OXYGENATED HYDROCARBON-BASED AND HYDROCARBON-BASED CO2 SOLUBLE SURFACTANTS

摘要

The objectives of this work are to design, synthesize, and evaluate hydrocarbon-based or oxygenated hydrocarbon-based CO2 soluble surfactants. These surfactants would be able to form stable water-in-CO2 microemulsions with polar microenvironments capable of dissolving polar species in the bulk non-polar CO2 solvent, or to form metal precursors which can be reduced to nanoparticles in the presence of stabilizing ligands, or to generate foams in-situ for enhanced oil recovery application. Several oxygenated hydrocarbons, including acetylated sugars, poly(propylene glycol), oligo(vinyl acetate), and highly branched methylated hydrocarbons were used generate CO2-soluble ionic surfactants. Surfactants with vinyl acetate tails yielded the most promising results, exhibiting levels of CO2 solubility comparable to those associated with fluorinated ionic surfactants. For example, a sodium sulfate with single, oligomeric vinyl acetate (VAc) tails consisting of 10 VAc repeat units was 7 wt% soluble in CO2 at 25 oC and 48 MPa. Upon introduction of water to these systems, only surfactants with the oligomeric vinyl acetate tails exhibited spectroscopic evidence of a polar environment that was capable of solubilizing the methyl orange into CO2-rich phase. Silver bis(3,5,5-trimethyl-1-hexyl) sulfosuccinate, Ag-AOT-TMH, was synthesized from hydrocarbon-based ionic surfactant of sodium bis(3,5,5-trimethyl-1-hexyl) sulfosuccinate, Na-AOT-TMH through ion exchange. Ag-AOT-TMH exhibits 1.2 wt% solubility in dense CO2 at 40 oC and 52 MPa. Silver nanoparticles were produced by reducing the supercritical CO2 solution containing 0.06 wt% Ag-AOT-TMH and 0.5 wt% perfluorooctanethiol (stabilizing ligand) using a reducing agent of NaBH4. Iso-stearic acid, a short, stubby compound with branched, methylated tails, as a hydrocarbon-based nonionic surfactant, has been shown to have high solubility in carbon dioxide. The solvation of the tails by carbon dioxide has made isostearic acid sterically stabilize metallic nanoparticles as a ligand. The stability of CO2-water emulsion formed by ionic and nonionic surfactants was studied in CO2 at 22 oC and 34.5 MPa for 0.01-1.0 wt% surfactant mixed with equivalent volumes of CO2 and water. Emulsion stability was monitored by observing the rate of collapse of the white, opaque middle-phase emulsion between the transparent CO2 and water phases and the steady-state volume of the emulsion. It was found that at surfactant concentration of 0.01 wt%, oligo(vinyl acetate)10 sodium sulfate displayed the best emulsion, taking over 450 minutes to collapse.