(WO9955647-A1)   NOVELTY - Separation of a 4 carbon (C) hydrocarbon mixture (I) involves extractive distillation with N-methyl-2-pyrrolidinone (NMP) into 1,3-butadiene, butene and butane fractions and fraction(s) containing other 4 C hydrocarbons (II). The stages used comprise; (1) complete absorption of 1,3-butadiene and (II) from gaseous (I) with NMP and separating the solution (III) from a gas stream (IV) of unabsorbed butenes and butanes; (2) desorption of butadiene from (III) and separation from the liquid phase (V) containing most of (II); (3) desorption of (II) in one or more fractions from (V); (4) complete absorption of butenes in (IV) in NMP from stage (3) and separating the unabsorbed butanes; (5) desorbing the butenes from the solution; and (6) recycling the NMP free from stage (5) to one of the extraction zones. Each desorption zone operates at a lower pressure and/or higher temperature than the immediately preceding absorption or desorption zone.    USE - The process is useful for separating mixture (I) into a 95-99 wt.% or over 99 wt.% pure 1,3-butadiene fraction, together with a butene fraction containing at most 5 wt.% butanes and a butane fraction containing at most 15 wt.% butenes.    ADVANTAGE - The process is very efficient and economical. In particular, the amount of energy needed and capital costs are very low.    (EP1076638-A1)   NOVELTY - Separation of a 4 carbon (C) hydrocarbon mixture (I) involves extractive distillation with N-methyl-2-pyrrolidinone (NMP) into 1,3-butadiene, butene and butane fractions and fraction(s) containing other 4 C hydrocarbons (II). The stages used comprise; (1) complete absorption of 1,3-butadiene and (II) from gaseous (I) with NMP and separating the solution (III) from a gas stream (IV) of unabsorbed butenes and butanes; (2) desorption of butadiene from (III) and separation from the liquid phase (V) containing most of (II); (3) desorption of (II) in one or more fractions from (V); (4) complete absorption of butenes in (IV) in NMP from stage (3) and separating the unabsorbed butanes; (5) desorbing the butenes from the solution; and (6) recycling the NMP free from stage (5) to one of the extraction zones. Each desorption zone operates at a lower pressure and/or higher temperature than the immediately preceding absorption or desorption zone.    USE - The process is useful for separating mixture (I) into a 95-99 wt.% or over 99 wt.% pure 1,3-butadiene fraction, together with a butene fraction containing at most 5 wt.% butanes and a butane fraction containing at most 15 wt.% butenes.    ADVANTAGE - The process is very efficient and economical. In particular, the amount of energy needed and capital costs are very low.