Carbon dioxide is often promoted as a sustainable solvent, as CO 2 is non-flammable, exhibits a relatively low toxicity and is naturally abundant. However, injudicious use of carbon dioxide in a process or product can reduce rather than enhance overall sustainability. This review specifically examines the use of CO 2 to create greener processes and products, with a focus on research and commercialization efforts performed since 1995. The literature reveals that use of CO 2 has permeated almost all facets of the chemical industry and that careful application of CO 2 technology can result in products (and processes) that are cleaner, less expensive and of higher quality.

Supercritical and near-critical CO2 in green chemical synthesis and processing

Fourier transform IR spectroscopy has been used to investigate the interaction of carbon dioxide with polymers. IR transmission and attenuated total reflectance spectra were obtained for CO2 impregnated into polymer films. It has been shown that the polymers possessing electron-donating functional groups (e.g., carbonyl groups) exhibit specific interactions with CO2, most probably of Lewis acid−base nature. An unusual aspect is the use of the bending mode (ν2) of CO2 to probe polymer−CO2 interactions. The evidence of the interaction is the observation of the splitting of the band corresponding to the CO2 ν2 mode. This splitting indicates that the double degeneracy of the ν2 mode is removed due to the interaction of electron lone pairs of the carbonyl oxygen with the carbon atom of the CO2 molecule. This splitting has not been observed for polymers lacking electron-donating functional groups (e.g., poly(ethylene)). In contrast, the ν3 mode shows little if any sensitivity to this interaction, which is in ac...

Specific Intermolecular Interaction of Carbon Dioxide with Polymers

Polymerizations in Supercritical Carbon Dioxide

Carbon dioxide in the liquid and supercritical fluid states is useful as a replacement for toxic organic solvents. However, nonvolatile hydrophilic substances such as proteins, ions, and most catalysts are insoluble. This limitation was overcome by the formation of aqueous microemulsion droplets in a carbon dioxide-continuous phase with a nontoxic ammonium carboxylate perfluoropolyether surfactant. Several spectroscopic techniques consistently indicated that the properties of the droplets approach those of bulk water. The protein bovine serum albumin (BSA) with a molecular weight of 67,000 is soluble in this microemulsion and experiences an environment similar to that of native BSA in buffer.

https://science.sciencemag.org/content/sci/271/5249/624.full.pdf

Water-in-carbon dioxide microemulsions : an environment for hydrophiles including proteins

Liquid and supercritical carbon dioxide have attracted much interest as environmentally benign solvents, but their practical use has been limited by the need for high CO2 pressures to dissolve even small amounts of polar, amphiphilic, organometallic, or high-molecular-mass compounds. So-called 'CO2-philes' efficiently transport insoluble or poorly soluble materials into CO2 solvent, resulting in the development of a broad range of CO2-based processes, including homogeneous and heterogeneous polymerization, extraction of proteins and metals, and homogeneous catalysis. But as the most effective CO2-philes are expensive fluorocarbons, such as poly(perfluoroether), the commercialization of otherwise promising CO2-based processes has met with only limited success. Here we show that copolymers can act as efficient, non-fluorous CO2-philes if their constituent monomers are chosen to optimize the balance between the enthalpy and entropy of solute-copolymer and copolymer-copolymer interactions. Guided by heuristic rules regarding these interactions, we have used inexpensive propylene and CO2 to synthesize a series of poly(ether-carbonate) copolymers that readily dissolve in CO2 at low pressures. Even though non-fluorous polymers are generally assumed to be CO2-phobic, we expect that our design principles can be used to create a wide range of non-fluorous CO2-philes from low-cost raw materials, thus rendering a variety of CO2-based processes economically favourable, particularly in cases where recycling of CO2-philes is difficult.

Jacqueline Goveas

Papers

Water-in-Carbon Dioxide Microemulsions with a Fluorocarbon-Hydrocarbon Hybrid Surfactant