The conditions in which hydrochloric acid aerosol is predicted by the interaction of hydrogen chloride gas with the water vapor in humid air are analyzed. The liquid gas phase equilibrium for the HCL-H2O system is expressed in terms of relative humidity and hydrogen chloride concentration as parts per million, units commonly used in pollution studies. Presented are the concentration (wt %) of HC1 in the aerosol and the concentration of aerosol (ppm) predicted

Rhein, R. A.

English

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NATIONAL AERONAUTICS AND S P A C E  A D M I N I S T R A T I O N  
Technical Memorandum 33-658 
Hydrochloric Acid Aerosol Formation by the 
InteFaction of Hydrogen Chloride 
Witb Humid Air 
Robert A. Rhein 
J E T  P R O P U L S I O N  L A B O R A T O R Y  
C A L I F O R N I A  I N S T l T U T E  OF TECHNOLOQY 
PA 8 A DE N A ,  C A L I F 0 R W I A 
November 15,1973 
https://ntrs.nasa.gov/search.jsp?R=19740004706 2020-03-23T11:58:40+00:00Z

PHEFACE 
The work described in this report was performed by the Propulsion 
Division of the Jet Propulsion Laboratory. 
JPL Technical Memorandum 33-658 

CONTENTS 
I. Introduct ion.  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
11. R e s u l t s . .  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
111. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , 1 
IV. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 
R e f e r e n c e s .  . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . 2 
FIGURES 
1. HC1 ae roso l  formation v s  HC1 concentration, relative 
humidity, and ambient tempera ture .  . . . . . . . . . . . . . . . . 4 
2. Formation and proper t ies  of HC1 ae roso l  a t  263°K v s  HCl 
concentration and relative humidity. . . . . . . . . . . . . . . . . 5 
3. Formation and proper t ies  of HCl ae roso l  at 273'K vs HCl 
concentration and relative humidity. . . . . . , . . . . . . . . . . 6 
4. Formation and proper t ies  of  HC1 ae roso l  at 283°K vs HCl 
concentration and relative humidity. . . . . . . . . . . . . . . . . 7 
5. Formation and proper t ies  of HC1 a e r o s o l  at 293°K v s  HCl 
concentration and relative humidity. . . . . . . . . . . . . . . . . 8 
Formation and proper t ies  of MC1 ae roso l  a t  303°K v s  HC1 
c onc e .it r a tion and t e l a  t ive humid it y , . . . . . . . . . . . . . . . . 9 
Formation and proper t ies  of HC1 a e r o s o l  at 313 "K v s  HC1 
concentration and 1: e lative humidity. . . . . . . . . . . . . . . . . 10 
6. 
7. 
ABSTRACT 
vi 
This  paper  desc r ibes  the  conditions in  which hydrochloric acid aerosol 
is predicted by the interact ion of hydrogen chlor ide g a s  with the water  vapor  
in  humid a i r .  
expyessed i n  terms of re la t ive  humidity and hydrogen chlor ide concentrat ion 
as p a r t s  p e r  mill ion,  units commonly used  i n  pollution s tudies .  
p re sen t s  the  concentration (wt %) of HC1 in the  aerosol and the concentrat ion 
of ae roso l  fppm) predicted. 
The  l iquid-gas phase equilibrium for the HC1-HZO s y s t e m  is 
This  paper  
JPL Technical  Memorandum 33-658 
I. INTR ODUC TION 
Air  pollution by hydrochloric aci! has been the subject of appreciable  
concern  in recent  y e a r s  (Ref s .  1 and 2). 
t i o n s  in which hydrochloric ac id  ae roso l  is predicted by the interact ion of 
hydrogen chlor ide g a s  w i t h  the  water vapor in  humid air. The liquid-gas 
phase equi l ibr ium for  the HC1-HZO sys t em is expres sed  in  t e r m s  of re lat ive 
humidity and hydrogen chlor ide concentration as  p a r t s  pe r  mill ion,  units 
commonly used in  pollution s tudies .  
(wt %) of HC1 in  the  ae roso l  and the  concentration of ae roso l  (pprn) 
predicted.  
Th i s  paper  desc r ibes  the condi- 
This  paper  p re sen t s  the  concentrat ion 
There  is a n  excellent paper  i n  German  (Ref .  3 )  descr ibing graphical ly  
the  phase equi l ibr ia  of the HCl-H20 sys tem,  wherr  par t ia l  p r e s s u r e s  of HCl 
and H20 are expres sed  in mm Hg. 
Enthalpy and heat of dilution data  are also available (Ref.  5). 
(The data are tabulated in  Ref .  4 . )  
11. RESULTS 
The HC1 concentrat ions cons idered  h e r e  ranged f r o m  1 to 1000 ppm, 
and t empera tu res  cons idered  ranged f r o m  263°K (-10°C) to  313°K. F igure  1 
is a phase d i ag ram showing the regions where  a e r o s o l  is expected, as a 
function of HCl concentration (ppm) and re la t ive  humidity, for the  va r ious  
tempera tures .  The regions in  Fig. 1 to the  r ight  of each  i so the rm rep resen t  
the  two-phase regions.  F igu res  2 - 7 presen t  the  expected HC1 concentra-  
tion (wt  %) in the  a e r o s o l  (solid l ines) and the  weight f ract ion (ppm) of liquid 
phase (aerosol )  t o  g a s  phase (dashed l ines).  
III. DISCUSSION 
An example of the  application of these  f igu res  to a typical problem 
might  be to de termine  what happens when 15 pprn HC1 in t e rac t s  with a i r  at 
293°K (20°C) and 84% relative humidity. 
predicted; Fig. 5 indicates  a n  a e r o s o l  of 10% HC1 at a quantity of 100 ppm. 
The HCl in  the  gas phase can  be determined f r o m  the interact ion of t h e  10% 
(sol id)  line and the  boundary l ine  of the  single- and  two-phase regions; it is 
seen  to be 6 ppm. 
Figure  1 indicates  that  ae roso l  is 
Likewise, if the  RH w e r e  75%, no aerosol is expected. 
JPL Technical Memorandum 33-658 1 
Likewise,  100 ppm HCl interact ing with air a t  303°K (30°C) and 
90% RH would resu l t  in 1200 pprn of an  8 wt % HCl aerosol ,  leaving 7. 2 ppm 
i1Cl i n  t h e  gas  phase. 
The cu rves  in Figs.  1 - 7 were  plotted f r o m  data computed from that  
avai lable  in  the l i t e ra ture  in  tabulated form relating phase equi l ibr ium to 
par t ia l  p r e s s u r e s  of HC1 and HzO in mm Hg ( R e f .  4 )  and for water  vapor  
p r e s s u r e  (mm Hg)  v s  t e m p e r a t u r e  (Ref .  6). 
Although t h e s e  c u r v e s  show the predicted formation of HCl aerosol ,  
whether o r  not a e r o s o l  is actual ly  formed depends upon the  p re sence  of 
nucleation sites. Exper iments  on t h e  formation of HCl aerosol (Ref .  7 )  
indicated a minimum of 78% RH at ambient t empera tu re  for aerosol formd-  
t ion and that  aqueous nuclei  w e r e  required;  however, fu r the r  study of HCl 
ae roso l  nucleation is indicated. 
IV. CONCLUSIONS 
By the  use  of Figs.  1 - 7 ,  one can de termine  predicted HC1 a e r o s o l  
formation,  including the  concentrat ion of HC1 i n  the aerosol, the  weight 
f ract ion of aerosol ,  and the gas-phase concentrat ion of HCI. This  informa- 
tion should be useful in  var ious  aspects of the  problem 0. nydrochloric acid 
air pollution. 
REFERENCES 
1. Stahl, Q. R. , "Air  Pollution Aspec ts  of Hydrochloric Acid," Litton 
Systems,  Inc. ,  Contract  PH-22-68-25 (prepared  f o r  the National Ai r  
Pollution Control Adminis t ra t ion) ,  Washington, D. C. , Sept. 1969. 
2. "Hydrochloric Acid and Ai r  Pollution: An Annotated Bibliography, I' 
Environmental  Pro tec t ion  Agency, Office of Ai r  P r o g r a m s ,  Publication 
No, AP-lOQ, Washington, D .C . ,  July 1971. 
3. Schmidt, A. ,  "The Sys tem Hydrochloric Acid/Water," Chem. Inn. Tech., 
Vol. 25, 455-66, 1953. 
4. P e r r y ,  H. H.,  Chemical  Engineer 's  Handbook, New York, IulcGraw-Hill 
Book GO., pp. 166-7, 1950. 
5 .  Van Nuys, C. C. ,  "Enthalpy and Heats  of Dilution of the System 
HCl-H$," AICHE T r a n s . ,  Vol. 39, 663-78, 1043. 
2 JPL Technical Memorandum 33-653 
4 .  - Handbook of Chemistry and Physics ,  37th E d . ,  Cleveland, Ohio, 
Chemical Rubber Pub. Co. , pp. 2142-2143, 1955. 
7. Gillespie, G.  R .  , and Johnstone, H. F. , Particle-Size Distribution in 
Some Hyproscopic Aerosols ,  Chem. Eng. Prop. Vol. 51, 74F-80F, 
1955. 
.TPL Technical Memorandum 33-658 3 
iooa 
HCI, wm 
4 
loa  
1 c  
I 
30 40 50 60 70 80 90 100 
RELATIVE HUM DlTY 
Fig.. 1. HCl aerosol  formation VB HC1 concentration, relative humidity, 
and ambient tempera tu r e 
JPL Technical Memorandum 33-658 
1000 
100 
HCI, 
PPm 
10 
1 
SOLI0 LINES: WT % HCI IN 
AEROSOL 
DASHED LINES: AEROSOL WT 
. FRACTION, ppm 
P 
d d  
10 40 50 60 70 
RELATIVE HUMIDITY 
80 90 100 
Fig, 2. 
concentration and relativc humidity 
Formation and properties of HCl aerosol  a t  263'K vs HCl 
JPL Technical Memorandum 33-658 5 
6 
1000 
100 
10 
1 
RELATIVE HUMIDITY 
Fig. 3. 
concentration and relative humidity 
Formation and properties of HC1 aerosol  at 273.K v s  HCI 
JPL Technical Memorandum 33-658 
1000 
100 
HCI, 
PPm 
10 
30 40 50 60 70 80 90 100 
RELATIVE HUMIDITY 
Fig. 4. 
concentratioi% Ind relative humidity 
Fc:*riation and properties of HC1 aerosol  a t  283.K vs HC1 
JPL Technical MemorLndum 33-658 7 
10 
8 
1 
RELATIVE HUMIDITY 
Fig. 5. 
concentration and relative humidity 
Formation and properties of HC1 aerosol at 293.K VI HC1 
JPL Technical Memorandum 33-658 
HCI, 
PPm 
1000' 
100 
10 
1 
I I - 
- 
- 
- 
- 
c 
- 
- 
- 
- 
- 
SOLID LINES: WT % HCI IN - AEROSOL 
DASHED LINES: AEROSOL WT 
FRACTION, p9m 
c 
- 
I 1 1 
30 40 50 60 7@ 80 90 100 
RELATIVE HUMIDITY 
Fig. 6 .  
concentration aad relative humidity 
Formation apd properties of HG1 aerosol at 303'K vs HC1 
JPL Technical Memorandum 33-658 
10 
30 40 50 60 70 80 90 100 
RELATIVE .HUMIDITY 
Fig. 7. 
concentration and relative humidity 
Formation and properties of HC1 aerosol at 313.h vs HC1 
JPL Technical Memorandum 33-658 
MA& - *I - W., LA., Calif. 


Hydrochloric acid aerosol formation by the interaction of hydrogen chloride with humid air

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