Estimating Chemical Properties
Applicability: Cranium, Synapse (core versions 0315+)

One of Cranium’s and Synapse's key capabilities is to estimate physical properties quickly, easily and accurately. To estimate a property the application first collects all applicable techniques, sorts them by accuracy, and then tries each one until an estimate is generated.

Example: Estimate 2-ethy-1-hexanol's physical properties
  1. Open a knowledge base document. (Open a "working" document or create a copy of a document (see here) if you are just experimenting with this functionality.)
  2. Change to the Chemicals Chapter and navigate to 2-ethy-1-hexanol. (See the Navigation Overview documentation for details on navigating chapters and pages.)
  3. Run the Compute Estimates command from the Commands menu.
    The application displays the Property Estimation Dialog.
  4. Press the dialog's Start button. The application estimates each property documenting its progress in the dialog.
  5. Once all estimates have been generated, expand the Boiling Point node, by clicking on the 'plus' sign to the left of the property, and continue to expand all child nodes. The display should appear similar to the following.
    This image shows that the knowledge base has three estimation techniques that can estimate the boiling point. The first technique tried was the 'Tb: Antoine Equation – PGL2001 [MKS]' technique. This technique failed. The second technique was the 'Tb: Stein + Brown Method [MKS]' technique. This technique succeeded – its estimate is reported at the end of the listing. The third technique was the 'Tb: Joback Method [MK S]' technique. This technique was not tried because an estimate had already been generated.
  6. Click the left mouse button on the 'Tb: Antoine Equation – PGL2001 [MKS]' technique. The dialog’s Details button will become active.
  7. Press the Details button. The application displays the Detailed Estimation Results dialog.
    Control showing the detailed results of the estimation.
    The dialog shows that the 'Tb: Antoine Equation – PGL2001 [MKS]' technique failed because it did not have the needed parameters for 2-ethyl-1-hexanol.
  8. Press the Done button to return to the Property Estimation Dialog.
  9. Press the Property Estimation dialog’s Save button. The application stores the estimates in the current knowledge base and displays them on 2-ethyl-1-hexanol's page.
    Column of data values.
    Column of estimated values.
Estimation Technique Selection

Cranium and Synapse store estimation techniques as entities just like chemicals, mixtures and references. Estimation techniques are stored in the Techniques Chapter of knowledge bases. (For details see documentation on the Techniques Chapter and Knowledge Base Documents.)

Every estimation technique contains two types of code: 1) accuracy/applicability code; 2) model code. When executed, the accuracy/applicability code returns two values: 1) a boolean true/false value indicating if the technique is applicable; 2) a numerical value denoting the technique's accuracy.

The accuracy/applicability code for several estimation techniques are shown here:

These example accuracy/applicability codes show how Cranium and Synapse decide which estimation technique should be used to estimate a particular property, of a particular chemical or mixture at a particular temperature, pressure and composition.

Before Cranium and Synapse perform an estimation, they first collect all estimation techniques for the property and execute each technique's accuracy/applicability code. Techniques whose codes return "false" are removed from consideration - those techniques are not applicable. The numerical result of each code represents the technique's accuracy. Techniques are sorted by this accuracy and the most accurate code is tried first. If this most accurate technique fails to generate and estimate, due to a missing parameter for example, the second most accurate technique is tried and so on.

Very often, Cranium and Synapse will need to estimate a dependent property during an estimation. For example, many estimation techniques for the liquid vapor pressure require values for the critical temperature. Cranium and Synapse will use the same technique selection procedure described previously in a recursive manner, selecting the best estimation technique for each dependent property.

For example, the Estimation Results shown below show how the application tried to estimate the vapor pressure using several techniques including the Ambrose + Walton Method. This method requires a value for the critical temperature. The application thus recursively tried to estimate the critical temperature using several techniques including the Joback's Method. This technique requires a value for the boiling point which is again estimated using this recursive method.

For additional documentation on estimation techniques see Estimate Chemical Properties Dialog and Techniques Chapter.

Example: Manually specify the boiling point estimation technique

Cranium and Synapse will automatically select the best applicable estimation technique. At times you may wish to manually specify which technique should be used for a particular property.

  1. Open a knowledge base document. (Open a "working" document or create a copy of a document (see here) if you are just experimenting with this functionality.)
  2. Change to the Chemicals Chapter and navigate to 2-ethy-1-hexanol. (See the Navigation Overview documentation for details on navigating chapters and pages.)
  3. Click the left mouse button on the boiling point field's estimate control. The application displays the Estimation Details dialog. This dialog shows the estimated value, the technique used to generate the estimate and comments.
  4. Make a mental note of the estimation technique used and then click the dialog's OK button to close the dialog.
  5. Click the right mouse button on the boiling point field’s estimate control. The application displays the control’s command menu.
  6. Choose the Select Technique command from the menu. The application displays the Estimation Technique Information dialog. The property’s estimation mode is currently set to Automatic Mode. In Automatic Mode, Cranium and Synapse select the best applicable technique.
  7. Change the Estimation Mode to Manual Mode and select the Joback Method. (Note: the actual techniques used and available may differ depending upon the knowledge base you are using. The key concept for this example, is to choose a different technique than the one the application automatically selected.)
  8. Press the dialog's OK button. The application will now use the Joback Method the next time it estimates the normal boiling point.
  9. Note 2-ethyl-1-hexanol's currently estimated boiling point. Use the previous procedure to estimate the chemical’s properties again. Note how the boiling point estimate has changed.
Estimating Temperature and Pressure Dependent Properties

To estimate properties dependent upon temperature, pressure or composition, you must first enter values for these state variables. Values can be entered individually or as a series. For examples, see the documentation for Temperature Dependent Section and Temperature and Pressure Dependent Section.

Estimating the Properties of Multiple Chemicals

The Command Menu's Estimate Multiple Chemicals command enables you to estimate a property for several chemicals at a time.

For temperature and pressure dependent properties, the dialog enables you to enter values for these state variables. Once these values are entered and one or more chemicals selected, pressing the dialog's Start button will generate estimates.

See documentation for the Estimate Multiple Chemicals Dialog for more details.

Tip: Estimate multiple chemicals after a design

A chemical design is often done on a limited set of physical property constraints. For example, in the design of a new refrigerant, we might design for constraints on vapor pressures, heat capacities and various thermodynamic derivatives. Once candidates have been designed, you can use the multiple chemical estimation capability to generate other properties, e.g., thermal conductivity, for each candidate at a series of temperatures for further evaluation.

Related Documentation
Topic Description
Estimating Chemical Properties a short video demonstrating how to estimate physical properties using either Synapse or Cranium.
Getting Started using Cranium provides a quick tour of Cranium's capabilities including a discussion of structure editing.
Chemicals Chapter the chemicals chapter contains numerous sections for entering and displaying data and estimates including the chemical structure section.