a method is provided for the removal of contaminating alkanes from the vaporized carbonylation products of a process wherein carboxylic acids are produced by the reaction in the liquid phase of an alcohol or an ester , halide or ether derivative of said alcohol with carbon monoxide in the presence of a catalyst system containing a rhodium or iridium component and an iodine or bromine component . the method involves distillation of the alkane - containing vaporized carbonylation products , phase separation of the overhead from said distillation , further distillation of a slipstream of the resulting heavy phase using carbon monoxide as stripping gas and removal of the alkanes as the bottoms stream from the latter distillation .