Democratising DAC CO2 Capture Using
Sodium Hydroxide or Soda Lime
Article by Rami Elias Kremesti M.Sc, CSci, CEnv, CWEM
© 2025 – Kremesti Environmental Consulting Ltd.
Introduction
The reaction of Sodium Hydroxide NaOH with CO2 – Carbon Dioxide is a well known high school chemical reaction. CO2 is also one of the major Green House Gases (GHG’s) responsible for global warming and climate change. Atmospheric concentrations of CO2 have risen globally from 280 ppm pre-industrial revolution to about 425 ppm currently. I was born in the year that atmospheric CO2 was at 330 ppm… Solving climate change is the greatest environmental challenge of the 21st Century.
A similar chemical reaction using NaOH and Lime is used on submarines to filter CO2 out of the air that the sub-mariners breathe out. Oxygen is produced using Direct Current and electrolysis of water.
Engineering and Kinetics of the Reaction
The engineering of reactors and the kinetics of the CO2 capturing reaction are discussed in detail in the following paper in the Journal Process Systems Engineering issue
Sodium Hydroxide-Based CO2 Direct Air Capture for Soda Ash Production─Fundamentals for Process Engineering
This is the boring bit dear reader that is of interest to the nerdy chemical engineers like myself…
*Max Planck Institute for Dynamics of Complex Technical Systems
Democratising the NaOH + CO2 Reaction
We at Kremesti Environmental Consulting Ltd hereby call for the democratisation of this CO2 capture reaction so that home made CO2 DAC (Direct Air Capture) reactors can be built using Drain Cleaner or NaOH pellets. A kid named Ethan built a reactor on YouTube.
The chemical reaction is:
NaOH + CO2 -> NaHCO3
40 grams + 44 grams -> 84 grams NaHCO3
The molecular weight of NaOH is about 40 grams/mole
The molecular weight of CO2 is about 44 grams/mole
Figure 1: Solid 100% Pure NaOH or Soda Caustic Pellets can be Left in the Open to capture CO2 from the air. NaOH is also hygroscopic and will capture the humidity in the air.
Sodium hydroxide (NaOH) pellets left exposed to air will gradually react with atmospheric carbon dioxide (CO2) to form sodium bi carbonate (baking soda), a process that can take weeks or months, depending on factors like humidity and air circulation.
So roughly One Kg of home bought NaOH will capture roughly 1 Kg of atmospheric CO2 and form about 2 tons of Sodium bi-Carbonate or Baking Soda which is a harmless but useful chemical.
If 8 billion concerned citizens bought 1 Kg of NaOH and left the pellets outside to react slowly with CO2, then 8 billion Kgs of atmospheric CO2 will be removed from the atmosphere. This is obviously a small dent in the Global annual carbon dioxide emissions from fossil fuels and industry which totalled 37.01 billion metric tons in 2023 or 37000 billion Kgs or as a percentage of removal it would be 8/37000 x 100% = 8/370 = 0.02 % CO2 removal.
HOWEVER,
If each citizen bought 100 Kgs of NaOH per annum, concerned citizens of the earth would be able to remove 2% of Atmospheric CO2 emissions anually …
and,
If each citizen bought 1000 Kgs of NaOH or 1 Ton per annum, citizens of the earth would be able to remove 20% of Atmospheric CO2 emissions annually!!!!
5 Tons of NaOH annually per citizen is their average CO2 Carbon Foot Print for 100% CO2 DAC.
It is a drop in the ocean that can develop into a torrent… Perhaps this idea can catch on in social media like FB and TikTok and more and more concerned citizens/sponsors/wealthy people will try to capture more and more CO2 under home funded conditions using NaOH – caustic soda. Please share this paper with your friends, MP’s and media contacts.
Always remember that the most natural way to capture atmospheric CO2 of course is planting trees…
What Would be Do With the Billions of Tons of Na2CO3?
A smart Swiss friend of mine made a simple calculation: He calculated his family’s average annual CO2 footprint per capita which is about 4 tons annually. He asked me:
“What would I do with 8 tons of Baking Soda if I capture my CO2 emissions?”
Very smart and valid question. What would we do with the billions of tons of Sodium Carbonate that we produce?
The answer is as simple as this:
1. Use Sodium bi-Carbonate as an industrial product produced this way instead of the Solvay Process.
2. Release the Sodium bi-Carbonate back to the Ocean which would correct the low pH and at the same time become fixed by Algae as Biomas. This way we have closed the Carbon-Cycle and returned the CO2 back to where it came from which is fossil fuels….
3. Use the baking soda as a soil conditioner for acidic soils.
Of course another possible solution to this problem is to heat the NaHCO3 and reverse the reaction:
Sodium bi-carbonate (NaHCO₃) begins to decompose into sodium oxide (Na₂CO3) and carbon dioxide (CO₂) above approximately 400°C.
2NaHCO3 -> Na2CO3 + CO2 + H2O
Cost and Alternatives
A ton of NaOH purchased from Alibaba will cost you about 500$ – it is relatively expensive. Less expensive and safer alternatives are CaO (Slaked Lime) and MgO (Magnesium Oxide). Note that CaO and MgO are di-protic bases which means they are more efficient pound per pound in removal of CO2 which is a diprotic acid.
Worldwide Production of NaOH
Worldwide production in 2022 of NaOH was approximately 83 million tons. Bummer !!! We need 8000 million tons to capture 10% of annual CO2 global emissions.
This is obviously not enough to capture all CO2 emissions world wide. However, if renewable power plants like solar and wind have excess DC energy, it can be used to produce NaOH using the Chlor-Alkali process. And if demand increases, production will increase…
In 2022, the market volume of magnesium oxide (MgO) amounted to approximately 15.18 million metric tons worldwide. By the year 2030, this figure is forecast to grow to around 22.6 million metric tons.
Safety WARNING and Disclaimer
NaOH is a highly corrosive substance and will damage human tissue on contact. It also reacts EXOTHERMICALLY with water. Keep away from Children.
Please download our NaOH safety presentation and take all necessary safety precautions (PPE: goggles, chemical gloves, long sleeves, safety shower, etc) to protect yourself and the environment. Kremesti Environmental Consulting cannot be held liable for any accidents that are a result of unprofessional supervision/execution of this reaction. Also note that some drain cleaners use Aluminum pellets that react with NaOH to produce Hydrogen gas which is explosive if it comes into contact with a flame.
Other CO2 Capture Ideas
Perhaps large container ships can drop hundreds of tons of MgO or CaO in the wake of their propellers, thus mixing these chemicals into the ocean water which would capture CO2 in the water and increase Ocean pH.
Figure 2: Ocean pH decrease over the years. Note that Pre-Industrial Revolution ocean pH is estimated to have been about 8.2. Below pH 8, carbonates start to dissolve…. Crustaceans suffer.
We have already published a paper about capturing CO2 in-situ in waste water treatment plants and one on converting FGD’s on power stations into CO2 absorbers by dosing NaOH.
Our research identified a company in Finland, Soletair, which offers regenerable CO2 capture solutions for large buildings.
We are in the process of presenting our idea to Vinci in the uK.
Ideas For Industry
Would it be possible to develop solid adsorbent CO2 capture filters for cars?
Absolutely Yes ! Ofcourse In the UK, the average petrol car emits roughly 150 grams of CO2 per kilometer which equates to roughly 300 grams Na2CO3 per Kilometer which is a lot of excess weight. It is theoretically possible though to have a CCUS system that is amine based and can capture and release CO2 into potentially a CO2 tank in the car….
Submarines capture CO2 from the air that the sailors breathe to keep it fresh.
Figure 3. A CO2 Capture Air Filter that uses NaOH and CaO pellets. This principle is used in Submarines.
The German company Drager has a CO2 sorbent known as DragerSorb used in artificial breathing apparatuses.
Ocean Alkalinity Enhancement (OAE) is one of the ideas that are being studied to counter high levels atmospheric CO2 levels. CO2 in the atmosphere dissolves in the ocean which results in a decreasing pH trend. Increasing the oceans’ alkalinity that counter this trend and fix CO2 in the ocean.
CSIRO Australia’s national science agency is looking into this in addition to a company called Planetary Tech.
MIT has an explainer on OAE.
Conclusion
Kremesti Environmental Consulting Ltd firmly believes that the time for solving climate change is NOW and that Chemistry will solve this problem. With citizen science and increased public awareness and activism WE the People can solve this scourge of the 21st century.
About the Author:
Rami Elias Kremesti Portrait
Rami Elias Kremesti is the founder and MD of Kremesti Environmental Consulting Ltd a consultancy that specialises in water and waste water treatment as well as power station and environmental chemistry. He lives in High Wycombe, UK, has two lovely teenage girls and enjoys hiking the Chilterns AONB as well as playing guitar. The ability of plants and trees to convert inorganic chemistry to organic chemistry never ceases to amaze him. He is the author of three books on philosophical themes which is his other passion besides chemistry his first love.
© 2025 Kremesti Environmental Consulting – All Rights Reserved