(365g) Middle Distillates from Ethanol-Technoeconomic and Life CYCLE Assessment

Ethanol has been established as the most commonly used biofuel. In the U.S. alone, its production capacity has increased from 2 to 16 billion gallons in the last twenty years. However, ethanol has an important limitation, it cannot be incorporated in significant amounts in middle distillates. This limitation becomes more relevant if we consider fuel consumption projections for the upcoming decades [1]. While gasoline demand, where ethanol is typically blended, is expected to decrease, middle distillates demand, especially that of diesel, is expected to increase. An additional consideration is that the electrification of aviation and freight transportation sectors, where middle distillates are used, is not expected in the near term. This scenario leaves us with two problems: a large infrastructure built for the production of a biofuel whose demand may decrease (i.e. ethanol) and the lack of sustainable alternatives for the fossil fuels whose demand is expected to increase (i.e. aviation fuel and diesel). One strategy that can address these two challenges simultaneously relies on the upgrading of ethanol. A large number of different pathways for ethanol upgrading may be used. One particular alternative based on Guerbet coupling and etherification seems promising [2]. In this alternative ethanol is first transformed into higher alcohols using Guerbet coupling, and then these alcohols are used to produce ethers in an etherification reaction. The main advantage of this approach is the possibility of producing diesel blends of high quality with a high content of ethers, known for their high cetane number.

In this work, we present the results of a techno-economic and life cycle assessment for the upgrading of ethanol to diesel using a biorefinery based on Guerbet coupling and etherification. This work is the result of an iterative and collaborative effort between experimentalists and process engineers. This synergistic collaboration has allowed us to explore the economic and environmental impacts of variables such as conversion and feed composition, using data obtained from experiments designed based on process modeling needs. In particular, we have established the effects that changes in conversion and selectivity have on the minimum selling price and the separation train associated with the designed biorefineries. The results presented constitute the first analysis of this kind for this system and reveal the main economic drivers of the process and its environmental impacts. In particular, the feedstock cost appears as the most important cost component, pointing toward the need of minimizing the production of low molecular weight by-products not suitable to be blended in diesel fuel. Notably, using lignocellulosic ethanol as a feedstock can lead to a 50% reduction in greenhouse gas emissions. The properties of the resulting fuel (cetane number, density, viscosity, low heating value, flash point, and distillation curve) are evaluated and satisfy the ASTM requirements for diesel.

1. Dagle, R. A., Winkelman, A. D., Ramasamy, K. K., Lebarbier Dagle, V. & Weber, R. S. Ethanol as a Renewable Building Block for Fuels and Chemicals. Ind. Eng. Chem. Res. 59, 4843–4853 (2020).
2. Eagan, N. M. et al. Catalytic Synthesis of Distillate-Range Ethers and Olefins from Ethanol through Guerbet Coupling and Etherification. Green Chem. (2019).