BureauofMines
ReportofInvestigations5484
EQUILIBRIUMSTUDYOFTHESYSTEMPOTAS SIUM SIUM
CARBONATE,POTAS SIUMBI CARBONATE,
CARBONDIOXIDE ,ANDWATER ,ANDWATER
ByJ.S.Tosh,J. H.Field,H.E.Benson,andW.P. Haynes
CALIF0Rft!*
INSTITUTEf.2F!
JUL2-1959 I
TECHNOLO GY' GY'
GEOLOGIC
LfBWAHf*-
UNIVERSITYOFMICHIGAN
39015078542415
UnitedStatesDepartmentoftheInterior1959
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 2 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
TheLibraryofCongresshascatalogedthispublicationasfollows:
Tosh,JohnS
Equilibriumstudyofthesystempotassiumcarbonate,
potassiumbicarbonate,carbondioxideandwater,byJ.S.
Tosh(andothers.Washington]U.S.Dept.ofthe Interior,
BureauofMines,1959.
ii,23p.illus. 27cm.(U.S.BureauofMines.Report ofinves-
tigations,5484)
Bibliographicalfootnotes.
1.Potassiumcarbonates.2.Carbondioxide.3.Chemicalequi-
librium,r.Title.(Series)
[TN23.U43no.5484]Int59-72
V.S.Dept.ofthe Interior.Library
forLibraryofCongress
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
CONTENTS
Page
Summary1
Introduction1
Descriptionofequipment4
Operatingprocedure5
Experimentalresultsanddiscussion...8
Correlationofdata18
ILLUSTRATIONS
Fig.
1.Rockingautoclaveunitusedincarbonateequilibrium
studies3
2.Schematicofrockingautoclaveunit4
3.Autoclaveandcondenserassembly5
4.Rockingautoclaveunitandgassamplingmanifold
usedincarbonateequilibriumstudies6
5.Equilibriumpressureofcarbondioxideover20-
percentequivalentpotassiumcarbonatesolution...13
6.Equilibriumpressureofcarbondioxideover30-
percentequivalentpotassiumcarbonatesolution.. .13
7.Equilibriumpressureofcarbondioxideover40-
percentequivalentpotassiumcarbonatesolution.. .14
8.Equilibriumpressureofcarbondioxideover20-
percentequivalentpotassiumcarbonatesolution.. .15
9.Equilibriumpressureofcarbondioxideover30-
percentequivalentpotassiumcarbonatesolution.. .15
10.Equilibriumpressureofcarbondioxideover40-
percentequivalentpotassiumcarbonatesolution.. .16
11.Equilibriumpressureofwatervaporover20-percent
equivalentpotassiumcarbonatesolution17
12.Equilibriumpressureofwatervaporover30-percent
equivalentpotassiumcarbonatesolution17
13.Equilibriumpressureofwatervaporover40-percent
equivalentpotassiumcarbonatesolution18
14.Equilibriumpressureofwatervaporover20-percent
equivalentpotassiumcarbonatesolution19
15.Equilibriumpressureofwatervaporover30-percent
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
equivalentpotassiumcarbonatesolution20
16.Equilibriumpressureofwatervaporover40-percent
equivalentpotassiumcarbonatesolution20
17.VariationsofKwithconversionfor40-percent
equivalentpotassiumcarbonatesolution22
18.VariationsofKwithtemperatureandconcentration..23
19.Comparisonofconstantswiththoseofprevious
investigators23
ii
TABLES
No.Page
1.Typicalanalysesofduplicategassamplesbymass
spectrometer8
2.Equilibriumpressuresofcarbondioxideandwater
vaporover20-percentequivalentpotassiumcarbonate
solution9
3.Equilibriumpressuresofcarbondioxideandwater
vaporover30-percentequivalentpotassiumcarbonate
solution10
4.Equilibriumpressuresofcarbondioxideandwater
vaporover40-percentequivalentpotassiumcarbonate
solution.11
5.AveragevaluesofKfor 20-and30-percent
concentrations21
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
EQUILIBRIUMSTUDYOFTHESYSTEMPOTASSIUMCARBONATE
POTASSIUMBICARBONATE,CARBONDIOXIDE,ANDWATER-^
by
J.S.Tosh,^J.H. Field,2/H.E.Benson,^andW.P.Haynes^
SUMMARY
Anequilibriumstudyofthe systempotassiumcarbonate,potassiumbicar-
bonate,carbondioxide,andwaterhasbeenconductedwith solutionsof20-,
30-,and40-percentequivalentpotassiumcarbonateconcentrations.These
equilibriumdatacovertheoperatingrangeofthe hotcarbonatescrubbing
systemforremovingcarbondioxidefromgasmixtures.Suchdataare necessary
toestablishthelimitsof purificationandareusedto designabsorptionand
regenerationtowers.
ValuesofKin therelationship:K=(KHC03)2/(K2C03)PC02we*edeter-
minedforhighertemperaturesof70° to140° C.andgreaterconcentrations,
20to40percent,than employedbypreviousinvestigators.Forthe20-and
30-percentconcentrations,Kisconstantata giventemperature;thus,onceK
hasbeendeterminedtheequilibriumpressureofcarbondioxidec anbecalcu-
latedforanyconversion.VariationofK valueswithchangingconversionwas
observedwiththe40-percentsolutions,sothatequilibriumcalculated pres-
suresarelessreliablefrom averageKvalues.
INTRODUCTION
Anew,improvedprocessforremovingcarbondioxidefrom gasmixturesby
hotsolutionsofpotassiumcarbonate,hasbeendevelopedbythe Bureauof
M-fnp.s.56/xheprocessprovidesaneffectiveandeconomicalmethodforremov-
ingcarbondioxidefromsynthesisgas,a mixtureofcarbonmonoxideandhydro-
gen,usedinproducingsyntheticliquid fuelsfromcoal.Inthis purification
1/ManuscriptcompletedJanuary7,1959.Titlesof publicationscitedherein
inparenthesesaretranslationsfromthelanguagein whichtheywere
published.
7JChemicalengineer,BureauofMines,RegionV, Pittsburgh,Pa.
3/Actingchief,GasSynthesisSection,Bureau ofMines,RegionV,Pittsburgh,
Pa.
4/Formerchief,GasSynthesisSection,Bureauof Mines,RegionV,Pittsburgh,
Pa.
5/Benson,H.E.,Field,J. H.,andJimeson,R.M.,CO2AbsorptionEmploying
HotPotassiumCarbonateSolutions:Chem.Eng.Prog.,vol.50,No.7,
1954,pp.352-364.
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
6/Benson,H.E.,Field,J. H.,andHaynes,W.P.,ImprovedProcessforCO2
AbsorptionUsesHotCarbonateSolutions:Chem.Eng.Prog.,vol.52,No.
10,1956,pp.433-438.
processtheacidgasis absorbedatelevatedpressuresatornearthe tempera-
tureprevailingintheregenerator.Thesolutionis depressurizedandregener-
atedbyconventionalsteamstripping.Theneedforheatingthe spentsolution
betweentheabsorptionandregenerationstepsiseliminated,andcosts are
savedforbothsteamandheat-exchangeequipment.
Equilibriumdataforthesystempotassiumcarbonate-potassiumbicarbonate-
carbondioxide-waterarenotavailableattheoperatingconditionsused inthis
process.SeveralinvestigatorsZrJ-Q/previouslypublishedequilibriumdatafor
carbondioxideoversolutionsofpotassiumcarbonate.Allof thesestudies
useddilutesolutions,0.1to2 Natlowtemperatures,generallylessthan
100°C.
Toevaluatetheeffectivenessofthepilotplant inremovingcarbondiox-
idefromgasmixtures,astainlesssteel autoclavewasoperatedconcurrently
toprovidethenecessaryequilibriumdata.Partialpressuresof carbondioxide
andwatervaporwerefirst measuredbetween110° and140°C.oversolutionsof
potassiumcarbonateandpotassiumbicarbonateequivalenttoanoriginal40-
percentconcentrationofpotassiumcarbonate.Equilibriumcurvesforthese
datawerepublishedpreviously.11.'Subsequentmeasurementsweremadedownto
70° C.and0-percentconversiontoextendtheseequilibriumcurves.Theex-
pandeddataareincludedinthis report.Tobroadenthescopeofthe original
study,equilibriumpressuresoverboth30-percentand20-percentequivalent
potassiumcarbonatesolutionsweredeterminedsincetheseconcentrationsalso
areofpracticalinterest.
"Equivalentconcentrationofpotassiumcarbonate"referstoasolutionin
whichonlypotassiumcarbonateandwaterare present.Thusa40-percentequiv-
alentsolutionmeansasolutionthatwould contain40gramsofpotassiumcar-
bonateand60gramsofwater ifallthe bicarbonateinthesystemwerecon-
vertedbacktocarbonate.l^/
7/Sieverts,A.,andFritzsche,A.,(PotassiumCarbonateSolutionsandCO2.1):
Ztschr.anorg.Chem.,vol.133,1924,pp.1-16.
8/Walker,A.C,Bray,U.B., andJohnson,J.,EquilibriuminSolutionsof
AlkaliCarbonates:Jour.Am.Chem.,vol.49,1927,pp.1235-1256.
9/Brukner,B.,andWachtler,E.,(PartialPressuresof CarbonDioxidein
AqueousSolutionsofAlkaliCarbonatesandBicarbonates):Ztschr.
WirtschuftsgruppeZuckerind.,vol.91,1941,pp.254-274.
10/Dryden,I.G.C.,EquilibriumBetweenGaseousCarbonDioxideandHydrogen
SulphideandSolutionsofAlkaliCarbonates,BicarbonatesandHydro-
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
sulphides.PartI.PotassiumSalts:Jour.Soc.Chem.Ind.,vol.66,
1947,pp.59-62.
11/Workcitedinfootnote6, p.1.
12/A40-percentpotassiumcarbonatesolutioncompletelyconvertedtobicar-
bonatecontains0percentK2CO3,51.4percentKHCO3,and 48.6percent
H20.
FIGURE1.-RockingAutoclaveUnitUsedinCarbonateEquilibriumStudies.
5 1 4 2 4 5 8 7 0 5 1 0 9 e 3 . l p g d o o m g / 7 d 2 p 0 # 2 e / t s e u _ n . s e s l d e n c a c a h . / g l d r o h . / t / : s p u r t t t h i h t / a ) . i h p w p w 0 w 5 / / 1 ( : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
DESCRIPTIONOFEQUIPMENT
Inertgas-
60-100ps.i.g.
-M-
Pressureregulator
Flexible
connection
Bleedline
-Kr—
Vacuum
Open-end
manometer
Bleedline
Manostat
pressure
controller
Theequilibriumstudywasconductedin therockingautoclaveshownin
figure1.Aschematicof theunitis giveninfigure2.Theautoclavecon-
sistsofa3-inch schedule-
40pipeofstainlesssteel
(Type304)approximately3
feetlong,jacketedbya4-
inchschedule40-pipeofcar-
bonsteel.Across-sectional
viewoftheautoclave-conden-
serassemblyisshownin fig-
ure3.Theassemblyis
flangedononeendto facili-
tatecharginganddischarging.
Internalpressuresareindi-
catedon4gagescoveringthe
rangefrom30inchesof mer-
curyvacuumto1,000p.s.i.g.
Thesegagesarecalibrated
periodicallywithadead-
weighttester.Theaccuracy
is±0.1p.s.i.g.between30
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
inchesofmercuryvacuumand
60p.s.i.g.,and±0.25
p.s.i.g.between60and300
p.s.i.g.Thepressureat
equilibriuminthesetests
didnotexceedtherangeof
the300p.s.i.g.gage.A
shutoffvalveisprovidedfor
eachgagetoallowselection
oftheappropriatepressure
rangeforbestaccuracy.The
pressuregages,theircon-
nectinglines,andallother
partsofthesystemthat come
incontactwitheither the
gasesintheautoclaveor
(©
Thermometer
t
■*—(Condenser)*■—I
Cooling-water
c
i
Gos-samplingvalve
Autoclave
4sThermocouplewel
f
Liquid-sampling
valve
FIGURE2.-SchematicofR ockingAutoclaveUnit,
withthecarbonatesolutionsareconstructedof stainlesssteel.
Heatisappliedthroughan electricwindingontheoutside ofthejacket.
Tojacket-pressure
controller
Cooling-water
exitâ–"•—
Cooling-water
inlet
Pressuretap
^/Thermocouplewell
Liquid-sampling
port
FIGURE3.-AutoclaveandCondenserAssembly.
A1/3-hp.electricmotorcoupledwith a72:1gearreducerrocks theauto-
clavecondenserassemblythroughanarcofapproximately30° atarateof 24
cyclesperminute.Therockingmotionconveyedtothe autoclaveinsuresuni-
formtemperatureinthecontainedcharge,thoroughdissolutionofthe solids,
andintimatecontactbetweentheliquidand thegasphase.Thesefactors
assistinattainingequilibriumin areasonabletime.
Whenequilibriumisreached,asindicatedby aconstantpressure,samples
ofthegasare drawnintoagas-samplingapparatus(fig.4)through alength
ofglasstubingconnectingtheapparatusto thegas-samplingport.Thegas-
samplingvalveisheatedbymeansofan electricaltapeheater.Itstempera-
tureisdeterminedthroughathermocoupleattachedto thevalvebody.By
maintainingthetemperatureofthevalveat,or slightlyabove,theequilibrium
temperature,condensationofwatervaporpassingthroughthevalveduringsam-
plingisprevented.Thegas-samplingapparatusconsistsofa glassmanifold
towhichareattachedthe samplebottles,avacuumpump,aclosed-endmercury
manometerformeasuringtheabsolutepressureofthesamples;anda 10-liter
bottle,which,becauseofitsvolume,ensuresan efficientpurgeoftheline
leadingtothegas-samplebottles.Withthis equipmentduplicategassamples
aretakenwithoutstoppingtherockingmotionof theautoclaveandtherefore
withoutdisturbingequilibriumconditions.
OPERATINGPROCEDURE
Weighedamountsofcommercial-gradecalcinedpotassiumcarbonate!-/and
13/Typicalchemicalanalysisofpotassiumcarbonate(analysissuppliedby
HarshawChemicalCompany):K2CO399.50,KOH0.07,KC10.03,Fe203
0.0002,AS2O30.00002,Pb0.0001,Na200.045percent.
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
FIGURE4.-RockingAutoclaveUnitandGas-SamplingManifoldUsedinCarbonate
EquilibriumStudies.
5 1 4 2 4 5 8 7 0 5 1 0 9 e 3 . l p g d o o m g / 7 d 2 p 0 # 2 e / t s e u _ n . s e s l d e n c a c a h . / g l d r o h . / t / : s p u r t t t h i h t / a ) . i h p w p w 0 w 5 / / 1 ( : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
reagent-gradepotassiumbicarbonatelz'arechargedtotheautoclave.Thefol-
lowingformulas,basedonamassbalanceof thereaction:
(K2C03+co2+H2° ^2KHC03),
areusedtodeterminetheweights ofingredientsthatmakeupa solution:
FC=(l-FVCC"1+0.3182F),
Ffi=1.4486/[(CF)-1+0.3182],
Fw=[(1-C)- 0.1304CF]/[(1+0.3182CF)];
where:
Fq=weightfractionof potassiumcarbonateinconvertedsolution,
Fg=weightfractionof potassiumbicarbonateinconvertedsolution,
Fjj=weightfractionof waterinconvertedsolution,
C=weightfractionof potassiumcarbonateintheoriginalor unconverted
solution,
F=fractionofpotassiumcarbonateconvertedto bicarbonate.
Theweightfractionsofingredientsthus determinedyieldasolutionof
setconcentrationandconversionatroomtemperature.Whenthesolutionis
heatedtoequilibriumtemperature,aportionofthebicarbonatedecomposes,
liberatingcarbondioxide.Therefore,thefractionofcarbonate,convertedto
bicarbonateunderfinalequilibriumconditions,mustberecalculated;this
takesintoaccounttheamountofcarbon dioxideinthegasphase.
Afterthesolidshavebeenadded,the autoclaveisassembled,evacuated
toabout5mm.Hg toeliminatemostoftheair andleak-testedwithinertgas
at50to100 p.s.i.g.Whenthesystemisleakfree,thepressureis againre-
ducedtoapproximately5mm.Hg.Thequantityof waternecessarytoyieldthe
desiredconcentrationisdrawnintothe autoclavethroughthegas-sampling
port.Therockingmechanismisstarted,theappropriatepressureset inthe
steamjacket,andheatapplied.Whenthedesiredtemperaturehasbeen maintained
14/Typicalchemicalanalysisofpotassiumbicarbonate(Fischercertificateof
analysislot754945):
PercentPercent
Insolublematter0.007Sulfate(SO4)0.000
Normalcarbonate00Calcium,magnesiumand
Chloride(CI)0002NH4OHppt003
Nitrogen(N)0003Heavymetals(asPb) 0001
Phosphate(PO4)000Iron(Fe)0000
Sodium(Na)02
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
foratleastone-halfhour,gas samplesaretakentobeanalyzedby themass
spectrometerforcarbondioxideandwatervapor.Sincethe gasintheauto-
clavecontainswatervapor,thepressureof thegassampleduringthesampling
proceduremustbekeptbelowthe saturatedwater-vaporpressuretoprevent
condensation.
Tosamplethegas,thesamplingapparatusis attachedtothegas-sampling
portandevacuatedtoabout1 mm.Hg.Thevacuumlineis closedandthegas-
samplingvalvethrottled.Thisvalvepermitsgasfromtheautoclaveto flow
intothesamplingapparatus.Whenthemanifoldpressurereaches20 mm.Hgthe
samplingvalveisclosed,the10-literbottle isisolatedfromthesystem,
andthepressureisagain reduced.Aftertwomorepurges,thesamplebottles
arepressurizedto20mm.Hg andremovedfromthemanifold.Theamountofgas
usedinthisprocedureis approximately200cc.Thisvolumehasbeenfound
adequatetopurgethesamplebottleseffectively.Duplicatesamplesofgas
aretakenforeachtest andordinarilyanalyzedthesamedaytominimizeair
contamination.Foraparticularanalysis,theprecisionofthe massspectrom-
eterisapproximately±0.2percent.Toshowthe overallreproducibilityof
theanalyticalresults,typicalanalysesoftwo setsofduplicatesamplesare
shownintable1, whereeachsamplewasanalysedtwotimes bythemass
spectrometer.
TABLE1.-Typical analysesofduplicategassamples
bymassspectrometer
Water,
volume-percent
Carbondioxide,
volume-percent
SampleNo.
83A-l
51.1
52.6
48.9
47.4
83A-2
51.0
50.0
49.0
85A-l
59.0
58.7
50.0
41.0
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
85A-2
59.4
58.9
41.3
40.6
41.1
EXPERIMENTALRESULTSANDDISCUSSION
Equilibriumpartialpressuresofcarbondioxideandwater vaporwerede-
terminedat70° to130° C.over20-and30-percentequivalentpotassiumcarbon-
atesolutions,andat70° to140° C.overa40-percentsolution.Theseresults
aresummarizedinthefirst fivecolumnsoftables2to 4.
TABLE2.-Equilibriumpressures ofcarbondioxideandwatervapor
over20-percentequivalentpotassiumcarbonatesolution
("Conversion"meansconversionofK2CO3toKHCO3)
Equilibrium
Total
Equilibrium
pressure,
equilibrium
Temperature,
Conversion,
pressure,
watervapor,
pressure,
°C.
percent
CO2,p.s.i.
p.s.i.
p.s.i.a.
K
70
0
-
4.18
4.18
-
10.1
0.03
4.14
4.17
0.045
20.1
.17
3.96
4.13
.039
33.4
.56
3.89
4.45
.039
33.5
.46
4.12
4.58
.048
50.0
1.69
3.49
5.18
.038
66.9
4.30
3.15
7.45
.040
81.1
10.3
2.84
13.1
.044
90
0
-
9.23
9.23
-
10.0
0.08
9.47
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
10
TABLE3.-Equilibriumpressures ofcarbondioxideandwatervapor
over30-percentequivalentpotassiumcarbonatesolution
("Conversion"meansconversionofK2CO3toKHCO3)
Equilibrium
Total
Equilibrium
pressure,
equilibrium
Temperature,
Conversion
pressure,
watervapor,
pressure,
°C.
percent
CO2,p.s.i.
p.s.i.
p.s.i.a.
K
70
0
-
3.67
3.67
-
0
-
3.99
3.99
-
10.0
0.04
3.90
3.94
0.056
20.0
.17
3.53
3.70
.063
33.2
.51
4.07
4.58
.068
49.4
1.97
3.59
5.56
.051
65.2
4.44
3.43
7.87
.057
64.8
4.46
3.31
7.77
.055
81.0
12.0
3.32
15.3
.058
90
0
-
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 5 d 0 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
11
TABLE4.-Equilibriumpressures ofcarbondioxideandwatervapor
over40-percentequivalentpotassiumcarbonatesolution
("Conversion"meansconversionofK2CO3toKHCO3)
Equilibrium
Total
Equilibrium
pressure,
equilibrium
Temperature,
Conversion,
pressure,
watervapor,
pressure,
°C.
percent
C02,p.s.i.
p.s.i.
p.s.i.a.
K
70
10.1
0.04
3.42
3.46
0.085
20.1
.20
3.66
3.86
.078
33.4
.61
3.30
3.91
.084
42.2
1.32
2.89
4.21
.070
90
10.0
0.08
7.41
7.49
0.042
20.0
.34
7.68
8.02
.045
33.3
1.22
7.26
8.48
.041
41.9
2.49
6.97
9.46
.036
110
0
-
15.6
15.6
-
10.0
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 0 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
12
TABLE4.-Equilibriumpressures ofcarbondioxideandwatervaporover
40-percentequivalentpotassiumcarbonatesolution(Con.)
("Conversion"meansconversionofK2CO3toKHCO3)
Equilibrium
Total
Equilibrium
pressure,
equilibrium
Temperature,
Conversion,
pressure,
watervapor,
pressure,
°C.
percent
CO2,p.s.i.
p.s.i.
p.s.i.a.
K
130
0
-
29.8
29.8
-
10.0
0.20
27.7
27.9
0.017
19.9
1.36
29.1
30.5
.011
29.2
3.94
29.5
33.4
.009
34.6
6.03
28.1
34.1
.009
40.2
6.61
27.7
34.3
.012
54.0
20.5
23.6
44.1
.009
56.8
19.5
20.7
40.2
.011
58.0
30.6
17.5
48.1
.007
61.7
29.8
20.9
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 0 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
0240660100
PERCENTOFK2C03CONVERT EDTOKHCO3
FIGURE5.-EquilibriumPressureofCarbonDioxide
Over20-PercentEquivalentPotassium
CarbonateSolution.
080408080100
PERCENTOFK2C03CONVERT EDTOKHCO3
FIGURE6.-EquilibriumPressureofCarbonDioxide
Over30-PercentEquivalentPotassium
CarbonateSolution.
u>
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 0 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
14
200
UJ
cr
z>
CO
CO
UJ
cr
a.
X
o
o
CD
cr
<
beforebeingadmittedtothe
topoftheabsorptioncolumn.
Bothstepseffectivelylower
theequilibriumpressureof
carbondioxideoverthesolu-
tion.
Thepartialpressures
ofcarbondioxidearealso
showninaClausius-Clapeyron-
typeplot,wherethelogarithm
ofpressureisplottedas a
functionofreciprocalabso-
lutetemperatureforselected
levelsofconstantconversion.
Forthe20-percentsolution
(fig.8)andthe 30-percent
solution(fig.9)JJL'families
ofstraightparallellines
wereobrained.Whenthedata
forthe40-percentsolution
weresimilarlyplottedin
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 4 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
figure10,thelineswere
slightlycurvedratherthan
straight.Theseplotsoffer
aconvenientmethodforex-
trapolatingthecarbondiox-
idepressureoverawiderange
oftemperatures.Oncethe
pressureatonetemperatureis
known,thepressureatany
temperatureforthesamelevel
ofconversioncanreadilybe
obtainedbydrawingaline
throughthepointparallelto
theexistinglines.
.03
Water-vaporpressures
areshowninfigures11 to
13.Plotsofthe20-percent
(fig.11)and30-percent(fig.
12)dataarequitesimilar.
Inbothinstancesthevapor
pressureseitherremainnear-
lyconstantorincreaseslightlytoa maximumatapproximately20-to40-percent
conversionbeforestartingtodecline.Aplotofthe 40-percentdata(fig.13)
020406080100
PERCENTOFK2C03CONVERT EDTOKHC03
FIGURE7.-EquilibriumPressureofCarbonDioxideOver
40-PercentEquivalentPotassiumCarbona te
Solution.
15/Thepressuresofcarbondioxideplottedin figures8to10 aretakenfrom
thesmoothedcurvesinfigures5to 7.
FIGURE8.
EquilibriumPressureofCarbonDioxideOver
20-PercentEquivalentPotassiumCarbonate
Solution.
2.75
KX1.000
2.95
-4—
-.6
-.8—
-1.0
2.45
2.552.652.75
l/T°KX1,000
2.65
2.95
FIGURE9.-EquilibriumPressureof CarbonDioxideOver
30-PercentEquivalentPotassiumCarbonate
Solution.
t-n
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 5 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
16
24
20
-.12—
-.8
2.728
l/T°Kx1.000
FIGURE10.-EquilibriumPressureof CarbonDioxideOver40-Per-
centEquivalentPotassiumCarbonateSolution.
showsthesameten-
dencyforthepres-
surestoholdsteady
toapproximately30-
or40-percentcon-
version,followedby
arapidrateof de-
clinebetween30-
and60-percentcon-
version.
Thewater-vapor
pressuresarealso
plottedinaClaus-
ius-Clapeyronform
(figs.14to16).W
Ifavaporis assum-
edtoobeytheideal
gaslaw,thisequa-
tioncanbeinte-
gratedtoyieldlog
P=-L/2.303RT+ C,
wherePisvapor
pressure,Listhe
heatofvaporiza-
tion,n adCisa
constant.Whenlog
Pisplottd easa
functionofrecip-
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 5 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
rocaltemperature,
theslopeofthe
lineis:
-L/2.303Ror L=- (slopex2.303x1.987).
TheClausius-Clapeyronequationnormallyappliestoequilibriumbetween
twophasesofa purecomponent;thesamemethodofcalculationwasusedfor
thewatervapordata.A heatofvaporizationofapproximately9,300calories
pergrammole.(980B.t.u.perpound) wasobtained,whichisclose tothe
averagevaluebetween70° and130° C.obtainedfromthesteamtables.Forthe
morehighlyconverted40-percentsolutions,asshowninfigure 16,theheat
ofvaporizationapparentlyisnotconstantsincethe slopeofthelinebegins
tochangewhenabout50-percentofthe potassiumisintheformof bicarbonate
Thismaybedueto anincreasedconcentrationofsaltsformedin thesolution
whenonemoleculeofcarbonatereactingwith carbondioxideandwaterforms2
moleculesofbicarbonate.
16/Thepressuresofwatervapor plottedinfigures14to 16aretakenfrom
thesmoothedcurvesinfigures11 to13.
06406060100
PERCENTOFK2C03CONVERT EDTOKHC03
FIGURE11.-EquilibriumPressureofWaterVa-
porOver20-PercentEquivalent
PotassiumCarbonateSolution.
40
08046060100
PERCENTOFK2C03CONVERT EDTOKHC03
FIGURE12.-EquilibriumPressureofWaterVa-
porOver30-PercentEquivalent
PotassiumCarbonateSolution.
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 5 d 1 : e z 4 i 1 t i g 8 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
18
45
O.
UJ
cr
z>
to
in
UJ
cr
Q.
(T
o
Q_
<
>
i
cr
LlI
\-
<
10
90°C.
-A-
020406080100
PERCENTOFK2C03CONVERTEDTO KHC03
FIGURE13.- EquilibriumPressureofWaterVaporOver
40-PercentEquivalentPotassiumCarbon-
ateSolution.
CORRELATIONOFDATA
McCoyiZ/firstdeter-
mined,fordilutesolutions
ofsodiumcarbonateatcon-
stanttemperature,that
equilibriuminthesystem
canbeexpressedasa rela-
tionshipbetweenthepartial
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 2 d 0 : e z 9 i 0 t i g 9 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
pressureofcarbondioxide
inthegasphase, thecation
concentration,theconcen-
trationsofcarbonicacid,
normalcarbonate,andbicar-
bonateinsolution.Later
SievertsandFritzschei^/
workedwithmoreconcentrated
solutionsathighertempera-
tures.Theyderivedamodi-
fiedexpression,relatingthe
concentrationofcarbonate
andbicarbonate,andthepar-
tialpressureofcarbondi-
oxidetoaconstant,K. The
basisforthederivationof
thisconstantisthe rela-
tionshipbetweentheeffec-
tiveconcentrationoractiv-
ityofcarbonicacid insolu-
tionand(1)the firstand
secondionizationconstants
ofcarbonicacidand(2) the
partialpressureofcarbon
dioxideinthevaporphase.
Forthereaction
K2C03+H2O+CO2
2KHC0
3'
constantKisexpressedas;
K=(KHC03)2/(K2C03)PC02.
Theconcentrationsof
19
1.7
1.5
.4—
1.2—
UJ
or
=>
to
11
if)
UJ
or
Q_
10
UL
o
0.
<
>
0.9
or
UJ
<
0.8
£
o
o
0.7
0.4
1111
~\~~
\\
\^\
X^\
V\
\^\
\\xx
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 9 i 0 t i g 9 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
ConversionofK2C03toKHCO3 \\\\
5*\\>
_ ^vs.\N ~~
—I\\
1111\
0.6—
0.5
2.45
FIGURE14.
2.55
2.65
l/T
2.75
KX1,000
2.85
2.95
EquilibriumPressureofWaterVaporOver20-Percent
EquivalentPotassiumCarbonateSolution.
ofcarbondioxideisexpressedin mm.Hg.OnceK hasbeendetermined,the
equilibriumpressureofcarbondioxidecanbe calculatedforanyconversion.
AttheconcentrationsandtemperaturespreviouslyinvestigatedbySieverts
andFritzscheJ^-'andDryden,2£/K wasindependentoftheconversiontobicar-
bonatebutvariedwithtemperature.
Kvaluesforthe solutionsandtemperaturesusedinthisinvestigation
aregiveninthe lastcolumnsoftables2 to4.For the20-and30-percent
19/Workcitedin reference7,p.2.
20/Workcitedin reference10,p.2.
20
11111111
111L
//
//
//
//
//
//
/y
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
/'
rO
//
O
—
U
jt's
X
/?//
///
o
/'//
o
—
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 9 i 0 t i g 9 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
^—ho—|io—|cjcviHO »|m
—
/'/
o|11I1
c!j;
/''i
o1I111
n
—
Jr//
2
—
v/1
3
1IlIIliI
1111
^tocm—oo>cor-
"Sd'3dnSS3adU0dVA-eJ3iVM901
>o
o-s
21
concentrations,Kwasconstantat agiventemperatureforeachconcentration.
Intable5the averageKvaluesforeachtemperaturearesummarized.For the
40-percentconcentrationKdoesnotremainconstantat 110° C.andhigherbut
tendstodecreasewithincreasingconversionto bicarbonate.Thustheequil-
ibriumpressureofcarbondioxiderises morerapidlywithconversionofthe
40-percentconcentrationthanforthemoredilutesolutions. Thevariationof
Kwithconversionat the40-percentconcentrationisillustratedinfigure 17.
Kvaluesusedtoprepare thisfigurearecalculatedfromthe smoothedequilib-
riumpressurecurvesoffigure7 tominimizevariationsfromtheindividual
tests.ThevariationinK occursatthe40-percentconcentrationbecausethere
isgreaterdeviationfromidealityofthe ionizationconstantsofcarbonic
acid-oneof thebasesforderivingK -asthesolution becomeslessdilute.
TABLE5.- AveragevaluesofKfor 20-and30-percentconcentrations
Averagepercent
deviationfrom
arithmeticmean
Temperature,
Number
oftests
Arithmetic
meanofK
Meanerrorof
arithmeticmean
20
-percentcon
centrations
70
7
0.042
.022
.013
.0086
±0.001
.001
.0003
.0001
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 9 i 0 t i g 9 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
±7.8
90
7
8.4
7.7
4.4
110
12
130
9
30
-percentcon
centrations
70
7
6
9
8
0.058
.030
.017
.011
±0.004
.003
.001
.001
±7.6
9.4
5.9
90
110
130
22
.024
.020—
015—
.010—
005
obtainedlowervalues
thanSievertsand
Fritzsche23/at30° to
60° C.Becausethe
slopesofthecurves
differappreciably,if
Dryden'scurveisex-
tendedtohighertem-
peratures,itcrosses
thatofSievertsand
Fritzscheatabout75°
C,indicatingthat
furtherextrapolation
wouldgivehigher
valuesforDrydenabove
thistemperature.Dry-
den'scurvebetween0°
and30° C.showsalin-
earchangeoftheloga-
rithmofKwith recip-
rocaltemperature.
However,thereisade-
viationfromthelinear
relationshipfrom30°
to60° C.Thedatafor
20-percentconcentration
between70° and130° C.
showsaslightupward
slope,andverynearly
linesupwithDryden's
databetween0° and30°
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 9 i 0 t i g 9 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
C.Thiswouldindicate
thatthechangeinslope
exhibitedbyDryden's
databetween30° and60°
C.isnotconsistent.
20406080
PERCENTOFK2C03CONVERTEDTOKHC03
100
FIGURE17.-Variationsof KWithConversionfor40-
PercentEquivalentPotassiumCarbon-
ateSolution.
23/Sieverts,A.,andFritzsche,A.(PotassiumCarbonateSolutionsandCO;
1):Ztschr.anorg.Chem.,vol.133,1924,pp.1-16.
.02
006
JL
2.42.52.62.72.8
l/T'KX1,000
2.93.0
FIGURE18.-Variationsof KWithTemperatureand
Concentration.
.2
i
.06
.06
.04
.02
.006-
0.1
.08
.06
.04
.01
.008
a-20percentsolution
â–¡-30percent solution
.01
.006
.004
2.32.5
2.7
DSievertsandFritzsche2.0N
ODryden2.0N
XBruknerondWbchtlerO.IN
AThisstudy3.44N
JiL
2.93.1
l/T°Kx1,000
3.33.53.7
FIGURE19.-ComparisonofConstantsWithThose
5 1 4 2 4 5 l e 8 g 7 o 0 o 5 g 1 0 d 9 p 3 . # p e d s u _ m s / 7 s 2 e 0 c 2 c / a t / e g r n . o . e t l d s n u r a t i h . h l t d a h / h . / : w p w t t w h / / / : p t T t h M G / 3 d 0 : e z 9 i 0 t i g 9 i 2 - d 1 l e 0 - g 3 o 1 o 0 G 2 , n n i o a d m e o t D a r c e i l n b e u G P
ofPreviousInvestigators.
INT„-BU.0FMINES.PGH..A P .252
