電解基礎(chǔ)知識

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(xué)Basics基本原理Electrolysis,inthiscase,isthesplittingofachemicalcompoundusinganelectriccurrent.電解，定義是這樣的，通過導(dǎo)入電流來對化合物進(jìn)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(yùn)行，產(chǎn)出優(yōu)質(zhì)產(chǎn)品，嚴(yán)格控制生產(chǎn)過程中所有因素和進(jìn)液時(shí)的雜質(zhì)量顯得很重要。Wemustalsotakeextremecarewhenhandlingmembranesinthatanyfaultsintroducedinthemembranewillallowmorecausticbackmigrationwhenitisinoperation.在操作離子膜時(shí)，我們同樣也必須極度小心。因?yàn)橐稽c(diǎn)小的缺陷操作都將會導(dǎo)致運(yùn)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(qiáng)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(yīng)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(jìn)口堿濃度來控制的TheAnodeorAnolyteCompartmentChemistry

陽極及其電解液室化學(xué)反應(yīng)TheAnodeorAnolyteCompartmentReactionse-Cl2Cl--ClNa+HO2Na+HO2Anode陽極Cathode陰極TheAnode陽極Electricallyconductivetitaniummetalbase金屬鈦是導(dǎo)電基Electro-catalyticcoating電解反應(yīng)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(yīng)（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(yīng)2Cl-(aqueous)在水中→

Cl2(gas)氣體+2e

SideReactions副反應(yīng)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(xué)或電氣化學(xué)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(xué)反應(yīng)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(xué)反應(yīng)TheCathodeorCatholyteCompartmentReactionsNa+HO2CausticFeed28-32%w/wNaOHCausticExit

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

→H2(gas)+2OH-

Hydroxideionscombinewithsodiumionscomingthroughthemembranetoformcausticsoda氫氧離子與通過離子膜的鈉離子結(jié)合，形成酸性鈉LookingattheAnodeReactions

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

+Cl-

+HOClHOCl→H++OCl-TheproductionofHypochlorousAcidanditsdissociationintoprotonsisthesourceoftheacidityintheanolytecompartment.次氯酸的產(chǎn)生及其進(jìn)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(jié)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(shí)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(yùn)行一段時(shí)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(shí)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(dāng)電槽電壓高于2.4伏時(shí)，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(yīng)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(shí)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(jìn)口鹽水高1個(gè)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(jìn)槽鹽水PH大約是5，出槽時(shí)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(dāng)整流器通電，槽電壓上升超過2.4V時(shí)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(yùn)轉(zhuǎn)時(shí)支管產(chǎn)生氣體，增加負(fù)荷至3KA，等45分根據(jù)下面的指導(dǎo)來評估單元槽，30分鐘后進(jìn)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(fù)荷為3kA(1.04kA/m2)，20分鐘內(nèi)，如果膜電壓超過2.3V，這個(gè)電壓會無限制的上升。2、Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)in20–30minutesthemoduleshouldbereplacedwithin1month.在負(fù)荷為3kA(1.04kA/m2)，20~30分鐘內(nèi)，如果膜電壓超過2.3V，這個(gè)模塊需要在一個(gè)月內(nèi)更換。3.Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)ingreaterthan30minutesthemoduleshouldbereplacedwithin1week.在負(fù)荷為3kA(1.04kA/m2)，超過30分鐘，如果膜電壓超過2.3V，這個(gè)模塊需要在一個(gè)星期內(nèi)更換。4.Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)ingreaterthan45minutestheelectrolysershouldbeshut-downanthemodulereplaced.在負(fù)荷為3kA(1.04kA/m2)，超過45分鐘，如果膜電壓包括或超過2.3V，應(yīng)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(dǎo)電解關(guān)閉，因?yàn)檫@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(gè)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(gè)氯濃度低點(diǎn)。A01也顯示了氯氣濃度低點(diǎn)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(dāng)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(gè)很好的指標(biāo)IntermsofCurrentEfficiency(CE)wewouldnotrunanelectrolyserwithaCElessthan92%andintermsofOxygenlevelsthatisapproximately4%vol/volOxygen.在當(dāng)前的電流效率下，我們不應(yīng)該高負(fù)荷運(yùn)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(gè)，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(shí)，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(yùn)行48小時(shí)，使所有膜細(xì)胞通道打開，讓鈉離子遷移完整均勻發(fā)生在膜表面。BecausethereisverylittlecausticbackmigrationtheexitbrinepHissetmainlybytheproductionofhypochlorousacidanditsprotonsandduringthefirst48hoursofmembranelifetheexitbrinepHisveryacidic.因?yàn)榉催w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(jì)，在開始的48小時(shí)內(nèi)膜