7 D-AI5e 889 THE VAPOR PRESSURE OF HCL - WATER AND SALT - HCL- /

WATER SOLUTIONS BELOW..(U) MACKAY SCHOOL OF MINES RENONY DEPT OF CHEMICAL AND METALLURG. E MILLER JAN 84

IUNCLASSIFIED RFOSR-TR-85-0084 RFOSR-77-3333 FIG 7/4 MLA ~~Eh~E

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MICROCOPY RESOLUTION TEST CHARTNATIONAL BUREAU OF STANDAROS-1963-A

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UNIVERSITY OF NEVADA RENODeprtment of Chemical andMetallurgical EleeringMackay School of Mines 7University of Nevada RenoReno, Nevada 89557-0047 .(702) 784-6961

00o January 1984

Ln Final Rer-irt Covering Period I- - to 30 Nov 83-

THf.- VAF'O f ;:.E-SUFRE IF H .1 -- WAITER ,NV SALT -- HCI - WArERSOLUTION'; iELOW C"

P-c.p-zr-ed by: Etq*?ne Mi I I et

W."'-! Per+ormed by: Eugjene Mz I Jer

2Contracts: Grants AFO13R-77-333 4 LAFLOSR-82-0049

Pr(eared +-or: AIR FORCE OFFICE OF ESLIFNTIFIC RESEARCH (NA)Building 410 CBolling AFE,, DC 20332 ETAtt: Dr. Leonard H. Caveny

FEB 27 .4... .

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the National Technical Information Service. 0

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AIR JOROI OFFTCLP> SCIKTIIC RZSKAR( (API'S!t"~~~NT oiC1 OF TR.X'fs* TTL O DT I C:i-This tec!1i *1 P-1" riw' i nd isapproved 'or .,.::i ;. ': ... : J.V, AFh 190-1.

Disftribution 1:: )nlliinted.MATTIW J. XW "-"ChioatI Toohnioal Intormtioa Divlul2 oll

INTRODUCTION

The vapor pressures of hydrochloric acid solutions areimportant to the modelling of secondary smoke in reducedsmoke ammonium perchlorate solid propellant rocket plumes,ref 1, since the growth of secondary smoke droplets isdependent on their equilibrium behavior. In addition, thebehavior o+ strong electrolytes in aqueous solution is o+fundamental theoretical interest. Inorganic salts dissolvedin hydrochloric acid will significantly modify its equilibriumbehavior due to their effects on the activities of the HCIand water in the liquid phase, ref 2. The resulting changein the solution vapor pressure alters the rate of formationand the chemical composition of the secondary smoke, refs3, 4. The major contaminants found in ammonium perchlorateare sodium and potassium salts. In addition, tricalciumphosphate added to ammonium perchlorate for ease in processingprovides a major source of soluble electrolyte. All thesecations are found in the rocket plume in sufficient quantityto nucleate the secondary smoke droplets, and to subsequentlydissolve and influence the dynamics of growth and the chemicalcomposition of the smoke, re+ 5. If iron and copper combustionmodifiers are avoided, none of the others commonly added topropellants will produce salts soluble enough to effectsigiificant changes in the behavior- of the hydrochloricacid smoke droplets. The original choices of NaCl and CaClaas the salts for- study were baser' on these considerati-nsas well as for interest in studying the effects of theirdifferences in ionic strength. A very limited study of KCiwas subsequently added for consideration but time did notpermit actual experimental measurements to be made.

Prior to the measurements made by the principalinvestigator under sponsorship of AFDSR, no vapor pressuredata were available for either pure hydrochloric acid or forhydrochloric acid containing dissolved NaCi or CaClz fortemperatures below OC, the temperatures of primary interestfor secondary smoke formation. Data exist for these solutions,either primary vapor pressure or activities from which thevapor pressure may be predicted, only for temperatures ator above OC. The low temperature vapor-liquid equilibria .'_. dmeasurements for the pure hydrochloric acid and for solutionscontaining NaCI have been completed and are published in K....refs 6 and 7. The experimental vapor-liquid equilibria ofCaCla-HCI-H=O solutions for nominal temperatures from 0 to-40C are given in ref 8, completing the study of the pureand salted hydrochloric acid solutions.

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ABSTRACTS OF PUBLISHED RESULTS

_LUI_____W_OC: Ref 6.The vapor-liquid equilibria of 4-36 wt % (0.0411-0.2145

mole fraction) HCl-water solutions were determined fortemperatures between 0 and -40C. Total pressures were measuredby capacitance gauges, vapor compositions by direct vapor-phase Lsampling into a quadrupole mass filter-, and liquid compositionsby electric conductivity. Vapor com,,positions were alsopredicted thermodynamically from the total pressure andliquid composition data by means of the Gibbs-Duhem equation.

(2) VAPOR-LIQUID EQUILIBRIAOF HYDROGEN CHLg gE:_SgDIUMCHLORIDE-WATER SOLUTIONS BELOWOC_: Ref 7.

The vapor-liquid equilibria of HCI-NaC1-H=O solutionswere determined for HCI mole fractions on a salt-free basisof 0.0361 to 0.2229, and NaCl molalities ranging from 0 tonear saturation, for the nominal temperature range of 0 to-40C. Total pressures were measured by capacitance gauges,vapor compositions by direct vapor phase sampling into aquadrupole mass filter, and liquid compositions by electricconductivity. Results are compared with data previouslyobtained for the same temperature ranre for pure HCI-H=Osolutions. Solubility data for NaCl in the acid solutionsat these temperatures suggest the formation of an NaC]water or HC adduct in equilibrium with the saturated solution.

(3) THE VAPOR PRESSURE OF CALCIUM _H'L:W,-_; PHYDROG'ENCHLORIDE -..-..-WATER SOLUTIONS BELOW OC: Ref 8.

Vapor-liquid equilibria data are presented forhydrochloric acid solutions rangin in nominal HCI molfraction from 0.110 to 0.225, saturat-d with CaCla, at nominal -1solution temperatures between 0 and -40C. Total pressureswere measured by capacitance gauges, vapor compositions bydirect vapor-phase sampling into a quadrupole mass filter,and liquid compositions by electric conductivity. The additionof CaCla to hydrochloric acid breaks the azeotrope andgenerally increases the vapor pressures of HCl and water.

Solubility and solution densities have also been measured.Solution compositions have not been completed to date.These are presently being done. It is probable that theeffect of CaCt, on the formation o4 secondary smoke in areduced smoke rocket plume has less an effect than doesNaCl.

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REFERENCES CITED

(1) Miller,E., "Smokeless Propellants," Chap 15; "Fundamentalsof Solid Propellant Combustion," Kuo, K. and M Summerfieldeds. Progress in Aero- and Astronautics. AIAA. In printing.(2) Harned, H.S. & B.B. Owen, "The Physical Chemistry ofElectrolytic Solutions," Reinhold (1958)(3) Hoshizaki, H. et al. "Plume Visibility Detection Study,"Report AFRPL-TR-78-32, Vol. I. (Nov 78)(4) Miller, E., J.W. Connaughton & L.B. Thorn, "Measuredand Predicted Laser Attenuation Throutgh a Solid RocketPlume," JANNAF Propulsion Meeting (1980)(5) Miller, E., "Comparison of Experimental & PredictedSecondary Smoke Optical Signal Attenuation," 13th JANNAFPlume Technology Meeting (1982)(6) Miller, E., "Vapor-Liquid Equilibria of Water-HydrogenChloride Solutions Below OC," J. Chem. Eng. Data 28, 363-367(Oct 83)(7) Miller, E., "Vapor-Liquid Equilibria of Hydrogen Chloride-Sodium Chloride-Water Solutions Below OC," Submitted to J.Chem. Eng. Data for publication.(8) Miller, E., " The Vapor Pressure of CaCl2-HCl-WaterSolutions Below OC," Annual Report to AFOSR - 1 Dec 82 to30 Nov 83 (Jan 84) -

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UNIVERSITY OF NEVADA RENODepartment of Chemical andMetallurgical EngineeringMackay School of MinesUniversity of Nevada RenoReno, Nevada 89557-0047(702) 784-6961

December 1984

Addendum to Final Report Covering Period 1--? to 30 Nov 83

THE VAPOR PRESSURE OF HC- WATER AND SALT - HC - WATERSOLUTIONS BELOW OC

Prepared by: Eugene Miller

Work Performed by: Eugene Miller

Contracts: Grants AFOSR-77-3333, AFOSR-82-0049

Prepared for: AIR FORCE OFFICE OF SCIENTIFIC RESEARCH (NA)Building 410Salling AF, DC 20332,Att: Dr. L, onard H. Caveny

P.

Approved for public releasa; diitribution unlimited.

lualiFied raquestors may obtain additional copies From the(.iense Occumentation Centerl all others should ,apply tothe National rechnical Information Service.

Reproduction, tran%'Lation, publication$ use and disposal inwhole or in part by or for the United States Government ispermitted.

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ABSTRACT " '

Liquid solution analyses are presented which supplementthe vapor-liquid data previously reported. The completevapor-liquid equilibria data are tabulated for hydrochloric

,I, acid solutions ranging in molality from 5.0 to 15.7, saturated Lwith CaCla at nominal temperatures ranging from 0 to -40C. Itwas found that the CaCla-HCl-water system exhibits a maximumpressure azeotrope under these conditions. Pure hydrochloricacid and NaCI-HCl-water systems exhibit minimum pressureazeotropes in the same temperature range. At acid molalitiesgreater than about 9, the vapor phase contains about 94%HC1 and for all molalities there is an increase in the partialpressures of HCI and water over what is observed with purehydrochloric acid. Because of these characteristics, it ispredicted that the presence of CaCl in reduced smoke rocketplumes will not contribute as strongly to secondary smokeas will NaCI.

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INTRODUCTION

-Prior to the measurements made by the principalinvestigator under sponsorship of AFOSR, no vapor pressuredata were available for either pure hydrochloric acid or forhydrochloric acid containing dissolved NaC1 or CaCl= fortemperatures below OC, the temperatures of primary interestfor secondary smoke formation. Data exist in the literaturefor these solutions, either primary vapor pressure oractivities from which the vapor pressure may be predicted,only for temperatures at or above OC. The low temperaturevapor-liquid equilibria measurements for the pure hydrochloricacid and for solutions containing NaCl have been completedand are given in refs I and 2. The experimental vapor-liquidequilibria of CaCl-HCI-H=O solutions for nominal temperaturesfrom 0 to --40C are given in ref 3, completing the study ofthe pure and salted hydrochloric acid solutions.

Ref 3 and the final report on the salt-HCl-water vaporliquid equilibria studies, ref 4, did not include the analysesof the liquid solutions in equilibrium with the vapor phaseand the solid phase of precipitated calcium chloride. Thesehave been completed and are reported here together with atabular summary of the vapor phase compositions and equilibriumpressures. Details of the experimental equipment, experimentalmethods and analytical procedtres are given in ref 1.

RESULTS AND DISCUSSION

Total pressure P', partial pressures of HC and water-,-" p'H., and p'2o respectively, molality of CaCl.a at saturation,

mcd.czzo vapor phase compositions o-f HCl and water. y'mc, andY'm=o respectivel/, are given as a function of the molalityof the HCl in the liquid phase, mHaz, and solution temperature,T, in Table I. The original acid composition before theaddition of CaCl2 dihydrate at room temperature is alsonoted in terms of molality and mol Fraction HCI, Xm.."

The concentration of the CaCl in equilibrium withhydrochloric acid is a complicated Function of acidconcentration and solution temperature as may be seen Fromthe Table. Since the CaCl= was added to the acid solutionas a dihydrate, initially the molality of the HCl decreased.However, as the solution temperature was lowered the CaCl

precipitated from the solution extracting in most instancesmore water from the solution than was added by the dihydrateinitially i.e. the CaCla evidently formed higher orderhydrates, resulting in a higher acid concentration than its

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initial concentration at room temperature. There was noexcess of CaCI. present as a solid phase when the solutionwas transferred to the 2 L boiler except for a small quantityof small particles that may have been in suspension.CaCl=.2H=O CaCl=.4H=O and CaCl=..6H=O are all known toI exist in equilibrium with hydrochloric acid at 25C, ref 5.At low acid molalities the number of water molecules associatedwith the CaCl decreases with increasing acid molality. Thepresent data indicate that at higher acid molalities andlower temperatures, the behavior is not the same.

A maximum pressure azeotrope occurs for this system atall temperatures from 0 to -40C. This is surprising sincepure hydrochloric acid and saturated NaCl-hydrochloric acidexhibit minimum pressure azeotropes in the same temperaturerange. Refs 6 and 7 report on the CaCl2 -HCl-water vapor-liquidequilibria for a range of unsaturated solutions for acidcompositions up to mmcx = 12.9 at 750 mm constant pressureand boiling temperatures between 50 to 129C. They noted aminimum pressure azeotrope and found that the azeotropedisappeared for a solution containing 31 wt pct CaCl. Thepresent solutions contain from 1.1 to 32.1 wt pct CaCla butan azeotrope was found for all the temperatures studied.The presence of the azeotrope is also evidenced by thevapor phase mol fractions given in Table I.

..cti increases with acid molality at a constanttemperature from a value less than to one greater thany'Mq=. Except for the starting acid solution of m, =6.798, for more concentrated starting acid compositions theliquid phase acid composition increased rapidly to a highacid molality and the vapor phase composition increasedalso to a value greater than 0.94.

Both p"Hc, and p'm=o exhibit maxima as acid molalityincreased at constant temperature. The fact that both p' -and p'Nmo increase and decrease together as acid molalityis increased at constant temperature requires someinterpretation. The Gibbs-Duhem equation requires thesolid state of the CaCl= to change with acid composition inorder to permit this behavior. The complex solubility behaviorof the CaCl with acid molality and temperature suggeststhat this does indeed occur. Unfortunately, the quadrupolemass filter used for vapor analysis is most inaccurate atthe higher y'HMc values and the changes in partial pressure

4. could be explatned by experimental error as well. Withoutadditional experimental data and an improved analyticaldevice, the question cannot be resolved.

The data from the experiments does not show the plannedvariation of the independent variables that is desirable

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for ease in correlation of the results. Efforts to correlatethe results by statistical analysis have been modestly A,successful but the question of possible experimental errorscannot be so resolved.

The conclusion concerning the effects of CaCla on theformation of secondary smoke in reduced smoke rocket exhaustspreviously given in ref 4, that CaCla would not cause asserious an effect as NaCl or KCl, is reaffirmed.

REFERENCES CITED

(1) Miller, E., "Vapor-Liquid Equilibria of Water-Hydrogen .Chloride Solutions Below OC," J. Chem. Eng. Data 28, 363-367(Oct 83)(2) Miller, E., "Vapor-Liquid Equilibria of Hydrogen Chloride-Sodium Chloride-Water Solutions Below OC," Submitted to J.Chem. Eng. Data for publication.(3) Miller, E., " The Vapor Pressure of CaCl2 -HCl-WaterSolutions Below OC," Annual Report to AFOSR - 1 Dec 82 to30 Nov 83 (Jan 84)(4) Miller, E., " The Vapor Pressure of HCl - Water andSalt - HC1 - Water Solutions Below OC," Final Report CoveringPeriod 1 May 77 to 30 Nov 83 (1984)(5) Seidell, A., Linke, W.F., "Solubilities." 4th ed.,American Chemical Society. Washington, D.C. p. 566 (1965)(6) Synowiec, J., Bobrownicki, W., "Investigations of theDesorption of Hydrogen Chloride from Aqueous Solutions. II.The Vapor-Liquid Equilibria in H2O-HCl-MgCI2 and HmO-HCl-CaCl=Systems," Chemie Stosowana 4A, 383-403 (1964)(7) Synowiec, J., "The Production of Pure HC1 from WasteAcid by Distillation with Additives," Ind. Chim. Belge 33.,No.4, 351-357 (1968)

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TABLE I

VAPOR-LIQUID EQUILIBRIA OF NaC1-HCl-WATER SOLUTIONS

Smoothed Experimental Data

m"-, T, c P', Y" Nc yWHua P'Nc, pH0 ,

qmol/kg H=O deg C gmol/kg H=O torr torr torr

C6.798/0. 1103+

5.013 - 2.5 5.035 (2.20)* 0.3777 0.6223 0.83 1.37

- 2.8 2.16

7.420 -10.8 3.824 (1.02) 0.4040 0.5960 0.40 0.60

-10.3 1.04

7.840 -- 2.5 2.076 (0. 321) 0.4109 0.5891 0. 132 0.189

-22.7 0.3057

7.055 -31.5 1.235 (0.134) 0.4597 0.5403 0.062 0.072

-31.6 0. 13518.644 -42.6 0.893 (0.046) 0.5174 0.4826 0.024 0.022

-43.7 0.0405

E 8.128/0. 1281

14.718 0.8 .3.458 (34.G0) 0.9417 0.0583 32. 7 7 2.03

- 0.7 34.86

15.016 -12.8 0.833 13.71 0.9440 0.0560 12.94 0.77

13.682 -22.3 0.573 6.22 0.9431 0.0569 5.87 0.35

15.387 -31.5 0.286 (2.72) 0.9382 0.0618 2.55 0.17

-30.8 2.94

* 15.691 -38.6 0.160 (1.46) 0.9494 0. 0506 1.39 0.074

-39.7 13I 9.561/

0.147'9.218 - 0.7 2.923 (44.26) 0.9376 0.0624 41.50 3.76

0.0 47.30

*.- 12.866 - 2.8 3.845 (36.23) 0.9509 0.0491 34,45 1.78S3.2 34. 77

14.077 - 9.7 1.376 (18.17) 0.9246 0.0754 16.80 1.37

-10.0 17.49

13.471 -24.0 0.519 (5.81) 0.9324 - 6 76 5.42 0.39

-22.7 6.38

12.524 -31.2 0.300 (3.56) 0.9441 0.0559 3.36 0.20

-- 31.33.54[16.062/

o.225314.519 - 1.9 2.020 (54.00) 0.9491 0°0509 51.25 2.75

- 1.4 56.10

14.070 -11.4 1.422 29.29 0.9467 0.0533 27.73 1.56

11.468 -25.4 0.550 (9.75) 0.9395 0.0605 9.16 0.59

-25.5 9.7112.004 -36.0 0.248 (4.00) 0.9473 0.0527 3.88 0.22,"

-35.8 4.73

+Initial moal/XmcI*Interpolated value

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17 OBTCE SUBJECT TERMS (Continue on ,wvev,. liery and identUify by block numfi N1 p ..

FED GROUP SuB. OR. LUMS1 4HYDROCHLORIC ACID)SALT SOLUTIONS i ' SODIUM CHLORIDE,

~PARTIAL PRESSURE;-/IS. A7AC (Conin~aue on tvwa.v if necoeagi and idi. by block numbwr

Liquid solution analyses were completed. The complete vapor-liquid equilibriadata are tabulated for hydrochloric acid solutions. ranging in molality from. to 15.7, saturated with CaCl2 at nominal temperatures ranging from 0 to

-40C. The CaCl2-H0-water system exhibits a maximum pressure azeotrope underthese conditions. Pure hydrochloric acid and Na&040~-water systems exhibitminimum pressure azeotropes in the same temperature range. \.At acid molalitiesgreater than about 9, the vapor phase contains about 94%\ H0 and for allmolalities there is an increase in the partial pressures of IItl and water overwhat is observed with pure hydrochloric acid. sec aso of thesecharacteristics, it is predicted that the presence of Ca12 I reduced smoke~ket plums will not contribute as strongly to secondary sock~ as will MaCi.

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