10 Phase Equilibria from Equations of State T. E. DAUBERT
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Pennsylvania State University, University Park, PA 16802
As I am last to make opening remarks I have decided to take a slightly different approach to the problem. The previous six speakers have alluded to the meaning and application of various equations--their advantages, disadvantages and accuracy. As co-director of the API Technical Data Book project my major interest is in ascertaining what equation is the most generally interpolatable and extrapolatable with reasonable accuracy over a wide range rather than what is the most accurate equation within a limited range of applicability. My major premise is: No equation of state is necessarily better than the data used to validate it. In order to be generally valid any equation must be tested over a wide range of molecular type and weight of components, a wide range of compositions, and the entire temperature and pressure span. We've evaluated many of the equations available and conclude that a decision as to the universally "best" possible equation cannot be made with current data. In addition, I personally would suggest that until more data are available further refinements of existing base equations may be empty exercises. Thus, what I would like to do is show some examples of the data that are available and then point out where the largest gaps exist and what must be done aboutit.My discussion will be limited to hydrocarbon systems and systems of hydrocarbons and the industrially important gases--H, N2, HS, CO, and CO. It will become apparent that the easy data already have been taken and the difficult data are yet to be determined. 2
2
2
Discussion Table 1 shows the data which have been gathered for our work from a comprehensive survey of the literature. All binary data were rigorously tested for thermodynamic consistency using the method of Van Ness and co-workers (jL, 2) using the general coexistence equation reduced to constant temperature or constant pressure according to the data source. It is readily apparent that less than 224
In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. Nonhydrocarbon
Nonhydrocarbon Hydrogen Nitrogen Hydrogen + Hydrogen
Nonhydrocarbon Hydrogen Hydrogen S u l f i d e Carbon Dioxide Carbon Monoxide Nitrogen
Quaternary Hydrocarbon Hydrocarbon - Water Petroleum F r a c t i o n s
Ternary Hydrocarbon -
Binary Hydrocarbon -
Binary Hydrocarbon Ternary Hydrocarbon Quaternary Hydrocarbon F i v e and S i x Component Hydrocarbon
Type System
Sulfide
Types and Amounts of VLE Data A v a i l a b l e
Table 1
209 97 54
750 350 700 240 450
2836 670 134 60
430 240 323 156 184
1850
P o i n t s of Data Available "Consistent"
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226
P H A S E EQUILIBRIA A N D F L U I D PROPERTIES I N C H E M I C A L
INDUSTRY
t w o - t h i r d s of the b i n a r y data were c o n s i s t e n t . Thus, only the c o n s i s t e n t p o i n t s were used f o r data e v a l u a t i o n . The method was extended t o t e r n a r y systems. However, s i n c e necessary parameters f o r t e s t i n g o f t e n were not a v a i l a b l e f o r many data s e t s , a l l a v a i l a b l e data which were not o b v i o u s l y i n e r r o r were used f o r testing. From t h i s t a b l e i t i s apparent that data on t e r n a r y hydrocarbon-non-hydrcarbon systems are i n short supply as are data on a l l four and h i g h e r component systems. However, the former need i s the most c r i t i c a l f o r t e s t i n g purposes as e s t i m a t i n g equations which are a c c u r a t e f o r t e r n a r i e s , i n g e n e r a l , are accurate f o r higher multicomponent systems. The t a b l e a l s o shows no e n t r i e s f o r hydrocarbon-water o r petroleum f r a c t i o n systems. Such systems w i l l be d i s c u s s e d l a t e r . Table 2 breaks down the c o n s i s t e n t b i n a r y hydrocarbon data by Table 2 C o n s i s t e n t B i n a r y Hydrocarbon VLE Data
System Types A
Number o f Points
Carbon Number Range
B
B
A
r s
Paraffin - Paraffin
727
c
Paraffin - Olefin
160
c -c
Olefin - Olefin
c
2
?
C
2~ 10
C
C
2- 6
C
A 6" 7
C
29
C
P a r a f f i n - Naphthene
133
c
r 8
C
P a r a f f i n - Aromatic
450
c
r s
VS
O l e f i n - Aromatic
128
V 8
V 8
Naphthene - Aromatic
160
V 8
C
6" 8
C
C
7
C
7- 10
Naphthene - Naphthene
3
Aromatic - Aromatic
60
Total
1850
3 c
c
C
C
6
V 9 C
C
C
C
C
molecular type systems and carbon number range. Of systems of r e a l i n t e r e s t , date i s very sparse f o r naphthene-naphthene and aromaticaromatic systems. Data are n o n e x i s t e n t above C^Q f o r any of the system types.
In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
10.
Phase Equilibria
DAUBERT
227
from Equations of State
Table 3 shows the d i s t r i b u t i o n of pressure ranges of the data Table 3 Pressure Range of B i n a r y Hydrocarbon Pressure Range (psia) P < 14.7 Downloaded by UNIV OF AUCKLAND on May 8, 2015 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0060.ch010
14.7
24
Olefin (C ) 3
Naphthene (C >
8
Aromatic (C^)
9
3
323 Carbon Monoxide
Paraffins
V
105 51
Aromatic (C^)
156 Nitrogen
P a r a f f i n s (CAromatic (C^)
C
10>
168 16 184
In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
10.
Phase Equilibria
DAUBERT
229
from Equations of State
Table 5 3, 4, 5, and 6 Component Systems
Type System
No. of Systems
No. of Data Points
12 1 2
435 13 67
Hydrocarbon Ternary Hydrocarbon Paraffin (Ci - C ) P a r a f f i n - O l e f i n (Ci - C3 P a r a f f i n - Naphthene - O l e f i n (C5 - C7) M i s c e l l a n e o u s Systems w i t h P a r a f f i n s , O l e f i n s , Acetylenes
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1 0
152 668
Quaternary Hydrocarbon P a r a f f i n ( C - Cy) P a r a f f i n - O l e f i n - D i o l e f i n - Acetylene ±
(c ) 3
P a r a f f i n - O l e f i n - D i o l e f i n - Acetylene (C ) 5
F i v e and S i x 5 Paraffin 6 Paraffin 6 Paraffin
4
15
1
53
1
Carbon Atom Hydrocarbon (C-^ - C^Q) (C^ - C ) - O l e f i n (C4)
66 134
28 17 15
1 0
60
Nonhydrocarbon Ternary Nonhydrocarbon Hydrogen - Methane - Ethane Hydrogen - Methane - Propane Hydrogen - Methane - Ethylene N i t r o g e n - Methane - Ethane N i t r o g e n - Methane - Hexane Hydrogen - Hydrogen S u l f i d e - C^ aromatic or p a r a f f i n o r naphthene Quaternary Nonhydrocarbon Hydrocarbon N i t r o g e n - Methane Ethane Hydrogen - Benzene - Cyclohexane - Hexane Hydrogen - Hydrogen S u l f i d e - Methane Isopropylcyclohexane
82 30 97 44 53 54
1 1
360
7 36
1 52
In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
230
P H A S E EQUILIBRIA
2. 3.
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4. 5. 6.
A N D F L U I D PROPERTIES
IN C H E M I C A L
INDUSTRY
Aromatic and naphthenic b i n a r y and t e r n a r y hydrocarbon systems. Nonhydrocarbon-naphthenic and aromatic b i n a r y and t e r n a r y systems, e s p e c i a l l y hydrogen-aromatic-naphthenic systems. Water-hydrocarbon b i n a r y and t e r n a r y systems of a l l types. Water-hydrocarbon-nonhydrocarbon t e r n a r y systems. Petroleum f r a c t i o n and petroleum fraction-nonhydrocarbon systems.
Progress i n o b t a i n i n g new data i s e s s e n t i a l i f the users of equations of s t a t e ever hope to adopt a r e l i a b l e , dependable, and accurate p r e d i c t o r .
References Cited 1. Van Ness, H. C., "Classical Thermodynamics of Non-Electrolyte Solutions," Pergamon Press, Oxford (1964). 2. Van Ness, H. C., Byer, S. M., Gibbs, R. E. AIChE Journal, (1973) 2, 238. Acknowled gment The R e f i n i n g Department of the American Petroleum I n s t i t u t e i s g r a t e f u l l y acknowledged f o r f i n a n c i a l support of t h i s work.
In Phase Equilibria and Fluid Properties in the Chemical Industry; Storvick, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.