Most commercial CO2 isn’t made from scratch. It’s captured as a byproduct of other industrial processes, primarily ammonia production, hydrogen manufacturing, natural gas processing, and fermentation. The gas is then purified, compressed, and either liquefied for transport or piped directly to end users. A smaller but growing share comes from post-combustion capture at power plants and direct air capture facilities.
Ammonia Production: The Largest Source
Ammonia plants are the single biggest source of commercial CO2 worldwide. Ammonia (NH3) is a carbon-free molecule, so all the carbon that enters the process as natural gas or coal exits as CO2. In the most efficient ammonia factories, every ton of ammonia produced generates about 1.6 tons of CO2. The global average is higher: roughly 2.86 tons of CO2 per ton of ammonia.
The process starts with steam methane reforming. Natural gas reacts with steam at high temperatures, breaking apart methane molecules and releasing hydrogen and CO2. The hydrogen goes on to combine with nitrogen to form ammonia (the Haber-Bosch process, in use since the 1910s), while the CO2 is separated out. About 92% of the carbon monoxide produced in the reforming step is converted to CO2 through a water-gas shift reaction, then removed using pressure swing adsorption units. Because ammonia plants already need to strip CO2 from the gas stream before synthesis can proceed, capturing it is a natural, low-cost step rather than an add-on.
Hydrogen Production and Steam Reforming
Hydrogen plants that use natural gas as a feedstock generate CO2 by the same chemistry as ammonia plants, since steam methane reforming is the first step in both. For every kilogram of hydrogen produced, roughly 5 to 9 kilograms of CO2 are released depending on how much is captured. At an 80% capture rate, the carbon intensity drops to about 1.25 kg of CO2 equivalent per kilogram of hydrogen. At a 50% capture rate, it’s closer to 3.13 kg. Facilities that capture and sell this CO2 are sometimes described as “blue hydrogen” plants, distinguishing them from “grey hydrogen” plants that vent the CO2 to the atmosphere.
Natural Gas Sweetening
Raw natural gas pulled from wells often contains significant amounts of CO2 and hydrogen sulfide, both of which must be removed before the gas can be sold. Pipeline specifications require CO2 levels below 1%. The removal process, called gas sweetening, uses chemical solvents in over 95% of commercial operations.
The setup is an absorber-stripper system. Raw gas enters the bottom of an absorber column and rises through a descending flow of lean solvent, which chemically binds to the CO2 and hydrogen sulfide. Clean “sweet gas” exits the top. The now CO2-rich solvent flows to a regenerator, where it’s heated with steam to release the absorbed gases. The CO2 exits the top of the regenerator at around 93°C, and the regenerated solvent cycles back to the absorber. The absorption works best at high pressure and low temperature, while regeneration requires the opposite: low pressure and high temperature.
Some facilities use physical solvents (organic compounds that attract CO2 without reacting chemically), and newer hybrid solvents combine both approaches. The CO2 stream from sweetening plants is relatively concentrated, making it one of the cheaper sources to purify to commercial grade.
Fermentation and Ethanol Plants
Breweries and fuel ethanol plants produce nearly pure CO2 as yeast converts sugars into alcohol. This stream requires minimal cleanup compared to combustion-derived CO2, which makes ethanol plants a particularly cost-effective source. Many of the CO2 suppliers serving the food and beverage industry source their gas from large-scale ethanol facilities.
Post-Combustion Capture at Power Plants
Capturing CO2 from the flue gas of coal or natural gas power plants is more complex because the CO2 concentration in exhaust is relatively low (typically 4 to 15%), diluted by nitrogen from the air. Before capture can begin, the flue gas needs pretreatment: removing sulfur compounds, nitrogen oxides, and particulate matter.
The most commercially proven method uses amine-based chemical solvents in an absorber-stripper system similar to gas sweetening. Other approaches are gaining ground. Pressure swing and temperature swing adsorption use solid materials that grab CO2 molecules and release them when conditions change. Membrane systems pass flue gas across selective barriers that allow CO2 through while blocking other gases, offering lower capital costs and easier scaling. Cryogenic separation compresses and cools flue gas until the CO2 condenses into a high-purity liquid or solid phase, useful when very high purity is needed.
Direct Air Capture
Direct air capture (DAC) pulls CO2 straight from ambient air, where it exists at only about 420 parts per million. This extremely low concentration makes DAC far more energy-intensive and expensive than capturing CO2 from industrial streams. Current commercial pricing ranges from $600 to $1,000 per ton of CO2 removed, though tax credits in the United States now offer up to $180 per ton for permanently stored CO2 under the Inflation Reduction Act’s expanded 45Q credit. DAC is a small fraction of total commercial CO2 supply today, but several large-scale plants are under construction.
Purification to Commercial and Food Grade
Raw CO2 captured from any of these sources contains impurities: moisture, hydrocarbons, carbon monoxide, sulfur compounds, and trace metals. The purification process depends on the end use.
Food-grade CO2 (used in carbonated drinks, food packaging, and dry ice) must meet strict standards set by bodies like the European Industrial Gases Association and the Joint FAO/WHO Expert Committee on Food Additives. The minimum purity is 99%, with tight limits on contaminants: moisture below 0.05%, carbon monoxide under 10 parts per million, total hydrocarbons under 50 to 100 ppm, and no detectable odor. Heavy metals are capped at trace levels, including arsenic below 3 mg/kg, lead below 5 mg/kg, and mercury below 1 mg/kg.
Purification typically involves multiple steps. Activated carbon beds remove hydrocarbons and odor-causing compounds. Desiccants strip moisture. Catalytic converters oxidize carbon monoxide. Distillation columns separate remaining non-condensable gases. The exact sequence varies by source: CO2 from ethanol fermentation needs less treatment, while CO2 from combustion flue gas or coal-based ammonia plants requires more extensive scrubbing.
Liquefaction and Transport
Once purified, CO2 is usually liquefied for storage and transport. There are two main approaches.
The low-pressure method compresses and dries the CO2 to about 17 bar, then uses an external refrigeration system to cool it until it condenses. The high-pressure method compresses CO2 beyond its critical point (73.8 bar) and then cools it below its critical temperature of 31.1°C. In a common industrial design, CO2 is compressed in four stages up to 52 bar with cooling between each stage, then expanded through throttling valves to produce liquid CO2 at approximately -52°C and 6.5 bar.
Liquid CO2 is stored in insulated, pressurized tanks and transported by tanker truck, rail car, or pipeline. For some applications, the liquid is further cooled and solidified into dry ice pellets or blocks, which sublimate directly from solid to gas at -78.5°C under normal atmospheric pressure.
Which Sources Supply Which Markets
The commercial CO2 supply chain matches sources to end-use purity requirements. Ammonia and hydrogen plants provide the bulk of industrial-grade CO2, used for enhanced oil recovery, welding shielding gas, and chemical manufacturing. Ethanol and fermentation plants supply much of the food and beverage market because their CO2 is inherently cleaner. Natural gas processing plants contribute a steady stream, particularly in regions with large gas fields. Post-combustion capture is growing but still represents a smaller share, partly because the capture cost is higher and the gas requires more intensive cleanup.
Global commercial CO2 production totals roughly 230 million tons per year, though only a fraction of that is captured and sold. Most CO2 generated by industry is still vented to the atmosphere, meaning the commercial supply chain captures what the market demands rather than everything that’s available.