(372c) Electrification of Thermochemical Processes Involving Reaction-Separation Coupling – Ethanol Production Via Acetic Acid Hydrogenation

The declining cost of variable renewable electricity (VRE) supply is motivating growing interest in electrification-based decarbonization of chemical processes, with a particular focus on novel unit operations for electricity use within chemical processes, such as novel chemical reactors (e.g. electrochemical, microwave) and separations (e.g. membranes). In contrast, the prospects of electrification within existing chemical processes, which are predominantly reliant on thermochemical reactors coupled with thermally-driven separation schemes (e.g. distillation, absorption) is relatively underexplored. Although electrification of high-temperature (>400 ^oC) heat supply is an emerging area, technologies for electrification of low-to-medium temperature heat supply (<400°C), that was responsible for approximately 21% of CO₂ emissions from the chemicals and refining sector in 2020, are more commercially mature. However, a critical research gap remains in the systematic evaluation of strategies for integrating heat electrification technologies, such as resistance heating and heat pumps, into existing chemical processes.

Here, we investigate the energetic, economic, and greenhouse gas (GHG) impacts of low-to-medium temperature heat electrification of chemical processes involving thermochemical reactions and thermally-driven separations. As a case study, we focus on the process of acetic acid hydrogenation to produce ethanol, a pathway of growing interest due to its relevance for the energy transition via: a) enabling production of bio-based chemicals and fuels (e.g. ethanol-derived products like jet fuel and ethylene), b) producing a dense liquid hydrogen carrier (ethanol) for long-distance energy transport and energy storage. In addition, this process involves complex separations (e.g. azeotropic distillations) for ethanol purification as well as reaction-separation coupling due to the exothermic nature of the reaction and formation of side-product ethyl acetate during the reaction.

We simulate the process for four levels of ethanol carbon recovery (77%, 83%, 91%, and 96%), spanning different reactor operating conditions, for the baseline case without electrification and two electrification scenarios: a) so-called moderate electrification involving use of resistive heating alone to replace process hot utility requirements, b) so-called advanced electrification that combines use of resistive heating for hot utility + heat pump-distillation via vapor recompression cycles (VRC). In each case, the process simulation accounts for the complete acetic acid hydrogenation system, including a kinetics-based reactor, hydrogen recovery unit, acetic acid recovery unit, and extractive distillation to produce high purity ethanol. For each process configuration, we performed heat integration, followed by techno-economic and life cycle GHG analyses, covering scope 1 and 2 emissions, to quantify the impacts of electrification.

Our results highlight that electrification reduces total process energy (fuel+ electricity input) consumption compared to the baseline process, with reduction of 11 – 13% for the moderate electrification case and 24 – 34% for the advanced electrification case. This reduction in energy consumption, which stems from improved equipment efficiency and tailored heat integration schemes, also translates into reduced energy-related life cycle emissions for the process. Interestingly, this is true even considering the relatively high carbon-intensity of the existing U.S. grid electricity supply. For example, based on the 2025 Texas grid electricity supply, the energy-related GHG emissions of the moderate and advanced electrification processes are 25 – 26% and 35 – 44% lower than the baseline process.

The impact of electrification on process capital costs (capex per kW of product), however, are dependent on the level of electrification, with moderate electrification resulting in similar to lower overall capital costs while advanced electrification increasing capital costs by 6 – 25% across the carbon recovery scenarios evaluated. Interestingly, we find that the incremental capital cost impact of advanced electrification decreases with increasing carbon recovery, potentially making it more attractive for higher ethanol yielding process configurations. Overall, these findings highlight the varying impacts of alternative electrification strategies on process energy efficiency, economics and life cycle GHG emissions. It also underscores the need for systematic assessment of tailored electrification strategies considering process-specific design and operations.