(548a) Techno-Economic Analysis and Life Cycle Assessment of Hydroxylamine Eco-Manufacturing Via Wastewater Electrochemical Reduction

The manufacturing of nitrogen-based chemicals is dependent mainly on the Haber-Bosch process, which produces cheap ammonia (NH₃) from hydrogen (H₂) and atmospheric nitrogen (N₂) gas. However, this process has high energy requirements due to the high process temperature (500⁰ C) and pressure (100-150 bar). It is also responsible for significant CO₂ emissions (400 metric tons annually) and is energy-intensive- it consumes around 2% of the world's primary energy.

Hydroxylamine (NH₂OH) is an important chemical intermediate currently produced from NH₃ formed by the Haber-Bosch process, followed by the Ostwald process (which generates nitric oxide, NO from NH₃) and NO reduction by H₂. We propose an alternative reaction mechanism to the conventional method described above, which involves the electroreduction of nitrate ions (NO₃^-) to NH₂OH, as depicted in figure 1. Wastewater from fertilizer run-offs, nuclear power plants, and slaughterhouses is a rich source of NO₃^-, which harms the ecosystem.

Many researchers are now focusing on manufacturing chemicals via electrochemical processes. Electrochemical processes are typically executed at ambient temperature and pressure, thus requiring mild operating conditions and low process energy.

We conducted a techno-economic analysis (TEA) and a life cycle assessment (LCA) of this electrochemical system converting NO₃^- to NH₂OH. We conducted TEA using a general model by Orella et al., 2020.¹ We performed a sensitivity analysis to calculate the maximum possible reduction in NH₂OH production cost and discover its influencing parameters. The most dominant parameter influencing the cost was the separation factor, followed by lifetime, product Faradaic Efficiency, electricity price, and catalyst loading. We obtained the optimum projected cost of NH₂OH as $1.65/kg, lower than its market price estimated at $1.72/kg. We obtained the base cost, or the current production cost, as $6.03/kg. Our analysis suggests an immense potential for cost reduction, which motivates further research.

We also conducted an LCA of the process system depicted in figure 1. The goal of this LCA study is to calculate the environmental impacts of the proposed eco-manufacturing pathway to produce NH₂OH in a wastewater treatment plant in Iowa. We determined if the proposed alternate method of producing NH₂OH is a sustainable option compared to the most prevalent method of producing almost every N-based chemical, the Haber-Bosch process.

This study's life cycle inventory (LCI) data was obtained from balanced chemical reactions, the preliminary TEA model, and literature, scaled to the functional unit: 1 kg of NH₂OH produced. We performed a "Cradle to Gate" LCA study, focusing on the system from resource extraction to transport and not including the use and waste management phases of NH₂OH. We used openLCA 1.11.0 to perform LCA using Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) 2.1 as the impact assessment method. It evaluates these impact categories- acidification, carcinogenics, ecotoxicity, eutrophication, fossil fuel depletion, global warming, non-carcinogens, ozone depletion, respiratory effects, and smog. We modeled the NO₃^- reduction unit process in openLCA based on Dominguez-Ramos et al. (2013) and Orella et al. (2020).^1,2

We compared our LCA results for the proposed pathway with the conventional method of NH₂OH production. We found that the proposed method is environmentally friendly for most impact categories while using grid electricity to operate the electrical components. We also observed that the proposed pathway is better than the conventional method for all the impact categories considered if we use solar photovoltaic (PV) energy instead of grid electricity.

Figures 2 and 3 show the life cycle impacts comparison of producing 1 kg NH₂OH produced using the conventional and proposed route in Iowa using grid and solar PV electricity, respectively.

Our analysis shows that the proposed electrochemical pathway has less environmental impact than the conventional pathway. The economic feasibility is expected to improve based on future technological considerations. The proposed pathway has massive potential and could be used as an alternative to conventional processes, including the Haber-Bosch process, followed by the Ostwald process and hydrogenation to manufacture NH₂OH.

Acknowledgments: The authors gratefully acknowledge the funding for the project from the National Science Foundation (NSF) with the NSF Award number 2036944. We thank our collaborators- Dr. Shuang Gu, Dr. Wenzhen Li, and his students (Hengzhou and Yifu), for performing the experimental work for the project.

References

[1] Orella, M. J., Brown, S. M., Leonard, M. E., Román-Leshkov, Y., & Brushett, F. R. (2020). A General Technoeconomic Model for Evaluating Emerging Electrolytic Processes. Energy Technology, 8(11).

[2] Dominguez-Ramos, A., Singh, B., Zhang, X., Hertwich, E. G., & Irabien, A. (2015). Global warming footprint of the electrochemical reduction of carbon dioxide to formate. Journal of Cleaner Production, 104, 148–155.