Lam Phan

Organic liquid CO2 capture agents with high gravimetric CO2 capacity

We report a new class of CO2 binding organic liquids that chemically capture and release CO2 much more efficiently than aqueous alkanolamine systems. Mixtures of organic alcohols and amidine/guanidine bases reversibly bind CO2 chemically as liquid amidinium/guanidinium alkylcarbonates. The free energy of CO2 binding in these organic systems is very small and dependent on the choice of base, approximately −9 kJ mol−1 for DBU and Bartons base and +2 kJ mol−1 for 1,1,3,3-tetramethylguanidine. These CO2 capturing agents do not require an added solvent because they are liquid, and therefore have high CO2 capacities of up to 19% by weight for neat systems, and slightly less when dissolved in acetonitrile. The rate of CO2 uptake and release by these organic systems is limited by the rate of dissolution of CO2 into and out of the liquid phase. Gas absorption is selective for CO2 in both concentrated and dilute gas streams. These organic systems have been shown to bind and release CO2 for five cycles without losing activity or selectivity.

A solvent having switchable hydrophilicity

A new kind of switchable solvent, a switchable-hydrophilicity solvent, is hydrophobic and has very low miscibility with water when in air but is hydrophilic and has complete miscibility with water when under an atmosphere of CO2. We report here the first example of such a solvent, N,N,N′-tributylpentanamidine. Solvents such as these could be used for the extraction of low-polarity organic products, such as vegetable oils, followed by the removal of the solvent from the product by carbonated water. Carbonated water is able to extract the solvent from the product because the CO2 converts the solvent to its hydrophilic form. The solvent can then be separated from the carbonated water upon removal of the CO2, because this removal triggers the conversion of the solvent back to its hydrophobic, water-immiscible form. Importantly, distillation is not required for removal of the solvent from the product.

Soybean oil extraction and separation using switchable or expanded solvents

The extraction of soy oil from soybean flakes in industry requires large amounts of hexane solvent and results in significant losses and energy consumption during the distillative removal of the solvent. Hexanes and related hydrocarbon extractants are also becoming an environmental and health concern. A new method for extraction of the oil is sought, that would require neither hexane nor distillative removal of solvent. This article presents a preliminary assessment of several new methods for soy oil extraction and subsequent solvent removal from the oil. The most promising are (a) extraction by an amidine switchable solvent that can then be removed from the soy oil by carbonated water and (b) extraction by a moderately hydrophilic solvent that can then be removed from the oil by water.

Reversible Uptake of COS, CS2, and SO2: Ionic Liquids with O-Alkylxanthate, O-Alkylthiocarbonyl, and O-Alkylsulfite Anions

CO(2)-binding organic liquids (CO(2)BOLs) are mixtures of a base (typically an amidine or guanidine) and an alcohol, and have been shown to reversibly capture and release CO(2) with low reaction energies and high gravimetric CO(2) capacity. We now report the ability of such liquid blends to chemically bind and release other acid gases such as CS(2), COS, and SO(2) analogously to CO(2). These systems bind with sulfur-containing acid gases to form colored ionic liquids with new O-alkylxanthate, O-alkylthiocarbonyl, and O-alkylsulfite anions. The capture and thermal stripping of each acid gas from these systems and their applicability towards flue gas desulfurization is discussed.

Switching the hydrophilicity of a solute

An amidine appendage gives a solute switchable hydrophilicity. Upon the introduction of CO2 gas, a hydrophobic solute can turn into a hydrophilic solute, with the corresponding partition coefficient changed by over 2 orders of magnitude.

Effects-driven chemical design: the acute toxicity of CO2-triggered switchable surfactants to rainbow trout can be predicted from octanol-water partition coefficients

For both environmental protection and improved energy efficiency, CO2-triggered switchable surfactants have been developed to change surface activity and solubility upon command. Surfactant activity is turned on by introduction of one atmosphere of CO2 and reversed by purging with air or nitrogen. These surfactants have numerous potential industrial applications related to their ability to stabilize and destabilize emulsions upon command. To assess their potential environmental impacts, we tested the acute toxicity of nine switchable surfactants to rainbow trout (Oncorhyncus mykiss) at pH ∼8.0, typical of natural surface waters. The surfactants were synthesized in several variations, differing in the structure of the hydrophobic tail group, the hydrophilic head group, or both. A strong correlation between the log of the estimated octanol/water partition coefficients (log P) and the toxicity of eight switchable surfactants formed the basis of a structure–activity relationship that was used to design a ninth compound. That new compound had the lowest toxicity of all of the switchable surfactants tested. The effect of log P on acute toxicity was similar to that reported in the literature for other organic compounds. This model shows that despite the addition of varying functional groups, switchable surfactant toxicity remains largely dependent on log P and differs little from traditional non-switchable surfactants. The log P relationship developed provides a very useful tool for screening new compounds for acute toxicity.