Fluid phase coexistence for the oxidation of cyclohexane

PROF. DR.-ING. HABIL. JADRAN VRABEC ThET

Fluid phase coexistence for the oxidation

of cyclohexane in CO2 expanded liquids:

COSMO-SAC vs. molecular simulation

International Workshop Molecular Modeling an Simulation:

Natural Science meets Engineering

Frankfurt, 12 March, 2013

C.-M. Hsieh1, T. Merker2, S.-T. Lin3, H. Hasse2, J. Vrabec1

1Thermodynamics and Energy Technology, University of Paderborn, Germany 2 Lab. of Engineering Thermodynamics, University of Kaiserslautern, Germany 3 Department of Chemical Engineering, National Taiwan University, Taiwan


Oxidation of cyclohexane to KA-oil (mixture of and )

Cyclohexane oxidation: industrial application

Use of supercritical carbon dioxide expanded media to improve

the rates of conversion and selectivity (enhance the mobility of

reactants and products)

Usually, contact cyclohexane with air low conversion rates (~10%)

for high selectivity (~ 85%)

= O

Air (O2) OH

+ COOH

COOH COOH HOOC

Used for the production of adipic acid / Nylon 6.6


Molecular models for investigated compounds

Cyclohexane

Cyclohexanol

CO2

Cyclohexanone

O2

Experimental measurements

VLE

Henry’s law constant

Molecular simulations

ms2

Thermodynamic models

COSMO-SAC

Peng-Robinson EOS

=O OH

Mixtures investigated:

10 (10) binary, 6 (10) ternary,

2 (5) quaternary, 1 pentenary

[1] T. Merker, et al.: J. Chem. Eng. Data, 56: 2477 (2011)

[2] T. Merker, J. Vrabec, H. Hasse: J. Chem. Thermodyn., 49: 114 (2012)

[3] S. Deublein, et al.: Comput. Phys. Commun., 182: 2350 (2011)

q: point charge, m : point dipole, Q: point quadrupole

+

H

-

O

+

CH

6 LJ-site

7LJ-site + 3 q 7 LJ- site + m

3 LJ-site + Q

2 LJ-site + Q

PROF. DR.-ING. HABIL. JADRAN VRABEC ThET 4

DIPPR correlation Equation of state (EOS) Simulation

Development of molecular pure fluid models

CO2

0.4%

0.4%

0.9%

0.8% p 1.6%

p 3.0%

p 2.7% p 3.0%

[1] T. Merker, J. Vrabec, H. Hasse: J. Chem. Phys., 129: 087101 (2008)

[2] T. Merker, C. Engin, J. Vrabec, H. Hasse: J. Chem. Phys., 132: 234512 (2010)

[3] T. Merker, J. Vrabec, H. Hasse: Fluid Phase Equilib., 315: 77-83 (2012)

[4] T. Merker, J. Vrabec, H. Hasse: Soft Mater., 10: 3-25 (2012)

=O

OH CO2

=O

OH


A A

B B σB, εB

σAB, εAB

Interaction between A and B:

Polar interaction: laws of electrostatics

Lennard-Jones parameters: combination rule

Molecular model of mixtures

AB A B+= / 2σ σ σ

AB A B=ε ε ε

or

Fitting to ONE experimental

datum of p(T,x) or H(T)

ξ = 1 Prediction

Modified

Lorentz-Berthelot

combining rule

σA, εA


COSMO-SAC (Gex model)

The activity coefficient of species i in mixture S is determined from:

[1] S.-T. Lin, S. I. Sandler: Ind. Eng. Chem. Res., 41: 899 (2002) [2] C.-M. Hsieh, et al.: Fluid Phase Equilib. 297, 90

(2010).

combSG,

/

*

/

*

// lnln Si

res

ii

res

SiSi

RT

GG

Combinatorial contribution:

Size and shape effect (Staverman−Guggenheim)

Residual contribution: Molecular interactions

water

hexane

1-octanol

Geometry opt.

-0.025 0.025 (e/Å2) (e/Å2)

COSMO

Quantum mechanics Statistical mechanics

Å2

Å2

s-profile

Å2

)(ln)(

*

/mSmii

res

Si

m

pnRT

Gss

s

Segment Activity Coefficient


Cyclohexane

(C6H12)

Cyclohexanol

(C6H12O)

CO2

Cyclohexanone

(C6H10O) Oxygene

Carbon dioxide

Cyclohexane

Cyclohexanone

Cyclohexanol

O2

-0.025 0.025 (e/Å2) (e/Å2)

s-profiles of investigated compounds

[1] C.-M. Hsieh, S.I. Sandler, S.-T. Lin: Fluid Phase Equilib.: 297, 90-97 (2010).

[2] T. Merker, C.-M. Hsieh, S.-T. Lin, J. Vrabec, H. Hasse: AIChE J. in press, (2013)

i

iimix pxp )()( sss-profiles for mixture:


COSMO-SAC

Gex

Prediction: kij = 0 and lij =0.

Or fitting to ONE experimental datum of p(T,x) or H(T)

VDW mixing rule

a(T,x),

b(x)

PR EOS

1i j ii jj ij

i j

a x x a a k

i i

i

b x b

Van der Waals mixing rule

kij

MHV1 mixing rule

a(T,x), b(x)

PRSV EOS VLE, H(T)

calculation

Peng-Robinson equation of state (PR EOS)

( ) ( )

RT ap

v b v v b b v b

E1ln

0.53

ii

i ii i

a a g bx

bRT b RT RT b

12

i j

i j ij

i j

b bb x x l

Modified Huron-Vidal 1st order

lij

[1] D.Y. Peng, D.B. Robinson: Ind. Eng. Chem Fundam., 15: 59 (1976) [2] M.L. Michelsen: Fluid Phase Equilib., 60: 47 (1990)

[3] R. Stryjek, J.H. Vera: Can. J. Chem. Eng., 64: 323 (1986)


Experiment

Simulation (Prediction)

Simulation (with ij)

+

O2

[1] T. Merker, et al.: J. Chem. Thermodyn., 49: 114 (2012) [2] T. Merker, et al.: Fluid Phase Equilib., 315: 77 (2012)

COSMO-SAC (Prediction)

COSMO-SAC (with lij)

PR EOS (with kij)

Henry‘s law constant CO2

OH

=O

OH

=O

.....

- - -


O2 + CO2

Experiment


+




PR EOS (with kij)

+ OH

CO2 + =O

.....

- - -

Selected binary VLE (I)


+ OH =O Experiment


+




PR EOS (with kij) .....

- - -

Selected binary VLE (II)


Analysis of all 10 binary systems

Rating from - - (0 points, very bad) to ++ (4 points, very good)

Mixture Molecular Simulation COSMO-SAC Peng-Robinson EOS

Prediction with ij Prediction with lij Prediction with kij

O2 + CO2 ++ ++ - ++ - ++

O2 + - ++ - ++ - - ++

O2 + - ++ - ++ - - ++

O2 + - ++ - ++ - - ++

CO2 + - + - + - - 0

CO2 + + ++ + ++ 0 ++

CO2 + - + 0 + - - 0

+ 0 ++ 0 ++ - ++

+ ++ ++ ++ ++ - - 0

+ ++ ++ 0 + - - - -

Overall 22 38 18 37 5 30

=O

OH

=O

OH

=O OH

=O

OH



Henry‘s law constant for three ternary subsystems

313 K Experiment


+


O2

CO2

=O

OH



Experiment


( and are in equal-molar concentration)

313 K


Henry‘s law constant for two quaternary subsystems

=O OH

O2

CO2 =O

OH



xi / mol mol

-1

0,0 0,2 0,4 0,6 0,8 1,0

p /

MP

a

0

2

4

6

8

Pure O2

CO2 (with constant molar fraction

0.04 of O2 in the mixture)

Pure CO2

CO2 (with constant molar fraction

0.02 of O2 in the mixture)

Experiment


+


VLE of quaternary subsystems and pentenary system

The composition (without O2 and CO2) of the fluid is constant: : 0.325 mol/mol, : 0.35 mol/mol, : 0.325 mol/mol =O OH

313 K



Conclusions

• Models can be used in industrial process design

• Good predictions from molecular simulation and

COSMO-SAC

• Capable to predict multi-component VLE

• Excellent accuracy achieved with binary parameters

• Molecular models can be used for atomistic simulations of

e.g. fluid behavior in nanostructured catalysts


Thank You for Your Attention!


Mixture (i + j) ij lij kij

O2 + CO2 1 -0.0526 0.132

O2 + C6H12 0.90 -0.0547 0.22

O2 + C6H10O 0.93 -0.0342 0.355

O2 + C6H12O 0.91 -0.0266 0.345

CO2 + C6H12 0.95 -0.0523 0.217

CO2 + C6H10O 0.985 -0.0082 0.049

CO2 + C6H12O 0.918 -0.0418 0.225

C6H12+ C6H10O 0.982 -0.0228 0.065

C6H12+ C6H12O 0.982 -0.0035 0.07

C6H10O+C6H12O 1 -0.0027 0

Values of binary interaction parameters in this work



CO2 +

Experiment


+




PR EOS (with kij)

CO2 + OH

+ =O


Contribution of molecular simulation

• powerful predictive capabilities (thermodynamic data)

• works under any physical conditions

• low cost

Why is molecular simulation not a mainstream solution for

thermodynamic data retrieval?

• suitable molecular models

• today’s MS software: only a few independent properties

• new properties require implementation

• development is impossible for an inexperienced user


Peng-Robinson Equation of State (PR EOS)

( ) ( )

RT ap

v b v v b b v b

22 2

,

, ,

0.45724 1 1c i

i i

c i c i

R T Ta

p T

,

,

0.0778 c i

i

c i

R Tb

p

Peng-Robinson-Stryjek-Vera EOS

E1ln

0.53

ii

i ii i

a a g bx

bRT b RT RT b

12

i j

i j ij

i j

b bb x x l

2

3

1,

, ,

0.378893 1.4897153 0.17131848

0.0196654 1 0.7

i i i

i i

c i c i

T T

T T

PRSV EOS + MHV1 + COSMOSAC

Original Peng-Robinson

1i j ii jj ij

i j

a x x a a k

i i

i

b x b

21 0.37464 1.54226 0.26992i i i

PR EOS + VDW

Modified Huron-Vidal 1st-order Mixing Rule

Prediction: kij = 0 and lij =0.

Or fitting to ONE experimental datum of p(T,x) or H(T)

Van der Waals Mixing Rule

[1] D. Y. Peng, D.B. Robinson: Ind. Eng. Chem. Fundam., 15: 59-64 (1976)

[2] R. Stryjek, J.H. Vera: Can. J. Chem. Eng., 64: 323-333 (1986)

[3] M. L. Michelsen: Fluid Phase Equilib., 60: 213-219 (1990)

Documents

Fluid phase coexistence for the oxidation of cyclohexane