(317a) Biorefinery Synthesis-a Route Towards Engineered Advanced Fuels

The consumption of liquid transportation fuels in the U.S. is close to 16 billion gallons per year, accounting for 28% of the country’s greenhouse gas emissions. The development of sustainable biofuels, particularly those derived from lignocellulosic materials has been identified as an alternative for the mitigation of the negative impacts of uncontrolled fossil fuel consumption. However, most available biofuels have limited fungibility. This limitation has prompted the search for alternative biofuels with better fungibility. A promising platform to achieve this goal relies on the upgrading of ethanol. This platform offers three main advantages: (1) it can use the existing infrastructure for ethanol manufacture; (2) it can produce fuels in the whole distillation spectrum, from gasoline to diesel; and (3) it offers the possibility of using the advances in ethanol chemistry to produce fuels with superior properties. However, the identification of optimal strategies for ethanol upgrading remains challenging. On the one hand, the search space, characterized by the chemistries and catalysts that are used in a biorefinery for ethanol upgrading, is very large. Additionally, the multidisciplinary nature of the problem calls for the simultaneous design of processes and products integrating information of different areas (catalysis, process engineering, and fuel property modeling).

Accordingly, we present optimization-based approaches to address this problem. We give special emphasis to a recently developed superstructure-based framework that enables the early design of biorefineries for ethanol upgrading [1,2]. This framework relies on correlations and targeting methods to estimate capital and operating costs, enabling the identification of optimal upgrading strategies and the exploration of a large number of alternatives, without requiring extensive simulations. The design space considered is representative of the state-of-the-art for ethanol upgrading including twenty-two different chemistries and 112 different catalysts. The proposed framework is used to design optimal ethanol upgrading biorefineries for the production of gasoline, diesel, and jet fuel. We identify trade-offs between biorefinery complexity (measured as the number of chemical transformations) and profit. In general, we observe that increasing the number of chemical transformations improves the economic viability of the process due to an increase in the fuel yield. The possibility and the economic impact of producing fuels of superior quality (e.g. diesel with high cetane number, and gasoline with high octane number) is also studied. Specifically, we discuss how changing product specifications impacts fuel composition, process characteristics, and profit. The use of a system-level analysis allows us to identify non-intuitive processes for ethanol upgrading, both toward drop-in biofuels with properties similar to their fossil counterparts as well as toward biofuels with superior properties.

1. Restrepo-Flórez, J. M. & Maravelias, C. T. Advanced fuels from ethanol-a superstructure optimization approach. Energy Environ. Sci. 14, 493–506 (2021).
2. Ryu, J. & Maravelias, C. T. Efficient generalized shortcut distillation model with improved accuracy for superstructure-based process synthesis. AIChE J. (2020)