Abstract: A novel construction of a heat exchanger such as a vertical type thermosiphon reboiler having a removable tube bundle and optional removable shell is disclosed. The inlet tube sheet is matingly, engagably secured to a ledge portion which is, in turn, secured to one flange of the shell and the opposite tube sheet is matingly, engagably secured to the opposite flange of the shell. Sealing members are more favorably located in such construction. The assembly is easily disassembled for cleaning.

Abstract: A novel construction of a heat exchanger such as a vertical type thermosiphon reboiler having a removable tube bundle and optional removable shell is disclosed. The inlet tube sheet is matingly, engagably secured to a ledge portion which is, in turn, secured to one flange of the shell and the opposite tube sheet is matingly, engagably secured to the opposite flange of the shell. Sealing members are more favorably located in such construction. The assembly is easily disassembled for cleaning.

Abstract: C.sub.n dienes are efficiently separated and produced from a C.sub.n hydrocarbon feed stream, wherein n is 4-8. For example, 1,2- and 1,3-butadienes are separated and produced from a C.sub.4 hydrocarbon feed stream comprising C.sub.4 alkynes, n- and isobutenes, n- and isobutanes and 1,2- and 1,3-butadienes by sequentially:A. hydrogenating the C.sub.4 alkynes and removing any heavy residue produced thereby;B. separating the 1,2- and 1,3-butadienes into a first stream and the remaining C.sub.4 hydrocarbons into a second stream;C. removing first the isobutene and second the n- and isobutanes from the second stream; andD. converting the remaining alkenes of the second stream to 1,2- and 1,3-butadienes and then recycling said butadienes to the first stream of (b).This process affords greater product flexibility with less physical plant than that afforded by conventional processes.