Exceeding Single‐Pass Equilibrium with Integrated Absorption Separation for Ammonia Synthesis Using Renewable Energy—Redefining the Haber‐Bosch Loop

Abstract

The synthesis of ammonia through the Haber‐Bosch process has been at the foundation of the chemical industry for over 100 years, but when the energy and feedstock sources switch from fossil fuels to renewable electricity, the process needs to be reimagined. Herein, the successful integration of ammonia synthesis and separation is demonstrated in a recycle‐less process setting the foundations of green ammonia technology. The ruthenium‐based catalyst uses a nanostructured CeO2 support and Cs electronic promotion to remove hydrogen and ammonia inhibition, respectively, creating a catalyst with low‐temperature (<300 °C) activity that quickly approaches equilibrium. The absorbent uses MnCl2 to avoid the acid releasing decomposition of conventional absorbents like MgCl2, and a support of SiO2 to simultaneously enhance MnCl2 dispersion and improve stabilization. This integrated catalyst‐absorbent system reproducibly exceeds single‐pass ammonia synthesis equilibrium. Kinetic models of the catalyst and absorbent successfully predict the experimental long‐term behavior and facilitate the design of an integrated system. These results present a framework for aligning intermittent and isolated renewable energy with ammonia synthesis by decreasing capital complexity and increasing process agility—adapting to a shifting energy landscape to continue providing fertilizers with minimum CO2 penalty and pioneer energy storage.

Process Intensification Strategies for Power-to-X Technologies

“…Importantly, the complete separation of NH 3 is crucial for the process energy efficiency, as NH 3 remaining in the recycle stream leads to a decrease in the formation rate due to unfavorable equilibrium constraints [37]. To overcome this challenge, the replacement of condensation with adsorptive or absorptive NH 3 separation for low pressure processes was discussed as a promising option in various publications [38][39][40][41][42][43][44][45][46][47]. These techniques, which can be carried out at elevated temperatures, provide a selective separation of NH 3 and can reach a low residual NH 3 concentration in the recycle stream (<1%) [31].…”

“…Moreover, the sorptive in situ removal replaces the inefficient condensation of NH 3 at a low pressure. First approaches for the realization of a multifunctional reactor using a Ru-based catalyst for NH 3 synthesis and metal halide salts for separation were published recently [41].…”

Chelation‐activated multiple‐site reversible chemical absorption of ammonia in ionic liquids

“…where n gas is the amount of gas absorbed (mol); ρ P0 gas , ρ P1 gas , and ρ P2 gas are the densities of gas at P 0 , P 1 , and P 2 , respectively (mol/cm 3 ); V GR and V AT are the volumes of storage tank and absorption tank respectively (cm 3 ); w liquid is the mass of liquid sample (g); ρ liquid is the density of liquid solvent (g/cm 3 ). The values of ρ P0 gas , ρ P1 gas , and ρ P2 gas were obtained from the NIST Chemistry WebBook.…”

“…summarizes the NH 3 solubilities of various ILs, including[Li-TEG][Tf 2 N] and other ILs reported in the literature [36][37][38]47,48. It can be seen that the NH3 solubilities of Li-PEG-chelated ILs are higher than those of most other ILs reported in the literature. For examples, [EtOHim][Tf 2 N] with both hydroxyl site and weak acidic protic site can absorb 3.11 mol/mol of NH 3 at 313.2 K and 100 kPa; [Bim][Tf 2 N] and [HOOC(CH 2 ) 3 mim][NTf 2 ] with weak acidic protic sites but no hydroxyl site can absorb 2.69 and 1.54 mol/mol of NH 3 , respectively, under similar condition.…”

“…Direct synthesis of ammonia (NH 3 ) from nitrogen (N 2 ) and hydrogen (H 2 ) is one of the most important innovations in the past century 1–3 . Since the conversion of N 2 and H 2 to NH 3 is a reversible reaction, the efficient separation of NH 3 from gas products is required.…”