(131e) Design and Control of a Methyl Methacrylate Separation Process with a Middle Decanter

In the industrial process to produce methyl methacrylate (MMA), a mixture including methyl methacrylate, methanol and water needs to be separated. The methyl methacrylate and water are designed to be drawn out of this separation process as two product streams while methanol as an excess reactant should be recycled back to the esterification reactor. This ternary system has two azeotropes and a distillation boundary with two regions. One binary homogeneous azeotrope (MMA/MeOH) has the lowest azeotropic temperature of the ternary system. Another binary heterogeneous azeotrope (MMA/H2O) is a saddle having the azeotropic temperature not the lowest nor the highest temperature of the system. The feed composition with about 70 mol% MeOH is very close to the distillation boundary and in the region with water as the corner component. The industrial separation process is very complex including three distillation columns, a decanter and two internal recycle streams.

In this work, a much simple separation process is devised with a distillation column, a bottom decanter and a stripper. The aqueous phase of the decanter is drawn out of the system as water product while the organic phase is fed to stripper for further purification of the methyl methacrylate product to high purity specification. The top stream of the stripper is recycled back to the decanter. This column/decanter/stripper design can be simplified further into an even simpler design flowsheet with only one distillation column and a middle decanter. The optimal design flowsheet of this simple separation process is obtained by minimizing the Total Annual Cost (TAC) of the process with high MMA recovery. Furthermore, the overall control strategy of this process is also developed to handle feed composition variations and also the throughput changes.