GB826763A - Improvements in and relating to the production of oxygenated hydrocarbons - Google Patents

Abstract

Aldehydes containing 4 to 6 carbon atoms and each containing the same number of carbon atoms are produced by the liquid phase catalytic carboxylation of alkene(s) having one less carbon atom than the desired product, preferably using a cobalt catalyst, separating the products as vapour in a hot gas/liquid separator and then as liquid in a cold gas/liquid separator and subjecting the liquid product to at least two distillations at a lower pressure to obtain separate streams of isomeric aldehydes. In a first embodiment the crude aldehyde is flash distilled at the lower pressure, e.g. atmospheric, to obtain a mixture enriched in aldehydes overhead which is again distilled in a packed column to obtain n-aldehyde as bottoms and iso-aldehydes overhead preferably using a packed column. The crude aldehyde is preferably passed through a decobalting step in which cobalt is precipitated and removed; the bottoms from the flash distillation are then preferably passed to the decobalter following the cold gas/liquid separator. The second distillation is preferably carried out in the presence of water in an amount greater than that needed to produce the iso-aldehyde-water azeotrope, this azeotrope is then obtained overhead and aqueous n-aldehyde as bottoms. The condensates are separated into aqueous layers which are returned as the main supply of water to the distillation and the organic layer is dried or distilled to take azeotrope overhead and dry aldehyde a bottoms, the overhead again being separated into an aqueous layer which is discarded and an aldehyde layer used as reflux. The iso-aldehyde stream obtained if it contains more than one isomer may be further distilled to separate the isomers, water again being added if desired. In a second embodiment the crude aldehyde is distilled in the presence of water to obtain iso-aldehyde azeotrops overhead and aqueous bottoms from which an organic layer is separated and distilled in a small column or flash distilled to obtain aqueous n-aldehyde or its azeotrope overhead. The amount of water added in the aqueous distillation is preferably in a weight ratio to the organic compound between 1 : 1 and 1 : 25 using columns of 25-40 theoretical plates. The heavy bottoms from the second column may be returned to the decobalter in the carbonylation process. In a fourth variant the crude aldehyde is distilled to obtain an aldehyde mixture overhead which is distilled in the presence of water to obtain iso-aldehyde azeotrope overhead, and either n-aldehyde is removed as vapour from the boiler or a few plates above the bottom of the column or the bottoms are further distilled in the presence of more water if desired to obtain aqueous n-aldehyde. Specifications 633,184, [Group IV (b)], 655,976, 678,211, 684,673, 684,958, 692,089, [all in Group IV (b)], 698,279, 701,434, 703,683, [both in Group IV (b)], 703,755, [Groups IV (a) and IV (b)], 704,942, 706,009, 721,272 and 738,161, [all in Group IV (b)], are referred to.