Communication pubs.acs.org/jchemeduc
Developing Students’ Understanding of Industrially Relevant Economic and Life Cycle Assessments Claudia J. Bode,*,† Clint Chapman,‡ Atherly Pennybaker,§ and Bala Subramaniam†,∥ †
Center for Environmentally Beneficial Catalysis (CEBC), The University of Kansas, Lawrence, Kansas 66047, United States Baker University, Baldwin City, Kansas 66006, United States § Colorado State University, Fort Collins, Colorado 80523, United States ∥ Department of Chemical and Petroleum Engineering, The University of Kansas, Lawrence, Kansas 66045, United States ‡
S Supporting Information *
ABSTRACT: Training future leaders to understand life cycle assessment data is critical for effective research, business, and sociopolitical decision-making. However, the technical nature of these life cycle reports often makes them challenging for students and other nonexperts to comprehend. Therefore, we outline here the key takeaways from recent economic and life cycle assessments for three major commodity chemicalsethylene, ethylene oxide, and terephthalic acidthat are precursors for plastics, synthetic fibers, and many other consumer products. The five lessons and 10 discussion prompts (provided in the Supporting Information) serve as useful teaching tools for introductory chemistry and chemical engineering courses.
KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Chemical Engineering, Environmental Chemistry, Interdisciplinary/Multidisciplinary
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LEARNING FROM LIFE CYCLE ASSESSMENTS The first well-known environmental study was conducted for Coca Cola Company in 1969.1 While it pales in comparison to the more memorable headlines for that yearsuch as Neil Armstrong’s walk on the moon and Jimi Hendrix at Woodstockthis study and many others since then have changed the course of history. Tools for quantifying ecological harm pave the way for public policies, from aluminum can recycling in the case of the early Coke study to recent efforts to curb greenhouse gas emissions. They are also critical for designing new chemical processes in a way that mitigates harm to the environment and human health. Environmental impact studies have evolved over the years and are now called life cycle assessments (LCAs).1−3 LCAs assess a variety of metrics for a given process or product, such as the potential to cause acid rain, ozone depletion, cancer, global warming, smog, and so on. Learning to evaluate LCA data is a skill that will help students in their future careers as chemists and engineers make research, business, and sociopolitical decisions. However, the technical nature of LCA reports makes them challenging for students to comprehend. Several exercises have been proposed to teach students about LCAs.4−7 Here we present a set of discussion prompts that can complement these exercises or be used independently in courses and outreach events where time is more constraining or with an audience that is less technically savvy. © XXXX American Chemical Society and Division of Chemical Education, Inc.
The discussion prompts are based on actual data from our LCAs and economic assessments for ethylene, ethylene oxide, and terephthalic acid.8−10 These three common building blocks are used to make all sorts of products, such as plastic bottles for water, soda pop, and peanut butter and polyester fibers for clothing, couches, and carpets. The LCAs reveal key lessons that help students think about sustainability metrics in the context of economics. We used these prompts in a green chemistry workshop for our Research Experiences for Undergraduates program. A survey indicated that 16 of the 17 participants enjoyed the session and thought it helped them understand LCAs. Lesson 1: Think inside a Bigger Box
LCA studies start by establishing the scope of the assessment; in other words, the boundaries for which inputs and outputs to include in the calculations. For example, a box could include the complete product life cycle, everything from extracting the raw materials from the earth to disposal in a landfill. This is known as a “cradle-to-grave” LCA. Alternatively, a box could include everything from raw materials to the exit gate of the manufacturing plant (“cradle-to-gate” LCA) or only what Special Issue: Polymer Concepts across the Curriculum Received: July 20, 2016 Revised: January 6, 2017
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happens from the entrance to the exit of the manufacturing plant (“gate-to-gate” LCA). How big or small the boundary box is drawn affects the outcome. A bigger box leads to more comprehensive results but more complicated analysis. Conversely, a narrower scope is relatively easier to conduct but might fail to capture significant ecological impacts that merit further consideration. Take for example the LCA study for the novel ethylene epoxidation process being developed at the University of Kansas Center for Environmentally Beneficial Catalysis.8 The new process uses liquid hydrogen peroxide as the oxidant to convert ethylene to ethylene oxide (Figure 1) and has zero
Figure 2. To fully appreciate ecological burdens for a given process, the scope of an LCA study must be expanded to include factors upstream and downstream from the manufacturing plant.
why it is so critical to conduct LCAs early in the design process to ensure that impacts are actually mitigated rather than just shifted upstream or downstream from the processing plant. Lesson 2: Do the Math or Risk Missing the Mark
It is well-known that the 12 principles of green chemistry15 and engineering16 are good guides for steering chemists toward more eco-friendly reactions and processes. However, “greener” in qualitative terms is not always the case when the ecological impacts for a given chemical process are quantitatively added up. For example, Ghanta et al.9 conducted a cradle-to-gate LCA study for ethylene production from three feedstocks: crude oil, natural gas, and corn ethanol. While most of the predicted impacts for the three feedstocks are similar, corn has much greater soil and water pollution than oil and gas because of pesticides and fertilizers, which run off into nearby land and waterways. Greenhouse gas emissions are also much higher for corn-derived ethylene because harvesting, transporting, and processing the biomass requires the burning of fossil fuel. The lesson is clear: do not be fooled by qualitative metrics. Qualitatively, it makes sense that a “feedstock should be renewable”, as advised by the principles of green chemistry.15 However, the only way to verify that renewable feedstocks cause less ecological harm than fossil-based feedstocks is to use comparative LCAs. Students learn this lesson in discussion prompts 2−4 in the Supporting Information.
Figure 1. High operating temperatures for the conventional gas-phase ethylene oxide process14 result in burning of approximately 15% of the feedstock and product and emission of CO2. The new liquid phase process of Ghanta et al.8 eliminates burning and CO2 byproduct by operating at mild temperatures with hydrogen peroxide as the oxidant and methyl trioxorhenium (MTO) as the catalyst.
carbon dioxide byproduct.11−13 In contrast, the conventional process14 with air as the oxidant burns roughly 15% of the feedstock, making it one of the industry’s largest emitters of CO2 in terms of waste byproduct from a chemical process. Eliminating the wasteful burning that occurs in the conventional ethylene epoxidation process would lead one to assume that the LCA metrics would be more favorable in terms of greenhouse gas emissions, but this is not the case. The scope for this assumption is too narrow: it fails to consider upstream impacts from generating energy and processing the raw materials. Expanding the scope of the LCA to include onsite as well as upstream ecological burdens tells a much different tale than anticipated. The cradle-to-gate LCA by Ghanta et al.8 quantifies these upstream impacts and predicts that the new process has slightly higher greenhouse gas emissions than the conventional process (about 100 million kg of CO2 equivalents per year per 200,000 tons of ethylene oxide production). Wait, what happened? If the new process eliminates the CO2 byproduct, how can it emit more CO2? The answer lies in the manufacturing process for hydrogen peroxide, which gets its hydrogen from steam reforming of methane. This offsets the CO2 savings in the new process because for each mole of methane reformed, 4 moles of H2 are made along with 1 mole of CO2. This example, along with discussion question 1 in the Supporting Information, illustrates how important it is to think inside a bigger box. As highlighted in Figure 2, LCAs need to evaluate impacts that occur upstream from the factory to the exit gate at the factory (i.e., cradle-to-gate) and downstream of the factory if possible (e.g., cradle-to-grave) in order to fully appreciate the ecological burdens. This lesson also underscores
Lesson 3: Greener Can Actually Mean Cheaper
While environmental impacts have some influence on corporate business strategies, the biggest driver is cost. The good news is that “eco-friendly” processes can save money by reducing waste and energy. The LCA study by Li et al.10 on a new method for oxidizing p-xylene to form terephthalic acid (TA) illustrates how greener can mean cheaper and confirms the idea that sustainability makes sense as a business strategy. Figure 3 shows how TA is currently made by a two-step process. In the first step, air is bubbled into a liquid mixture of p-xylene, acetic acid, and a Co/ Mn/Br catalyst. Rapid stirring and heat help some oxygen dissolve in the liquid, but not enough to fully oxidize p-xylene. The resulting TA has a troublesome impurity (4-carboxybenzaldehyde) that must be removed in a second purification step. The new spray process concept flips things around. It showers a fine mist of the same liquid mixture used in the conventional process into a vessel loaded with oxygen. Oxygen penetrates the tiny droplets as they cascade downward, exposing more pxylene to oxygen to form highly pure, polymer-grade TA. According to Li et al.’s LCA study,10 eliminating the purification step with the new spray process would save energy and reduce greenhouse gas emissions, smog, and acid rain. It B
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Figure 4. Global warming potential for the conventional TA process compared with that of the new spray process, which cuts the gate-togate global warming potential by 75%. The inset shows that 80% of gate-to-gate greenhouse gases come from making the energy to power the process. Data adapted from Li et al.10
manufacturing would lead to major environmental benefits worldwide.
Figure 3. Current process for making terephthalic acid (TA) from pxylene (pX) compared with a new spray process.10
Lesson 5: Look Beyond the Lab To Interpret LCA Data
With at least 15 metric categories, LCA reports often reveal a complex array of positive and negative impacts to air, water, land, and human health. Making sense of these complicated data is challenging. For example, are some categories more important than others? If so, who decides? Furthermore, how does one know what the numbers really mean? Answers to these questions reside at the nexus between science and society. Scientists, business leaders, and policymakers are bound to pay more attention to some categories over others for political, economic, and geographical reasons. For example, consider the “human health non-cancer air” impact category for the conventional process for manufacturing ethylene oxide. It is reported to be 302 kg of toluene equivalents per year (based on a cradle-to-gate LCA).8 This number refers to the amount of toluene that would have to be released into the air to pose a similar level of risk to human health. In this case, it reflects the amounts of metals, inorganics, and halogenated substances emitted during electricity generation for the process. The problem is that it is hard to tell whether this level merits grave concern. While some insights can be gleaned from the U.S. Environmental Protection Agency18 and the National Institute for Occupational Safety and Health,19 sifting through toxicology data is cumbersome. Discussion prompts 9 and 10 in the Supporting Information address this complexity. The key insight here is that interpreting, communicating, and acting upon LCA data is difficult. Exposing students to such conundrums will help them develop life cycle thinking skills and prepare them to consider such multifaceted challenges in their future careers. Furthermore, teaching them how to communicate dataincluding LCA resultsto their peers and to the public is also critical in order to avoid oversimplifications or misinformation.
would also cut capital investment costs in half and save 16% in production costs. When the scale of production is on the order of a billion pounds per year, cost savings like this can become economic game changers, saving millions of dollars annually (see discussion prompts 5−7 in the Supporting Information). Lesson 4: Energy Demands a Closer Look
Of the thousands of chemicals manufactured each year, just 18 account for 75% of the industry’s greenhouse gas emissions.17 Blockbuster giants like ethylene, ethylene oxide, and TA are on this list as the building blocks for plastics, detergents, paints, textiles, antifreeze, and many other consumer products. These huge carbon footprints result from the enormous energy demands for the manufacturing processes. In fact, 80% of the industry’s energy demand goes into making these 18 chemicals. Two of our recent LCA studies illustrate this point well. For example, roughly 85% of ethylene’s overall environmental impact comes from burning of fossil fuel to provide the energy needed to power the process. Its most energy-intensive steps include the endothermic catalytic reforming of naphthas to produce ethane and the separation of ethylene from ethane.9 A similar situation applies to TA10 (Figure 4). Chemists and engineers often focus on the conversion step(s) for making ethylene oxide and TA when seeking efficiencies. However, the impacts associated with these steps the ones that occur gate-to-gate at the manufacturing plant make up a small sliver of the overall environmental impact. Figure 4 shows how significant the upstream impacts are for TA from extracting, processing, and transporting the raw materials and energy for the process. While the tendency is to focus on developing better and greener conversion steps, more efforts should also be focused upstream to reduce the overall energy demand for chemical manufacturing (see discussion prompt 8 in the Supporting Information). The key takeaway here is more of a reiteration to the calls made by other groups, such as the International Energy Agency. 17 Scaling back energy demands for chemical
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CONCLUSION While LCA studies have matured since 1969, students are rarely taught how to collect, calculate, interpret, and communicate LCA data. The discussion prompts presented in the Supporting C
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(9) Ghanta, M.; Fahey, D.; Subramaniam, B. Environmental Impacts of Ethylene Production from Diverse Feedstocks and Energy Sources. Appl. Petrochem. Res. 2014, 4 (2), 167−179. (10) Li, M.; Ruddy, T.; Fahey, D.; Busch, D. H.; Subramaniam, B. Terephthalic Acid Production via Greener Spray Process: Comparative Economic and Environmental Impact Assessments with Mid-Century Process. ACS Sustainable Chem. Eng. 2014, 2 (4), 823−835. (11) Lee, H.-J.; Ghanta, M.; Busch, D. H.; Subramaniam, B. Toward a CO2-Free Ethylene Oxide Process: Homogeneous Ethylene Oxide in Gas-Expanded Liquids. Chem. Eng. Sci. 2010, 65 (1), 128−134. (12) Lee, H. J.; Shi, T. P.; Busch, D. H.; Subramaniam, B. A Greener, Pressure Intensified Propylene Epoxidation Process with Facile Product Separation. Chem. Eng. Sci. 2007, 62 (24), 7282−7289. (13) Subramaniam, B.; Busch, D. H.; Lee, H. J.; Ghanta, M.; Shi, T.P. Process for Selective Oxidation of Olefins to Epoxides. U.S. Patent 8,080,677B2, Dec 20, 2011. (14) Rebsdat, S.; Mayer, D. In Ullmann’s Encyclopedia of Industrial Chemistry; Hawkins, S., Russey, W. E., Pilkart-Muller, M., Eds.; WileyVCH: New York, 2005; Vol. 13, p 23. (15) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford University Press: New York, 2000. (16) Anastas, P. T.; Zimmerman, J. B. Peer Reviewed: Design through the 12 Principles Of Green Engineering. Environ. Sci. Technol. 2003, 37 (5), 94A−101A. (17) Technology Roadmap: Energy and GHG Reductions in the Chemical Industry via Catalytic Processes; International Energy Agency: Paris, 2013; https://www.iea.org/publications/freepublications/ publication/Chemical_Roadmap_2013_Final_WEB.pdf (accessed November 2016). (18) U.S. Environmental Protection Agency. Health Effects Notebook for Hazardous Air Pollutants. https://www.epa.gov/haps/healtheffects-notebook-hazardous-air-pollutants and https://www.epa.gov/ sites/production/files/2016-09/documents/toluene.pdf (accessed December 2016). (19) The National Institute for Occupational Safety and Health (NIOSH). http://www.cdc.gov/niosh/npg/npgd0619.html (accessed November 2016). (20) Allen, D. T.; Hwang, B.-J.; Licence, P.; Pradeep, T.; Subramaniam, B. Advancing the Use of Sustainability Metrics. ACS Sustainable Chem. Eng. 2015, 3 (10), 2359−2360.
Information will help students build the skills to decipher LCA metrics. In this era of population growth and rising demand for chemicals, quantitative LCAs are critical for pinpointing hotspot targets for research and development.20 By building skills in this area, the future workforce will be better prepared to shape research and development, business strategies, and public policy.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00548. Questions (with answers) designed to promote discussion and improve understanding about LCA studies, building on the insights of the lessons described in the text (PDF, DOCX) Slide presentation to help explain and deliver the content (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Claudia J. Bode: 0000-0001-9627-1398 Bala Subramaniam: 0000-0001-5361-1954 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This material was created as part of the Research Experiences for Teachers program (RET: SHIFTED) at the Center for Environmentally Beneficial Catalysis, University of Kansas, with funding from National Science Foundation Grants EEC1301051 and NSF-0070960.
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REFERENCES
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