CHETAH 8.0

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CHETAH 8.0

• ASTM E27-07
• Tutorial

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CHETAH Computer Program for Energy Release
Evaluation and Prediction of Chemical
Thermodynamic Properties.

• The CHETAH program is a unique tool for
  predicting both thermochemical and flammability
  properties and certain reactive chemicals hazards
  associated with a pure chemical, a mixture of
  chemicals, or a chemical reaction. The
  calculations are made using only information
  concerning the molecular structure of the
  components

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Capabilities of CHETAH

• Gas phase thermochemistry
• heats of reaction
• heat of combustion
• equilibrium constants
• misc. thermodynamic properties
• Energy Release Evaluation
• tendency for a material to explode
• Predicts Lower Flammable Limit and other
  flammability properties

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Unique Capabilities

• Largest Database for Benson Groups (886!)
  Suggests substitutes for missing groups!
• Prediction of Reactive Chem. Hazards (ERE)
• Large whole molecule database from DIPPR (1200
  species!)

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Bensons Method Example

• Atom Benson Contribution to
  Group DfH(g), kcal/mol
• 1 NH2 - ( C) 4.80
• 2 CH2 - ( N, C) -6.60
• 3 CH2 - (2C) -4.93
• 4 CHCl - (2C) -14.80
• 5 CH - (O, 2C) -7.20
• 6 OH - (C) -37.88
• 7 CH3 - ( C) -10.08
• Total -76.69

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• Dont Know How to Specify Benson Groups? Dont
  Despair!Graphical User Interface May Be Used
• Uses ChemDraw
• Molecular Drawing
• Software
• Save structure
• as SMILES string
• Cut and Paste
• into CHETAH
• Automatically converts to Benson groups!

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ASTM CHETAH

• Thermodynamic Table Demo

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Main Screen for CHETAH. The user can directly
enter the molecules from the database or use
Benson groups to describe the new molecule.
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As an alternative, we can describe the molecule
using an appropriate molecular drawing program.
Here we draw a molecule in ChemdrawTM Software (
www.camsoft.com)
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Next we select the drawn molecule and copy it as
a SMILES string
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We now return to the CHETAH program and choose
SMILES Input. Next we paste the SMILES string we
that copied from the other application and choose
OK.
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Now we see a screen showing the Benson groups
composing the molecules. We select Next.
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Select Thermodynamic Table from the
Calculations menu.
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Next we see a screen asking for information
relating to the Thermodynamic Table that we wish
to calculate. Select Calculate.
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The following is the resulting table of
calculated thermodynamic values
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ASTM CHETAH

• Combustion Calculations Demo

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CHETAH Heat of Combustion

• CHETAH can calculate heat of combustion for any
  compound or mixture composed of any of
  approximately 70 elements.
• CHETAH calculates the heat of combustion based on
  the reactant(s) being ideal gases at 298 K.
• CHETAH chooses combustion products based on a
  standard set of rules.

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On this screen the user can enter molecules from
the database or from Benson groups. Here we
search for the chemical Phenol.
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The search box was used to locate phenol in the
gas molecules database. The component phenol is
then selected and Add Group is clicked.
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Note the changes. Phenol has been added in first
row of the first column with its molecular
weight shown above.
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Select the name bar above the first column and
enter the desired name for the component.
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Choose Combustion Heat from Calculations
menu.
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Next we see a screen asking for information
related to Combustion Calculations. Select
Calculate.
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These are the results for the combustion
calculations.
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ASTM CHETAH

• Energy Release Calculations Demo

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CHETAH for Reactive Hazard Evaluation

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• Conservative screening tool
• Energy related hazards frequently not known
• Experimentally determined thermochemical data are
  often not available
• CHETAH can perform an energy release
• evaluation based on structure only
• Can give the maximum energy of decomposition
• Hazard evaluations are valid for gas, liquid, or
  solid materials

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On this screen the user can enter molecules from
the database or from Benson groups. Here we will
enter Tri Nitro Toluene (TNT) from Benson groups.
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For TNT, select Benson Groups as shown on the
following slides. Enter the numbers of each group
in the Count column.
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This completes the selection of groups for TNT.
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Select Energy Release from the Calculations
menu.
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Next we see a screen asking for information
related to Energy Release Evaluation. Select
Calculate.
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This screen represents the results of the
calculations.
Page 1 of 2
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Page 2 of 2
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Maximum Heat of Decomposition

• Easiest to understand and most intuitively sound
• In a material capable of harmful energy release,
  all of the energy is obtained from the material
  itself
• CHETAH chooses products which maximize the
  enthalpy of decomposition

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ASTM CHETAH

• Chemical Reaction Evaluation

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Reaction Thermochemistry in CHETAH

• Build all species
• Click on Reaction button
• Specify stoichiometry

CH3-(C) CHCl-(2C) CH2-(2C) CH2-(C,O) OH-(C)
CH3 - (C) CHCl - (C, C) CH - (C) CH2
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Think Simplification!!!

• "Analog Reaction Hypothesis" states that the
  heats of reaction for structurally similar
  reactions are identical
• Example R(g) Cl2(g) R-Cl(g) HCl(g)
• Species, R ?rH, kcal/mol, 25 C
• Ethane -28.8
• Octane -29.3
• Toluene -29.6
• Naphthalene -29.4

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Example of a Reaction Which can be Simplified
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Simplified Analog Reaction
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On this screen the user can enter molecules from
the database or from Benson groups. Here we will
describe the reaction between sulfuric acid and
sodium hydroxide.
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Select all the components for both reactants and
products.
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Select Chemical Reaction from Calculations
menu.
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Change the classification according to Reactant
or Product. Balance the reaction by choosing the
number of moles. Select Calculate.
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Results are now shown. Page 1 of 2
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Page 2 of 2
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Phase Effects

• CHETAH Calculations are gas phase values!
• If chemistry takes place in condensed phase (i.e.
  in a solvent), corrections need to be considered
• many times these corrections cancel but not
  always!
• Rule of thumb vaporiz. heat 100cal/g (150
  cal/g for a H-bonded species, 80 cal/g for a
  chlorinated species)
• Estimation methods for heat of vaporization are
  available.

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ASTM CHETAH

• Flammability

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CHETAH Flammability

• CHETAH calculates LFL, LOC, MIE and a number of
  other flammability parameters using Brittons
  method.
• CHETAH will calculate LFL at temperatures besides
  298 K.
• CHETAH also calculates LFL by Bothwells method.
• CHETAH can calculate LFL for mixtures.

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To find the flammability parameters of a gas
mixture, the user should enter molecules from the
Gas Molecules database or enter molecules by the
use of Benson Groups.
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Here Propane and N-butane have been selected
from the Gas Molecules database.
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After selecting the components, choose
Flammability from the Calculations menu.
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Next we see a screen asking for the composition
of the mixture. Choose the amount of each
chemical. Select Calculate.
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The first part of the results page for this
flammability example. This part shows results
from Brittons method.
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This section highlights predictions by Bothwells
method.
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Clicking on Definitions will display a list of
definitions

• LFL The Lower Flammable Limit is the minimum
  concentration of a combustible substance that is
  capable of propagating a flame through a
  homogeneous mixture of the combustible and a
  gaseous oxidizer under specified conditions.
• LOC The Limiting Oxygen Concentration of a
  fuel-oxidant-inert system is the oxygen (oxidant)
  concentration at the limit of flammability for
  the worst case (most flammable) fuel
  concentration.
• Etc. for LLFT, T-max, Su, qd, MIE
  
  
  
  
  
  

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For more information or to purchase CHETAH 8.0,
please visit this link www.astm.org/chetah.htm