propriedades termofísicas e modelos termodinâmicos para ...nuno/eps/conteudos/aula10/prop...

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

-

NIST Chemistry Webbook

NIST IL Thermo

DETHERM

Web of Knowledge

The properties of gases and liquids

CRC Handbooks

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 densidades de Líquidos

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


Erro médio de 3.2 % para 4000 compostos.

Parâmetros nas tabelas seguintes

KKTb 9.33246.8822.2498.212.198)( =+++=


1. Estime o ponto de ebulição do etanol, tolueno e acetaldeido pelos dois métodos discutidos

KKTb 6.393)53.28(576.3098.212.198)( =+++=

KKTb 6.30338.8398.212.198)( =++=

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 de Joback

Modelo de Han e Peng para ω

Modelos para entalpia de vaporização

• Equação de Antoine

CT

BAP

+−=σlog

( )2

2)15.273(303.21

ln

CT

TRB

Td

PdRH vap

++=

−=∆

σ

Modelo de Orrick Erbar para Viscosidades

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

-

Influência de Tc no nº de andares


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


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

-

Influência de Pc no nº de andares

-

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


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

-

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

-

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

-

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

-

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


-

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



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


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


Exemplo

1. Qual o melhor modelo para descrever a mistura 1-Propanol + H2O.

E?Polar

Non-electrolyteSee Figure 2

Figure 1

Polarity

R?Real or pseudocomponents

P? Pressure

E? Electrolytes


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


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 182

84

86

88

90

92

94

96

98

100

1-Propanol mol. frac.

T [o

C]

TXY diagram for 1-Propanol, H2O

Perry NRTL PRSV UNIQUAC Van-Laar (Built-inVan-Laar(Perry)

Diagrama de fases

propriedades termofísicas e modelos termodinâmicos para ...nuno/eps/conteudos/aula10/prop...

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