Formation Target Calculation - Calcination
This example illustrates the calculation of a formation target where the temperature is solved at which a chemical reaction becomes spontaneous. This temperature point is where the change in Gibbs energy is zero, changing from a positive to negative value. This functionality of the app is illustrated in finding the temperature from which the thermal decomposition (calcination) of calcium carbonate (CaCO3) would proceed spontaneously.
This examples requires a process system to be created with the following components and chemical reactions (see Get Started Guide):
Components: CO2(g), CaCO3(s), CaO(s)
Chemical Reactions: CaCO3(s) → CaO(s) + CO2(g)
Note, ideally the chemical reaction should be defined in the direction such that it would not be spontaneous at lower temperatures.
Process systems view with process system listed for the current calculation example.
Process system view configured with components and reactions for the current calculation example.
This examples illustrates calculating the calcination temperature of calcium carbonate as the temperature at which the change in Gibbs energy (of the chemical reaction that defines calcination) is zero when changing from a positive to negative value.
Before using the transformation target functionality of the app that would yield the calcination temperature, the calculation is setup to calculate the change in Gibbs energy over a range of temperatures.
The change in Gibbs energy is calculated between the initial and final states, which for each temperature step is calculated at the same temperature for the reactants transformed to products.
For this example, temperature is set as the calculation target, varied between 800 and 1000°C, in steps of 10°C. The component amount of reactant CaCO3(s) is set to 1 kg, and the reaction extent to 1.
In the Calculation view, configure the new calculation as follows:
- Keep Initial Conditions off.
- Keep the Calculation Target on Temperature, and enter the Temperature values for FROM, TO, and STEP as 800, 1000, and 10 °C.
- Keep the units of the gas components as mol, and of solids components as kg.
- Keep the component amount for CaO(s) as 0 kg, and of CO2(g) as 0 mol.
- Change the component amount for CaCO3(s) to 1 kg.
- Keep the reaction extent specified as 1.
Calculation view with temperature configured.
Calculation view with component amounts and reactions configured.
After configuring the calculation, tapping on the Calculate button would display the Results view as below. The plot button can be selected for ΔGibbs Free Energy and the plots generated to illustrate the calculated change in Gibbs energy as a function of varied temperature.
The results illustrate that for the calcination reaction the change in Gibbs energy is positive for the temperature steps up 890°C. The calcination reaction at these temperatures is therefor not spontaneous, and the CaCO3(s) expected not to decompose to CaO(s) and CO2(g). From the temperature step of 900°C the change in Gibbs energy is negative, indicating the calcination reaction to be spontaneous.
These results therefor indicate the calcination temperature of the calcium carbonate to be just above 890°C, where the change in the Gibbs energy is zero and changes from a positive to negative value.
Calculation result values calculated for a temperature of 890°C.
Calculation result values calculated for a temperature of 900°C.
Results plot of the change in Gibbs energy as a function of temperature.
To find now the calcination temperature at which the thermal decomposition of calcium carbonate would become spontaneous, the transformation target functionality of the app can be used to find the temperature where the change in Gibbs energy is close to zero when it changes from a positive to negative value. This is an alternative to narrowing the calculation temperature range, and making the step size smaller.
For this example, on the calculation view change the Calculation Target from Temperature to Transformation, as illustrated below.
Tapping on the Calculate button would display the Results view as below. The calcination temperature is now displayed as 892.8°C, the Temperature of the FINAL state presented in the results. The change in Gibbs energy is also reported in the results as 0 kJ.
The results also indicate the heat of reaction at 892.8°C to be 1668 kJ per 1 kg of calcium carbonate. This is the value reported for ΔEnthalpy, with the basis being specified as 1 kg. To note, this represents the amount of energy required only for the thermal decomposition, and excludes heating of the calcium carbonate from ambient temperature. To include heating from ambient temperature, the initial condition would have to be specified in the calculation configuration.