DIY CO2 Scrubber

[Randy Holmes-Farley Verified Community Expert]

I did some calculations. The overall reaction is 2NaOH + CO2 = Na2CO3 + H2O. The molecular weight of NaOH is 40, Na2CO3 is 106. So For each 100g of Na2CO3 will come from 75g of NaOH.

Solubility of Na2CO3 around room temperature is 18~20% weight. So it's like 250g of it to 1L of water. That equals to 187.5g of NaOH. So if we dissolve more than that, it will Na2CO3 will start to precipitate when NaOH close to deplete. Given some margin of error, we can make 200~250g sodium hydroxide per liter of water, and change it when precipitation start to appear. Sounds about right?

The calculation is not technically perfect because sodium carbonate is less soluble in a sodium hydroxide solution than in pure water (due to the common ion effect of the sodium present), but it sounds like a fine plan to try.

 

[Randy Holmes-Farley Verified Community Expert]

Just tried out a simple setup with just water:

There are couple problem.

First problem is the back pressure. The water height in the reactor is about 7". That enough to stop the skimmer from being able to pull air completely. The skimmer was running at 60%. When I turn it up to 100% it is able to pull air through. So the back pressure is a big factor and highly depends on the skimmer's performance and water height of the reactor. Even after adjusted accordingly, it still need to make sure every time to refill it's back to the same height, or it will need to be readjusted again. Also evaporation might be a problem, if one refill can last long enough time.

Second problem is the bubble size. It's big chunk raising up in water column. I imagine that won't be very efficient for the reaction to take place. Will it be efficient enough to make an impact to tank pH? To increase contact area, it could run through a air stone to produce finer bubble. But that will put even more back pressure to the skimmer.

I imagine the actual reactor will need to incorporate an air pump to dry air through the solution to relief the back pressure to the skimmer. It's not as simple as it initially sounds.

Yes, I agree than an air pump is needed due to back pressure. The deeper the water, the more is the back pressure.

 

[GuppyHJD]

The resistance of the weight of the water will make it to hard for the air to bubble through the reactor and the skimmer pump will probably only pump water rather than a mix of water and air.

Why not a small air pump forcing air through the solution and the skimmer drawing the air into the system?

 

[Tombones]

This is what worked for me.

The container is 12X17" with 1 to 1and 1/2 gallons of RODI water and 100g of sodium hydroxide. It has been running for 6 weeks and my highest tank PH reading was 8.29. Each day the ph lowers a little and after 9 days and when the ph reaches 8.03 in the morning before lights on I add 2 liters of water with 100g of sodium hydroxide.
The biggest problem was finding an air defuser that would not clog after a few days. On line I found these no clog bubblers (5 in a pack) and chained them together. I could weigh the bubbler down more but it seems to be ok the way it is. One other problem was the long line I had to run for the air pump intake to the skimmer would have condensate so placing a plastic jar at the lowest point and drilling two holes in the lid attaching air tubes the condensate would drain.
Something I have not tried yet was adding more sodium hydroxide. Would that make it last longer or just have a higher ph. Something to consider. My ph was 7.8 to 7.9 and some times lower before and now it never goes below 8.

 

[LadAShark]

Don't want to revive a dead thread, but would like to ask how one might go about setting up an NaOH CO2 scrubber.

 

[Randy Holmes-Farley Verified Community Expert]

Don't want to revive a dead thread, but would like to ask how one might go about setting up an NaOH CO2 scrubber.

@Garf

 

[Garf]

Don’t mix the “in” line, with the “out” line (make it impossible to mix up by using dissimilar fittings, or permanently connect them). Make sure saltwater cannot syphon into the container, make sure the solution cannot syphon into the tank, leave an air gap to account for the bubblyness. All precautions should be considered carefully.

Kalk slurry aeration

With ref to @Doctorgori thread a while ago; https://www.reef2reef.com/threads/pulling-air-through-saturated-kalk.580645/ His thread was based around changing a saturated calcium hydroxide into calcium carbonate by reducing the CO2 content in air passed through it to ultimately reduce CO2 in...

www.reef2reef.com

Mine is kalk slurry, but works in the same manner,

Don't want to revive a dead thread, but would like to ask how one might go about setting up an NaOH CO2 scrubber.