A DFT study on selective adsorption of NH₃ from ammonia synthesis tail gas with typical aliphatic boranes

Abstract

Stimulated by agricultural development, ammonia becomes the second buck chemical in the world, and many ammonia synthesis plants will discharge ammonia-containing wastewater and destroy the ecological balance. In this work, Density Functional Theory (DFT) method was used to study the adsorption characteristic of typical aliphatic boranes on NH₃ as well as N₂, H₂ and CH₄. The results showed that the adsorbents could selectively adsorb NH₃ over N₂, H₂ and CH₄. The chain length of CH₂ has little effect on the adsorption characteristic of boranes while the adsorption energy strongly affected by the number of CH₃ groups directly attached to B for boranes. The analysis of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) indicated that LUMO is contributed by adsorbent and HOMO is contributed by adsorbate. Molecular electrostatic potential indicated that the positive charge of B and the negative charge of N can form the optimal configuration. The selectivity coefficient showed that the adsorbent has high selectivity to ammonia. The desorption of NH₃ could be readily achieved by increasing temperature. This study can provide the adsorption mechanism of this system and give a guidance on designing reusable aliphatic borane resin to selectively adsorb and recover NH₃.

GRAPHICAL ABSTRACT

KEYWORDS:

• Borane
• ammonia
• adsorption
• density functional theory

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Applied basic Research Program of Xinjiang Bingtuan [grant number 2015AG004]; the National Natural Science Foundation of China [grant number NSFC grant number 21968029]; the Major Science and Technology Project of Xinjiang Bingtuan [grant number 2017AA007, 2020AA004]; the Major Science and Technology Project of Bashi Shihezi City [grant number 2020ZD02].