[pfdietz]

A problem with making methane is some will leak, and in the short to medium term methane is a very powerful greenhouse gas.

A step before making methane is making hydrogen. If you can get away with just using hydrogen, it will be more efficient than going through the extra steps to make methane.

[AdamTReineke]

Isn't the problem with hydrogen that it's harder to store? I thought it was a big problem. Keeping it from leaking out of storage vessels and pipes because the molecule is so small.

[pfdietz]

Thus the "if you can get away with using".

Hydrogen can be stored underground just like methane can (and is). Also, the problems with hydrogen are overstated. The world economy does use many millions of tonnes of hydrogen each year, so the problems are demonstrably solvable.

[stickyricky]

Doesn't methane break down in the atmosphere relatively quickly? I think the goal of this proposal is to reduce CO2 in the atmosphere. Producing hydrogen doesn't contribute to that goal (which isn't to say its a bad idea only that the hydrogen production facilities can exist independently of this proposal).

[feoren]

If you turn 100kg of CO2 into Methane you get about 36kg. Methane is somewhere around 25x (potentially 31x) worse for global warming than CO2 by weight, so you end up with 909kg of "Carbon Dioxide equivalent", or CO2e. Let's say 2% of that leaks to atmosphere, and you burn the other 98%. Burning the 98% gets you back 98kg of CO2 (it's just the reverse process), plus 2% of that 909kg CO2e, and you end up with 116kg of CO2e, starting with 100kg. You've made global warming worse.

In fact any percentage leaking back to atmosphere (and it will) makes the numbers look pretty bad. You need a significant portion going to plastics or some other sequestered use for this to actually be a net benefit.

[jnwatson]

Thank you. This is the calculation I was looking for.

2% leakage is very conservative. The amount of additional pipeline infrastructure necessary to achieve this at scale is daunting. It will have a lot of leaks.

[pfdietz]

A possible solution is to make the hydrogen by electrolysis of brine. This can make hydrogen and chlorine (and alkali) instead of hydrogen and oxygen.

If the chlorine is released into the troposphere during the day, it is quickly photolysed (in about 10 minutes at noon) into chlorine radicals, which near instantly react with methane, extracting a hydrogen atom. It should be possible for this to more than make up for small leaks of methane (or to counteract other independent sources of methane).

[hx8]

1. Methane is a much more powerful greenhouse gas, so we should be limiting our emissions.

2. Methane lingers for decades. Short in planetary timelines. Long in human timelines.

[Veedrac]

There's a useful principle of focusing on the big picture items first, moving off non-renewable methane by doing the easiest thing that works. Hydrogen is at least marginally cleaner than methane, but if it's cheaper to change methane supplies than rebuild an industrial plant, that's still most of the win!