Investigation of alternative routes for ammonia production in reduced-pressure Haber-Bosch systems

• Grant number: 25/22529-0
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: April 01, 2026
• End date: July 31, 2029
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Cauê Ribeiro de Oliveira
• Grantee: Vinicius Ferraz Majaron
• Host Institution: Embrapa Instrumentação Agropecuária. Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA). São Carlos , SP, Brazil

Abstract

Since its industrial-scale implementation in the early 20th century, the Haber-Bosch process has been consolidated as one of the most significant discoveries in modern chemistry, enabling the synthesis of ammonia from nitrogen and hydrogen, which is fundamental for the large-scale production of nitrogen fertilizers. However, the typical operating conditions of Haber-Bosch reactors involve temperatures in the range of 400-500 °C and pressures exceeding 150 bar, resulting in extremely high energy consumption. In this context, various strategies have been explored to reduce both the energy demand and the environmental footprint of the process. Recent studies have demonstrated that the adsorption of NH¿ onto inorganic salts during the synthesis process-such as alkaline earth metal chlorides-can promote reductions in temperature and pressure requirements by shifting the equilibrium through removal of the product from the gas phase into a solid medium. Simultaneously, this strategy allows for selective recovery of the product. Nevertheless, these salts still present limitations in terms of cyclic stability and heat transfer, which compromise their continuous application in reaction systems. Within this framework, the present project proposes to investigate the selective adsorption of ammonia onto solid media (selected and synthesized adsorbents) during the synthesis of ammonia from the N¿-H¿ reaction, as a means of shifting the equilibrium and enhancing the Haber-Bosch process under reduced pressures. To this end, different materials with potential for NH¿ adsorption will be evaluated, including zeolites, mesoporous materials, lamellar systems such as clay minerals, and salts impregnated into these supports (e.g., magnesium, calcium, and strontium chlorides), compared against the use of salts in granular form. The immobilization strategies of these adsorbents (e.g., fibers, Raschig rings, honeycomb-type structures, etc.) will also be examined to determine the most effective conditions for access of freshly formed ammonia to the adsorption surface. A laboratory-scale reactor will be designed and constructed to promote the Haber-Bosch reaction in batch mode using commercial catalysts. Internally, the reactor will consist of a primary reaction chamber connected to a second pressure vessel under isobaric conditions, filled with varying amounts of adsorbents. The study will address the adsorbent-to-reactant ratio, residence time, and operating parameters of temperature and pressure. Additional parameters will include the regeneration capacity of the capture media and their long-term stability. Finally, for the fixation of the NH¿ produced, the process will be extended to the direct conversion of ammoniacal adducts into struvite (MgNH¿PO¿·6H¿O) within the reaction system itself, a compound of agronomic interest with high nutritional value as a fertilizer. To achieve this, tests incorporating P¿O¿ sources into the adsorption chamber will be carried out to assess struvite formation under Haber-Bosch synthesis conditions. By integrating synthesis, capture, and conversion into a solid fertilizer, this proposal aims to lower operational pressures and temperatures, minimize the energetic and environmental costs of the process, and generate a product of immediate agronomic value in compact systems. The investigation will combine the preparation and characterization of adsorbent materials, bench-scale reactor testing coupled with an adsorption module, and statistical evaluation of results, with the aim of producing publications in high-impact international journals. (AU)