(243c) System Level Analysis of Intermitent Photocatalytic Processes for the Production of Liquid Fuels

Traditional chemical engineering process design has relied on the assumption that energy and resources are available in a continuous way. However, if new production paradigms based on renewable energy sources are to be deployed a radically new approach to the design of chemical processes needs to be developed. Specifically, to take advantage of renewable energy sources like wind or the sun it is fundamental to develop ways to deal with intermittency and variability at the process synthesis stage. Accounting for intermittency and variability requires incorporating these aspects explicitly in process models. In this work, we present a comprehensive discussion of current efforts, including our own, to develop alternative process synthesis frameworks for the design of photocatalytic systems accounting for intermittency and variability in sunlight. We discuss current approaches and challenges in the design of these processes. Special emphasis is placed on describing optimization-based frameworks leading to the formulation of mixed-integer non-linear programs (MINLP). We discuss how the use of stochastic programming enables us to account for variability in solar irradiance. From an application perspective, we focus on the photocatalytic synthesis of fuels based on CO₂ capture and reduction. A technology that may be of capital importance in mitigating the effects of global warming. Since there is a large set of technologies that can be used to go from CO₂ to liquid fuels (e.g., CO₂ reduction to methanol followed by multiple methanol chemistries available, CO₂ to syngas followed by Fischer Tropsch synthesis, and CO₂ methanation followed by methane chemistry), we develop a general superstructure-based optimization framework to explore this large design space and assess the energetic and economic feasibility of these processes. Additionally, historic data on solar irradiation at different regions in the US, available from public databases, is used to discuss the effect of geographic location on the process economics. Our work presents a roadmap for future research in the field of photocatalytic conversion systems for the production of CO₂-derived fuels, emphasizing the need for more integrated approaches that consider the variability of sunlight and the use of optimization tools to accelerate the implementation of this promising technology as a cost-effective solution.