Catalyst, method and apparatus for an on-stream particle replacement system for countercurrent contact of a gas and liquid feed stream with a packed bed

This invention makes possible substantially continuous flow of uniformly distributed hydrogen and hydrocarbon liquid across a densely packed catalyst bed to fill substantially the entire volume of a reactor vessel by introducing the fluids as alternate annular rings of gas and liquid (i.e. a mixture of liquid hydrocarbon and a hydrogen-containing gas) at a rate insufficient to levitate or ebullate the catalyst bed. Catalyst are selected by density, shape and size at a design feed rate of liquids and gas to prevent ebullation of the packed bed at the design feed rates. Catalysts are selected by measuring bed expansion, such as in a large pilot plant run, with hydrocarbon, hydrogen, and catalyst at the design pressures and flow velocities. The liquid and gas components of the feed flow into the bed in alternate annular rings across the full area of the bed. At the desired flow rate, such catalyst continually flows in a plug-like manner downwardly through the reactor vessel by introducing fresh catalyst at the top of the catalyst bed by laminarly flowing such catalyst in a liquid stream on a periodic or semicontinuous basis. Catalyst is similarly removed by laminarly flowing catalyst particles in a liquid stream out of the bottom of the catalyst bed.