INEXPENSIVE CO{sub 2} THICKENING AGENTS FOR IMPROVED MOBILITY CONTROL OF CO{sub 2} FLOODS

Abstract

The objective of this research was the design, synthesis and evaluation of inexpensive, nonfluorous carbon dioxide thickening agents. We followed the same strategy employed in the design of fluorinated CO 2 polymeric thickeners. First, a highly CO 2 -philic, hydrocarbon-based monomer was to be identified. Polymers or oligomers of this monomer were then synthesized. The second step was to be completed only when a CO 2 -soluble polymer that was soluble in CO2 at pressures comparable to the MMP was identified. In the second step, viscosity-enhancing associating groups were to be incorporated into the polymer to make it a viable thickener that exhibited high CO 2 solubility at EOR MMP conditions. This final report documents the CO 2 solubility of a series of commercial and novel polymers composed of carbon, hydrogen, oxygen and, in some cases, nitrogen.In the first section of the report, we demonstrate that poly(vinyl acetate), PVAc, is the most CO 2 soluble, inexpensive, commodity polymer that has yet been identified. The pressure required to dissolve PVAc in CO 2 was 6000 -9000 psia; thousands of psi greater than the range of MMP values. Therefore PVAc was not soluble enough in CO 2 to serve as the "base polymer" from which CO 2 thickeners would be developed. The next objective of this investigation was to determine if any polymer (composed of C, H, O, N and/or S) could exhibit CO 2 solubility greater than that of PVAc.The second section is a report on the comparison of CO 2 -philicity of oxygenated hydrocarbon side groups on a PDMS polymer. These side-functionalized PDMS polymers are not candidates for a CO 2 thickener because they contain silicon, nonetheless the PDMS backbone provides a highly CO 2 -soluble molecular framework onto which the side chains composed of C, H, O and N can be grafted. The side groups that interacted most favorably with CO 2 caused the functionalized PDMS molecule to have the greatest miscibility with CO 2 . These results provided a useful tool for comparing the CO 2 -philicity of various side chains, and the most promising side groups were incorporated into a polymer containing neither silicon nor fluorine. Both ethers and acetates appeared particularly promising. To date, these polymers have not been more CO 2 -soluble than PVAc.The third section is a report on a novel class of highly CO 2 soluble compounds known as sugar acetates. Low molecular weight sugar acetates are remarkably CO 2 soluble. Although we were successful in designing CO 2 soluble hydrogen bonding compounds, they were not capable of thickening the CO2. High molecular weight sugar acetate polymers, cellulose triacetate and peracetlyated xanthan gum, were insoluble in CO2.The fourth section is a report on a novel type of phase behavior that was discovered while studying the sugar acetates. Highly CO 2 -philic solids, including small molecules and polymers, can exhibit melting point depression in dense CO 2 , i.e. these solids melt instantly in dense CO 2 . This phenomenon is symptomatic of a favorable thermody...

Research Progress of Thickening Agents for Supercritical CO₂

“…Enick et al [21] researched solubility of some hydrocarbon polymer in CO 2 , and found that Poly(vinyl acetate)-PVAc had the highest solubility among those polymers. PVAc can dissolve in CO 2 at 298K and 13.6-67.6Mpa.They attributed CO 2 -philic property of PVAc to the the high free volume from ample side chain and interaction between acetate group and CO 2 .…”