For all positive reaction orders and any specified duty, the size of a plug flow reactor (PFR) is _____________________ that of a mixed flow reactor?
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Answer: C. Smaller than
Explanation
Plug flow reactors maintain higher average reactant concentrations throughout their entire axial length. Higher reactant concentrations drive faster reaction rates compared to back-mixed continuous stirred tanks. Faster reaction rates mean a smaller reactor volume is required to achieve identical conversions. Plug flow reactors operate without mixing along the flow direction, preserving concentration gradients. Mixed flow reactors achieve instantaneous uniform composition throughout the entire active vessel volume. Reactor sizing equations integrate local reaction rates inversely to determine total required reactor volume.
Plug flow reactors are widely preferred for gas-phase reactions due to superior space-time yields. Capital investment costs for chemical plants depend heavily on minimizing required reactor physical volumes. Engineering designs choose PFR configurations whenever positive reaction orders permit smaller reactor footprints. Option A is incorrect because plug flow reactors are always smaller, never larger, for positive orders. Option B applies only to zero-order reactions where reactor type does not affect required volume. Option D is wrong because reaction kinetics provide predictable sizing differences for all positive orders.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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