NOVEL CO2-THICKENERS FOR IMPROVED MOBILITY CONTROL
The first carbon dioxide thickeners have been successfully designed. Each thickener is characterized by a highly carbon dioxide-phobic functionality that imparts CO{sub 2}-solubility and a carbon dioxide-phobic group that facilitates viscosity-enhancing intermolecular associations. The design of each thickener required that appropriate balance of these groups to yield a compound that was at least several weight percent soluble in CO{sub 2} and capable of thickening the carbon dioxide by a factor of 2-20. Four types of thickeners were identified, fluoroacrylate-styrene copolymers (polyFAST), fluorinated telechelic ionomers, semi-fluorinated trialkyltin fluorides and small, fluorinated hydrogen-bonding compounds. Although significant viscosity increases (e.g. doubling the viscosity) were evidenced for each thickener during falling cylinder viscometry analysis, the polyFAST thickener provided the most dramatic increases at dilute concentration. PolyFAST is a bulk-polymerized, random copolymer of fluoroacrylate and styrene with a number-average molecular weight of about 500,000. It appears as a white, slightly waxy solid at ambient conditions. The fluoroacrylate enhances the CO{sub 2} solubility, while the styrene promotes intermolecular stacking of the aromatic groups. Although concentrations between 20-29 mol% styrene yield a thickener, the optimal composition of polyFAST for thickening was 29mol% styrene and 71mol% fluoroacrylate. Mobility measurements with a Berea sandstone core indicated that at a superficial velocity of one foot per day, a 0.5wt% concentration of 29%styrene--71%fluoroacrylate polyFAST tripled the viscosity. At concentrations of 1% and 1.5wt%, the CO{sub 2} viscosity increased by a factor of 8 and 19, respectively. If lower proportions of styrene are used, the compound will dissolve more readily in carbon dioxide but the viscosity enhancement will diminish. At higher proportions of styrene, the CO{sub 2} solubility decreases and the thickening capability also decreased, apparently due to the increased number of non-viscosity enhancing intramolecular interactions between the aromatic groups. The high price, environmental persistence, and lack of availability of bulk amounts of the fluoroacrylate monomer guided our final efforts of this work (and all of our efforts in its continuation) toward the development of inexpensive non-fluorous compounds. We have therefore initiated the design highly CO{sub 2} soluble polymers that can replace the fluoroacrylate. These hydrocarbon-based CO{sub 2}-philic compounds will then be incorporated into the structure of a compound that contains CO{sub 2}-phobic associating groups, yielding a commercial thickener.
- Research Organization:
- University of Pittsburgh (US)
- Sponsoring Organization:
- (US)
- DOE Contract Number:
- AC26-98BC15108
- OSTI ID:
- 825007
- Resource Relation:
- Other Information: PBD: 1 Oct 2001
- Country of Publication:
- United States
- Language:
- English
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Novel CO{sub 2}-thickeners for improved mobility control
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