Patent GB-693167-A (GB)
Title: Concentration of unsaturated aldehydes
Filed: 1949-12-21
Abstract: Unsaturated aldehydes produced by catalytic oxidation of olefines with free oxygen are recovered in concentrated form from their dilute aqueous solutions by first heating the solutions at a pressure not greater than atmospheric and at or near to the boiling point of the solution at the selected pressure until substantially all the oxygen present is expelled, and subsequently distilling the so treated solution directly or after cooling.  The treatment prevents polymer formation in the still.  As a further precaution hydroquinone may be introduced into the still and/or a nitrogen seal may be used to prevent access of air.  Passing the solution over iron or copper turnings before heating facilitates complete removal of oxygen. While heating, the pH should be from 5 to 8, preferably 6-7.  The heating is preferably at reduced pressure, e.g. 100 mm. Hg.  The heating time may be from a few seconds to as long as a few minutes when a low pressure and temperature are used.  The heating may be indirect or by the introduction of live steam, the aqueous solution preferably passing in a film through a heated vertical tube or, with low pressure, through a packed column.  Aldehyde carried away by released gas may be recovered by scrubbing, e.g. with water. Three examples are given of the concentration of 0.4 per cent solutions of acrolein and methacrolein with preliminary heating in (1) a steam-jacketed tube; (2) and (3) a packed column into the base of which live steam was injected.  Contact times in the heated zone were from a few seconds to three minutes.  Pressures were atmospheric and 100 mm. Hg.ALSO:Unsaturated aldehydes produced by catalytic oxidation of olefines with free oxygen are recovered in concentrated form from their dilute aqueous solutions by first heating the solutions at a pressure not greater than atmospheric and at or near to the boiling point of the solution at the selected pressure until substantially all the oxygen present is expelled, and subsequently distilling the so treated solution directly or after cooling.  The treatment prevents polymer formation in the still. As a further precaution hydroquinone may be introduced into the still head.  Alternatively or in addition a nitrogen seal may be used to prevent access of air. Passing the solution over iron or copper turnings before heating facilitates complete removal of oxygen.  While heating, the pH should be from 5 to 8, preferably 6-7.  The heating is preferably at reduced pressure, e.g. 100 mm. Hg.  The heating time may be from a few seconds to as long as a few minutes when a low pressure and temperature are used.  The heating may be indirect or by the introduction of live steam, the aqueous solution preferably passing in a film through a heated vertical tube, or through a packed column if low pressure is used. Aldehyde carried away by released gas may be recovered by scrubbing, e.g. with water.  Three examples are given of the concentration of 0.4 per cent solutions of acrolein and melhacrolein with preliminary heating in (1) a steam-jacketed tube, (2) and (3) a packed column into which live steam was injected, and with contact times in the heated zones of from a few seconds to three minutes.  Pressures were atmospheric and 100 mm. Hg.