GB866421A - Distillation apparatus - Google Patents

Abstract

Fractional distillation apparatus for use at subatmospheric pressure includes a reboiler, a condenser, a vacuum system and at least one distillation column, means being provided for compressing the vapour of the material being fractionated to a pressure not higher than the pressure in the reboiler during its <PICT:0866421/III/1> <PICT:0866421/III/2> passage through the distillation column or columns, or during its passage from one distillation column to the next when a plurality of columns are used in series. In Fig. 1 apparatus comprising two columns T1 and T2 each containing 60 plates can be used for the separation of a mixture of para- and orthonitrochlorobenzene. A vapour compressor B is included in the conduit from the top of T1 to the bottom of T2. Liquid mixture is fed by a pipe F to the bottom of T2 (or at any position in either column depending upon the composition of the mixture) and distillate is removed from a condenser C through a pipe D, the reflux from the bottom of T2 being pumped by pump P to the top of T1 while residue is removed from the reboiler R through a pipe W. By regulating the vacuum pump VP and compressor B the pressures in the columns can be controlled to avoid decomposition of the mixture being fractionated. Whatever the number of columns n only one reboiler, condenser and vacuum system is employed, while n-1 compressors are necessary, each column and the next having a compressor between them. In Fig. 2 the column T is of the rotary disc type in which discs a mounted upon a rotatable shaft s revolve between annular discs c fixed to the column wall. Vanes b attached to the discs a compress the vapour as it rises up through the column, thereby rendering unnecessary the use of a separate compressor whether one column is used or two, as in Fig. 1.