(28f) Sustainability Analysis of Condensed-Phase n-Butanol Production from Ethanol

Bioethanol is one of the most valuable replacements for or additives to fossil fuels. However, ethanol is not without its limitations that include low energy density, corrosivity, and contamination issues when mixed with water. In contrast, n-butanol has a notable advantage in these aspects, as it is more miscible in gasoline, has higher energy density, and has an air to fuel ratio comparable to that of gasoline. As a result, there has been growing interest in the production of biobutanol and higher alcohols as biofuels as well as for use in the chemical industry.

The condensation of ethanol to butanol and higher alcohols is known as Guerbet chemistry [1]. The reactions are well known and have been substantially investigated. The path to Guerbet chemistry commercialization, however, has been hindered by substandard yields, catalyst stability concerns, and high capital and energy costs.

Our research group has studied the condensed-phase Guerbet reaction of ethanol to higher alcohols [2], [3]. Recently, we have optimized a condensed phase continuous flow reactor using multi-metallic catalysts on γ-Al₂O₃ support modified with La₂O₃. We have achieved higher alcohols selectivity of 80% at ethanol conversions of 40%. These encouraging results have prompted us to explore the economic feasibility and environmental impact of industrial-scale higher alcohol production using Guerbet chemistry.

An economic and environmental assessment of a first-generation facility producing 25 million gallons of n-butanol per year has been performed for a range of butanol and higher alcohol selectivities. Simulation of the catalytic reactor and the recovery and purification processes have been conducted using AspenPlus. Economic parameters such as capital costs, operating costs, annual profit, and return on investment have been determined for several scenarios. The results obtained show n-butanol required selling prices are reasonably competitive for conversion and selectivity combinations achieved in laboratory reactions. Interestingly, analysis of the separation train indicate significant economic benefit by carrying out distillations at elevated pressures. Environmental impacts such as climate change, resource depletion, water use, and eutrophication are also assessed.

References

[1] D. Gabriëls, W. Y. Hernández, B. Sels, P. Van Der Voort, and A. Verberckmoes, “Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization,” Catal. Sci. Technol., vol. 5, pp. 3876–3902, 2015.

[2] T. L. Jordison, L. Peereboom, and D. J. Miller, “Impact of Water on Condensed Phase Ethanol Guerbet Reactions,” Ind. Eng. Chem. Res., vol. 55, no. 23, pp. 6579–6585, 2016.

[3] T. L. Jordison, C. T. Lira, and D. J. Miller, “Condensed-Phase Ethanol Conversion to Higher Alcohols,” Ind. Eng. Chem. Res., vol. 54, no. 44, pp. 10991–11000, 2015.