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Green Ammonia-Mediated CO₂ Capture and Conversion to Valuable Chemicals

Wenzhen Li^1,*, Hengzhou Liu¹, Yifu Chen¹, Shuang Gu²

1 Chemical & Biological Engineering Department, Iowa State University, 617 Bissell Rd, Ames, IA 50011, USA
2 Mechanical Engineering Department, Wichita State University, 1845 Fairmount St, Wichita, KS 67260, USA

* Corresponding Author: Wenzhen Li. Email:

The International Conference on Computational & Experimental Engineering and Sciences 2024, 31(1), 1-1. https://doi.org/10.32604/icces.2024.012577

Abstract

Direct electrochemical conversion of CO₂ capture solutions (instead of gaseous CO₂) into valuable chemicals can circumvent the energy-intensive CO₂ regeneration and pressurization steps. While commonly used CO₂ capture agents include alkali and amine solutions, ammonia has been rarely investigated. In another aspect, mismanagement of reactive nitrogen (Nr) in waste has emerged as a major problem in water pollution to our ecosystems, causing severe eutrophication and health concerns. Sustainably recovering Nr [such as nitrate (NO₃⁻)-N] and converting it into green ammonia (NH₃) could mitigate the environmental impacts of Nr and reduce the NH₃ demand from the carbon-intensive Haber-Bosch process, as well as a possible CO₂ capture agent due to its alkaline nature.    In this talk, we will present our rencet research on integration of electrodialysis and electrocatalysis for ammonia synthesis from dilute waste Nr sources [1], and green ammonia-mediated CO₂ capture (to ammonium bicarbonate, NH₄HCO₃) and subsequent reduction to ammonium formate (NH₄HCO₂) as a new approach to CO₂ capture and utilization (CCU) [2]. We have demonstrated a record-high NO₃⁻-to-NH₃ performance in a scalable, versatile, and cost-effective membrane-free alkaline electrolyzer (MFAEL): an unprecedented NH₃ partial current density of 4.22 ± 0.25 A cm⁻² with a faradaic efficiency of 84.5 ± 4.9%. We also discovered that an ammonium bicarbonate (NH₄HCO₃)-fed electrolyzer with an anion exchange membrane (AEM) outperforms the state-of-the-art KHCO₃ electrolyzer with a bipolar membrane (BPM) owing to its favorable thermal decomposition property, which allows for a 3-fold increase in the in situ CO₂ concentration, a maximum 23% increase in formate faradaic efficiency, and a 35% reduction in cell voltage by substituting BPM with the AEM. Our integrated process by combining NH₄HCO₃ electrolysis with CO₂ capturing by on-site generated green ammonia from the electro-reduction of nitrate in MFAEL has shown a remarkable 99.8% utilization of CO₂ capturing agent. Our recent progress in this direction will also be briefly presented. Such a multi-purpose process may offer a sustainable route for the simultaneous removal of Nr wastes and streamlined CO₂ capturing and upgrading to valuable chemicals.

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Keywords

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