In a process for liquid phase carbonylation of alcohols by carbon monoxide, the carbonylation reaction is carried out in a reaction zone at a temperature of 50° C. to 150° C. at a pressure in the range 0.5 MPa to 20 MPa in the presence of at least one catalyst comprising at least one rhodium and/or iridium complex and a halogenated promoter in at least one non-aqueous ionic liquid comprising at least one salt with general formula Q+A−, in which Q+ represents a quaternary ammonium and/or a quaternary phosphonium cation, said salt having a melting point of less than 90° C.; the non-aqueous ionic liquid containing at least the major portion of the catalyst is separated; and the separated non-aqueous ionic liquid containing at least the major portion of the catalyst is returned to the reaction zone.