High-pressure sapphire cell for phase equilibria measurements of CO2/organic/water systems.

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition.

Design, synthesis, and evaluation of nonaqueous silylamines for efficient CO2 capture.

A series of silylated amines have been synthesized for use as reversible ionic liquids in the application of post-combustion carbon capture. We describe a molecular design process aimed at influencing industrially relevant carbon capture properties, such as viscosity, temperature of reversal, and enthalpy of regeneration, while maximizing the overall CO2 -capture capacity. A strong structure-property relationship among the silylamines is demonstrated in which minor structural modifications lead to significant changes in the bulk properties of the reversible ionic liquid formed from reaction with CO2 .

The synthesis and the chemical and physical properties of non-aqueous silylamine solvents for carbon dioxide capture.

Silylamine reversible ionic liquids were designed to achieve specific physical properties in order to address effective CO₂ capture. The reversible ionic liquid systems reported herein represent a class of switchable solvents where a relatively non-polar silylamine (molecular liquid) is reversibly transformed to a reversible ionic liquid (RevIL) by reaction with CO₂ (chemisorption). The RevILs can further capture additional CO₂ through physical absorption (physisorption).

Novel solvents for sustainable production of specialty chemicals.

We discuss novel solvents that improve the sustainability of various chemical reactions and processes. These alternative solvents include organic-aqueous tunable solvents; near-critical water; switchable piperylene sulfone, a volatile dimethylsulfoxide substitute; and reversible ionic liquids. These solvents are advantageous to a wide variety of reactions because they reduce waste and energy demand by coupling homogeneous reactions with heterogeneous separations, acting as in situ acid or base catalysts, and providing simple and efficient postreaction separations.

Combining the benefits of homogeneous and heterogeneous catalysis with tunable solvents and nearcritical water.

The greatest advantage of heterogeneous catalysis is the ease of separation, while the disadvantages are often limited activity and selectivity. We report solvents that use tunable phase behavior to achieve homogeneous catalysis with ease of separation. Tunable solvents are homogeneous mixtures of water or polyethylene glycol with organics such as acetonitrile, dioxane, and THF that can be used for homogeneously catalyzed reactions.

Organic aqueous tunable solvents (OATS): a vehicle for coupling reactions and separations.

In laboratory-based chemical synthesis, the choice of the solvent and the means of product purification are rarely determined by cost or environmental impact considerations. When a reaction is scaled up for industrial applications, however, these choices are critical: the separation of product from the solvent, starting materials, and byproduct usually constitutes 60-80% of the overall cost of a process. In response, researchers have developed solvents and solvent-handling methods to optimize both the reaction and the subsequent separation steps on the manufacturing scale.

Combining homogeneous catalysis with heterogeneous separation using tunable solvent systems.

Tunable solvent systems couple homogeneous catalytic reactions to heterogeneous separations, thereby combining multiple unit operations into a single step and subsequently reducing waste generation and improving process economics. In addition, tunable solvents can require less energy than traditional separations, such as distillation. We extend the impact of such solvents by reporting on the application of two previously described carbon dioxide tunable solvent systems: polyethylene glycol (PEG)/organic tunable solvents (POTS) and organic/aqueous tunable solvents (OATS).

Molecular Dynamics Simulations of Solvation and Solvent Reorganization Dynamics in CO2-Expanded Methanol and Acetone.

Composition-dependent solvation dynamics around the probe coumarin 153 (C153) have been explored in CO2-expanded methanol and acetone with molecular dynamics (MD) simulations. Solvent response functions are biexponential with two distinct decay time scales: a rapid initial decay (∼0.1 ps) and a long relaxation process.

One-component, switchable ionic liquids derived from siloxylated amines.

A new class of one-component, thermally reversible, neutral to ionic liquid solvents derived from siloxylated amines is presented and characterized.

Effects of solute structure on local solvation and solvent interactions: results from UV/vis spectroscopy and molecular dynamics simulations.

Solvation of heterocyclic amines in CO(2)-expanded methanol (MeOH) has been explored with UV/vis spectroscopy and molecular dynamics (MD) simulations. A synergistic study of experiments and simulations allows exploration of solute and solvent effects on solvation and the molecular interactions that affect absorption. MeOH-nitrogen hydrogen bonds hinder the n-pi* transition; however, CO(2) addition causes a blue shift relative to MeOH because of Lewis acid/base interactions with nitrogen.

Local polarity in CO2-expanded acetonitrile: a nucleophilic substitution reaction and solvatochromic probes.

Many processes that use highly tunable gas-expanded liquids (GXLs) rely on the fact that CO2 addition can greatly affect the polarity of the solvent. We have examined several measures of bulk and local polarity in CO2-expanded acetonitrile to enable more effective exploitation of these polarity changes. The rate of the nucleophilic substitution reaction of tributylamine with methyl p-nitrobenzenesulfonate has been analyzed as a function of solvent composition by using in situ high-pressure UV/vis spectroscopy.

A spectroscopic and computational exploration of the cybotactic region of gas-expanded liquids: methanol and acetone.

Local compositions in supercritical and near-critial fluids may differ substantially from bulk compositions, and such differences have important effects on spectroscopic observations, phase equilibria, and chemical kinetics. Here, we compare such determinations around a solute probe dissolved in CO2-expanded methanol and acetone at 25 degrees C from solvatochromic experiments with molecular dynamics simulations. UV/vis and steady-state fluorescence measurements of the dye Coumarin 153 in the expanded liquid phase indicate preferential solvation in both the S0 and S1 states by the organic species.

Reversible in situ catalyst formation.

Acid catalysts play a vital role in the industrial synthesis and production of a plethora of organic chemicals. But, their subsequent neutralization and disposal is also a giant source of waste. For example, for a Friedel-Crafts acylation with AlCl 3, a kilogram of product yields up to 20 kg of (contaminated) waste salt.

Molecular dynamics simulation of the cybotactic region in gas-expanded methanol-carbon dioxide and acetone-carbon dioxide mixtures.

Local solvation and transport effects in gas-expanded liquids (GXLs) are reported based on molecular simulation. GXLs were found to exhibit local density enhancements similar to those seen in supercritical fluids, although less dramatic. This approach was used as an alternative to a multiphase atomistic model for these mixtures by utilizing experimental results to describe the necessary fixed conditions for a locally (quasi-) stable molecular dynamics model of the (single) GXL phase.

Switchable surfactants.

Many industrial applications that rely on emulsions would benefit from an efficient, rapid method of breaking these emulsions at a specific desired stage. We report that long-chain alkyl amidine compounds can be reversibly transformed into charged surfactants by exposure to an atmosphere of carbon dioxide, thereby stabilizing water/alkane emulsions or, for the purpose of microsuspension polymerization, styrene-in-water emulsions. Bubbling nitrogen, argon, or air through the amidinium bicarbonate solutions at 65 degrees C reverses the reaction, releasing carbon dioxide and breaking the emulsion.

Probing the cybotactic region in gas-expanded liquids (GXLs).

Gas-expanded liquids (GXLs) are a new and benign class of liquid solvents, which may offer many advantages for separations, reactions, and advanced materials. GXLs are intermediate in properties between normal liquids and supercritical fluids, both in solvating power and in transport properties. Other advantages include benign nature, low operating pressures, and highly tunable properties by simple pressure variations.

The path forward for biofuels and biomaterials.

Biomass represents an abundant carbon-neutral renewable resource for the production of bioenergy and biomaterials, and its enhanced use would address several societal needs. Advances in genetics, biotechnology, process chemistry, and engineering are leading to a new manufacturing concept for converting renewable biomass to valuable fuels and products, generally referred to as the biorefinery. The integration of agroenergy crops and biorefinery manufacturing technologies offers the potential for the development of sustainable biopower and biomaterials that will lead to a new manufacturing paradigm.

Green chemistry: reversible nonpolar-to-polar solvent.

Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide.

Amidines have been reported to react with CO(2) to form a stable and isolable zwitterionic adduct but previous studies were performed in the presence of at least some water. However, spectroscopy of the reaction between DBU and CO(2) detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO(2) and does not indicate that an isolable zwitterionic adduct between DBU and CO(2) forms either in the presence or the absence of water.

Use and recovery of a homogeneous catalyst with carbon dioxide as a solubility switch.

A method for fluorous biphasic catalysis is described,in which the fluorous liquid is replaced by fluorinated silica, the fluorous catalyst is induced to dissolve in the organic solvent by the presence of CO2, and the recovery of the catalyst after the reaction is achieved by release of the CO2 pressure.

Phase-transfer catalyst separation by CO2 enhanced aqueous extraction.

CO2 is used to enhance the environmentally benign and efficient recovery of phase transfer catalysts with aqueous extraction; this method can alter the distribution of phase transfer catalysts so dramatically that even in dilute organic solutions they can be separated selectively from an organic reaction mixture with only a small fraction of the water required in a traditional aqueous extraction.

Carbon dioxide as a solubility "switch" for the reversible dissolution of highly fluorinated complexes and reagents in organic solvents: application to crystallization.

Highly fluorinated organic or organometallic solid compounds can be made to dissolve in liquid hydrocarbons by the application of 20-70 bar of CO(2) gas. Subsequently releasing the gas causes the compounds to precipitate or crystallize, giving quantitative recovery of the solid. The resulting crystals can be of sufficient quality for single-crystal X-ray crystallography; the structures of Rh(2)(O(2)CCF(2)CF(2)CF(3))(4)(DMF)(2), Rh(2)(O(2)C(CF(2))(9)F)(4)(MeOH)(2), Cr(hfacac)(3), and P[C(6)H(3)(3,5-CF(3))(2)](3) have been determined from crystals grown in this manner.