Brantley, N.H., Bush, D., Kazarian, S.G., and Eckert, C.A., Spectroscopic measurement of solute and cosolvent partitioning between supercritical CO2 and polymers. Journal of Physical Chemistry B, 1999. 103 (45): p. 10007-10016.
Cosolvents exhibit significant effects on the partitioning behavior of dilute solutes between a supercritical CO2 fluid phase and cross-linked siloxane-based polymers. A spectroscopic technique was developed and applied that allows us to measure the partition coefficients of both the cosolvents and solutes between the two phases. The Sanchez-Lacombe lattice fluid equation of state was extended to represent a two-phase, four-component system and was quantitatively successful in representing the volumetric and phase-equilibria properties of such systems. We then apply the model and our data to investigate the magnitudes of stationary-phase effects in supercritical fluid chromatography and explore opportunities to use the model for a priori prediction of separation.
Thompson, R.L., Glaser, R., Bush, D., Liotta, C.L., and Eckert , C.A. , Rate variations of a hetero-Diels-Alder reaction in supercritical fluid CO2. Industrial & Engineering Chemistry Research, 1999. 38 (11): p. 4220-4225.
The hetero-Dials-Alder reaction between anthracene and excess 4-phenyl-1,2,4-triazoline-3,5-dione has been investigated in supercritical CO2 at 40 degrees C and pressures between 75 and 216 bar. Bimolecular reaction rate constants have been measured via fluorescence spectroscopy by following the decrease in anthracene concentration with reaction time. The reaction rate is elevated in the vicinity of the critical pressure. This difference is consistent with local composition enhancement and can be modeled with the Peng-Robinson equation of slate.
Brown, J.S., Lesutis, H.P., Lamb, D.R., Bush, D., Chandler, K., West, B.L., Liotta, C.L., Eckert, C.A., Schiraldi, D., and Hurley, J.S., Supercritical fluid separation for selective quaternary ammonium salt promoted esterification of terephthalic acid. Industrial & Engineering Chemistry Research, 1999. 38 (10): p. 3622-3627.
We report the selective removal of a desired reaction intermediate with a supercritical fluid in a new synthesis route to poly(ethylene terephthalate), avoiding ethylene glycol. We have successfully catalyzed the esterification of terephthalic acid with ethylene oxide in a supercritical fluid with a series of quaternary ammonium salts to form mono(2-hydroxyethyl terephthalate). This desired monoester was removed from the involatile bed of terephthalic acid and catalyst by continuous extraction with supercritical fluid before subsequent reaction to the diester could take place.
Castells, C.B., Carr, P.W., Eikens, D.I., Bush, D., and Eckert , C.A. , Comparative study of semitheoretical models for predicting infinite dilution activity coefficients of alkanes in organic solvents. Industrial & Engineering Chemistry Research, 1999. 38 (10): p. 4104-4109.
Five nonelectrolyte solution models are used to predict infinite dilution activity coefficients (gamma(infinity)) of five linear, four branched, and two cyclic alkanes in 67 solvents at 25 degrees C, and the results are compared with experimental data. The models use two distinct approaches to the prediction of gamma(infinity). The solution of groups concept provides the basis for three versions of the UNIFAC model: original UNIFAC, gamma(infinity)-based UNIFAC, and modified UNIFAC ( Dortmund ). The MOSCED and the SPACE models avoid the group concept and use only pure component parameters. For a database of 737 Limiting activity coefficients, the SPACE model gave an average absolute error of 8.1%, and in only 13.3% of the cases were the errors worse than 15%. The modified UNIFAC model gave an absolute average error of 9.8%, and 32% of the predicted gamma(infinity) had errors larger than 15%. The SPACE approach also produced the most reliable estimations over a wide range of activity coefficient values.
Lesutis, H.P., Glaser, R., Liotta, C.L., and Eckert , C.A. , Acid/base-catalyzed ester hydrolysis in near-critical water. Chemical Communications, 1999(20): p. 2063-2064.
Hydrolyses of substituted benzoic acid esters in near-critical water (250-300 degrees C) show autocatalytic kinetic behavior and surprisingly give the same rate constant regardless of substituent, suggesting that an acid-catalyzed mechanism predominates under our reaction conditions.
Jones, J.R., Liotta, C.L., Collard, D.M., and Schiraldi, D.A., Cross-linking and modification of poly(ethylene terephthalate-co-2,6-anthracenedicarboxy by Diels-Alder reactions with maleimides. Macromolecules, 1999. 32 (18): p. 5786-5792.
Poly(ethylene terephthalate) (PET) copolymers containing 2,6-anthracenedicarboxylate structural units are modified by Diels-Alder reactions with maleimides. Low molecular weight bis(maleimide)s are used to chain extend and cross-link the polymers. The resulting materials were characterized by H-1 NMR, UV-vis, DSC, and dilute solution viscometry. The Diels-Alder reaction of low molecular weight anthracenes and maleimides is thermally reversible at 250 degrees C. However, the reverse reaction is slow, and the PET-anthracene copolymers are prone to thermal decomposition at; these higher temperatures.
Connor, D.M., Collard, D.M., Liotta, C.L., and Schiraldi, D.A., Difunctional pyrene derivatives as fluorescent brightening agents for condensation polymers. Dyes and Pigments, 1999. 43 (3): p. 203-206.
Dimethyl esters of four pyrene dicarboxylic acids were synthesized and incorporated into poly(ethylene terephthalate). The spectroscopic properties of the polymers and monomers are assessed for their effectiveness and potential as covalently-bound fluorescent brightening agents. (C) 1999 Elsevier Science Ltd. All rights reserved.
Kazarian, S.G., Brantley , N.H. , and Eckert , C.A. , Applications of vibrational spectroscopy to characterize poly(ethylene terephthalate) processed with supercritical CO2. Vibrational Spectroscopy, 1999. 19 (2): p. 277-283.
FT-IR and FT-Raman spectroscopy have been applied to elucidate the morphology and structure of poly(ethylene terephthalate) (PET) processed with supercritical CO2 (scCO(2)). Infrared and Raman spectra of PET samples show an increased degree of crystallinity after being subjected to scCO(2). FT-Raman spectroscopy has also been utilized to study the supercritical dyeing of PET samples with azo dyes. These results may aid optimization of 'solvent-free' processes for advanced processing of packaging materials and supercritical fluid dyeing of textiles. (C) 1999 Elsevier Science B.V. All rights reserved.
Scott, L., Bush, D., Brantley , N.H. , and Eckert , C.A. , Development and evaluation of a more precise excess Gibbs energy expression for vapor-liquid and liquid-liquid phase behavior. Industrial & Engineering Chemistry Research, 1998. 37 (11): p. 4512-4519.
The rational design of separations in multicomponent systems depends on the quality of vapor-liquid equilibrium (VLE) data and the precision to which these data can be represented. In recent years, new experimental techniques have begun to yield better quality VLE data. Often these data warrant the use of more than two parameters per binary pair, which is common in the empirical Gibbs energy of mixing expressions used to represent such data. In this work, we propose two new expressions for representing the Gibbs free energy of mixing: the four parameter Scott-Wilson and the five parameter Scott-Regular Solution-Wilson. A method for evaluating such expressions is presented, including our proposed technique of predicting gamma(infinity) in a mixed solvent from binary data only. For this, we measured gamma(infinity) in a mixed solvent system using differential ebulliometry.
Bush, D. and Eckert , C.A. , Prediction of solid-fluid equilibria in supercritical carbon dioxide using linear solvation energy relationships. Fluid Phase Equilibria, 1998. 151 : p. 479-492.
Solid-fluid equilibria are important for supercritical fluid processing design. Few data are available, and predictions require a model for the solute-solvent interactions. An activity coefficient model for solids in supercritical CO2, based on linear solvation energy relationships, is developed. The model fits solubility data at liquid-like densities to an average error of 65%. Extrapolations to gas-like densities are shown. (C) 1998 Elsevier Science B.V. All rights reserved.
Dillow, A.K., Brown, J.S., Liotta, C.L., and Eckert , C.A. , Supercritical fluid tuning of reactions rates: The cis-trans isomerization of 4-4 '-disubstituted azobenzenes. Journal of Physical Chemistry A, 1998. 102 (39): p. 7609-7617.
Remarkable tuning of reaction rates has been achieved for the isomerization of several dye molecules in supercritical fluid solvents using both small pressure changes and small additions of cosolvents. Rates of the thermal cis-trans relaxation were measured spectroscopically following irradiation for three dyes in supercritical carbon dioxide and ethane, pure and with several polar and protic cosolvents. The results are explained in terms of local density and composition enhancements, as well as by a change of mechanism due to strong hydrogen bonding. This study demonstrates the versatility of supercritical fluid solvents both to examine reaction mechanisms and as a means to tune rates.
Chandler , K., Liotta, C.L., Eckert , C.A. , and Schiraldi, D., Tuning alkylation reactions with temperature in near-critical water. Aiche Journal, 1998. 44 (9): p. 2080-2087.
Quantitative kinetics for the alkylation reactions of phenol and p-cresol with tert-butyl alcohol in near-critical water as a function of temperature are reported The reaction products of the alkylation reactions were ortho- and para-substituted phenols, which are used extensively as antioxidants in numerous polymer systems. A new experimental reaction apparatus was designed, constructed, and successfully operated to allow pressure central and sampling of the reaction systems which provided rate constants in the temperature range 250 - 300 degrees C. Additionally, activation energies and heats of formation were calculated from the temperature dependence of the rate constants, and ortho-substitution was found to be exothermic whereas para-substitution was found to be endothermic. These results demonstrate that product distribution of the alkylation reactions could be tuned with temperature to produce specific products.
Kazarian, S.G., Vincent, M.F., West, B.L., and Eckert , C.A. , Partitioning of solutes and cosolvents between supercritical CO2 and polymer phases. Journal of Supercritical Fluids, 1998. 13 (1-3): p. 107-112.
In situ Fourier transform IR and UV-vis spectroscopy have been used for partitioning of solutes between supercritical (sc) CO2 and polymer phases. Partitioning of deuterated water and ate-dyes between poly(methyl methacrylate) and scCO(2) have been measured. Despite the low solubilities of polar ate-dyes in scCO(2) the partition coefficient of these dyes is ca. 10(4). In addition, the degree of partitioning of cosolvents methanol and acetone from scCO(2) into cross-linked poly (dimethylsiloxane) as well as the pressure dependence of the partition coefficient have been determined. Specific intermolecular interactions have been identified and related to the cosolvent partitioning between scCO(2) and polymer phases. (C) 1998 Elsevier Science B.V.
Eckert , C.A. and Chandler , K., Tuning fluid solvents for chemical reactions. Journal of Supercritical Fluids, 1998. 13 (1-3): p. 187-195.
Remarkable opportunities exist for the fruitful exploitation of the special properties of supercritical and nearcritical fluids as solvents for chemical reactions. Solution properties may be tuned, with thermodynamic conditions or cosolvents, to modify rates, yields, and selectivities, and supercritical fluids offer greatly enhanced mass transfer for heterogeneous reactions. Also, both supercritical fluids and nearcritical water can often replace environmentally undesirable solvents or catalysts, or avoid undesirable byproducts. Furthermore, rational design of solvent systems can also modify reactions to facilitate process separations. (C) 1998 Elsevier Science B.V.
Chandler , K., Culp, C.W., Lamb, D.R., Liotta, C.L., and Eckert , C.A. , Phase-transfer catalysis in supercritical carbon dioxide: Kinetic and mechanistic investigations of cyanide displacement on benzyl chloride. Industrial & Engineering Chemistry Research, 1998. 37 (8): p. 3252-3259.
This work reports the first studies designed to examine the detailed mechanism of a phase-transfer catalyzed reaction between a supercritical CO2 phase and a solid salt phase. The nucleophilic displacement of benzyl chloride with potassium cyanide to form phenylacetonitrile and potassium chloride was carried out with a tetraheptylammonium salt as the phase-transfer catalyst, The effects of various reaction variables on the kinetics were investigated, including the amount of catalyst, the amount of potassium cyanide, the presence of acetone cosolvent, and temperature. The kinetic data, along with catalyst solubility measurements, indicate that. the operating reaction mechanism is a three-phase system consisting of a supercritical CO2 phase, a catalyst-rich phase, and a solid salt phase and that the reaction actually occurs in the catalyst-rich phase. Further, the reaction mechanism was investigated with two additional phase-transfer catalysts, 18-crown-6 and poly(ethylene glycol), and these results are consistent with the postulated three-phase mechanism.
West, B.L., Bush, D., Brantley , N.H. , Vincent, M.F., Kazarian, S.G., and Eckert , C.A. , Modeling the effects of cosolvent-modified supercritical fluids on polymers with a lattice fluid equation of state. Industrial & Engineering Chemistry Research, 1998. 37 (8): p. 3305-3311.
A single Sanchez-Lacombe lattice fluid equation of state is used to model both phases for a polymer-supercritical fluid-cosolvent system. This method represents well over a wide pressure range both volumetric and phase equilibrium properties for a cross-linked poly(dimethyl siloxane) phase in contact with CO2 modified by a number of cosolvents. A single adjustable binary interaction parameter, obtained from swelling data of the polymer, is used to correlate both polymer dilation and solvent sorption.
Chandler , K., Eason, B., Liotta, C.L., and Eckert , C.A. , Phase equilibria for binary aqueous systems from a near-critical water reaction apparatus. Industrial & Engineering Chemistry Research, 1998. 37 (8): p. 3515-3518.
For any valid study of reaction kinetics the phase equilibria involved must, be known. We present an apparatus designed to measure both phase equilibria and kinetics for reactions in near-critical water. Liquid-liquid mutual solubilities are reported for the benzene-water and toluene-water systems from 200 to 275 degrees C at the three-phase pressures and 172 bar. These data were found to be in good agreement with data reported in the literature. Additionally, the near-critical water reaction apparatus was used to verify one-phase regions for the phenol-water and p-cresol-water systems from 250 to 300 degrees C at 172 bar.
West, B.L., Kazarian, S.G., Vincent, M.F., Brantley , N.H. , and Eckert , C.A. , Supercritical fluid dyeing of PMMA films with azo-dyes. Journal of Applied Polymer Science, 1998. 69 (5): p. 911-919.
In situ ultraviolet-visible spectroscopy has been used to study diffusion of two azo-dyes in a CO2-swollen matrix of poly(methyl methacrylate) (PMMA). The diffusivity of both dyes can be tuned simply be changing the system pressure. Higher pressure of CO2 enhances diffusion of a dye in PMMA. The diffusion of dyes in CO2-swollen PMMA can also be influenced by specific interactions. The partitioning of the dyes between the polymer phase and the fluid phase was measured, and the partition coefficients are large (10(4)-10(5)). Thus, supercritical fluid dyeing is possible, although the solubility of the dyes in the fluid phase is low. (C) 1998 John Wiley & Sons, Inc J Appl Polym Sci 69: 911-919, 1998.
Kriegel, R.M., Collard, D.M., Liotta, C.L., and Schiraldi, D.A., Thermal transesterification of bis(hydroxymethyl)propane-1,3-diyl units in poly(ethyl terephthalate) and poly(butylene terephthalate): A route to thermoset polyesters. Macromolecules, 1998. 31 (8): p. 2475-2479.
Copolymerization of 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane with dimethyl terephthalate and either ethylene glycol or 1,4-butanediol affords polyesters with pendant ketals. Acid-promoted debenzalation provides 2,2-bis(hydroxymethyl)propane-1,3-diyl structural units. Thermal transesterification to afford rigid, adhesive thermosets is controlled by the composition of the copolymer and curing conditions (temperature and time).
Vincent, M.F., Kazarian, S.G., West, B.L., Berkner, J.A., Bright, F.V., Liotta, C.L., and Eckert , C.A. , Cosolvent effects of modified supercritical carbon dioxide on cross-linked poly(dimethylsiloxane). Journal of Physical Chemistry B, 1998. 102 (12): p. 2176-2186.
Supercritical fluid chromatography is a powerful technique for analysis, and it also provides a useful tool for the measurement of thermodynamic properties. For any application, the method involves equilibration between the mobile supercritical fluid phase and the polymeric stationary phase. The mobile-phase properties ale often modified substantially with the addition of polar or protic cosolvents, but these adducts also cause changes in the stationary phases. In situ FTIR spectroscopy and the swelling of poly(dimethylsiloxane) (PDMS) are combined to quantify these changes due to partitioning of the cosolvent into and the swelling of the polymeric stationary phase as a function of fluid pressure. These results are used to evaluate the magnitude of the corrections for the changes in retention time of analytes, which affects both analytical methods and thermophysical property measurement.
Liu, Z.G., Cao, W.X., Sun, Y.H., Su, A.C.L., and Liotta, C.L., Synthesis of polycondensable anthraquinone dyes and coloured nylon fibres: III. Polymer International, 1997. 44 (4): p. 461-464.
A series of 1,5-diaryl- and 1,8-diaryl-substituted anthraquinone dyes, which contain -COOH or -NH2 groups, were prepared. The aryl-substituted anthraquinone dyes possess excellent thermostability and will keep their original colour in polycondensation with caprolactam at 260-280 degrees C. With different aryl substituents the anthraquinone dyes exhibit different colours and can be used to prepare a series of coloured nylon-6 fibres.
Chandler , K., Deng, F.H., Dillow, A.K., Liotta, C.L., and Eckert , C.A. , Alkylation reactions in near-critical water in the absence of acid catalysts. Industrial & Engineering Chemistry Research, 1997. 36 (12): p. 5175-5179.
We report successful alkylation reactions in near-critical water in the absence of added acid catalysts. Water has a strong tendency to ionize as the temperature is increased, allowing water in the near-critical region (250-350 degrees C) to act as an effective acid catalyst. By simultaneously employing near-critical water as the reaction solvent and catalyst, the need for environmentally hazardous organic solvents and acid catalysts is eliminated. The high hydronium ion content of near-critical water proved to be sufficient to synthesize a variety of substituted phenols with tertiary, secondary, and even primary alcohols. The reaction products for each of these reactions are reported.
Bush, D. and Eckert , C.A. , Estimation of solid solubilities in supercritical carbon dioxide from solute solvatochromic parameters , in Supercritical Fluids . 1997. p. 37-50.
Good estimating methods for solid solubilities in supercritical fluids are valuable tools in supercritical fluid processing. Experimental measurements of solid solubilities are time-consuming and may have large uncertainties. A linear solvation energy relationship has been developed for the enhancement factor, the ratio of solubility of a solid in an SCF to its solubility in an ideal gas. The solute parameters used are pi(2)*, the dipolarity/polarizability, Sigma alpha(2)(H), the effective hydrogen-bond acidity, Sigma beta(2)(H), the effective hydrogen-bond basicity, and V-x, the McGowen characteristic volume. A database of 37 solids containing sublimation pressure, solubility in carbon dioxide, and solute solvatochromic parameters was assembled and regressed. The average deviation of the estimated solubilities is 55 percent, which in some cases appears within the experimental uncertainty of the measurements. With over 1000 experimentally determined solute solvatochromic parameters available, this equation greatly expands the small database from which this correlation was developed. In addition, this empirical equation gives some physical insight to the nature of carbon dioxide - solute interactions.
Liu, Z.G., Cao, W.X., Sun, Y.H., Su, A.C.L., and Liotta, C.L., Synthesis of polycondensable anthraquinone dyes and coloured nylon fibres .2. Polymer International, 1997. 44 (2): p. 134-136.
Without addition of any metal ions or other catalysts, 1-chloroanthraquinone reacts readily with 6-aminocaproic acid or hexamethylenediamine in dimethylsulphone as solvent to give 1-(6-aminocaproic acid)anthraquinone and 1-(6-aminohexyl)amino]anthraquinone, respectively. 1,5-Dichloroor 1,8-dichloroanthraquinone can also be used in this reaction to give bis-substituted derivatives of anthraquinone. As a kind of functional dye, which contains -COOH or NH2 groups and dissolves easily in nylon melt, the products were designed for preparing coloured nylon by polycondensation with caprolactam or nylon-6,6 salt. Nylon fibres with different colours were obtained directly.
Kazarian, S.G., West, B.L., Vincent, M.F., and Eckert, C.A., Spectroscopic method for in situ analysis of supercritical fluid extraction and impregnation of polymeric matrices. American Laboratory, 1997. 29 (16): p. B18-&.
A novel high-pressure cell is described that permits the IR spectra of both polymer solution and SCF solvent to be determined rapidly and sequentially by a simple movement of the two-compartment cell within the light beam.
Vincent, M.F., Kazarian, S.G., and Eckert , C.A. , ''Tunable'' diffusion of D2O in CO2-swollen poly(methyl methacrylate) films. Aiche Journal, 1997. 43 (7): p. 1838-1848.
Opportunities exist to exploit the unique properties of carbon dioxide to process polymers for advanced applications. The diffusion of deuterated water in poly(methyl methacrylate) films swollen by carbon dioxide at 35 degrees C over the pressure range 0 to 90 bar (corresponding density range: 0.0 to 0.66 g/cm(3)) was measured using in situ FTIR spectroscopy. The mechanism and time scale of the diffusion of deuterated water in PMMA are easily controlled by manipulation of the applied CO2 density. The enhancement of mass transport rate is consistent with the degree of plasticization of the polymer clue to the absorption of carbon dioxide.
Kazarian, S.G., Brantley , N.H. , West, B.L., Vincent, M.F., and Eckert , C.A. , In situ spectroscopy of polymers subjected to supercritical CO2: Plasticization and dye impregnation. Applied Spectroscopy, 1997. 51 (4): p. 491-494.
In situ FT-IR spectroscopy has been used to study poly(methyl methacrylate) films subjected to high-pressure and supercritical CO2. Spectral changes indicate increased molecular mobility of ester groups due to the plasticization effect of CO2 on PMMA. This increase in PMMA segmental mobility has been used to impregnate Disperse Red 1 dye (DR1) into polymer film from a supercritical fluid solution. The enhanced diffusion process was observed in situ via FT-IR and UV/vis spectroscopy.
Knutson, B.L., Sherman , S.R., Bennett, K.L., Liotta, C.L., and Eckert , C.A. , Benzophenone as a probe of local cosolvent effects in supercritical ethane. Industrial & Engineering Chemistry Research, 1997. 36 (3): p. 854-868.
The n --> pi* shift of benzophenone has been used to quantify solute-cosolvent interactions in supercritical ethane. Dilute solutions of benzophenone in cosolvent/supercritical ethane mixtures were studied at 35 degrees C from 50 to 100 bar over a range of cosolvent concentrations. The following cosolvents were chosen for investigation on the basis of their varying abilities to interact with benzophenone: 2,2,2-trifluoroethanol, ethanol, chloroform, propionitrile, 1,2-dibromoethane, and 1,1,1-trichloroethane. In the supercritical systems investigated here, hydrogen bonding of protic cosolvents to the carbonyl oxygen of benzophenone is the primary mechanism of the n --> pi* shift. The results of this investigation are consistent with a chemical-physical interpretation of cosolvent effects in supercritical fluids in the presence of strong specific solute-cosolvent interactions. The experimental results for the ethane/TFE/benzophenone system were analyzed by using integral equations in order to study the assumptions of the chemical-physical model. This combination of spectroscopic data with radial distribution function models provides a powerful tool for understanding cosolvent effects.
Dillow, A.K., Hafner, K.P., Yun, S.L.J., Deng, F.H., Kazarian, S.G., Liotta, C.L., and Eckert, C.A., Cosolvent tuning of tautomeric equilibrium in supercritical fluids. Aiche Journal, 1997. 43 (2): p. 515-524.
Cosolvents offer a sensitive tool to tailor equilibria, rates or yields of chemical reactions in supercritical fluid solvents. The tautomeric equilibrium of a Schiff base was chosen as a model system, and small amounts of protic cosolvents shift the position of tautomeric equilibria. The equilibrium was tuned from essentially one tautomer to another by modifying the solvent of pure SCF ethane with less than 2 mol % hexafluoroisopropanol cosolvent. The equilibrium constant was a function of cosolvent concentration and mixture density. A chemical-physical model of equilibrium constants deviates from the measured values in the near-critical region, which may have been caused by local composition enhancement of cosolvent around the Schiff base. Decrease in the degree of hydrogen bonding with pressure or density affects the keto-enol equilibria by decreasing the amount of the keto formation. Thus, solution density, as well as the degree of hydrogen bonding, is manipulated to tune the position of tautomeric equilibria.
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