Nitrogen fertilizer is essential for food production and made from ammonia (NH₃). NH₃ is mainly produced by the Haber–Bosch process using nitrogen and fossil hydrocarbons. However, other obtaining method of NH₃ is required in order to reduce use of fossil fuels. On the other hand, releasing NH₃ into the environment causes environmental issues (e.g. PM2.5). In order to reduce use of fossil fuels and NH₃ emission, recovery and reuse of NH₃ from exhaust gas is key technology.
At the view of nitrogen resource, NH₃ recovery as ammonium salts has the advantage of density, comparing with that as ammonia gas. When high concentration of NH₃ and CO₂ gases are mixed under humid conditions, solid state ammonium bicarbonate (NH₄HCO₃) is synthesized. We aimed to demonstrate a novel method to obtain powder of NH₄HCO₃ from fetid air in pig farm.
The treatment of NH₃ for agricultural industry is necessary, because NH₃ emissions are mainly from the agricultural sector. However, NH₃ recovery at agricultural sector is a tough target because of humid condition. Selective adsorption is efficient for molecule recovery from trace concentration in humid gas. Copper Prussian blue analogues (CuPBA) has ammonia selectivity and adsorption capacity even in trace concentration. We succeeded to obtain solid NH₄HO₃ from trace NH₃ and CO₂ by adsorption and sublimation using ammonia adsorbent of CuPBA. Interestingly, CuPBA adsorbs some amount of H₂O and CO₂ with adsorbing NH₃, which are raw materials of NH₄HCO₃. With heating CuPBA adsorbing NH₃, the adsorbed molecules were desorbed into gas, resulting that solid NH₄HCO₃ was obtained with cooling the gas. We will talk about demonstration of the harvesting of NH₄HCO₃ from malodorous air in pig farm.

NHtrapping system in piggery using CuPBA and obtained powder of NH<sub>4</sub>HCO<sub>3</sub>. Reprinted with permission from <i>ACS Sustainable Chem. Eng.</i> 2021, 9, 50, 16865–16869. Copyright 2022 American Chemical Society.

Akira Takahashi

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