Over the past three lessons, we looked into different methods and frameworks that can be used for evaluating technologies or technology-dependent systems. Those methods involved both qualitative and quantitative metrics. The main challenge, however, is that there is no unified system of evaluation developed or recommended so far, and we have to be case-sensitive when choosing our path for the evaluation of a particular project. In further lessons, we visit different areas of industry and technology and see how the evaluation approaches are adapted to those specific topics. We will learn from real-life case studies and try to see which of the previously reviewed methods would be applicable for analysis and which would be not. Lesson 4 explores the areas of green chemistry and advanced materials. We will see how the principles of sustainable development are tuned for these areas and what steps are taken to implement them.

Learning Objectives

By the end of this lesson, you should be able to:

• understand and explain the principles of green chemistry;
• articulate the benefits and obstacles of green chemistry applications;
• evaluate the promise of alternative chemical technologies;
• explain the ways the multifunctional materials can impact the technological systems.

Readings

• Website: 12 Principles of Green Chemistry, American Chemical Society, 2014.

Reading materials for this lesson are mostly contained within the course website. The lesson contains multiple links to web resources, and you are alerted to open the most important ones. Some optional reading resources are referenced in blue boxes in the body of the lesson.

Questions?

If you have any questions while working through this Lesson, please post them to our Message Board forum in Canvas. You can use that space any time to chat about course topics or to ask questions. While you are there, please feel free to post your own responses if you are able to help out a classmate.

Green chemistry is the approach in chemical sciences that efficiently uses renewable raw materials, eliminating waste and avoiding the use of toxic and hazardous reagents and solvents in the manufacture and application of chemical products. Green chemistry takes into account the environmental impact and seeks to prevent or lessen that impact through several key principles outlined below.

Here are the 12 key principles of green chemistry as formulated by P.T. Anastas and J.C. Warner, in Green Chemistry: Theory and Practice, 1998.

1. Prevention. It is better to prevent waste formation than to treat it after it is formed.
2. Atom economy. Design synthetic methods to maximize incorporation of all material used into final product.
3. Less hazard. Synthetic methods should, where practicable, use or generate materials of low human toxicity and environmental impact.
4. Safer chemicals. Chemical product design should preserve efficacy whilst reducing toxicity.
5. Safer solvents. Avoid auxiliary materials - solvents, extractants - if possible, or otherwise make them innocuous.
6. Energy efficiency. Energy requirements should be minimized: conduct synthesis at ambient temperature and pressure.
7. Renewable feedstocks. Raw materials should, where practicable, be renewable.
8. Reduce derivatives. Unnecessary derivatization should be avoided where possible.
9. Smart catalysis. Selectively catalyzed processes are superior to stoichiometric processes.
10. Degradable design. Chemical products should be designed to be degradable to innocuous products when disposed of and not be environmentally persistent.
11. Real-time analysis for pollution prevention. Monitor processes in real time to avoid excursions leading to the formation of hazardous materials.
12. Hazard and accident prevention. Materials used in a chemical process should be chosen to minimize hazard and risk for chemical accidents, such as releases, explosions, and fires.

Chemists are guided to use these 12 principles as a checklist for evaluation of a specific process or chemical technology at the stage of design and scale-up.

Initiation and development of the above-listed principles was closely tied to the Pollution Prevention Act enacted in the USA in 1990. This document was a turning point in environmental policy by putting a particular focus not on environmental remediation and clean-up (i.e., fixing the damage at the end of the pipe) but rather on waste minimization and elimination of pollutants at the point of origin. This strategy of pollution prevention is also referred to as source reduction and is viewed as the first-choice measure to reduce risk to human health and the environment. Some of the attractive features of the source reduction are cost effectiveness, reduction in raw material use, pollution control savings, reduced risk to workers and the environment.

During the following year (1991), the Environmental Protection Agency (EPA) and National Science Foundation (NSF) initiated the Green Chemistry Program. A number of other similar initiatives were formed in the UK and some other countries. US Presidential Green Chemistry Challenge Award was founded in 1996. All these actions mark stepping stones in the green chemistry movement and philosophy, which gained more momentum in the following decades.

The green chemistry philosophy seeks to respond to public perceptions that chemistry and its applications via chemical technology have been primarily responsible for many of the ways the world degrades the environment. To reverse this stereotype, one of the central goals of green chemistry is to reduce risk to humans and environment from chemical synthesis, manufacturing, and application of chemical products through design of clean and closed-loop procedures.

Mitigating Risk and Hazard

Is there difference? Formally, in chemical fields, risk can be defined as a function of hazard and exposure:

Risk = f (hazard, exposure)

Traditionally, in industry and society, the reduction of risk is achieved through the reduction of exposure. By characterization of hazards (toxicity data) and knowing the effectiveness of the exposure controls ('containing the hazard'), risk can be manipulated or dissipated, especially at the early stages of the chemical chain, when it is easy to identify and measure. However, exposure controls may be not as useful downstream. The farther the hazard is from its source, the less the awareness of the potential hazard. With uncertainties in chronic effects, bio-accumulation, synergistic effects of chemicals, there is an uncertainty in risk mitigation.

The Green chemistry approach, in contrast with traditional practice, targets risk reduction through reduction of hazard. This is a safer approach because, if hazard is eliminated in the first place, there is no way risk can increase through any unpredicted spontaneous exposure increase anywhere downstream (Anastas and Warner, 1998).

Green Chemistry Control Keys

So, what are possible avenues for changing the existing practices towards the minimum-risk alternatives? There are several controls that can be manipulated at different stages of a chemical manufacturing process.

Using alternative feedstock or starting materials: Selection of the starting materials has a major effect through the whole synthetic pathway. It determines what hazards will be faced by the workers extracting the substance, shippers transporting the substance, chemists handling the substance. It also predetermines possible future risks from the end-products and wastes. Using more environmentally benign alternative feedstock may improve the environmental profile of the whole process (this links to green chemistry principle #7). One of the examples of this step is choosing between the petroleum feedstock and biological feedstock. Currently, 98% of all organic chemicals in the USA are produced from petroleum. Petroleum refining is extremely energy-consuming (15% of total national energy use) and contains high-pollution oxygenation processes. Agricultural feedstocks can be a great alternative that eliminate much of that hazard. Research has shown that many agricultural products (e.g., corn, soy, molasses) can be transformed via a variety of processes into textile, nylon, etc. (Anastas and Warner, 1998).

Using alternative reagents: Reagents are needed to transform the starting molecules into a target substance. Reagents are not necessarily consumed and are often recycled, but can still bear harm to people and environment exposed to the process. At this point, a chemist must balance the criteria of chemical efficiency and availability with potential hazards. This practice taps into green chemistry principles #2, 4, and 5.

Using alternative solvents: Solvents are a very common focusing point because a wide range of syntheses are performed in the liquid media. Many of the currently used solvents are volatile organic compounds. Many of those are responsible for air quality problems (smog, etc.) when released to air. While the traditional organic solvents are easily available, well characterized, and regulated, there is a push for alternative systems that are more environmentally benign in the long run – aqueous solvents, ionic liquids, immobilized solvents, supercritical fluids, etc. (Principle #5) The choice of an alternative solvent requires careful and specific analysis, which determines if the new process would be as efficient or as cost-effective. How such trade-offs are resolved is discussed later in this lesson.

Changing target product: Chemistry is function oriented – the target chemical is needed to perform a certain function or possess certain properties. This avenue is related to the search of the alternative final product, which may require radical change in the way synthesis is done (Principle #3). Through chemical research, it is possible to identify those parts of a molecule that provide the chemical with a desired function as well as those parts that provide toxicity. Maximizing the former and minimizing the latter is a worthy challenge for chemical design.

Process monitoring: Real time measurements (sensing) of process parameters and concentrations sometimes provide valuable information and hints how the process should be tuned to avoid adverse effects or risk (Principle #11). Also, process monitoring may open avenues for making the process more cost-effective.

Alternative catalysis: Catalysis bears enormous benefits, not only from the standpoint of technical efficiency. Environmental benefit results from the use of a much smaller amount of reagents in catalyzed reactions, which otherwise would contribute to the waste stream. Using less chemicals is also economically profitable. It should be noted, though, that many classes of catalysis (e.g., heavy metals) are very toxic. Hence, the challenge of alternative catalysis is to develop environmentally benign options (Principle #9).

As you can see, most of these measures are oriented towards reducing hazard in the first place. Eliminating, minimizing, or neutralizing toxic components at earlier stages of the process allows for more relaxed exposure control at later stages. Item 5 is more universal, as sensing can help monitor and control both toxicity and exposure at both inlet and outlet of the chemical system.

The green chemistry principles are also important as guidance for designing metrics for chemical technology evaluation. Some examples of those metrics are discussed further in section 4.3.

Case of Dead Fish - Lake Ariel

The following Video is text set to music. The text of the slideshow can be found in the transcript in the caption below.

Video: Intro to Lake Ariel Case (1:01)

Another example we can look into is the chemical incident on Lake Ariel in Wayne County, Pennsylvania. In 2014, the owners of the land where the recreational lake is located, contracted a New Jersey company to help clean the lake of algae. Accelerated algae growth is believed to be the result of lake pollution due to illegal septic systems flushing their waste into the lake. The contractor applied two algaecide treatments of copper sulfate to the lake, which resulted in killing around 10,000 fish. The Department of Environmental Protection issued a fine stating that copper sulfate applications should be spaced 7 to 14 days apart, whereas the company made two applications spaced only 3 days apart. The owner argued that the extremely hot day during that summer was what ultimately caused the fish death. Nevertheless, the shortened time in between applications was considered negligence.

Check the link below to collect additional facts about this case, then work through a few questions to analyze the situation:

NBC News - Philadelphia

From this example, we see that dealing with sensitive ecosystems requires extra diligence when chemical flows are involved. Quite often, certain aquatic species are only tolerant to a very narrow range of chemical parameters, such as ligand and metal concentration, alkalinity, and pH. Even small fluctuations may turn out lethal for sensitive species and can result in quick and irreversible ecological damage.

This example also provides an opportunity for exercising system thinking, during which we can try to establish multiple causal connections and understand the coupling effects, which are able to quickly amplify the ecological stress. In this case, we observed it with the heat factor. Hotter temperature not only "purges" water of oxygen (due to lower solubility levels), but also promotes algae growth, which in turn removes oxygen from water even further. The system analysis can help reveal this sort of double impact, alert us of the increased risk, and prevent hasty actions.

So, what does it take to change the conventional practice with possibly hazardous or harmful chemicals or processes to a more sustainable solution?

The major step is assessment of alternative solutions, which takes into account a wide range of criteria. When thinking about replacing the existing process with an innovative alternative, chemists and engineers try to avoid so-called "regrettable substitutions". In other words, avoid switching to an alternative process or chemical that either transfers risk to another point in the production chain or lifecycle or contains unknown future risks.

Ideally, in the concluded assessment, chosen alternatives must:

• be technologically feasible;
• provide the same or better value in performance and cost;
• have an improved profile for human health and environment;
• account for economic and social considerations;
• have potential to be sustainable over long period of time (look out for restrictions that may arise in the future; for example, shortage of rare elements, etc.).

We see that choosing the best alternative requires careful investigation! Such investigation must be comprehensive, i.e., would require cross-disciplinary expertise, and based on high quality data.

Let us look at some typical criteria that may be used in chemical industry and research for evaluation of various processes and reactions. In the "green chemistry" context, the main emphasis is put on the environmental profile of a chemical alternative, while economic feasibility is included in the picture at the stage of technology transfer.

Evaluation criteria

Table 4.1 below represents the set of criteria that can be effectively used for assessing alternatives in chemical and material manufacturing. On the left, the top-level criteria are listed, which are key points of concern when introducing new chemicals to the manufacturing process. The middle column lists some sub-criteria, which show how the impacts can be distributed. The right column specifies specific measures for each type of impact, which basically become guides for data search and analysis.

The list of criteria given in Table 4.1 has been proved effective for some case studies. While it puts the main emphasis on the hazard assessment and environmental impact, the technical and economic criteria are also included and can play a significant role even at the stage of selection of particular chemical reagents for the process. Note that the above list of criteria and sub-criteria is not something written in stone. It is presented here as an illustration. For each specific assessment project, choice of criteria needs to be justified through expert and stakeholder involvement and will depend on the goals of assessment. Depending on the assessment team decision, some criteria can be added, some – removed, and weights of all factors can be tuned. Clear identification and justification of the selected criteria is critical.

Data collection

In any assessment project, clear and consistent requirements should be set for the sources of data to be used. Information should meet specific data quality criteria for inclusion into the assessment. Quality of data will determine their utility. Data selection should follow the internationally recognized definition for reliable information: "Reliable information is from studies or data generated according to valid accepted testing protocols in which the test parameters documented are based on specific testing guidelines or in which all parameters described are comparable to a guideline method. Where such studies or data are not available, the results from accepted models and quantitative structure activity relationship (QSAR) approaches may be considered. The methodology by Organization for Economic Cooperation and Development (OECD) can be used for the determination of reliable studies." (Principles of Alternative Assessment, 2012)

Preferably, data should be obtained from authoritative bodies, those referenced by US government agencies (e.g. EPA). The following are links to some of such resources:

• U.S. EPA PBT Profiler software can be used to gain information on persistence, bioaccumulation potential and toxicity of organic substances.
• Government Toxicology Data Network

Technical data sources

Information should be obtained from published studies or directly from technical experts or users of the alternatives. In other cases, information can be requested from product manufacturers. The specific performance information (reactions, energy effects, thermodynamic analysis) available from experimental labs may be needed to draw conclusions about technical feasibility for each individual application. Clear referencing of the data sources is important.

Economic data sources

Data sources for financial information may include manufacturers, stakeholders, the Chemical Economics Handbook, and other standard reference sources. For many emerging alternatives, hard cost information may be unavailable. Cost comparisons today may not be directly extrapolated to emerging technologies because learning curves, scaling, and other factors can affect costs over time. Assumptions and use of surrogate data should be clearly explained in the assessment.

Ranking the alternatives

Quantification (scoring) of the impacts based on the criteria listed above is typically done via a multi-criteria analysis (MCA) model, appropriately build for the project. MCA provides techniques for comparing and ranking different outcomes of existing and alternative processes. When setting up an assessment project, it is important that the scoring system is transparent and is consistently applied to all scenarios under consideration.

MCA is a great tool for comparison of different options, but it is hardly objective because choice of criteria and metrics to quantify impacts varies from case to case. In contrast, cost analysis is aimed at providing objective measure of economic feasibility based on predicted cash flow. Cost analysis requires impacts to be expressed in monetary terms. MCA can use both monetary and non-monetary measures, as well as both quantitative and qualitative measures.

In MCA, ranking of chemicals or processes with respect to the listed criteria can be done in a variety of ways. One way is to assign each criterion a score that spans from 0 to 1, with the value of 1 corresponding to the best (most preferable) choice and the value of 0 corresponding to the worst (least preferable) choice among the available. The rest of the choices would score in between.

Another possible approach for assigning scores is outranking. There is no relative scoring, but instead, alternatives are compared by each criteria in pairs (two at a time). This way, we try to identify the extent to which one alternative out-performs the other. In the end, the dual performance scores (1 - "win"; 0 - "lose") are aggregated, and the preference index is calculated for each alternative.

Evaluation of the economic impacts associated with the implementation of a new product or practice generally focuses on the changes in capital and operational costs and revenues. (These terms of cost analysis were overviewed in Lesson 3.). The main areas where impact is expected are:

• cost of new equipment or production process;
• operation and maintenance costs (labor costs, energy costs, etc.);
• cost differences for different substances;
• cost of transportation;
• cost of design, monitoring, and training;
• regulatory costs.

The data on economic impacts is collected in consultation with relevant supply chain actors and possibly trade associations. Evaluation can be an iterative process, starting from qualitative comparison of the old and new scenarios and ending at quantification of impacts with monetary values.

The European Chemicals Agency (ECHA) website provides a more detailed guide to economic assessment of alternatives and can be used as a resource for this task. There are some documents linked that you are not required to read unless you're specifically interested in the socio-economic assessment.

Weighing factors

In most situations, decision-makers are not equally concerned about all highlighted criteria. For instance, a particular decision-maker may place more importance on whether a household cleaner causes cancer than on whether it contributes to smog formation. Thus, the decision-making method should account for respective “weight" of each criterion in the evaluation process. Since different stakeholders may place different weights upon criteria, the weighting raises significant questions in the context of a regulatory program. For example, can we consistently compare the alternatives without regulating the weight of factors? This is something to watch out for.

The criteria weights can be established by three methods:

1. using generic or recommended weights;
2. calculating the weights based from objective measures; and
3. eliciting weights from stakeholders or experts.

Method (1) is exemplified by Table 4.2 which lists several sets of generic weights recommended by National Institute of Standards and Technology (NIST) based on the data of Environmental Protection Agency (EPA) and Harvard Study for a set of criteria usually used in life cycle assessment (LCA).

In the above table, the NIST panel generated weights from stakeholder consulting that involved 7 building product manufacturers, 7 product users, and 5 LCA experts. EPA weights and Harvard weights were derived by NIST from sets of qualitative rankings of impacts developed respectively by EPA’s Science Advisory Board in 1990 and Harvard researchers in 1992.

Method (2) of calculating corresponding weights can be based on distance-to-target approach, when each criterion is weighted by the variance between the existing and desired conditions. For example, if the global community is further away from achieving the goal for global warming than it is for ozone depletion, then greater weight is given to the global warming potential. Another way to such calculation is monetary evaluation, when weighing is done based on the cost of environmental consequences.

Method (3), which assumes obtaining weights from stakeholders directly, may be based on public opinion surveys, community working group decisions, and different multi-criteria analysis models. The main types of stakeholders to consider: (1) Environmental Non-Government Organizations, Industry, Policymakers, and Consumers (Public). Weight assignments collected through surveys are then averaged across the board of stakeholders and then normalized to 100%.

Use of any of the methods depends on the goals of the assessment project, its scope, resources, and timeline. When building an assessment project, the weighing process should be transparent and well justified. When comparing different cases within one study, keep the weighing scale the same across the evaluation criteria.

Within the MCA approach, the final score (S_i) of a particular option (alternative) with respect to any major top-level criterion i is estimated as an average of all sub-criteria scores under that criterion:

$$S_i=\frac{{\displaystyle {\sum }_{j=1 }^n{s}_j}}{n}$$

where n is number of sub-criteria or metrics used to assess the option under top-level criterion i. The final total score (S_tot) is the weighted sum of all top-level criteria scores:

$$S_{tot }={\displaystyle \sum _{i=1 }^N{S}_i{w}_i}$$

where N is the number of top-level criteria considered in assessment; w_i is the weight factor of a particular criterion. The example study presented in the next section of this lesson demonstrates how the MCA scores are calculated and compared.

Consider the following supplemental reading materials on this topic:

The case study presented below exemplifies the application of a range of criteria to the process in the dry cleaner industry. This kind of analysis can help decision-making process in the green chemistry context.

(Source: UCLA Sustainable Technology & Policy Program, 2011)

Baseline and alternatives

The existing process of garment cleaning utilizes chlorine-based solvent technology, which is not sufficiently benign. This case study examines a few alternative technologies, which aim at making it a greener process. Table 4.3 below lists the alternatives under consideration.

The criteria for evaluation were selected from the list in Table 4.1.

Criteria weighting

Criteria weighting was based on stakeholder elicitation. Four stakeholder groups were considered by the authors: Environmental Non-governmental Organizations (NGO), Industry, Policymakers, and Consumers. The elicitation process was also designed to obtain stakeholder reactions to the criteria; for example, whether any relevant criteria have been left out. During interviews, stakeholder representatives were asked to rank the major criteria on the 100 point scale, and the average weight of that criterion was obtained by averaging scores over all interviews. The list of relative (percentage) weights of all major evaluation criteria, as voted by different stakeholders, is presented in Table 4.4.

As was noted by the authors of the study,

"on average, all stakeholder groups (except Industry) placed more weight on human health and ecological hazards as well as on environmental impact criteria. Industry and Policymakers assigned more weight to technical feasibility as compared to Consumers and Environmental NGOs. Industry placed more weight on economic feasibility than the other three groups. As discussed above, however, the sample sizes for the stakeholder groups were quite small (three in each group), with the goal of getting a sense of the potential differences across and within groups." (UCLA.., 2011)

Scoring methods

One of the goals of this project was to demonstrate the application of two techniques for multi-criteria decision analysis: (1) multi-attribute utility theory MAUT and (2) outranking.

"MAUT is an optimization approach, meaning that it represents the decision-maker's preferences as utility functions, and attempts to maximize the decision-maker's overall utility. MAUT is premised on the assumption that the decision-maker has a fairly well-defined set of preferences that can be represented on a dimensionless utility scale. It also assumes that the decision-maker is rational; that is, they prefer more utility rather than less and are consistent in those preferences. In the context of this project, therefore, a utility function was generated for each criterion, which reflects how a decision maker's preference changes for different values of that criterion. This utility function spans from 0 to 1, with a utility of 1 being assigned to the value of the best (or highest) alternative score for that criterion and 0 being assigned to the value of the worst (or lowest) alternative score. In this case, a linear utility function was used; which assumes that increases in utility are directly related to increases in the alternative's score for the criterion in question. Linear utility function was used as a default. Because the weighted scores for all criteria are added to produce the alternative's total score, MAUT is a 'compensatory' method. This means that poor performance on one criterion can be compensated by better performance on another.

Outranking models do not create utility functions, but instead directly compare the performance of two alternatives at a time, in terms of each criterion, to identify the extent to which one alternative out-performs the other. It then aggregates that information for all possible pairings to rank the alternatives based on overall performance on all criteria. Generally speaking, the PROMETHEE code used in the project creates a 'preference index' for each alternative, which is calculated by reference to the alternative's positive flow (i.e., those instances in which the alternative outperforms another alternative on a given criterion) and negative flow (i.e., those instances in which the alternative is outperformed by another alternative). The value awarded for winning a particular pairing is weighted, meaning it is adjusted to reflect the value placed upon that criterion by the decision-maker. Thus, outperforming another alternative in a minor criterion is worth less than outperforming it with respect to a more highly weighted criterion. As a default in PROMETHEE and most other outranking methods, any difference in performance - however small - will result in an increase in positive flow for the better performing alternative. As in MAUT, PROMETHEE recognizes that a decision-maker may be indifferent to how alternatives perform on certain criteria until certain levels are met or after certain levels are exceeded. Because outranking techniques aggregate the results of pairings for all criteria, they allow superior performance on some criteria to compensate for inferior performance on other criteria. However, they do not necessarily reflect the magnitude of relative under performance in a criterion versus the magnitude of over-performance in another criterion. In other words, if Alternative A is marginally worse than Alternative B in one criterion, but substantially better with respect to another, outranking may not fully 'compensate' Alternative A for its overall better performance. Therefore, outranking models are known as 'partially compensatory.'" (UCLA.., 2011)

Results

As Figures 4.1 and 4.2 demonstrate, for garment care, the two MCDA approaches ranked the alternatives in the same order. Both methods identified wet cleaning as the best overall performer. It was followed by CO₂ cleaning and perchloroethylene. Figure 4.1 displays the total score received by each garment care alternative under MAUT; the higher the score, the better the overall performance.

Figure 4.1. Garment assessment outcome using MAUT scoring system.

Credit: (UCLA.., 2011)

Figure 4.2. Garment care assessment outcome using outscoring method

Credit: Mark Fedkin - adapted from UCLA.., 2011

Figure 4.3 shows the breakdown of scores by each criterion. It is demonstrated that, "taking into account weighting, wet cleaning and CO₂ cleaning's impact on human health, environmental, and ecological criteria drove the outcome in this case. This was so despite CO₂ cleaning's very poor performance in terms of economic impact. Poor performance by DF-2000, nPB, Rynex and Green Earth in terms of physical and chemical hazards placed those alternatives behind the existing technology-perchloroethylene dry cleaning."

Figure 4.3. Garment care criteria contribution to MAUT scores.

Credit: (UCLA.., 2011)

Example of score calculation

Wet cleaning technique, which outscored the other methods based on selected criteria, obtained a score of 0.15 for environmental impacts. This number is the product of the number of points assigned by the MAUT code and the average criterion weight (as prescribed in Table 4.2):

Score (Wet cleaning) = MAUT (Env. Impact) x Weight = 0.82 x 0.1833 = 0.15

The same technique received a MAUT ranking of 1 for physicochemical hazards (meaning it is least hazardous of all considered alternatives). Considering the weight of that criterion of 13.75% we calculate:

Score (Wet cleaning) = MAUT (Phys-Chem) x Weight = 1 x 0.1375 = 0.1375 ~ 0.14

In spite of better performance of wet cleaning on this criterion, its weighted score is lower than that obtained for the environmental impact, because of the lower weighing factor put on this category.

Since chemical products are present in virtually any sphere of technology, we can find numerous examples of studies and innovations that illustrate the application of green chemistry principles. Some of them are given below. In the end of this lesson, you will be asked to research one of these cases (of your choice) in more detail and to provide a brief evaluation of its promise.

A. Innovative propylene oxide process

Companies DOW and BASF jointly developed a technology of conversion of hydrogen peroxide into propylene oxide (HPPO) that has significant "green" advantages over competing technologies:

• It uses hydrogen peroxide and propylene as raw materials, producing only propylene oxide and water.
• It reduces waste water by 70-80%.
• It uses 35% less energy.
• Its capital cost is 25% less.
• It avoids need for co-product infrastructure and markets.

Source: www.epa.gov

B. Advanced amine technology for carbon capture

Alstom-DOW pilot plant captures CO2 from new or existing industrial facilities with an improved sustainability profile:

• Pilot plant in West Virginia is designed to capture 1,800 tons CO2 per year.
• Advanced Amine process leads the industry in carbon capture efficiency.
• Capture rate ~90% with 99.5% purity of CO2.
• Process significantly reduces parasitic energy requirements.

Source: Pump Industry Analyst, 2009

C. Metathesis catalysis for making high-performing, green specialty chemicals at advantageous costs

Elevance employs Nobel-prize-winning catalyst technology to break down natural oils and recombine the fragments into novel, high performance green chemicals. These chemicals combine the benefits of both petrochemicals and biobased chemicals. Elevance produces specialty chemicals for many uses, e.g., concentrated cold-water detergents that provide better cleaning with reduced energy costs.

• Significant energy savings
• Reduction of greenhouse gas emissions by 50% (compared to petrochemical technologies)

Source: ACS

D. An efficient biocatalytic process to manufacture simvastatin

Simvastatin, a leading drug for treating high cholesterol, is manufactured from a natural product. The traditional multistep synthesis was wasteful and used large amounts of hazardous reagents. Professor Y. Tang (UCLA) conceived a synthesis using an engineered enzyme and a practical low-cost feedstock. Codexis optimized both the enzyme and the chemical process.

• great reduction of hazard
• less amount of waste
• cost-effective approach
• better meets needs of customers

Some manufacturers in Europe and India use this process to make Simvastatin.

Source: ACS

E. Enzymes save energy and wood fiber for manufacturing high-quality paper and paperboard

Traditionally, making strong paper required costly wood pulp, energy-intensive treatment, or chemical additives. But that may change. Buckman’s Maximyze®enzymes modify the cellulose in wood to increase the number of "fibrils" that bind the wood fibers to each other, thus making paper with improved strength and quality − without additional chemicals or energy. Buckman's process also allows papermaking with less wood fiber and higher percentages of recycled paper, enabling a single plant to save $1 million per year.

Source: ACS

F. Gas-expanded liquids for sustainable catalysis

Gas-expanded liquid (GXL) is a substance generated by dissolving a compressible gas (for example, CO₂ or a light olefin) in a regular liquid substance at mild pressures (tens of bar). When CO₂ is used as the expansion gas, this process produces CO₂-expanded liquid (CXL). An attractive feature of GXLs is that they combine the advantages of compressed gases and of traditional solvents. GXLs retain the beneficial attributes of the conventional solvent (polarity, catalyst/reactant solubility) but provide higher miscibility of permanent gases (O₂, H₂, CO, etc.), as compared to organic solvents at ambient conditions. GXLs also results in enhanced transport rates compared to regular liquid solvents. The enhanced gas solubility in GXLs have been exploited to alleviate gas starvation (often encountered in homogeneous catalysis with conventional solvents). Environmental advantages of GXL include:

• replacement of harmful organic solvents with environmentally benign CO₂;
• reduced flammability due to CO₂ presence in the vapor phase;
• lower process pressures (tens of bar) compared to supercritical CO₂ (hundreds of bar) which is linked to energy savings.

GXLs thus have many characteristics of an ideal alternative solvent.

Source: Anastas and Zimmerman, 2013, pp. 5-36. (This book is available online through the Penn State Library system.)

G. Synthesis of magnetite (Fe₃O₄) nanoparticles "green" way

Shape-controlling studies of magnetite nanomaterials are pursued actively since their magnetic and electrochemical properties, as well as their catalytic activities, greatly depend on their nanostructures. As catalysts, Fe₃O₄ nanoparticles possess some advantages over natural enzymes (e.g., horseradish peroxidase, HRP) because (i) they can maintain relatively high catalytic activities under a wide range of environmental changes, even in severe conditions (pH = 2–7, 70 °C) and (ii) their preparation and purification procedures are reproducible and cheaper than those of natural enzymes. The robustness, repeatability, and low price of Fe₃O₄ nanoparticles make them suitable as catalysts for H₂O₂ oxidation for a broad range of applications in biotechnology and environmental chemistry.

However, the synthesis of Fe₃O₄ nanoparticles with controlled morphology is still a challenge. Current approaches, such as a hydrothermal process, solvothermal process, and thermal decomposition, involve toxic sources (e.g., organic solvents and surfactants), rigorous conditions (high temperature, high pressure), and tedious synthetic procedures, which prevent the large-scale production and widespread practical applications of Fe₃O₄ nanoparticles. Additionally, the recovery of Fe₃O₄ nanoparticles for repeated use is still difficult. Therefore, nontoxic, water-based approaches for the fabrication of morphology controllable Fe₃O₄ nanoparticles, which can be produced on a large-scale and effectively recovered, are urgently needed.

This article introduces a new straightforward approach developed for fabricating Fe₃O₄ nanoparticles/hydrogel magnetic nanocomposites, in which the morphology of the nanoparticles can be controlled under nontoxic and water-based conditions. The 3D hydrogel networks, which contain a liquid-like microenvironment facilitating small molecule diffusion and transport, can act as an ideal nano/micro-reactor but also as a great carrier for the synthesis and immobilization of nanoparticles. This study was inspired by magnetotactic bacteria, which are capable of producing bacterial magnetic particles (BacMPs) with a highly controlled morphology (e.g., nanocube, nanooctahedron, and nanododecahedron) due to their nanoscaled magnetosome vesicles acting as nanoreactors, and negatively charged proteins playing the role of iron ion-binding sites. With a higher catalytic activity, the magnetic nanocomposite loaded with Fe₃O₄ nanooctahedra has a sensitive response towards H₂O₂ detection with a limit of 5 × 10⁻⁶ mol L⁻¹.

An additional benefit of this work is that the magnetic nanocomposite can be recovered more effectively and easily using the hydrogel as a carrier. "Based on the facile, economical fabrication strategy, large-scale production of this magnetic nanocomposite with a tunable peroxidase-like activity can be expected to revolutionize catalysis applications in biotechnology and environmental chemistry."

Source: Geo et al., 2013

Assignment Details

At the end of this lesson, you will be asked to choose one of the above cases or any other you may find on the Internet for more detailed evaluation. More information can be found on the Lesson 4 Activity Sheet on Canvas.

Multifunctional materials are the materials that perform multiple functions in a system due to their specific properties. Multifunctional materials can be both naturally existing and specially engineered.

For example, some traditional materials that provide, for instance, high mechanical strength can be modified at the nanoscale to attain other properties such as energy absorption, self-healing, etc. The applications of such new "smart" materials include energy, medicine, nanoelectronics, aerospace, defense, semiconductor, and other industries.

Numerous examples of multifunctional materials can be found in nature. Bio-materials routinely contain sensing, healing, actuation, and other functions built into the primary structures of an organism. For example, the human skin consists of many layers of cells, each of which contains oil and perspiration glands, sensory receptors, hair follicles, blood vessels, and other components with functions other than providing the basic structure and protection for the internal organs. Through biological evolution, these structures were seamlessly integrated into the body to serve their functions (Nemat-Naser et al., 2005).

The ability for materials to respond to their environment in a useful manner has broad technological impact. Such "smart" systems are being developed in which material properties (such as optical, electrical, or mechanical characteristics) respond to external stimuli. Materials of this kind have tremendous potential to impact new system performance by reducing size, weight, cost, power consumption, and complexity while improving efficiency, safety, and versatility. The multifunctionality of materials often occurs at scales from nano through macro and on various temporal and compositional levels (Nemat-Nasser et al., 2005).

Innovative advanced materials make a direct and positive impact on economic growth, the environment, and quality of life. They allow for improved processes and products and create several avenues to increasing sustainability.

Note the following areas of impact:

1. reducing environmental effects
2. increasing efficiency of processes
3. lightening the weight of products
4. lowering power consumption
5. reducing system size
6. reducing system weight
7. reducing system cost
8. reducing complexity
9. increasing safety
10. increasing fuel flexibility
11. increasing versatility

Most of these impacts may result in higher efficiency of the system and cost savings.

Examples of advanced materials studies

The following are several examples of sustainable solutions through improved materials chemistry or using alternative innovative materials.

A. Power-generating structural composites

"Researchers at ITN Energy Systems and SRI International have integrated a power-generating function into fiber reinforced composites. Individual fibers are coated with cathodic, electrolytic, and anodic layers to create a battery. The use of the surface area of fibers as opposed to that of a foil in a thin film battery allows greater energy outputs, measured on the order of 50 Wh/kg in a carbon fiber reinforced epoxy laminate. These batteries may be deposited on various substrates, including glass, carbon, and metallic fibers."

Source: Nemat-Nasser, S., et al., Multifunctional Materials, Figure 12.2. in Biomimetics: Biologically Inspired Technologies, Bar-Cohen, Y., Ed., CRC Press, 2005. (This book is available online through the Penn State Library system.)

B. Thermostructural materials for gas turbines

Gas turbines are a core technology in aero-propulsion and industrial power generation. Technological progress in this area depends on advances in thermostructural materials. The requirements to reduce emissions, increase fuel flexibility, and resist environmental attack call for development of new material systems with multifunctional properties. University of California Santa Barbara researchers employ a holistic approach that embraces and integrates all critical aspects of materials technology, including alloys, coatings, and composites, processing, and simulations to create the thermostructural materials that combine mechanical strength and exceptional thermal stability. Materials issues relevant to the high-pressure turbine include higher temperature single crystal alloys that act in concert with coatings, advanced bond coat alloys for environmental protection with improved thermochemical and thermomechanical compatibility with the load-bearing alloy, and thermal barrier oxides with new compositions that enhance temperature capabilities. Ceramic matrix composites (CMCs) and associated environmental barrier coatings are also incorporated in next generation engines, especially for combustors.

C. Nanoparticle assembly using DNA strands

"Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials with special properties. The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA—based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C. After coating the nanoparticles with a chemically standardized "construction platform" and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then "self-assembles" the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed materials and their properties."

Source: Brookhaven National Laboratory

D. Organic batteries provide better recallability

A typical battery consists of two electrodes - anode and cathode, electrolyte layer, separator, and current collectors. Most of traditional battery technologies use metals or metal oxides as electrode-active materials, and metals are not renewable resources. This study describes the use of organic materials as electrodes. The advantage of such organic-based batteries over Li-ion batteries in terms of sustainability is improved recallability, safety, adaptability to wet fabrication process, and extraction of starting material from less limited resources. One recently developed type of organic battery is based on organic radical polymers - "aliphatic or nonconjugated redox polymers with organic robust radical pendant groups as the redox site". The organic batteries have lower energy density compared to Li-ion technology, but this limitation is expected to be overcome in the near future.

Source: Anastas, P.T., Zimmerman, J.B., Innovations in Green Chemistry and Green Engineering, Chapter 8, pp. 235-246. Springer 2013. (This book is available online through the Penn State Library system.)

Lesson 4 introduced a very wide topic - green chemistry - which covers numerous innovations in chemical process design, manufacturing, and materials. Chemistry penetrates almost every aspect of modern technology, so such questions as how the technological components are made, where the starting materials come from, and what happens to them through the lifecycle are pivotal points for decision makers looking for increasing sustainability. There are ongoing efforts in both the US and Europe to develop guidance for assessment of chemical technologies, and a variety of methodologies have been tested so far. There is no unified system of assessment, which is understandable considering the diversity of subjects within the area of green chemistry. What you should take home from this lesson is the understanding of main steps and principles, plus a list of key resources which can help with consistent analysis of emerging chemical technologies. This lesson activity provides you with hands-on practice of examination of a real-life case and should stimulate some critical thinking with respect to what works and what does not in the recommended assessment protocols.

References for Lesson 4: