Process and apparatus for separating gas from a multi-phase mixture being recycled in a reactor

A reactor in which a multi-phase mixture, including gas and a catalyst slurry or liquid, is to be conducted. The reactor includes a reaction chamber having a substantially unencumbered center portion through which the multi-phase mixture is conducted upwardly. A downcomer arrangement is disposed laterally outwardly of the center portion and adjacent to an inner surface of the reaction chamber. An external pump communicates with a lower portion of the reaction chamber for circulating components of the mixture downward from an upper end of the downcomer arrangement to a lower end thereof. A collection chamber is disposed below the reaction chamber into which the components exiting the downcomer arrangement are introduced and where the gas is separated from the remainder of the components. The separated gas can be reintroduced into the reaction chamber.