In reactor design, recycle means:

• A. A stream that is vented to the atmosphere
• B. A portion of the product stream is returned to the reactor
• C. The feed is heated before entering the reactor
• D. A purge stream is removed to prevent buildup

Answer: (B)

Returning a portion of the reactor effluent to the reactor inlet is recycle. This reintroduces unreacted reactants back into the reactor so they have another chance to react, which increases the overall conversion you can achieve without needing a larger reactor. The fresh feed blends with the recycled stream, and the combined flow goes through the reactor again, effectively extending the contact time and improving yield. Recycling also offers a way to manage heat and composition by moving heat-rich product back into the reactor loop.

This differs from simply venting a stream, which removes material from the system; preheating the feed, which is about energy input before the reactor; or removing a purge stream to prevent buildup, which is about controlling inventory rather than reusing reactor contents.