Methods and apparatus for removing catalyst from oxidation reactor effluent

Methods and apparatus for removing a catalyst from a reaction mixture formed by reacting a hydrocarbon or an oxygenated hydrocarbon with an oxidant in the presence of the catalyst in a reactor, in which the reaction mixture contains one or more dibasic acids. The catalyst is removed by adding water and/or cooling the reaction mixture to cause phase separation, recycling the polar phase to the reactor, and transferring the less-polar phase to an ion exchange unit to remove catalyst contained therein.