Patent GB-705601-A (GB)
Title: Process for the separation of alcohols from mixtures with other organic compounds
IPC: C07C29/74
Filed: 1951-03-09
Abstract: Alcohols are separated from mixtures thereof with other organic compounds by adding an aldehyde and a condensation agent to the mixture to convert the alcohols into acetals, distilling the mixture so obtained to yield the acetals as residue, subjecting the acetals to hydrolysis and separating the alcohols from the products of hydrolysis.  The process is particularly useful for the separation of alcohols from the products obtained during the catalytic hydrogenation of carbon monoxide and from the products obtained by hydrogenating aldehydes formed in the OXO synthesis reaction.  In addition to the aldehyde it is preferred to add a component, e.g. a low boiling hydrocarbon capable of forming an azeotrope with water. Specified aldehydes are aliphatic aldehydes such as propionaldehyde or butyraldehyde, aromatic aldehydes such as benzaldehyde, and heterocyclic aldehydes, e.g. furfural. Specified condensation agents are anhydrous salts preferably anhydrous copper sulphate, p-toluene sulphonic acid, and concentrated hydrochloric acid, the use of a small amount, e.g. 0.1 per cent. to 1.0 per cent. by volume of concentrated hydrochloric acid relative to the total reaction mixture is preferred.  Small amounts of gaseous hydrogen chloride may also be used.  In processing the products of the catalytic hydrogenation of carbon monoxide it is advantageous to fractionate the products prior to the treatment in accordance with the invention.  The fractionation should be effected so that the boiling point of the lowest boiling acetal is at least 20 DEG C. and preferably 50 DEG C. higher than the boiling point of the highest boiling hydrocarbon in the treated fraction.  The fractionation may suitably be such as to yield three fractions boiling within the ranges 30-220 DEG C., 220-320 DEG C. and 320-380 DEG C. and a residue boiling above 380 DEG C. and the process of the invention may be applied to each fraction.  The 220 DEG -320 DEG C. fraction contains C10-C15 alcohols and C13-C18 hydrocarbons and the treatment of this fraction may be effected by first adding a low boiling hydrocarbon such as a C5 hydrocarbon which functions as the azeotrope-forming component and then adding an aldehyde, e.g. propionaldehyde, in an amount in excess of the stoichiometric quantity required to form the acetals on the basis of the alcohol content of the treated fraction.  A condensation agent, preferably concentrated hydrochloric acid, is then added and the mixture heated to boiling point until no more water distils over, the added low boiling hydrocarbon and small amount of aldehyde which distil over with the water being recycled during the process.  Heating is then continued until the low boiling hydrocarbon and excess aldehyde distil over and the acetals are then separated from the hydrocarbons and any other organic oxygen containing compounds present in a vacuum distillation apparatus using a fractionating column.  If desired these hydrocarbons may be removed by azeotropic distillation by adding a dihydric alcohol such as glycol, butanediol, or diethylene glycol as azeotropic-forming component.  The residual acetals may be hydrolysed with hot water which may be admixed with steam although in some cases small amounts of acid such as hydrochloric acid or p-toluene sulphonic acid may be added.  The re-formed aldehyde is then distilled off and may be re-used in the process.  The hydrolysis may also be carried out continuously by passing the acetal into the lower end of a tube filled with hot water, whereby the aldehyde distils off continuously from the top of the water column.  The excess water is then separated from the alcohol mixture which is finally purified by vacuum distillation. In examples the process is applied to the recovery of alcohols from fractions boiling in the range (1) 220-320 DEG C., (2) 90-160 DEG C., and (3) 180-320 DEG C., each fraction being derived from the products obtained by catalytic hydrogeneration of carbon monoxide using an iron catalyst.  In (1) the acetalisation is effected with propionaldehyde in the presence of hydrochloric acid and a C5 hydrocarbon fraction whilst the hydrolysis step is effected with hot water; in (2) the acetalisation is effected with benzaldehyde in the presence of hydrochloric acid and a C5 hydrocarbon fraction whilst the hydrolysis is effected with aqueous hydrochloric acid at 100 DEG C to yield C3-C6 alcohols including propanol and butanol, and in (3) the acetalisation is effected with butyraldehyde in the presence of hydrochloric acid and benzene whilst the hydrolysis is effected with a boiling aqueous solution of hydrochloric acid, the alcohols obtained having from 7 to 15 carbon atoms in the molecule.