GB736984A - Improvements in or relating to the dehydration of liquids by azeotropic distillation - Google Patents

Abstract

An aqueous solution of an organic compound which forms with water an azeotrope of minimum boiling-point is dehydrated by feeding the solution into an upper section of a fractionating column, introducing into the column, at a <PICT:0736984/III/1> level below the aqueous feed inlet, an entrainer consisting of a mixture of the organic compound and a liquid immiscible with water having a boiling-point below that of said azeotrope, maintaining the temperature at the head of the column at a degree such that a ternary vapour mixture comprising water, water-immiscible liquid and some of the organic compound to be dehydrated passes over as distillate, condensing the distillate, allowing the condensate to separate into an aqueous layer and a non-aqueous layer, returning the non-aqueous layer to the column as entrainer, and withdrawing anhydrous organic compound from the base of the column. The process may be applied to the dehydration of methyl ethyl ketone (M.E.K.) using pentane or hexane as water-immiscible liquid. Aqueous M.E.K. containing 11.3 per cent water (i.e. the azeotrope) is fed (100 parts per hour) through line 3 to the top plate of column 2, which contains 23 plates and is heated by reboiler 4. A mixture of pentane (50 per cent) and M.E.K. is passed from vessel 5 on to the thirteenth plate from the base of the column at 384 parts per hour. The mixture is supplied, via line 7, decanter 8 and line 9, until the temperature at the head of the column reaches 55 DEG C.; valve 6 is then closed. The distillate from the column is condensed in condenser 11, and the condensate is passed to decanter 8 through line 12. The upper pentane/M.E.K. layer is returned to the column through line 9, and the lower aqueous layer is withdrawn. The temperature in the column just below the inlet of line 9 is maintained at about 64 DEG C. M.E.K. containing only 0.017 parts of water is withdrawn from the base of the column. If the temperature at the head of the column rises above 56 DEG C., a thermally-controlled element 13 opens valve 6 via connection 14, to allow an additional amount of pentane to enter the system from vessel 5; but if the head temperature falls below 54 DEG C., some of the pentane is withdrawn from the system. The aqueous layer withdrawn from decanter 8 contains 2.8 parts M.E.K.; this layer may be subjected to distillation to obtain the M.E.K./water azeotrope which is then recycled back to column 2. The dehydration of tetrahydrofurane is referred to.