Propriedades termofísicas e modelos termodinâmicos para ...nuno/eps/Conteudos/aula10/Prop...
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Propriedades termofísicase modelos termodinâmicos
para simulação de processos
João A. P. CoutinhoDepartamento de Química, Universidade de Aveiro
Disclaimer
• O material constante desta apresentação foi composto a partir de várias fontes (livros, artigos e internet) das quais não sou já capaz de retraçar as origens…Ficam os meus agradecimentos aos autores que usei e as minhas desculpas àqueles que não menciono como tal…
Equilibrium controlled separation processes:By the addition of energy or a substance, a homogeneous mixture is separated into (at least) two phases of different composition.
Costs of a chemical production process are influenced strongly (50 - 80 %) by costs for separation processes; this is a big incentive to know phase equilibria involved in the process precisely.
Distillation is the dominant technology in the chemical process industries. Worldwide, about 95% of all separations are made with it. In the U.S. alone, some 40000 columns represent a capital investment of about $8 billion . They take up the energy equivalent of approximately 54.106 t/year of crude oil - some 15% of all U.S. industrial energy consumption.
Feed
Bottomsproduct
side stream
distillate
Importância das separações nos processos químicos
compressorρρρρV, cP
V, ηηηηV
heat exchanger (gas)ρρρρV, cp
V, ηηηηV, λλλλV
gas phase reactorρρρρV, cP
V, ηηηηV, λλλλV, ∆∆∆∆hr, ∆∆∆∆gr, r
reboilerρρρρV, ρρρρL, cp
L, ηηηηL, λλλλL,∆∆∆∆hVL, PSat, σσσσLV
condenserρρρρV, ρρρρL, cP
L, ηηηηL, λλλλL,∆∆∆∆hVL, PSat, σσσσLV
decanterρρρρL, ηηηηL, σσσσLL
K i = xIi/xII
i
pumpρρρρV, cP
L, ηηηηL,PSat
distillation columnρρρρV, ρρρρL ,cP
L, PSat, ∆∆∆∆hVL,K i = yi/x i, ηηηηL, σσσσLS
Propriedades termofísicas
“Reliable values of the properties of materials are necessary for the design of industrial processes.”John Prausnitz, in “The Properties of Gases and Liq uids”, 2001
-
Modelos para densidades de Líquidos
• Equação de Rackett
• GC VOL (Elbro et al, 1991)
( ) 7/21 rTccZVV −=
2TCTBAv
vnV
iiii
ii
++=∆
∆=∑
V
M w=ρ
iimix VxV ∑=
Modelos para Temperatura de ebulição
• Equação de Antoine
• Equação de Joback e Reid modificada
CT
BA
+−=)760log(
Temperatura de ebuliçãoJoback-Reid GC formula (1987) and Stein-Brown, modified(1994)
∑+=i
gi
nKb
T 2.198)(
]700[)(0007705.05577.084.94)( 2 KTTTTcorrectedb
Tbbbb
≤−+−=
]700[5209.07.282)( KTTTcorrectedb
Tbbb
>−+=
Tb : Temperatura de ebulição @ 1 atm [K]ni: número de grupos de tipo i na moléculagi: contribuição de cada grupo
Modelos para Temperatura de ebulição
Erro médio de 3.2 % para 4000 compostos.
Parâmetros nas tabelas seguintes
KKTb 9.33246.8822.2498.212.198)( =+++=
Modelos para Temperatura de ebulição
1. Estime o ponto de ebulição do etanol, tolueno e acetaldeido pelos dois métodos discutidos
Temperatura de fusão
Joback
Lyman
)(5839.0)( KTKT bm =
Lyman, W.J., “Estimation of Physical Properties,” Environmental ExposureFrom Chemicals, volume 1, Neely, W.B. and Blau, G.E., eds. CRC PressBoca Raton, FL 38-44 (1985)
Modelos para temperatura de fusão
∑+=i
gi
nKm
T 122)(
Modelos para entalpia de vaporização
• Equação de Antoine
CT
BAP
+−=σlog
( )2
2)15.273(303.21
ln
CT
TRB
Td
PdRH vap
++=
−=∆
σ
Separação Tolueno - Clorobenzeno
Clorobenzeno
Tolueno
Tolueno + Clorobenzenoxi = 0,5 mol/mol; P=101,3 kPa
Toluene + Chlorobenzene
100
105
110
115
120
125
130
135
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0
xToluene, yToluene (mol/mol)
SRK-EOS
SRK Tc+3%
SRK Tc-3%
P = 101,3 kPa
-
Influência de Tc tolueno no equilíbrio
Toluene + ChlorobenzeneFeed: 0,5 mol/mol; P=101,3 kPa
0
10
20
30
40
50
60
-3% -2% -1% 0% 1% 2% 3%
deviation of TC of Toluene
Min
imum
num
ber
of s
tage
s
1% C7H8 in Bottom0,1% C7H8 in Bottom0,01% C7H8 in Bottom
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Influência de Tc no nº de andares
Toluene + ChlorobenzeneFeed: 0,5 mol/mol; P=101,3 kPa
40 theoretical stages
0,001
0,01
0,1
1
10
100
1000
10000
100000
-5% -4% -3% -2% -1% 0% 1% 2% 3%
deviation of TC of Toluene
Tol
uene
in B
otto
m (
ppm
)
Influência de Tc no produto de cauda
Toluene + ChlorobenzeneFeed: 0,5 mol/mol; P=101,3 kPa
0
5
10
15
20
25
30
35
-3% -2% -1% 0% 1% 2% 3%
deviation of PC of Toluene
Min
imum
num
ber
of s
tage
s
1% C7H8 in Bottom
0,1% C7H8 in Bottom0,01% C7H8 in Bottom
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Influência de Pc no nº de andares
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Influência de ω no nº de andares
0
5
10
15
20
25
30
35
-3% -2% -1% 0% 1% 2% 3%
deviation of acentric factor ω of Toluene
Min
imum
num
ber
of s
tage
s
1% C7H8 in Bottom
0,1% C7H8 in Bottom0,01% C7H8 in Bottom
Toluene + Chlorobenzene
105
110
115
120
125
130
135
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0
xToluene, yToluene (mol/mol)
Unifac
Uniquac
SRK-EOS
P = 101,3 kPa
-
Influência do modelo no equilíbrio
Toluene + ChlorobenzeneFeed: 0,5 mol/mol; P=101,3 kPa
0
5
10
15
20
25
30
35
0,0000010,000010,00010,0010,010,1
Toluene in bottom product (mol/mol)
Min
imum
num
ber
of s
tage
s
UnifacUniquacSoave-RK
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Influência do modelo no nº de andares
Avaliação dos dados disponíveis- Colecta todos os dados disponíveis- Avalia a qualidade dos dados- Avalia a dependencia de outras propriedades- Identifica equações adequadas- Ajusta parâmetros às equações
X X X X X X XX X X X X X XX X X X X X XX X X X X X XX X X X X X XX X X X X X XX XX X X X X X XX XX X X X X X XX X X X X X X
X X X X
X X
X X
Definir componentes importantes
Ethylene OxidePropylene OxideGlycerinePropylene GlycolTrimethylol PropaneEthylene Diamineo-TDASorbitolSucroseTolueneWaterDP 1113DP 1115F 3020F 3022GSE 1500GP 420LHT 240...
Definir propriedades importantes
Mol
ecul
ar W
eigh
t
Liqu
id D
ensi
ty
Liqu
id V
isco
sity
Spe
cific
Hea
t Liq
uid
Liqu
id T
herm
al C
ondu
ctiv
ity
Vap
or P
ress
ure
Hea
t of V
apor
izat
ion
...
Completa os dados em faltaMedição ou estimativa most important properties
-
Estimativa das propriedades termofísicas
Example: distillation columndiameter: 4.5 mheight: 85 minvestment costs: 4.5 M€
At a separation factor of 1.1 an error of 5% for αααα more than doubles the number of stages . Construction of two columns instead of one column.
Extra costs: 4.5 M€
The closer the separation factor lies to 1, the bigger is the possible relative error. This is very bad, since difficult separations ( αααα close to 1) need many theoretical stages and high investment costs.
-40%
-20%
0%
20%
40%
60%
80%
100%
-5% -4% -3% -2% -1% 0% 1% 2% 3% 4% 5%
Error in separation factor α=(y1/x1)/(y2/x2)
Err
or in
min
imum
num
ber
of s
tage
s
alpha=1.05alpha=1.1alpha=1.2
Influência de α na separação
HexafluorobenzeneQuality Code 5: error < 10%
real error: 202 %
0
1
2
3
4
280 300 320 340 360
T / K
dyn.
Vis
cosi
ty /
mP
as
. DIPPRDDB
Qualidade de dados termofísicos
Methyl-Tert.-Butylether MTBEQuality-Code 4: Fehler < 5%tatsächlicher Fehler: 20,6%
0
0,03
0,06
0,09
0,12
0,15
0,18
0,21
150 200 250 300 350
T / K
Wär
mel
eitfä
higk
eit /
Wm
-1K
-1
DIPPRDIPPR komplettDDB (Assael 1991)
-
Qualidade de dados termofísicos
2-Propanol
-5%
0%
5%
10%
15%
250 300 350 400 450 500 550 600
Temperature / K
(VP
exp
-VP
calc
)/VP
exp
/ %
DIPPR
DECH
DODB
ESDU
DODB
DODB
Shulgin 1989
Barr-David 1959
Ambrose 1963
Biddescombe 1963
Parks 1928
Dejoz 1997
Brown 1956
Livares 1984
Ambrose 1978
Ortega 1991
Lydersen 1990
Ambrose 1970
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Exemplo: Pvap de 2-propanol
2-Propanol
-5%
0%
5%
10%
15%
20%
250 300 350 400 450
Temperature / K
(KLI
Qex
p-K
LIQ
calc
)/KLI
Qex
p /
%VDI-W ärmeatlas
DIPPR
Jamieson 1980
Smith 1930
Sakiadis&Coates 1955
Cai, Zong, 1993
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Condutividade térmica de 2-propanol
Ethylbenzene:51,0 kmol/h
Styrene:47,8 kmol/h
Bottom product (kmol/h)Simul 1Simul 2 Simul 3
Ethylbenzene 2,90 8,55 5,63Styrene 26,76 21,10 24,03
Model: SRK-EOSwith all three simulators
Ref.: Sadeq et al. AIChE Annual Meeting, 1995
“Without reliable properties,
a process simulator is
just an expensive
random number generator.”
A. Harvey, A. Laesecke, 2002
“Without reliable properties,
a process simulator is
just an expensive
random number generator.”
A. Harvey, A. Laesecke, 2002
Comparação de simuladores de processo
-
1 Define the important substances of the process
• important pure components, • if needed: pseudo-components, • dummies for intermediates
Propriedades termofísicas em simulação de processos
2 Validate the physical properties
• Plotting pure-component and mixture data• comparison with literature data
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3 Describe non-databank components
• Is this a major component in the mixture? If it is minor, is it needed for the simulation?
• Does the component take part in VLE?
• Is the component non-volatile?
• Can data of similar components be used?
• Which data are crucial for the simulation?
• Use of property constant estimation methods.
• Mandatory properties: • molecular weight• vapor pressure• ideal-gas heat capacity
Propriedades termofísicas em simulação de processos
-
4 Obtain and use physical property data , from
• critically evaluated data sources, • nonevaluated sources,
• experimental measurements or • estimation techniques
• binary parameters: • by fitting experimental data
→ use the right parameters
→ estimate as few parameters as possible→ specify the right number of phases (VLLE)
• directly from literature sources
Propriedades termofísicas em simulação de processos
Propriedades termofísicas em simulação de processos
5 Estimate any missing property parameters
• pure-component data from group contribution methods or empirical correlations
• binary parameters from data generated with predictive methods (e.g. Unifac, PSRK) or from g∞ data
6 Select an appropriate physical property model
• EOS or gE-model?• Which gE-model? e.g. Wilson, NRTL, Uniquac, Unifac• Which EOS? e.g. SRK, Peng-Robinson, Yu-Lu• Which mixing rule?
gE ou EOS?Ou EOS-gE?
UNIQUAC ou UNIFAC?PR ou SRK?
PC-SAFT, VR-SAFT, soft-SAFT ou CPA?
Como escolher o modelo adequado para descrever um sistema
Importância de seleccionar o modelo adequado
• Correct predictions of the physical properties of the mixture as a function of temperature and pressure.
• Each method is suitable only for particular types of components and limited to certain operating conditions.
• Choosing the wrong method may lead to incorrect simulation results.
• Particularly important for reliable computations associated with separation operations (distillation, LL extraction, etc.).
Recomendações para a selecção do modelo
Eric Carlson, “Don’t gamble with physical properties for
simulations,” Chem. Eng. Prog. October 1996, 35-46
Eric Carlson’s Recommendations
Peng-Robinson,Redlich-Kwong-Soave,Lee-Kesler-Plocker
E?
R?
P?
Polar
Real
Electrolyte
Pseudo & Real
Vacuum
Non-electrolyte
Braun K-10 or ideal
Chao-Seader,Grayson-Streed or Braun K-10
Electrolyte NRTLOr Pizer
See Figure 2Figure 1
Polarity
R?Real or pseudocomponents
P? Pressure
E? Electrolytes
All Non-polar
P?
ij?
ij?
LL?
(See alsoFigure 3)
P < 10 bar
P > 10 bar
PSRKPR or SRK with MHV2
Schwartentruber-RenonPR or SRK with WSPR or SRK with MHV2
UNIFAC and itsextensions
UNIFAC LLE
PolarNon-electrolytes
No
Yes
Yes
LL?No
No
Yes
Yes
NoWILSON, NRTL,UNIQUAC and their variances
NRTL, UNIQUACand their variances
LL? Liquid/Liquid
P? Pressure
ij? Interaction ParametersAvailable
Figure 2
Eric Carlson’s Recommendations
VAP?
DP?Yes
No Wilson, NRTL,UNIQUAC, or UNIFAC* with ideal Gas or RK EOS
Wilson NRTLUNIQUACUNIFAC
Hexamers
Dimers Wilson, NRTL, UNIQUAC,UNIFAC with Hayden O’Connellor Northnagel EOS
Wilson, NRTL, UNIQUAC,or UNIFAC with special EOS for Hexamers
VAP? Vapor Phase Association
Degrees of PolymerizatiomDP?UNIFAC* and its Extensions
Figure 3
Eric Carlson’s Recommendations
E?Polar
Non-electrolyteSee Figure 2
Figure 1
Polarity
R?Real or pseudocomponents
P? Pressure
E? Electrolytes
Eric Carlson’s Recommendations
P?
ij?
LL?
(See alsoFigure 3)
P < 10 bar
UNIFAC and itsextensions
PolarNon-electrolytes
Yes
LL?No
No
No
WILSON, NRTL,UNIQUAC and their variances
LL? Liquid/Liquid
P? Pressure
ij? Interaction ParametersAvailable
Figure 2
Eric Carlson’s Recommendations