Improvement of Kinetics of Ammonia Synthesis at Ambient Pressure by the Chemical Looping Process of Lithium Hydride

In this work, the reaction properties of ammonia (NH₃) synthesis via the chemical looping process of lithium hydride (LiH) are investigated, and kinetic improvement is carried out. During the heating process up to 500 °C under 0.1 MPa nitrogen flow conditions, LiH reacts with N₂ and changes to lithium imide (Li₂NH) with hydrogen desorption. However, the kinetics of the reaction between LiH and N₂ is slow due to agglomeration of the products. Lithium oxide (Li₂O) as a scaffold is effective to drastically improve the reaction kinetics because Li₂O suppresses the agglomeration. In this case, the reaction of LiH and N₂ is completed within 20 min, which is drastically short compared with that of LiH (more than 1000 min). NH₃ can be generated by reaction between Li₂NH as the product and 0.1 MPa H₂ from about 350 °C. Crushing the agglomerated particles and addition of Li₂O can improve the reaction kinetics of NH₃ synthesis, and then, the reaction completely proceeds at a lower temperature and shorter time. It is expected from the experimentally obtained reaction products and thermodynamic database that the N₂ dissociation and NH₃ generation are exothermic reactions. From the abovementioned results, it is concluded that NH₃ can be produced at ambient pressure via successive reactions of LiH with N₂ and H₂ by exothermic processes, and the kinetics can be controlled using scaffolds.