TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The C4H6 stream is discharged as side stream and the solvent (I) as sump stream from zone C; or both are discharged as sump stream. The C4 cut is fed into zone A. Two or more, preferably 2 or 3, thermally coupled columns can be used instead of the partitioned extractive distillation column, which has 10-80 (preferably 25) theoretical plates. Selective hydrogenation of hydrocarbons (II) with triple bonds to hydrocarbons (III) with double bonds may also be carried out in the extractive distillation column, using heterogeneous catalysis. Alternatively, the C4H6 stream is passed to a first distillation column, in which it is separated into a top stream of buta-1,3-diene, propyne, optionally other low-boiling compounds and optionally water and a sump stream of buta-1,3-diene, buta-1,2-diene, acetylenes and optionally other high-boiling compounds. The fraction of buta-1,3-diene in the sump stream is regulated so that it is at least high enough to dilute the acetylenes beyond the spontaneous decomposition range. The top stream is passed to a second distillation column, in which it is separated into a top stream comprising propyne, optionally other low-boiling compounds and optionally water and a sump stream of pure buta-1,3-diene. The sump stream from the first distillation column and top stream from the second may be passed to a reactive distillation column for selective hydrogenation of (II) to (III), with partial conversion of acetylenes, to give a top stream of buta-1,3-diene, butanes, butenes and unhydrogenated (II) and sump stream of high-boiling compounds.Work-Up: (all claimed) The methods of working up the stream (C4H8) of butenes, comprising isobutene (i-Bu), but-1-ene (1-Bu) and but-2-enes (2-Bu), from this process, are as follows:(1) separation into a top stream of mainly i-Bu and a sump stream of mainly 2-Bu in a reactive distillation column, in which 1-Bu is hydroisomerized to 2-Bu;(2) selective etherification of i-Bu and separation into an i-Bu ether stream and stream of 1-Bu and 2-Bu, then worked up the latter to a mainly 1-Bu stream by gas phase isomerization of 2-Bu or to a mainly 2-Bu stream by hydroisomerization of 1-Bu;(3) skeletal isomerization of 1-Bu and 2-Bu to mainly i-Bu stream;(4) separation of isobutene and skeletal isomerization of a stream of mainly 1-Bu and 2-Bu;(5) separation of isobutene and hydrogenation to a mainly i-Bu stream, which is preferably passed to a cracker or worked up by skeletal isomerization to a mainly n-butane stream and dehydrogenation to a stream of mainly 1-Bu and 2-Bu;(6) selective dimerization of the i-Bu to the corresponding C8 hydrocarbons and separation by distillation into a stream of 1-Bu and 2-Bu and a C8 hydrocarbon stream.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Solvents: The selective solvent is dimethylformamide, acetonitrile, furfurol and/or N-methylpyrrolidone (NMP), preferably NMP in aqueous solution. EXAMPLE - A 4 carbon (C) cut from a steam cracker had the composition (wt.%) 0.02 % propene, 0.04 % propadiene, 0.06 % propyne, 5.74 % n-butane, 2.44 % i-butane, 13.88 % n-butene (n-Bu), 25.63 % i-butene (i-Bu), 4.44% t-but-2-ene, 2.95 % cis-but-2-ene, 43.81 % buta-1,3-diene, 0.14 % buta-1,2-diene, 0.12 % but-1-yne and 0.73 % vinylacetylene. The extractive distillation column used had 80 theoretical plates, of which 25 were in the part divided by a partition extending from the top of the column. The cut was introduced into zone A at plate 68 (from the bottom). The selective solvent was N-methylpyrrolidone (NMP) with 8.3 wt.% water. The top stream from zone A comprised mainly butanes and contained 0.19 % propene, 62.02 % n-butane, 27.98 % i-butane, 6.63 % n-Bu, 2.71 % i-Bu, 0.24 % trans-but-2-ene and 0.23 % water. The top stream from zone B comprised mainly butenes and contained 0.07% propadiene, 0.91 % n-butane, 0.10 % i-butane, 28.57 % n-Bu, 54.55 % i-Bu, 9.48 % trans-but-2-ene and 6.32 % cis-but-12-ene. This process gave an energy saving of about 20 % compared with an existing process in which butanes and butenes together are separated in an extractive distillation column and then separated from one another in additional apparatus.