Patent GB-788889-A (GB)
Title: Process for resolving mixtures consisting predominantly of acrolein acetaldehyde allyl alcohol and water
Filed: 1956-02-22
Abstract: <PICT:0788889/III/1> In a process for the separation of mixtures comprising acrolein, acetaldehyde, allyl alcohol and water, the mixture is contacted with a water-insoluble, non-polar organic solvent, whreby two liquid phases are formed, viz. an aqueous phase, which is rejected, and an organic phase; the organic phase is introduced into the side of a fractionating column which is operated under reflux so that all the remaining water in the mixture becomes concentrated in a middle section of the column and is withdrawn (together with some acrolein and acetaldehyde) as a liquid side-stream from the column; anhydrous vapours containing acetaldehyde are taken-off from the head of the column, and an anhydrous mixture of solvent, acrolein and allyl alcohol is withdrawn from the base of the column.  The aqueous side-stream is preferably recycled to the solvent-contacting zone.  Aliphatic hydrocarbons having a boiling-point of at least 125 DEG  C., and aromatic hydrocarbons having a boiling-point of at least 110 DEG  C., may be used as solvents.  Normally-liquid, high molecular-weight alcohols and ethers may also be used.  A mixture containing 66.5 mol. per cent acrolein, 13.0 mol. per cent acetaldehyde and 3.0 mol. per cent allyl alcohol, the balance being water containing a minor amount of water-soluble organic impurities such as acetone and propionaldehyde, obtained by the controlled catalytic incomplete oxidation of propylene, is pumped through line 10 where it mixes with naphtha (B.R. 150-160 DEG  C.) supplied through line 14; the mol. ratio of solvent to organic compounds in the synthesis mixture being about 0.5 : 1.  The mixture enters chamber 12, which is maintained at about 60 DEG  C., and two liquid phases separate out.  The aqueous phase is eliminated through line 17. The organic phase is withdrawn from chamber 12 and passed through line 18 into column 20, the base of which is heated by coil 32. Overhead vapours containing acetaldehyde, together with other low-boiling components and gases, are passed to cooler 22; and liquid acetaldehyde is collected in accumulator 23. The liquid acetaldehyde is in part withdrawn from the system via line 25, and in part supplied to the top of column 20 as reflux.  The reflux ratio is 12 mols. per mol. of acetaldehyde product.  An aqueous fraction containing 66 mol. per cent acrolein and 20 mol. per cent of acetaldehyde, the balance consisting of water, collects in tray 30, and is withdrawn therefrom via line 31, and returned to line 10.  An anhydrous mixture comprising naphtha, acrolein and allyl alcohol is withdrawn from the base of column 20, and is pumped to column 36, which is heated by coil 38.  Substantially pure acrolein is taken off at the top of column 36.  The mixture of naphtha and allyl alcohol withdrawn as bottoms from column 36 is pumped through line 39, where it is extracted with water which is pumped in via line 43.  The mixture is allowed to stratify in chamber 40, which is maintained at a temperature of 30 DEG  to 70 DEG  C. The aqueous phase withdrawn from chamber 40 is fractionated in column 50.  The allyl alcohol/water azeotrope is taken off from the head of column 50; and water containing high-boiling impurities is discharged from the base of the column.  The hydrocarbon phase is pumped from chamber 40 through line 45 to chamber 12.