Every commercial CO₂ buyer has the same question when they evaluate a new supply source: what is the purity? For beverage producers, that question is existential. The CO₂ going into a can of soda or a keg of beer has to meet the ISBT (International Society of Beverage Technologists) specification, which defines allowable limits for dozens of individual contaminants. Miss the spec on any one of them and the product is unusable.
Cryogenic purification is the technology that consistently gets raw CO₂ across that threshold. Not because it is new or exotic, but because the underlying physics give it an inherent advantage that other purification methods struggle to match.
What Raw CO₂ Actually Looks Like
CO₂ captured from industrial sources is not pure. It never is. A raw stream coming off an RNG upgrader or fermentation process typically contains water vapor, hydrogen sulfide, ammonia, volatile organic compounds, siloxanes, and trace amounts of other gases that were present in the original feedstock. Depending on the source, the raw CO₂ concentration might be anywhere from 40% to 98%, with the balance being nitrogen, oxygen, methane, and whatever else was in the waste gas.
Most of those contaminants exist in small concentrations. Parts per million or even parts per billion. But the ISBT spec has limits at those same levels. Total sulfur under 0.1 ppm. Acetaldehyde under 0.2 ppm. Total hydrocarbons under 50 ppm calculated as methane. Hitting those targets requires removing trace amounts of specific compounds from an already concentrated CO₂ stream. That is a harder engineering problem than it sounds.
The Physics of Cryogenic Separation
Cryogenic purification works by exploiting the fact that different compounds change phase at different temperatures. CO₂ has a triple point at negative 56.6°C. Below that temperature (at atmospheric pressure), it exists as a solid. Above it, depending on pressure, it transitions between liquid and gas. The contaminants mixed in with the CO₂ have their own phase transition temperatures, and most of them are significantly different from CO₂'s.
By compressing the raw gas stream and then cooling it through a series of heat exchangers and separation columns, a cryogenic system forces the CO₂ to condense into liquid while many contaminants remain in the gas phase. Those gas phase impurities are vented off. The liquid CO₂ is then further distilled to remove dissolved contaminants, with heavier compounds settling to the bottom and lighter ones rising to the top.
It is the same principle that refineries use to separate crude oil into its component products. Different boiling points, different phases, physical separation. No chemical reagents. No solvents. No consumable media that degrades over time.
Why Temperature Control Matters for Purity
The advantage of cryogenic systems is precision. Temperature and pressure are continuous, controllable variables. An operator can dial in exact conditions that maximize CO₂ recovery while pushing contaminant concentrations below detectable levels. This is fundamentally different from adsorption or scrubbing systems where performance degrades as the media saturates or the solvent accumulates impurities.
In a well designed cryogenic column, the liquid CO₂ product coming off the bottom has gone through multiple theoretical stages of separation. Each stage provides another opportunity for trace contaminants to partition into the gas phase and exit the system. The result is CO₂ purity levels above 99.99% with individual contaminant concentrations consistently below ISBT limits.
This is not a best case scenario. It is the normal operating condition. Cryogenic systems produce beverage grade CO₂ as a matter of physics, not as a matter of luck or careful batch management.
Comparing Approaches
Chemical absorption systems, typically amine based, capture CO₂ by binding it to a solvent. The CO₂ is then released by heating the solvent. These systems are effective for capturing CO₂ from low concentration flue gas streams, but the released CO₂ carries traces of the solvent and its degradation products. Getting that CO₂ to beverage grade usually requires a secondary polishing step.
Membrane systems separate gases based on selective permeability. They work well for bulk separation but lack the precision to hit ISBT trace contaminant limits without additional downstream cleanup.
Activated carbon beds and molecular sieves can remove specific contaminants, but they saturate and need regeneration or replacement. Performance drifts between maintenance cycles. For a beverage grade application where consistency is non-negotiable, that drift is a real operational concern.
Cryogenic purification handles bulk separation and trace contaminant removal in a single integrated process. The product comes off the column ready for certification without additional polishing or media replacement. That simplicity translates directly into reliability.
What This Means at the Facility Level
At our Lewiston, North Carolina facility, we operate a patent pending cryogenic purification system that processes the CO₂ stream from an adjacent RNG upgrader. The raw gas comes in with the full cocktail of biogas contaminants: sulfur compounds, siloxanes, VOCs, moisture. It leaves as FDA registered, ISBT compliant, beverage grade liquid CO₂.
The system runs continuously. It does not require batch processing, media replacement, or solvent management. Purity is monitored in real time, and because the separation physics are deterministic, the product quality is predictable. There are no surprises at the analytical lab.
This matters for buyers who need to commit to supply contracts. A beverage producer signing a multi-year CO₂ supply agreement needs confidence that the source will deliver consistent quality every load, every month. Cryogenic purification provides that confidence because the underlying mechanism does not degrade.
The Broader Opportunity
The U.S. has hundreds of RNG facilities, ethanol plants, and anaerobic digesters producing concentrated CO₂ streams that are currently vented to the atmosphere. The barrier to turning those streams into commercial products has always been purification. Getting from raw gas to beverage grade is hard, especially at smaller distributed sites where the economics of traditional purification systems do not work.
Cryogenic systems that are purpose built for distributed deployment change that calculation. A modular cryogenic unit co-located at an RNG facility can convert a waste stream into a revenue generating product without the complexity of chemical handling or the ongoing cost of consumable media. The capital intensity is higher upfront, but the operating cost profile is fundamentally better over the life of the equipment.
Every new cryogenic purification facility that comes online adds another source of verified beverage grade CO₂ to the domestic supply chain. That is how you build resilience: not by making existing sources bigger, but by creating new independent sources at facilities that already have the raw material.
The technology works. The feedstock exists. The market needs the product. The only question is how fast we build.
