Chemical reaction that uses CO2 to make useful substances and releases energy. As good as it sounds?

http://www.mtu.edu/news/stories/2012/lemons-lemonade-reaction-uses-carbon-dioxide-make-carbon-based-semiconductor.html

Is there anything to this? Is this one of those “breakthroughs” that never panned out? Can it remove CO2 from the atmosphere, incorporate it into two useful solids, and return more energy than it required? There has to be a catch, right?

I’m thinking that maybe the creation of lithium nitride (Li3N) takes a lot of energy, or that it releases carbon dioxide when it’s manufactured.

Well, plants have been doing that for a billion or two years, albeit they throw sunlight into the equation, too. When plants do it a lot of oxygen is produced which sort of screwed up the environment for the anaerobic life forms for whom oxygen is poisonous.

Yeah, there are probably “side effects”. Whether or not they’re a problem is a different question.

You are correct that we need to examine the entire supply chain.

Lithium nitride forms spontaneously from lithium metal and nitrogen. However, reduced lithium is not found in nature, so we have to account for that energy input. We can dig into the numbers if your curious.

That said, carbon dioxide is a cheap carbon source that can be acquired from existing waste streams (which are higher concentration than air)

We could calculate what volume of this or other material (carbonate polymers get some attention) you’d need to make to mitigate carbon dioxide from fossil sources in this country. That would be fun. I bet it’s a big cube.

My (layman’s) understanding has been as follows.

Say you’re burning coal to generate energy. This creates a gaseous waste stream that is rich (at least compared to the atmosphere) in CO2. To do something other than sequester it underground is going to take as much, or more, energy than the process is generating. Is that correct? Are there exceptions?

My suspicion is that any exceptions (such as this claimed process) simply consume the energy somewhere else in the supply chain. Are there any cases where this isn’t true? Is it even theoretically possible for it not to be true?

What happens to the oxygen? CO2+Li3N=C3N4+Li2Cn2? Where do the oxygen atoms go? This doesn’t add up.

I imagine it’s released to the atmosphere or perhaps bottled for industrial or medical use.

The abstract picture has the full reaction. You end up with lithium oxide.

It depends on where you start your supply chain. But in general, yes, most any full chemical process requires a net energy input. Even burning a hydrocarbon; you’re just reversing a process that was fueled by the sun.

Again, it depends where you say the process starts. For the process in question, we can pretend we start with lithium chloride, nitrogen, and CO2 for free. I have not checked the thermodynamics, but my guess is the energy output of the published prices in question is smaller than that required to reduce lithium chloride.

Okay, I’m not a chemist so I guess this is all a little over my head. When you say “reduce lithium chloride” are you talking about the creation of lithium nitride, or something else?

Lithium nitride is made from lithium metal, which is made from lithium chloride. Li[sup]+[/sup] is reduced (an electron is added) to Li[sup]0[/sup] to make the metal. Lithium really doesn’t want that electron.

Okay, so you’re saying what I thought. That overall there’s no gain in this process.

But if we can reduce the lithium chloride using a carbon neutral energy source, then maybe we could come out ahead environmentally. But if you’re going to do that, then why not just use the carbon neutral source for your energy to begin with rather than burning a fossil fuel, right? Or will the fossil fuel still produce more electricity than is needed to produce sufficient lithium nitride to ameliorate the CO2?

OP is specifically asking about reactions that take up CO[sub]2[/sub] and release energy. Plants do exactly the opposite: When doing their photosyntheses schtick, they soak up all that solar power which they pack into the carbohydrates that they build. All that energy doesn’t get released (as OP specifies) until later when you burn (or smoke) said carbohydrates, which just puts all that CO[sub]2[/sub] right back into circulation again.

You probably could use solar or something to refine the lithium. Aluminum plants are typically sited near hydro plants. If you just need electricity, it doesn’t matter too much where it comes from.

As for when and where to renewable sources, for what, and when do you come out ahead – it depends. I doubt using fossil fuels for this process would be carbon-neutral. Using renewable sources for this process might make it carbon-negative.

It’s clearly not a way of producing energy. Creating the lithium will require more energy than you release by reacting it with the carbon dioxide.

I guess it’s a way to sequester CO2 if you want, in a nice solid form. They claim some of the materials are also useful for other things. That might be true, but I suspect that the amount you would have to produce to make a dent in the CO2 emissions would vastly outstrip the market for these materials.

Right now, the only way anyone’s trying to sequester carbon on a large scale is geologic sequestration: pump it down into depleted gas wells, where the geologic structures will trap it.

This would be an example of mineral sequestration, where the CO2 is converted into a carbonate. Currently the most common ways to do that are to use calcium oxide or magnesium oxide (which would also fit the headline: “uses CO2 to make useful substances and releases energy”). My gut feeling is that this method with lithium doesn’t really offer any advantages over calcium oxide or magnesium oxide. It probably takes a similar amount of energy to make the chemical, and calcium and magnesium are much more common than lithium, and both lime and magnesia are industrial chemicals produced on very large scales, while lithium nitride is decidedly not.

Often made accidentally by grad students who forget to use the lithium in the argon glovebox instead of the nitrogen glovebox :smiley:

Going out on a tangent…

Sometimes I half joke that the best solution to the CO2 problem is to produce more garbage and stuff it into landfills, plastic crap to be precise.
Just have to find the way to turn atmospheric CO2 into plastics (crop based plastics for example), ban recycling and let consumerism save the day, 'cause altruism and ecological responsibility are not cutting it so far.

We could make a list of the problems with this, starting with converting food producing acreage to plastics production, but I know you’re not making a serious suggestion.

I do wonder though, if we could artificially ramp up what plants do when they absorb CO2. Engineered algae in tanks, maybe? Or some purely non-living chemical process driven by the sun? We have a lot of sunny desert acreage in this country.

I once saw Alton Brown use a CO2 fire extinguisher to make ice cream in about 30 seconds. Not just ice cream but carbonated ice cream.