A fluid catalytic cracking (FCC) process and apparatus which employs relatively more elutriatable catalyst particles comprising intermediate pore zeolite, particularly ZSM-5, and relatively less elutriatable catalyst particles comprising large pore zeolite, preferably zeolite Y. The process and apparatus employ a first stripping vessel which also separates a more elutriatable first portion of catalyst from a less elutriatable second portion of catalyst. The more elutriatable first portion passes to a second stripping vessel, and subsequently recycles to a fluid catalytic cracking reactor riser. The second portion of less elutriatable catalyst passes from the first stripping vessel to a fluid catalytic cracking regenerator vessel and, after being regenerated, recycles to the reactor riser. The more elutriatable first portion contains a higher ratio of intermediate pore catalyst particles to large pore catalyst particles than does the second portion. Also disclosed is an apparatus for separating more elutriatable particles from less elutriatable particles which employs a vessel and concentric cylinders.