クリーンなアンモニアのために、MITのエンジニアが地下への進出を提案(For clean ammonia, MIT engineers propose going underground)

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2025-01-21 マサチューセッツ工科大学 (MIT)

MITの研究者たちは、地球を「地球化学リアクター」として活用し、地下でクリーンなアンモニアを生成する新しい方法を提案しました。このプロセスでは、水、窒素源、触媒を鉄分豊富な岩石に注入し、地熱と圧力を利用して水素とアンモニアを生成します。従来のハーバーボッシュ法と比べて化石燃料を必要とせず、温室効果ガス排出を大幅に削減できます。この技術は、農業用肥料の持続可能な生産に貢献する可能性があります。

<関連情報>

地質アンモニア: 岩石からの刺激NH3生成 Geological ammonia: Stimulated NH3 production from rocks

Yifan Gao∙ Ming Lei∙ Bachu Sravan Kumar∙ … ∙ Lokesh Sangabattula∙ Ju Li∙ Iwnetim I. Abate
Joule  Published:January 21, 2025
DOI:https://doi.org/10.1016/j.joule.2024.12.006

Graphical abstract

クリーンなアンモニアのために、MITのエンジニアが地下への進出を提案(For clean ammonia, MIT engineers propose going underground)

Context & scale

Ammonia (NH3) is the most produced chemical globally and a major contributor to greenhouse gas emissions, largely due to the energy-intensive Haber-Bosch process. Alternative methods are needed to achieve cost parity, CO2 reduction, independence from critical minerals, and decentralized NH3 production. Here, we propose and demonstrate a completely different approach, where NH3 is produced by injecting nitrate-containing water into iron-rich formations. Through a chemical redox reaction, ferrous iron in the rock converts nitrate into NH3 under ambient conditions and subsurface heat and pressure (130°C–300°C and 0.25–8.5 MPa). This geological process does not require H2, electricity, or application of external temperature or pressure, and emits no CO2. Our work paves the way for using Earth’s subsurface as a reactor, with abundant rocks as feedstock, to theoretically produce enough NH3 for 2.42 million years while minimizing environmental impact and achieving sustainability and decarbonization in the chemical and energy sectors.

Highlights

•Stimulated and in situ geological NH3 as a new approach for NH3 production at scale
•NH3 is produced by injecting nitrate-containing water into iron-rich formations
•Using Cu2+ as a catalyst, 1.8 kg NH3/t olivine was produced at 300°C in 21 h
•This approach requires no external H2 or electric current and emits no direct CO2

Summary

Although ammonia production is crucial for global agriculture, it comes with substantial carbon footprints. Here, for the first time, we propose and demonstrate a different method for stimulated (proactive) and in situ geological ammonia (Geo-NH3) production directly from rocks. Our approach demonstrated that NH3 can be efficiently generated by reacting natural (Fe,Mg)2SiO4 (olivine) minerals with nitrate-source water at 130°C–300°C and 0.25–8.5 MPa, and even at ambient temperature and pressure. Using both actual rocks and synthetic mineral Fe(OH)2, we investigated mechanisms and optimized conditions through experiments and theoretical calculations. We revealed the basic chemistry enabling Geo-NH3 production: Fe2+ contained in rocks reduces the nitrate source to NH3. Our approach, involving only the injection of nitrate-source water into the subsurface to utilize in situ subsurface heat and pressure, requires no external H2 or electric current and emits no direct CO2, offering a feasible alternative to sustainable NH3 production at scale.

0500化学一般
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