Pyrolysis is a less energy intensive way to produce hydrogen, and does deserve more attention. But it still requires methane as a feedstock.

So why is methane as feedstock a problem?

Isn't it better to spend less energy convert a ubiquitous, but environmentally harmful gas into hydrogen along with useful materials, than spend 4x more energy to convert a critical resource -- fresh water -- into hydrogen without any valuable by-products?

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MobiusHorizons 12 hours ago | parent | next [-]

I tend to be a fan of methane for its high hydrogen content per unit carbon as well as how much easier it is to store than hydrogen. However the argument against methane that I do find convincing is that the infrastructure for transporting and distributing methane leaks a lot. The argument is most compelling against residential distribution, where maintenance is harder to justify, but large leaks regularly occur, and that is very bad for greenhouse emissions.

I’ve always been curious about generating methane in industrial composting or from landfills and using it onsite for hydrogen generation. Not sure if the generating capacity is enough though, there is probably a reason it isn’t being done.

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_aavaa_ 16 hours ago | parent | prev | next [-]

Water is critical but not hard to get. The energy and cost required to take a m3 of dirty water and turn it into pure water is a rounding error compared to the energy required to hydrolyze it.

Yes methane is an environmental problem, even small methane leakages have a large GHG impacts. But the best way to deal with that environmental problem is to not pull it out of the ground in the first place

Plus for pyrolysis, you have to deal with the carbon which makes up 75% of the methane by weight. A non-trivial issue.

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XorNot 13 hours ago | parent | next [-]

Except we already pull it out of the ground, and people are heavily invested in that process. Working with what we have is the best option here: far easier to enthusiastically go after methane leaks when the industry is otherwise being told "we will buy a lot of your product forever.

Which is really the stakes here: if you can "burn" fossil fuels without putting GHG in the air...there's no reason to stop using them at all. In fact we should vastly expand their use.

	▲	_aavaa_ 6 hours ago \| parent [-]
		Why would the go after me than leaks if they know people will by their products? A lot of the methane leaks are not “leaks” but intentional releases to “protect” equipment or to simply get rid of it. Until there are fines on the pollution it won’t stop.

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georgecmu 16 hours ago | parent | prev [-]

Water is critical but not hard to get.

Right. https://en.wikipedia.org/wiki/Water_scarcity

You would want to use solar power for electrolysis. In the US, regions with abundant solar power are also the ones that: - have true water scarcity - Nevada and Arizona - have low population and industrial density, so any generated hydrogen would need transported to the point of use.

The bigger problem is the energy disparity. Electrolysis of water requires 50 kWh/kgH2 or more. Even a 70% efficient fuel cell would get ~25 kWh/kgH2 -- horrible roundtrip efficiency. With pyrolysis, that equation is exactly inverted: at 9-12 kWh/kgH2, you can generate excess electricity with no CO2 emissions.

Plus for pyrolysis, you have to deal with the carbon which makes up 75% of the methane by weight. A non-trivial issue.

Exactly. 20 kg of methane costs $3 today, but contains 15 kg of carbon that could be worth $20-$30. It's a non-trivial issue if you hate generating value.

https://www.chemanalyst.com/Pricing-data/carbon-black-42

	▲	_aavaa_ 6 hours ago \| parent \| next [-]
		> In the US, regions First of all the US isn’t the whole world. Like you said transportation is a problem which is why you would produce it close to where it’s needed (say Nebraska). You don’t need an “ideal” solar output location. Yes I am well aware of the energy difference. > Exactly. 20 kg of methane costs $3 today, but contains 15 kg of carbon that could be worth $20-$30. It's a non-trivial issue if you hate generating value If carbon free hydrogen is going to be worth doing at scale it will be because there is a price on the carbon. So the input methane will go up in price. As for the output, global demand for carbon black is currently ~14 million metric tones a year [0]. Current hydrogen demand is ~100 million metric tones a year [1]. 100 Mt of hydrogen needs ~400 Mt of methane and produces ~300 Mt of carbon. 300 Mt vs 14 Mt of current demand. What do you supposed will happen to that carbon black price when you produce even a fraction of total hydrogen demand through pyrolysis? It’s non-trivial cause you’re gonna be having to create reverse coal mines to store all that shit. [0]: https://www.chemanalyst.com/industry-report/carbon-black-mar... [1]: https://www.iea.org/reports/global-hydrogen-review-2025/dema...
	▲	forgotoldacc 15 hours ago \| parent \| prev [-]
		A lot of those countries with water scarcity are oil rich. A lot of those countries that don't have water scarcity are oil poor. Seems one forward step would be for countries that have an abundant source of alternative fuel to go for it and stop importing so much oil. Countries that don't have much water can import alternative energy sources or keep using the oil that they're rich in.

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kumarvvr 16 hours ago | parent | prev | next [-]

Methane is not abundant, as such. There are specific sources of it, mainly through manual agricultural processes, or in natural systems. Natural gas is mostly methane, I guess.

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pfdietz 16 hours ago | parent | prev [-]

> So why is methane as feedstock a problem?

There is inevitably leakage, and if even a small fraction does that it negates any global warming advantage on relevant timescales.

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SoftTalker 15 hours ago | parent [-]

Methane in the form of natural gas is piped all over almost every city in North America, at least those areas where people need to heat their homes in the winter.

Any leakage from a pyrolysis plant is going to be negligible compared to what's undoubtedly already leaking from gas infrastructure installed in the 1950s (or earlier), as well as the continual accidental leaks caused by excavating.

	▲	pfdietz 12 hours ago \| parent [-]
		Yes, leakage of methane for direct use is also a problem. Especially problematic is leakage upstream, near the wellheads.