Process for monitoring a continuous acetic acid and/or methyl acetate production

A method for monitoring a continuous preparative process of production of a product selected from the group consisting of acetic acid, methyl acetate and mixtures thereof, by carbonylation, in an industrial installation, of methanol or a carbonylatable derivative of methanol with carbon monoxide in a liquid phase in the presence of water and a homogeneous catalyst system, said preparative process comprising the steps of:

• in a reaction zone I comprising a reactor, carrying out said carbonylation in the liquid phase at a temperature of 150 to 250° C., under a pressure of 5·105 to 200·105 Pa and with venting of part of a gaseous canopy above a liquid phase level in said reactor;
• in a vaporization or flash zone II, partially vaporizing a liquid originating from the zone I at a pressure below that of zone I, to form a liquid fraction which is recycled into the reactor and a vaporized fraction;
• and
• in a purification zone III, distilling the vaporized fraction originating from said flash zone II on at least one distillation column, and recovering at an outlet of said at least one distillation column said product selected from the group consisting of acetic acid, methyl acetate and mixtures thereof, other constituents of said vaporized fraction being at least partially recycled into said reactor,
• wherein said monitoring method comprises bringing reactor temperature and feed rate of the methanol or carbonylatable derivative in said reactor under control of the carbon monoxide feed rate and of at least one of the parameters defining the composition of the reaction medium or of the venting or of both the reaction medium and the venting.