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Development of Methods for Predicting Solvation and Separation of Energetic Materials in Supercritical Fluids. Jason Thompson, Casey Kelly, Benjamin Lynch, Christopher J. Cramer and Donald G. Truhlar Department of Chemistry and Supercomputing Institute University of Minnesota

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Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Development of Methods for Predicting Solvation and Separation of Energetic Materials in Supercritical Fluids

Jason Thompson, Casey Kelly, Benjamin Lynch,

Christopher J. Cramer and Donald G. Truhlar

Department of Chemistry and Supercomputing Institute

University of Minnesota

Minneapolis, MN 55455


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

• Environmentally problematic Separation of Energetic Materials in Supercritical Fluids

• Expensive

What cosolvent? What conditions?

The goal of this work

To develop a predictive model

for solubilities of high-energy materials

in supercritical CO2: cosolvent mixtures.

Methods for the demilitarization of excess stockpiles containing high-energy materials

• burning

• detonation

• recycling explosive materials by extraction using

supercritical CO2 along with cosolvents


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

What Do We Usually Predict with Our Separation of Energetic Materials in Supercritical FluidsContinuum Solvation Models?

gas-phase

gas-phase

solvent A

pure solution of solute

solvent B

liquid solution

Absolute free energy of solvation

Solvation energy

Free energy of self-solvation

Vapor pressure

Transfer free energy of solvation

Partition coefficient


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

A(g) Separation of Energetic Materials in Supercritical Fluids

o

o

G

(self

):

G

(

aq

):

D

D

S

S

equilibrium standard-state aqueous free energy of solvation

can be calculated or obtained from expt.

equilibrium standard-state free energy of self-solvation

can be calculated or obtained from expt.

defines pure-solute vapor pressure of A

o

o

G

(

aq

)

G

(self)

D

D

S

S

A(aq)

A(liq)

o

G

(aq

liq)

D

«

S

solubility of A

S

o

A

G

(aq

liq)

RT

ln

D

«

=

-

S

l

M

A

molarity of A

Similar relationships exist for other liquid solvents or when A is a solid.


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

The SM5.43R Solvation Model Separation of Energetic Materials in Supercritical Fluids1,2

o

G

G

G

D

=

D

+

S

EP

CDS

  • Bulk-electrostatic contribution to free energy of solvation

    • Solute-solvent polarization energy

    • Electronic distortion energy of solute and solvent cost

  • Generalized Born approximation

    • Solute is collection of atom-centered spheres with empirical Coulomb radii and atom-centered point charges

      • Need accurate charges

  • Need dielectric constant of solvent

1Thompson, J. D.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. A2004, 108, 6532.

2Thompson, J. D.; Cramer, C. J.; Truhlar, D. G. Theor. Chem. Acc.2004, in press.


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

The SM5.43R Solvation Model Separation of Energetic Materials in Supercritical Fluids1,2

o

G

G

G

D

=

D

+

S

EP

CDS

  • Non-bulk-electrostatic contribution to free energy of solvation

    • Cavitation, dispersion, solvent structure, and other effects

  • Model: proportional to solvent-accessible surface areas of atoms in solute

    • Constants of proportionality are surface tension coefficients

  • Need index of refraction, Abraham a and b parameters, and macroscopic surface tension of solvent

H bond acidity, basicity

1Thompson, J. D.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. A2004, 108, 6532.

2Thompson, J. D.; Cramer, C. J.; Truhlar, D. G. Theor. Chem. Acc.2004, in press.


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

SM5.43R Uses CM3 Separation of Energetic Materials in Supercritical Fluids1-3 charges

  • CM3 charge model

    • Maps lower level charges to improved charges as trained on dipole moments

    • Uses a larger training set than previous charge models

    • Is less sensitive to basis set size than previous charge models

    • Uses redistributed Löwdin population analysis (RLPA)4 charges when diffuse functions are used

    • Is available for many combinations of hybrid-density functional theory and basis set

  • How accurate is CM3 for high-energy materials?

1Winget, P.; Thompson, J. D.; Xidos, J. D. Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. A2002, 106, 10707.

2Thompson, J. D.; Cramer, C. J.; Truhlar, D. G. J. Comput. Chem. 2003, 24, 1291.

3Kelly, C. P.; Cramer, C. J.; Truhlar, D. G. Theor. Chem. Acc. 2004, in press.

4Thompson, J. D.; Xidos, J. D.; Sonbuchner, T. M.; Cramer, C. J.; Truhlar, D. G. PhysChemComm2002, 5, 117.


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Accurate Separation of Energetic Materials in Supercritical Fluids, Density, andCM3Dipole Moments

nitramide

Cs C2v Cs C2v

3.94

3.59

3.84

4.31

3.93

4.19

2.97

2.712.89

3.28

3.07

3.27

Accurate: mPW0/MG3S density dipole

Approximate dipoles

MUE  mean unsigned error:

MUE (density) = 0.30 debyes

MUE (CM3) = 0.08 debyes

from mPW0/MIDI!


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Accurate Separation of Energetic Materials in Supercritical Fluids, Density, andCM3Dipole Moments

dimethylnitramine

4.81

4.21

4.67

5.04

4.43

4.87

3.43

2.99

3.33

3.69

3.38

3.77

MUE  mean unsigned error:

MUE (density) = 0.49 debyes

MUE (CM3) = 0.12 debyes

Accurate: mPW0/MG3S density dipole


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Accurate Separation of Energetic Materials in Supercritical Fluids, Density, andCM3Dipole Moments

: RDX

5.97

5.22

6.20

7.19

6.22

7.34

MUE  mean unsigned error;

MUE (density) = 0.86 debyes

MUE (CM3) = 0.19 debyes

Accurate: mPW0/MG3S density dipole


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Accurate Separation of Energetic Materials in Supercritical Fluids, Density, andCM3Dipole Moments

: HNIW; CL-20

[hexa-nitrohexaaza-iso-wurtzitane]

1.56

1.32

1.80

0.31

0.42

0.79

2.56

1.95

2.41

MUE  mean unsigned error:

MUE (density) = 0.32 debyes

MUE (CM3) = 0.29 debyes

Accurate: mPW1PW91/MG3S density dipole


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

All 14 nitramines Separation of Energetic Materials in Supercritical Fluids

(0.2)

(2.8)

(2.9)

MUD (CM3) = 0.1

MUD (ChElPG) = 5.7

MUD (Löwdin) = 5.9

CM3 Delivers Consistent Partial Atomic Charges

Polarization energies (in nitromethane) calculated using different charge schemes by wave function (kcal/mole):

electrostatic

fitting

MUD  mean unsigned deviation:

population

analysis


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

The new CDS Term for SM5.43R Separation of Energetic Materials in Supercritical Fluids

  • Parameters in surface tension coefficients optimized using a large training set of solvation data

    • 2237 experimental free energies of solvation in water and 90 organic solvents, partition coefficients between water and 12 organic solvents, and free energies of self-solvation

  • Parameters are universal

    • Parameters optimized for specific wave functions are similar to one another

  • 2–8 times more accurate than the polarizable-continuum models (PCMs) in Gaussian 03, such as IEF-PCM


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

smaller errors, and yet… Separation of Energetic Materials in Supercritical Fluids

better density functional

better basis

universal in solvents

broader range of software packages

Mean-Unsigned Errors (MUEs) of Free Energies of Solvation

B3LYP/6-31G(d)IEF-PCM

Gaussian03

MPW0/6-31+G(d)SM5.43R

HONDOPLUS

GAMESSPLUS

SMXGAUSS

mean unsigned error:

257 neutrals in water 1.240.54

621 neutrals in 16 organic solvents 3.96 0.51

1359 neutrals in 74 other org. solvents not available0.53

16 self-solvation energies 3.93 0.56

74 other self-solvation energies not available 0.55


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

SM5.43R for Supercritical CO Separation of Energetic Materials in Supercritical Fluids2with and without cosolvents

  • Need to develop solvent descriptors as a function of T and P

    • Dielectric constant, index of refraction, Abraham’s hydrogen bond parameters, macroscopic surface tension, possibly others


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Dielectric Constant Predictions Separation of Energetic Materials in Supercritical Fluids

Dielectric constant as a function of pressure at 323 K

Dielectric constant, e

1 MPa = 10 atm

Similar accuracy at other temperatures

Pressure (MPa)


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

SM5.43R for Supercritical CO Separation of Energetic Materials in Supercritical Fluids2with and without Cosolvents

  • Develop solvent descriptors as a function of T and P

    • Dielectric constant, index of refraction, Abraham’s hydrogen bond parameters, macroscopic surface tension, possibly others

  • Need training set of solvation data

    • Mostly solubility data

      • Relate free energies of solvation to solubility?1

1Thompson, J. D.; Cramer, C. J.; Truhlar, D. G. J. Chem. Phys. 2003, 119, 1661.


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Test Relationship Separation of Energetic Materials in Supercritical Fluids

  • Use a test set of 75 liquid solutes and 15 solid solutes

    • Compounds composed of H, C, N, O, F, and Cl

      • Each solute has a known experimental aqueous free energy of solvation, pure vapor pressure, and aqueous solubility

  • Predict using experimental quantities

  • Predict using experimental vapor pressures and calculated aqueous free energies of solvation

  • Predict using calculated vapor pressures and aqueous free energies of solvation

log

S

log

S


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Mean-Unsigned Errors of the Separation of Energetic Materials in Supercritical FluidsLogarithm of Solubility

calculated from experimental values, from theoretical free energies and experimental vapor pressures, and from theoretical values

requires “solvent” descriptors for solutes;

we have the required solvent descriptors for only 7


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Other Progress Separation of Energetic Materials in Supercritical Fluids

  • Optimized electronic structure computer programs for hybrid density functional methods

    • Up to 4 times faster

  • Assembling training set of solubility data in supercritical CO2

  • New theoretical models to estimate solvent descriptors for free energy of self-solvation calculations


Jason thompson casey kelly benjamin lynch christopher j cramer and donald g truhlar

Acknowledgments Separation of Energetic Materials in Supercritical Fluids

Casey P. Kelly (grad. student)

Dr. Benjamin J. Lynch (postdoctoral associate)

Jason D. Thompson (graduate student; Ph. D. completed summer ’04)

Christopher J. Cramer (co-PI)

Department of Defense Multidisciplinary University Research Initiative (MURI)

Minnesota Supercomputing Institute (MSI)