By Sarah Kennedy, PhD and Henry Nowicki, PhD
What stage is your company in along its path to profit from green chemistry and to improve sustainability? There are several obvious stages: not even thinking about green; no educational and corporate culture focused on green; not aware of costs and benefits; interested but do not have a plan to implement; lacking a hierarchical list of green projects to work on; committed and actively engaged in making green concepts to create revenue; improve firm’s and customer’s sustainability and thinking about how to evaluate a specific process to improve its sustainability. It is important to assess your firm’s stage at going green because sustainable products and services are critical for long-term successful business growth. This article provides guidance on how you can begin to assess a chemical process for sustainability using green metrics.
Two fundamental, quantitative green metrics
Individuals in the chemical industry recognize the benefits of being more environmentally friendly and utilizing green chemistry in their processes, but how does an individual or business actually assess for green attributes? While it is nearly impossible to quantify the complete impact of a process on environment and health, many accessible metrics have enabled chemists and engineers to evaluate their processes and make significant improvements. Development of green metrics has been the topic of much research in industry and academia for several years; contributions are continually being made to make green assessment more manageable. This article serves to provide an overview of state-of-the-art metrics used in green evaluation, as well as give good examples of implementation.
Calculating two of the original green metrics, percent atom economy (AE) and environmental factor (E-factor), is a base line for green assessment of any chemical process. AE can be calculated by dividing the molar mass of the desired products by the molar mass of all reactants in the stoichiometric reaction equation.1 This gives a simple measure of how many reactant atoms are incorporated into the desired product. By definition, rearrangement and addition reactions have the highest percent atom economy. Roger Sheldon’s E-factor, is calculated by dividing kilograms (kg) total waste by kg product.2 Published E-factors in industry segments including oil refining, bulk chemicals, fine chemicals and pharmaceuticals, revealed the gravity of the issue of waste production and spurred many companies to action.3 One exemplary model using these metrics is the development of a greener ibuprofen synthesis by the BHC Company, which was awarded a Presidential Green Chemistry Award for its success in increasing the atom economy of ibuprofen synthesis from 40 to 77 percent.4 Calculating AE and E-factor provide a base line for current processes and will provide a benchmark for assessing improvements.
Quantitative metrics for specific chemical types
If only the atom economy and E-factor metrics are utilized, the type and impact of the waste products and starting materials are ignored. It is imperative to conjugate AE and E-factor with metrics that evaluate human health and environmental impact from specific chemicals. All chemicals do not have the same hazards. An academic exercise, which may be adapted to any chemical process, has been used to quantitatively evaluate competing synthetic routes with nine metrics.5 All materials in a synthesis, whether consumed or produced in the reaction, are evaluated by each metric, after which the competing routes can be compared for greenness. These metrics include acidification potential, ozone depletion potential, smog formation potential, global warming potential, human toxicity by ingestion or inhalation, persistence, bioaccumulation and abiotic resource depletion potential. The cumulative risk index equation is I = Pm, where the risk potential of each metric (P) is multiplied by the mass (m) of chemical released into the environment to give an overall risk index (I). Each of the nine metrics is compared against a relevant compound depending on the subject of impact. Depending upon the nature of the process being evaluated, some metrics may carry more importance than others. This provides considerations for improvements.
Land use and its important metrics
In addition to the above metrics, the use of land contributes significantly to the overall greenness of a particular process. The sustainable process index (SPI) operates on the principle that land is a limiting resource and must be included in process evaluations. The SPI includes factors such as maintaining biodiversity, rate of renewable resources utilization and generation and flow of anthropogenic materials in a given land area.6 Each metric contributes to better understanding the impact of a given process. There are several more metrics than those mentioned here. In fact, the American Institute of Chemical Engineers’ Center for Waste Reduction Technologies (AIChE/CWRT) has developed several sustainability metrics that can be found by searching their website (www.aiche.org/cwrt).
LCA environmental metrics
The best way to measure the environmental impact of a product is to do a complete life cycle assessment (LCA). A useful tool is the Handbook on Life Cycle Assessment: Operational Guide to the ISO Standards available to act as a guide for performing a complete LCA in compliance with ISO standards. An LCA considers all impact factors from cradle-to-grave, starting from exploration, extraction, manufacturing, transportation to use and ending with the need for disposal/recycling at the conclusion of the product’s usefulness. Four stages of evaluation are required for an LCA: 1) identifying the LCA goal and scope; 2) data collection on material mass and energy flow; 3) impact assessment using green metrics and 4) interpretation and evaluation.7 Identifying the goal of the LCA requires defining the processes that will be evaluated and which environmental impacts will be calculated. The LCA outcome is only useful if the goal and scope are decided upon prior to implementation. Data collection is the process of creating energy and material flow sheets to account for all inputs and outputs of a process. This requires some database searching as well as educated guesstimates. The third step is to apply the chosen green metrics to the energy and mass flow sheets that were created. Comparison of the metrics during the interpretation/evaluation step will reveal those areas of the process that can be improved.
Green chemistry case study
In a 2001 review article in Green Chemistry, several scientists from GlaxoSmithKline (GSK) explained how they developed a sustainability-based approach to assessing their synthetic organic reactions, an approach very similar to a life cycle assessment.8 The group adopted some of the CWRT metrics to develop a Design for the Environment Tool Kit, which helped guide their scientists in synthetic route decisions. In addition to the metrics, the scientists added Life Cycle Inventory/Assessment (LCI/A) and Total Cost Assessment (TCA) data methodology to their toolkit. Next, they categorized 200 of their reactions by chemistry type and applied the metrics of atom economy and reaction mass efficiency to identify the best green chemistries. Implementation of this tool kit has revealed that solvent waste had the largest negative impact on the LCA. Also, they concluded that it is imperative for chemists and engineers to work together to improve the green impact of a process because both synthetic methods and design influence the green metric calculations. In a related article, a GSK team presented a relatively simple flow sheet to monitor reactions for green impact, which they have implemented in research and development.9 Using this flow sheet along with the company’s Solvent Selection Guide helped decrease the environmental impact of their synthetic methodologies.
These examples can be a guide for implementing some green changes at a wide variety of companies, including water and air purification products and services. The main take-home lesson to remember is that improvement toward green is always possible, no matter what stage of the firm’s green chemistry development. Sustainability and green chemistry are required for the success of the chemical industry worldwide. Using the metrics discussed here, and researching others that are used in the industry, will ensure that processes are continually moving toward sustainability.
Collaborations with green chemistry experts
The quantitative solutions explained here require those experienced in green chemistry to work closely with industry partners to bridge knowledge gaps regarding green assessment. Working together with green experts to evaluate processes using green metrics is an important step in companies’ path to sustainability.
As an example, the Oregon Green Chemistry Advisory Group (OGCAG), consisting of academia, industry, public and non-governmental agencies, studied the green chemistry landscape in Oregon and presented four key recommendations to help the state remain a leader in sustainable business and green innovation.10 One of the main recommendations, to “enhance Oregon’s existing and future workforce through education and training,” implied the need for green experts to propagate information to businesses about green assessment. In addition, OGCAG clearly demonstrated the necessity for collaboration between green chemistry educators, industry leaders and consumers to help increase awareness of sustainable practices.
In a prior article,11 the authors provided green chemistry that gives guidance on how to approach green assessment for a given process. Counting percent atoms in reactants that end up in a sellable product is important. Reactant atoms lost on the way to sellable products create major dollar-cost for regulatory waste disposal. The waste disposal of side reactions and unreacted reactants, low yields and solvents is a major cost of manufacturing. Recycling waste and cutting disposal costs through green chemistry principles can be important to your sustainability. It is cheaper to avoid waste production using green chemistry than to clean it up at the end of the pipeline to protect health and the environment. Working with green chemists and creating a team focused on green assessment will move your company in a positive direction.
- Trost, B.M. “The atom economy-a search for synthetic efficiency.” Science 1991,254 (5037), 1471-1477.
- Sheldon, R.A. “Organic Synthesis-past, present, and future.” Chem. Ind. (London) 1992, (Dec.), 903-906.
- Sheldon, R.A. The E factor: fifteen years on. Green Chemistry. 2007, 9, 1273-1283.
- Cann, M.C. and Connelly, M.E. “Real-World Cases in Green Chemistry.” American Chemical Society and U.S. Environmental Protection Agency. 2000, vol. 1.
- Mercer, S.M.; Andraos, J. and Jessop, P.G. “Choosing the Greenest Synthesis: A Multivariate Metric Green Chemistry Exercise.” Journal of Chemical Education 2012, 89, 215-220.
- Doble, M. and Kruthiventi, A.K. “Green Chemistry & Engineering.” Elsevier 2007.
- Lancaster, M. “Green Chemistry: An Introductory Text.” Royal Society of Chemistry: Cambridge, 2010; Vol. 2.
- Curzons, A.D.; Constable, D.J.C.; Mortimer, D.N. and 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 Chemistry 2001, 3, 1-6.
- Constable, D.J.C.; Curzons, A.D.; Firetas 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. and Yu, M. “Green Chemistry measures for process research and development.” Green Chemistry 2001, 3, 7-9.
- Oregon Green Chemistry Advisory Group. Advancing Green Chemistry in Oregon 2010 Report. Oregon Environmental Council. Website accessed September 2012. http://www.oeconline.org/our-work/economy/green-chemistry/advancing-green-chemistry-in-oregon.
- Kennedy, Sarah and Nowicki, Henry. “Going Green Basics and Benefits of Green Chemistry.” Water Conditioning & Purification, 2012, (July), 42-44.
About the authors
Sarah A. Kennedy, PhD, is Assistant Professor of Chemistry at Westminster College and Director of the PACS short course on green chemistry. Participants in this PACS course will learn basics of green chemistry and leave with a toolbox of metrics and examples to help guide their implementation of sustainable chemistry and business. Kennedy’s PACS course is provided at client’s time and place and on public schedule. See www.pacslabs.com for details.
Henry Nowicki, PhD and MBA, is President and Senior Scientist for PACS Laboratories, Consulting and Training Services. He has been awarded SBIR R&D grants on activated carbon new product development. Nowicki teaches the introductory class for the Activated Carbon School. Questions, comments and suggestions for future green chemistry articles are welcomed: phone (724) 457-6576 or email Henry@pacslabs.com.
About the company
Professional Analytical and Consulting Services Inc. (PACS) and Activated Carbon Services Inc. is a 29-year-old incorporated firm providing activated carbon laboratory testing services, R&D, consulting and short-course programs for scientists and engineers. The short-course program includes 59 different short courses for scientists, managers and engineers. PACS also provides a short course and consulting on green chemistry.