CO₂ Recovery from Ethanol Fermentation
Converting Fermentation Off-Gas into Commercial Liquid CO₂
Ethanol fermentation is one of the most attractive industrial sources for CO₂ recovery because the fermentation process naturally generates a CO₂-rich gas stream.
During fermentation, sugars are converted approximately according to:CO₂ recovery plant captures carbon dioxide from an industrial gas stream, removes contaminants, compresses and dries the gas, and finally converts it into purified gaseous or liquid CO₂ for reuse or commercial sale.
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂brewery fermentation, ethanol fermentation, molasses fermentation, chemical processes, biogas upgrading, dry ice production, or CO₂-rich industrial gas streams.
This means ethanol and CO₂ are produced simultaneously.
A typical YTC process is:
Fermentation Off-Gas → Washing → Compression → Purification → Drying → Adsorption → Liquefaction → Rectification → Liquid CO₂ Storage
What Is in Ethanol Fermentation CO₂?
Although the raw gas is CO₂-rich, it is not automatically food-grade.
Potential contaminants include:
- Water vapor
- Ethanol vapor
- Fermentation odors
- VOCs
- Oxygen and nitrogen from air ingress
- Foam and droplets
- Trace process contaminants
The purification system must therefore be designed around actual feed-gas analysis.
YTC Vietnam Project Example
One YTC engineering project for ethanol-fermentation off-gas was designed for approximately 21,000 tonnes per year of high-purity liquid CO₂.
The design basis was approximately 2,900 kg/h and 7,200 operating hours per year.91% CO₂ and 8% methane, requiring a different purification strategy from fermentation CO₂.
The process configuration incorporated:
Multi-Stage Water Washing → CO₂ Compression → Primary/Secondary Purification → Low-Temperature Dehydration → PSA Adsorption & Deodorization → Liquefaction → Rectification → Light-Component Recovery → Liquid CO₂ Storage
The storage section included three 100 m³ liquid CO₂ tanks.
The project design target was 99.998% CO₂ purity.
This illustrates an important point: ethanol fermentation CO₂ recovery is not simply a compressor plus liquefier. Product quality depends on the complete purification train.
The cleaned gas is compressed to the pressure required for downstream purification and liquefaction.
Compression is one of the major energy-consuming operations in a CO₂ recovery plant, making compressor selection, staging and cooling important to overall plant efficiency.
Step 4: Purification
Different feed gases require different purification technologies.
Depending on the project, YTC systems can incorporate:
- Multi-stage water washing
- Activated-carbon adsorption
- Molecular-sieve adsorption
- PSA purification
- Deodorization
- Impurity separation
- Final rectification
The objective is not simply to increase total CO₂ concentration, but to control individual contaminants according to the required product specification.
Step 5: Drying
Water must be removed before low-temperature liquefaction.
Residual moisture can freeze in low-temperature equipment and cause operating problems. Adsorption drying therefore provides the very low moisture level required for stable refrigeration and liquefaction.
Step 6: CO₂ Liquefaction
Purified and dried CO₂ is cooled under pressure until it condenses into liquid CO₂.
Non-condensable gases such as oxygen and nitrogen remain preferentially in the gas phase and can be separated during the liquefaction and purification process.
Step 7: Final Purification and Storage
Depending on product requirements, additional rectification or stripping can further remove light impurities.
The finished liquid CO₂ is then transferred to insulated storage tanks before being supplied to tankers, tank containers, dry ice systems or downstream users.
YTC systems can be engineered to produce CO₂ purity up to 99.998%, depending on feed-gas composition and process configuration.
YTC CO₂ Recovery Experience
YTC has executed more than 200 CO₂ treatment and recovery projects worldwide, covering fermentation, brewery, ethanol, industrial gas, flue gas and biogas applications.
Its engineering capability ranges from approximately 80 kg/h to 20,000 kg/h, allowing the process to be configured for both relatively small recovery systems and large industrial plants.
The fundamental principle remains the same:
Capture CO₂ that would otherwise be lost, remove the contaminants, convert it into a usable product, and return that CO₂ to the industrial value chain.
