Control process for the production of acetic acid by using the measurement of the density of the heavy phase.

A method for effecting process control in a reaction for the production of acetic acid through the reaction of methanol and carbon monoxide in a reaction mixture comprising methyl acetate, comprising the steps of: measuring the density of the heavy phase of a distillation column of the light fraction comprising methyl iodide and methyl acetate with a densitometer; and controlling reaction conditions in the reactor in response to the measured density.