At present, electrolysis (splitting water into hydrogen and oxygen with electricity) is in the early stages of commercialisation, and is zero emissions assuming you’re using renewable electricity. But it’s still more expensive than fossil fuels, or indeed emissions-intensive hydrogen.
One promising method – methane pyrolysis – could be cheaper than electrolysis technology. But while it could be a negative emissions product, it could also be emissions-intensive.
Where it ends up will be down to regulation and certification, says Professor Gus Nathan, director of The University of Adelaide’s Centre for Energy Technology, and a member of the new Global Hydrogen Production Technologies, or HyPT, Centre.
Methane pyrolysis is the process of splitting methane gas (CH4) into hydrogen gas (H2) and pure, “hard” carbon (C).
This can be done in a number of ways: using plasma (basically a super-reactive gas), microwaves, or a molten metal. A company in the US is upscaling their plasma method to the commercial level, but most other techniques are still at the experimental stage.
“The energy needed for [methane pyrolysis] is only about a quarter of the energy of water splitting,” says Nathan.
Plus, as well as hydrogen, the hard carbon can be used in other products, like car tyres, black inks, and graphite.
“You potentially make two valuable products instead of one,” says Nathan.
“Currently, there’s already quite a big carbon market – probably not as big as could be, if we start to make quite a bit of it.”
“If we’re going to have large volumes of hydrogen, you rapidly saturate current markets. So then you need to go to things like construction materials – carbon can be blended into cement, which therefore displaces some of that CO2.”
The most common source of methane at the moment is a fossil fuel: “natural” gas. But, says Nathan, the methane could come from biogas: made by the breakdown of organic matter, like plants or animal waste.
The source of the methane plays a big part in deciding whether the process releases emissions or not.
“If you start with a purely a biogas, then obviously at that extreme, any carbon that you make – unless you burn it – is going to become captured,” says Nathan.
A mixture of biogas and natural gas could still have net negative emissions. But the methane’s source isn’t the only problem.
“You have to worry about whether any methane leaks,” says Nathan.
Methane has 27-30 times the warming effect of carbon dioxide by weight, making methane leaks a major source of greenhouse gas emissions.
“There are already companies emerging who can do certification and management of the of the methane supply chain,” says Nathan.
Added to this is the complication of whether the hard carbon is turned into products that get back into the atmosphere at end of life, and how fast that happens. If it’s turned into a single-use plastic and then incinerated, for instance, that’s no net benefit.
But the carbon could also be buried in the ground – “reverse coal” – or made into biochar for use in fertilisers, or sequestered in other long-term products like concrete.
“Conceptually, [methane pyrolysis] can be net zero. It can be negative, but it could also be positive,” says Nathan.
“At the end of the day, you need to have proper certification and tracking.”
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