Patent GB-715390-A (GB)
Title: Improvements in or relating to preparation of aldehydes
IPC: C07C27/22
Filed: 1951-09-06
Abstract: Substantially pure aldehydes are recovered from the crude aldehyde product produced by the carbonylation of olefins with carbon monoxide in the presence of a cobalt carbonylation catalyst at elevated temperatures and pressures by withdrawing the crude aldehyde product from the carbonylation zone, immediately cooling it, passing the cooled product to a decobalting zone operating at relatively low temperatures not exceeding about 250 DEG  F., preferably between 100 DEG  and 150 DEG  F., to prevent the formation of secondary reaction products, topping the decobalted aldehyde product to remove low boiling impurities and distilling the topped decobalted aldehyde product in a reduced pressure distillation zone having a still-pot temperature below that at which the aldehyde product decomposes and in any case below 430 DEG  F, the residence time in the distillation zone being less than one hour. The crude aldehyde may be cooled by passage through a suitable cooling means and in addition, preferably by contact with a liquid-quenching agent such as an inert hydrocarbon or alcohol solvent.  In the carbonylation step the olefin may be dissolved in a solvent, e.g. a low molecular weight alcohol such as methanol or ethanol, the alcohol being chosen such that it is readily separable by distillation from the aldehyde product.  If an alcoholic solvent is used the acetals formed are hydrolysed and the solvent removed before the reduced pressure distillation step. The decobalting may be a chemical decobalting in the presence of water or of dilute acidic material such as dilute formic, acetic or sulphuric acid or potassium hydrogen sulphate.  In an example, a heptene fraction, taken from the product produced by polymerizing propylene and butylene in the presence of solid phosphoric acid deposited on kieselguhr, is passed through a carbonylation zone in the presence of cobalt naphthenate and subjected to a pressure of about 3,000 pounds per square inch and a temperature of 300-350 DEG  F. in the presence of about equimolar ratios of hydrogen and carbon monoxide.  The crude aldehyde product is immediately cooled and then passed to a chemical decobalting zone operating at between 100 DEG  and 150 DEG  F. and after decobalting the crude aldehyde is topped by fractional distillation to remove low boiling impurities.  The topped aldehyde is then divided into four portions, three of which are distilled in a column under reduced pressure of 40 to 43 mm. of mercury at pot temperatures of 230 DEG , 240 DEG  and 273 DEG  F. respectively for residence times of less than one hour, whilst the fourth portion is distilled at atmospheric pressure at a pot temperature varying from 393 DEG  to 479 DEG  F. with a residence time of more than one hour, and a table is given to show that the isooctyl aldehydes are recovered in higher yield and with less thermal degradation by the reduced pressure distillation procedure.  A flow diagram is given to illustrate the process as applied to a C7 olefin boiling in the range 180 DEG  to 210 DEG  F., the carbonylation being carried out in the presence of a solvent such as methanol or ethanol and of a cobalt soap such as cobalt naphthenate, stearate or oleate as catalyst, a small amount of carbon disulphide or sodium methylate being also added along with the olefin feed as hydrogenation inhibitors.  An oxidation inhibitor consisting of phenyl alpha (or beta) naphthylamine, di-secondary butyl para phenylene diamine, or hydroquinone may be added to the recovered aldehyde product or to the crude aldehyde in the carbonylation zone or decarbonylation zone.  In one embodiment the chemical decobalting is carried under such conditions as to hydrolyse completely the acetals formed, alternatively the decobalter may be operated under conditions to avoid substantial hydrolysis of the acetals and the decobalted product submitted to a continuous extractive distillation in the presence of an acidified aqueous solution of the sodium salt of a hydrotropic agent such as mixed xylene sulphonic acid, whereby the acetals are hydrolysed and aldehyde is separated together with some water as an overhead vapour stream whilst a lower aqueous layer containing the alcohols is withdrawn from the bottom of the still. Water is separated from the aldehyde by passing the vapours through a decanter prior to the final distillation step.