GB702197A - Improvements in or relating to the production of carboxylic acids - Google Patents

Abstract

Carboxylic acids are obtained by reacting an olefin with carbon monoxide and hydrogen in a synthesis zone, under the conditions of temperature and pressure of the OXO synthesis reaction and in the presence, as catalyst or as the source of catalytic material, of cobalt metal or a cobalt compound, whereby a product is obtained containing an aldehydic compound derived from the olefin and together with said aldehydic compound a cobalt carbonyl as defined below, and then treating at least part of the product comprising the aldehydic compound with a gas comprising molecular oxygen in the presence, as oxidation catalyst or as the source of an oxidation catalyst, of said cobalt carbonyl. Alternatively the process may be carried out by treating at least part of the product comprising the aldehydic compound with a gas comprising molecular oxygen in the presence, as oxidation catalyst or as the source of an oxidation catalyst, of a cobalt-containing product obtained from said cobalt carbonyl by thermal decomposition in the presence or absence of hydrogen. The term "cobalt carbonyl" is defined as a true carbonyl such as Co2(CO)8 or a cobalt carbonyl hydride such as Co(CO)4H. The OXO synthesis product is preferably treated for the removal of unreacted olefin prior to the oxidation and this may be effected by fractionation in a continuous column, the residual aldehyde containing the catalyst being subjected to the oxidation process. Alternatively olefin may be recovered during the separation of the oxidation products and loss of olefin during the oxidation may be reduced by raising the oxidation pressure or by refrigerating the exit gas to condense any volatile material. Specified olefines which may be used are propylene, butenes, pentenes, olefinic polymers of olefines containing 2 to 5 carbon atoms per molecule, e.g. dimers of butenes such as the material known as codimer. The oxidation may be carried out with pure oxygen, oxygen of high concentration, or with oxygen-containing gaseous mixtures such as air, and is preferably conducted at temperatures below 200 DEG C. The aldehyde products may be emulsified with water during the oxidation and any unreacted aldehyde may be recycled to the oxidation. When the acids obtained have a yellow colour the colour may be removed by making an aqueous solution of the sodium salts of the acid and washing with a solvent such as petroleum ether, a pentane or hexane, or a halogenated hydrocarbon such as carbon tetrachloride. A flow sheet is given to illustrate the process as applied to the production of trimethylhexoic acid from diisobutene using cobalt carbonyl as catalyst in the OXO synthesis stage, the unreacted olefin from this stage being removed by fractionation and recycled to the OXO synthesis whilst the bottom product comprising the C9 aldehyde and cobalt carbonyl is oxidised with air in aqueous emulsion. In examples: (1) diisobutylene and water gas are reacted at 160 DEG C. under a pressure of 200 atmospheres using cobalt carbonyl as catalyst and the product containing C9 aldehyde and cobalt carbonyl is then emulsified with distilled water and air passed through for 16 hours at about 20 DEG C. to yield the C9 acid; (2) as in (1) except that the oxidation temperature is 100 DEG C.; (3) as in (1) except that the OXO product is processed through a continuous fractionating column and unreacted olefin taken overhead, the residue containing C9 aldehyde and cobalt carbonyl being then oxidized as in (1) except that the treatment with air is carried out for six hours at 40 DEG C. Reference is also made to the production of mixed isononanoic acids from codimer and to the production of C10 acids from propylene trimer fractions. Specifications 702,192, 702,221 and 702,222 are referred to.