CHETAH 8.0

ASTM E27-07

Tutorial

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

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

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!)

Benson’s Method Example

Atom Benson Contribution to Group fH(g), kcal/mol

1 NH2 - ( C) 4.802 CH2 - ( N, C) -6.603 CH2 - (2C) -4.934 CHCl - (2C) -14.805 CH - (O, 2C) -7.20

6 OH - (C) -37.887 CH3 - ( C) -10.08

Total: -76.69

Cl

OH

H2N

12

3 4

5

6

7

Don’t Know How to Specify Don’t Know How to Specify Benson Groups? Don’t Despair!Benson Groups? Don’t Despair!Graphical User Interface May Be Graphical User Interface May Be Used:Used:•Uses ChemDraw®

Molecular Drawing

Software

•Save structure

as “SMILES” string

•Cut and Paste

into CHETAH

•Automatically converts to Benson groups!

ASTM CHETAH

Thermodynamic Table Demo

Main Screen for CHETAH. The user can directly enter the molecules from the database or use Benson groups to describe the new molecule.

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)

Next we select the drawn molecule and copy it as a SMILES string

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.

Now we see a screen showing the Benson groups composing the molecules. We select Next.

Select “Thermodynamic Table” from the “Calculations” menu.

Next we see a screen asking for information relating to the Thermodynamic Table that we wish to calculate. Select “Calculate”.

The following is the resulting table of calculated thermodynamic values

ASTM CHETAH

Combustion Calculations Demo

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.

On this screen the user can enter molecules from the database or from Benson groups. Here we search for the chemical Phenol.

The search box was used to locate phenol in the gas molecules database. The component phenol is then selected and “Add Group” is clicked.

Note the changes. Phenol has been added in first row of the first column with its molecular weight shown above.

Select the name bar above the first column and enter the desired name for the component.

Choose “Combustion Heat” from “Calculations” menu.

Next we see a screen asking for information related to Combustion Calculations. Select “Calculate”.

These are the results for the combustion calculations.

ASTM CHETAH

Energy Release Calculations Demo

CHETAH for Reactive Hazard Evaluation

 •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

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.

For TNT, select Benson Groups as shown on the following slides.Enter the numbers of each group in the ‘Count’ column.

This completes the selection of groups for TNT.

Select “Energy Release” from the “Calculations” menu.

Next we see a screen asking for information related to Energy Release Evaluation. Select “Calculate”.

This screen represents the results of the calculations.Page 1 of 2

Page 2 of 2

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

ASTM CHETAH

Chemical Reaction Evaluation

Reaction Thermochemistry in CHETAH

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

Cl

+ H2O

Cl

OH

CH3 - (C)CHCl - (C, =C)=CH - (C)=CH2

CH3-(C) CHCl-(2C)CH2-(2C)CH2-(C,O)

OH-(C)

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

Example of a Reaction Which can be Simplified:

+CH CH2 NH2 CH Cl CH2 CH C CH C O

OH

CH CH2 NH CH CH2 CH C CH CO

OHHCl+

Simplified Analog Reaction:

NH2 + Cl

N+ HCl

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.

Select all the components for both reactants and products.

Select “Chemical Reaction” from “Calculations” menu.

Change the classification according to Reactant or Product. Balance the reaction by choosing the number of moles. Select “Calculate”.

Results are now shown.Page 1 of 2

Page 2 of 2

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.

ASTM CHETAH

Flammability

CHETAH Flammability

• CHETAH calculates LFL, LOC, MIE and a number of other flammability parameters using Britton’s method.

• CHETAH will calculate LFL at temperatures besides 298 K.

• CHETAH also calculates LFL by Bothwell’s method.

• CHETAH can calculate LFL for mixtures.

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.

Here Propane and N-butane have been selected fromthe Gas Molecules database.

After selecting the components, choose “Flammability” from the “Calculations” menu.

Next we see a screen asking for the composition of the mixture.Choose the amount of each chemical. Select “Calculate”.

The first part of the results page for this flammability example. This part shows results from Britton’s method.

This section highlights predictions by Bothwell’s method.

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

For more information or to purchase CHETAH 8.0,

please visit this link: www.astm.org/chetah.htm