Presentation on theme: "CHETAH 8.0 ASTM E27-07 Tutorial. CHETAH ® Computer Program for Energy Release Evaluation and Prediction of Chemical Thermodynamic Properties. The CHETAH."— Presentation transcript:
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!)
Bensons Method Example Atom Benson Contribution to Group f H(g), kcal/mol 1NH2 - ( C) 4.80 2CH2 - ( N, C)-6.60 3CH2 - (2C)-4.93 4CHCl - (2C)-14.80 5CH - (O, 2C)-7.20 6OH - (C)-37.88 7CH3 - ( C)-10.08 Total: -76.69
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!
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.
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.
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
Reaction Thermochemistry in CHETAH Build all species Click on Reaction button Specify stoichiometry 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) + Cl 2 (g) => R-Cl(g) + HCl(g) –Species, R r H, kcal/mol, 25 C –Ethane-28.8 –Octane-29.3 –Toluene-29.6 –Naphthalene-29.4
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.
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.
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 from the 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 Brittons method.
This section highlights predictions by Bothwells 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
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