化工专业英语-unit 6.ppt

Unit6Chlor AlkaliandRelatedProcesses ByZhaoYa qiDepartmentofChemicalEngineering Contents 1 Lime BasedProducts2 Soda Ash3 ElectrolyticProcessesforChlorine CausticSoda4 TheUsesofChlorineandSodiumHydroxide Guidingquestions Listsomemajorproductsinthechlor alkaliprocesses DescribebrieflytheSolvayammoniasodaprocess Outlinethemainstepsinmarkingsulfuricacid Pointoutthemajorusesofsomemainproductsdescribedinthetext Prelude Historicallythebulkchemicalindustry 大化工 wasbuiltonchlor alkaliandrelatedprocesses Thesegmentisnormallytakentoincludetheproductionofchlorinegas causticsoda sodiumhydroxide soda ash derivativesofsodiumcarbonateinvariousforms and forconvenience lime basedproducts Soda ashandsodiumhydroxidehavecompetedwitheachotherasthemajorsourceofalkalieversinceviableprocesseswerediscoveredforboth Thepeculiareconomicsofelectrolyticprocessesmeanthatyouhavetomakechlorineandcausticsodatogetherinafixedratiowhatevertherelativedemandforthetwototallydifferenttypesofproduct andthiscausesswingsinthepriceofcausticsodawhichcanrendersoda ashmoreorlessfavorableasanalkali Bothchlorine causticsodaandsoda ashproductionaredependentoncheapreadilyavailablesuppliesofrawmaterials Chlorine causticsodarequiresareadysupplyofcheapbrineandelectricity soda ashrequiresbrine limestoneandlotsofenergy Soda ashplantsareonlyprofitableiftheirrawmaterialsdonothavetobetransportedfar Theavailabilityofsuchsuppliesisamajorfactorinthelocationofmanyofthechemicalindustry sgreatcomplexes Oneofthekeyrawmaterialsislime Limestoneconsistsmostlyofcalciumcarbonate CaCO3 laiddownovergeologicaltimebyvariousmarineorganisms High qualitylimestonesareoftengoodenoughtobeuseddirectlyascalciumcarbonateinfurtherreactions LimestoneisusuallyminedinvastoLine BasedProductspen castquarries manyofwhichwillalsocarryoutsomeprocessingofthematerials Thetwokeyrawproductsderivedfromlimestonearequicklime CaO andslakedlime Ca OH 2 Quicklimeismanufacturedbythethermaldecomposition 1200 1500 oflimestoneaccordingtotheequation CaCO3 CaO CO2 Lime BasedProducts Typicallylimestoneiscrushedandfedintothehigherendofaslopingrotatingkilnwherethedecompositiontakesplaceandquicklimeisrecoveredfromtheend Mostfrequently however thequicklimeisnotisolatedforfurtherreactions rather othercompoundsarefedinwiththelimetogivefinalproductsatthelowerendofthekiln Forexample alumina ironoreandsandcanbefedintogivePortlandcement Soda ashmanufactureoftenaddscoketothelimestonewhichburnstogiveextracarbondioxideneededforsoda ashmanufacture Slakedlimewhichismoreconvenienttohandlethanquicklime ismanufacturedbyreactingquicklimewithwater About40 oftheoutputofthelimeindustrygoesintosteel making whereitisusedtoreactwiththerefractory 难溶的 silicapresentinironoretogiveafluidslagwhichfloatstothesurfaceandiseasilyseparatedfromtheliquidmetal Smaller butstillsignificant amountsareusedinchemicalmanufacture pollutioncontrolandwatertreatment Themostimportantchemicalderivedfromlimeissoda ash 2 Soda Ash TheSodaprocess Theprocess whichwasperfectedbyErnestSolvayin1865 isbasedontheprecipitationofNaHCO3whenanammoniatedsolutionofsaltiscarbonatedwithCO2fromacoke firedlimekiln TheNaHCO3isfiltered dried andcalcinedtoNa2CO3 Thefilteredammoniumchlorideprocessliquorismadealkalinewithslakedlimeandtheammoniaisdistilledoutforrecycletothefrontendoftheprocess Theresultantcalciumchlorideisawasteorby productstream ForasimplebasicproducttheSolvayprocessappearsexceedinglycomplicated Thebasicprincipleofthereactionistotakesalt NaCl andcalciumcarbonate CaCO3 asinputsandtoproducecalciumchlorideandsodiumcarbonateasoutputs However thereactionsoccurringbetweeninputandoutputarenotremotelyobviousandinvolvetheuseofammoniaandcalciumhydroxideasintermediatecompounds Theessentialprincipleisthat bycarefullycontrollingtheconcentrationofthecomponents especiallyammoniaandsalt sodiumbicarbonatecanbeprecipitatedfromsolutionscontainingsalt carbondioxideandammonia Thekeytomakingtheprocessworkiscontrollingthestrengthofthesolutionsandtheratesofcrystallization Theessentialstepsoftheprocessareasfollows Ammoniaisabsorbedinanammoniaabsorberintobrinewhichhaspreviouslybeenpurifiedtoreducetheamountofcalciumandmagnesiumions whichtendtoprecipitateduringtheprocessinallthewrongplaces blockingpipe work Thesolution nominallycontainingsodiumchlorideandammoniumhydroxide isthenpasseddownatowerwhereitabsorbscarbondioxide passingupthetower toformammoniumcarbonateatfirstandlaterammoniumbicarbonate Bythenextstageoftheplantchlorideandammoniumbicarbonatehavemetathesistosodiumbicarbonate whichprecipitates andammoniumchloride Filtrationseparatesthesolidbicarbonatefromtheremainingsolution Thebicarbonateispassedtoarotarydryerwhereitloseswaterandcarbondioxidetogiveafluffycrystallinemassknownaslightsoda ashwhichismostlysodiumcarbon Thefluffymassislightbecausetheoriginalcrystalshapeisretainedonthelossofcarbondioxide leavingmanyvoids Itisusuallymoreconvenienttomakeamoredensematerialandthisisachievedbyaddingwater whichcausesrecrystallizationinadenserform andfurtherdrying Itisdebatablewhethertheactualchemistrygivenaboveisagooddescriptionoftheprocess butitcertainlyaidsunderstanding Foradetailedunderstanding agreatdealneedstobeknownaboutsolubilityproducts 溶度积 ofmulticomponentsystems Theimportantthingtoknowisthatthesystemiscomplexandrequirescarefulcontrolatallpartsoftheprocessinorderforittooperateeffectively Onedisadvantageoftheprocessistheamountofcalciumchlorideproduced Farmoreisproducedthancanbeused somuchoftheproductionissimplydumped itisnotaparticularlynoxiousornastyproduct Itwouldbeadvantageoustousealltheinputmaterialinthisprocess forexampleproducinghydrogenchloridefromthechloride Usesofsoda ash Ofallsoda ash 50 issoldtotheglassmakingindustryasitisaprimaryrawmaterialforglassmanufacture Thefortunesoftheindustryarethereforestronglytiedtoglassdemand Soda ashalsocompetesdirectlywithsodiumhydroxideasanalkaliinmanychemicalprocesses Sodiumsilicatesareanotherimportantclassofchemicalsderivedfromsoda ashbyreactionwithsilicaat1200 1400 Silica gelisafinesodiumsilicatewithalargesurfaceareaandisusedincatalysts chromatographyandasapartialphosphatereplacementindetergentsandsoaps 3 ElectrolyticProcessesforChlorine CausticSoda Introduction Bothchlorineandcausticsodahave atvarioustimesinthehistoryofthechemicalindustry beengreatlyindemand butunfortunatelyforoperatorsofelectrochemicalplants notalwaysatthesametime Chlorinehasbeenvaluedasableach orarawmaterialfortheproductionofbleachingpowder asadisinfectantinwatersuppliesandasarawmaterialforplasticsandsolventsmanufacture Causticsodahasbeenusedintheproductionofsoda ash soap textiles andasaveryimportantrawmaterialinanincrediblevarietyofchemicalprocesses Alltheelectrolytic 电解的 processeshaveincommontheelectrolysisofsalttogivechlorineandsodiumhydroxide Thevastmajorityofproductionelectrolyses 电解 asodiumofsalt buttherearesomesignificantplantsthatelectrolyzemoltensalttogiveliquidsodiumandchlorine Theseareusedbyindustriesthatneedtheliquidsodium mainlyintheproductionoftetra alkyllead 四烷基铅 petroleumadditives thoughthepetroleumadditivecompaniesarediversifying 多无化的 andotherusesmayappear Thereareessentiallythreedifferenttypesofcell 电池 usedforaqueouselectrolysis mercurycells diaphragmcellsandmembranecells Membranecellsarereallytheonlytechnologythatisviablefornewcapacityinmodernplants butalargeamountofoldcapacitystillexistsandmanycompanieshavenotfountiteconomicaltoreplaceeventheirmercurycells despitetheenvironmentalimplications Allelectrolyticreactionsarebasedontheideaofusingelectronsasareagentinchemicalreactions Thebasicreactionsofbrineelectrolysiscanbewrittenasfollows Anode2Cl 2e Cl2Cathode2H2O 2e H2 2OH Theoverallreactionis 2Na 2Cl 2H2O NaOH Cl2 H2Thisreactionhasapositivefreeenergy G 421 7 J molat25 andneedstobedrivenuphillbyelectricity Likemanybasicchemicalprocessesthoughthereactionappearstobegloriouslysimply therearesomesignificantcomplications Forastart thereactionproductsneedtobekeptapart hydrogenandchlorinewillreactexplosivelyiftheyareallowedtomix Chlorinereactswithhydroxidetogivehypochlorousacid HOCI andchloride bothwastingproductandcreatingby products Thehypochlorousacidandhypochlorite ClO inturnreacttogivechlorate ClO3 protonsandmorechloride Hydroxidereactsattheanodetoformoxygen whichcancontaminatethechlorine Allthereactionsreduceefficiencyand orcreatedifficultseparationorcontaminationproblemsthatneedtobesortedoutbeforeanyproductscanbesold Thekeytounderstandingthevarioustypesofprocessusedfortheelectrolysisisthewaytheyseparatethereactionproducts Therearebasicallythreetypesofelectrolyticcell 电解池 forbrineelectrolysis thoughtherearemanyvariationsofdetailamongthecellsfromdifferentmanufacturers 4 TheUsesofChlorineandSodiumHydroxide Sodiumhydroxidehassomanychemicalusesthatitisdifficulttoclassifythemconveniently Oneofthelargestusesisforpaper making wherethetreatmentofwoodrequiresastrongalkali Insomecountriesthisconsumes20 of