A rotating packed bed unit comprising: a rotor vessel comprising: a rotor, wherein the rotor comprises: a first plate; a second plate; a plurality of sets of rings concentrically interposed between the first plate and the second plate, wherein each set of rings comprises a plurality of rings arranged cylindrically, wherein each ring comprises a plurality of packing elements; at least one metallic ring interposed between the plurality of sets of rings; and a gas inlet nozzle coupled to a gas impingement plate to affect inflow of gas into the rotor vessel, the gas impingement plate including a plurality of holes mounted at an exit of the gas inlet nozzle for distributing gas in the rotor vessel; and a liquid inlet and gas outlet pipe assembly coupled to the rotor, the liquid inlet and gas outlet pipe assembly comprising: gas outlet pipe to affect expulsion of gas from the rotor; and a liquid inlet pipe housing the gas outlet pipe to form a region to affect inflow of liquid into the rotor; and a shaft coupled to one of the first plate and the second plate of the rotor to rotate the rotor, wherein an outer surface of the shaft comprises a plurality of sequential steps tapered along the length of the outer surface. a rotor vessel comprising: a rotor, wherein the rotor comprises: a first plate; a second plate; a plurality of sets of rings concentrically interposed between the first plate and the second plate, wherein each set of rings comprises a plurality of rings arranged cylindrically, wherein each ring comprises a plurality of packing elements; at least one metallic ring interposed between the plurality of sets of rings; and a gas inlet nozzle coupled to a gas impingement plate to affect inflow of gas into the rotor vessel, the gas impingement plate including a plurality of holes mounted at an exit of the gas inlet nozzle for distributing gas in the rotor vessel; and a liquid inlet and gas outlet pipe assembly coupled to the rotor, the liquid inlet and gas outlet pipe assembly comprising: gas outlet pipe to affect expulsion of gas from the rotor; and a liquid inlet pipe housing the gas outlet pipe to form a region to affect inflow of liquid into the rotor; and a rotor, wherein the rotor comprises: a first plate; a second plate; a plurality of sets of rings concentrically interposed between the first plate and the second plate, wherein each set of rings comprises a plurality of rings arranged cylindrically, wherein each ring comprises a plurality of packing elements; at least one metallic ring interposed between the plurality of sets of rings; and a gas inlet nozzle coupled to a gas impingement plate to affect inflow of gas into the rotor vessel, the gas impingement plate including a plurality of holes mounted at an exit of the gas inlet nozzle for distributing gas in the rotor vessel; and a first plate; a second plate; a plurality of sets of rings concentrically interposed between the first plate and the second plate, wherein each set of rings comprises a plurality of rings arranged cylindrically, wherein each ring comprises a plurality of packing elements; at least one metallic ring interposed between the plurality of sets of rings; and a gas inlet nozzle coupled to a gas impingement plate to affect inflow of gas into the rotor vessel, the gas impingement plate including a plurality of holes mounted at an exit of the gas inlet nozzle for distributing gas in the rotor vessel; and a liquid inlet and gas outlet pipe assembly coupled to the rotor, the liquid inlet and gas outlet pipe assembly comprising: gas outlet pipe to affect expulsion of gas from the rotor; and a liquid inlet pipe housing the gas outlet pipe to form a region to affect inflow of liquid into the rotor; and gas outlet pipe to affect expulsion of gas from the rotor; and a liquid inlet pipe housing the gas outlet pipe to form a region to affect inflow of liquid into the rotor; and a shaft coupled to one of the first plate and the second plate of the rotor to rotate the rotor, wherein an outer surface of the shaft comprises a plurality of sequential steps tapered along the length of the outer surface.