The technical objectives of this proposal are to develop, demonstrate, and evaluate a liquid CO₂ (LCO₂) fabric cleaning technology for application to the cleaning of DoD generated hazardous cleaning rags. The most promising candidate technology to accomplish this objective is the use of liquid CO₂ (LCO₂) with surfactant additives. The economics of LCO₂ /surfactants systems will be critically dependent on recovery and separation of surfactants, CO₂, and contaminants. LCO₂ has no associated environmental impacts and few safety concerns: it is non-hazardous, non-flammable, non-ozone-depleting, and non-toxic. Thus, there are none of the concerns which might be found with conventional cleaning technologies using organic solvents or aqueous solutions. Also, a system using liquid phase CO₂ is expected to be less destructive to fabrics. Finally, there is no pollution control process cost associated with achieving environmental compliance using the potential LCO₂ technology.

The initial focus of the program will be using CO₂ in the liquid phase, and not supercritical phase, unless research directions dictate a technical efficiency in the supercritical. Some studies outlined in the references on the use of CO₂ indicate that the use of CO₂ in the liquid phase will present a more efficient system for the cleaning of fabrics. A system operating in the liquid phase will present a more efficient system for the cleaning of fabrics. A system operating in the liquid phase is expected to be less destructive to fabrics and clothing as well as to attachments, such as buttons on work clothing.

The major objective during the FY98 Phase I portion of the program will be to conduct and complete research to design and synthesize LCO₂ compatible amphiphilic surfactants. The proposed surfactants will have a micelle-forming capability to emulsify lipophilic contaminants within a continuous LCO₂ phase. These surfactant systems must be applicable to a broad range of contaminants which will be defined by the potential users.

The chemical design philosophy of the candidate, micelle-forming surfactants to be synthesized during the Phase I effort is based upon results of surfactant research investigations recently published by Dr. J. DeSimone at the University of North Carolina. To date, two nonionic, amphiphilic copolymers have been synthesized. Accordingly, families of these amphiphilic surfactants will be tailored to meet the specific requirements necessary to emulsify and displace the contaminants typically found in industrial rags.

The use of CO₂ in the supercritical phase is a proven technology for certain applications such as precision metal cleaning and solid waste decontamination, or where the contaminant is primarily light organic compounds and non-particulate. However, LCO₂ has yet to be proven for fabric cleaning, or for military cleaning requirements which contain heavy molecular weight organic compounds, inorganic salts, metal oxides, proteins, and solid matter.

A survey was completed in March 1998 by the project team to establish the magnitude of the rag contamination and disposal problem. This assessment concluded that over 7 million pounds of rags are generated each year by the military services. The cost of rag waste disposal is estimated to be more than 24 million dollars. The project team also completed a preliminary rag pollutant identification and characterization assessment. This information is required to assist researchers in developing the correct surfactant formulation to address the cleaning requirements presented by DoD waste products. At the direction of the SERDP Science Advisory Board, a preliminary cost benefits analysis was completed by the project team. This analysis indicated that the 10 year cost savings can be as much as $360,000,000 in waste disposal savings and decreased purchases.

If contaminants contained on the rags can be removed successfully and collected, the rags can be recycled back to the operation and will eliminate rags as a source of hazardous waste pollution from DoD and related facilities.

A 1996 study, conducted for the Chief of Naval Operations, found that a minimum of $5M in rags are procured each year by the U.S. Navy for U.S. based facilities. This study did not include shipboard or foreign facilities. A major part of these rags is disposed of as hazardous waste at a disposal cost estimated to be in excess of $7M. This estimate results in an annual rag procurement and disposal cost for the U.S. Navy in excess of $12M. Rags generated on ships and at foreign facilities are required by many host countries to be transported back to the U.S. for disposal. It is reasonable to assume that an equal amount of rags are procured and disposed of by the remaining military Services. This would result in an additional $24M in rag procurement and disposal cost for U.S. military services. The estimated cost savings in rag procurement and disposal for all U.S. military Services is therefore estimated at more that $360M over a 10-year period.