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> An uncoated catalyst works just fine, he said, but only produces methane Given that Putin's about to turn off natural gas to Europe, there's no need to go al
by csense 4y ago
> An uncoated catalyst works just fine, he said, but only produces methane
Given that Putin's about to turn off natural gas to Europe, there's no need to go all the way to gasoline. Being able to produce methane from CO2 would be a pretty useful technology all by itself.
Suppose you mix up a batch of catalyst, porosify it somehow, and put it into a vessel ready to accept input CO2 to turn into methane. What do you send into the input? Lab grade 99.97% pure CO2? Smokestack output from some industrial factory? Plain old air pulled straight from the ambient atmosphere?
What kind of temperature and pressure does it need to be? You get energy by burning methane to produce CO2, doesn't that mean thermodynamically you have to supply equal energy to reverse the process? Is that energy supplied in the form of heat and pressure, or does it come from somewhere else?
Where does the hydrogen come from and where does the oxygen go? Does it need water or steam input too?
If we assume input energy is the dominant cost of the system, can we put some economic numbers to it? How much methane per second would be produced by a 1 kW solar panel? How many years of methane production does it take for the methane output to repay the cost of the solar panel?
Can we figure out if the catalyst cost is small enough to be negligible? How much catalyst do you need to support a 1 kW solar panel? How much does that much ruthenium cost at current prices? How long would it take methane output to pay for the cost of panel + catalyst?
Are the methane and oxygen outputs come out mixed together, or do they form separate streams? If they're mixed together, how do you separate them? How do you make the system safe, considering the potential explosiveness of the mixture of methane and oxygen before they're separated?
- melony 4y agoYou can read the paper yourself: https://www.pnas.org/doi/10.1073/pnas.2114768119 https://www.pnas.org/doi/10.1073/pnas.2114768119
- csense 4y agoI skimmed the paper. It does mention 6 bar of pressure and 250 degrees C, so that's a pretty straightforward answer to one question. It says 5% or less of CO2 converted at 15-25% of input, the rest of which is H2. The number seems to be 500 mg of Ru catalyst can process 30 mL / minute of input gas at 6 bar. So ideal gas law (pV = nRT) we know p = 600 kPa, V = 30 mL, T = 250C = 520K, R = 8.3 J/(K mol). n = 600 kPa x 30 mL / (8.3 (J / (K mol)) x 520 K) = 600 (kJ / m^3) x 30 mL / (4316 J / mol) = 600 (J / m^3) x 30 L / (4316 J / mol) = 4.17 mol x (L / m^3) = 0.00417 mol So 4.17 mmol of gas. I'm tempted to multiply by 25% since it says 25% CO2, but I think that only really applies if it's 25% of moles are CO2, but the paper doesn't say if it's 25% by mole, 25% by mass, or 25% by something else (volume maybe?). Assuming this multiplication is legitimate, we get 1.04 mmol (about 1 mmol) of CO2. It says only 5% is converted. So that means 500 mg of Ruthenium can process 0.05 mmol / minute. So the factor is 0.05 mmol / 500 mg, or 0.1 mmol / minute / g. Multiplying by 60x24, we get 144 mmol / day, or 52.56 mol / year assuming 100% uptime. Some quick Googling shows methane costs $1.40 / L and has a volume of 29 L / mol. So the molar price of methane is $40.60 / mol. That means 1g of ruthenium can process $2100 / year worth of methane. Ruthenium is $525 / ounce, or $19 per gram. So to answer my question, I calculate $20 worth of catalyst can produce $2000 worth of methane per year. My formal education in chemistry ended in high school, and that was many years ago, so there might be bad mistakes in these numbers / calculations. Obviously there are some other costs (atmospheric CO2 is free, but purifying it to 25% is not, nor is swapping out the oxygen and nitrogen for hydrogen), I'm not sure it's been established if the catalyst remains effective forever or degrades over time, and they're not simply using ruthenium -- it's Ru / TiO2 and there's some preparation involved. Regardless of those disclaimers, it seems like a catalyst that can pay for itself in a matter of days by turning CO2 into natural gas could be a game changer.
- Maursault 4y ago> Being able to produce methane from CO2 would be a pretty useful technology all by itself. Totally. With this process, we could get the planet heated back up in no time![1] [1] Methane is more than 25 times as potent as carbon dioxide at trapping heat in the atmosphere.
- amts 4y ago> considering the potential explosiveness of the mixture of methane and oxygen In Sabatier reaction [1] oxygen binds to hydrogen to produce H2O. Oxygen being highly electronegative could easily bind +1/+2 valence compounds. Alternatively, nickel and aluminum catalysts for CH4 production from CO2 are also effective. The fact that EU officials make so much idiotic hustle regarding fossil fuels only shows how severely underdosed in compounds from a number of categories they are. [1] https://en.wikipedia.org/wiki/Sabatier_reaction#Creation_of_synthetic_natural_gas https://en.wikipedia.org/wiki/Sabatier_reaction#Creation_of_...