Even though hydrogen is a colorless element, it is often categorized using a color code. The colors correspond to different sources and methods used to produce it. This article focuses on turquoise hydrogen. Learn about how it is produced and used below.
What is turquoise hydrogen?
Turquoise hydrogen is created using methane pyrolysis. The process uses fossil fuels in production, but it does not typically emit carbon dioxide (CO2) like other fossil-fueled hydrogen technologies. Therefore, it is considered a low-carbon alternative overall.
How is turquoise hydrogen produced?
Methane pyrolysis is a process that uses thermal decomposition to split methane (CH4) into gaseous hydrogen and solid carbon. Methane can come from natural gas or biomethane. Biomethane is a renewable natural gas produced by removing CO2 and other contaminants from biogas (gas derived from the decomposition or conversion of biomass).
Methane pyrolysis is a one-step endothermic (heat absorbing) process that breaks down methane by exposing it to high temperatures. Further operations may be needed to purify or upgrade the hydrogen produced.
There are three primary variations of methane pyrolysis:
- Catalytic pyrolysis.
Thermal pyrolysis exposes methane to temperatures between 1,000 °C and 1,500 °C (1,832 °F and 2,731 °F), splitting it into hydrogen and solid carbon. A typical catalyst for this reaction is molten metals, such as tin, lead, and copper. In this process, methane is injected into a reactor containing the molten metal, and hydrogen leaves the reactor at the top. BASF and TNO are developing thermal pyrolysis technologies.
Plasma pyrolysis uses a plasma torch to split methane molecules. It can be done using cold plasma or hot plasma technologies. Cold plasma separates methane at temperatures around 1,000 °C (1,832 °F). This plasma typically has lower conversion rates (around 50 percent). Hot plasma pyrolysis methane at temperatures around 2,000 °C (3,632 °F), at a higher conversion rate (approximately 90 percent). Monolith has created a hot plasma pyrolysis technology (information on the process can be found here).
Catalytic pyrolysis splits methane at a lower temperature (typically under 1,000 °C/1,832 °F) using a metal catalyst. Catalysts are often nickel-based or iron-based. Hazer Group is developing technology that uses an iron-ore catalyst.
Benefits and drawbacks of turquoise hydrogen technologies
One of the main advantages of methane pyrolysis is that it is generally low-emission and produces minimal to no carbon dioxide. This eliminates the need and costs associated with capturing, removing, or storing CO2. It can also reduce overall greenhouse gas emissions related to hydrogen production.
Another benefit is the solid carbon by-product, which can be sold for profit. However, there is not a large market for solid carbon, so carbon storage or removal methods may be needed.
One of the drawbacks of methane pyrolysis is that it uses fossil fuels, a finite resource. A way to combat this issue is by using biomethane.
Biomethane is isolated from biogas, a gas derived from the decomposition or conversion of biomass. Biomass is abundant and readily available in many parts of the world, and biomass-to-biomethane efficiency is relatively high (around 70 percent). However, CO2 and other contaminants must be removed from the biogas to create biomethane. This adds an additional step (and potential cost) to methane pyrolysis methods. Biogas also produces similar greenhouse gas emissions to natural gas (e.g., carbon monoxide).
Another drawback of methane pyrolysis is its efficiency. Methane pyrolysis is reasonably efficient (around 58 per cent efficiency) but has a lower efficiency than other fossil-fuel hydrogen technologies, such as steam methane reformation (about 65 to 75 percent). Methane pyrolysis may also require additional processes to purify or upgrade the hydrogen produced.
Other issues include high processing temperatures and higher costs compared to other methods. Methane pyrolysis is also relatively new and is unlikely to reach commercial-scale operations for several years. However, methane pyrolysis has good prospects overall but requires more research to address current issues.
General hydrogen fuel challenges must also be considered. A significant issue with hydrogen is storage. Hydrogen has a high energy content by weight but low energy content by volume, and it must also be compressed and stored at low temperatures. Hydrogen is also highly combustible, so if there is a leak and the gas comes in contact with an ignition source, the pressure can cause dangerous explosions.
How is turquoise hydrogen used?
Turquoise hydrogen, like other forms of hydrogen, has many applications. Hydrogen is predominantly used in industrial applications such as oil refining and methanol production. In addition, hydrogen can be used as rocket fuel, in treating metals, producing fertilizer, processing foods, producing electricity, transportation, and more.
In terms of turquoise hydrogen, it is a great way to bridge the gap between blue hydrogen and green hydrogen.
Blue hydrogen is produced using fossil fuels (e.g., steam methane reforming). Unlike methane pyrolysis, carbon dioxide is produced. However, it is not released into the atmosphere but is stored underground for industrial use.
Green hydrogen uses renewable energy to create hydrogen through electrolysis (a process that separates hydrogen and oxygen in water molecules). Similar to methane pyrolysis, no carbon dioxide is emitted throughout the production process.
One of the main issues with blue hydrogen is that it uses a finite resource. Additional resources and costs are also associated with capturing and storing carbon dioxide. In contrast, green hydrogen technologies use renewable resources, which are better for the environment. However, these processes are generally more expensive and less efficient than fossil fuel methods.
Like blue hydrogen technologies, turquoise hydrogen is produced using fossil fuels. However, carbon dioxide is not emitted, which eliminates the need and costs associated with storage. It is also more efficient than green hydrogen technologies. Methane pyrolysis is not carbon neutral but is pretty sustainable overall. That is why companies like Ebara, a Japanese industrial machinery and plant engineering company, are working to produce turquoise hydrogen, in support of the drive toward decarbonization.