IDENTIFICATION, DESIGN AND SYNTHESIS OF OXYGENATED HYDROCARBON-BASED CO2-SOLUBLE POLYMERS FOR CHEMICAL AND PETROLEUM ENGINEERING APPLICATIONS

摘要

Over the past two decades the use of near-/super-critical carbon dioxide has received much attention as a green alternative to organic solvents for chemical reactions, separations, and extractions because of its pressure-tunable physicochemical properties and economic advantages. However the advantages are diminished because of a relative narrow range of CO2-soluble materials. The goal of this work is to identify, design and synthesize oxygenated hydrocarbon-based CO2-soluble polymers that are able to serve as construction blocks for copolymers, dispersants, surfactants, thickeners, and chelating agents. Without concerning on the cost and the environmental persistence like fluorinated materials, the inexpensive, environmentally benign materials would significantly enhance the viability of near-/super-critical carbon dioxide-based technology. Based on both experimental heuristics and ab initio simulation results of molecular modeling (performed by Dr. Johnson's group), we proposed specific new polymer structures: poly(3-acetoxy oxetane) (PAO), poly(vinyl methoxymethyl ether) (PVMME), poly(vinyl 1-methoxyethyl ether) (PVMEE), and cellulose triacetate (CTA) oligomers. Phase behavior studies were also performed with novel CO2-philic compounds containing vinyl acetate, propylene glycol, or multiple tert-butyl groups. PAO, PVMME and PVMME were soluble in CO2, but not as soluble as poly(vinyl acetate). Oligomers of cellulose triacetate with as many as four repeat units solubilized into dense CO2 less than 14 MPa in the concentration range of 1-5 wt%. Phase behaviors of more than thirty compounds in dense CO2 were studied in this project. A new type of phase behavior for solid (at ambient temperature) CO2-philes that melt and dissolve in CO2 was detailed using a model binary mixture of β-D-maltose octaacetate and CO2. Copolymers of tetrafluoroethylene (TFE) and vinyl acetate (VAc) exhibited lower miscibility pressures than either of the homopolymers, probably due to quadradentate binding configurations with CO2. Phase behavior investigation of poly(propylene glycol) (PPG) monobutyl ether in CO2 demonstrated ether-CO2 interactions should receive as much attention as carbonyl-CO2 interactions when designing CO2-philic functional groups. 1,3,5-tri-tert-butylbenzene and tri-tert-butyl-phenol were both extraordinarily soluble in CO2, and are excellent candidates for CO2-soluble sand binders. In summary, although a new CO2 thickener was not identified, new non-fluorous CO2-soluble materials were identified that were, in general, acetate-rich with flexible chains, weak self-interactions, and multidentate interaction between CO2 and solute functional groups.