A process for reacting a fluid phase (gaseous and/or liquid phase) in contact with a solid phase in a reaction zone, wherein the improvement in said process comprises reacting the fluid phase in contact with the solid phase in a horizontally-oriented fluidized bed vessel. The vessel includes at least two compartments or stages, and includes means for vibrating the vessel. The process of the present invention enables one to effect fluidization of the solid phase independently of the flow rate or velocity of the fluid phase, thus enabling proper contact time of the fluid phase with the solid phase and minimizing the amount of fluid phase reactant to be recycled.