Caleb James DeLisle on Nostr: I made a mistake in computing storage in an H2 tank. 1Kwh of power makes about 15g of ...

I made a mistake in computing storage in an H2 tank.

1Kwh of power makes about 15g of H2 (assume 50% efficiency).
At 200 bar (3000 PSI) it's about 15g/liter.
So in a 200 liter high pressure tank, it's about 200Kwh of input energy that is stored.

So we can say: Rule of thumb, at pressure, 1 liter = 1 kWh. In a balloon, 1 cubic meter = 6 kWh.

But there's another way to lock up hydrogen, it's a lot more annoying but if you're making a lot of it, it could be worth it. That's methanol.

Methanol is a liquid, it can be used in an engine, it can be used to make biodiesel out of vegetable oil.

To make methanol from hydrogen, you need carbon monoxide and/or carbon dioxide. The canonical way to make this is using charcoal, which can obviously be produced from wood.

Making charcoal into CO is straightforward if you use O2 to do it - you even have O2 coming from your electrolysis cell. This produces a lot of energy (you're burning charcoal), and you end up dumping it, but you can be a little more clever by adding steam to the reaction which adds an endothermic component H2O + C -> CO + H2. This has the benefit that you are making even more H2.

The methanol formula is: CO + 2 H₂ → CH₃OH

So for every 1 CO, you need 2 H2, so you need 1 mol of carbon, 1 mol of water, and 1 mol of H2 from the electrolyzer. When you add O2, you need to increase the amount of H2 you supply from the electrolyzer in proportion.

Unfortunately, the methanol reaction is annoying. Methanol wants to react at 100 bar (1500 PSI) and 280C, it *makes* heat as it runs, so you need to cool it.

So you have to get the temperature down so that the CO and H2 can be compressed. A SCUBA style compressor should work. Then once they're compressed, you put them through a heat exchanger with the exiting methanol. Since the methanol reaction is exothermic you only need to keep it from losing too much heat, you don't need to heat it.

The reaction wants to be 250-280C, but at this pressure methanol condenses at 250C so condensing out the methanol is not a huge deal, but unreacted gasses are going to end up at the methanol condenser and you really need to cycle them back around again. So I'm not sure if a circulator pump can be avoided. Obviously at 280C (just under the melting point of lead) and 100 bar of pressure, the last thing I want is moving parts and electricity, but I don't think it can be avoided.

Because the reactor makes heat, it will melt down unless you keep it cool, but this can be achieved by running water or steam over the condenser section. Some of that steam can be then used in the charcoal gasification section.

The syngas reactions are:
1. 6 C + 3 O2 -> 6 CO (-550kJ exothermic)
2. 4 C + 4 H2O -> 4 CO + 4 H2 (+524 kJ endothermic)

Combined that is:
10 C + 4 H2O + 3 O2 -> 10 CO + 4 H2 (-26kJ exothermic)

And the methanol reaction is:
CO + 2 H2 -> CH3OH

Or in this case: 10 CO + 20 H2 -> 10 CH3OH

So we need to supplement 16 H2 from our electrolyzer.

So to make useful numbers:
120 grams of carbon + 72 grams of water + 96 grams of oxygen + 40 grams of hydrogen makes 320 grams of methanol (0.4 liters).

2.6Kwh of energy to make 40 grams of hydrogen.

So for 1kg of carbon, we use 21.6 Kwh of energy making hydrogen, and we end up with 2.6 Kg of methanol (3.36 liters).

If we're making 100kwh per day, we need about 5kg of carbon per day to use them all, and we would of course get about 16 liters of methanol per day.

The charcoal demand is significant, making it from wood implies 4-5kg of wood per 1kg of charcoal, so 50 days a year of 100kWh/day production requires one metric ton of wood to produce the necessary charcoal. However this does make 800 liters of methanol (211 gallons).