Abstract: An apparatus for separating and stripping a mixture of gas and particles comprises an envelope having separation chambers and circulation chambers distributed about a reactor, the upper portion of each separation chamber comprising an inlet opening communicating with the reactor and with a zone for rotating the mixture in a vertical plane. Each separation chamber comprises two lateral walls which are also walls for the circulation chamber, at least one of the walls of each chamber comprising a lateral outlet opening for mixing gas and particles into the adjacent circulation chamber. Each separation chamber also comprises an axial opening for particles to enter a stripping chamber, the envelope further comprises a conduit for evacuating a gas-particle mixture connected to at least one secondary separator and the stripping chamber communicating with the conduit via circulation chambers. Application of this apparatus is to fluidized bed catalytic cracking of hydrocarbons in a riser and/or dropper.