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 degrees C under 0.1 MPa nitrogen flow conditions, LiH reacts with N-2 and changes to lithium imide (Li2NH) with hydrogen desorption. However, the kinetics of the reaction between LiH and N-2 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 N-2 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 H-2 from about 350 degrees 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 N-2 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 N-2 and H-2 by exothermic processes, and the kinetics can be controlled using scaffolds.

Automated summary

This study investigates the reaction properties of ammonia synthesis via the chemical looping process of lithium hydride and proposes a kinetic improvement. The use of lithium oxide as a scaffold significantly improves the reaction kinetics by suppressing product agglomeration. The reaction between lithium hydride and nitrogen can be completed in just 20 minutes with the addition of lithium oxide, compared to more than 1000 minutes without it. Ammonia can be generated at ambient pressure through successive reactions of lithium hydride with nitrogen and hydrogen, which are exothermic processes. The kinetics of the reactions can be controlled by using scaffolds.