Patent GB-718702-A (GB)
Title: Improvements in and relating to the dehydration and fractionation of crude pyridine
Filed: 1951-05-08
Abstract: Aqueous crude pyridine is dehydrated by fractional distillation in a system comprising two columns wherein wet vapours are withdrawn overhead from both columns and are condensed in a common condenser, the condensate being passed to a decanter together with a substance (soda-lye benzole) which causes the condensate to separate into a water-rich layer and a pyridine-rich layer. Anhydrous crude pyridine is obtained at the base of one column (the "pyridine-column"), and water is obtained at the base of the other (the "water-column").  The pyridine-rich layer is withdrawn from the decanter and introduced into the upper part of the pyridine-column, while the water-rich layer <PICT:0718702/III/1> is introduced into the upper part of the water-column.  The feed is introduced into the system at a position in accordance with its composition and with the presence or absence of an entraining agent in the pyridine-column.  The fractionation of the anhydrous crude pyridine withdrawn from the base of the pyridine-column is preferably effected continuously in two or more columns connected in series, the first column being operated at atmospheric pressure and the subsequent columns under vacuum.  This series of columns may be provided with side columns.  Part of the vapour formed in the boiler of the atmospheric column may be used as indirect heating-medium for the boilers of the other columns.  In the Figure aqueous crude pyridine is fed through pipe 1 on to an upper tray of pyridine-column 2.  The head of column 2 and that of water-column 8 are connected to condenser 3.  The condensate formed in condenser 3 is passed to decanter 4, which is supplied through pipe 5 with benzol and soda lye.  The pyridine-rich phase formed in the decanter, which also contains the benzol, is refluxed to column 2 through pipe 6, while the water-rich phase is fed to column 8 through pipe 7.  Water containing soda lye, but free from pyridine, is withdrawn from the base of column 8 through pipe 9.  Anhydrous crude pyridine, withdrawn from the base of column 2 through pipe 10, is introduced into the side of column 11, which is heated by tubular furnace 22, and is operated at atmospheric pressure.  Pyridine is obtained as product from the head of column 11.  A picoline fraction is withdrawn from the foot of side column 14; and a base fraction of boiling range 145 DEG -180 DEG  is withdrawn from the foot of side column 15.  The bottoms from column 11 is introduced through pipe 16 into the side of column 17, which is operated at a pressure of 80 mm. Hg.  A base fraction having a boiling range 180 DEG -220 DEG  (under atmospheric pressure) is removed from the head of column 17, while at the foot of side column 20 there is obtained a fraction rich in quinoline. Part of the liquid withdrawn from the sump of column 11 is vaporized in furnace 22.  Some of the vapour so formed is returned to the sump of column 11 through pipe 24, the remainder is distributed to the boilers 26, 28, 30, 32, 34, 36 of columns 2, 8, 15, 14, 20, 17 respectively.  The liquid condensed in these boilers is returned to the sump of column 11 through pipes 37 and 38.