An ionic liquid reactor unit and a process for controlling heat generation from an ionic liquid reactor unit. The ionic liquid reactor unit may include an external heat exchanger. The effluent from the reactor is separated in a separation zone allowing the hydrocarbon phase to transfer heat to a cooling fluid. The heat exchanger may be a tube-in-shell, a spiral plate heat exchanger, a hair pin heat exchanger. The heat exchanger accommodates the separation of the ionic liquid from the hydrocarbon phase, and may allow for the ion liquid to be drained.