Which statement accurately describes the plug flow reactor flow?

• A. The contents are perfectly mixed with no gradient along the length.
• B. The feed is introduced at one end and the products exit from the same end.
• C. The feed is introduced at one end and products exit from the other end.
• D. It is used for batch processing.

Answer: (C)

In a plug flow reactor, fluid elements move through the reactor along the length with minimal mixing in the flow direction, so the composition (and temperature) can vary from inlet to outlet while remaining uniform across the cross-section. This means reactants enter at one end and products exit from the opposite end.

The idea that the contents are perfectly mixed with no gradient along the length would describe a well-mixed, constant composition situation like a CSTR, not a PFR. The notion of feeding at one end and exiting at the same end implies recirculation or a closed loop, which isn’t how a straight PFR operates. And batch processing is inherently non-continuous—no feed at one end and exit at the other during a continuous run—which doesn’t fit the continuous-flow nature of a plug flow reactor.