Chemical Reactor Design (CSTR / PFR) Calculator

Chemical Reactor Design (CSTR / PFR) Calculator

Wiratama

11/16/20252 min read

1. Definition

A chemical reactor is a process vessel used to carry out chemical reactions under controlled conditions. Two of the most widely used reactor types in chemical engineering are:

  • CSTR — Continuous Stirred Tank Reactor
    Reactants are continuously fed into a well-mixed tank, and products leave at the same rate. Concentration is uniform throughout.

  • PFR — Plug Flow Reactor
    Reactants flow through a tubular reactor without back-mixing. Concentration and reaction rate change along the length of the reactor.

This calculator helps determine the reactor volume (V) required to achieve a specified conversion (X) for a first-order reaction, given flow rate, concentration, and rate constant.

2. Background Theory

First-Order Reaction Kinetics

For a first-order irreversible reaction:

A→Products

the rate law is:

−rA=kCA

where:

  • k = rate constant (1/s)

  • CA = concentration of A

CSTR Design Equation

For a CSTR operating at steady state:

Key idea:
The concentration inside the reactor is the same as the exit concentration, because the reactor is ideally mixed.

PFR Design Equation

For a plug flow reactor:

Key idea:
The reaction proceeds along the length of the reactor, and concentrations vary continuously.

Comparison Between CSTR and PFR

  • CSTR requires larger volume than a PFR for the same conversion (for first-order reactions).

  • PFR is more efficient, especially at high conversion.

  • CSTR provides uniform conditions, useful for heat transfer or multiphase mixing.

3. How the Calculator Works

Step 1 — User Inputs

The calculator accepts:

  • Reactor type: CSTR or PFR

  • Feed molar flow rate (Fₐ₀)

  • Initial concentration (Cₐ₀)

  • Rate constant (k)

  • Desired conversion (X)

Step 2 — Select the reactor model

Depending on the dropdown selection:

  • If CSTR, the calculator uses the CSTR design equation.

  • If PFR, the calculator uses the PFR design equation.

Step 3 — Compute required reactor volume

Based on the chosen reactor type, the program evaluates one of:

Step 4 — Display Results

The calculator outputs:

  • Reactor Type (CSTR or PFR)

  • Required Reactor Volume (m³)

  • Conversion achieved

The results help in early-stage chemical process design, feasibility studies, and academic reactor design calculations.