Chemical Reaction Engineering - Lecture # 4 - Design Equations for Batch Reactor, CSTR, PFR & PBR

Summary

In this Aspen Tech Channel lecture, the focus is on chemical reaction engineering, particularly chapters one and two. The lecture begins by solving an example from chapter one involving a first-order reaction in a tubular reactor. It then delves into chapter two, discussing conversion and reactor sizing. The presenter derives design equations for various reactors, including batch, CSTR, PFR, and PBR, emphasizing the importance of conversion in determining reaction progress. The lecture concludes with a teaser for upcoming topics on reactor comparison and sizing.

Takeaways

• 📚 Today's lecture is part of the Aspen Tech Channel's chemical reaction engineering series, focusing on lecture number four.
• 🔄 The lecture revisits chapter one to solve the last problem, then moves on to chapter two about conversion and reactor sizing.
• 🔍 A recap of the mole balance equation is provided, emphasizing the relationship between inflow, outflow, generation, and accumulation.
• 🌐 The characteristics of different reactors (batch, CSTR, PFR, and PBR) are discussed, highlighting their steady-state and uniform/non-uniform properties.
• 📉 The concentration profile for a PFR is sketched, showing how reactant concentration decreases along the reactor length.
• ✏️ An equation relating reactor volume to entering and exiting concentrations, rate constant, and volumetric flow rate is derived.
• 🔢 Given values for the rate constant (0.23 per minute), volumetric flow rate (10 cubic decimeters per minute), and concentration ratio (0.1 times C_a naught) are used to calculate the required reactor volume.
• 📐 The required volume for the reaction is calculated to be 100 liters, based on the given data and derived equations.
• 🔄 The concept of conversion is introduced, defined as the ratio of reacted moles of a reactant to the moles fed into the system.
• 📘 Equations for conversion in different types of reactors (batch, CSTR, PFR, and PBR) are derived, showing how they relate to reactor design and operation.
• 🔗 The lecture concludes with a summary of the key equations and a teaser for upcoming lectures on reactor sizing and comparison.

Q & A

What is the main topic discussed in lecture number four?

The main topic discussed in lecture number four is the continuation from chapter one, specifically solving the last problem of example 1.2, and then moving on to chapter two which is about conversion and reactor sizing.

What is the mole balance equation mentioned in the script?

The mole balance equation mentioned in the script is 'F_A0 - F_A + ∫(R_A * dV) = dNA/dt', where F_A0 is the inlet flow rate, F_A is the outlet flow rate, R_A is the rate of reaction, and NA is the accumulation of moles.

What are the characteristics of the four industrial reactors discussed in the script?

The characteristics of the four industrial reactors are as follows: Batch Reactor is unsteady state and uniform, CSTR is steady state and uniform, PFR and PBR are both steady state but non-uniform.

What is the reaction discussed in the script for the example problem?

The reaction discussed in the script is the liquid phase trans isomerization of butane, symbolically represented as A → B, where A is the reactant and B is the product.

How is the rate of reaction equation written for the trans isomerization of butane?

The rate of reaction equation for the trans isomerization of butane is written as -r = k * C_A, where k is the specific reaction rate constant and C_A is the concentration of the reactant A.

What are the three tasks the script mentions to be done for the system?

The three tasks mentioned in the script are: 1) Sketch the concentration profile, 2) Derive an equation relating reactor volume to entering and exiting concentrations of A, the rate constant, and the volumetric flow rate, and 3) Calculate the required volume using the given values.

What is the final concentration profile described in the script?

The final concentration profile described in the script starts at C_A0 at the inlet of the reactor and ends at C_A at the outlet, which is 0.1 times C_A0.

How is the equation relating reactor volume to concentrations derived in the script?

The equation relating reactor volume to concentrations is derived by using the mole balance equation for PFR, substituting the rate law, and integrating with respect to concentration while considering the constant volumetric flow rate.

What is the significance of the conversion concept in reactor sizing?

The conversion concept is significant in reactor sizing as it quantifies how far a reaction proceeds, indicating how much reactant has been converted to product, which is crucial for designing reactors to achieve desired yields.

What are the design equations derived for each type of reactor in the script?

The design equations derived for each type of reactor are: for batch reactor in terms of time, for CSTR in terms of volume, for PFR in terms of volume, and for PBR in terms of weight of catalyst.

What is the role of the limiting reactant in the stoichiometric coefficients?

The role of the limiting reactant in the stoichiometric coefficients is to make its coefficient as one, which serves as the basis for calculations, by dividing the other coefficients by the limiting reactant's coefficient.