Process for recovering a reaction product while preventing decomposition of the catalyst

In a process for recovering an aliphatic carboxylic acid and/or an ester thereof by distilling a liquid mixture containing the aliphatic carboxylic acid and/or the ester thereof and a catalyst of a metal of Group VIII of the periodic table of elements, the improvement wherein carbon monoxide is introduced into the distillation system to carry out the distillation in the presence of carbon monoxide at a partial pressure of at least 0.05 kg/cm.sup.2 (absolute) in the distillation system to prevent the decomposition of said catalyst, there being no catalyst removed from said liquid mixture to be distilled, the amount of said catalyst in said liquid mixture to be distilled being 10.sup.-4 to 10.sup.-1 mole per liter of the total of the starting material and solvent used to obtain said liquid mixture.