(146c) A General Technoeconomic Analysis of Power Ultrasound Process for Separation of Azeotropic Mixtures

Thermal energy-based industrial processes in which distillation plays a major role, are significant sources of CO₂ emissions. Governments, industry, and academia are highly interested in the development of nonthermal electrically-based unit processes that can act as alternatives to traditional thermal processes. In particular, a tremendous amount of thermal energy has been consumed by distillation processes, which account for 95% of the energy used in the chemical process industry for separations [1], 45-55% of the total energy in the chemical and process industries, and 10-15% of US energy consumption [2].

This work is part of an effort to develop power ultrasound techniques for nonthermal, nonequilibrium separation of ethanol/water solutions. The main advantage of power ultrasound separation over distillation is avoidance of heat transfer losses and the azeotropic bottleneck [3]. Our preliminary estimation of energy savings via power ultrasound separation is potentially large. Comparing the energy requirement of current industrial process (7 MJ per kg of highly enriched fuel-quality ethanol; separation using distillation and molecular sieves) [4], to a conservative upper bound of 3.0 MJ kg^-1 for the ultrasonic process for essentially pure ethanol using four stages of power ultrasound separation modules with multiple transducers, we estimate a 55% energy reduction. However, the economics of the power ultrasound separation technology still remain to be assessed and need to account for diverse process combinations (e.g. pre-distillation followed by ultrasound, multi-stage ultrasound, parallel vs. serial configurations, etc.), and capital cost of fabrication of ultrasound separator modules including piezoceramic ultrasound transducers.

Here, we report a technoeconomic analysis of the power ultrasound azeotropic separation process for ethanol/water solution to produce fuel quality ethanol (Ethanol: 92.1% Volume minimum, Water: 1% Volume maximum). The automated process synthesis framework [5] is used for a comparative study of a conceptual process including azeotropic distillation, extractive distillation, adsorption, and membrane separation. We rely on the conceptual design of a process superstructure that considers a large number of candidate azeotropic separation processes. The conceptual design is automatically analyzed by process simulators, which determine the net present value (NPV), including CAPEX and OPEX for each element of the entire process. Finally, we identify the global sensitivity of the results to variation in the prices of thermal energy and electrical energy, recycle ratio, feed concentration, and production rate across various combinations of power ultrasound separation processes to understand both the optimal configuration and the CO₂ footprint compared with traditional processes. The results offer a basis for preliminary assessment of the potential of power ultrasound separation processes to reduce the energy cost and CO₂ footprint of ethanol-water separation.

References

[1] U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technology Program. (2005). Hybrid separations/distillation technology: research opportunities for energy and emissions reduction

[2] Ritter, S.K. (2017). Taking the heat off distillation. Chemical & Engineering News, June 19, 2017.

[3] Kirpalani, D. M., & Toll, F. (2002). Revealing the physicochemical mechanism for ultrasonic separation of alcohol–water mixtures. J. Chem. Phys. 117, 3874-3877.

[4] Baeyens, J., Kang Q., Appels L., Dewil R., Lv Y., & Tan, T. (2015) Challenges and opportunities in improving the production of bio-ethanol. Prog. Energy Comb. Sci. 47, 60–88.

[5] Na, J., Seo, B., Kim, J. et al. (2019) General technoeconomic analysis for electrochemical coproduction coupling carbon dioxide reduction with organic oxidation. Nature Commun. 10, 5193.