As can be seen from the preceding discussion, developing green metrics for chemical processes requires a holistic, systems point of view across a range of disciplines. Metrics are also generally context dependent; that is, one type or one set of metrics does not fit all situations. Instead, different organizations or companies will have to undertake some very hard work to identify, assess, and implement metrics that are most applicable to their needs.
The good news is that there are a large number of metrics that have already been identified, and many of these will meet the needs of most organizations or companies. Any one person is unlikely to possess sufficient knowledge in all areas of interest to identify key metrics, so it should be common practice for green metrics to be developed drawing on the resources of cross-disciplinary teams. In addition, to truly drive the design of greener, safer processes, there is a need to resist the temptation of addressing metrics in a compartmentalized manner, as many of these metrics are interrelated. Finally, one should apply the 80/20 rule liberally;
that is, don’t strive for the perfect set of metrics that covers all situations if a few metrics meet your needs most of the time.
PROBLEMS
4.1 Why is, or isn’t, mass productivity (mass efficiency) a useful metric for businesses?
Explain your answer.
4.2 Do you think that there is a correlation between any of the metrics discussed in this chapter and the molecular complexity of a particular molecule?
4.3 Do you think that it would be possible to create a model for molecular complexity that could be correlated with reaction mass efficiency?
4.4 Could realistic targets be set for reaction mass efficiency based on this complexity model?
4.5 Estimate the reaction mass efficiency, mass intensity, mass productivity, andE-factor for Example 4.1.
4.6 Estimate the reaction mass efficiency, mass productivity,E-factor, and atom econo- my for Example 4.2.
4.7 Calculate selectivity towardn-butanol for Example 4.5.
4.8 Calculate energy intensity for Example 4.5 assuming that isobutanol is also a salable material.
4.9 Calculate reaction mass efficiency, mass productivity, mass intensity, and yield for Example 4.5, assuming that:
(a) Bothn-butanol and isobutanol are useful, salable products.
(b) Onlyn-butanol is a usable, salable product.
4.10 It has been estimated that the process for Example 4.5 has the emissions shown in Table P4.10. Estimate the intensity of emissions (kg/kg) of each of the chemicals emitted.
4.11 Dimethyl malonate is produced by the following chemistry:
ClCH2COOHþNaOH
monochloracetic acid !ClCH2COONaþH2O
sodium monochloroacetate
ClCH2COONaþNaCN
sodium monochloroacetate !NCCH2COONaþNaCl
sodium cyanoacetate
2ðNCCH2COONaị ỵ4CH3OHỵ5H2SO4
sodium cyanoacetate !2C5H8O4þNa2SO4þ2NH3þ4H2SO4
dimethyl malonate
Monochloroacetic acid in water is mixed with cracked ice. Sodium hydroxide is added until the solution is made alkaline. Subsequently, sodium chloroacetate is
TABLE P4.10 Emissions
Gas Emissions Amount (kg/h)
n-Butanol 9.97
Propylene 11.9
Isobutanol 0.5
Hydrogen 0.302
Carbon monoxide 2.00
cyanoacetate. This solution is evaporated under reduced pressure to form a crude sodium cyanoacetate cake. The cake is hydrolyzed and esterified in the presence of methanol and sulfuric acid. Three extractions are performed with toluene. The dried product is distilled, at first under atmospheric pressure, and finally under reduced pressure, to remove any remaining toluene. To produce 1000 kg/h of 97% pure monomethyl malonate, 3.5 MJ/h of electricity, 101 MJ/h of steam, and 57 MJ/h of refrigeration are needed, and it is required to dissipate 3165 MJ/h of heat using cooling water.
(a) Estimate the energy intensity of the process.
(b) How is the required energy produced?
4.12 Estimate the yield, mass intensity, mass productivity, atom economy, reaction mass efficiency, and waste intensity (E-factor) for the dimethyl malonate process of Problem 4.11. Assume that the amounts of materials listed in Table P4.12 are required to produce 1000 kg/h of monomethyl malonate.
REFERENCES
1. Bennett, M., James, P., Eds.Sustainable Measures. Greenleaf Publishing, Lebanon, TN, 1999.
2. Committee on Industrial Environmental Performance Metrics. National Academy of Engineer- ing, National Research Council.Industrial Environmental Performance Metrics: Challenges and Opportunities. NCR, Washington, DC, 1999.
3. Corporate Environmental Performance 2000, Vol. 1,Strategic Analysis. Haymarket Business Publications, London, UK, 1999.
4. Curzons, A. D., Constable, D. J. C., Mortimer, D. N., Cunningham, V. L. So you think your process is green, how do you know? Using principles of sustainability to determine what is green—a corporate perspective.Green Chem., 2001, 3, 1–6.
5. Constable, D. J. C., Curzons, A. D., Freitas dos Santos, L. M., Geen, G. R., Hannah, R. E., Hayler, J. D., Kitteringham, J., McGuire, M. A., Richardson, J. E., Smith, P., Webb, R. L., Yu, M. Green chemistry measures for process research and development.Green Chem., 2001, 3, 7–9.
6. Douglas, J.Conceptual Design of Chemical Processes. McGraw-Hill, New York, 1988.
7. Peters, M. S., Timmerhaus, K. D., West, R. E. Plant Design and Economics for Chemical Engineers, 5th ed., McGraw-Hill, New York, 2002.
TABLE P4.12 Amounts of Chemicals
Chemical Amount (Kg/hr) Comments
Toluene 55
Chloroacetic acid 715
Sodium sulfate 40
Methanol 470
Sodium cyanide 372
Sodium hydroxide 688 50% purity (344 kg/h water)
Sulfuric acid 1835 98% purity (37 kg/h water)
Water 3254
8. Center for Waste Reduction Technologies. Collaborative Projects – Focus Area: Sustainable Development, American Institute of Chemical Engineers (AIChE), New York, NY, 2000.
9. Azapagic, A., Howard A., Parfitt, A., Tallis, B., Duff, C., Hadfield, C., Pritchard, C., Gillett, J., Hackitt, J., Seaman, M., Darton, R., Rathbone, R., Clift, R., Watson, S., Elliot S. The Sustainability Metrics. Institution of Chemical Engineers, 30 pp., Rugby, UK, 2003, http://
cms.icheme.org/.
10. Constable, D. J. C., Curzons, A. D., Cunningham, V. L. Metrics to green chemistry: Which are the best?Green Chem., 2002, 4, 521–527.
11. Jimenez-Gonzalez, C., Curzons, A. D., Constable, D. J. C., Overcash, M. R., Cunningham, V. L.
How do you select the “greenest” technology? Development of guidance for the pharmaceutical industry.Clean Products Process., 2001, 3, 35–41
12. Jimenez-Gonzalez, C., Constable, D. J. C., Curzons, A. D., Cunningham, V. L. Developing GSK’s green technology guidance: methodology for case-scenario comparison of technologies.Clean Technol. Environ. Policy, 2002, 4, 44–53.
13. Jimenez-Gonzalez, C., Curzons, A. D., Constable, D. J. C., Cunningham, V. L. Expanding GSK’s solvent selection guide: application of life cycle assessment to enhance solvent selections.Clean Technol. Environ. Policy, 2005, 7, 42–50.
14. Jimenez-Gonzalez, C., Curzons, A. D., Constable, D. J. C., Cunningham, V. L. Cradle-to-gate life cycle inventory and assessment of pharmaceutical compounds: a case-study.Int. J. Life Cycle Assess., 2004, 9(2), 114–121.
15. Butters, M., Catterick, D., Craig, A., Curzons, A. D., Dale, D., Gillmore, A., Green, S. P., Marziano, I., Sherlock, J. P., White, W. Critical assessment of pharmaceutical processes: a rationale for changing the synthetic route.Chem. Rev., 2006, 106(7), 3002–3027.
16. Marteel, A. E., Davies, J. A., Olson, W. W., Abraham, M. A., Green chemistry and engineering:
drivers, metrics, and reduction to practice.Annu. Rev. Environ. Resour., 2003, 28, 401–428.
17. Wrisberg, N. D., Haes, H. A. U., Bilitewski, B., Bringezu, S., Bro-Rasmussen, F., Clift, R., Eder, P., Ekins, P., Frischknecht, R., Triebswetter, U. InAnalytical Tools for Environmental Design and Management in a Systems Perspective, Wrisberg, N., de Haes, H. A. U., Triebswetter, U., Eder, P., Clift, R., Eds. Kluwer Academic, Dordrecht, The Netherlands, 2002, pp. 45–73.
18. Lapkin, A. InRenewables-Based Technology: Sustainability Assessment, Dewulf J., von Lan- genhove, I. H., Eds. Wiley, Hoboken, NJ, 2006, pp. 39–53.
19. Brunner, N., Starkl, M. Decision aid systems for evaluating sustainability: a critical survey.
Environ. Impact Assess. Rev., 2004, 24, 441–469.
20. de Haes, H. U., Ed.Life Cycle Assessment: Striving Towards Best Practice. SETAC Press, Brussels, Belgium, 2002.
21. Barnthouse, L., Fava, J., Humphreys, K., Hunt, R., Laibson, L., Noesen, S., Norris, G., Owens, J., Todd, J., Vigon, B., Weitz, K., Young, J., Eds. Life-Cycle Impact Assessment: The State-of- the-Art. SETAC Press, Brussels, Belgium, 1998.
22. Jimenez-Gonzalez, C., Kim, S., Overcash, M. R. Methodology for developing gate-to-gate life cycle inventory information.Int. J. Life Cycle Assess., 2000, 5(3), 153–159.
23. Jimenez-Gonzalez, C., Overcash, M. R. Energy sub-modules applied in life-cycle inventory of processes.Clean Products Process., 2000, 2(1), 57–66.
24. Hudlicky, T., Frey, D. A., Koroniak, L., Claeboe, C. D., Brammer, L. E. Toward a “reagent-free”
synthesis—tandem enzymatic and electrochemical methods for increased effective mass yield (EMY).Green Chem.1999;1(2), 57–59.
25. Sheldon, R. A. Organic synthesis; past, present and future.Chem. Ind. (London), 1992, 903–906.
26. Sheldon, R. A. Catalysis and pollution prevention,Chem. Ind. (London), 1997, 12–15.
1471–1477.
28. Ajmera, S. K., Losey, M. W., Jensen, K. F., Schmidt, M. A. Microfabricated packed-bed reactor for phosgene synthesis.AIChE J., 2001, 47, 1639–1647.
29. Cann, M. C., Connelly, M. E.Real World Cases in Green Chemistry. American Chemical Society, Washington, DC, 2000. Available at: http://www.chemistry.org/portal/resources/ACS/ACSCon- tent/education/greenchem/case.pdf.
30. Anastas, N. D., Warner, J. C. The incorporation of hazard reduction as a chemical design criterion in green chemistry.Chem. Health Saf.12(2), Mar–Apr 2005, 9–13.
31. Anastas, N. D., Incentives for using green chemistry and the presentation of an approach for green chemical design. InGreen Chemistry Metrics, Lapkin, A., Constable, D. J. C., Eds. Blackwell, London, 2008, pp. 27–40.
32. American Institute of Chemical Engineers.Dow’s Chemical Exposure Index Guide. AIChE, New York, 1998.
33. See, e.g., Hurme, M., Rahman, M., Implementing inherent safety throughout process lifecycle.
J. Loss Prev. Process Ind., 2005, 18(4–6), 238–244.
34. American Institute of Chemical Engineers.Dow’s Fire and Explosion Index Hazard Classifica- tion Guide, 7th ed., AIChE, New York, 1994.
35. Stoessel, F. What is your thermal risk?Chem. Eng. Prog., 1993, 89(10), 68–75.
36. Edwards, D. W., Lawrence, D. Assessing the inherent safety of chemical process routes: Is there a relation between plant costs and inherent safety?Trans. IChemE B, 1993, 71, 252–258.
37. Heikkil€a, A.-M., Hurme, M., J€arvel€ainen, M. Safety considerations in process synthesis.Comput.
Chem. Eng., 1996, 20, S115–S120.
38. Center for Waste Reduction Technologies. 1999. Total Cost Assessment Methodology. American Institute of Chemical Engineers, New York, NY. http://www.aiche.org/IFS/Products/TotalCost- AssessmentMethodology.aspx.
39. U.S. Environmental Protection Agency. An Introduction to Environmental Accounting as a Business Management Tool: Key Concepts and Terms. EPA 742-R-95-001. U.S. EPA, Washington, DC, June 1995. Available at http://www.epa.gov/oppt/library/pubs/archive/acct- archive/resources.htm.