TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The side draw stream(s) of liquid free of compounds of light class of compounds in the feedstream, is withdrawn from the stripping section of the fractionating unit. The side draw stream(s) further comprises a portion or whole of the heavy class of compounds in the feedstream, and is free of compounds of the light class of compounds in the feedstream. The side draw stream(s) free of compounds of the heavy class of compounds and comprising a portion or whole of the light class of compounds in the feedstream, is withdrawn from the rectifying section of the fractionating unit. The bottom stream further comprises a portion or whole of the intermediate class of compounds in the feed stream. A portion or whole of side draw stream(s) of liquid is cooled and directed into the fractionating unit. A differential in absolute operating pressure is maintained in a portion of the rectifying 50% or more higher than absolute pressures in the stripping section of the fractionating unit. Alternately, the fluid feedstream is subjected to solvent aided fractionation using preselected liquid solvent in a fractionating unit including stripping and rectifying sections, to obtain 3 or more effluent streams comprising overhead stream (I) comprising 1 or more component of the light class of compounds but free of solvent and compounds of the heavy and optionally intermediate class, bottom stream (I) comprising a portion of the solvent and component(s) of the heavy class of compounds and optionally a portion of intermediate class of compounds of feedstream and free of compounds of the intermediate class and light class respectively, and side draw stream(s) of liquid comprising a portion of the solvent, a portion of the heavy class and component(s) of the intermediate class of compounds, or side draw stream(s) of liquid comprising a portion of the solvent, a portion of light class and component(s) of intermediate class compounds and free of compounds of heavy class or side draw stream(s) of liquid, from the rectifying section of the fractionating unit, comprising a portion of the solvent, a portion of compounds of the light class, and component(s) of the intermediate class of compounds, but essentially free of compounds of the heavy class, and side draw stream(s) of liquid, from the stripping section of the fractionating unit, comprising a portion of the solvent, a portion of the heavy class and component(s) of the intermediate class of compounds, but essentially free of compounds of the light class. The overhead stream (I) further comprises a portion or whole of the intermediate class of compounds in the feedstream. The effluent stream of vapor from the lower-pressure section is compressed and directed into the rectification section.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Fluid: The fluid feedstream comprises methane, ethylene and ethane, and portions of the ethylene in the feedstream are distributed into the bottom stream and side draw stream(s). The preselected liquid solvent comprises a mixture of 2 or more component(s) chosen from organic compounds having 3 or more carbon atoms.