Each human exhales 42grams of CO2 per hour (1.1Kg per day).

*** Chemical reaction

**** Basic

A process commonly used to teach CO2 scrubbing to chemical engineering students involves sodium hydroxide (NaOH). The reaction is exothermic and is as follows: CO2 (g) + 2 NaOH (aq) → Na2CO3 (aq) + H2O (l)

The aqueous sodium carbonate is subsequently treated with calcium hydroxide (Ca(OH)2) to precipitate out calcium carbonate (CaCO3): Na2CO3 (aq) + Ca(OH)2 (aq) → 2 NaOH (aq) + CaCO3 (s)

Disclaimer:

This is usually done with much higher concentrations of CO2 (e.g. >10%) than you would find in the atmosphere (~400 ppm). The point of scrubbing in a chemical plant is to reduce emissions to a level that is still much higher than atmospheric CO2 levels but lower than governmental standards. I suspect that you would not see a noticeable change in ambient CO2 levels from putting something like this in a place with such (relatively) low CO2 to begin with. There is a very low driving force to push gaseous CO2 into the liquid and solvate it when the partial pressure of CO2 is low.

There exists a unique relationship between the partial pressure of CO2 above a solution, the dissolved carbon in the solution, and the pH of the solution.

So if you wanted to see what was going on in a controlled environment with no other species in the solution / that could enter the solution, you could just use a pH probe to see how much carbon was pushed into the solution.

Calcium hydroxide can be produced when quicklime (CaO) is mixed with water (H20). quicklime is usually made by the thermal decomposition of calcium carbonate (CaCO3). This is accomplished by heating the material to above 825C (1,517F) CaCO3 (s) → CaO (s) + CO2 (g)

The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it will be completely converted back to calcium carbonate unless slaked with water.

**** Apollo Spacecraft

***** Lithium hydroxide (outputs water)

2 LiOH + CO2 → Li2CO3 + H2O One gram of anhydrous lithium hydroxide can remove 450 cm^3 of carbon dioxide gas.

Lithium hydroxide is often produced industrially from lithium carbonate in a metathesis reaction with calcium hydroxide: Li2CO3 + Ca(OH)2 → 2 LiOH + CaCO3 The initially produced hydrate is dehydrated by heating under vacuum up to 180C.

You will need 1.1Kg per person per day. If you are not going into space, buy calcium hydroxide, it is much cheaper ($125 per ton vs $30 per kilogram)

***** Lithium peroxide (outputs oxygen)

It is prepared by the reaction of hydrogen peroxide and lithium hydroxide. This reaction initially produces lithium hydroperoxide: LiOH + H2O2 → LiOOH + H2O

This lithium hydroperoxide may exist as lithium peroxide monoperoxohydrate trihydrate (Li2O2·H2O2·3H2O). Dehydration of this material gives the anhydrous peroxide salt: 2 LiOOH → Li2O2 + H2O2

Li2O2 decomposes at about 450C to give lithium oxide: 2 Li2O2 → 2 Li2O + O2

And absorbs CO2 in the following: Li2O2 + CO2 → Li2CO3 + 1⁄2 O2

Similar to the reaction of lithium hydroxide with carbon dioxide to release 1 Li2CO3 and 1 H2O, lithium peroxide has high absorption capacity and absorbs more CO2 than does the same weight of lithium hydroxide and offers the bonus of releasing oxygen instead of water.

**** Amine gas treating

The primary application for CO2 scrubbing is for the enclosed atmosphere of nuclear submarines. The technology being involves the use of various amines, e.g. monoethanolamine. Cold solutions of these organic compounds bind CO2, but the binding is reversed at higher temperatures: CO2 + 2 HOCH2CH2NH2 ↔ HOCH2CH2NH+3 + HOCH2CH2NHCO−2

The above reaction has been utilized as a primary part of atmosphere control in nuclear submarines since the late 1950s.

The amine concentration in the absorbent aqueous solution is an important parameter in the design and operation of an amine gas treating process. Depending on which one of the following four amines the unit was designed to use and what gases it was designed to remove, these are some typical amine concentrations, expressed as weight percent of pure amine in the aqueous solution: Monoethanolamine(MEA): About 20% for removing H2S and CO2, and about 32% for removing only CO2. Diethanolamine (DEA): About 20 to 25% removing H2S and CO2 Methyldiethanolamine (MDEA): About 30 to 55% for removing H2S and CO2 Diglycolamine: About 50 % for removing H2S and CO2

Additionally you could use: Diisopropanolamine (DIPA) Aminoethoxyethanol (Diglycolamine) (DGA)

Both H2S and CO2 are acid gases and hence corrosive to carbon steel. However, in an amine treating unit, CO2 is the stronger acid of the two. H2S forms a film of iron sulfide on the surface of the steel that acts to protect the steel. When treating gases with a high percentage of CO2, corrosion inhibitors are often used and that permits the use of higher concentrations of amine in the circulating solution.

MEA and DEA are primary and secondary amines. They are very reactive and can effectively remove a high volume of gas due to a high reaction rate. However, due to stoichiometry, the loading capacity is limited to 0.5 mol CO2 per mole of amine. MEA and DEA also require a large amount of energy to strip the CO2 during regeneration, which can be up to 70% of total operating costs. They are also more corrosive and chemically unstable compared to other amines.

Piperazines have been proposed for carbon capture and storage (CCS) because piperazine protects other amines from degradation. Piperazine can be thermally regenerated through multi-stage flash distillation and other methods after being used in operating temperatures up to 150C and recycled back into the absorption process, providing for higher overall energy performance in amine gas treating processes.

Typical absorption column operating range: 35-50C and 5-205 atm of absolute pressure.

*** Fractional Distillation of Liquid Air

Effectively you need only have a good phase diagram for the gases and control the temperature, pressure or both. But lacking those phase diagrams, the following list of triple points should be sufficient to build an approximate working distillation:

(The below looks best in fix width font in a textfile)

| Substance | Temperature (C) | Pressure (kPa) | % of Air | |----------------------+-----------------+----------------+------------| | Air | -213.40 | 5.265 | 100% | | Nitrogen | -209.97 | 12.6 | 78.084% | | Oxygen | -218.79 | 0.152 | 20.9476% | | Water | 0.01 | 0.611657 | 5% - 0.25% | | Argon | -189.34 | 68.9 | 0.934% | | Carbon dioxide | -56.60 | 517 | 0.04% | | Neon | -248.58 | 43.2 | 0.001818% | | Methane | -182.47 | 11.7 | 0.0002% | | Helium | -271.378 | 30.016 | 0.000524% | | Krypton | -157.39 | 74.12 | 0.000114% | | Hydrogen | -259.31 | 7.04 | 0.00005% | | Xenon | -111.8 | 81.5 | 0.0000087% | | Ozone | -192.55 | 0.00114 | 0.000007% | | Nitrogen Dioxide [0] | -11.25 | 18.728 | 0.000002% | | Iodine | 113.50 | 12.07 | 0.000001% | | Acetylene | -80.7 | 120 | Trace | | Ammonia | -77.75 | 6.076 | Trace | | Arsenic | 820 | 3628 | Trace | | Butane | -138.6 | 0.0007 | Trace | | Carbon (graphite) | 4492 | 10132 | Trace | | Carbon monoxide | -205.05 | 15.37 | Trace | | Chloroform | -97.72 | 0.870 | Trace | | Deuterium | -254.52 | 17.1 | Trace | | Ethane | -183.26 | 0.0008 | Trace | | Ethanol | -123 | 0.00000043 | Trace | | Ethylene | -169.2 | 0.12 | Trace | | Formic acid | 8.25 | 2.2 | Trace | | Hexafluoroethane | -100.07 | 26.60 | Trace | | Hydrogen chloride | -114.19 | 13.9 | Trace | | Isobutane | -159.60 | 0.000019481 | Trace | | Mercury | -39.0 | 0.000000165 | Trace | | Nitric oxide | -163.65 | 21.92 | Trace | | Nitrous oxide | -90.81 | 87.85 | Trace | | Palladium | 1552 | 0.0035 | Trace | | Platinum | 1772 | 0.00020 | Trace | | Radon | -71 | 70 | Trace | | Sulfur dioxide | -75.46 | 1.67 | Trace | | Titanium | 1668 | 0.0053 | Trace | | Uranium hexafluoride | 64.02 | 151.7 | Trace |

[0] numbers are a bit questionable

If you have a random sample of gases, you can separate them by gradually cooling the sample until each component gas liquifies. The liquified compound falls to the bottom of a collection vessel. After all of the liquid has been retrieved, cooling continues until the temperature drops to the boiling point of the next compound and it liquifies. Some compounds, such as carbon dioxide, never liquify. Instead, they turn directly into solids, which are easier to retrieve than liquids. (CO2 turns into a liquid over 516.7575kPa between 31.1C and -56.6C)

Put your sample in a vessel that is slightly warmer at the bottom (-185C) than it is at the top (-190C). Oxygen liquifies at -183C, so it flows out of the flask through a tube in the bottom. Nitrogen turns back into a gas, however, because its boiling point is -196C. It flows out through a tube connected to the top of the flask. Repeat to isolate all other gases.

If you only want to isolate CO2, compress it to between 5.11atm (516.7575kPa) and 72.79atm (7375.447kPa) and cool to -57C or at standard atomospheric pressure cool t0 -78C, CO2 gas will directly convert to solid (dry ice) You can do 750 kg/hr at 11Kw or 80 kg/hr at 3Kw