Chemical Looping of Manganese to Synthesize Ammonia at Atmospheric Pressure: Sodium as Promoter

Abstract

Affordable synthetic ammonia (NH3) enables the production of nearly half of the food we eat and is emerging as a renewable energy carrier. Sodium‐promoted chemical looping NH3 synthesis at atmospheric pressure using manganese (Mn) is here demonstrated. The looping process may be advantageous when inexpensive renewable hydrogen from electrolysis is available. Avoiding the high pressure of the Haber‐Bosch process by chemical looping using earth‐abundant materials may reduce capital cost, facilitate intermittent operation, and allow operation in geographic areas where infrastructure is less sophisticated. At this early stage, the data suggest that 0.28 m3 of a 50 % porosity solid Mn bed may suffice to produce 100 kg NH3 per day by chemical looping, with abundant opportunities for improvement.

Chemical Looping Ammonia Synthesis with High Performance Supported Molybdenum-based Nitrogen Carrier

“…然而, 此类型载氮体存在反应温度高、载氮体易烧结、 产氨率低等问题. 过渡金属因其具有丰富可变的价态, 被认为是潜在的载氮体 [19][20][21][22] . 目前为止, 已报道的过渡 金属基载氮体主要包括: 锰基载氮体和铬基载氮体等, 但产氨速率低是其现阶段主要的问题.…”

Activating dinitrogen for chemical looping ammonia Synthesis: Mn nitride layer growth modeling

“…An alternative method to produce NH 3 at atmospheric pressure and elevated temperature is chemical looping ammonia synthesis (CLAS). As reported elsewhere (Aframehr et al, 2020;Aframehr and Pfromm, 2021) this method consists of converting the bulk of a fixed bed of solid manganese (Mn) particles to Mn nitrides by contacting with N 2 gas at atmospheric pressure and elevated temperature. Then by switching the gas from N 2 to H 2 over the nitrided Mn, NH 3 is produced at atmospheric pressure and elevated temperature.…”

“…Then by switching the gas from N 2 to H 2 over the nitrided Mn, NH 3 is produced at atmospheric pressure and elevated temperature. The looping process is completed by again nitriding the now partially N depleted Mn (Aframehr et al, 2020). The rationale for the choice of Mn as the solid for CLAS is that a balance must be struck between the activation of dinitrogen and absorption of N into the solid, and the subsequent activation of dihydrogen at the solid surface, and release of N atoms from the solid to produce NH 3 .…”

“…In our previous study, a two-step chemical looping process operating under relatively mild conditions to produce NH 3 was studied regarding Mn nitride phases and the particle surface morphology and composition (Aframehr et al, 2020). The time and temperature dependencies of Mn nitride layer growth and diffusion zone growth (microstructural development) during nitridation were investigated (Aframehr and Pfromm, 2021).…”

“…The overall goal of this work is to contribute to the understanding and quantification of non-steady state nitride formation from solid Mn and gaseous N 2 via splitting of N 2 at the gas/solid interface, followed by simultaneous diffusion of N atoms into the solid and reaction with Mn. This is the first step in a chemical looping approach to synthesize NH 3 by subsequently contacting Mn nitride with gaseous H 2 (Aframehr et al, 2020;Aframehr and Pfromm, 2021). This looping NH 3 synthesis process is quite unique in that N atoms emanating from the bulk nitride react with hydrogen from the gas phase at the solid/gas interface.…”