Wouldn’t that be nice? Set up some giant leaves of a special membrane that can just convert the passing CO2 into methane and oxygen? Perhaps just cap the smokestacks of a power plant and get extra methane from the CO2 that is spewed out of it? Maybe have a new converter that converts the fumes that come out of the tailpipe of your car into nice clean oxygen and methane?
Well speaking of pipe dreams….
Ok that was a little harsh. I would love for this to be real, and as good as these guys are imagining, but alas we are a long way off from there.
Lets do some basics to understand what this technology is about.
What is methane?
Methane is one of the simplest hydrocarbons there is. It generally comes as a gas, but it can be compressed into a liquid (LNG) and delivered that way. Its the same thing as natural gas and has a chemical formula of CH4, one carbon atom surrounded by 4 hydrogen atoms. You are familiar with this, because many of you use it to cook on in your kitchen. When you burn methane the result is heat (energy being released), some water, and some carbon dioxide. So it makes sense that if you can add energy to water and carbon dioxide, perhaps you can reassemble the methane molecule.
What is a catalyst?
A catalyst is a material that helps lower the amount of energy for a reaction to take place. Catalysts do not get consumed in the reaction. In biology, enzymes are catalysts. In fuel cells, Platinum is generally used as a catalyst. In this case it looks like Titanium Dioxide was formed into inorganic nanotubes with a copper catalyst sputters on the top.
How does this work?
Water and carbon Dioxide would enter one side of a sheet made of these nanotubes. Energy would be added. It’s proposed here that this energy would be from the sun in the form of photons. None of the articles I see on this describe exactly what part of the sunlight is required to make this work, they simply claim that they catalyst-nanotube combination maximizes the use of the sunlight energy.
So, reagents enter on one side and products come out the other. Cool!
- The stuff coming out the other is an explosive mix of gases that then need to be separated to be useful. And sadly…this will require energy also.
- The gases will need to be pushed through the membrane, this will require a compressor or blower…..more energy required.
- What is the efficiency? This really pisses me off about these articles. I realize that this is research, but come on. Its not useful to say things like…
Using outdoor, visible light, they reported a 20-times higher yield of methane than previously published attempts conducted in laboratory conditions using intense ultraviolet exposures
…if you don’t say what those original yields were! 20 times a the volume of a newts breath is the volume of a hamsters breath. Big deal! However, the discovery article mentions this metric:
The scientists have created thin membranes that cover either 3.8 or 15.5 square inches. So far, those membranes have produced an estimated 66 gallons of methane…Adding more light and CO2 creates more methane. Grimes estimates that focusing the light collected from 1,100 square feet onto one of the membranes would generate more than 132 gallons of methane on a sunny day
umm… ok, first off, is that in gas form or liquid form? That’s a gigantic difference! I’m guessing gas form, since in order to maintain a liquid form, they would have to keep the exit side of the membrane either very cold or under quite a bit of pressure. They didn’t indicate they did either of those things.
So the claim is that eventually 1100 square feet of space can yield 132 gallons of methane gas per day. Ummm, what does 1100 square feet of solar panels give you? Well that's about a million square centimeters, which could pretty easily yield 20kW of power from solar panels (20mW/cm2 is not high tech). That is enough to power 5 homes easily.
What about about the energy comparison? Lets get some numbers out there (yeah, I know you hate it)
- The energy density of Methane is about 50 MJ/kg (1 megajoule is about .278 kWh)
- The density of Methane in gas form is 0.717 kg/m3 (kilograms per cubic meter)
- Thirteen gallons of gas is about 0.5 cubic meters.
So how many kWh of energy will you get per 1100 square feet of area required for their energy solution? About 50kWh of energy, or about 5 dollars worth .
How much energy did those solar panels make assuming a 5 hour sunny day? 100kWh.
What if you want a fuel, like methane? Could you grow it instead thereby gaining both the energy and the CO2 removal? Of course you could. Right now we idiotically try to get biodiesel from corn and soy (that rant is for another post someday). Lets pretend we actually get smart and try to solve how to get it from algae.
Algae could produce 5000-15000 gallons of oil per acre per year (1.3-4 lbs/sq ft/per year). Lets use the lower end. So that means this same space, 1100 square feet, could be producing 4 gallons of algae oil per day. Oil gets converted to biodiesel with an efficiency of about 98% (but this does not include the other ingredients required like methanol and lye). What is the energy in 4 gallons of biodiesel? About 140 kWh.
The nanotube material sounds great, it really does….in concept. But while they are laughing at the idea of burying CO2, the reality seems to be that solar panels and large pools of algae truly provide a better solution right now and very little new research needs to be done to provide superior performance.
I hope that the journalists were lazy and the scientists are not media savvy. I would live to hear some idea of what they think the actual potential of this material could be.. its not like they are off by an order of magnitude…but still, its not really that close either.
As a side note:this proposed technology is not new, only this implementation. The new implementation is claimed to have way better efficiency than previous attempts.