Sustainability Perspective and Chemistry-Based Technologies

Sustainability Perspective and Chemistry-Based Technologies. Subhas K. Sikdar*. National Risk Management Research Laboratory, United States ...
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Ind. Eng. Chem. Res. 2007, 46, 4727-4733

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COMMENTARIES Sustainability Perspective and Chemistry-Based Technologies Introduction The evolution of technology has given us sustained economic growth since the beginning of the industrial revolution. It has also been a story of accelerated use of the Earth’s material and energy resources. In 1987, Our Common Future,1 which is the report of the World Commission on Environment and Development (commonly known as the Bruntland Commission), and later the U.S. National Research Council’s Our Common Journey,2 warned that the way and the rate at which we have been using our declining natural resources are causing unacceptable environmental degradation and will deprive the future generations of the resources they need to sustain comparable living standards. The Bruntland Commission issued a call to action for sustainable development, which would allow economic development with improving environmental health and shared prosperity across economic strata of society, both intragenerational and intergenerational. In 1992, The United Nations organized a conference of the member nations in Rio de Janeiro, Brazil, where pledges were made to preserve the global natural resources, reduce global pollution, and improve living standards (Agenda 21). A more commitment-oriented conference was organized 10 years later in Johannesburg, South Africa, where both Agenda 21 of the Rio conference and the UN Millennium Development Goals,3 which had been agreed to earlier, were further emphasized for implementation. Separately, other treaties were negotiated to phase out ozonedepleting chlorofluorocarbons (Montreal Protocol) and to reduce emissions of global warming gases, particularly carbon dioxide (Kyoto Protocol). However, the level of success of the Montreal Protocol was not repeated by other treaties and agreements, and there is now a general dissatisfaction with the progress of sustainable development.4 A series of perspectives in the journal Science in 2003 analyzed the state of the Earth, featuring declining lifesupporting ecological resources and increasing environmental pollution resulting from ever-greater economic development and human consumption.5-10 These effects, together with the persistent economic gap between developed and developing nations, are at the core of the sustainable development movement. Mitigating these problems, especially in the face of increasing population, occurring mainly in the developing nations, remains a huge challenge before humankind. Proposed policy enablers of sustainability typically imply restrictions on human consumption of known exhaustible resources and the attendant emissions of substances that are, one way or another, offending to the environment. However, these proposed limits to the current mode of exhaustible resource use create innovation opportunities for newer scientific technologies. Thus, ultimately, clever application of science to solve both the resource use and environmental impact problems could prove to be the greatest enabler of sustainability. * Tel.: 513-569-7528. Fax: [email protected].

513-569-7549. E-mail address:

Sustainable development can be defined as “improving the quality of human life while living within the carrying capacity of supporting ecosystems”.11 It represents continued global economic development that incorporates ecological considerations, while fostering intragenerational and intergenerational societal and economic equity, eventually reaching, over time, conditions that will support civilization for as long as humans exist. To be helpful, technologies must include these ideas at the stage of design and development. The science framework needed for this purpose has been called “sustainability science”,12 which can be considered to be a pooled knowledge base derived from many scientific and socioeconomic disciplines. One must note that there is no generally agreeable framework for sustainability science. However, the idea of sustainability has appealed to people of all walks of life, including stewards of industry, practitioners of science and technology, social scientists, and policy wonks. Therefore, we must find the scientific foundation that would be helpful to designers of technology for providing what may be called sustainable technologies. To establish itself as a science-based field, tools and technologies for sustainability must deliver quantifiable realworld solutions to well-defined systems. Attempts at this goal have already begun in industry worldwide, as industry finds opportunities for creating wealth by “going green”, i.e., by producing products with less attendant wastes and that require less energy and materialsin other words, by reducing ecological footprints. The evolution of technologies so far has been focused on delivering benefits without much concern for the consequences. Some examples are nuclear energy without addressing waste, CFCs without looking at greenhouse potential, chlorine compounds without examining persistence in the environment, or drug efficacy without considering endocrine disruption. In many such cases, the knowledge of the consequences came later, but now the developers of technologies, working collaboratively with appropriate regulators, should actively look for the impacts on the environment and human heath before introducing such processes and products. Another issue is that those who are developing technologies for their benefits are not the same people who are necessarily concerned about the impacts. This professional gulf certainly exists between disparate disciplines, but also exists even in the fields of chemistry and biology. Dialogues across scientific, engineering, and socio-economic disciplines at the technology development levels must happen to address sustainability issues effectively. Recently, industry has initiated the process by starting to work with regulators and environmental groups. Sustainability and Science-Based Approaches The Brundtland Commission’s report supported economic development all around, while insisting on not depriving future generations of adequate material and energy resources. That is,

10.1021/ie0700056 CCC: $37.00 © 2007 American Chemical Society Published on Web 06/01/2007

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Figure 1. Per-capita gross domestic product (GDP) of nations versus the ecological footprint (EF). (Reproduced from Bell and Morse.16)

to secure its living standards, the present generation must not exploit natural capital that is degradable and exhaustible, such as minerals, plants, land animals, aquatic creatures, clean water, land, and fossil fuels, at higher than their regeneration and recycle rates, as it does now.13 Currently, humanity is using the aggregate natural capital 21% faster than the Earth can renew it.14 Wackernagel and Rees15 proposed the use of an ecological footprint as a rough measure of natural capital consumption. The ecological footprint is the hypothetical measure of land and water that an average person requires to produce what he/she desires for consumption and waste disposal, expressed in terms of hectares per capita. As shown in Figure 1, the economic productivity of nations, expressed as the real gross domestic product (GDP) per capita, on the basis of purchase power parity, plotted against the ecological footprint (EF), shows a sharp increase at low EF but levels off at EF ≈ 5 hectares/capita.16 Economic success and consumption for a modern lifestyle requires the use of natural capital; this might explain the part of the curve where EF rises with per capita GDP. However, the developed nations fall at the high end of the EF scale and the temptation may be to conclude that these economies are comparatively wasteful (for reference, the EF for the United States is 9.6 hectares/capita). In that case, if EF can be used as a rough guide for comparing efficiencies of natural capital use among nations, the developed nations, in theory, can greatly reduce resource use (at least by 50%) for the same GDP/capita, by applying more-efficient innovative technologies. A comparison of the EFs of the United Kingdom and Germany (both 4.6) with that of the United States would be instructive. The GDP/capita values are comparable but the EFs are not. However, it is not easy to explain the discrepancy in simple terms. Per capita GDP may be one indicator of national productivity, but it is not a good indicator of preferred lifestyles, which may be part of the explanation. The EF may be a useful metric of sustainability of nations, but by no means is it the only one. Other metrics are needed for meaningful discussions of sustainability. For a comprehensive review of the EF analysis, the reader is referred to the Global Footprint Network (www. footprintnetwork.org). Sustainability Systems and Surroundings. It is helpful to discuss sustainability in system context defined by boundaries. Initially, sustainability meant judicious use of global resource reserve, environmental protection, and societal equity. Literally, it would imply the maintenance of an envisioned state at which the net depletion of global natural resources is zero forever, while economic development continues. The reality of this everchanging world is that, by 2050, the world population is expected to rise to, and perhaps stabilize at, 10 billion people, with attendant increased consumption to support them at an average living standard higher than today’s. Over time, however,

various other descriptions, such as economic sustainability, societal sustainability, and environmental sustainability, have appeared in the literature. For instance, the seventh of the United Nations’ (UN’s) millennium development goals is the attainment of environmental sustainability.3 There are mentions in the literature of place-based sustainability at various scales, such as sustainability of communities, ecosystems, towns, villages, and watersheds. The Sustainable Seattle Project16 is an example of place-based sustainability. Other objectives focus on specific problems, such as water sustainability and energy sustainability. There then is also industrial sustainability. From a practical viewpoint, however, the approach of place-based, problem-based or industrial sustainability does attempt to tangibly define the systems. When a system to be sustained is well-defined, it is easier to identify the variables that affect the system and to manipulate the variables to take it to the desired sustainable state. Very often, a system at a larger scale will have subsystems inherent in it. In chemistry-based industrial operations, an example would be a manufacturing network producing many products in several plants. The task at hand would then be to sustain the network without making any of the desirable subsystems unsustainable. However, it should be mentioned in passing that Voinov17 argued that, from a systems analysis viewpoint, there is an inherent conflict among hierarchical systems in ecology, economy, and social sciences characterized by conservation and renewal. He provides examples where systems at higher levels become sustainable at the expense of subsystems. If one were to apply this logic to a multiplant manufacturing scenario, the processes that are environmentally and economically inferior to competing processes would have to be redesigned or shut down. Such events are not uncommon in the industrial sector. However, a defined system cannot be considered in isolation, because a system and its surrounding are intricately linked by their impacts on each other. Thus, a system and its surrounding should be simultaneously defined and the sustainability of the system-surrounding pair should be considered. System-Surrounding Paradigm in Assessing Technologies. In the context of the application of chemistry-based sciences, the purpose would be to produce sustainable products and processes. This objective cannot be achieved simply by ideas such as pollution prevention or design for the environment. A scientific approach to sustainability should consist of defining the system to be sustained together with its surrounding, envisioning a sustainable state of the system, finding practical approaches toward the envisioned state, and applying appropriate metrics to quantify the improvement. Figure 2 shows a schematic of the importance of system definition and metrics development for decision making in processes that might involve, among other things, chemistry, material, and biological sciences. The outcome of this approach can establish if the system and the surroundings, as a result of a planned intervention, is “more sustainable” than before. A key technical approach is to determine what economic, societal, and environmental impacts of the system are expected on itself and on the surroundings. These metrics must be identified. For a system to have a favorable sustainability outcome, the metrics for both must show benefits. For instance, at the scale of a chemical process system, our concerns for the surroundings are (a) health and ecological impacts on air, water, and land; (b) the type and amount of energy used; and (c) end-of-life fate and societal benefit/cost of the products and byproducts. The corresponding impacts of the system that are expected on itself would consist of potential health and safety of the workers. The familiar

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Figure 2. Moving to a more sustainable solution. Table 1. Examples of Commonly Used Systems with Surroundings system objective product manufacturing water sustainability

scale

surroundings

process technology

desired impact

environment, proximate product benign to environment and community, consumers, human health, beneficial to society supply chain, and economy, greatly reduced end of life products emissions and wastes business location, surrounding community, states, quality water for business, potable water community nations for inhabitants, tourism, elimination of conflicts with neighbors

energy sustainability regional, national environment, international community, human health, living standards of people

method of lifecycle analysis (LCA), which is used to provide an account of pollution, health and environmental impacts, energy expenditure, societal benefits, and costs incurred for a product or process, can be helpful in characterizing the surroundings. At the current stage of development, the application of LCA is time-consuming, data-intensive, and expensive. To facilitate rapid adoption of LCA, simpler low-cost methods must be developed. In Table 1, three common sustainability system objectives are shown with their surroundings, the scale, desired impact, and the technology approaches to be deployed for sustainable development. Chemistry and allied disciplines have significant roles in these three systems. Table 1 by no means is exhaustive and similar descriptions for other systems can easily be developed. Progress toward Sustainable Technologies. Systems for sustainability can be classified as belonging to four types: technology, business (or institutional), regional, and global.18 Table 1 was constructed with systems that belong to the first three types. The number of attributes that adequately describe a system grows, as does the uncertainty in modeling it, as the system complexity is increased from a process technology to a business enterprise to a regional or global problem. For a

science/engineering green chemistry/engineering, biotechnology, nanotechnology

separation science, environmental engineering, recycle/purification technology, source protection, energy technology, use efficiency such as drip irrigation or use of information technology in agriculture greenhouse gas reduction, great reduction energy technology, biotechnology, in potential water pollution and pollutants material science, ecology, transfer across geographical boundaries. process chemistry, chemical Also, one nation’s energy sustainability engineering may undermine that of other nations.

chemical process, these attributes may be purity of the raw materials, the process chemistry, the reaction rates, the separation factors of species, the recycle rates of streams, the overall yields of products, and byproduct or waste generation rates. These process attributes are controllable. The attributes of the surroundings are to be so chosen as to reflect the three aspects of sustainability: economic, ecological, and societal. The metrics needed for tracking the system and the surrounding are likely to be better known for less-complex systems. A redesigned system can be considered improved only if the chosen metrics representing the system and the surroundings improve as a result of technical improvement in the system. For a chosen process technology system, the sustainability question, given the superior performance of the attributes of the process, is this: Is the process safer and more protective of the workers? The corresponding sustainability questions for the surrounding are as follows: (1) What are the economic benefits of the system improvement for the manufacturer and its employees (economic)? (2) What are the additional human health and environmental benefits as a result of the process modification (ecological)?

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(3) What are the benefits to consumers, in terms of convenience or improved lifestyle, to the neighborhood population, their infrastructure, and the like (societal)? The desired metrics need to assist in answering these questions. Currently, much interest in sustainability is observed in all the science and engineering literature. Promises of a moresustainable world have been discussed for chemistry-based sciences.19-25 Metrics for Sustainable Processes and Products Metrics development is the most urgent of the sustainability research needs. Metrics used for analyzing the sustainability of systems will have to reflect all three aspects of sustainability: ecological, economic, and societal. Some progress has been made in the development of sustainability metrics for chemistrybased sciences and engineering.18,26-32 For systems that involve chemical and biological changes, some metrics have been used (atom efficiency, energy intensity, material intensity, pollution intensity, toxicity index, ecoefficiency, ecological impact, health effects, etc.) So far, no recommended set of metrics for process systems is available from which appropriate metrics could be chosen for individual systems. For instance, the U.K. Institution of Chemical Engineers (IChemE; www.icheme.org/sustainability) proposed a long list of metrics that belongs to the three aspects of sustainability. These metrics were suggested for application to individual processes or a manufacturing site with multiple production units. On the other hand, the Center for Waste Reduction Technologies (CWRT) of the American Institute of Chemical Engineers (AIChE)30,31 proposed a small set of metrics that includes material intensity, energy intensity, pollution intensity, toxic release intensity, and water use intensity. These metrics were termed “sustainability metrics”. Sikdar18 argued that some of these metrics proposed by AIChE do represent all three aspects of sustainability and could be used for some industrial processes. Nevertheless, metrics development, for industrial processes as well as all other sustainability systems previously mentioned, is an emerging area, and the success of sustainability analyses, from a sound science perspective, is critically dependent on it. Broader Sustainability Picture for Technology Research: Energy, Materials, and Water The scope of the contribution to the sustainability of chemistry and allied sciences and engineering can be described as accomplishing cleaner technologies that use minimum of energy and material, generating little waste and, at the same time, minimizing the emissions of toxic materials to the environment. The expected outcome is the production of “more sustainable” technologies. When we map our technology needs to the availability of material and energy resources, we are forced to consider some major global issues that must be addressed for the success of systems at any level. We recognize the global or local availability of energy and material resources that do not harm the environment as the main constraints. The most important concern about global sustainability is the need for affordable energy for improving the lifestyle of humans. Smalley33 suggested that, of the ten most important challenges facing humanity in the present century, energy is the foremost, ahead of any other issues. The predominant energy sources today are fossil fuels, but continued reliance on these sources increases atmospheric greenhouse gases, which are suspected by many

as contributing to global warming. Known reserves of fossil fuels (mainly, petroleum and natural gas) are believed to become completely depleted in the foreseeable future.34 However, Huber and Mills35 argue that energy is not scarce; it is the useful highergrade energy that is in short supply at reasonable and affordable prices. As the prices of easily obtainable energy increase, other fossil sources (such as oil shale and Canadian tar sands,36 and even ocean floor methane hydrate37), can become practical. Similarly, there are plenty of coal reserves, which can be relied upon for power generation, and for the conversion to liquid fuels for use in transportation. The reality is that, as long as there are no alternative energy available to replace fossil fuels for power and transportation needs, fossil fuels (coal, natural gas, oil) will continue to be used, ensuring that atmospheric greenhouse gases will reach levels that are thought to be dangerous. Even with full compliance with the Kyoto Protocol, which exempts some rapidly developing nations such as China and India from any emissions limits, the atmospheric carbon dioxide level is expected to reach 550 ppm by the end of the century.4,34 Yet, many researchers believe that ill effects of global climate change are expected to begin to appear above a level of 450 ppm.38 Of all the threats to sustainability, global warming due to the accumulation of greenhouse gases in the atmosphere is potentially the gravest. Climate models show that the net absorption of solar energy by the Earth is 0.85 W/m2, which could lead to an increase of 0.6 °C in the global average temperature in this century,39 the effects of which are not known precisely but are believed to be quite undesirable. If this is a probable scenario, carbon dioxide sequestrationsmost significantly, from coal usesis the only option available for mitigation in the short term. The United States Department of Energy has identified several different options for sequestration (deep ocean, depleted oil and gas reservoirs, etc.40). A significant fraction of the power generated from fossil fuels will be consumed in achieving sequestration, resulting in a gross reduction in the overall efficiency of power generation. Sequestration of carbon dioxide is an area that would require much chemical and engineering research. This option will be expensive and is subject to public policy choices. The developed nations have made impressive gains in energy efficiency since the Arab oil embargo of the 1970s, and more gains are expected. As it stands today, the carbon emission per unit of GDP (a metric of economic efficiency) of developed economies is better than average for all nations, even though the per-capita carbon emission (a metric of standard of living) is among the highest,41 as shown in Figure 3. In addition, relative oil use efficiency of advanced economies is among the best,42 as shown in Figure 4. The developing nations have a bigger challenge in energy efficiency. These efficiency gains will come not just from power generation but from chemical and allied industries, domestic uses, and heating and air conditioning. The alternative to fossil fuels is that renewable energy and power must be developed in quantities sufficient to supply the needs of an increasingly technologically sophisticated population. At this juncture, it should be clear that the urgency for alternatives to fossil fuel is not so much due to the potential shortage of such fuels but the potential of serious climate changes that are caused by the accumulation of greenhouse gases in the atmosphere. For the United States, it is also politically expedient to become independent of imported oil. In all likelihood, the replacement of fossil fuels would be a combination of different methods, depending on opportunities that are specific to the geographic locations. For stationary power generation, an increasing fraction could come from nuclear

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Figure 3. Carbon emission per capita and per-unit GDP of nations.

Figure 4. Relative oil use efficiency of economies.

power plants. However, significant concerns exist about the handling of radioactive waste, availability of a sufficient amount of uranium, and international safeguards. There is also public reluctance in permitting nuclear power plants in several countries. Solar thermal power also has a future.43 Wind and photovoltaics can be thought to have potential as peak-power suppliers to stationary base-power stations. Technology development and market in both these areas are rapidly increasing; however, for the short term, these sources will remain a minute fraction of the aggregate demand. Biomass-derived energy seems to have a particular potential for the transportation sector, which is almost exclusively petroleum-dependent. The approach of making ethanol from corn has received attention in the United States, but corn alone cannot be expected to meet the demand for transportation fuels, and there will be a tradeoff with corn as food or feed. Significant

interest is observed in the industrial development of ethanol or other fuel alcohols from cellulosics (including energy crops such as switchgrass) and biodiesel from vegetable oils and animal wastes. The National Energy Policy Commission (NEPC)44 estimated that transportation fuels from cellulosics are quite promising in regard to meeting the needs of half the passenger vehicles in the United States, without affecting food supplies and land use restrictions. However, research and development in this area is still embryonic, despite some breakthroughs in enzymatic hydrolysis of cellulose and pilot-plant-scale testing. This approach currently is not cost-competitive with corn ethanol. NEPC also recommends plug-in hybrid vehicles, which will provide electric power for the first 20 miles before switching to the hybrid mode. Research on improving storage batteries is a key for this development. However, biomass ethanol cannot use the existing petroleum distribution network. Biodiesel, on

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the other hand, is compatible; however, its promise is not as extensive. Overall, when all the technical hurdles are overcome, transportation fuels do seem to have a future for significantly relieving the dependence on petroleum and, hence, carbon dioxide emissions into the atmosphere. As a solution to the potentially harmful effects of global warming, the replacement of fossil fuels with alternatives can only be achieved by concerted international efforts, if the technical hurdles can be overcome. In regard to the hurdles of market forces, there are no easy answers here. In the area of materials use, to minimize extraction from the Earth, energy-efficient and durable materials syntheses (such as those for buildings and construction) and recycle/reuse are the primary research areas where significantly more effort must be spent. Most of the metal recycle can be recovered for the original use; however, for plastics, rubber, and fiber, the recycle material usually finds lower-grade use (hence the lower price), and it is a matter of time before they ultimately become trash again. Depolymerization makes technical sense; however, the technologies, except for condensation polymers, are not available. For this reason, although 32% of plastic milk containers are recycled, plastics as a whole enjoys only 2%-4% recycle. In cost and energy terms, the recycling of metals such as iron and aluminum is preferable to processing virgin materials. However, for metals that are in wastes in oxidized form and/or dispersed in the environment, recycle/reuse may not be an option. The general approaches of green chemistry and engineering are experiencing a great surge in research and development in industry and academia throughout the world. Syntheses of chemicals and polymers under milder conditions that require less energy and result in fewer waste, elimination of the use of toxic chemicals and solvents that may end up in the environment, syntheses of alternate chemicals to replace those which are offending to the environment and human health, and reaction pathways for new chemicals that can substitute many of the chemicals currently in use are some of the promises of these approaches. However, all green chemistry processes cannot be construed as sustainable on face value; appropriate sustainability metrics must be used to validate their promise. Smalley’s second most global concern was the availability of safe water; it is also a UN Millennium Goals priority. Given the rapid urban development that is occurring around the world now, the demand for safe water has been rapidly increasing. Yet, there are parts of the world that are water-starved. In addition, many of the rivers and much of the aquifers are polluted. The production of safe water for industry, agriculture, and human consumption from brackish water and seawater, as well as wastewaters, require affordable technologies. Technology needs in this area are appreciated by private sector companies, who are making aggressive investments to make water, as well as water-producing equipment and systems, a commodity business. The largest reverse-osmosis plant for drinking water has been producing 600 000 m3/day, at a cost close to $0.6/m3, at the Ashkelon plant in Israel since 2006. This plant uses seawater, and the brine discharge is still an unsolved problem. Much research must be conducted on problems related to water production in the future. The sustainability challenges of the day are being addressed by governments everywhere with regulatory measures that are creating market demands for technologies. The potential for chemistry-based approaches is vast. The United States commands the largest share (31.9%) of the global research and development.45 Many of the solutions for these challenges, over

time, will be achieved by innovations made in the United States. Research dimensions of these challenges for chemistry-based sciences have been recently addressed by the National Research Council.46 Despite the best intentions, many promising approaches discussed here, in regard to sustainability analyses, may ultimately appear to have unintended and undesirable consequences. The application of sustainability metrics to determine impacts early in the process is a prudent path to ensuring that technologies of the future do lead us to a moresustainable world. There are many barriers to attaining sustainability. Yet, individual processes and industrial networks are the two sustainability systems that will benefit most directly by the application of chemistry-based sciences and engineering, and these procedures could provide sustainable technology systems. Such is not the case for regional and global systems, for which science and technology could provide solutions that could only be put to use via sociopolitical means. Conclusion The application of chemistry and allied sciences can have a significant role in the attainment of sustainability when the broader issues of sustainability are integrated at the technology development phase. Several main points constitute the conclusion of this work: (1) Sustainability is system-based. The development of any technology or a cluster requires defining it as a system and identifying its surrounding. (2) Appropriate metrics for sustainability analysis must be identified and applied to both the system and the surroundings on a lifecycle basis. The resulting technology solution should improve both. (3) Sustainability concerns of economic development and environmental and societal impacts require that those involved in technology design and development have a working awareness of the consequences of products and processes and, for quantifying the consequences, work collaboratively with other experts and regulators. (4) Because sustainability transcends the basic practice of these sciences, constraints imposed by exhaustible energy and material resources must be recognized. Energy at local and global levels is the primary constraint on sustainable development. Both efficiency and climate change potential must be considered at the design phase. (5) Chemistry and allied sciences will see many opportunities in solving many of the economic and environmental issues of sustainability, including the broad energy and material resources problems. Acknowledgment The technical opinion expressed in this paper is that of the author only, and not necessarily that of the Environmental Protection Agency. The author gratefully acknowledges benefiting from reviews of the manuscript by Jeff Siirola (Eastman Chemical), Earl Beaver (Practical Sustainability), Dennis Hjeresen (Los Alamos National Laboratory), and Alva Daniels (U.S. Environmental Protection Agency). Literature Cited (1) World Commission on Environment and Development. Our Common Future; Oxford University Press: Oxford, U.K., 1987. (2) Board on Sustainable Development, Ploicy Division, National Research Council. Our Common Journey: A Transition Toward Sustainability; National Academy Press: Washington, DC, 1999.

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Subhas K. Sikdar* National Risk Management Research Laboratory, United States EnVironmental Protection Agency, Cincinnati, Ohio 45268 IE0700056