A CO2 scrubber is a device that removes carbon dioxide from the air in an enclosed space or from an exhaust stream. These systems keep people breathing safely in submarines, spacecraft, and operating rooms, and they’re increasingly used in industrial settings to pull CO2 out of smokestack emissions or even the open atmosphere. The core idea is simple: air passes through or over a material that chemically or physically traps carbon dioxide, letting the remaining air recirculate or vent cleanly.
How CO2 Scrubbers Work
Every CO2 scrubber relies on a material that grabs carbon dioxide molecules out of a gas mixture. The two main approaches are chemical absorption and physical adsorption. In chemical systems, CO2 reacts with a substance (most commonly an amine solution or a hydroxide compound) and gets locked into a new chemical form. In physical systems, CO2 molecules cling to the surface of a porous solid, like a zeolite mineral, without a permanent chemical change.
The most widely used chemical approach runs air or gas through a liquid amine solution. Amines act as a reactive base that attacks the CO2 molecule and binds it. Once the solution is saturated, it can be heated to release the captured CO2 and reused. Solid chemical scrubbers work differently: materials like soda lime (a mix of roughly 80% calcium hydroxide with small amounts of sodium or potassium hydroxide and about 15% water) react with CO2 to produce calcium carbonate, water, and heat. One hundred grams of soda lime can absorb about 26 liters of carbon dioxide.
Where CO2 Scrubbers Are Used
Submarines
U.S. Navy submarines use an electrically powered regenerative scrubber that runs air through a water-based solution of monoethanolamine. The solution captures CO2, then gets heated to release the gas so the solution can be reused continuously. As a backup, submarines also carry canisters of lithium hydroxide, a non-regenerative material that reacts with CO2 in a one-time chemical process. These backup canisters are critical during emergencies when power may be unavailable, though their limited supply creates a time constraint for crew survival.
Spacecraft
The International Space Station uses a system called the Carbon Dioxide Removal Assembly (CDRA), which pairs a water-absorbing desiccant bed with a bed of zeolite, a porous mineral that traps CO2. Once the zeolite is full, the system heats it to release the captured gas and regenerate the material for reuse. An updated version, called 4BCO2, swaps in a different type of zeolite (13X instead of 5A) but follows the same basic four-bed cycle. ISS cabin air typically contains 1,500 to 3,000 ppm of CO2, and the system works within that range. Newer experimental materials could combine CO2 capture and conversion into a single step, potentially cutting the power needed for air cleaning by about 22%.
Medical Anesthesia
During surgery, anesthesia machines recirculate breathing gases through a canister of CO2 absorbent so the patient doesn’t rebreathe their own exhaled carbon dioxide. Soda lime is the most common material here. Newer products like Amsorb use calcium hydroxide with calcium chloride as a moisture-retaining agent, eliminating sodium and potassium hydroxide entirely. This matters because those stronger bases can react with certain anesthetic gases to produce unwanted byproducts. The absorbent canisters include color-changing indicators that signal when the material is spent.
Diving Rebreathers
Closed-circuit rebreathers, used by military, technical, and recreational divers, pass exhaled air through a scrubber canister before recirculating it. The scrubber duration depends heavily on how hard the diver is working and the water temperature. At high exertion (producing about 2 liters of CO2 per minute), a canister depletes far faster than during a relaxed dive (around 0.67 liters per minute). Cold water slows the chemical reaction and shortens canister life. Manufacturers rate their canisters under worst-case conditions, so real-world duration is often longer than advertised, but divers treat those ratings as hard limits for safety.
Regenerative vs. Non-Regenerative Systems
The choice between these two types comes down to power, space, and mission length. Regenerative scrubbers use energy (usually heat or pressure changes) to release captured CO2 and reset the absorbent material for another cycle. They’re ideal for long-duration applications like submarines on patrol or space stations, where carrying enough disposable material would be impractical.
Non-regenerative scrubbers are simpler and need no power. A canister of lithium hydroxide or soda lime reacts with CO2 until it’s chemically spent, then gets replaced. These work well as backups or in short-duration applications, but they create a storage problem. Every hour of breathing requires a finite weight of material, and in an emergency scenario with no resupply, limited stores may not last until rescue arrives.
Why CO2 Levels Matter
Carbon dioxide is invisible and odorless at low concentrations, which makes it a quiet hazard in sealed environments. The workplace exposure limit set by OSHA is 5,000 ppm averaged over an eight-hour day. The ceiling that should never be exceeded, even briefly, is 30,000 ppm for 10 minutes. At 40,000 ppm, CO2 is considered immediately dangerous to life. For context, outdoor air contains about 420 ppm. In a sealed room, submarine, or spacecraft, CO2 levels climb quickly with every exhaled breath, making scrubbers essential rather than optional.
Even at sub-dangerous levels, elevated CO2 causes headaches, difficulty concentrating, and drowsiness. Studies on indoor air quality have found cognitive performance drops noticeably above 1,000 ppm, which is why CO2 scrubbing matters not just for survival but for the ability to think clearly and work effectively in enclosed spaces.
Industrial and Climate Applications
Beyond keeping people alive in enclosed spaces, CO2 scrubbers are scaling up for climate purposes. Industrial carbon capture systems attach to power plants and factories, pulling CO2 from flue gas before it reaches the atmosphere. These typically use large amine-based liquid systems that absorb CO2 at low temperatures, then get heated in a separate chamber to release concentrated CO2 for storage or reuse. The energy cost of that heating step is the biggest challenge, accounting for much of the system’s operating expense.
Direct air capture (DAC) takes this further by pulling CO2 straight from the ambient atmosphere, where concentrations are far lower (around 420 ppm versus 10-15% in flue gas). This requires moving enormous volumes of air and using highly selective sorbents. One promising class of materials, called metal-organic frameworks (MOFs), can be engineered at the molecular level to grab CO2 while ignoring other gases. Recent research has shown that humidity, long considered a problem for these materials, can actually boost CO2 capture in certain MOF designs. In these structures, water molecules within the pores help trap CO2 rather than competing with it, a finding that could make real-world deployment more practical since outdoor air is rarely dry.