9 Sour Water Equilibria Ammonia Volatility down to PPM Levels; pH vs. Composition; and Effect of Electrolytes on Ammonia Volatility GRANT M . WILSON, RICHARD S. OWENS, and MARSHALL W. ROE
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Wilco Research Company, 488 South 500 West, Provo, Utah 84601
Undesirable sulfur, nitrogen, and oxygen compounds are often encountered in commercial gas production and gas treating f a c i l i ties relating either to natural sources or to synthetic processes. Water also occurs as condensate in these gas streams or water is brought in contact with gas streams in various processing steps. As a result aqueous waste streams are produced in which undesir able sulfur, nitrogen, and oxygen compounds are present. Their concentrations in the aqueous waste streams depend on their equi librium concentrations in gas streams from which the aqueous streams are derived. Present and future environmental control restrictions dictate that the concentrations of these undesirable compounds be maintained at very low levels before the streams can be released to the environment. Thus, methods must be developed for controlling these concentrations. One method used in refin eries for controlling the concentrations of undesirable compounds in aqueous waste streams is by means of a steam stripper called a sour water stripper where these trace compounds are steam dis t i l l e d and then condensed as a concentrated product in the con denser of the stripping column. The principal components in these strippers are hydrogen sulfide, carbon dioxide, and ammonia. This concentrated product stream is then further processed for removal of these undesirable compounds. Similar processes un doubtedly will be necessary in existing and new gas production or gas treating f a c i l i t i e s . The design of these processes requires data regarding the equilibrium concentrations of undesirable com pounds absorbed into various aqueous waste streams, and then equilibrium data are required relating to the removal of these compounds from aqueous waste streams. T h i s paper r e p o r t s on measurements made i n t h r e e a r e a s p e r t a i n i n g t o t h e p r o c e s s i n g o f aqueous w a s t e s t r e a m s as f o l l o w s . A. B. C.
V a p o r - l i q u i d e q u i l i b r i u m measurements on N H 3 - H 2 O m i x t u r e s a t 80 and 120°C pH o f NH3-H S-C0 -HoO m i x t u r e s a t 25 and 80°C E f f e c t - o f sodium h y d r o x i d e and sodium a c e t a t e on N H 3 v o l a t i l i t y a t 80°C 2
2
0-8412-0569-8/80/47-133-187$10.00/0 © 1980 American Chemical Society
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
188
THERMODYNAMICS
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Measurement
OF
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Apparatus
A f l o w - t y p e v a p o r - l i q u i d e q u i l i b r i u m a p p a r a t u s shown s c h e m a t i c a l l y i n F i g u r e 1 was used f o r t h e v a p o r - l i q u i d e q u i l i b r i u m measurements on N H 3 - H 2 O . The method i n v o l v e s t h e a n a l y s i s o f an e q u i l i b r i u m n i t r o g e n s t r e a m f o r NHU a f t e r e q u i l i b r a t i o n w i t h a N H 3 - H 2 O m i x t u r e c o n t a i n e d i n c y l i n d e r s 1 and 2 o f F i g u r e 1 . The p a r t i a l p r e s s u r e o f N H 3 i s t h e n c a l c u l a t e d f r o m t h e v a p o r mole f r a c t i o n of N H 3 times the t o t a l pressure o f the system. Two c y l i n d e r s were used t o s a t u r a t e t h e n i t r o g e n s t r e a m i n o r d e r t o m i n i m i z e l i q u i d d e p l e t i o n e f f e c t s and t o i n s u r e e q u i l i b r i u m b e tween t h e gas and l i q u i d p h a s e s . Vapor phase a n a l y s e s were made by a b s o r b i n g t h e N H 3 i n t o an aqueous HCI s o l u t i o n w h i c h was s u b s e q u e n t l y t i t r a t e d and by m e a s u r i n g t h e amount o f n i t r o g e n i n t h e sample by use o f a c a l i b r a t e d wet t e s t m e t e r a c c u r a t e t o + 1 % . P r e s s u r e s were measured by means o f c a l i b r a t e d p r e s s u r e gauges a c c u r a t e t o + 0 . 1 % , and t e m p e r a t u r e s were measured by means o f c a l i b r a t e d thermocouples a c c u r a t e to + 0.05°C. The c o m p o s i t i o n o f b o t h t h e v a p o r and t h e l i q u i d s a m p l e s were d e t e r m i n e d by p o t e n t i o m e t r i c t i t r a t i o n by a d d i t i o n o f s t a n d a r d i z e d NaOH s o l u t i o n t o samples which i n i t i a l l y c o n t a i n e d a s l i g h t excess o f HCI. T h i s method worked v e r y w e l l even a t t h e ppm l e v e l s s t u d i e d i n some o f t h e r u n s . The same t i t r a t i n g s o l u t i o n was used f o r a n a l y z i n g b o t h t h e v a p o r and t h e l i q u i d s a m p l e s o f each r u n t h u s m i n i m i z i n g e r r o r s p r o d u c e d i n s t a n d a r d i z i n g t h e NaOH s o l u t i o n . F i g u r e 2 g i v e s a s c h e m a t i c o f t h e a p p a r a t u s used f o r pH measurements a t 25 and 8 0 ° C . It consisted o f a stoppered Erlenmeyer f l a s k submerged i n a t e m p e r a t u r e b a t h r e g u l a t e d a t e i t h e r 25 o r 8 0 ° C . The c o n t e n t s o f t h e f l a s k were s t i r r e d by means o f a m a g n e t i c s t i r r e r c o u p l e d t o a m o t o r b e n e a t h t h e b a t h . A pH p r o b e and t h e r m o m e t e r were i n s e r t e d t h r o u g h t h e s t o p p e r a t t h e t o p o f t h e f l a s k and a n o t h e r h o l e was s t o p p e r e d f o r use i n p i p e t i n g s o l u t i o n i n t o or out o f the f l a s k . Measurements were made by f i r s t c a l i b r a t i n g t h e pH p r o b e u s i n g two b u f f e r s o l u t i o n s a t p H ' s o f 7 and 10 s u p p l i e d by Van Labs o f Van W a t e r s and Rogers Equipment Company . These s o l u t i o n s have been c e r t i f i e d by t h e N a t i o n a l B u r e a u o f S t a n d a r d s t o be a c c u r a t e t o + 0.01 pH u n i t a t 2 5 ° C . T h i s pH c a l i b r a t i o n was made w i t h t h e p r o b e i n s e r t e d i n b u f f e r s o l u t i o n a t t h e same t e m p e r a t u r e as t h e pH measurements were made. A f t e r c a l i b r a t i o n t h e p r o b e was i n s e r t e d i n t o t h e f l a s k shown i n F i g u r e 2 . A concentrated s o l u t i o n of NH3-H2S-CO0-H2O o f measured d e n s i t y was t h e n p i p e t e d i n t o t h e f l a s k and a f t e r t e m p e r a t u r e and pH e q u i l i b r a t i o n t h e pH was r e a d . This normally took a period of f i v e minutes f o r the e q u i l i b r a t i o n process. A f t e r r e a d i n g t h e p H , t h e s o l u t i o n was d i l u t e d w i t h w a t e r by f i r s t r e m o v i n g by p i p e t a p o r t i o n o f t h e s o l u t i o n i n t h e f l a s k and by s u b s e q u e n t a d d i t i o n o f w a t e r t o r e p l a c e t h e s o l u t i o n
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Figure L
3
2
Schematicflowapparatus used for NH -H 0 rium measurements
(and electrolyte) vapor-liquid equilib-
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oo VO
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Figure 2. Schematic of apparatus used for pH (or NH
3
probe) measurements
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9.
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AL.
191
removed. B o i l e d d i s t i l l e d w a t e r was used f o r b o t h t h e s o l u t i o n p r e p a r a t i o n and d i l u t i o n s t a g e s o f t h e e x p e r i m e n t . A f t e r each d i l u t i o n , t h e pH was a g a i n r e a d . The c o n c e n t r a t e d s o l u t i o n s were p r e p a r e d by b u b b l i n g a c i d gas i n t o a s o l u t i o n o f ammonia and w a t e r . No gas was a l l o w e d t o e s c a p e so t h a t t h e i n c r e a s e i n t h e w e i g h t o f t h e s o l u t i o n r e p r e s e n t e d t h e amount o f HoS o r C 0 a d d e d . No p r o b l e m s were e n c o u n t e r e d when a d d i n g H^S by t h i s m e t h o d , but C 0 i s a b s o r b e d v e r y s l o w l y and l o n g p e r i o d s o f a g i t a t i o n o f t h e s o l u t i o n i n c o n t a c t w i t h gaseous C 0 were n e c e s s a r y t o a c h i e v e t h e d e s i r e d l e v e l s . A t t h e h i g h e r l o a d i n g s o f a c i d gas t o ammonia, p r o b l e m s were e n c o u n t e r e d when t h e s e s o l u t i o n s were h e a t e d t o 80°C b e c a u s e t h e a b s o r b e d gases t e n d e d t o be d r i v e n o f f . T h i s p r o b l e m was s o l v e d by c o n n e c t i n g t h e a b s o r p t i o n t r a i n composed o f d i g l y c o l a m i n e (DGA) on sand shown i n F i g u r e 2 . By t h i s m e t h o d , any components d i s c h a r g e d from t h e c e l l were a b s o r b e d i n t h e s e s c r u b b e r t u b e s . The t u b e s were t h e n weighed and a c o r r e c t i o n was made i n t h e c o m p o s i t i o n o f the s o l u t i o n i n the Erlenmeyer f l a s k . Some p r o b l e m s were e n c o u n t e r e d w i t h t h e pH p r o b e s used i n t h e pH measurements because t h e r e f e r e n c e e l e c t r o d e i s s a t u r a t e d with AgCl. Hydrogen s u l f i d e can r e a c t w i t h t h e AgCl i n s o l u t i o n , t h u s p r e c i p i t a t i n g AgS a t t h e KCl j u n c t i o n between t h e r e f e r e n c e e l e c t r o d e and t h e s o l u t i o n . In t h i s r e g a r d i t was f o u n d t h a t c e r t a i n p r o b e s work b e t t e r t h a n o t h e r s . Our o b s e r v a t i o n s a r e as follows. 2
2
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2
1.
Some r e f e r e n c e e l e c t r o d e s have an e x p o s e d f i l l i n g h o l e f o r a d d i n g A g C l - s a t u r a t e d K C l . The h o l e i s l o c a t e d on t h e s i d e o f t h e probe where H S can r e a d i l y e n t e r and contaminate the s o l u t i o n . These e l e c t r o d e s p r o v e d entirely unsatisfactory. Some e l e c t r o d e s have t h e KCl s o l u t i o n i n a g e l f o r m . These e l e c t r o d e s work f a i r l y w e l l but e v e n t u a l l y t h e g e l becomes c o n t a m i n a t e d w i t h s i l v e r s u l f i d e and t h e p r o b e must be r e p l a c e d . T h i s t y p e o f p r o b e was used f o r t h e measurements g i v e n i n t h i s r e p o r t . Two p r o b e s were a c t u a l l y used f o r t h e e n t i r e s e t o f m e a s u r e m e n t s . T h e r e a r e a l s o e l e c t r o d e s a v a i l a b l e w h i c h have a g r o u n d g l a s s j u n c t i o n between t h e r e f e r e n c e e l e c t r o d e and t h e s o l u t i o n b e i n g m e a s u r e d . These p r o b e s w o u l d p r o b a b l y be most s u i t a b l e b e c a u s e t h e y can be d i s m a n t l e d and cleaned. A probe a r r i v e d as o u r measurements were b e i n g c o m p l e t e d so t h i s t y p e o f p r o b e has not y e t been t e s t e d i n our l a b o r a t o r y . 2
2.
3.
The e f f e c t s o f sodium a c e t a t e and sodium h y d r o x i d e on NH3 v o l a t i l i t y a t 80°C were s t u d i e d by two m e t h o d s . Data on t h e e f f e c t o f sodium a c e t a t e were measured i n t h e same a p p a r a t u s used t o measure t h e NH3-H0O d a t a shown i n F i g u r e 1. In t h i s c a s e , sodium a c e t a t e was a l s o added t o t h e l i q u i d phase w i t h s u b s e q u e n t
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
192
THERMODYNAMICS
OF
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
N H 3 p a r t i a l p r e s s u r e measurements made i n t h e same manner used f o r the N H 3 - H 2 O measurements. Data on t h e e f f e c t o f sodium h y d r o x i d e were measured by means o f an N H 3 probe s u p p l i e d by O r i o n R e s e a r c h Company w h i c h o p e r a t e s i n a manner a n a l o g o u s t o a pH p r o b e e x c e p t t h a t a mem b r a n e i s used t h r o u g h w h i c h o n l y t h e N H 3 p e r m e a t e s . Thus t h e response o f the probe i s p r o p o r t i o n a l t o t h e a c t i v i t y (or p a r t i a l p r e s s u r e ) o f ammonia. E . m . f . d a t a on t h e e f f e c t o f sodium h y d r o x i d e were c o n v e r t e d t o ammonia p a r t i a l p r e s s u r e d a t a u s i n g t h e f o l l o w i n g e q u a t i o n . mv - m v
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% 3
=
where f
f
NH 3
f
ref
m v
r
5
=
f
u
9
a
c
i
t
y
·
1
(
= f u g a c i t y o f NH
N H 3
N H 3 *
F
1 0
r e f
°f
N
H
3
1
)
3
Ί
'
η
a
reference solution of
NH^-H 0 2
e . m . f . o u t p u t o f NFL e l e c t r o d e i n m i l l i v o l t s mv ^ u . .4-t p » .u.4-t o ~ -Γ ef.= o f NM Hi 3l e_ 1l e c tX.r .o—d eI « i *_ n tΛ-h Ue ~ r e f e-C~w.~ r e n c e ~ s o l"Iu. t i o n βΤ = m i l l i v o l t s p e r d e c a d e , a t 80°C Τ = 70.1 mv/decade
A t l o w p r e s s u r e s t h e f u g a c i t y o f a component can be r e p l a c e d by i t s p a r t i a l p r e s s u r e so t h a t E q u a t i o n 1 can be a p p r o x i m a t e d as follows. mv - mv
ref.
N H - NH3f* (2) One p r o b l e m e n c o u n t e r e d w i t h t h e N H p r o b e was t h a t i t s c a l i b r a t i o n d r i f t e d w i t h t i m e , thus r e q u i r i n g frequent r e c a l i b r a t i o n of the probe. For t h i s r e a s o n t h e p r o b e was abandoned when t h e measurements w i t h sodium a c e t a t e were made. P
3
P
1 0
T
3
Measurement
Results
Vapor-Liquid E q u i l i b r i u m Data. Vapor-liquid equilibrium measurements on N H - H 0 m i x t u r e s a t 80 and 120°C a r e summarized i n T a b l e s 1 and 2 , r e s p e c t i v e l y . A t each c o n d i t i o n , s e v e r a l v a p o r and l i q u i d s a m p l e s were removed f o r a n a l y s i s b e f o r e p r o ceeding to the next c o n d i t i o n . These t a b l e s summarize t h e a n a l y s e s o f t h e s e s a m p l e s a t each c o n d i t i o n and t h e n g i v e an a v e r a g e v a l u e f o r each r u n c o n d i t i o n . The c h a r g e a n a l y s e s a r e based on a n a l y s e s o f t h e s o l u t i o n c h a r g e d t o t h e measurement a p p a r a t u s a t t h e b e g i n n i n g o f each run and l i q u i d a n a l y s e s a r e based on sam p l e s removed from t h e a p p a r a t u s d u r i n g t h e r u n . A c o m p a r i s o n o f t h e s e a n a l y s e s shows t h a t t h e l i q u i d a n a l y s e s a r e a l l s l i g h t l y l o w e r t h a n t h e c h a r g e a n a l y s i s and t h a t t h e l i q u i d a n a l y s e s d e c r e a s e s l i g h t l y w i t h each s a m p l e . T h i s e f f e c t i s due t o l o s s o f ammonia t o t h e v a p o r phase i n s a m p l i n g t h e v a p o r and t h u s 3
2
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
WILSON
ET
TABLE 1.
Ammonia-Water Vapor-Liquid E q u i l i b r i u m Measurements a t 80°C by Flow C e l l Method
wt % NH, in in liquid charge
1.39 1.40 1.37 1.39
1.24 1.25 1.22 1.24
1.240 1.250 1.247 1.246
6.80 6.80 6.80 6.80
8.04 8.05 8.05 8.05
1.25 1.28 1.31 1.28
1.23 1.26 1.29 1.26
.122 .119 .119 .120
6.86 6.86 6.86 6.86
6.98 6.98 6.98 6.98
1.23 1.21 1.23 1.23
1.25 1.23 1.25 1.25
99.2 ppm 97.7 96.0 94.3 96.8
.0111 .0113 .0112 .0110 .0112
6.87 6.87 6.87 6.87 6.87
6.88 6.88 6.88 6.88 6.88
1.12 1.16 1.17 1.17 1.16
1.18 1.22 1.23 1.23 1.22
10.08 ppm 10.04 9.93 10.02
.00108 .00108 .00107 .00108
6.87 6.87 6.87 6.87
6.87 6.87 6.87 6.87
1.07 1.08 1.08 1.08
1.26 1.27 1.27 1.27
average
.0991 .0983 .0965 .0980
.0993
average
10.09 ppm
average
3
b
—3
13.39 13.37 13.16 13.31
.994 .974 .950 .973
average
Total V o l a t i l i t y Ratio Pressure, PNH /wt % . Uncorr. Corr. > psi a
6.51 6.51 6.51 6.51
1.000
100.0 ppm
Partial Pressure, psia
6.88 6.86 6.65 6.80
4.94 4.90 4.86 4.90
4.97
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^Actual measurements were made under nitrogen pressure according to conditions summarized i n Table 4. The p a r t i a l pressure o f water as given here i s based on Raoult's Law which applies a t the low NHo concentrations given here. By t h i s method the p a r t i a l pressure of water i s given as f o l l o w s . P
P
X
H 0 " H 0 H 0' 2
2
P° Q = vapor pressure of pure water
2
x
u
n
= water mole f r a c t i o n
in liquid
The vapor pressure o f water was taken from the CRC Handbook, 52nd Ed., page D-147. b)See t e x t f o r c o r r e c t i o n s applied.
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
194
THERMODYNAMICS
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TABLE 2.
OF
AQUEOUS
3
average
average 9.83 ppm
Partial Pressure, p s i a % \ -
Total V o l a t i l i t y Ratio Pressure, ^NHo/wt % psia Uncorr. Corr. 4..00 4..02 4..09 4,.04
3.81 3.83 3.89 3.85
28.52 28.53 28.54 28.53
32.1 32.1 32.1 32.1
3,.99 4,.03 4,.09 4..04
3.97 4.01 4.07 4.02
.342 .341 .329 .315 .332
28.77 28.77 28.77 28.77 28.77
29.1 29.1 29.1 29.1 29.1
3,.64 3..73 3,.75 3..75 3..72
3.69 3.78 3.80 3.80 3.77
92.2 ppm 90.0 87.8 84.8 88.7
.0332 .0332 .0326 .0317 .0327
28.79 28.79 28.79 28.79 28.79
28.8 28.8 28.8 28.8 28.8
3.,60 3..69 3.,71 3..74 3..69
3.77 3.86 3.88 3.91 3.86
9.72 ppm 9.44 9.12 . 9.43
.00358 .00368 .00367 .00364
28.80 28.80 28.80 28.80
28.8 28.8 28.8 28.8
3.,68 3. 90 4.,02 3.,86
4.24) 4.49(appear 4.63( high 4.45)
.0940 .0914 .0878 .0840 .0893
93.4 ppm
APPLICATIONS
46.4 45.9 45.6 46.0
.0955
average
INDUSTRIAL
27.35 27.39 27.44 27.39
.900 .880 .850 .877
.0898 .0856
average .
4.75 4.60 4.45 4.60
.905 .889 .867 average ,
WITH
Ammonia-Water Vapor-Liquid E q u i l i b r i u m Measurements a t 120°C by Flow Cell Method
wt % NH in in charge liquid 4.83 4.68
SYSTEMS
19.0 18.5 18.2 18.6 3.59 3.55 3.48 3.54
See footnote'a" at the bottom of Table 2. See t e x t f o r c o r r e c t i o n s applied.
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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AL.
195
r e p r e s e n t s s l i g h t d e p l e t i o n o f t h e l i q u i d w i t h each v a p o r s a m p l e . The l i q u i d a n a l y s e s i n t h e s e t a b l e s a r e a v e r a g e s o f a n a l y s e s made b e f o r e and a f t e r s a m p l i n g t h e v a p o r so t h e c o n c e n t r a t i o n s g i v e n r e p r e s e n t t h e a v e r a g e l i q u i d c o m p o s i t i o n d u r i n g t h e v a p o r sam pling process. The ammonia p a r t i a l p r e s s u r e s g i v e n i n T a b l e s 1 and 2 a r e based on t h e c o n c e n t r a t i o n o f ammonia f o u n d i n t h e v a p o r s t r e a m times the t o t a l pressure. The a c t u a l p r e s s u r e s a p p l i e d a t each run c o n d i t i o n a r e summarized i n T a b l e 3 where t h e p r e s s u r e s v a r i e d f r o m 15 p s i a a t 80°C t o 90 p s i a a t 120°C. B e c a u s e n i t r o gen was used as a p r e s s u r i z i n g f l u i d , t h e p a r t i a l p r e s s u r e o f w a t e r and t h e t o t a l p r e s s u r e e x c l u d i n g n i t r o g e n have been compu t e d i n T a b l e s 1 and 2 based on R a o u l f s l a w f o r w a t e r as n o t e d a t t h e b o t t o m o f T a b l e 1. R a o u l t ' s law a p p l i e s f o r the p a r t i a l p r e s s u r e o f w a t e r because t h e a c t i v i t y c o e f f i c i e n t o f w a t e r i s v i r t u a l l y u n i t y a t t h e l o w l e v e l s o f ammonia used i n t h e l i q u i d phase. M i n o r e f f e c t s due t o v a p o r non- i d e a l i t y have n o t been applied. The l a s t two columns o f T a b l e s 1 and 2 g i v e e q u i l i b r i u m v o l a t i l i t y r a t i o s o f ammonia p a r t i a l p r e s s u r e d i v i d e d by t h e w e i g h t p e r c e n t o f ammonia i n t h e l i q u i d p h a s e . The column l a beled " U n c o r r . " gives the v o l a t i l i t y r a t i o computed s i m p l y as t h e p a r t i a l p r e s s u r e o f ammonia d i v i d e d by t h e t o t a l w e i g h t p e r c e n t o f ammonia i n s o l u t i o n . The s e c o n d column g i v e s a c o r r e c t e d v o l a t i l i t y r a t i o based on t h e d i s s o c i a t i o n o f ammonia a t l o w c o n c e n t r a t i o n s and e x t r a p o l a t i o n t o z e r o c o n c e n t r a t i o n o f ammonia. The d i s s o c i a t i o n c o r r e c t i o n was a p p l i e d by d i v i d i n g t h e u n c o r r e c t e d v o l a t i l i t y r a t i o by t h e computed r a t i o o f f r e e ammonia o v e r t o t a l ammonia i n s o l u t i o n . The r a t i o o f f r e e ammonia o v e r t o t a l ammonia was computed from t h e d i s s o c i a t i o n c o n s t a n t o f ammonia g i v e n by Edwards and P r a u s n i t z (]_) as f o l l o w s . NH 0H-^NH 4
Temperature
4
+
+ OFT
°C
Dissociation
25 80 120
Constant
1.78 χ 1 0 ~ 1 .66 χ Ι Ο " 1 .19 χ 1 0 " 5
5
5
W i t h no o t h e r i o n s p r e s e n t t h e c o n c e n t r a t i o n o f f r e e ammonia o v e r t o t a l ammonia p r e s e n t i s g i v e n by t h e f o l l o w i n g e q u a t i o n : (NH*)-
0 1
( 3)total where k = d i s s o c i a t i o n c o n s t a n t o f NFL C = t o t a l c o n c e n t r a t i o n o f NHg m o l e s / K g w a t e r N H
4 C
In a d d i t i o n t o t h i s c o r r e c t i o n t h e v o l a t i l i t y r a t i o o f ammonia
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
196
THERMODYNAMICS
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TABLE 3.
Temp. °C
80
OF
AQUEOUS
WITH
INDUSTRIAL
APPLICATIONS
Measurement Pressures f o r Ammonia-Water Vapor-Liquid E q u i l i b r i u m Runs
NH wt j
NaAc wt %
q
5
0
1
Measurement Pressure with Ν 2 psia
30
0
20
.1
0
15
100 ppm
0
15
10 ppm
0
15
25
20
1
15
20
1
5
20
5
0
90
1
0
60
.1
0
60
100 ppm
0
60
10 ppm
0
60
1 wt
120
SYSTEMS
%
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
197
Sour Water Equilibria
WILSON E T A L .
v a r i e s due t o t h e s o l v e n t e f f e c t o f f r e e ammonia a c c o r d i n g t o t h e f o l l o w i n g equation given in Table 1 of reference 2. 1n(H
N H 3
)
- ln(H^
H 3
)
+
fiC
N
H
(4)
3
where H ° = v o l a t i l i t y r a t i o a t z e r o c o n c e n t r a t i o n o f f r e e ammonia CJS^HO e f f e c t o f f r e e ammonia on t h e v o l a t i l i t y 3 = t e m p e r a t u r e d e p e n d e n t c o n s t a n t ; β = 131.4/T°R - .1682 =
CNH3
=
c
o
n
c
e
n
t
r
a
t
Solving for ln(HNH ) 3
1Π(ΗΝΗ )
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R
NH
H
=
3
H
o
NH
3
E
X
P
°^
n
f
r
e
e
a m m o n l
" »
moles/Kg water
a
gives the f o l l o w i n g equation.
= ln(H
3
O
l
N H 3
)
- 3 C
N
H
(5)
3
(^ NH ) C
(
3
E q u a t i o n s 2 and 5 can be combined t o g i v e a t o t a l follows. /
6
)
c o r r e c t i o n as
P u \° (P /wt % N F L ) exp(-BC ) 3 j = H Uncorr. 3 (7) Iwt % N H I . p^jr JTlNfT Π ' free total Thus t h e l a s t column i n T a b l e s 1 and 2 c o r r e s p o n d s t o t h e v o l a t i l i t y r a t i o o f ammonia based on f r e e ammonia and e x t r a p o l a t e d t o z e r o c o n c e n t r a t i o n o f f r e e ammonia. T h i s number s h o u l d be i n d e pendent o f t h e c o n c e n t r a t i o n s s t u d i e d a t a g i v e n t e m p e r a t u r e , and any v a r i a t i o n r e p r e s e n t s e r r o r s i n e i t h e r t h e measured d a t a o r i n t h e a p p l i e d c o r r e c t i o n s . The f o l l o w i n g i s a c o m p a r i s o n o f t h e a v e r a g e s f r o m each r u n . M U
N
N H
N
3
C
o
r
M U
3
3
N H
r
J
NH Concentration 3
5 wt % 1 wt % .1 wt % 100 ppm 10 ppm A v e r a g e ( E x c l u d i n g 10 ppm p o i n t a t 120°C)
(P u N
m
3 80°C
3
/wt % ) ° Corr. 120°C
1.24 1 .26 1.25 1 .22 1.27
3.85 4.02 3.77 3.86 4.45
1 .25 + 2%
3 . 8 8 + 4%
(appears
high)
T h i s agreement i s c o n s i d e r e d t o be q u i t e good when a l l o w a n c e i s made f o r t h e f a c t t h a t t h e s e a r e i n d e p e n d e n t l y measured r u n s a t c o n c e n t r a t i o n s v a r y i n g by a r a t i o o f 5000 t o 1! The 10 ppm r u n a t 120°C i s p r o b a b l y i n e r r o r due t o a t r a c e c o n t a m i n a n t i n t h e vapor samples observed i n t h e p o t e n t i o m e t r i c t i t r a t i o n c u r v e . T h i s p r o b l e m was n o t o b s e r v e d a t 8 0 ° C . The f a v o r a b l e c o m p a r i s o n g i v e n above shows t h a t t h e ammonia
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
198
THERMODYNAMICS
O F AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
v o l a t i l i t y r a t i o can be r e l i a b l y e x t r a p o l a t e d t o l o w c o n c e n t r a tions without loss o f accuracy. T h i s i s i m p o r t a n t because t h e b u l k o f p u b l i s h e d l i t e r a t u r e d a t a on t h e v o l a t i l i t y o f ammonia a r e a t c o n c e n t r a t i o n s o f λ% NhL o r h i g h e r . A c o m p a r i s o n o f t h i s new v o l a t i l i t y r a t i o w i t h measured l i t e r a t u r e d a t a i s g i v e n i n F i g u r e 3 where d e v i a t i o n r a t i o s o f N H 3 ( m e a s ) / 3 ( c a l c ) a r e p l o t t e d v e r s u s t e m p e r a t u r e where com p a r i s o n i s made w i t h t h e SWEQ c a l c u l a t i o n model o f r e f e r e n c e 2 . T h i s p l o t shows t h a t t h e s e new d a t a a r e i n f a i r agreement w i t h t h e c a l c u l a t e d v a l u e s w i t h r a t i o s o f a b o u t 1.05 a t b o t h 80 and 120°C. F o r t u n a t e l y f o r the authors these data a l s o agree q u i t e w e l l w i t h p r e v i o u s l y measured d a t a r e p o r t e d by M i l e s and W i l s o n P
PNH
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(3). In summary t h e f o l l o w i n g can be c o n c l u d e d from t h e g i v e n i n T a b l e s 1 and 2 . 1.
2.
data
The v o l a t i l i t y o f ammonia a t ppm l e v e l s can be c a l c u l a t e d from t h e i o n i z a t i o n c o n s t a n t o f ammonia combined w i t h v o l a t i l i t y d a t a measured a t h i g h e r c o n c e n t r a t i o n s o f ammonia. The v o l a t i l i t y o f ammonia a t 80 and 1 2 0 ° C i s a b o u t 5% h i g h e r t h a n i s now p r e d i c t e d by t h e SWEQ m o d e l . This means t h a t t h e SWEQ model w i l l p r e d i c t s l i g h t l y more steam f o r a g i v e n s e p a r a t i o n , a l l o t h e r e f f e c t s b e i n g e q u a l , t h a n w i l l a c t u a l l y be r e q u i r e d .
pH o f NH3-H2S-CO2-H2O M i x t u r e s . pH measurements on NHo- H SCO2-H0O m i x t u r e s have been made a t 2 5 ° C and 8 0 ° C a s o u t l i n e d i n P a r t Β o f t h e Measurement P r o g r a m . The r e s u l t s o f t h e s e m e a s u r e ments a r e g i v e n i n T a b l e s 4 t o 2 2 . Each t a b l e g i v e s t h e c o m p o s i t i o n o f each s o l u t i o n a t v a r i o u s d i l u t i o n s and measured and c o r r e l a t e d pH d a t a a t each c o m p o s i t i o n . The SWEQ c o m p u t e r program ( 2 j does n o t a c c u r a t e l y p r e d i c t t h e s e pH d a t a , so an e m p i r i c a l c o r r e l a t i o n o f t h e d a t a was made i n o r d e r t o g i v e c o m p a r i s o n s between t h e d a t a and a s m o o t h i n g f u n c t i o n . T h i s s m o o t h i n g f u n c t i o n i s based on t h e f o l l o w i n g e q u i l i b r i u m w h i c h i s assumed t o be a f u n c t i o n o f t h e c o n c e n t r a t i o n o f t h e components i n s o l u t i o n . 2
NH3 + H ~ > N H +
4
(8)
+
(9) In E q u a t i o n 9, t h e hydrogen i o n c o n c e n t r a t i o n i s g i v e n by t h e pH m e a s u r e m e n t s ; and t h e r a t i o o f N r ^ / N H ^ can be a p p r o x i m a t e d from t h e m o l e s o f a c i d gas per mole o f NH3 a s s u m i n g a l l o f t h e a c i d gas r e a c t s a s f o l l o w s . NH
3
+ HA — > N H
4
+
+A"
,
A ' = HCO3
o
r H S
~
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
(10)
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9.
WILSON
ET AL.
20
30
199
Sour Water Equilibria
40
50
70
80
Ί00 110 120 130 140 150
Temperature, °C Figure 3. Ammonia mean ratio of measured over calculated partial pressures based on SWEQ correlation (®) new data; see Figure 2 of Réf. 1 for the following: (O) Miles & Wilson; Ο Clifford; (A) Van Krevelen NH -C0 ; (V) Cardon & Wilson; Badger & Silver; ( 0 ) Breitenback & Perman) 3
2
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
200
THERMODYNAMICS
OF
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
TABLE 4.
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of Water-Ammonia Mixtures with no Acid Gas Present, 25°C
Ratio 3
Ammonia ^ wt %
NH3/NH4
(SWEQ)
Meas.
PH Correl.
Diff.
2.82
9.491
9.606
-.115
.00308
5.19
9.807
9.875
-.068
.00925
9.34
10.123
10.137
-.014
.00103
.0277
16.5
10.369
10.397
-.028
.111
33.4
10.726
10.733
-.007
.335
58.6
11.014
11.021
-.007
1.01
102
11.283
11.337
-.054
3.05
177
11.597
11.709
-.112
6.17
254
11.883
11.997
-.114
8.30
293
12.066
12.130
-.064
11.21
339
12.272
12.276
-.004
15.20
391
12.588
12.436
.152
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
WILSON
ET AL.
201
Sour Water Equilibria
TABLE 5. Measured and Correlated pH o f Water-Ammonia Mixtures with 0.253 Mole of H S/Mole o f NhU 25°C 9
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ù
0
Ammonia ^ wt %
HS> wt %
Ratio NH /NH (SWEQ)
Meas.
PH Correl.
Diff.
.00135
.00068
1.69
9.303
9.385
-.082
.00404
.00205
2.26
9.414
9.517
-.103
.0121
.00612
2.66
9.495
9.604
-.109
.0364
.0184
2.85
9.567
9.643
-.076
.109
.0552
2.91
9.669
9.680
-.011
.328
.166
2.94
9.772
9.732
.040
.985
.499
2.95
9.896
9.818
.078
3
a
2
+
3
4
2.96
1.50
2.95
9.996
9.963
.033
5.97
3.02
2.96
10.083
10.108
-.025
8.90
4.50
2.96
10.155
10.216
-.061
10.50
5.31
2.96
10.196
10.267
-.071
14.11
7.14
2.96
10.230
10.370
-.140
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
202
THERMODYNAMICS
OF
TABLE 6.
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of Water-Ammonia Mixtures with 0.491 Mole of H-S/Mole of NH 25°C
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?
Ratio 3
Ammonia ^ wt %
H S wt %
a )
2
Meas.
PH Correl.
Diff.
9.040
9.143
-.103
NH3/NH4
(SWEQ)
.00407
.00400
.0122
.0120
1.01
9.080
9.178
-.098
.0366
.0359
1.03
9.174
9.204
-.030
.110
.108
1.04
9.290
9.239
.051
.330
.324
1.04
9.405
9.292
.113
.952
1.04
9.497
9.383
.114
2.97
2.91
1.05
9.599
9.546
.053
5.94
5.83
1.04
9.649
9.697
-.048
9.92
9.73
1.04
9.758
9.852
-.094
13.23
12.98
1.04
9.734
9.958
-.224
.990
.971
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
WILSON
ET
AL.
203
Sour Water Equilibria
TABLE 7.
Measured and Correlated pH of WaterAmmonia Mixtures with 0.251 Mole of C0 / Mole o f NH , 25°C ?
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
3
aï Ammonia wt %
a) C0 wt %
.00180
Ratio (SWEQ)
Meas.
PH Correl.
Diff.
.00117
1.66
9.343
9.379
-.036
.00457
.00296
1.93
9.438
9.461
-.023
.0116
.00750
2.18
9.463
9.512
-.049
.0295
.0191
2.27
9.509
9.543
-.034
.0748
.0485
2.29
9.573
9.569
.004
.190
.123
2.29
9.606
9.605
.001
.481
.312
2.25
9.644
9.653
-.009
.791
a;
1.22
a ;
2
NH3/NH4
2.19
9.735
9.731
.004
1.75
1.13
2.17
9.768
9.775
-.007
5.72
3.71
2.07
10.005
9.988
.017
7.60
4.92
2.06
10.095
10.065
.030
10.1
6.53
2.04
10.210
10.153
.057
13.4
8.65
2.03
10.379
10.256
.123
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
204
THERMODYNAMICS
OF
TABLE 8.
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of WaterAmmonia Mixtures with 0.520 Mole of C0 / Mole o f NH , 25°C ?
3
3
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
Ammonia ^ wt %
a )
C0 wt % 2
Ratio NH /NH (SWEQ) 3
+
Meas.
PH Correl.
Diff.
4
.000297
.000400
.452
8.579
8.810
-.231
.000754
.00102
.592
8.789
8.929
-.140
.00191
8.951
9.003
-.052
.00257
.695
.00486
.00654
.746
9.028
9.040
-.012
.0123
.0166
.761
9.074
9.060
.014
.0313
.0421
.768
9.096
9.080
.016
.0794
.107
.748
9.105
9.096
.009
.201
.271
.704
9.127
9.112
.015
.661
.890
.597
9.138
9.133
.005
.507
9.162
9.146
.016
1.31
1.77
1.74
2.35
.466
9.163
9.154
.009
2.31
3.11
.428
9.176
9.168
.008
3.06
4.12
.388
9.189
9.184
.005
4.04
5.44
.349
9.210
9.204
.006
5.32
7.16
.314
9.240
9.233
.007
6.97
9.38
.280
9.277
9.268
.009
9.10
12.25
.248
9.329
9.311
.018
11.81
15.89
.220
9.430
9.366
.064
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
WILSON
ET
AL.
205
Sour Water Equilibria
TABLE 9.
Measured and Correlated pH of WaterAmmonia Mixtures with .755 Mole of C0«/ Mole o f NH , 25°C
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
3
a) Ammonia* wt %
*) C0 wt %
Ratio ΝΗο/ΝΗλ (SWEQ)
Meas.
PH Correl.
Diff.
.00238
.00463
.278
8.629
8.608
.021
.00579
.0113
.283
8.679
8.623
.056
.0141
.0274
.289
8.709
8.644
.065
.0342
.0664
.285
8.716
8.657
.059
.0828
.161
.271
8.725
8.664
.061
.201
.391
.244
8.718
8.664
.054
.486
;
;
2
.201
8.698
8.650
.048
1..17
2..27
.145
8.641
8.616
.025
2..31
4..49
.0990
8.577
8.574
.003
4..50
8..74
.0632
8.500
8.549
-.049
5..90
11..46
.0513
8.472
8.545
-.073
.944
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
206
THERMODYNAMICS
OF AQUEOUS
TABLE 10.
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of WaterAmmonia Mixtures with 0.886 Mole of C0 / Mole o f NH , 25°C ?
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
3
3
Ammonia ^ wt %
a )
C0 wt % 2
Ratio NH /NH (SWEQ) 3
Meas.
PH Correl.
Diff.
+
4
.000902
.00207
.110
8.265
8.200
.065
.00219
.00501
.119
8.345
8.239
.106
.00532
.0122
.119
8.393
8.247
.146
.0129
.0295
.122
8.400
8.270
.130
.0314
.0719
.118
8.391
8.274
.117
.0761
.174
.113
8.400
8.285
.115
.185
.423
.0996
8.382
8.276
.106
1.02
.0789
8.335
8.245
.090
1.07
2.46
.0521
8.233
8.174
.059
2.11
4.83
.0346
8.131
8.120
.011
2.78
6.37
.0281
8.084
8.093
-.009
.446
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
WILSON
ET
207
Sour Water Equilibria
AL.
TABLE 11. Measured and Correlated pH of WaterAmmonia Mixtures with .124 Mole of C0 and .124 Mole o f H S per Mole of NhL, 25°C
2
?
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
ά
Ratio Ammonia ^ wt %
co wt %
H S wt %
0.00298
0..000954
0.000737
0.00724
0,.00232
0.00179
0.0176
0.,00563
0.0427
3
2
a )
a )
2
N H
3
/ N H /
PH
Meas.
Correl.
Diff.
2.003
9,.248
9.463
-0.215
2.311
9,.435
9.531
-0.096
0.0435
2.494
9,.489
9.574
-0.085
0.,0137
0.0106
2.568
9..476
9.601
-0.125
0.104
0.,0332
0.0256
2.623
9.,546
9.634
-0.088
0.252
0.,0806
0.0623
2.622
9.,631
9.670
-0.039
0.612
0.,196
0.151
2.613
9.,733
9.724
0.009
1.49
0.476
0.367
2.603
9.,845
9.811
0.034
3.61
1. 16
0.893
2.562
9. 975
9.941
0.034
7.24
2.32
1.79
2.556
10. 116
10.100
0.016
9.67
3.09
2.39
2.560
10. 194
10.185
0.009
4. 13
3.19
2.554
10. 298
10.281
0.017
12.91
(SWEQ)
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
208
THERMODYNAMICS
OF
TABLE 12.
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
Measured and Correlated pH o f WaterAmmonia Mixtures with .277 Mole of CO. and .277 Mole o f H S per Mole of NH ' 25°C ?
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
APPLICATIONS
V
Ratio Ammonia ^ wt %
co wt %
H S wt %
0.00136
0.000964
3
2
a )
a )
2
NH3/NH4
pH
(SWEQ)
Meas.
Correl.
Diff.
0.000753
0..635
8..576
8. 961
-0. 385
8.,745
9.,011
-0.,266
0.00363
0.00257
0.00201
0..704
0.00967
0.00686
0.00535
0..732
8.,877
9.,036
-0.,159
0.0258
0.0183
0.0143
0.,740
8.,934
9.,055
-0.,121
0.0687
0.0488
0.0382
0.,730
9.,002
9.,072
-0. 070
0.183
0.130
0.102
0. 706
9.,085
9.,095
-0.,010
0.408
0.346
0.271
0.,682
9.,150
9. 127
-0. 023
1.296
0.919
0.720
0.,587
9.,209
9. 177
0.,032
3.422
2.428
1.900
0.,499
9.,293
9. 273
0. 020
6.443
4.571
3.577
0.,447
9. 376
9.388
-0. 012
8.380
6.013
4.653
0.,417
9.,416
9. 443
-0.,027
7.800
6.035
0.,399
9. 479
9. 519
-0. 040
10.87
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
WILSON
ET
209
Sour Water Equilibria
AL.
TABLE 13 .
Measured and Correlated pH of WaterAmmonia Mixtures with 0.375 Mole of H S and 0.372 Mole o f CO? per Mole of NhL, 25°C ?
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
0
Ratio 3
Ammonia ^ wt %
C0o wt %
a)
H S wt %
a )
2
(SWEQ)
Meas.
PH Correl.
Diff.
NH3/NH4
0.00280
0.,00269
0.00210
0.3074
8.542
8.650
-0.108
0.00680
0..00653
0.00509
0.3176
8.598
8.671
-0.073
0.0165
0.,0159
0.0124
0.3155
8.643
8.679
-0.036
0.0401
0.,0385
0.0300
0.3183
8.686
8.700
-0.014
0.0973
0..0934
0.0729
0.3091
8.732
8.714
0.018
0.0236
0..227
0.177
0.2886
8.768
8.647
0.121
0.0572
0..549
0.428
0.2573
8.774
8.617
0.157
1.38
1..33
1.034
0.2055
8.764
8.746
0.018
3.30
3..17
2.47
0.1514
8.740
8.772
-0.032
5.92
5,.69
4.44
0.1145
8.719
8.805
-0.086
7.56
7,.27
5.67
0.1003
8.715
8.827
-0.112
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
210
THERMODYNAMICS
OF
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
TABLE 14.
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of WaterAmmonia Mixtures with No Acid-Gas Present, 80°C
Ratio 3
Ammonia ^ wt % 0.00202
Meas.
PH Correl.
Diff.
8.077
8.138
-.061
NH3/NH4
(SWE0)
4.4484
0.0121
11.565
8.432
8.636
-.204
0.0273
17.572
8.636
8.881
-.245
0.0614
26.638
8.826
9.143
-.317
0.221
51.020
9.156
9.597
-.441
10.127
-.601
0.887
102.43
9.526
1.79
145.48
9.717
10.396
-.679
3.61
208.46
9.865
10.662
-.797
b)
Balance i s water These differences i n d i c a t e that the NH /NH r a t i o from the SWEQ computer program are too high. 3
+ 4
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
9.
WILSON
ET
AL.
Sour Water Equilibria
211
TABLE 15. Measured and Correlated pH o f WaterAmmonia Mixtures with 0.258 Mole o f H?S/ Mole o f N H 80°C V
Ratio 3
Ammonia ^ wt %
H S wt %
a )
2
(SWEQ)
Meas.
PH Correl.
Diff.
NH3/NH4
0.00292
0.00151
2.150
7.805
7.840
-.035
0.00709
0.00366
2.504
7.966
7.950
.016
0.0172
0.00889
2.709
8.057
8.045
.012
0.0418
0.0216
2.818
8.208
8.147
.061
0.102
0.0524
2.869
8.323
8.265
.058
0.246
0.127
2.891
8.470
8.400
.070
0.600
0.309
2.898
8.575
8.550
.025
1.46
0.756
2.894
8.675
8.699
-.024
3.58
1.85
2.891
8.777
8.836
-.059
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
212
THERMODYNAMICS
OF
TABLE 16 .
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of WaterAmmonia Mixtures with 0.480 Mole of H S/ Mole o f N H , 80°C
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
?
3
Ratio 3
Ammonia ^ wt %
H S wt %
a )
(SWEQ)
Meas.
PH Correl.
Diff.
0.00178
.948
7.511
7.472
.039
0.00468
0.00451
1.041
7.618
7.553
.065
0.0119
0.0114
1.085
7.724
7.631
.093
0.0302
0.0291
1.105
7.863
7.722
.141
0.0767
0.0738
1.113
7.952
7.836
.116
0.195
0.187
1.115
8.062
7.975
.087
0.494
0.477
1.111
8.152
8.128
.024
1.26
1.22
1.107
8.235
8.283
-.048
3.21
3.12
1.096
8.324
8.422
-.098
0.00185
N H
2
3
/ N H /
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
9.
WILSON
ET
AL.
213
Sour Water Equilibria
TABLE 17.
Measured and Correlated pH of WaterAmmonia Mixtures with .555 Mole of H S/ Mole of NH , 80°C 2
3
a) Ammonia wt %
d;
a) H S wt %
Ratio
Eb
a ;
2
NH0/NH4
(SWEQ)
Meas.
Correl.
Diff.
.0935
.104
0.8439
7.809
7.750
.059
.187
.208
0.8453
7.853
7.855
-.002
.375
.416
0.8453
7.874
7.970
-.096
0.8453
7.916
8.088
-.172
.752
.834
1.55
1.70
0.8628
7.985
8.215
-.230
3.07
3.89
0.6293
8.094
8.187
-.093
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
214
THERMODYNAMICS
OF
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
TABLE 18.
AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of WaterAmmonia Mixtures with .315 Mole of CO?/ Mole o f NH , 80°C 3
Ratio 3
Ammonia ^ wt %
C0 wt %
3 )
2
(SWEQ)
Meas.
PH Correl.
Diff.
NH3/NH4
0.00175
0.,00142
1,.572
7.,830
7.687
.143
0.00425
0.,00346
1,.845
7.,927
7.792
.135
0.0103
0..00840
2..011
8..048
7.880
.168
0.0878
0,,0714
2..108
8.,272
8.118
.154
0.213
0..173
2,.075
8.,405
8.242
.163
0.515
0..420
1,.989
8..496
8.371
.125
1.25
1..02
1,.853
8.,591
8.491
.100
3.01
2..46
1..665
8..692
8.584
.108
5.98
4..95
1,.487
8..830
8.630
.200
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
9.
WILSON
ET
AL.
Sour Water Equilibria
215
TABLE 19. Measured and Correlated pH of WaterAmmonia Mixture with .429 Mole of CO?/ Mole of N H 80°C V
Ratio 3
Ammonia ^ wt %
co wt % 2
a )
(SWEQ?
Meas.
PH Correl.
Diff.
NH0/NH4
0.00244
0.00269
1.164
7.557
7.571
-.013
0.00548
0.00605
1.260
7.601
7.643
-.042 -.058
0.0123
0.0136
1.309
7.654
7.712
0.0278
0.0306
1.327
7.742
7.789
-.047
0.166
0.183
1.297
7.950
8.011
-.061
0.373
0.412
1.243
8.039
8.125
-.086
1.33
1.46
1.079
8.141
8.282
-.141
2.63
2.96
.908
8.210
8.316
-.106
5.13
6.08
.690
8.308
8.293
.015
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
216
THERMODYNAMICS
OF AQUEOUS
TABLE 20.
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
Measured and Correlated pH of WaterAmmonia Mixtures with .121 Mole of H S and .126 Mole of C0 per Mole of NFU, 80°C
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
?
?
ù
0
Ratio NH3/NH4 (SWEQ)
Meas.
E±L Correl.
Diff.
0.000430
1.962
7.737
7.783
-.046
0.,00131
0.000968
2.051
7.794
7.834
-.041
0.00902
0.,00294
0.00218
2.675
7.816
7.992
-.176
0.0542
0. 0176
0.0131
2.954
8.124
8.196
-.072
0.122
0. 0397
0.0295
2.977
8.264
8.306
-.042
0.275
0.,0895
0.0664
2.967
8.416
8.429
-.013
0.765
0.,252
0.185
2.889
8.609
8.589
.020
2.78
0. 925
0.670
2.740
8.787
8.777
.010
5.70
1.,90
1.39
2.622
8.901
8.858
.043
3
Ammonia ^ wt %
a )
C0 wt %
H S wt %
0.00178
0.000581
0.00401
2
a )
2
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
9.
WILSON
ET
111
Sour Water Equilibria
AL.
TABLE 21 . Measured and Correlated pH of WaterAmmonia Mixtures with .188 Mole of H S and .225 Mole o f CO? per Mole of NH,7 80°C ?
ά
Ratio.
co wt %
HS> wt %
0.00439
0.00236
0.00988
3
Ammonia ^ wt %
6
a
(SWEQ)
Meas.
PH Correl.
Diff.
0.00165
1.481
7.579
7.700
-.120
0.00530
0.00372
1.573
7.607
7.773
-.166
0.0593
0.0318
0.0223
1.635
7.833
7.962
-.129
0.133
0.0716
0.0502
1.643
8.020
8.074
-.054
0.300
0.161
0.113
1.608
8.158
8.193
-.035
1.08
0.581
0.406
1.522
8.336
8.387
-.051
2.16
1.26
0.813
1.214
8.408
8.406
.002
4.33
2.56
1.65
1.097
8.465
8.463
.002
8.68
5.28
3.50
0.933
8.596
8.480
.116
2
a )
2
NH3/NH4
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
218
THERMODYNAMICS
OF AQUEOUS
SYSTEMS
WITH
INDUSTRIAL
APPLICATIONS
TABLE 22 . Measured and Correlated pH o f WaterAmmonia Mixtures with .363 Mole o f H S and .328 Mole of C 0 per Mole of N H L , 80°C ?
o
Ratio co wt %
wt %
(SWEQ)
Meas.
0.988
0.838
0.717
.4244
7.903
7.851
.052
1.97
1.71
1.45
.3584
7.926
7.889
.037
3.92
3.45
2.93
.2903
7.970
7.897
.073
3
Ammonia ^ wt %
2
a )
H
2
S
A
)
N H O / N H /
PH Correl.
Diff
Balance i s water
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
9.
WILSON
ET
free N H 3
"
n
NHt = 4 free
NH
NH NH
4
=
NH
n
NH
3
N
R
(11 )
±™1
α
«
+
- α
3
α
+
= τ .
3
NH
4
3
219
Sour Water Equilibria
AL.
= m o l e s a c i d gas p e r m o l e N H 3
' P
R
N
NH
NH3 (12)
3
T h i s e s t i m a t e d r a t i o can be i m p r o v e d by u s i n g t h e SWEQ c o m p u t e r program w h i c h t a k e s t h e i o n i z a t i o n o f N H i n t o a c c o u n t a t l o w c o n centrations. For example i n T a b l e 5 , E q u a t i o n 12 g i v e s a N H 3 / N H J ratio of 2.95. T h i s a g r e e s w i t h t h e SWEQ program a t h i g h c o n c e n t r a t i o n s , b u t a t l o w c o n c e n t r a t i o n s t h e r a t i o d e c r e a s e s due t o t h e i o n i z a t i o n o f ammonia. In o r d e r t o t a k e t h i s i o n i z a t i o n e f f e c t i n t o a c c o u n t , t h e SWEQ c o m p u t e r program has been used t o c a l c u l a t e t h e N h L / N H ^ r a t i o s i n each t a b l e f o r use i n t h e s m o o t h i n g f u n c t i o n . These c a l c u l a t e d r a t i o s a r e t h e r e f o r e g i v e n i n e a c h t a b l e , and t h e s m o o t h i n g f u n c t i o n now i n v o l v e s a c o r r e l a t i o n o f t h e e q u i l i b r i u m c o n s t a n t g i v e n by E q u a t i o n 9 as a f u n c t i o n o f t h e c o n c e n t r a t i o n s o f t h e c o m p o n e n t s . The r e s u l t i n g equations are the f o l l o w i n g .
Downloaded by UNIV LAVAL on May 26, 2014 | http://pubs.acs.org Publication Date: October 29, 1980 | doi: 10.1021/bk-1980-0133.ch009
3
B\/(1 log
1 0
(k)
where A , B,
= A +
C
+
D>
/(1
+ R)(
wt % N H ) 3
+ R)(wt
% NH )
U
3
3
C, and D = c o n s t a n t s
ΝΤΓ+ + NH P °9 4 3 R = moles a c i d gas/mole NH wt % N H = t o t a l w e i g h t p e r c e n t o f ammonia i n V a l u e s o f t h e p a r a m e t e r s were f o u n d t o be as f o l l o w s . R
=
Η
F
R
O
M
S
W
E
Q
R
R A M
3
3
Temp.
soin.
Parameter
°C
A
25 80
Β
9.15 7.42
C
.178 1.36
1
D 0 1
.9
The f i r s t p a r a m e t e r , A , i s t h e p K o f N H w h i c h c a n be compared w i t h l i t e r a t u r e d a t a ; t h e c o m p a r i s o n i s as f o l l o w s . a
Temp.
3
pJC
°C
Meas.
LU.(2,4)
25 80
9.15 7.42
9.25 7.84
Difference -.10 -.42
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
)
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From t h i s c o m p a r i s o n t h e agreement i s q u i t e good a t 2 5 ° C . A t 80°C t h e agreement i s n o t a s g o o d , but t h e l a r g e r d i f f e r e n c e i s n o t s u r p r i s i n g because b o t h t h e measurements r e p o r t e d h e r e and measurements i n t h e l i t e r a t u r e s u f f e r from measurement p r o b l e m s at higher temperatures. However, i t would be s u r p r i s i n g i f t h e d a t a r e p o r t e d h e r e a r e o f f by 0 . 4 u n i t because NBS recommended b u f f e r s o l u t i o n s a c c u r a t e t o + 0.01 pH u n i t o v e r t h e t e m p e r a t u r e r a n g e t o 80°C were u s e d . I f the data given here are r i g h t , i t p r o b a b l y means t h a t t h e d i s s o c i a t i o n c o n s t a n t o f ammonia a t 80°C i s a b o u t 0 . 6 5 χ 1 0 ~ r a t h e r t h a n 1.66 χ 1 0 " computed from t h e e q u a t i o n o f Edwards and P r a u s n i t z (1_). D i f f e r e n c e s between measured and c o r r e l a t e d pH d a t a a r e g i v e n i n each o f T a b l e s 4 t o 2 2 . No a t t e m p t was made t o do a l e a s t - s q u a r e f i t o f t h e d a t a so i n some c a s e s d e v i a t i o n s between t h e c o r r e l a t i o n and t h e d a t a can be r a t h e r l a r g e w i t h o u t any s i g n i f i c a n t e r r o r i n t h e measured d a t a . N e v e r t h e l e s s , most o f t h e d e v i a t i o n s a r e l e s s t h a n + 0.1 pH u n i t . One e x c e p t i o n i s d a t a i n T a b l e 14 on t h e pH o f NH3-H0O a t 80°C w i t h no a c i d gas p r e s e n t ; i n t h i s c a s e t h e c a l c u l a t e d pH d a t a depend h e a v i l y on t h e NH3/NH4" r a t i o g i v e n by t h e SWEQ m o d e l . D i f f e r e n c e s up t o 0 . 7 9 7 pH u n i t i n d i c a t e t h e m a g n i t u d e o f e r r o r i n t h e SWEQ model a t 8 0 ° C . S i m i l a r d a t a a t 25°C i n T a b l e 3 a r e b e t t e r p r e d i c t e d . The d a t a i n T a b l e s 4 t o 13 a t 25°C p l o t n e a r l y as v e r t i c a l l i n e s i n d e p e n d e n t o f t h e wt % NH3 i n s o l u t i o n e x c e p t f o r pure ammonia. A t low c o n c e n t r a t i o n s t h e curves tend t o d e v i a t e b e c a u s e o f t h e i o n i z a t i o n o f NH3 and w a t e r . I f t h e amount o f am monia i n s o l u t i o n i s a p p r o x i m a t e l y known, t h e s e c u r v e s can be used t o e s t i m a t e t h e m o l e s o f a c i d gas p e r mole o f NH3 w i t h f a i r l y good a c c u r a c y . A t 80°C t h e c u r v e s t e n d t o s l a n t more so t h e amount o f ammonia i n s o l u t i o n w o u l d have t o be known more a c c u r a t e l y b e f o r e an e s t i m a t e o f t h e r a t i o o f a c i d gas t o ammonia c o u l d be made. A l s o we do n o t recommend t h e use o f a pH probe a t 80°C a s a c o n t r o l i n d i c a t o r because t h e r e s p o n s e o f t h e p r o b e i s more e r r a t i c , and p r e c i s e d a t a a r e d i f f i c u l t t o o b t a i n . The use o f an i n d i c a t o r p r o b e a t 25°C seems more l o g i c a l because t h e o u t put i s more s t a b l e . One o b s e r v a t i o n t h a t can be made from t h e pH d a t a i n T a b l e s 4 t o 22 i s t h a t t h e pH a p p e a r s t o be a f f e c t e d a b o u t e q u a l l y by e i t h e r H2S o r CO2. T h i s r e s u l t c a n be seen f r o m an e x a m i n a t i o n o f t h e p l o t s g i v e n i n F i g u r e s 4 and 5. I n t h e s e f i g u r e s t h e pH i s p l o t t e d v e r s u s t h e m o l e s o f a c i d gas per mole o f NH3 a t a f i x e d c o n c e n t r a t i o n o f 1.0 wt % NH3. The c u r v e s i n F i g u r e 4 c o r r e s p o n d t o r e s u l t s a t 2 5 ° C , and t h e p l o t i n F i g u r e 5 c o r r e s ponds t o r e s u l t s a t 8 0 ° C . The p o i n t s p l o t t e d i n t h e s e two f i g u r e s r e p r e s e n t smoothed v a l u e s o b t a i n e d from T a b l e s 4 t o 2 2 . Data a t 25°C i n F i g u r e 4 c l e a r l y s e p a r a t e i n t o t h r e e d i s t i n c t curves although the curves a r e c l o s e t o g e t h e r . T h i s shows t h a t t h e r e i s some d i f f e r e n c e between t h e a c i d g a s e s , b u t n o t a l a r g e difference. The p o i n t s i n F i g u r e 5 a t 80°C do n o t r e s o l v e i n t o s e p a r a t e c u r v e s because t h e r e i s some s c a t t e r i n t h e p o i n t s . 5
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O F AQUEOUS
5
4
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
WILSON
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9.
ET AL.
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101
7
1
I
.
1
1
ι
ι
1
j
ι
1
1
1
.
.
.5
0
1
ι
r
ι
I
1.0
moles a c i d gas/mole Ν Η ,
Figure 5.
The pH of LO wt % H S-C0 -NH^-H 0 mixtures vs. acid gas loading at 80°C ((A) 100% CO,; Ο 100% H S; (0)50:50 H S/C0 ) 2
2
2
2
2
2
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
222
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W i t h i n t h i s s c a t t e r , t h e t h r e e t y p e s o f d a t a a p p e a r t o be c o r r e l a t e d by a s i n g l e c u r v e ; t h u s s h o w i n g t h a t t h e r e i s n o t a g r e a t d i f f e r e n c e i n t h e e f f e c t o f the a c i d gases a t 80°C. In summary t h e f o l l o w i n g c a n be c o n c l u d e d r e g a r d i n g t h e pH data i n Tables 4 to 2 2 . 1. 2.
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3.
4.
5.
The d a t a can be c o r r e l a t e d u s i n g an e q u i l i b r i u m c o n s t a n t a p p r o a c h w i t h most d e v i a t i o n s b e i n g l e s s t h a n + 0.1 pH unit. The p K o f ammonia d e r i v e d f r o m t h e s e d a t a a g r e e s w i t h l i t e r a t u r e d a t a w i t h i n 0.1 pH u n i t a t 25°C and 0 . 4 2 pH u n i t at 80°C. The m o l a r r a t i o s o f H S / N r L o r C 0 / N H have a b o u t e q u a l e f f e c t s on t h e p H . A t 2 5 ° C , CO^ a p p e a r s t o have a s l i g h t l y greater e f f e c t . A s i m i l a r c o n c l u s i o n a t 80°C can be made e x c e p t t h a t no d i s t i n c t i o n between t h e a c i d g a s e s i s v i s i b l e b e c a u s e o f some s c a t t e r i n t h e d a t a . The pH p r o b e i s more s t a b l e a t 25°C t h a n a t 8 0 ° C . For t h i s r e a s o n i t i s recommended t h a t i f a pH p r o b e i s used as a c o n t r o l s e n s o r i n a p r o c e s s t h a t i t be used a t 25°C so t h a t t h e r e s p o n s e w i l l t e n d t o be more a c c u r a t e . pH d a t a a t 25°C i n T a b l e s 4 t o 13 can be used t o e s t i mate t h e m o l e s o f a c i d gas p e r m o l e s o f N H i n s o l u t i o n w i t h o n l y an a p p r o x i m a t e knowledge o f t h e t o t a l amount o f NH i n s o l u t i o n . a
2
2
3
3
3
Sodium H y d r o x i d e and Sodium A c e t a t e E f f e c t on NHg V o l a t i l i t y . Ammonia v o l a t i l i t y measurements a t v a r i o u s c o n c e n t r a t i o n s o f s o dium h y d r o x i d e and s o d i u m a c e t a t e a t 80°C a r e g i v e n i n T a b l e s 23 and 24 r e s p e c t i v e l y . Data on t h e e f f e c t o f sodium h y d r o x i d e were measured u s i n g an ammonia p r o b e f r o m O r i o n R e s e a r c h Company. These measurements were r e d u c e d t o NHo p a r t i a l p r e s s u r e m e a s u r e ments u s i n g E q u a t i o n 2 g i v e n a b o v e . In t h i s c a s e , t h e r e f e r e n c e s o l u t i o n i s the composition reached at zero s a l t c o n c e n t r a t i o n at t h e bottom o f T a b l e 2 3 . The ammonia p a r t i a l p r e s s u r e above t h i s s o l u t i o n can be i n f e r r e d f r o m T a b l e 1 where P N H 3 / w t % N H 3 a t 0.1 wt % N H 3 has a v a l u e o f 1 . 2 3 . This i n f o r m a t i o n gives the f o l l o w i n g v a l u e s f o r PjJ[jf- and m v r e f
Pj^fmv
ref.
= 0 . 1 0 0 5 χ 1.23 = 0 . 1 2 4
psia
_ = - 5 7 . 3 mv
These v a l u e s and t h e p r o b e o u t p u t d a t a i n T a b l e 23 were s u b s t i t u ted i n t o Equation 1 to give the p a r t i a l pressure data given i n Table 23. The d a t a i n T a b l e 24 on t h e e f f e c t o f sodium a c e t a t e were measured i n t h e same manner as d a t a i n T a b l e s 1 and 2 , so no a s s u m p t i o n s a b o u t t h e ammonia probe b e h a v i o r were n e c e s s a r y . This was done b e c a u s e r e a d i n g s f r o m t h e N H p r o b e became e r r a t i c a f t e r 3
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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TABLE 23. E f f e c t o f Sodium Hydroxide E l e c t r o l y t e on Ammonia V o l a t i l i t y a t 80°C from Ammonia Probe Data )
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3
NH Probe Output mv
NH psia
NH /wt psia
3
wt % i n L i q u i d NH NaOH 3
p P
3
3
0800
22.5
-57.1
.123
1.54
0891
12.7
-57.5
.125
1.40
0944
6.82
-57.3
.124
1.31
0974
3.60
-57.2
.124
1.27
.124
1.25
0995
1.27
1005
0
a
-57.3 ref
b
mv =-57.3 )
1.23
^ 0 r i o n Research Company ^This value of -57.3 mv was not d i r e c t l y measured, but i s a value obtained by e x t r a p o l a t i n g mv vs wt % NaOH to zero wt NaOH.
r) 'This p a r t i a l pressure f o r NFU was obtained from the NH p a r t i a l pressure data i n Table 2 a t 0.1 wt % ίΙΗ . The same r a t i o o f P N H 3 / ^ % NH , uncorr. was used at .1005 wt % NH to give P j ^ as follows. 3
3
w
3
3
P
N H
= 1.23 χ .1005 = .124 psia
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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TABLE 24. E f f e c t of Sodium Acetate E l e c t r o l y t e on Ammonia V o l a t i l i t y a t 80°C from Flow C e l l Data
N H
charge, wt % NH NaAc 3
.802
25
average
.931
15
average .931
5
averaqe
1.00
0
i n
3 Liquid wt %
η *\ NH psia
.781 .734 .684 .644 .711
1.838 1.778 1.712 1.620 1.737
2.35 2.42 2.50 2.51 2.45
.992 .975 .959 .942 .967
1.812 1.817 1.796 1.756 1.795
1.83 1.86 1.87 1.86 1.86
.995 .985 .974 .964 .980
1.381 1.411 1.405 1.380 1.394
1.39 1.43 1.44 1.43 1.42
.973
1.246
1.28 average from Table 2
p
a ;
3
F
NH?M %
^Sampled a t 20 psia
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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t h e measurements a t 80°C on t h e e f f e c t o f sodium h y d r o x i d e . These d a t a were measured a t a b o u t 1 wt % N H i n t h e l i q u i d phase i n s t e a d o f 0.1 wt % N H used f o r t h e NaOH m e a s u r e m e n t s . For t h i s r e a s o n t h e y do n o t e x t r a p o l a t e t o t h e same v o l a t i l i t y r a t i o a t zero concentration of e l e c t r o l y t e . When c o r r e c t i o n i s made f o r i o n i z a t i o n and s o l v e n t e f f e c t s o f ammonia, t h e n t h e two i n t e r cepts agree. From t h e d a t a i n T a b l e s 23 and 2 4 , t h e f o l l o w i n g can be c o n cluded. 3
3
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1.
2.
The v o l a t i l i t y o f ammonia can be s i g n i f i c a n t e l y a f f e c t e d by h i g h c o n c e n t r a t i o n s o f d i s s o l v e d i o n s i n t h e l i q u i d phase. In sodium a c e t a t e t h e v o l a t i l i t y i n c r e a s e s by a f a c t o r o f 1.9 a t 25 wt % o f s a l t . In sodium h y d r o x i d e t h e v o l a t i l i t y i s enhanced t o a l e s s e r d e g r e e w i t h an i n c r e a s e o f 1.25 a t 2 2 . 5 wt % NaOH. Both e l e c t r o l y t e s p r o d u c e i o n s w i t h o n l y one e l e c t r o n i c c h a r g e , but t h e i r e f f e c t s on t h e v o l a t i l i t y o f ammonia a r e s i g n i f i c a n t l y different. Thus t h e e f f e c t s o f v a r i o u s i o n i c components must be s t u d i e d i n d i v i d u a l l y i n o r d e r t o d e t e r m i n e t h e i r e f f e c t on t h e v o l a t i l i t y o f N H 3 . At the low i o n i c c o n c e n t r a t i o n s encountered i n sour wat e r s t r i p p e r s , the e f f e c t of d i s s o l v e d ions i s probably small. Thus a t a 1% c o n c e n t r a t i o n o f sodium a c e t a t e t h e v o l a t i l i t y o f ammonia o n l y i n c r e a s e s a b o u t 2 . 5 % due t o the s a l t . This i s w i t h i n the p r e d i c t i o n accuracy o f the ammonia v o l a t i l i t y d a t a and no c o r r e c t i o n i s t h e r e f o r e required. However s i g n i f i c a n t i o n i c e f f e c t s c o u l d e x i s t i n t h e c o n d e n s e r where h i g h c o n c e n t r a t i o n s o f t h e i o n i c components c o u l d e x i s t .
Summary and
Conclusions
Ammonia p a r t i a l p r e s s u r e d a t a have been d e t e r m i n e d a t c o n c e n t r a t i o n s from 10 ppm up t o 5 wt % i n w a t e r a t t e m p e r a t u r e s o f 80 and 120°C. The pH o f N H o - H S - C 0 - H 0 m i x t u r e s have a l s o been measured a t 25 and 8 0 ° C . A l s o t h e e f f e c t s o f sodium h y d r o x i d e and sodium a c e t a t e on ammonia v o l a t i l i t y d a t a have been measured a t 80°C. V a r i o u s c o n c l u s i o n s made from t h e d a t a a r e as f o l l o w s . 2
1.
2. 3.
2
2
The v o l a t i l i t y o f N H 3 a t ppm l e v e l s can be c a l c u l a t e d from t h e i o n i z a t i o n c o n s t a n t o f ammonia combined w i t h v o l a t i l i t y d a t a measured a t h i g h e r c o n c e n t r a t i o n s o f ammonia. The v o l a t i l i t y o f ammonia a t 80 and 120°C i s a b o u t 5% h i g h e r t h a n i s now p r e d i c t e d by t h e SWEQ m o d e l . The v o l a t i l i t y o f ammonia can be s i g n i f i c a n t l y a f f e c t e d by h i g h c o n c e n t r a t i o n s o f d i s s o l v e d i o n s i n t h e l i q u i d phase. U n f o r t u n a t e l y t h e e f f e c t v a r i e s d e p e n d i n g on t h e t y p e s o f i o n s i n s o l u t i o n . Sodium a c e t a t e p r o d u c e s a
In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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THERMODYNAMICS
4.
5.
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6.
7.
OF AQUEOUS
SYSTEMS
WITH
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APPLICATIONS
much l a r g e r enhancement i n t h e v o l a t i l i t y t h a n i s p r o duced by sodium h y d r o x i d e . A t t h e low i o n i c c o n c e n t r a t i o n s encountered i n sour w a t e r s t r i p p e r s , the e f f e c t o f d i s s o l v e d ions i s probably small. A 1% c o n c e n t r a t i o n o f sodium a c e t a t e o n l y e n hances t h e v o l a t i l i t y o f ammonia by a b o u t 2 . 5 % . High i o n i c c o n c e n t r a t i o n s i n t h e c o n d e n s e r may p r o d u c e b i g g e r effects. M e a s u r e d pH d a t a on NH3-H2S-CO2- H 0 m i x t u r e s can be c o r r e l a t e d u s i n g an e q u i l i b r i u m c o n s t a n t a p p r o a c h w i t h most d e v i a t i o n s b e i n g l e s s t h a n + 0.1 ρ H u n i t . The p K o f ammonia d e r i v e d f r o m t h e pH d a t a a g r e e s w i t h l i t e r a t u r e d a t a w i t h i n 0.1 pH u n i t a t 2 5 ° C . A t 80°C t h e agreement i s n o t as good w i t h a d i f f e r e n c e o f 0 . 4 2 pH unit. HoS and CO? have a b o u t e q u a l e f f e c t s on t h e pH o f H SCOo-NHo-H^O m i x t u r e s w i t h C 0 s h o w i n g a s l i g h t l y g r e a t e r e f f e c t a t 25°C. pH measurements a t 25°C t e n d t o be more r e l i a b l e t h a n d a t a a t h i g h e r t e m p e r a t u r e s b e c a u s e t h e o u t p u t from t h e p r o b e i s more s t a b l e a t 2 5 ° C . For t h i s reason i t i s recommended t h a t i f a pH p r o b e i s used as a c o n t r o l s e n s o r i n a p r o c e s s t h a t i t be used a t 2 5 ° C . Measured pH d a t a on H0S-CO0-NH3- H 0 m i x t u r e s a t 25°C c a n be used t o e s t i m a t e t h e m o l e s o f a c i d gas per mole o f ammonia i n s o l u t i o n w i t h o n l y an a p p r o x i m a t e knowledge o f t h e t o t a l amount o f ammonia i n s o l u t i o n . C e r t a i n t y p e s o f r e f e r e n c e e l e c t r o d e s a r e f o u n d t o be more s u i t a b l e t h a n o t h e r s when d e t e r m i n i n g t h e pH o f s o l u t i o n s c o n t a i n i n g H2S. Recommendations r e g a r d i n g various electrodes a r e given i n t h e t e x t o f the paper. 2
a
2
2
8.
9.
10.
2
Acknowledgment T h i s work was s u p p o r t e d by t h e Gas P r o c e s s o r s A s s o c i a t i o n a n d the American Petroleum I n s t i t u t e . The c o n s c i e n t i o u s work o f K e n t C . W i l s o n i n d o i n g many o f t h e p o t e n t i o m e t r i c t i t r a t i o n s and K a t i e Toepke f o r t y p i n g t h i s r e p o r t is appreciated.
Literature Cited
1. Edwards, T. J. and Prausnitz, J. M. A.I.Ch.E. Journal, 1975, 21, (2), 248-259. 2. Wilson, G. M. "A New Correlation of NH , CO , and HS Volatil ity Data from Aqueous Sour Water Systems", American Petroleum Institute, February 1978. 3. Miles, D. H. and Wilson, G. M. "Vapor-Liquid Equilibrium Data for Design of Sour Water Strippers", Annual Report to the American Petroleum Institute for 1974, October 1975 (Data in this report are also summarized in reference 2). 4. CRC Handbook, 51st Edition, page D-122 (1970-1971). 3
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RECEIVED February 27, 1980. In Thermodynamics of Aqueous Systems with Industrial Applications; Newman, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.