A fluid catalytic cracking (FCC) process and apparatus for elutriatable catalyst mixtures. An additive, preferably comprising intermediate pore zeolites, such as ZSM-5⁻, and conventional FCC catalyst are used. An elutriating stripper separates the catalyst mixture. The additive is recycled to the FCC reactor. The conventional catalyst passes to a regenerator and then to the FCC reactor. The elutriating stripper employs a vessel and concentric cylinders forming an annular space.