Microscopic insight into evaporation and condensation of binary system ammonia-water with the effect of hydrogen bond

Abstract

Ammonia recovery for fertilizer and energy production faces a critical bottleneck: inaccurate prediction of evaporation and condensation rates in dilute solutions due to strong hydrogen bonds between ammonia and water. The presence of these bonds deviates the thermodynamics properties of ammonia water from standard laws like Henry's Law and Raoult's Law, hampering process optimization. As results, many of the ammonia water separation studies were conducted using specifically designed apparatus, and the results are bounded to said apparatus. This study introduces a novel method using Molecular Dynamics Simulations to tackle this challenge. We developed a simulation framework accounting for hydrogen bond interactions in low-concentration (20% wt%) ammonia-water mixtures. By systematically varying temperature under constant pressure, our approach tracks evaporation and condensation rates, revealing an efficient recovery strategy. At 140°C, ammonia evaporates at a rate of 609.22 kg·m-2·s-1 while condensate at 9.18 kg·m-2·s-1 under 20°C with, both at 0.4 MPa. Importantly, this strategy minimizes water loss, maximizing ammonia separation. These findings highlight the limitations of traditional models and demonstrate the power of molecular simulations in overcoming hydrogen bond challenges. Future work includes further validation against experimental data and exploring more complex mixtures for broader applicability. By unlocking accurate rate predictions, this work paves the way for optimizing ammonia recovery processes, boosting efficiency and sustainability in diverse fields. Mathematics Subject Classification 65Z05, 76T06, 76T10, 80-10.