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Conference paperGiambra EM, Hallett JP, Lu J, et al., 2005,
Polyethylene glycol: A benign solvent for fine chemical synthesis
Liquid polyethylene glycol (PEG) is a new and exciting solvent for benign chemical synthesis. We have utilized the unique physiochemical properties of this solvent for a variety of chemical processing techniques, with a focus on homogeneous catalysis and separations. By combining PEG with extraction using supercritical CO2 or gas-expanded liquids, we have been able to utilize the unique aspects of the solvent while developing techniques for facile recovery of products and recycle of homogeneous catalysts. Applications include the use of organometallic catalysts, enzymes, and high pressure phase behavior of PEG-CO2-organic systems.
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Conference paperKitchens CL, Hallett JP, Bush D, et al., 2005,
Thermophysical properties of gas expanded liquids
Gas expanded liquids (GXLs) are a new class of tunable solvents which take advantage of the solvent strength of conventional organic liquids combined with the attractive properties of supercritical fluids. GXLs utilize the high solubility of gaseous CO<inf>2</inf> in organic solvents resulting in a highly tunable solvent, at sub-critical pressures. GXLs have recently been applied to gas anti-solvent methods of crystallization and separation, as well as creating tunable solvent environments for reactions. This study investigates the thermodynamic and transport properties of GXLs by a wide range of experimental methods including spectroscopic methods, molecular dynamics simulation and neutron scattering. Comparison of the local environments of solute probe molecules versus bulk solvent properties demonstrate the unique properties of GXL's as a solvent / reaction media. Specific interactions within the media impact the structure and solvent properties are also investigated and provide a synergism between experiment and computation. Further understanding of the tunable thermophysical properties of GXL's is necessary for the application of these fluids for novel reactions and separations.
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Conference paperGrilly JD, Thomas CA, Weikel RR, et al., 2005,
Sulfoxide solvents and surfactants for facile separations
We show that thiirane oxide combines reactions with separations by providing a reaction medium with a built-in switch for solvent removal. Dipolar, aprotic solvents such as DMSO have the ability to dissolve both salts and organics, making them viable solvents to homogeneously run reactions that alternatively must be run heterogeneously with a phase transfer catalyst. In these cases, product isolation is often difficult as DMSO has a high boiling point and its solubility with other organic solvents makes liquid extraction difficult. Thiirane oxide represents the cyclic analog to DMSO and has solvent properties that are similar to DMSO; however, thiirane oxide undergoes thermal decomposition at elevated temperatures to form ethylene and SO. The cleavable nature of this solvent allows for separation and product purification at conditions that are milder than we could otherwise achieve. We have demonstrated the versatility and separation advantage of this cleavable solvent using example reactions. Using similar chemistry, we have developed a cleavable surfactant, n-octyl thiirane oxide, which is composed of a thirane oxide headgroup and an alkyl tail. The surfactant is thermally degradable enabling the irreversible breaking of an emulsion with temperature and a two phase separation at ambient temperatures. This work demonstrates a novel approach to coordinate synthesis and separation by designing a reaction media that will facilitate both.
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Conference paperHallett JP, Lu J, Pallet P, et al., 2005,
Recovery of asymmetric homogeneous catalysts using CO2
Asymmetric catalysts, both organometallic and enzymatic, are an important component of pharmaceutical processing. However, these catalysts are usually expensive and toxic and their recovery from product streams is crucial. Our approach involves designing solvent systems whereby a reversible stimulus induces a phase change enabling easy recover of homogeneous catalysts. The purpose is to preserve the high enantioselective activity of homogeneous catalysts while taking advantage of simple separation techniques, such as filtering and extraction, normally applied to heterogeneous or biphasic catalytic systems. Specific examples include the application of gaseous CO2 as a benign agent in gas-expanded liquids to induce catalytic recycle of water/organic, fluorous/organic, liquid polymer/organic and solid/liquid biphasic systems. The efficiency of catalyst recovery and recycle is detailed.
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Conference paperJanakat ME, Kitchens CL, Hallett JP, et al., 2005,
Diffusion and viscosity in gas-expanded liquids
Gas-expanded liquids are a new class of tunable solvents in which novel applications in separations and catalysis depend on the interactions of solutes with the cybotactic region. We report diffusion coefficients of benzene, pyridine, pyrimidine, pyrazine and 1,3,5-triazine by the Taylor-Aris dispersion technique in CO2-methanol mixtures. Viscosities of the CO2-methanol mixtures will be determined by measuring the pressure drop across a tube. These data will be compared with measurements of viscosity in the cybotactic region obtained by the rotation of a chromaphore. The comparison of these with the Stokes-Einstein relationship will help elucidate differences between bulk and local properties.
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Journal articleWyatt VT, Bush D, Lu J, et al., 2005,
Determination of solvatochromic solvent parameters for the characterization of gas-expanded liquids
, JOURNAL OF SUPERCRITICAL FLUIDS, Vol: 36, Pages: 16-22, ISSN: 0896-8446- Cite
- Citations: 95
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Conference paperPopov AV, Eckert CA, Liotta CL, et al., 2005,
The cybotactic structure in gas-expanded liquids: Numerical simulations
Supercritical CO<inf>2</inf> is now commonly used in the formulation of several successful strategies for producing specialty chemicals satisfying environmentally "green" conditions while providing a simple route for separation of the product. Recent observations that some of these same objectives may be achieved using CO<inf>2</inf> with cosolvents below supercritical conditions appear promising. In particular, the fluid phase of these mixturestermed gas-expanded liquids, GXLs-can provide chosen solutes (e.g. reactants, catalysts, and products) substantial solubility and fast transport not available without the CO<inf>2</inf> cosolvent. What is not known entirely from experiment, however, is the degree of heterogeneity in the GXL, the possible persistence of local density enhancements seen in the supercritical phase into the GXL, and the possible existence of anisotropy in the cybotactic region around a probe. Such questions can be exquisitely addressed using numerical simulations. The present work will report the results of the anisotropic pair-correlation for several CO<inf>2</inf>-cosolvent mixtures. The synergy between these calculations and the experimental observations in addressing the possible use of this anisotropy to control reactivity will also be discussed.
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Conference paperEckert CA, Liotta CL, Bush D, et al., 2005,
Vapor-liquid-liquid equilibria of carbon dioxide-organic water systems
Homogeneous catalysts offer exciting opportunities for organic synthesis due to high activity and selectivity, but implementation is limited by difficulties in catalyst recycle. The addition of a polar organic co-solvent to a water/organic biphasic system, coupled with subsequent phase splitting induced by the dissolution of gaseous CO<inf>2</inf> creates the opportunity to run homogeneous reactions in an organic/aqueous mixture with a water-soluble catalyst. High-pressure phase equilibria for the systems containing carbon dioxide, an organic solvent (tetrahydrofuran, acetonitrile, or 1,4-dioxane) and water were measured using a variable-volume view cell. These systems are well predicted with the Peng-Robinson Equation of State with Huron-Vidal type mixing rules from correlations of the binary systems. Applications of the phase behavior on reaction conditions and separations will be discussed.
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Conference paperPopov AV, Eckert CA, Liotta CL, et al., 2005,
A phenomenological molecular dynamics model for gas-expanded liquids
Gas-expanded liquids (GXLs) are novel solvents with potential applications in nanotechnology, drug delivery, reactions and separations. GXLs are liquid mixtures consisting of an organic solvent combined with a high fluidity gas, such as carbon dioxide, in the nearcritical regime. Recent experimental investigations of GXLs have established that replacing 80-90% of an organic solvent with CO<inf>2</inf> can enhance reaction efficiency while greatly reducing process waste. Under these conditions, the GXL phase has improved transport and contains areas of local heterogeneity. A complete atomistic model for these mixtures requires a multiphase approach, and is being pursued by several groups. An alternative approach, pursued here, utilizes the experimental results to describe the necessary fixed conditions for a locally (quasi-) stable molecular dynamics model of the GXL phase. The local anisotropic pair correlation function and orientational correlation functions have been obtained. The specific systems investigated include CO<inf>2</inf>-expanded methanol and acetone at 298 K and pressures up to 6 MPa.
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Conference paperJessop PG, Heldebrant DJ, Li XW, et al., 2005,
Switchable solvent systems for catalysis and catalyst recovery.
, 229th National Meeting of the American-Chemical-Society, Publisher: AMER CHEMICAL SOC, Pages: U971-U971, ISSN: 0065-7727- Author Web Link
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- Citations: 7
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