Design and Control of a Methyl Acetate Process Using Carbonylation of Dimethyl Ether

The production of methyl acetate from the raw materials of methanol and carbon monoxide offers a potentially attractive alternative to other routes. The process has two distinct reaction and separation steps. First, methanol is dehydrated to form dimethyl ether (DME). Then carbon monoxide is combined with DME to produce methyl acetate. Each section involves reactors and distillation columns with either liquid or gas recycle. The purpose of this paper is to develop the economically optimum design of the two-step process and to study its dynamic control. The economics consider capital costs (reactors, distillation columns, heat exchangers, and compressors), energy costs (compressor work, reboiler heat input, and condenser refrigeration), the value of steam produced from the exothermic reactions, the cost of the carbon monoxide, and the heating value of a vent stream that is necessary for purging off the inert hydrogen that enters in the fresh carbon monoxide feed. The process illustrates a number of important design trade-offs among the many design optimization variables: reactor temperatures, reactor pressures, distillation column pressures, reactor sizes and purge composition. A plantwide control structure is developed for the entire two-section process that is capable of effectively handling large disturbances in production rate and fresh feed compositions.