Thread: Calcium Oxide. A good way to get pure CO2 from the Air?

Calcium oxide - Wikipedia, the free encyclopedia

From what I find in this article, it looks like you can scrub CO2 from the air simply by heating and cooling Calcium Oxide.

Calciumoxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO₃; mineral calcite) in alime kiln. This is accomplished by heating the material to above 825 °C,^[1] a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO₂); leaving quicklime. The quicklime is not stable and, when cooled, will spontaneously react with CO₂ from the air until, after enough time, it is completely converted back to calcium carbonate.

So If I'm reading this correctly, you could start with CaCO3, and heat it up until it liberates it's CO2 (which you then collect), leaving just CaO. Then you can react CaO again with the air, and it grabs CO2 atoms to convert itself back into CaCO3. And we start the process over again.

I wonder how much energy is lost? Clearly some of the energy used to super heat the CaCO3 can be recovered by harnessing the heat from the CaO + CO2 reaction. But I don't know how much. I wonder if it would be possible to come close to a balance?

Chemical of the Week -- Lime


According to this article, the CaO + CO2 reaction actually goes faster if you make Ca(OH)2 out of the CaO first. So I've got part of the reaction here:

CaO (s) + H₂O (l) Ca(OH)₂ (aq) (ΔH_r = −63.7 kJ/mol of CaO)

But I can't find a reaction with the energy released for the next step

Ca(OH)2(s) + CO2(g)

CaCO3(s) + H2O(l)

So the main question: is there a good reason we couldn't use this to sequester lots and lots of CO2 from the air? Or maybe.... just maybe.... use that CO2 to make something like Methanol?

Too energy intersive ,hopw are you ging to provide the heat?

Sigh. Someone has taken all the fun out perpetual motion by inventing the 1st and 2nd laws of thermodynamics.

Originally Posted by fizzlooney

Too energy intersive ,hopw are you ging to provide the heat?

Obviously. burn a bunch of coal to make the electricity

Originally Posted by fizzlooney

Too energy intersive ,hopw are you ging to provide the heat?

I was thinking you would get a lot of the heat back. After the CaCO3 splits into CO2 and CaO, you take the CaO, put it in the furnace, and combine it with water to create Ca(OH)2, releasing a good amount of heat from the reaction. You won't get as much energy back as the energy that was consumed, of course, but you might get a lot of it back.

The main loss is that I think you may have to let the CaO cool before combining it with water (not sure if you do or not).


Calcium oxide - Wikipedia, the free encyclopedia

Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide) are important commodity chemicals.
Quicklime produces heat energy by the formation of the hydrate, calcium hydroxide, by the following equation:^[2]
CaO (s) + H₂O (l) Ca(OH)₂ (aq) (ΔH_r = −63.7 kJ/mol of CaO)The product, commonly called "quicklime", has many uses on its own. As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction. One litre of water combines with approximately 3.1 kilograms (6.8 lb) of quicklime to give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient portable source of heat, as for on-the-spot food warming in a self-heating can.

The goal is to find a convenient way of getting CO2 for Methanol production, which in turn is an attempt to store energy from renewable power sources like Solar and Wind. Clearly some energy loss is expected, but if it's not extreme energy loss, then it might still be worth doing so as to capture a fraction of the excess energy produced during strong winds and/or a sunny day, instead of none.

Besides that, if there were enough infrastructure built, maybe Methanol could begin to compete with gasoline.

Originally Posted by fizzlooney

Too energy intersive ,hopw are you ging to provide the heat?

Solar cells in the desert pumping CO2 into a deep saline aquifer? Just a thought...

The rate doesn't need to be particularly high, we have time on the order of decades to use them in.

Totally assinine

Suppose nuclear were the power source. There's plenty of heat in those reactions.

I wonder if it would be possible to work the CaO + H2O -> Ca(OH)2 + Heat reaction into the steam process of a nuclear power plant? Instead of waiting for the CaO to cool after the CaCO3 + Heat -> CaO + CO2 reaction, maybe we could just throw it straight into unheated cold water and let it react. Then we're not really losing any energy we weren't already going to lose anyway from the basic inefficiency of steam engines.

Originally Posted by kojax

Suppose nuclear were the power source. There's plenty of heat in those reactions.

Or geothermal maybe?

Originally Posted by fizzlooney

Totally assinine

How would you remove carbon dioxide from the atmosphere then?

Plant a lot of trees!

You can only absorb as much CO2 as you liberated to get to CaO, so that doesn't sound like a practical solution.

-R

I believe the point was to store/bury the liberated carbon.

If you're serious about extracting CO2 from the atmosphere and the oceans, you first need to look at the way this has always happened with natural processes. There are several biological processes, but the main one for permanent sequestration is geological.

Weathering of exposed rocks. This is a very slow process by human timeframes, but normal for geological processes. Olivine rocks are the go. Normally this happens by movement of tectonic plates shoving mountains up and exposing previously buried rock formations, some of them containing olivine deposits. If you can find a process that's low energy input required, and that can continue indefinitely with little further maintenance to ensure maximum efficacy, you're on a winner. My personal speculation for solving this problem is just simple quarries with attached windmills, not power generating turbines but grinding mills, converting quarried rocks into gravels and dusts. Just an accelerated version of the natural process - but it needs a lot of tweaking. Unfortunately, you can't just accelerate this process without clogging rivers with sludge because there'll be too much 'stuff' to be carried easily. Eventually, someone will come up with something a bit less clumsy and a lot more manageable but with the same outcome.

your idea is correct. but you should consider the reactions taking place in a practical manner. i don't think its an appropriate method. it requires much energy. it should occur in a close container and the pressure created by the liberation of CO2 may damage the whole system.you can rather do it by reacting a carbonate with concentrated acid and collecting the gas using an appropriate method

Originally Posted by Refracktory

Plant a lot of trees!

You can only absorb as much CO2 as you liberated to get to CaO, so that doesn't sound like a practical solution.

-R

Well, the main problem is getting pure CO2. It's not easy to filter it out of the air. The goal of burning lime to liberate it's CO2, and then reacting the CaO to capture it again is that each time you capture it again, you're breaking it free from the mix of CO2, O2, Nitrogen, and other elements.

When you then liberate it again, what you're liberating is CO2 in its pure form, so you can put in a storage tank or something, and not just turn around and mix it back into the atmosphere. If you then react that pure CO2 with pure hydrogen to get Methanol, you're creating a petroleum substitute, and you can either store that methanol indefinitely (permanently reducing the CO2 in the air), or put it on the market so it competes with OPEC's natural petroleum (thereby lowering the price of transportation and improving the USA's overall economy). Either option sounds good to me.

All we need is plenty of power for your setup plus getting the hydrogen from water. This would generate a lot of heat and I thought that this was what we are trying to avoid, so?

We need the heat. Heating up CaCO3 is how you make it release its CO2, so the more heat the better.

By all means let us have more heat, current doctrine hereabouts seems to hold that carbon dioxide can generate heat in abundance. Problem solved. More than this I cannot say for fear of appearing inflammatory.

Jax go back to the military forum , youhave no nbusiness here

I'm thinking so long as we don't let the heat escape, how does it matter how hot we need our system to get? Just insulate it well.

Limestone has to be heated to 1450C to decarbonize it. A better approach might be the use of magnesium carbonate that will decarbonize at 700C, so uses less fuel and loses less heat through insulation. There are cement technologies being developed that use MgCO3/MgO while recycling the CO2. I am skeptical of this firm's claims, but will be interested to see how it develops:

Our solution « Novacem

Originally Posted by adelady

Weathering of exposed rocks. This is a very slow process by human timeframes, but normal for geological processes. Olivine rocks are the go. Normally this happens by movement of tectonic plates shoving mountains up and exposing previously buried rock formations, some of them containing olivine deposits. If you can find a process that's low energy input required, and that can continue indefinitely with little further maintenance to ensure maximum efficacy, you're on a winner. My personal speculation for solving this problem is just simple quarries with attached windmills, not power generating turbines but grinding mills, converting quarried rocks into gravels and dusts. Just an accelerated version of the natural process - but it needs a lot of tweaking.

I'm not convinced this would work. For the weathering process to happen at significantly higher rates than in nature, you'd need a much more concentrated carbonic acid - and if you've already collected the CO2, why spend time and energy converting it to silicic acid and carbonates and you can just bury it?

Under 'normal' concentrations of carbonic acid, I doubt you could ever match the weathering of the entire sediment load of every river in the world.

For the weathering process to happen at significantly higher rates than in nature, you'd need a much more concentrated carbonic acid -

No. What you do is change the way, and maybe where, the weathering happens. There's plenty of carbon dioxide in the air and the oceans, no need to 'concentrate' it. The natural process is for rock to be exposed gradually - at least by human time perceptions. In the high cold mountains freezing and thawing will crack rocks progressively and expose more surfaces to the air and weathering processes. That's how tectonic and natural processes do it.

What we want to do is to geoengineer by speeding up this process, not to substitute a laboratory style instant chemical conversion. Well, we don't "want "to do it. We just have to find the least dangerous way of sequestering carbon to match the dangerous speeding up we've done of the carbon release processes. It's taken a couple of centuries to get to where we are now with release. Our "matching" sequestration process will be badly time lagged but it should be set up to run steadily for at least another couple of centuries.

Remember, during those centuries we will be dealing with all kinds of disruptions to economic and political life because things will get desperately bad in far too many parts of the world. So the process has to be simple, cheap, repeatable and scalable. Quarrying in the first place, milling the rock into gravels and dusts is pretty straightforward. The biggest question will be how much precious energy can we spare to control the release of dusts or to move gravels and dust to where they'll have a bigger, faster impact. "Crop-dusting" mangroves and marshes would be a good strategy initially - but there are probably specific places where acidic ocean waters upwell that would need first and fastest attention.

It's not up to me or you to work out the best way to do this now. But it's got to be done sometime or we really will cook all our food sources long before they get near harvest or table.

The rate of the reaction depends on both the surface area of the sillicates, and the pH of the water. Exposed sillicates are already abundant on Earth, and down the length of a river sediment fines to the sorts of scale you're talking about.

Now, the Amazon river has an output of around 600 Megatons per year, around 30-50% of which will be sillicates. I find it unlikely that any geoengineering/mining project will have a productivity this high, and this is only a single river. Not to mention that siliceous oozes are still being deposited as abyssal sediments around the world, indicating chemical sillicate weathering occurs at a smaller rate than sillicate sediments enter the oceans.

What is the use/advantage of this idea?

Originally Posted by Robinol

What is the use/advantage of this idea?

To remove CO₂ from the air as one weapon against climate change. There is a market for CO₂ in the chemical industry, so that could, perhaps, cover some of the costs.

But for removing that CO2, we are producing CO2. So how can that be beneficial?

Originally Posted by Robinol

But for removing that CO2, we are producing CO2. So how can that be beneficial?

Not sure what you mean by "producing CO2" but if we remove CO2 from the atmosphere and use it to create fuels (methane or more complex hydrocarbons) and then burn that then it is better than where we are now because we are not introducing "new" CO2 into the system. And if we use those hydrocarbons to produce plastics, say, then it is sequestered for longer (and we are still not introducing new CO2).

(Not that I think CaO is the right way to do this)

CCS is looking like the most likely technique to be put into widespread use right now, in my opinion.