🧵 Methane Pyrolysis
Anonymous at Mon, 9 Sep 2024 01:44:08 UTC No. 16369081
The pyrolysis of methane into hydrogen and solid carbon requires 37.5 kJ per mole of hydrogen produced. That's cheaper than electrolysis of water at 237 kJ and even steam-methane reforming, at 41.4 kJ per mole. A mole of hydrogen can produce 237 kJ of energy when burned, so if you made hydrogen from natural gas, then burned the hydrogen for power, you could power the process of converting the natural gas to hydrogen using that power and have 199.5 kJ of energy to spare. Now, you could generate more energy by just burning the natural gas, but with this method, there are no co2 emissions. Why aren't we doing this? Fossil fuel companies would support it because it would allow them to keep drilling, piping and selling natural gas indefinitely no matter what climate regulations and restrictions are placed on it by the government and enviromental groups would approve because it would be free from carbon emissions. What's the downside?
Anonymous at Mon, 9 Sep 2024 02:19:46 UTC No. 16369113
>>16369081
Operating a continuous process which produces solid carbon is going to be a bitch and a half.
Anonymous at Mon, 9 Sep 2024 03:03:14 UTC No. 16369146
>>16369081
Cheaper per mole but:
>30 kg of H2 per MWh (~ $30) -> 1 dollar per kg
The cost of methane alone is similar but the electrolysis of water is far simpler and can take advantage as power sink to deal with overgeneration (renewable power sources needs excess capacity to achieve a stable power grid)
Anonymous at Mon, 9 Sep 2024 03:56:19 UTC No. 16369180
>>16369113
The current method is to simply bubble the methane through molten tin apparently.
Anonymous at Mon, 9 Sep 2024 04:11:36 UTC No. 16369192
>>16369146
Do you know how many moles of methane are in a cubic meter? I'm trying to figure out the cost to compare.
Anonymous at Mon, 9 Sep 2024 04:17:47 UTC No. 16369203
>>16369192
methane prices are in dollars per million of BTU (1050 * 10^6 joules)
Anonymous at Mon, 9 Sep 2024 06:28:14 UTC No. 16369297
>>16369081
>What's the downside?
Higher cost and no one cares about global warming
Anonymous at Mon, 9 Sep 2024 22:59:03 UTC No. 16370690
>>16369297
Fossil fuel companies already do stupid shit to make themselves look green, like buying captured co2 for advanced oil recovery. Doing this on some scale doesn't seem that far fetched.
Anonymous at Mon, 9 Sep 2024 23:01:39 UTC No. 16370693
I assure you, they would love to grab as much hydrogen as they can from methane. I have worked at multiple ammonia plants, the first section of which is a steam-methane reformer to produce the hydrogen used for ammonia production...
Anonymous at Mon, 9 Sep 2024 23:04:32 UTC No. 16370696
>>16370693
Currently they use the steam-reforming process for Haber-Bosch though, right? Is it easier to deal with co2 gas than solid carbon? How do they seperate the mixture of hydrogen and co2 after steam reforming? Do they have to fractionally distill it like they do in the process of removing nitrogen from the air?
Anonymous at Mon, 9 Sep 2024 23:50:58 UTC No. 16370775
>>16370696
>nitrogen from the air?
They use PSA units for that
CO2 is much easier to handle. Solid carbon is awful. Look at delayed coker units in a refinery. Big coke drums they have to open up and cut out the coke with 2000 psig steam on a batch process.
>Fractionally distill it
If I'm remembering correctly they do not need crazy high purity hydrogen so a PSA isn't necessary. It goes to a CO2 absorber/stripper and then a methanater to convert CO. Around this area they generally have a purification system using membranes that produces decently pure hydrogen (not as good as a PSA ofc).
Anonymous at Mon, 9 Sep 2024 23:54:11 UTC No. 16370780
>>16370775
But doesn't CO2 poison the Haber-Bosch catalyst?
Anonymous at Tue, 10 Sep 2024 00:05:05 UTC No. 16370801
>>16370780
It's easy to remove CO2 with an absorbent liquid of some sort. Forget what they used for this. MDEA maybe. And then that liquid goes to a stripper where the CO2 is heated off and...goes elsewhere :') after the methanater it's like trace amounts of CO2 left that's from the conversion of CO to CO2.
Don't believe CO2 poisons the catalyst. CO would. CO2 will reduce hydrogen purity tho, take up space in the recycle loop, probably pressure up shit more than youd want ....
Anonymous at Tue, 10 Sep 2024 11:21:22 UTC No. 16371943
>>16369081
Or we could give up the communist hype over carbon dioxide. It's all just an excuse for taxation and slavery.
Anonymous at Wed, 11 Sep 2024 05:54:38 UTC No. 16373756
>>16369081
>What's the downside?
you know what? Scientifically, this actually seems valid. The hard part is engineering a proper process.
>CH4 --> H2 + C
you're going from 1 mole of gas to 2 moles of gas. Treating methane like an ideal gas, double the gas pressure. You would need to design a special vacuum chamber which can deal with expanding gas, along with a way to continually remove the depositing carbon.
>step 1: isolate CH4 from other molecules in the air. This is extremely important since any oxygen or nitrogen will FUCK up your efficiency
>step 2: place the pure CH4 gas into a chamber, and heat it
>step 3: evacuate the H2 gas
>step 4: repeat
those are all the hard steps. Additionally, you will need to clean out all the carbon that deposits on the walls of your chamber.
Anonymous at Wed, 11 Sep 2024 12:41:11 UTC No. 16374126
>>16373756
I guess removing carbon from reactor is good job for some robotics...
Anonymous at Wed, 11 Sep 2024 19:40:23 UTC No. 16374719
>>16369081
>natural gas indefinitely
you sure about that?