Difference between revisions of "Process-Simulation-using-DWSIM/C2/Define-a-Kinetic-Reaction/English"

Title Slide

Learning Objective

• Specify the order of a reaction using Arrhenius rate equation
• Define the reaction phase
• Specify rate constants for direct and reverse reactions using Arrhenius equation
• Specify units for reaction rate

System Requirements

To record this tutorial, I am using

• DWSIM 9.0.4 and
• Windows 11

The process demonstrated in this tutorial is identical in other OS like

• Linux,
• Mac OS X or
• FOSSEE OS on ARM.

But, this process is identical in Linux, Mac OS X, or FOSSEE OS on ARM.

The process demonstrated in this tutorial is identical in other OS as well.

Pre-requisites

To practice this tutorial, you should know to

• Add components to a flowsheet.
• Select thermodynamic packages

Add the kinetic rate equation for liquid phase isomerization of n-butane

Components present in the system are n-Butane, isopentane and isobutane

Reaction: n-C₄H₁₀ ⇌ iso-C₄H₁₀

Use Peng-Robinson property package

Components present in the system are n-Butane, isopentane and isobutane.

The reaction is: n-butane isomerizes to form isobutane.

Use the Peng-Robinson property package.

Reaction Kinetics

rate = k_fC_N-butane - k_bC_Isobutane kmol / m³ s

where

• C is the molar concentration of respective components in kmol/m3
• k_f is the forward rate constant
• k_b is the backward rate constant

Where

• C is the molar concentration of respective components in kilomol per meter cube
• k_f is the forward rate constant
• k_b is the backward rate constant

Forward Reaction Rate Constant

k_f = k_f0 exp(<math>\frac{-Ef}{\mathit{RT}}</math>)

K_f0 = 2.94 <math>\times </math>10⁷

E_f = 65300 J/mol

Backward Reaction Rate Constant

k_b = k_b0 exp(<math>\frac{-Eb}{\mathit{RT}}</math>)

K_b0 = 1.176 <math>\times </math>10⁸

E_b = 72200 J/mol

N-butane, Isobutane, Isopentane

Property package - Peng-Robinson property package.

System of Units C5

I have,

• Added the compounds as n-butane, isobutane and isopentane
• Selected Peng-Robinson property package and
• Selected system of units as C5

Click Settings

The Settings window opens.

Under Identification, enter the Name as Butane Isomerization.

It indicates the components that will take part in the reaction.

Under Include, check the check boxes against the components N-butane and Isobutane.

Isopentane is inert here and doesn’t participate in the reaction.

Tick N-butane

Under Base Component, check the N-butane check box as N-butane is the base component.

-1 for N-butane and 1 for Isobutane.

Then press Enter.

A negative sign is to indicate the components as Reactants.

So the reaction is balanced after entering the stoichiometric coefficients.

DO >> N-butane: 1

Press Enter.

We are considering the reaction to be First order with respect to N-butane.

So we will enter 1 in the DO column against N-butane.

And then press Enter.

RO >> Isobutane: 1

We are considering the reaction to be First order with respect to Isobutane.

So we will enter 1 in the RO column against Isobutane.

And then press Enter.

So, we will select Basis as Molar Concentrations.

It gives a temperature range within which rate expression is assumed to be valid.

Tmax (K) >> 2000

Direct Reaction >> Arrhenius

First is to select the type of rate law.

From the problem statement, it can be seen that Arrhenius Rate Law is followed.

By default, Arrhenius is already selected.

So let’s not change it.

As per the problem statement, the pre-exponential factor is 2.94E7, so type 2.94E+7 in A.

As per the problem statement, given value of Activation Energy is in J/mol.

It is the default unit, so we will not change anything.

Similar to the forward reaction, it can be seen that Arrhenius Rate Law is followed also for the backward reaction.

By default, Arrhenius is already selected.

So let’s not change it.

As per the problem statement, the pre-exponential factor is 1.176E8, so type 1.176E+8 in A'

As per the problem statement, given value of Activation Energy is in J/mol.

It is the default unit, so we will not change anything.

This is to indicate the units of Basis term selected in the Kinetic Reaction Parameters.

Here, Molar Concentrations is selected as Basis under Kinetic Reaction Parameters.

As per the problem statement, the units of Molar Concentration are mentioned as kmol/m3.

Click on the drop-down against Amount Units >> select kilomol per meter cube if not already selected.

So, let’s not change it.

Click >> Basis >> Partial Pressure

Amount Units >> Click on drop-down to show pressure units.

Select the unit in which partial pressure is expressed in the rate equation.

You can see that the drop-down against Amount Units shows the units of pressure.

Amount Units >> kmol/m3

Change the Basis to Molar Concentrations.

Ensure that the Amount Units is kmol/m3.

Rate Units >> kmol/[m3.s]

According to our question, the rate units are kilomol per meter cube second.

Click on the drop-down against Rate Units and select kilomol per meter cube second.

It is important to select the correct unit.

Summary

• Specify the order of a reaction using Arrhenius rate equation
• Define the reaction phase
• Specify rate constants for direct and reverse reactions using Arrhenius equation
• Specify units for reaction rate

Let us summarize.

Assignment

Compounds: Ethylene oxide, Water & Ethylene glycol

Reaction: C₂H₄O + H₂O ⇌ C₂H₆O₂

Property Package: NRTL

Reaction Rate:

r _A = KC_{ethyleneoxide} kmol/m3.h

C is the molar concentration in mol/m3

K = k₀ exp(<math>\frac{-E}{\mathit{RT}}</math>)

k₀ = 32324

E = 45584 J/mol

DWSIM Flowsheeting Project

Lab Migration Project

Acknowledgements

Thanks

Thank you for joining.