Carbon capture and storage is necessary if the world is to achieve the 1.5 degree target in the Paris Agreement in any way. And plants are already very good at absorbing CO2 from the atmosphere, so why not use it to our advantage?
That is one of the basic ideas of a new research project at Aarhus University, which will see the development of Denmark's first reactor for hydrogen production from biogas via catalytic pyrolysis. In the pyrolysis process, high temperatures are used to split the methane in the biogas into hydrogen and carbon.
- What we need right now is not only CO2-free technologies. We also need technologies that can bind carbon from the atmosphere and that have net negative carbon emissions. What we propose with this project is to adapt and optimize existing so-called turquoise hydrogen technology for biogas instead of natural gas. The result is a truly CO2-negative technology, says Patrick Biller, an associate professor from the Department of Bio- and Chemical Technology, who is leading the project, in a press release.
Turquoise hydrogen
Approximately three percent of the world's CO2 emissions today come from the production of so-called grey hydrogen, which is extracted from natural gas. The common alternative to this is green hydrogen, where electricity and water are converted into hydrogen through electrolysis.
However, green hydrogen production is at best CO2-neutral if electricity from renewable sources is used, but never CO2-negative. It requires large amounts of energy to split water, and if the energy is not renewable, the production emits CO2.
Currently, 95 percent of the world's CO2 emissions come from of global hydrogen production from the 'steam methane reforming' (SMR) process, where natural gas is converted into hydrogen and CO2. Turquoise hydrogen is increasingly being investigated as an alternative. It also involves the production of hydrogen from natural gas, but here pyrolysis is used to convert the carbon into a solid form. Normal turquoise hydrogen is carbon neutral, as the carbon comes from natural gas and thus fossil resources, but it is not emitted into the atmosphere.
What Patrick Biller is proposing is to design and develop a technology that produces turquoise hydrogen from biogas and not natural gas.
- Via photosynthesis, green plants capture CO2 every day, and they actually do it quite well. Biogas comes from plant material that has absorbed CO2 from the atmosphere in this way. In biogas pyrolysis, the carbon therefore comes from the atmosphere. The carbon is converted into a solid form in the process, a kind of black powder that is completely pure carbon, and can then either be deposited or used in industry for other high-value products,” he says and continues:
- In this way, there is no CO2 emission, but instead a net negative contribution to the atmosphere.
Will design a new system
The project has received support from the Independent Research Foundation of Denmark. With the grant, the research team will now design and develop a system that can handle the process. It is no small task, even though the goal is to adapt existing turquoise hydrogen technology:
- There is a big difference between natural gas and biogas, and there are, for example, completely different impurities in biogas to take into account. At the same time, methane pyrolysis requires high temperatures of around 1200 degrees Celsius. We would like to avoid this, so in the project we want to find metallic catalysts that can significantly reduce that amount energy required to activate the reaction. We expect to be able to run the reaction at temperatures around 500-600 degrees, says Patrick Biller.
The finished system is expected to be able to produce hydrogen for about one fifth of the amount of energy used for green hydrogen production. At the same time, the advantage is that this method binds carbon originating from the atmosphere. The system will be tested and run at Aarhus University's research center in Foulum, AU Viborg.
- Denmark has a world-leading biogas sector. We are doing great things within Power-to-X and hydrogen, and we have an energy system with large amounts of renewable energy. Turquoise hydrogen from biogas fits perfectly into this cocktail, and I can see great prospects for Denmark in this area in the future, concludes the associate professor.
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