Why is CO2 Service a One-Way Trip?

Liquid Nitrogen, Oxygen and Argon are typically produced by cooling atmosphere in air separation units to levels below their boiling points. In a form of reverse distillation, the gases liquefy and are collected as relatively pure products. Due to their purity and absence of residual contamination it is common for liquid cylinders or bulk tanks to be used for one product and switched to another following purging and testing.

Liquid carbon dioxide (CO2), on the other hand, is usually collected as a byproduct of manufacturing other products. Depending on the specific grade of CO2, trace levels of non-volatile organic residue (oil and grease) and total volatile hydrocarbons are common and tend to linger after the CO2 product is vaporized and used.

Conscientious gas producers, distributors and service companies go to great pains to avoid the potential for mixing oils, grease and hydrocarbons with pure oxygen. In turn, it is generally deemed unacceptable to convert a liquid CO2 vessel to any other service. It is just not possible to verify complete cleanliness of a vessel after it has been in CO2 service and there is not an acceptable level of risk above zero when it comes to oxygen possibly coming in contact with flammable and/or explosive residue.