The up to now available processes are characterized by the fact that no solid acid catalyst could be used, unless the catalyst is operated under unattractively severe conditions or unless the catalyst is combined with corrosive Lewis acid cocatalyst or unless the catalyst is used in a non-aqueous reaction system.
In particular from International Application WO 96/20154 a process is known for production of trialkylacetic acids from branched olefins and carbon monoxide in a non-aqueous reaction system using a solid resin catalyst comprising a cationic resin, having sufficient acid groups to provide requisite protons for conversion of branched olefin and carbon monoxide to trialkylacetic acids.
In particular the cationic resin was specified to have an acidity of at least equivalent to that of a 65 wt % sulphuric acid.
It will be appreciated by an average person skilled in the art that the process can only be performed in two steps, in the first step of which stoichiometric amounts of branched olefin and water will not lead to the desired products in an acceptable yield. Moreover, the process cannot produce more than 1 mole of converted olefin per mole active proton on the solid catalyst in one cycle of two steps.
In WO 92/18592 a process is suggested for manufacture of trialkylacetic acids and particularly of pivalic acid, from branched olefins and particularly isobutene, and carbon monoxide, using a solid acid catalyst together with minor amounts of a Lewis acid, such as boron trifluoride.
EP-A-0249976 suggests a process for the manufacture of branched carboxylic acids, by catalytic conversion of olefins with carbon monoxide and water in the presence of zeoliths as catalysts at temperatures of from 200 to 500.degree. C. and at pressures of 200 to 700 bar.
More in particular zeoliths of the pentasil type are used as catalysts. According to the exemplified embodiments only high temperatures (300.degree. C.) and pressures (300-500 bar) are used.
It will be appreciated that the disclosed reaction conditions will give rise to higher operation costs due to required measures as to safety and environment.
Therefore there is still a strong need for further improvement of the manufacturing process of branched carboxylic acids, starting from branched olefins and carbon monoxide.
An object of the present invention is to provide an improved manufacturing process for branched carboxylic acids, which process uses relatively mild conditions on the one hand and which shows high conversion and high selectivity to branched acids on the other hand.