Green Engineering

What is the difference between Green Engineering and Green Chemistry? The US Environmental Protection Agency website yields a very interesting analysis. Green Engineering is defined as “the design, commercialization, and use of processes and products, which are feasible and economical while minimizing 1) generation of pollution at the source and 2) risk to human health and the environment,”¹ whereas Green Chemistry is defined as “the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.”² From this, one would conclude that Green Engineering is concerned with the design, commercialization and use of all types of processes and products, whereas Green Chemistry covers just a very small subset of this—the design of chemical processes and products. So Green Chemistry is a subset of Green Engineering!

Green Engineering is, in fact, a very broad field, encompassing everything from improving energy efficiency in manufacturing processes to developing plastics from renewable resources. What we focus on in this issue is several aspects of Green Chemical Engineering. One important aspect of this is the development of mathematically-based tools that aid in decision-making when faced with alternatives. A number of the papers in this issue address this area. Another is the discovery and development of new technology that makes the design, commercialization and use of processes and products that reduce or eliminate pollution possible. In particular, one major focus of both Green Chemistry and Green Chemical Engineering is developing alternatives to the volatile organic solvents used so pervasively in chemical and manufacturing processes. In a representative year (1997) in the United States solvents comprised 66% of all industrial emissions.³ Efforts to address this pressing need of developing alternative solvents for synthesis, separation and processing are covered in four of the articles in this special issue. O’Neil and Watkins⁴ describe how supercritical carbon dioxide can be used not just to replace the copious amounts of organic and aqueous solvents used in the microelectronic industries, but also how CO₂ presents unique technical advantages in device fabrication. Subramaniam et al.⁵ demonstrate advantages in the rate of an oxidation reaction, by performing it in a liquid where part of the organic solvent has been replaced by CO₂ (a CO₂-expanded liquid). Eckert et al.⁶ show how strong mineral acids can be eliminated by choosing a solvent (either hot water or a CO₂-expanded liquid) where the acid catalyst can be produced reversibly in situ. In all these cases, the new solvent system presents some real technological advantage over conventional systems; i.e., it's not just solvent substitution. Rebelo and coworkers⁷ present a wealth of phase behavior and thermophysical property data on a system containing a completely non-volatile solvent—an ionic liquid. These are exactly the kind of data that are needed to evaluate the potential of ionic liquids for reaction and separation processes.

Hopefully, the articles in this special issue demonstrate that Green Chemistry and Green Engineering represent slightly different shades of a seamless continuum that ranges from discovery through design and decision-making all the way to commercialization and use of products and processes that prevent pollution.

 

Joan F. Brennecke

Keating-Crawford Professor

Department of Chemical and Biomolecular Engineering

University of Notre Dame

Notre Dame, IN 46556

E-mail: jfb@nd.edu

References

1. http://www.epa.gov/opptintr/greenengineering/whats_ge.html.
2. http://www.epa.gov/greenchemistry/whats_gc.html.
3. D. T. Allen and D. R. Shonnard, Green Engineering, 2002, Prentice-Hall, Englewood Cliffs, NJ.
4. A. O’Neil and J. Watkins, Green Chem., 2004, 6 10.1039/b403729d , this issue.
5. M. Wei, G. T. Musie, D. H. Busch and B. Subramaniam, Green Chem., 2004, 6 10.1039/b310523g , this issue.
6. T. S. Chamblee, R. R. Weikel, S. A. Nolen, C. L. Liotta and C. A. Eckert, Green Chem., 2004, 6 10.1039/b400393d , this issue.
7. L. P. N. Rebelo, V. Najdanovic-Visak, Z. P. Visak, M. Nunes da Ponte, J. Szydlowski, C. A. Cerdeiriña, J. Troncoso, L. Romaní, J. M. S. S. Esperança, H. J. R. Guedes and H. C. de Sousa, Green Chem., 2004, 6 10.1039/b400374h , this issue.

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