(205a) Process Design and Intensification of Dividing Wall Column for an Industrial Methyl Methacrylate Separation Process

In pursuit of more energy efficient distillation technologies, dividing wall column (DWC) designs have received increasing attention from the chemical industry for multi-component separation [1,2]. Comparing to conventional distillation sequences, DWC features a compact and intensified design structure with less investment costs by integrating the whole process into a single shell column. Significant energy savings (approximately 30%) have also been reported due to reduced re-mixing effects occurring in the column and thus higher thermodynamic efficiency [3]. One DWC application of industrial importance is for purification of the reaction product mixture from preparation of methyl methacrylate, which also contains methanol, water, and oligomers of methyl methacrylate [4,5]. A patented design alternative for this heterogeneous azeotropic separation problem consists of a dividing wall column integrated with a decanter, showing 7.6% higher product recovery rate than a conventional two-column design flowsheet given the same energy consumption rate [4].

In this work, we revisit this industrial methyl methacrylate separation process based on our recently proposed framework for design, synthesis, and operational analysis of process intensification systems [6]. Specifically, a phenomena-based synthesis representation is developed using the Generalized Modular Representation Framework (GMF) to capture DWC systems with fundamental chemical building blocks (i.e., mass/heat exchange module and pure heat exchange module) [7-9]. To describe the non-ideal vapor-liquid-liquid behavior, rigorous thermodynamic models (e.g. UNQUAC) is explicitly incorporated in the synthesis model. The base case DWC design presented in [4] is then simulated with a pre-fixed building block structure to validate the accuracy and efficiency of GMF for this specific case study. Thereafter, a superstructure optimization model is formulated to systematically generate the optimal and intensified process alternative(s) for improved cost performance without any pre-postulation of plausible process unit or flowsheets. The resulting phenomenological process alternatives are translated to unit operation-based flowsheet for rigorous design and simulation using Aspen Plus. Given the inherent highly nonlinear dynamics with multiple steady-states in DWC systems, explicit/multi-parametric model predictive controllers designed via the PAROC framework [9] are applied to the above derived DWC-based flowsheets to ensure feasible operation under disturbance and uncertainty. Two alternative case studies are also presented for comparison of design strategies as well as optimality of the process solutions: (i) unit operation-based optimization of the base case design, and (ii) unit operation-based optimization of the conventional two-column flowsheet design with heat integration.

References

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