Using the VTUsing the VT--2005 database2005 databaseA stepA step--byby--step tutorial on predicting liquidstep tutorial on predicting liquid--phase activity phase activity

coefficients using the VTcoefficients using the VT--2005 sigma profiles and the 2005 sigma profiles and the COSMOCOSMO--SACSAC--VTVT--2005 program2005 program

Richard Oldland, Eric Mullins, Michael Zwolak, Kevin Seavey, and Y. A. Liu

Honeywell Center of Excellence in Computer-Aided DesignSINOPEC/FPCC/AspenTech Center of Excellence in Process Systems Engineering

Department of Chemical Engineering, Virginia TechBlacksburg, VA 24061

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This presentation shows how to use VTThis presentation shows how to use VT--2005 sigma 2005 sigma profiles with the COSMOprofiles with the COSMO--SACSAC--VTVT--2005 program to 2005 program to predict activity coefficientspredict activity coefficients

1. Overview of sigma profiles

2. Outline of the COSMO-SAC model

3. Using the COSMO-SAC-VT-2005 program

0

2

4

6

8

10

12

14

16

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-0.025 -0.020 -0.015 -0.010 -0.005 0.000 0.005 0.010 0.015 0.020 0.025

Sigma (e/A^2)

P(s

igm

a)*A

rea(

sigm

a) (A

^2)

1,4-dioxanewatermethyl acetate

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The sigma profile depicts the surface charge The sigma profile depicts the surface charge distribution over the entire molecule.distribution over the entire molecule.

Graphically: Area vs. charge/Area

Unique to each molecule

Profiles are stored in a database

Sigma profiles are not specific to a COSMO extension Sigma profile [P(σσσσ)] = the probability a

specific surface segment will have a specific charge density.

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COSMO models use sigma profiles to predict COSMO models use sigma profiles to predict physical properties.physical properties.

40

45

50

55

60

65

70

75

80

85

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

water mole fraction

Pre

ssur

e (m

mH

g)

UNIFACUNIFACCOSMO-SACCOSMO-SACNRTLNRTL

• Solubility (SLE)

• Vapor-Liquid (VLE)

• Partition coefficients (KOW)

• pKa

P(σσσσ) COSMO-SAC or COSMO-RS

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Chemical components including alcohols, alkanes, fluorocarbons, ketones, aldehydes, solvents, etc.

The molecules contain the following elements: C, O, H, N, I, Cl, F, Br, P, F

We develop the VTWe develop the VT--2005 sigma2005 sigma--profile database profile database containing over 1200 molecules.containing over 1200 molecules.

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We create sigma profiles in a format that is We create sigma profiles in a format that is usable with COSMOusable with COSMO--SACSAC--VTVT--2005 program.2005 program.

The output file ‘Chemical’Sigma-profile.txt is located in the ‘C:\Profiles\’directory by default.Å

We can either use this file directly in the COSMO-SAC program or we can plot it in MS Excel.

Sigma values (e/Å2) [x-axis]

P(σσσσ) values (Å2) [y-axis]

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Lin and Sandler (2002) develop the continuumLin and Sandler (2002) develop the continuum--solvation model COSMOsolvation model COSMO--SACSAC

Model traits• Extension to COSMO• Liquid phase interactions• Thermodynamically consistent

Figure from:Lin and Sandler (2002a)

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We begin with the definition of the solvation free We begin with the definition of the solvation free energy (energy (∆∆∆∆∆∆∆∆GGsolsol))

We break the real solvation process into two “ideal”steps:

1. Cavity formation 2. Charge restoration

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Previous models for the activity coefficient use the Previous models for the activity coefficient use the free energy of solvation.free energy of solvation.

* */ /

/

* */ /

/ /

ln ln

ln ln

sol soli S i i S

i Si

res resSGi S i i

i S i S

G G cRT c

G GRT

γ

γ γ

∆ − ∆= +

∆ − ∆= +

In terms of the solvation free energy (Ben-Naim (1987))

In terms of the charge restoring free energy. (Lin and Sandler (2002a))

The authors approximate the solvation process with the charge restoration free energy. We calculate this quantity with sigma profiles and activity coefficients for each surface segment.

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The COSMOThe COSMO--SAC model predicts the activity SAC model predicts the activity coefficient using the sigma profile.coefficient using the sigma profile.

( ) ( ) ( )

( ) ( ) ( )

( ) ( ) ( )

**//

**//

/ /

ln

ln

ln ln ln ln

m

m m

m

m m

m

resresSi S

i m i i m S m

resresii i

i m i i m i m

SGi S i i m S m i m i S

GGn n p

RT RT

GGn n p

RT RT

n p

σ

σ σ

σ

σ σ

σ

σ σ σ

σ σ σ

γ σ σ σ γ

� �∆∆ = = Γ� �� �� �

� �∆∆ = = Γ� �� �� �

= Γ − Γ +� �� �

� �

� �

�

* */ /

/ /ln lnres res

SGi S i ii S i S

G GRT

γ γ∆ − ∆= + Starting with the charge restoring free energy

In terms of the sigma profile and the segment

activity coefficient

Rigorous derivation included in Lin and Sandler 2002

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We provide the COSMOWe provide the COSMO--SACSAC--VTVT--2005 program to 2005 program to predict activity coefficientspredict activity coefficients

The COSMO-SAC-VT-2005 program is:•FORTRAN90 based•Open literature•Quick to run•Binary mixtures only•Easily upgradeable for ternary and quaternary mixtures

Calculates liquid-phase activity coefficients for mole fractions ranging from 0.005-0.995 in steps of 0.01

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Locate the pure component sigma profilesLocate the pure component sigma profiles

This program is compatible with sigma profiles in a format similar to the VT-2005 sigma profiles.

COSMO-SAC-VT-2005.exe requires the profile nameAND location.

We store our sigma profiles in a central directory “C:\Profiles” to make them easy to locate. Create the directories “C:\Profiles” and “C:\Profiles\Gammas” at this time.

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Run Run ““COSMOCOSMO--SACSAC--VTVT--2005.exe2005.exe”” and follow the MSand follow the MS--DOS promptsDOS prompts

Required inputs:•System temperature•Species names•VT-2005 sigma profiles•Cavity volumes•Output file name

Creates the output file in the directory “C:\Profiles\Gammas”by default.

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COSMOCOSMO--SACSAC--VTVT--2005.exe creates an output text file2005.exe creates an output text file

The output file is in the format:Mole fraction component 1, γγγγ1 , γγγγ2 , Ln(γγγγ1), Ln(γγγγ2)

We can use the output to We can use the output to compare activity coefficient compare activity coefficient predictions or to predict predictions or to predict physical propertiesphysical properties

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Congratulations!Congratulations!

You have successfully used the COSMO-SAC model, COSMO-SAC-VT-2005.exe, to predict liquid-phase activity coefficients for a binary mixture.

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AcknowledgementsAcknowledgements

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We used the following articles in developing this We used the following articles in developing this procedure.procedure.

Klamt, Andreas, G. Shüürmann, “COSMO-A New Approach to Dielectric Screening in Solvents with Explicit Expressions for the Screening Energy and Its Gradient”, J. Chem. Soc. Perkin Trans., 2, 799, (1993).

Klamt, Andreas, “Conductor-like Screening Model for Real Solvents: A New Approach to the Quantitative Calculation of Solvation Phenomena” , J. Phys. Chem , 99, 2224 (1995).

Klamt, Andreas, “COSMO and COSMO-RS”, Encyclopedia of Computational Chemistry, Paul von Rague Schleyer, editor, Wiley, New York (1998), pp. 604-615.

Lin, Shiang-Tai, “Quantum Mechanical Approaches to the Prediction of Phase Equilibria: Solvation Thermodynamics and Group Contribution Methods”, PhD. Dissertation, University of Delaware, Newark, DE, 2000

Lin, Shiang-Tai and Stanley I. Sandler, “A Priori Phase Equilibrium Prediction from a Segment Contribution Solvation Model”, Ind. Eng. Chem. Res, 41, 899(2002a).

Lin, Shiang-Tai and Stanley I. Sandler, “Reply to Comments on “A Priori Phase Equilibrium Prediction from a Segment Contribution Solvation Model” Ind. Eng. Chem. Res., 41, 2332 (2002b).