Robert M. Enick

CO2 SOLUBILITY IN WATER AND BRINE UNDER RESERVOIR CONDITIONS

The reference Henrys constant was determined from 110 solubility data found in the literature for the CO2/H2O system over a temperature range of 298 to 523 K and a pressure range of 3.40 to 72.41 MPa. Since the Krichevsfcy-llinskaya equation was used to model the system, a correlation for the A parameter was also developed. In addition to the Krichevsky-Ilinskaya equation, another two-parameter correlation for the solubility of carbon dioxide in water was obtained by using the Krichevsky-Kasarnovsky equation. The reference Henrys constant and partial molar volume of carbon dioxide at infinite dilution were treated as adjustable parameters. The calculated values of the partial molar volume at infinite dilution did not correspond to experimentally determined values found in the literature. Therefore, a third correlation for the reference Henrys constant was obtained by using the Krichevsky-Kasarnovsky equation in conjunction with the correct values of the partial molar volume. This one parameter (Henrys...

The incorporation of a fluorinated ether functionality into a polymer or surfactant to enhance C02-solubility

Abstract A repeating fluorinated ether functional group, (hexafluoropropylene oxide) n , can enhance the solubility of compounds in dense carbon dioxide. A perfluorinated alkylpolyether which incorporates hexafluoropropylene oxide as the repeating unit, F(CF 3 CFCF 2 O) n C 2 F 5 , forms the most CO 2 -soluble polymers observed to date. The liquid-liquid dew point locus at 295 K of a poly(hexafluoropropylene oxide) (MW = 13,000)/carbon dioxide system was found to increase steadily with polymer concentration over the 1–10 wt % range, reaching a saturation pressure of only 17 MPa at 10 wt %. CO 2 -soluble surfactants were also made by replacing the hydrocarbon carboxylate tails of CO 2 -in-soluble surfactants with perfluoroalkylpolyether carboxylates. Nonionic surfactants, poly(hexafluoropropylene oxide) carboxylic acid (MW = 2,500) and hydroxyaluminum bis[poly(hexafluoropropylene oxide) carboxylate] (MW = 5,000), and an anionic surfactant, sodium poly(hexafluoropropylene oxide) carboxylate (MW = 2,500), exhibited complete miscibility with CO 2 at 313 K at pressures above 16 MPa. Despite the high bulk viscosity of the polymeric fluorinated oil (7,000 mpa-s at 293 K) and the associative thickening potential of hydroxyaluminum disoaps, no increases in solution viscosity, relative to pure CO 2 , greater than 10% were detected.

Phase behavior of fluoroether-functional amphiphiles in supercritical carbon dioxide

Abstract The observed low solubility of hydrophilic compounds in non-polar C02 can limit applications of supercritical-fluid technology in some high growth industries, such as biotechnology. Reverse micelle formation offers a means to overcome low solubility of hydrophilic compounds in carbon dioxide, yet commercially-available ionic surfactants exhibit relatively poor solubility in C02 at moderate pressures. Synthesis of amphiphiles containing functional groups which are known to interact favorably, in a thermodynamic sense, with carbon dioxide offers a potential solution to this problem. Our results with fluoroether-functional amphiphiles show this to be a valid premise. Apparently, there are several competing effects that determine the solubility of these materials in carbon dioxide: increasing molecular weight tends to drive the cloud-point curve to higher pressures, yet, addition of C0 2 -philic fluoroether groups and branching of the C0 2 -philic tails works to depress the cloud-point curve to lower pressures. Further, increasing the polarity of the polar head group induces the cloud-point curve to move to higher pressures. Finally, we have shown that fluoroether-functional amphiphiles permit extraction of thymol blue from aqueous solution into carbon dioxide.

Effect of structure on the cloud-point curves of silicone-based amphiphiles in supercritical carbon dioxide

Abstract The use of surfactants in nonpolar supercritical fluid (SCF) systems helps to increase solvating power of the SCF. Although C02 is the most widely used SCF, many commercially available surfactants generally exhibit poor solubility in this fluid. Our goal is to design and synthesize amphiphiles that are both functional and highly CO 2 -soluble, and evaluate the relationship between structure and solubility. The basis of the design involves the synthesis of molecules whose hydrophobic groups interact favorably, in a thermodynamic sense, with CO 2 while the hydrophilic group(s) interacts with the chosen solute (water, polar molecules, metals). In this work, we will explore the relationship between structure and solubility of silicone-based amphiphiles in CO 2 via high-pressure phase-behavior experiments. The phase-behavior results clearly indicate that the silicone-based amphiphiles exhibit high CO 2 solubility at temperatures of 313 K and pressures below 40 MPa.

Critical and three phase behavior in the carbon dioxide/tridecane system

The PT behavior of the carbon dioxide/normal alkane series exhibits a distinct transition in the CO2/nC13H28 system. This particular diagram is characterized by two liquid—liquid—vapor (l-l-g) loci, a lower liquid-upper liquid (l-l) critical branch extending from high pressures to the upper critical end point (UCEP) and two liquid—vapor (l-g) critical branches which cross near the lower critical end point (LCEP). An experimental PTx diagram in the vicinity of the CO2 critical point, LCEP and K point reveals the emergene at the LCEP of a l-l region which increases in size with temperture while the upper liquid—vapor (L2-g) region diminishes, eventually disappearing at the K point. The l-l-g surface illustrates the compositional changes of each phase with temperture. Detailed Px diagrams at three temperatures between the LCEP and K point are presented and each exhibits two critical points, a l-l-g locus and curves of constant phase volume ratio which show discrete changes in both value and slope at the l-l-g locus. Graphical and numerical methods of determining the phase densities and compositions from three phase volumetric behavior are presented.

Highly carbon dioxide soluble surfactants, dispersants and chelating agents

Several CO 2 -soluble compounds have been designed and synthesized in an attempt to broaden the spectrum of processes that can employ carbon dioxide as a solvent. A highly CO 2 -Philic fluorinated polyether tail was incorporated into each of these amphiphilic compounds. Chelating agents, copolymers, sorbitol esters, and surfactants were prepared for applications including heavy metal extraction, dispersion polymerization, protein extraction, and the formation of CO 2 /water emulsions, respectively. The results indicate that at near-ambient temperature and pressures between 10 and 30 MPa, the solubility of these compounds ranged from 1 mmole/li CO 2 to complete miscibility. Favorahle preliminary results were also realized when these compounds were dissolved in dense CO 2 and used in their proposed applications. These results include metal removal efficiencies of up to 98%, polymerization products with molecular weights of 110,000-140,000 for PMMA and 10,000,000 for polyacrylamides, extraction of proteins from aqueous solutions, and the formation of stable emulsions of water in a continuous CO 2 phase.

Rod-like micelles thicken CO2

A new approach to thicken dense liquid CO(2) is described using the principles of self-assembly of custom-made CO(2) compatible fluorinated dichain surfactants. Solutions of surfactants in CO(2) have been investigated by high-pressure phase behavior, small-angle neutron scattering (HP-SANS) and falling cylinder viscosity experiments. The results show that it is possible to control surfactant aggregation to generate long, thin reversed micellar rods in dense CO(2), which at 10 wt % can lead to viscosity enhancements of up to 90% compared to pure CO(2). This represents the first example of CO(2) viscosity modifiers based on anisotropic reversed micelles.

Aminosilicone Solvents for CO2 Capture

This work describes the first report of the use of an aminosilicone solvent mix for the capture of CO(2). To maintain a liquid state, a hydroxyether co-solvent was employed which allowed enhanced physisorption of CO(2) in the solvent mixture. Regeneration of the capture solvent system was demonstrated over 6 cycles and absorption isotherms indicate a 25-50 % increase in dynamic CO(2) capacity over 30 % MEA. In addition, proof of concept for continuous CO(2) absorption was verified. Additionally, modeling to predict heats of reaction of aminosilicone solvents with CO(2) was in good agreement with experimental results.

Design and evaluation of nonfluorous CO2-soluble oligomers and polymers

Ab initio molecular modeling is used to design nonfluorous polymers that are potentially soluble in liquid CO2. We have used calculations to design three nonfluorous compounds meant to model the monomeric repeat units of polymers that exhibit multiple favorable binding sites for CO2. These compounds are methoxy isopropyl acetate, 2-methoxy ethoxy-propane, and 2-methoxy methoxy-propane. We have synthesized oligomers or polymers based on these small compounds and have tested their solubility in CO2. All three of these exhibit appreciable solubility in CO2. At 25 degrees C, oligo(3-acetoxy oxetane)6 is 5 wt % soluble at 25 MPa, the random copolymer (vinyl methoxymethyl ether30-co-vinyl acetate9) is 5 wt % soluble at 70 MPa and random copolymer (vinyl 1-methoxyethyl ether30-co-vinyl acetate9) is 3 wt % soluble at 120 MPa. These oligomers and polymers represent new additions to the very short list of nonfluorous CO2-soluble polymers. However, none of these are more soluble than poly(vinyl acetate), which exhibits the highest CO2 solubility of any known polymer containing only the elements C, H, and O.

‘Gel’ formation in carbon dioxide-semifluorinated alkane mixtures and phase equilibria of a carbon dioxide-perfluorinated alkane mixture

Abstract A ‘gel’ has been observed in mixtures of dense carbon dioxide and semifluorinated alkanes. This gelation occurred when a liquid-vapor binary solution was isothermally expanded at ambient temperature until three-phase S-L-V equilibria was established. The solid phase formed microfibers which become interlocked in disarray with liquid CO 2 in the cavities. The ‘gel’ was actually the combined solid and liquid phases. This reversible ‘gel’ was observed in the CO 2 /F 12 H 8 , CO 2 /F 12 H 16 , and CO 2 /F 10 H 10 systems, but not in the CO 2 /F 12 H 2 O binary system due to the low solubility of this compound in liquid CO 2 . Phase equilibria results of the carbon dioxide-perfluorohexane system were also reported. These pressure-composition diagrams were compared to those of the carbon dioxide-hexane binary at two temperatures in order to illustrate that the fluorination of an alkane enhances its miscibility with carbon dioxide.