Date of Award


Document Type

Campus Access Dissertation


Chemical Engineering

First Advisor

Michael A. Matthews


Compressed carbon dioxide (CO2), both in the supercritical and sub-critical regions, may be envisioned as a cleaning solvent for the decontamination of biomaterials and medical devices. However, the use of CO2 in cleaning processes is limited due to its low solvent capacity for polar substances, such as proteins and biomolecules. This limitation can be overcome by adding small amounts of suitable surfactants. The strategy is to create a water-in-CO2 microemulsion phase to enhance the water content in CO2, and make it available for dissolving polar contaminants. This approach could out-perform traditional water-based cleaning processes, particularly for complex structures, since it should not be hampered by high surface tensions as occurs with water.

This dissertation evaluates the removal of E. coli endotoxin from smooth and porous titanium (Ti) surfaces and stainless steel (SS) lumens using compressed CO2 and CO2-based mixtures. Surfactant Ls-54 (a non-ionic and non-fluorinated surfactant) was incorporated to form water-in-CO2 microemulsions. It was found that the Ls-54 based microemulsion system in the liquid CO2 region (298 K and 27.6 MPa) removed 100% of the endotoxin from all the Ti surfaces and the SS lumens. Finally, a phase equilibrium study was performed to determine solubilities of surfactant Ls-54 in liquid CO2 and the molar water-to-surfactant ratios for the microemulsion system. Measurements were evaluated for a temperature range of 278.15 - 298.15 K using the static synthetic method. The study revealed that Ls-54 in CO2 has solubilities as high as 0.086 M at 278.15 K and 15.2 MPa. In addition, the Peng-Robinson equation of state (PREOS) with the van der Waals mixing rules were used to model the Ls-54/CO2 and water/CO2 binary systems. The PREOS model showed reasonable agreements with the experimental data for both Ls-54/CO2 and water/CO2 systems. These results confirm that liquid CO2 with additions of Ls-54 and water has great promise as a cleaning technique for biomaterials.