A process vessel containing both an evaporation zone for evaporating a liquid feed and a treatment zone for treating the resulting vapor comprises an injector having an orifice, the orifice being in the evaporation zone, at least one evaporation surface for evaporating feed and generating vapor, the evaporation surface being located in the evaporation zone, wherein the injector orifice and the evaporation surface are positioned to prevent the formation of a drop at the orifice, a treatment zone for treating the vapor and at least one heater associated with at least a portion of the process vessel.