Ammonia’s Relationship with Hydrogen

Known for its distinct pungent smell and home under household sinks across the country, ammonia has been produced at an industrial scale for many purposes since the early twentieth century. As a critical component of fertilizer, ammonia revolutionized modern farming by boosting the growth of crops. It is also used in cleaners, industrial manufacturing, refrigerant, explosives, and recently, as an energy source. In 2019 it is estimated that the world plant production of ammonia topped 150 million metric tonnes. While conventional ways of producing ammonia emit greenhouse gasses, hydrogen has emerged as a method of generating ammonia without the carbon. 

Ammonia Production

Ammonia has the chemical compound NH3, a nitrogen atom bonded to three hydrogen atoms. To create ammonia, one must combine nitrogen naturally found in air (N2) with hydrogen. In the early 1900s, the Haber-Bosch process popularized nitrogen fixing onto hydrogen. To source hydrogen for ammonia production, conventional methods focus on hydrocarbons such as fossil fuels to separate hydrogen atoms from coal or natural gas. Carbon emissions are predicated on the fuel source containing a carbon atom: methane, the main component of natural gas, has the structure CH4, and coal has a variety of structures primarily consisting of carbon. This concept is especially important when considering ammonia as a fuel, discussed later.

Ammonia as Fuel

Within the energy sector, ammonia has several prospects as a fuel. Since ammonia contains hydrogen atoms, it is a hydrogen carrier that can be used in fuel cells with the only byproduct being water and nitrogen, which is naturally found in the air. Some companies are already looking into ammonia-powered fuel cells.

Ammonia-Hydrogen Storage

Another promising use for ammonia is as a hydrogen carrier, meaning one can store hydrogen as ammonia for long term storage or for easier transport. Ammonia has a high boiling point compared to hydrogen, meaning it can be liquified easier. From there, ammonia can be used in storage or transportation and turned into hydrogen fuel at a later date. Though there will be some loss in energy due to the second law of thermodynamics, this provides a possible way to ease supply chains.

Green Ammonia

Due to ammonia’s reliance on fossil fuels, production causes about 1% of total global greenhouse gas emissions. In response, facilities are moving from methods that use fossil fuels to generate ammonia to new production methods utilizing hydrogen generated via electrolysis of renewable energy such as solar and wind. Electrolysis runs a current through water (H2O), splitting it into its hydrogen and oxygen components carbon-free (assuming the current is provided from carbon free sources). This creates zero-emission hydrogen, which downstream cleans the process of making ammonia. 

A trial green ammonia plant at the Fukushima Renewable Energy Institute in Japan uses solar-powered electrolysis to produce 20 – 50 kilograms of ammonia per day from green hydrogen. Siemens is working with Oxford University to do the same. 

Ammonia’s Future

As hydrogen is as fundamental to ammonia as it is to water, the only option for reaching deep-decarbonization in the ammonia production industry is through the use of renewable hydrogen. Ammonia producers must be encouraged to explore electrolysis and renewable energy at their plants, turning the bedrock of farming into a clean industry, and possibly enhancing the energy sector as well.