(586a) Superstructure Optimization Enabled Design Heuristics and Material Property Targets for Continuous Diafiltration Membrane Cascades
AIChE Annual Meeting
Thursday, November 11, 2021 - 8:00am to 8:21am
In diafiltration systems, dialysate is strategically fed to the retentate side of a membrane to mitigate concentration polarization which enables more efficient batch or continuous staged membrane cascades. Although diafiltration membrane systems have been studied for over 20 years, their industrial use is limited to high-value niche separations including buffer exchange and protein purification. One possible reason for less widespread use of diaflitration is the lack of systems engineering research related to diafiltration system design, operation, and control.
In this talk, we present a novel superstructure optimization framework to design diafiltration membrane cascades ; we show optimally designed diafiltration systems are efficient Li/Co fractionation steps for LIB recycling processes and quantify the process-scale benefits of next-generation membrane materials. Specifically, our framework encodes all realistic diafiltration cascade configurations into a superstructure; through continuous optimization, we systematically search over these configurations (with complex recycle and feed injection strategies) while considering membrane areas, flowrates, and concentrations of all streams as decision variables. The optimal system designs show how dialysate buffer is used to offset concentration effects in membrane filtration to recover highly concentrated metal rich solutions. Using an epsilon-constrained multiobjective optimization, we identify Pareto-optimal configurations that balance permeate (Li) and retentate (Co) product recoveries and explore tradeoffs in staging complexity versus membrane area. We then distill thousands of optimal diafiltration configurations into six design heuristics. We justify each design heuristic using governing transport and thermodynamic phenomena and draw analogies to design short-cut methods for other staged separations (e.g., absorption, distillation). Finally, we highlight how our framework enables top-down design by studying the effects of alternate membrane characteristics on the performance of the cascade. To our knowledge, this is the first optimization-based analysis of diafiltration cascade systems. We conclude by sharing opportunities for process systems engineering to advance diafiltration technologies and more broadly membrane science.
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