(212e) Impact of Chris Floudas on Recent Developments in Process Synthesis and Flexibility Analysis

In this talk we first provide a brief overview of the biography and academic career of Chris Floudas [1]. We highlight his most outstanding research, educational, and professional accomplishments, and the impact they have had in the area of Process Systems Engineering.

We next focus on two major areas in process systems engineering in which Chris Floudas was a pioneer and major source of inspiration to our group at Carnegie Mellon, namely in process synthesis and process flexibility. We describe our recent work on Pyosyn [2, 3, 4], an advanced computational tool for process synthesis. This work involves new representations, superstructure generation approaches, modeling, and solution strategies. The Pyosyn Graph representation consists of units, ports, and streams, and includes support for nested units, including “single-choice” units and modular superstructure construction. Superstructure generation strategies are based on library-assisted and direct-hierarchical means-ends analysis. We then describe high-level mathematical modeling of PSG based on Generalized Disjunctive Programming using Pyomo.Network and Pyomo.GDP [3]. Tailored logic-based decomposition algorithms are describerd to address “zero-flow” singularities characteristic of synthesis problems, and demonstrate the flexible use of Pyosyn tools on several case studies, that include bioethanol processing, synthesis of methane to syngas and methanol processes, and Kaibel column design.

Next, we describe our recent work on flexibility analysis aimed at the pharmaceutical industry, particularly for Design Space definition, a key goal of Quality by Design to determine limits of the design space for manufacturing flexibility and quality assurance. We describe new MINLP reformulations [5] to extended flexibility analysis, where we distinguish between process and model parameters, to calculate a new flexibility index for process parameters. This index defines a hyperrectangular operating region within a design space of a pharmaceutical process in terms of the process parameters and accounts for the uncertainty in the model parameters, described by hyperrectangle and ellipsoidal sets. We extend this analysis to the design centering problem whose goal is to find the optimal nominal point that yields the largest flexibility index [7]. We propose two methods for design centering problems. The vertex direction search method yields a single-level optimization model, which is applicable for convex regions. A derivative-free optimization (DFO) method [6] is also developed based on the proposed flexibility index model, which is applicable to convex and nonconvex problems. In order to find near global solutions, Latin Hypercube Sampling (LHS) is used to generate multiple starting points for the DFO solver. Several cases, including a CSTR and Michael Addition reactions to demonstrate the efficiency of the proposed methods for flexibility analysis.

References

[1] Chris Floudas (1959–2016), I.E. Grossmann, OPTIMA 102, pp.7-8 (2017).

[2] Chen, Q., and I.E. Grossmann, “Modern Modeling Paradigms using Generalized Disjunctive Programming,” Processes, 7, 839 (2019).

[3] Chen, Q., E.S. Johnson, D.E. Bernal, R. Valentin, S.Kale, J. Bates, J. D. Siirola and I.E. Grossmann, “Pyomo.GDP: an ecosystem for logic based modeling and optimization development,” to appear in Optimization and Engineering (2021).

[4] Chen, Q., Y. Liu, G. Seastream, J.D. Siirola and I.E. Grossmann, “Pyosyn: a new framework for conceptual design modeling and optimization,” submitted for publication (2020).

[5] Ochoa, M.P., S. García-Muñoz, S. Stamatis and I. E. Grossmann, “Novel flexibility index formulations for the selection of the operating range within a design space,” Computers and Chemical Engineering 149, 107284 (2021).

[6] Zhao, F., I.E. Grossmann, S. Garcia-Munoz and S.D. Stamatis, “Flexibility Index of Black-Box Models with Parameter Uncertainty through Derivative-Free Optimization,” to appear in AIChE J. (2020).

[7] Zhao, F., Ochoa, M.P., S. García-Muñoz, S. Stamatis and I.E. Grossmann, “Novel Formulations of Flexibility Index and Design Centering for Design Space Definition,” submitted for publication (2021).