Aqueous Polyglycol Solutions as Environmentally Benign Solvents in Chemical ProcessingEPA Grant Number: R828133
Title: Aqueous Polyglycol Solutions as Environmentally Benign Solvents in Chemical Processing
Investigators: Kirwan, Donald J. , Gainer, John L.
Institution: University of Virginia
EPA Project Officer: Karn, Barbara
Project Period: June 1, 2000 through May 31, 2003 (Extended to May 31, 2004)
Project Amount: $335,000
RFA: Technology for a Sustainable Environment (1999) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Organic solvents are extensively used in chemical manufacturing processes, with some of the more important uses being as reaction media for synthetic chemistry and as solvents (and anti-solvents) in separation and purification processes. A significant problem associated with solvent use is that literally billions of pounds of organic compounds are annually emitted into the environment in the form of volatile emissions or in aqueous discharge streams. New process integration techniques and improved containment systems are being investigated and implemented to deal with this problem. However, total containment is difficult to achieve in practice. Alternatively, replacing such organic solvents with benign solvents will eliminate the possibility of an adverse impact in the event of discharges to the environment. In this proposal we address the systematic exploration of an aqueous-based, benign, alternative solvent system for use in the process industries, including the development of a fundamental understanding of the solvation properties of such solutions.
Currently, some environmentally harmful solvents are being replaced, but often the new solvents are not benign but only less toxic than its predecessor. It would obviously be preferable to have a genuinely benign solvent system whose solvating properties are adjustable for particular applications. Aqueous solutions containing polyethylene glycol (PEG) or polypropylene glycol (PPG) have been shown, in preliminary results in our laboratory, to be capable of dissolving a large range of organic compounds. These studies suggest that such solvents and related derivatives might be used as replacement media for organic chemical reactions and as anti-solvents in precipitation-crystallization processes, among other possible uses. These solutions are also very non-toxic. PEG, for example, is currently used extensively in food products because it has been found to be safe for ingestion. Thus, aqueous solutions of PEG and PPG appear to have the potential to form flexible and tunable solvents system whose hydrophobicity can be varied.
In the proposed work the solubility properties of model solutes in such polyglycol solutions will be characterized both experimentally and theoretically. An extensive experimental database will be obtained in order to develop and test fundamental models for the hydrophobic/hydrophilic nature of these systems. A description of the thermodynamic activity of water, polyglycols and organic solutes in such polyglycol solutions will be developed. In addition, the implementation of such solvents as replacements in two important chemical processing operations, organic reaction and anti-solvent precipitation, will be investigated, particularly for applications in pharmaceutical and specialty chemical processes. The important characteristics for effective reaction solvents for different classes of organic reactions will be identified and the capability of polyglycol solutions to satisfy these requirements will be quantitatively established. Similarly, the properties of these mixtures as anti-solvents (solubility reduction and effect on crystallization kinetics and on crystal morphology) will be quantitatively assessed and compared to common anti-solvents used in the pharmaceutical industry.
An understanding and rationalization of the use of these systems as replacement solvents, anti-solvents, and reaction media will be realized at the end of this project. In addition, the project will provide opportunities for students to be trained in the fundamental sciences relevant to solvent selection for reaction and separations processing, and it also will enable them to become cognizant of the importance and seriousness of solvent choice with respect to environmental impact.