After CO2 is captured, it often contains impurities depending on the capture method and source. These can include water vapor, hydrocarbons, sulfur compounds (such as H2S), and other gases like methane, carbon monoxide, nitrogen, or oxygen. Such impurities can limit the CO2’s usability or damage downstream equipment. Some examples of the CO2 purity requirements are provided below or better the allowable impurities.
Before purification begins, compression is typically the first crucial step. Compressing CO2 reduces its volume, making purification more energy-efficient and cost-effective. The compression required will be depending on the selected purification processes. For instance, pressure swing adsorption process would require typically 10-40 bar. The purification process usually starts with drying, as the presence of water can lead to the formation of carbonic acid, which is corrosive to pipelines, and freezing issues during liquefaction. This can be done prior to the compression or as during the subsequent compression steps which will require interstage cooling at which the water will come out. Clearly, this is very dependent on the humidity of the input material. At a certain stage drying is commonly done using molecular sieves, such as zeolites, or glycols solution, which are simple, reliable, and effective. Further purification techniques, such as activated carbon adsorption, cryogenic distillation or selective membrane separation can then be applied depending on the impurity profile. The purified CO2 then is liquified to significantly reduce its volume and facilitate storage and transportation.
Depending on the purification method, some processes, such as cryogenic distillation, can directly yield clean, liquefied CO2. This CO₂ is typically stored at around -20 °C and 20 bar, a preferred storage option due to its lower pressure requirements compared to gas cylinder storage. When purification does not involve conditions suitable for liquefaction, the CO2 can be subsequently liquefied using cooling water and compressing it to 50–60 bar. The resulting liquid CO2 can then be stored in high-pressure gas cylinders. Both cryogenic storage and cylinder bottling consume approximately 1 MJ of energy per kilogram of CO2. Each method has its own advantages and limitations depending on the intended application, storage infrastructure, and operational scale. Regardless of the approach, at least two compression stages with interstage cooling are typically required.
At FeyeCon, we specialize in CO2 purification, compressing, liquefying and storage. From in-house CO2 recycling systems for our supercritical CO2 technologies to custom-built liquefaction units and intermediate storage solutions, we deliver integrated and sustainable systems tailored to our clients’ operational needs.
