Simulation-Based Development of Deep Eutectic Solvent-Driven Extractive Distillation for Butanol Separation

Abstract

Overreliance on fossil fuels such as coal, oil, and natural gas has led to severe environmental and human health concerns due to greenhouse gas (GHG) emissions and resource depletion. These issues have triggered the world to find renewable and environmentally friendly energy resources. Among these biofuels, biobutanol is the most promising fuel, primarily produced through the microbial fermentation process, and is a key component of the acetone-butanol-ethanol (ABE) fermentation process. However, the industrial scalability of biobutanol production is constrained by its low concentration in fermentation broths and the challenges of separating it from water due to azeotrope formation. Conventional separation processes, such as distillation, are energy-intensive and economically unviable for biobutanol recovery. Hybrid extractive distillation using ionic liquids (ILs) as an entrainer has shown potential as an alternative, with notable success in the dehydration of biobutanol. However, the limitations of ILs, such as toxicity, non- biodegradability, and high costs, pose significant barriers to their widespread adoption. To address these issues, deep eutectic solvents (DES) have emerged as a promising alternative. DES offers superior advantages over ILs, such as biodegradability, lower costs, and simple preparation. Recent research highlights their potential for separating lower alcohol, including biobutanol. However, the selection of optimal DES and the development of an efficient dehydration process for biobutanol remain unexplored. In this study, three new ideal hydrophobic deep eutectic solvents (DESs) were used for the effective extraction of butanol from aqueous mixtures: Thymol: Octanol (1:1), Thymol: Diphenyl (1:1), and Thymol: Octadecanol (3:1) in Aspen Plus V14. The DESs were used as selective entrainers to improve butanol recovery in the extractive distillation process, especially in cases in which the presence of azeotropes makes conventional separation energy intensive. At the distillate outlet, the Thymol: Octadecanol (3:1) mixture produced the highest 87% butanol purity among the evaluated DESs, demonstrating better performance. A thorough exergy analysis was carried out to assess the (DL-Menthol: Decanoic acid) and (Thymol: Octadecanol) DES-based configuration's sustainability and thermodynamic efficiency in further detail. The Thymol: Octadecanol (3:1) system had the best exergy efficiency, extractor column (99.96%), pump (99.99%), distillation column (5.03%), and cooler (99.99%), with the least amount of exergy destruction, according to the data, showing its capability as a highly efficient and energy-efficient solvent for sustainable butanol recovery. This work enhances the advancement of more environmentally friendly options for the purification of biofuels by offering a systematic method to choosing and evaluating the use of DESs in extractive distillation processes.