Process alternatives for methyl acetate conversion using reactive distillation. 1. Hydrolysis

In a polyvinyl alcohol (PVA) plant, reaction stoichiometry indicates that equal molar of methyl acetate is generated for every mole of PVA produced. This work explores an alternative to convert methyl acetate back to acetic acid (raw materials of PVA plant), methyl acetate (MeAc) hydrolysis. The design and control of methyl acetate hydrolysis using reactive distillation is studied. Because of the small chemical equilibrium constant (∼0.013) and unfavorable boiling point ranking (MeAc being the lightest boiler), the reactive distillation exhibits the following characteristics: (1) total reflux operation and (2) excess reactant (water) design. The proposed flowsheet consists of one reactive distillation column with a reactive reflux drum, two separation columns, and one water-rich recycle stream. A systematic design procedure is used to generate the flowsheet based on the total annual cost (TAC). Two dominate design variables are: recycle flow rate (for the degree of excess in water) and the overhead impurity level of acetic acid in the product column (to avoid tangent pinch). Finally, the operability of the hydrolysis plant is evaluated. A plantwide control structure is developed followed by process identification and controller tuning. The results show that reasonable control performance can be achieved using simple temperature control for feed flow and feed composition disturbances.