthemembraneispuncturedorcracked.Incomparisontobackmigrationafloodofcausticgoesthroughthemembrane.然而膜穿孔或破裂會反遷移量是非常大的。相比較，大量的燒堿會通過膜涌出來。Polarisation&Energisation

極化和通電WhenisHypochlorousAcidProduced?次氯酸鹽是什么時候產(chǎn)生的？Polarisation&EnergisationHypochlorousAcidisonlyproducedwhenchlorineisproduced.氯氣產(chǎn)生才會產(chǎn)生氯酸鹽Cl2(gas)氣體→Cl2(dissolved)溶解Cl2(dissolved)+H2O→H+

+Cl-

+HOClAndchlorineisonlyproducedwhenthecellvoltageisgreaterthan2.4Volts僅當電槽電壓高于2.4伏時，才能產(chǎn)生氯氣Remember:atpolarisation,themodulevoltageisonlyapprox1.6voltswithagoodmembrane.(Ifthemembraneispinholedthevoltagewillbelowerthanthisandifthereisanelectricalshortthevoltagewillbealmostzero).記住：極化作用下一張好膜單元的電壓只有1.6伏特。（如果膜有針孔，電壓會有所下降，如果有短路，電壓將會降至零）Atpolarisationtheanodereactionistoproduceoxygenbywaterhydrolysis陽極是由水電解生成氧氣2H2O→

O2(gas)

+4H++4e-AndtheCathodereactionistoproducehydrogenbywaterhydrolysis.陰極反應是由水電解成氫氣2H2O+2e-→H2(gas)+2OH-Chlorineisonlyproducedwhenthecellvoltageisgreaterthan2.4Volts氯氣只在電壓超過2.4伏特的時候產(chǎn)生Polarisation&Energisation極片&通電AtpolarisationwithnohypochlorousacidproducedexitbrinepHshouldmatchthefeedbrinepHwithin1pHunit.在極化作用下如果沒有次氯鹽，出口鹽水PH將會比進口鹽水高1個PHIftherearesignificantmembraneholeswithalargedegreeofcausticleakagetheexitbrinepHwillrise.如果膜有較多的孔，就會有大量的堿泄漏，出口鹽水PH值會上升。ForexampleelectrolyserGonpolarisationon14thOctshowedfeedbrinepHatapproxpH5withexitbrineatapproxpH10.例如在10月14日G槽進槽鹽水PH大約是5，出槽時大約是10Thelocationoftheleakscannotbedeterminedatthisstage:therecouldbeonemajorleakortherecouldbemanysmallerleakscontributingtotheoverallexitbrinepH.在這一階段泄漏的位置無法確定：沒有大量的泄漏或者有很多小的泄漏使得PH上升Thenextstepistoassessweretheleaksarebyenergisingthemainrectifierandobservingtheindividualvoltages.下一步評估就是通過整流器給電，觀察單元電壓Whenthemainrectifierisenergisedandthemodulevoltagerisestogreaterthan2.4Vthemodulewillbeproducingchlorineandhypochlorousacid.當整流器通電，槽電壓上升超過2.4V時就會產(chǎn)生氯氣和和次氯酸Ifthereiscausticleakingacrossthemembranethehydroxylionswillneutralisedthehypochlorousacidandthevoltageremainslow.Thatiswhywecanseeaspreadofvoltagesonstartup.如果有燒堿滲透過膜，羥基將要中和次氯酸，電壓維持很低。這就是我們看見電壓開始上升的原因ExampleofElectrolyserAStartUp29thMay2009MainrectifierenergisedA12A01A02WecanseeherethatmodulesA01,A02andA12havelowervoltagesthantherestofthegroup.Indicatingcausticleakageacrossthemembrane.(A12isespeciallylow).我們可以看到這里的模塊A01，A02和A12也比其他電壓低。表示膜泄漏。（A12尤其低）。GuideforAssessingModulesbytheirVoltagesonstartup通過電壓上升評估模塊指南Inthenormalstartupwiththeelectrolysergasesonsidestream,increasetheloadasnormalto3kAandthenwait45minstoassessthemodulesaccordingtotheguidebelow.After30minscollectthechlorinesampleandtheexitbrinepHsampleasnormal.電解開始運轉(zhuǎn)時支管產(chǎn)生氣體，增加負荷至3KA，等45分根據(jù)下面的指導來評估單元槽，30分鐘后進行氯氣樣本的采集和淡鹽水樣本的PH值1、Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)inlessthan20minutesthemodulecanberunindefinitely.在負荷為3kA(1.04kA/m2)，20分鐘內(nèi)，如果膜電壓超過2.3V，這個電壓會無限制的上升。2、Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)in20–30minutesthemoduleshouldbereplacedwithin1month.在負荷為3kA(1.04kA/m2)，20~30分鐘內(nèi)，如果膜電壓超過2.3V，這個模塊需要在一個月內(nèi)更換。3.Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)ingreaterthan30minutesthemoduleshouldbereplacedwithin1week.在負荷為3kA(1.04kA/m2)，超過30分鐘，如果膜電壓超過2.3V，這個模塊需要在一個星期內(nèi)更換。4.Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)ingreaterthan45minutestheelectrolysershouldbeshut-downanthemodulereplaced.在負荷為3kA(1.04kA/m2)，超過45分鐘，如果膜電壓包括或超過2.3V，應立即切斷電源直至模塊更換5、Ifallthemodulevoltagesrisewithin20minutescontinuetoputthegasstreamsontothemainheader.如果所有的電壓在20分鐘內(nèi)持續(xù)上升就將氣體切換到總管6、Ifanyofthemodulesfailthe45minuteguidethentheelectrolysercanbeshutdownmoreeasilythanifitwereonthemainheaders.如果45分鐘內(nèi)繼續(xù)衰弱接著就要指導電解關閉，因為這樣要比在氣相總管停車容易得多OnlinemonitoringofCausticLeakage在線監(jiān)測燒堿泄漏OnLineMonitoringThemostactivewaytomonitorthecausticleakageistolookattheoxygenandchlorineconcentrationsineachofthemodules.大多數(shù)的監(jiān)測燒堿泄漏方法都是觀察每片單元的氧氣和氯氣的濃度BelowisanexampleoftheconcentrationsfromElectrolyserAfromearly2009.以下是2009年早期的一個例子Comparingthefirst30moduleswiththestartupvoltagesearlierwecanseeherethatmoduleA12hasalowchlorineconcentration.A01alsoshowsalowerconcentration.ThevoltagedatabacksthisupshowingA12andA01havelowvoltagesindicatingcausticmigrationacrossthemembrane.(A02eventhoughithaslowvoltageshasgoodchlorine).與第30單元初始電壓比，我們可以看到A12單元有一個氯濃度低點。A01也顯示了氯氣濃度低點電壓數(shù)據(jù)備份說明A12和A01的低電壓表明在離子膜上有堿的遷移（A02即使電壓低，但氯氣純度好）。OnLineMonitoring在線監(jiān)控Rememberwhenthecausticleaksacrossthemembraneintotheanolytecompartmentitproducesoxygenviathehydrolysisofwater.記住，當燒堿通過膜泄漏至陽極，會水解產(chǎn)生氧氣。AnincreaseinOxygeninchlorineisagoodindicatorofcausticmigration.氯中含氧量上升是燒堿遷移的一個很好的指標IntermsofCurrentEfficiency(CE)wewouldnotrunanelectrolyserwithaCElessthan92%andintermsofOxygenlevelsthatisapproximately4%vol/volOxygen.在當前的電流效率下，我們不應該高負荷運轉(zhuǎn)使得電流效率低于92%，維持含氧量低于4%Otherbyproductconcentrationschangealso:其它產(chǎn)品濃度也發(fā)生改變HypochloriteionandChlorateionconcentrationsrisealsoalongwithexitbrinepH.次氯酸根和氯酸根含量會隨著出口鹽水PH上升而上升Ifthecausticleakisonlyin1or2modulesthesecomponentsarealwaysdiluteddownbythegoodexitbrinefromtheothergoodmodulessoittakesalotofcausticleakagetomakeachangeintheseparameters.如果燒堿泄漏的單元只有1、2個，而其它單元出口鹽水中這些成分含量一直很低，因此難以通過這些參數(shù)的改變來判別離子膜堿泄漏Astheoxygenandchlorineanalysiscanbedoneonanindividualmoduletheyarefarmoresensitivetochangeinthecausticmigrationacrossthemembraneandshouldbeusedinpreference.單槽做氧氣和氯氣純度時，在燒堿遷移的情況下，很容易通過數(shù)值改變來判斷SpecialCase:NewMembranes

特例：新膜NewMembranes新膜Newmembraneshaveverylittlebackmigrationofhydroxylions.Rememberweholdnewmembranesat3kA/m2loadfor48hourstoconditionthemembranetoallowallthechannelsinthemembranetoopenupandallowNa+migrationtohappenevenlyacrossthefullmembranesurface.新膜堿反遷移量很小。牢記膜的條件要求保持新膜在3kA/m2內(nèi)運行48小時，使所有膜細胞通道打開，讓鈉離子遷移完整均勻發(fā)生在膜表面。BecausethereisverylittlecausticbackmigrationtheexitbrinepHissetmainlybytheproductionofhypochlorousacidanditsprotonsandduringthefirst48hoursofmembranelifetheexitbrinepHisveryacidic.因為反遷移的燒堿量很少，出口鹽水PH產(chǎn)生的氯酸鹽及氯酸可以忽略不計，在開始的48小時內(nèi)膜