电解基础知识

CausticinBrine,

EffectonOperation&Monitoring

JSG,ZhangjiagangSite,PRChina

中华人民共和国张家港BrianBrandreth14th-20thOctober20092009年10月14日至29日CellChemistry

电池化学Basics基本原理Electrolysis,inthiscase,isthesplittingofachemicalcompoundusinganelectriccurrent.电解，定义是这样的，通过导入电流来对化合物进行快速分解IntheChlor-alkaliprocesssodiumchloridesolution(brine)isseparatedintochlorinegas,sodiumhydroxidesolution(causticsoda)andhydrogengas.在氯碱综合过程中，氯化钠溶液分解成氯气，氢氧化钠溶液（苛性钠）和氢气Toensuretheprocessoperatesefficientlygivinghighqualityproducts,itisessentialthatwekeepverytightcontrolofalloperatingparametersandimpuritiesinthefeedliquors.为确保高效操作运行，产出优质产品，严格控制生产过程中所有因素和进液时的杂质量显得很重要。Wemustalsotakeextremecarewhenhandlingmembranesinthatanyfaultsintroducedinthemembranewillallowmorecausticbackmigrationwhenitisinoperation.在操作离子膜时，我们同样也必须极度小心。因为一点小的缺陷操作都将会导致运行期间离子膜有更多苛性钠的反迁移BasicPrinciples基本原理Na+Cl-OH-FeedsandProductsAnode阳极Cathode阴极Membrane隔离物HydrogenGas氢气ChlorineGas氯气StrongCaustic强碱WeakCaustic弱碱WeakBrine稀盐水StrongBrine浓盐水Strongbrineisfedtoanodecompartment浓盐水注入阳极室Chlorideionselectrolysedonanodetoproducechlorinegas处于阳极的氯离子电解产生氯气Sodiumionsandwaterfromthebrinepassthroughthemembranedrivenbytheelectricfield.盐水中的钠离子和水在电场作用下透过离子膜Unreactedchlorideionsleaveasweakordepletedbrine未反应的氯离子随稀盐水或废盐水离开Weakcausticfedintocathodecompartments弱碱注入阴极室Waterelectrolysedatthecathodetoformhydrogengasandhydroxylions处于阴极的水电解形成氢气和氢氧根离子Sodiumionsandhydroxylionsformthecausticproduct钠离子和氢氧根离子生成苛性钠Exitcausticstrengthiscontrolledbycontrollingfeedcausticstrength出口碱浓度是通过进口碱浓度来控制的TheAnodeorAnolyteCompartmentChemistry

阳极及其电解液室化学反应TheAnodeorAnolyteCompartmentReactionse-Cl2Cl--ClNa+HO2Na+HO2Anode阳极Cathode阴极TheAnode阳极Electricallyconductivetitaniummetalbase金属钛是导电基Electro-catalyticcoating电解反应涂层: MainlyRuO2&TiO2mixture主要是RuO2和二氧化钛的混合物 Hastocatalysethechlorinereaction(havelowoverpotential)氯的催化加快反应（低超电势） MinimiseOxygenproduction降低氧气产生 Longlife&durableagainstfeedimpuritiesMn,F,heavymetals寿命长，可以阻止杂质，锰，氟及重金属的渗入PrincipalReaction主要反应2Cl-(aqueous)在水中→

Cl2(gas)气体+2e

SideReactions副反应Cl2(gas)气体→

Cl2(dissolved)溶解Cl2(dissolved)溶解

+H2O→H+

+Cl-

+HOClHOCl→H++OCl-TheAnodeorAnolyteCompartmentReactionsBrineFeedBrineExitO2inCl2H2NaClO3(recycledchlorate)（循环氯酸盐）HOCl&NaClO3OH-BackMigratione-TheFormationofChlorate氯酸盐的形成Formedbyachemicalorelectrochemicalroute.通过化学或电气化学的方式形成Bothroutesinvolvedissolvedchlorineandhypochlorite两种途径都涉及到氯和次氯酸盐的溶解OverallChemistry总化学反应Cl-

+3H2O→

ClO-3+6H++6e-FormationofOxygen氧气的形成2H2O→

O2(gas)

+4H++4e-TheCathodeorCatholyteCompartmentChemistry阴极及其电解液室化学反应TheCathodeorCatholyteCompartmentReactionsNa+HO2CausticFeed28-32%w/wNaOHCausticExit

30-33%w/wNaOHH2HO2H+OH-H+e-TheCathode阳极Electricallyconductivenickelmetalbase导电镍金属Electro-catalyticpreciousmetalcoating Hastocatalysethewaterreduction(havelowoverpotential) Bestabletoreversecurrents(shorting)andhypoattack.PrincipalReaction基本反应2H2O+2e-

→H2(gas)+2OH-

Hydroxideionscombinewithsodiumionscomingthroughthemembranetoformcausticsoda氢氧离子与通过离子膜的钠离子结合，形成酸性钠LookingattheAnodeReactions

请看阳极反应AnodeReactions阳极反应SideReactions副反应Cl2(gas)→Cl2(dissolved)Cl2(dissolved)+H2O→H+

+Cl-

+HOClHOCl→H++OCl-TheproductionofHypochlorousAcidanditsdissociationintoprotonsisthesourceoftheacidityintheanolytecompartment.次氯酸的产生及其进一步分离成质子根源在于阳极电解液室呈酸性ThehypochloriteionproducedondissociationcombineswithNa+intheanolytetoproducesodiumhypochlorite.分离产生的次氯酸盐离子和阳极电解液中的钠离子结合，产生次氯酸钠ThebackmigrationofhydroxylsfromthecatholytecompartmentthroughthemembraneisthepHadjusterandinfluencestheexitbrinepH.透过离子膜从阴极室反迁移过来的氢氧根可通过PH来调节，否则会影响出口淡盐水PHWenotedpreviously:我们先前的例子BackMigrationofCausticintotheAnodeAllmembranesallowbackmigrationofcaustic,theCationselectivityisnot100%effectiveinanymembrane.所有膜都允许烧碱往回迁移，任何膜的阳离子选择性不是100％有效。Thereisalwaysasmallbackmigrationofcausticacrossthemembrane,infactthepHprofileacrossamembranealwaysshowsahighpHrightuptotheboundarywiththebrine.总有一部分烧碱会透过膜往回迁移，事实上在膜与盐水的交界，盐水的PH比出口盐水显示的PH要高Brineimpurities,suchasSulphates,andIodates,Silicates,Barium,Calcium,Aluminiumallcombinetoreducetheeffectivenessofthecarboxyliclayersabilitytorejecthydroxylionsanditisnormalthatduringthemembranelifethebackmigrationofcausticincreasesovertime.盐水杂质，如硫酸盐，碘，硅酸盐，钡，钙，铝所有这些都将造成离子膜羧基酸降低氢氧离子返迁移的能力，这是正常的，在离子膜运行一段时间后，烧碱的迁移量会出现上升Howeverthisrateofbackmigrationisfargreaterifthemembraneispuncturedorcracked.Incomparisontobackmigrationafloodofcausticgoesthroughthemembrane.然而膜穿孔或破裂会反迁移量是非常大的。相比较，大量的烧碱会通过膜涌出来。Polarisation&Energisation

极化和通电WhenisHypochlorousAcidProduced?次氯酸盐是什么时候产生的？Polarisation&EnergisationHypochlorousAcidisonlyproducedwhenchlorineisproduced.氯气产生才会产生氯酸盐Cl2(gas)气体→Cl2(dissolved)溶解Cl2(dissolved)+H2O→H+

+Cl-

+HOClAndchlorineisonlyproducedwhenthecellvoltageisgreaterthan2.4Volts仅当电槽电压高于2.4伏时，才能产生氯气Remember:atpolarisation,themodulevoltageisonlyapprox1.6voltswithagoodmembrane.(Ifthemembraneispinholedthevoltagewillbelowerthanthisandifthereisanelectricalshortthevoltagewillbealmostzero).记住：极化作用下一张好膜单元的电压只有1.6伏特。（如果膜有针孔，电压会有所下降，如果有短路，电压将会降至零）Atpolarisationtheanodereactionistoproduceoxygenbywaterhydrolysis阳极是由水电解生成氧气2H2O→

O2(gas)

+4H++4e-AndtheCathodereactionistoproducehydrogenbywaterhydrolysis.阴极反应是由水电解成氢气2H2O+2e-→H2(gas)+2OH-Chlorineisonlyproducedwhenthecellvoltageisgreaterthan2.4Volts氯气只在电压超过2.4伏特的时候产生Polarisation&Energisation极片&通电AtpolarisationwithnohypochlorousacidproducedexitbrinepHshouldmatchthefeedbrinepHwithin1pHunit.在极化作用下如果没有次氯盐，出口盐水PH将会比进口盐水高1个PHIftherearesignificantmembraneholeswithalargedegreeofcausticleakagetheexitbrinepHwillrise.如果膜有较多的孔，就会有大量的碱泄漏，出口盐水PH值会上升。ForexampleelectrolyserGonpolarisationon14thOctshowedfeedbrinepHatapproxpH5withexitbrineatapproxpH10.例如在10月14日G槽进槽盐水PH大约是5，出槽时大约是10Thelocationoftheleakscannotbedeterminedatthisstage:therecouldbeonemajorleakortherecouldbemanysmallerleakscontributingtotheoverallexitbrinepH.在这一阶段泄漏的位置无法确定：没有大量的泄漏或者有很多小的泄漏使得PH上升Thenextstepistoassessweretheleaksarebyenergisingthemainrectifierandobservingtheindividualvoltages.下一步评估就是通过整流器给电，观察单元电压Whenthemainrectifierisenergisedandthemodulevoltagerisestogreaterthan2.4Vthemodulewillbeproducingchlorineandhypochlorousacid.当整流器通电，槽电压上升超过2.4V时就会产生氯气和和次氯酸Ifthereiscausticleakingacrossthemembranethehydroxylionswillneutralisedthehypochlorousacidandthevoltageremainslow.Thatiswhywecanseeaspreadofvoltagesonstartup.如果有烧碱渗透过膜，羟基将要中和次氯酸，电压维持很低。这就是我们看见电压开始上升的原因ExampleofElectrolyserAStartUp29thMay2009MainrectifierenergisedA12A01A02WecanseeherethatmodulesA01,A02andA12havelowervoltagesthantherestofthegroup.Indicatingcausticleakageacrossthemembrane.(A12isespeciallylow).我们可以看到这里的模块A01，A02和A12也比其他电压低。表示膜泄漏。（A12尤其低）。GuideforAssessingModulesbytheirVoltagesonstartup通过电压上升评估模块指南Inthenormalstartupwiththeelectrolysergasesonsidestream,increasetheloadasnormalto3kAandthenwait45minstoassessthemodulesaccordingtotheguidebelow.After30minscollectthechlorinesampleandtheexitbrinepHsampleasnormal.电解开始运转时支管产生气体，增加负荷至3KA，等45分根据下面的指导来评估单元槽，30分钟后进行氯气样本的采集和淡盐水样本的PH值1、Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)inlessthan20minutesthemodulecanberunindefinitely.在负荷为3kA(1.04kA/m2)，20分钟内，如果膜电压超过2.3V，这个电压会无限制的上升。2、Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)in20–30minutesthemoduleshouldbereplacedwithin1month.在负荷为3kA(1.04kA/m2)，20~30分钟内，如果膜电压超过2.3V，这个模块需要在一个月内更换。3.Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)ingreaterthan30minutesthemoduleshouldbereplacedwithin1week.在负荷为3kA(1.04kA/m2)，超过30分钟，如果膜电压超过2.3V，这个模块需要在一个星期内更换。4.Ifthemodulevoltagerisestogreaterthan2.3Vat3kA(1.04kA/m2)ingreaterthan45minutestheelectrolysershouldbeshut-downanthemodulereplaced.在负荷为3kA(1.04kA/m2)，超过45分钟，如果膜电压包括或超过2.3V，应立即切断电源直至模块更换5、Ifallthemodulevoltagesrisewithin20minutescontinuetoputthegasstreamsontothemainheader.如果所有的电压在20分钟内持续上升就将气体切换到总管6、Ifanyofthemodulesfailthe45minuteguidethentheelectrolysercanbeshutdownmoreeasilythanifitwereonthemainheaders.如果45分钟内继续衰弱接着就要指导电解关闭，因为这样要比在气相总管停车容易得多OnlinemonitoringofCausticLeakage在线监测烧碱泄漏OnLineMonitoringThemostactivewaytomonitorthecausticleakageistolookattheoxygenandchlorineconcentrationsineachofthemodules.大多数的监测烧碱泄漏方法都是观察每片单元的氧气和氯气的浓度BelowisanexampleoftheconcentrationsfromElectrolyserAfromearly2009.以下是2009年早期的一个例子Comparingthefirst30moduleswiththestartupvoltagesearlierwecanseeherethatmoduleA12hasalowchlorineconcentration.A01alsoshowsalowerconcentration.ThevoltagedatabacksthisupshowingA12andA01havelowvoltagesindicatingcausticmigrationacrossthemembrane.(A02eventhoughithaslowvoltageshasgoodchlorine).与第30单元初始电压比，我们可以看到A12单元有一个氯浓度低点。A01也显示了氯气浓度低点电压数据备份说明A12和A01的低电压表明在离子膜上有碱的迁移（A02即使电压低，但氯气纯度好）。OnLineMonitoring在线监控Rememberwhenthecausticleaksacrossthemembraneintotheanolytecompartmentitproducesoxygenviathehydrolysisofwater.记住，当烧碱通过膜泄漏至阳极，会水解产生氧气。AnincreaseinOxygeninchlorineisagoodindicatorofcausticmigration.氯中含氧量上升是烧碱迁移的一个很好的指标IntermsofCurrentEfficiency(CE)wewouldnotrunanelectrolyserwithaCElessthan92%andintermsofOxygenlevelsthatisapproximately4%vol/volOxygen.在当前的电流效率下，我们不应该高负荷运转使得电流效率低于92%，维持含氧量低于4%Otherbyproductconcentrationschangealso:其它产品浓度也发生改变HypochloriteionandChlorateionconcentrationsrisealsoalongwithexitbrinepH.次氯酸根和氯酸根含量会随着出口盐水PH上升而上升Ifthecausticleakisonlyin1or2modulesthesecomponentsarealwaysdiluteddownbythegoodexitbrinefromtheothergoodmodulessoittakesalotofcausticleakagetomakeachangeintheseparameters.如果烧碱泄漏的单元只有1、2个，而其它单元出口盐水中这些成分含量一直很低，因此难以通过这些参数的改变来判别离子膜碱泄漏Astheoxygenandchlorineanalysiscanbedoneonanindividualmoduletheyarefarmoresensitivetochangeinthecausticmigrationacrossthemembraneandshouldbeusedinpreference.单槽做氧气和氯气纯度时，在烧碱迁移的情况下，很容易通过数值改变来判断SpecialCase:NewMembranes

特例：新膜NewMembranes新膜Newmembraneshaveverylittlebackmigrationofhydroxylions.Rememberweholdnewmembranesat3kA/m2loadfor48hourstoconditionthemembranetoallowallthechannelsinthemembranetoopenupandallowNa+migrationtohappenevenlyacrossthefullmembranesurface.新膜碱反迁移量很小。牢记膜的条件要求保持新膜在3kA/m2内运行48小时，使所有膜细胞通道打开，让钠离子迁移完整均匀发生在膜表面。BecausethereisverylittlecausticbackmigrationtheexitbrinepHissetmainlybytheproductionofhypochlorousacidanditsprotonsandduringthefirst48hoursofmembranelifetheexitbrinepHisveryacidic.因为反迁移的烧碱量很少，出口盐水PH产生的氯酸盐及氯酸可以忽略不计，在开始的48小时内膜