Tsubame BHB, a Japanese cleantech startup founded in 2017, has developed an innovative ammonia synthesis technology. Their process employs electride catalysts to produce ammonia at low temperatures and pressures, resulting in a more energy-efficient and environmentally friendly method compared to the traditional Haber-Bosch process. This novel approach enables small-scale, distributed ammonia production, which can be customized for on-site and on-demand requirements.
Challenges: green ammonia
Ammonia is a vital chemical commodity with widespread applications. It serves as the foundation for fertilizers that underpin modern agriculture, contributing to about half of global food production. Beyond agriculture, ammonia shows promise as a renewable energy storage and transport medium. Its potential is being explored in various sectors, including Samsung in shipping, Toyota in automotive, and Boeing and NASA in aircraft, owing to its superior energy density compared to lithium-ion batteries and compressed hydrogen.
However, conventional ammonia production is a significant contributor to global carbon emissions. The process, which involves steam methane reforming, water-gas shift reaction, and the Haber-Bosch process, consumes approximately 1.8% of global energy output annually. This results in the emission of about 500 million tons of carbon dioxide, accounting for roughly 1.8% of global carbon dioxide (COâ‚‚) emissions.
Given the environmental impact of current production methods, there is an urgent need to develop more sustainable approaches to ammonia synthesis.
Tsubame BHB Technology
The Haber-Bosch process, utilizing iron-based catalysts, is the current industrial method for ammonia synthesis:
N₂ + H₂ ⇆ NH₃
Owing to strong N≡N triple bond of nitrogen gas (N₂), Haber-Bosh process for ammonia synthesis must be conducted at high reaction temperatures of 400−500 ºC to break the strong N≡N bond. Furthermore, high pressure (100−300 bar) is required due to thermodynamic limitations. Therefore, the Haber-Bosh process for ammonia synthesis requires large scale and robust plants.
A more sustainable approach to ammonia synthesis at small scale, operating at lower pressures and temperatures, has been in recent demand for onsite ammonia production. Electrochemical ammonia synthesis, which can occur at room temperature and ambient pressure, is one such promising alternative. This method requires stable electrocatalysts capable of producing ammonia with high yields and faradaic efficiency. Several startups, including NitroFix, are working to commercialize this technology.
Masashi Hatton and colleagues have developed a novel heterogeneous catalyst for ammonia synthesis that operates at just 1 bar and 50 ºC (also ref. JP2022070143A). This catalyst consists of ruthenium (Ru) nanoparticles deposited on a cubic CaFH solid solution. The catalyst is created by introducing fluoride anions into calcium hydride, resulting in a stable electron-donating material. However, the fabrication of this complex system remains challenging.
Tsubame BHB has developed a unique electride-supported catalyst that facilitates efficient ammonia synthesis from clean hydrogen and nitrogen at low temperature (300-400 ºC) and pressure (30-50 bar).
Tsubame BHB ammonia production system
Tsubame uses a reaction gas containing a small amount of ammonia gas to produce ammonia at low temperature and pressure with at least two series-connected ammonia synthesis reactors. The diagram below depicts the basic principle of Tsubame’s ammonia synthesis process.
The ammonia synthesis process involves two reactors operating in series. Reactor 1 receives a mixture of N₂ and H₂ with 4% volume NH₃ at 300 ºC (Point A). The pressure is raised to 30 bar to promote ammonia production. Due to the exothermic nature of the reaction, the gas temperature increases to 400 ºC, resulting in an outlet gas with 9% volume NH₃ (Point B).
The gas from reactor 1 is then cooled to 300 ºC while maintaining the 9% NH₃ concentration (Point C). This cooled gas feeds into reactor 2, where the pressure is again increased to 30 bar. The ongoing exothermic reaction raises the temperature to 350 ºC, producing an outlet gas with 13% volume NH₃ (Point D).
Through this two-stage process, the initial reaction gas containing 4% volume NH₃ is converted to a product gas with 13% volume NH₃.
As depicted in the diagram below, Tsubame’s ammonia synthesis system consists of at least two ammonia synthesis reactors connected in series, along with a heat exchanger, a cooler, a gas-liquid separator, and gas compressors.
The preheated Nâ‚‚ and Hâ‚‚ gas mixture is compressed and combined with unreacted gas and a small amount of ammonia product. Ammonia synthesis occurs in reactors 1 and 2 under low pressure and temperature conditions as described above.
A heat exchanger cools the output gas from reactor 1 while preheating the incoming reaction gas. The cooler liquefies ammonia from reactor 2’s output gas. The gas-liquid separator then separates the liquefied ammonia from the unreacted N₂ and H₂ gases. Unreacted gases containing a small amount of ammonia are combined with fresh N₂ and H₂ mixture and introduced to the reactors for continuous ammonia synthesis cycles.
Tsubame BHB electride catalyst
Tsubame has developed efficient electride catalysts (ref. JP7374920B2) for low-temperature ammonia synthesis, focusing on ruthenium-barium (Ru-Ba) core-shell structure supported on a Ba-doped Ca(NH₂)₂ matrix. This catalyst outperforms traditional iron-based catalysts and other Ru-based catalysts, especially below 300 ºC.
The Ru/Ba-Ca(NH₂)₂ catalyst requires hydrogen pretreatment to reorganize the Ru-Ba core-shell structures and transform the Ba-Ca(NH₂)₂ support into a mesoporous structure with a high surface area (>100 m²/g). This unique structure is crucial for its high catalytic performance in low-temperature ammonia synthesis.
Unlike traditional Ru-based catalysts that suffer from hydrogen poisoning, the Ru/Ba-Ca(NHâ‚‚)â‚‚ catalyst shows high resistance to hydrogen adsorption and maintains its activity under increased pressure and lower temperatures. The Ba-Ca(NHâ‚‚)â‚‚ support enhances electron donation to the Ru sites, facilitating Nâ‚‚ activation, with the Ba dopant playing a critical role in improving catalytic activity.
The Ru/Ba-Ca(NHâ‚‚)â‚‚ catalyst demonstrates excellent stability over prolonged reaction times, maintaining its structural integrity and catalytic performance without significant degradation.
Tsubame BHB Patent
- JP7374920B2 Ammonia synthesis system and ammonia production method
- JP7519655B2Â Molded sintered body and method for producing the same
Tsubame BHB Technology Applications
- Clean fertilizer production
Tsubame’s technology is particularly suited for producing fertilizers in remote areas or regions without existing ammonia production capabilities. This approach addresses both logistical challenges and environmental concerns associated with conventional ammonia supply chains.
Tsubame BHB Products
Tsubame offers small-scale, distributed ammonia production systems with the following capacities:
- 500 tons/year
- 3,000 tons/year
- 5,000 tons/year
For future applications in fuel and hydrogen carriers, Tsubame is developing larger systems:
- 10,000 to 50,000 tons/year
- 500,000+ tons/year
The company has engaged in partnerships with entities like Mitsubishi Chemical Corporation to explore advanced ammonia separation technologies, which could further enhance the efficiency of their processes.
Additionally, projects like the demonstration plant in Niigata Prefecture highlight their commitment to integrating carbon capture and storage (CCS) technologies with ammonia production.
Tsubame BHB Funding
Tsubame has raised a total of ¥11.6B in funding over 7 rounds:
Their latest funding was raised on Feb 20, 2024 from a Series C round.
Tsubame BHB Investors
Tsubame is funded by 16 investors:
- Ajinomoto
- Universal Materials Incubator
- MIRAI SOUZOU
- Mitsubishi UFJ Capital
- Energy & Environment Investment
- Sumitomo Mitsui Trust Bank
- Development Bank of Japan
- i-nest capital
- Yokogawa Electric Corp.
- Fuyo General Lease
- Heraeus
- Idemitsu Kosan
- Mitsubishi Chemical Corporation
- Daiichi Jitsugyo
- SANKYU
- Inpex
Yokogawa Electric Corp. and Energy & Environment Investment are the most recent investors.
Tsubame BHB CEO
Koji Nakamura is CEO.