(4aj) A Systems-Level Approach to the Design of Sustainable Processes

Global warming, resource scarcity, and growing pollution have prompted the search for alternatives to mitigate the anthropogenic environmental footprint. The complexity of these problems—often involving multiple solution alternatives, uncertainty in the parameters, and several competing objectives (e.g., economic and environmental)—calls for the development of analysis tools capable of capturing all their relevant features. Such tools would enable a systematic analysis leading to the identification of synergies and trade-offs, as well as non-intuitive solutions. The central goal of my research program is the development of methods and the formulation of models to tackle problems in the broader area of sustainability, with a special emphasis on the integration of process synthesis, materials design, and product formulation. In my group, we intend to leverage and integrate optimization tools, lifecycle analysis (LCA), multiphysics simulations, and techno-economic analysis (TEA) to illuminate different aspects associated with these problems. In terms of applications, my research revolves around two central themes:

• The identification, development, and integration of technologies that use alternative carbon sources, and renewable energy resources to produce fuels and chemicals. I am especially interested in technologies that lead to waste minimization and greenhouse gas emissions mitigation. In the case of alternative carbon sources, my research group will be focused on carbon capture and utilization (CCU), plastic upcycling, and biorefineries; while for alternative energy sources we will focus on solar-driven refineries; and electrochemical processes powered by excess capacity obtained from renewable sources. My work addresses three fundamental questions, the answers to which are instrumental for unlocking the full potential of these technologies: What are the major economic drivers determining the profitability of these technologies? What are their environmental and societal impacts? and How can we use them to obtain products with similar, or better, properties than those obtained from currently available technologies? To answer these questions, we develop and apply optimization-based tools, LCA, and TEA for the integrated analysis of systems, processes, and phenomena spanning different scales: feedstock production, supply chain, production processes, and end use of products.
• The development of methods for the analysis and design of energy-efficient separations with an emphasis on membrane and adsorption materials and processes. Separations account for 15% of the world's energy consumption. Therefore, designing energy-efficient separations is fundamental for mitigating the environmental impact of industrial processes. This relevance has motivated the search for alternative separations. Both membranes and adsorption processes appear as alternative energy-efficient unit operations, and the fundamental understanding of these technologies from the material to the unit operation scale may enable their widespread implementation. In this context, my research aims to develop systematic methods for the simultaneous design of materials and processes, and to facilitate the incorporation of multiphysics simulations information into the design of the associated unit operations. The development of these methods will allow for the identification of situations where the implementation of these alternative separations is beneficial, while simultaneously informing engineers of the physical characteristics of the materials required to achieve a desired outcome.

Research accomplishments

My research has focused on the use of mathematical modeling to inform problems in process synthesis [1] and materials design [2–3].

My most recent work focuses on the formulation of mathematical models for the co-optimization of biofuels, biorefineries, and engines. In contrast with traditional biofuels research, which is usually concentrated on finding strategies to produce biofuels similar to their fossil counterparts, we have embraced the possibility of tailoring the fuels produced in a biorefinery so that their properties surpass those of fossil fuels. To realize this vision, we have developed a superstructure-based optimization framework that integrates process design, biofuel design, catalyst selection, and engine emissions modeling, thus enabling the systematic design of biorefineries to produce advanced fuels with tailored properties at a minimum cost. One particular problem that I have explored is the upgrading of ethanol to drop-in biofuels. The relevance of ethanol upgrading becomes evident if we consider (1) that ethanol cannot be blended with middle distillates and (2) that its demand is expected to decrease over time. These conditions have motivated the search for ethanol-upgrading strategies to produce middle distillates using ethanol as a substrate. The number of chemistries, processes, and catalysts that can be used to achieve this goal is very large, making the systematic search for an optimal upgrading strategy challenging. The framework I have developed has enabled the first systematic analysis of ethanol upgrading into advanced drop-in biofuels and has allowed us to study the trade-off relations between fuel properties and profit, as well as the relationship between biorefinery complexity and profit.

At the material level, my work has been focused on bridging the gap between new physical developments in the field of mass diffusion and engineering applications in new separation processes. In particular, I have pioneered the development of mass diffusion metamaterials (i.e., composite materials with engineered properties resulting both from the geometric arrangement of their constituents and their composition) and the application of these materials in membrane separations. One physical feature that my work has exploited is the possibility of designing materials to precisely and independently control the trajectory that different molecules follow when diffusing across a material. By taking advantage of this feature, it is possible to design new membranes in which the separation of molecules occurs because they follow different prescribed trajectories. This is in contrast with typical membranes in which separation occurs because of differences in the flux magnitude of the molecules to be separated. The control of a molecule trajectory can be achieved by designing anisotropic materials with a tailored diffusivity tensor. During my Ph.D. studies, I developed a research program focused on the computational design of these materials. In my work, I addressed three questions: How can we design these materials? How can we realize them in concrete applications? and What advantages do they have, in comparison with available isotropic materials? I demonstrated that materials that effectively behave anisotropically can be designed using isotropic constituents that have been cleverly arranged to achieve the desired properties. From an engineering perspective, we demonstrated for the first time that anisotropic membranes have surprising capabilities, so that their selectivity can surpass all commonly available isotropic materials.

Teaching Interests

As an assistant professor I am prepared to teach undergraduate courses on transport phenomena, process and product design, separations, and computational methods in chemical engineering. I am also interested in the development of two graduate-level courses: advanced process synthesis and optimization, in which I would expose students to optimization-based process synthesis techniques, and another one dedicated to advanced separations, in which I would cover the description of transport phenomena in membrane materials and multicomponent mixtures and discuss recent techniques for the implementation of optimization techniques in the design of separation operations.

Selected Publications

[1] Restrepo-Flórez J.M., Maravelias C.T., Advanced fuels from ethanol – a superstructure optimization approach, Energy Environ. Sci. (2021) 14:493-506.

[2] Restrepo-Flórez J.M., Maldovan M., Breaking separation limits in membrane technology, J. Memb. Sci. (2018) 15:301-306.

[3] Restrepo-Flórez J.M., Maldovan M., Mass diffusion cloaking and focusing with metamaterials, Appl. Phys. Lett. (2017) 111:071903.