Question

In an ideal plug flow reactor, the concentration of reactants:

• A. Remains constant throughout the reactor
• B. Changes only with time
• C. Changes only along the length of the reactor
• D. Is the same as in CSTR

Hint:

Logic Tip: Think of a conveyer belt in a factory. As the product moves down the line (length), more work gets done to it. The state of the product depends entirely on how far down the line it has traveled.

Answer 1

The Correct Option is C

Concept:
An ideal Plug Flow Reactor (PFR) is a continuous tubular reactor where the fluid flows in discrete "plugs" or slices, with perfect mixing radially (across the tube) but absolutely zero mixing axially (along the length of the tube).

Step 1: Because a PFR is a continuous flow reactor, it operates at steady-state. This means that if you look at one specific point in the pipe, the concentration at that specific point never changes as time passes. This eliminates option (B).

Step 2: Imagine a thin disk of fluid entering the pipe. As this plug travels down the length of the reactor, the chemical reaction is continuously occurring inside it.

Step 3: Because the reaction is happening as the plug moves forward, reactants are being consumed. Therefore, the concentration of reactants is highest at the inlet and steadily decreases as you move further down the pipe toward the outlet.

Step 4: A Continuous Stirred Tank Reactor (CSTR) assumes perfect mixing everywhere, meaning the concentration is constant throughout the entire tank. This eliminates options (A) and (D).

Step 5: In a PFR, concentration is independent of time but highly dependent on spatial position (length/volume down the pipe).