A Method for Assessing Greener Alternatives ... - ACS Publications

Research Article pubs.acs.org/journal/ascecg

A Method for Assessing Greener Alternatives between Chemical Products Following the 12 Principles of Green Chemistry Ashley DeVierno Kreuder,*,‡ Tamara House-Knight,‡ Jeffrey Whitford,† Ettigounder Ponnusamy,† Patrick Miller,† Nick Jesse,† Ryan Rodenborn,† Shlomo Sayag,§ Malka Gebel,§ Inbal Aped,§ Israel Sharfstein,§ Efrat Manaster,§ Itzhak Ergaz,§ Angela Harris,‡ and Lisa Nelowet Grice‡ ‡

Ramboll Environ, 1560 Broadway, Suite 1905, Denver, Colorado 80202, United States MilliporeSigma, 545 S. Ewing, Saint Louis, Missouri 63103, United States § Merck KGA, 13 Kiryat Hamada Street, Jerusalem, 97770 Israel †

S Supporting Information *

ABSTRACT: Companies are interested in improving chemicals to reduce environmental impacts, also known as green chemistry. The 12 principles of green chemistry outline a framework for identifying a greener chemical or process, spanning aspects in health hazard, ecological risk, and resource efficiency across a product lifecycle. However, that framework does not detail how to measure performance. Furthermore, collecting the data required, beyond simple health hazard ratings, is resource intensive. This paper describes an approach for establishing green chemistry metrics (GCM), to evaluate chemicals and chemical processes against the 12 principles, using readily available data, such as the data compiled in compliance with the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). Using the GCM, chemicals or processes can be ranked by a hierarchy of metrics: (1) scores for each of the 12 principles, (2) three category rankings between new and improved chemicals/processes (improved resource use, increased energy efficiency, and reduced human and environmental hazards), and (3) a summary comparison ranking. The GCM approach is unique in that it is robust and flexible enough to encompass a diverse product portfolio, inexpensive to implement with on-hand data, based on generally accepted industry practices, and allows meaningful communications about chemical sustainability options. KEYWORDS: 12 Principles of green chemistry, Chemical products, Sustainability, GHS, Rank, Environment, Human health, Alternative, Safety data sheets

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INTRODUCTION Green chemistry is the concept of developing chemical products and processes that minimize the use and generation of hazardous substances, reduce waste, and reduce demand on diminishing resources. Anastas and Warner1 developed the framework that has served as the foundation for the green chemistry movement. That framework proposes 12 complementary principles around resource efficiency and risk (human health and environmental) minimization, targeting a lifecycle perspective (e.g., raw materials extraction, chemical production, and end-of-life bioaccumulation and biodegradation). Ultimately, these 12 principles were adopted by the Green Chemistry Institute (GCI)2 at the American Chemical Society (ACS). The 12 principles are as follows: (1) waste prevention, (2) atom economy, (3) less hazardous synthesis, (4) design of benign chemicals, (5) use of benign solvents and auxiliaries, (6) energy efficiency, (7) use of renewable feedstocks, (8) reduce derivatives, (9) use of catalysis, (10) design for degradation, (11) real-time analysis for pollution prevention, and (12) accident prevention. © XXXX American Chemical Society

The 12 principles are only conceptual and do not provide a quantitative framework. While various approaches to quantifying greener processes and products have been proposed, there is no unifying set of metrics in place. After a review of the current state of green chemistry methods, this paper proposes a green chemistry metric approach (i.e., the GCM) to developing metrics for each of the 12 principles that is flexible and leverages generally accepted industry practices. In review of the literature, we found that while a number of methods have been proposed to evaluate greener chemistry, there are hindrances to their implementation. Primary limitations include requiring a high level of effort,3−5 data that are not readily available,4,5 and access to specialized or proprietary data sets.4−6 Additional limitations include results that lack transparency and are difficult to communicate.6 Furthermore, some methods focused Received: October 5, 2016 Revised: February 14, 2017

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DOI: 10.1021/acssuschemeng.6b02399 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering

of California Alternative Analysis Guide detailing the methods for deriving the 16 factors is still in draft form. Baitz et al.5 advocate a green chemistry method that incorporates a lifecycle approach that includes reducing energy demand, increasing nonfossil resources in energy, increasing nonfossil resources as feedstock, improving product applications, and improving end-of-life routes. However, Baitz et al.’s5 green chemistry approach does not provide specific guidance on how to measure such improvements nor does it address several of the 12 principles such as atom economy, less hazardous chemical syntheses, and designing safer chemicals. In addition, GlaxoSmithKline and Merck8 have developed approaches to green chemistry. GlaxoSmithKline developed an approach that uses process mass intensity (PMI) and global warming potential to evaluate the lifecycle impacts for new compounds. GlaxoSmithKline’s approach is relevant for only one of the 12 principles, namely atom economy. GlaxoSmithKline also developed the Solvent Selection Guide, which compares solvents based on hazard characteristics and a solvent process LCA ranking. While only focused on a specific list of solvents and not all of the materials in the chemical synthesis, the Solvent Selection Guide incorporates indicators for waste prevention, atom economy, less hazardous chemical syntheses, designing safer chemicals, less hazardous chemical synthesis, safer solvents and auxiliaries, design for energy efficiency, and inherently safer chemistry for accident prevention. It does not explicitly include an indicator for use of renewable feedstocks, though this is potentially included in the waste and lifecycle indicators.9 GlaxoSmithKline has developed other LCA tools such as a tool to compare synthetic route lifecycle impacts from research through manufacturing. The FLASC (Fast Life Cycle Assessment of Synthetic Chemistry) tool does not include waste, solvent recovery, or specific chemical-related health and safety data and does not address all of the 12 principles, omitting for example atom economy and inherently safer chemistry for accident prevention, to name a few. 10 GlaxoSmithKline combined Merck’s PMI tool with their synthesis routes LCA tool to make a streamlined LCA tool for the pharmaceutical industry; however, the new tool still falls short of addressing the full suite of 12 principles, omitting for example inherently safer chemistry for accident prevention among others.11 A life cycle assessment (LCA) is a detailed modeling approach that can be used for green chemistry evaluation by quantifying impacts over a product’s lifecycle.12 However, collecting data and completing modeling for a rigorous LCA is a time-consuming activity, and at times representative input data are not readily available.13 Furthermore, LCA often does not address each of the 12 principles. LCA can be used to investigate specific environmental impacts of a product or process, to compare the impacts between products or processes, and to scrutinize the source of an impact by lifecycle stage or process component.14 However, the robustness of LCA results are dependent on a number of factors including the quality and treatment of input data, boundaries selected by the modeler, and the choice of characterization factors.15 As noted, LCA often omits one or more of the 12 principles. For example, worker safety, a key element of principle 12, is not routinely considered in LCA.16,17 Methods to create LCA characterization factors for work related exposures are in development, but data quality is limited.16 Studies indicate that results from LCA may differ from assessments using green design metrics. Tabone et al.18

on a subset of stewardship principles, rather than endeavoring to capture the full suite of the 12 principles.3,5 One example of a method to evaluate green chemistry is the iSUSTAIN Green Chemistry Index developed by Beyond Benign, Sopheon, and Cytec Industries Inc.6 This method provides an approach to generate a sustainability-based score for chemical products and processes following the 12 principles. iSUSTAIN provides a gate-to-gate assessment, whereas the GCM approach permits the company to set the assessment boundaries depending on flexibility of available information, such as expanding the boundaries to include product use or disposal. The iSUSTAIN assessment uses a proprietary database to provide safety, health, and environmental information for common raw materials, solvents, diluents, and other auxiliary materials. Data for new materials can be requested from iSUSTAIN. The specialized database is then used to populate formulas for each principle. Depending on the principle, scores are tabulated or normalized on a scale of 0 to 100 to put them on the same scale, making them additive. The ability to combine principles into a single score may mislead the user to consider the principles to be comparable and make comparing alternatives less transparent. Another approach to evaluating green chemistry is the NSF/ GCI/ANSI 355-2011 standard, developed by the NSF International (NSF), GCI, and American National Standards Institute (ANSI).3 Broadly, this standard provides guidance to report chemical characteristics (human health effects, toxicology, ecological impacts, and physical safety properties), chemical processes (resource efficiency, recycled or biobased materials, waste, water, energy), and social responsibility. While the NSF/GCI/ANSI 355-2011 standard was designed to improve communication and comparability of chemicals, it does not provide a method for tabulating scores to determine which chemical characteristics are less harmful to the environment and puts the onus on the customer. It also does not strictly follow the 12 principles in that it excludes chemical use and end-of-life stages and the specific principles of reduce derivatives, use of catalysis, design for degradation, and realtime analysis for pollution prevention. A recent development in green chemistry is the California Safer Consumer Products Regulations (SCP regulations).7 This regulation requires application of an alternative analysis that can be used to compare an existing product-chemical combination that contains a chemical of concern to a safer alternative. The Draft Alternative Analysis Guide4 includes 16 relevant factors at various stages of the product’s lifecycle. Many of these relevant factorsnamely the adverse public human health impacts, adverse environmental impacts, physical chemical hazards, adverse waste and end-of-life effects, materials and resource consumption impacts, and renewable resources consumption follow themes similar to the 12 principles. The Draft Alternative Analysis Guide provides high-level guidelines on how to identify relevant factors, screen alternatives, assess lifecycle impacts, and compare alternative chemicals, but it does not provide a method for tabulating scores to determine which alternative chemical is less harmful to the environment. The onus is put on the responsible entity to make decisions to either implement an alternative or retain the original priority product alternative. The impact assessment methodology in the Draft Alternative Analysis Guide can become complex due to the large number of hazard traits in the SCP regulations, accessibility of available data, and number of relevant factors to consider. Details for implementation are pending as the State B


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ACS Sustainable Chemistry & Engineering evaluated the ability to use the 12 principles to reduce lifecycle environmental impacts of polymers by comparing green design metrics with LCA, specifically for a case study of 12 polymers. The study found that polymers that adhere to green chemistry principles had lower lifecycle environmental impacts. However, results were not uniform; for example, polymers with biological feedstocks had higher environmental impacts than polymers with petroleum feedstocks while ranking higher in green design. This disparity is due to the assumption in green design metrics that using renewable resources is desirable (principle 7), contrasted with the complications inherent in evaluating the upstream impacts of biomaterial use. Certain biopolymers showed higher eutrophication, human health, and eco-toxicity impacts from fertilizer use, pesticide use, and land use in agricultural production, as well as fermentation and other chemical processing steps required to convert the biomaterial into plastic. However, the fundamental premise of principle 7 is that it is better to use renewable rather than depleting materials, with recognition that with time least impactful measures for deriving renewable materials will be established.19 Further study comparing results from LCA with this GCM approach may improve the usability and interpretation of the GCM. Rather than adopting a full LCA approach, the Green Chemistry Metric approach (GCM) relies on readily available standardized information, applied in a consistent and transparent fashion for purposes of comparing alternatives using a discrete set of widely agreed upon principles. The GCM approach relies on data that meet global industry standards, such as the globally harmonized system of classification and labeling of chemicals (GHS)20 and standardized boundaries to facilitate transparency and comparability. The GCM approach and LCA serve as complementary approaches. While the GCM approach, by virtue of its focus on the 12 principles, does not include all of the detail of a well-designed LCA, it does facilitate efficient consideration of key principles. In summary, none of the alternative methods identified offered the combined strategy of using readily available data to comprehensively, transparently, efficiently, and quantitatively evaluate chemical and process alternatives according to all of the 12 principles. The ability to capitalize on readily available data for green chemistry evaluation, as incorporated into this GCM approach, is a relatively recent phenomenon. This availability of data is tied to the timely development, use, and adoption of the GHS classification system, which provides an influx of information on the physical, health, and environmental hazards of individual chemicals. Additionally, the GCM approach leverages other product specific information to address the full complement of the 12 principles. The GCM approach and scoring method are described herein and demonstrated with a case study.

be based on generally accepted industry practices, when available; and (6) be easy to communicate the method and results to customers. Considering these guiding elements, we investigated and designed a best approach to evaluate and score chemical products and processes on each of the 12 principles. Framework for Scoring and Ranking Chemicals and Processes by GCM. The GCM approach incorporates principle-specific algorithms (P-GCM) to compare and rank chemical and process alternatives under consideration. The approach is to calculate a principle score (PS) for each of the 12 principles (PS 1−12) using chemical specific data readily available from a number of sources, including that of GHS. The PSs metrics are key for development of comparison and ranking strategies and, as such, contribute to the flexibility of the GCM approach. Principle-specific scores (e.g., PS-1) can be used for the assessment of alternative performance under individual GC principles. In other words, PS-1 values from alternatives can be compared, PS-2 values can be compared, and so on. Because chemical-specific PS are based on different end points and therefore different measurement scales, aggregate scores calculated by direct summation of individual PSs would disproportionately represent metrics with higher possible scores. Therefore, ranking strategies were developed to avoid the uncertainty and controversy associated with data conversions to a common scale. Ranking strategies for assessment of alternatives under GCM are based on a hierarchy of metrics based on individual principles, categories of principles, and a summation of all 12 principles. Elements of this hierarchy are described as follows. Individual GC Principles. Each principle-specific score (PS 1−12) is assigned a rank of 1-to-n (where n is the number of alternatives being compared) to derive the principle-specific score rank score (PSR 1−12). For example, when comparing three product alternatives on principle 1, the principle scores are ranked 1, 2, and 3 to derive principle specific rank scores of PSR 1−1, PSR 1−2, and PSR 1−3. These principle specific rank scores can then be considered together to rank alternatives by category, or across the full spectrum of 12 principles. Categories. The GCM also groups the 12 principles into like categories, allowing for a focus on overarching green chemistry categories of hazard, resource use, and energy efficiency. These category groupings are shown in Table 1: improved resource use, increased energy efficiency, and reduced human and environmental hazards.

GREEN CHEMISTRY METRIC APPROACH The design objectives developed by MilliporeSigma industrial chemists for the GCM included the following: (1) allow for direct comparison between alternative chemicals considered for the same application, as well as direct comparison between alternative synthesis manufacturing processes considered for the same chemical product; (2) allow transparent comparison against each of the 12 principles and for each of the three major stewardship categories: resource efficiency, human health and environmental hazard, and energy use; (3) provide sufficient flexibility to apply to the diverse product portfolio; (4) be inexpensive to implement by utilizing readily available data; (5)

principle 1: waste prevention

Table 1. 12 Principles Categories

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improved resource use

principle 2: atom economy principle 7: use of renewable feedstock principle 8: reduce derivatives principle 9: catalysis

increased energy efficiency principle 6: design for energy efficiency

reduced human and environmental hazards principle 3: less hazardous chemical synthesis principle 4: designing safer chemicals principle 5: safer solvents and auxiliaries principle 10: design for degradation principle 12: inherently safer chemistry for accident prevention

principle 11: real-time analysis for pollution prevention C



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The category rank (CR) is determined by ranking the average of PSRs in that category. For example, the CR for improved resource use is determined by ranking the average of the PSRs for principles 1, 2, 7, 8, 9, and 11 for each alternative. If five alternative chemicals are being compared, therefore, there will be category rankings of 1−5 for each category. It is important to note that while in some cases a principle may contribute to the environmental benefits of more than one category, this method groups principles into those categories where benefit is most relevant. Summary of All Principles. To allow the user to consider all 12 principles in comparisons of chemical products or processes, the GCM uses a summary rank (SR). The SR is the rank for each alternative of the average of all 12 PSRs. Approach to Leverage Readily Available Data. Given the breadth of global and U.S. agency adoption of the GHS, aligning the GCM with and using GHS data, where relevant, presents the best opportunity for integrating readily available data into the method. GHS data are relevant to most of the principles (principle 3, 4, 5, 10, and 12) encompassed in the reduced human and environmental hazards category. For example, for those principles related to health hazards, i.e., 3, 4, and 5, the GCM considers a combination of GHS toxicity ratings by exposure route across end points to assign a relevant PS. Relevant GHS health hazard criteria include those applicable to acute toxicity, skin corrosion/irritation, serious eye damage/eye irritation, respiratory or skin sensitization, aspiration toxicity, reproductive toxicology, target organ systemic toxicity (single and repeated exposure), germ cell mutagenicity, and carcinogenicity. Similarly, GHS-based classifications for environmental hazards and physical hazards are useful to scoring principles 10 and 12, respectively. Specifically, principle 10 uses GHS-derived information on environmental hazard criteria (e.g., acute aquatic toxicity) and biodegradation, and principle 12 uses a combined consideration of the 16 GHS-defined physical hazard categories (e.g., explosives, flammable gases, flammable aerosols, and oxidizing gases). In addition to the GHS, the GCM uses readily available information to represent other metrics such as energy use or waste generation. Such information may be a direct measurement or proxy data, such as time in various heating or cooling conditions to represent metrics, such as energy use. Flexibility with Lifecycle Stages. When using the GCM scoring method, boundaries must be established to ensure that the same lifecycle stagessuch as raw materials extraction, raw materials preprocessing, chemical manufacturing, or disposal are equally included or excluded from each of the chemicals or processes being compared. If the boundaries exclude a particular lifecycle stage, then whichever of the 12 principles require that lifecycle stage must also be excluded. For transparency, such exclusions and reasons for exclusions should be specified. For example, if three chemicals are to be compared and only one chemical has data for an applicable lifecycle stage, then that lifecycle stage and principles applicable to that lifecycle stage should be transparently excluded for all three chemicals. Further detail on the approach selected for computation of each principle specific green chemistry metric is presented below.

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GREEN CHEMISTRY METRIC RESULTS

Using the GCM approach described above, principle-specific algorithms (P-GCM) were developed to guide calculation of each of the 12 PS and associated rankings. For each of the three GCM categories, as shown in Table 1, we describe the principles included in that category, their P-GCM, and the complementary nature of the principles in the category. We describe herein the parameters engaged to develop the algorithm and basic approach. Improved Resource Use Category. The improved resource use category includes the principles that drive resource efficiency and waste reduction (Table 1). This collection of principles addresses resource use in a variety of manners. Principle 12 and principle 22 drive an overall approach to resource efficiency by considering the relationship between input materials and the desired product produced. The algorithm for calculating the PS for principle 1 (P1-GCM) focuses on managing waste with an eye toward waste hazards by including a waste severity factor. The P2-GCM complements the P1-GCM by focusing on the efficient use of inputs, rather than waste. Principle 76 and the accompanying P7-GCM focus on resource efficiency to the extent that renewable materials are used as inputs. P8-GCM, P9-GCM, and P11GCM address resource efficiency in the manufacturing process through reduction in derivatization waste, increased use of catalyst, and use of more careful monitoring, respectively. The P-GCMs for each of these principles are described below. Principle 1: Waste Prevention. “It is better to prevent waste than to treat or clean up waste after it has been created.”2 For P1-GCM, a waste severity factor is incorporated to address the environmental fate of waste (i.e., how waste is treated). Companies using the GCM would establish company-specific waste severity factors using either third party or custom analysis. Table 2 provides example waste severity factors adapted from Beyond Benign’s iSUSTAIN Green Chemistry Index6 and the GHG Protocol Scope 3 Calculation Guidance.21 Table 2. Waste Severity Table waste treatment

waste severity

incineration disposal in a landfill (inert material) disposal in a landfill with landfill-gas-to-energy composting wastewater treatment waste-to-energy or energy-from-waste recovery for recycling

15 7 5 3 1.5 1 1

The equation for P1-GCM is n

∑i (mass of waste (kg) × waste severity) mass of product (kg)

(1)

where waste severity is the waste severity factor from Table 2 for all synthesis steps i. Principle 2: Atom Economy. “Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.”2 The P2-GCM is, like the P1-GCM, a resource efficiency metric. To focus on the efficient use of inputs rather than generation of waste, it draws on the process mass efficiency (PME) equation from NSF/GCI/ANSI 355-2011 by including reactants, auxiliary chemicals, and recycled materials.3 D


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deviations from a plan, recognizing that the sooner deviations from a plan are corrected, the less likely a process is to generate additional waste or cause additional hazard. Specifically, P11GCM targets monitoring of process temperature or pH. Scoring relies on a monitoring rigor scale, based on the error detection monitoring systems available (digital or analog) at each stage (lab, pilot, or production) of chemical manufacturing for each synthesis step. If the plant has a digital monitoring system available, it is more accurate and likely results in less wastage than an analog monitoring system, so it receives a higher (i.e., less wasteful) monitoring rigor rating. Table 3 shows an example monitoring rigor table. GCM users can replace the example monitoring rigor table with a table that best represents their monitoring activities.

The P2-GCM can be calculated from process mass efficiency (PME) =

R (kg) + A (kg) − RR (kg) − RA (kg) mass of product (kg) + mass of co products (kg) (2)

where R is the mass of chemicals input to the process as reactants, RR is the mass of recovered and recycled reactant R used within the process, A is the mass of auxiliary chemicals (i.e., carriers (solvents, water), integral catalysts, and additional chemicals used to produce coproducts and recover input chemicals), and RA is the mass of auxiliary A that is recovered and reused as an integral part of the process. Principle 7: Use of Renewable Feedstock. “A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.”2 P7GCM focuses on the efficiency aspect of using renewable rather than nonrenewable feedstock; it is scored by considering the amount of renewable material used. It is important that the term “renewable material” be clearly defined by each GCM user in order to maintain the transparency and comparability of P7GCM analyses. The equation for the P7-GCM is

Table 3. Example Monitoring Rigor Table scale lab pilot production

monitoring system

monitoring rigor

analog digital analog digital analog digital

1 5 1 5 1 5

n

∑i (mass of raw material (kg) × %nonrenewable) mass of product (kg)

The P11-GCM is computed by (3)

(no. of synthesis steps without monitoring)

where % nonrenewable is the percentage of materials that do not fit the definition of renewable, and renewable is defined as “biobased product” (as defined by the USDA Biopreferred Program22), whose rate of growth is greater than or equal to its rate of use for all raw materials i. Materials that do not meet this definition of renewable, such as those derived from waste or CO2, will not receive a benefit in this category. However, these materials may receive a benefit from being recycled in principle 2: atom economy. Companies should clearly substantiate all renewable claims in the documentation of this principle for all raw materials i. Principle 8: Reduce Derivatives. “Unnecessary derivatization (use of blocking groups, protection/deprotection, and temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.”2 The P8-GCM can be calculated from

/(number of synthesis steps with monitoring × monitoring rigor + number of synthesis steps without monitoring)

where monitoring rigor is the monitoring rigor value from Table 3. Increased Energy Efficiency Category. The increased energy efficiency category focuses on principle 6: design for energy efficiency.2 Principle 6 focuses on energy use in the synthesis of a chemical. Addressing the reality that energy used (e.g., kilowatt-hours, Megajoules, therms) in the production of a chemical is not commonly measured, P6-GCM estimates energy impact by calculating the amount of reaction time that synthesis steps deviate from ambient pressure (i.e., atmospheric pressure at sea level or 1 atm) and ambient temperature (i.e., room temperature or 25 °C). Principle 6: Energy Efficiency. “Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.”2 The P6-GCM utilizes available chemical process datareaction time and mass of the product. The GCM requires that companies develop their own temperature and pressure severity factors based on current energy use practices. Tables 4 and 5 are examples of pressure and temperature severity factor tables, which were adapted from Beyond Benign’s iSUSTAIN Green Chemistry Index.6 The P6-GCM can be approximated by

n

∑i mass of derivative waste (kg) mass of product (kg)

(4)

for all synthesis steps i. Principle 9: Catalysis. “Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.”2 P9-GCM aims to recognize that catalytic steps are typically more efficient than stoichiometric steps. It serves as a complement to the P2GCM, likely driving improvements in atom economy via catalyst use. The P9-GCM can be approximated by 1 1 + number of catalytic steps

(5)

n

∑i [(SFT + SFP) × time (h) × mass of raw materials (kg)]

Principle 11: Real-Time Analysis for Pollution Prevention. “Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.”2 P11-GCM incorporates analytical chemistry, such as in-process analysis, to detect

mass of product (kg)

(6)

where SFT is the severity factor for temperature from Table 5, and SFP is the severity factor for pressure from Table 4 for all synthesis steps i. E


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where H score is the hazard score determined from evaluation and assessment of chemical specific E scores for all products i. Principle 5: Safer Solvents and Auxiliaries. “The use of auxiliary substances (e.g., solvents, separation agents) should be made unnecessary wherever possible and innocuous when used.”2 The equation for the P5-GCM is

Table 4. Example Pressure Table pressure ranges (atm)

severity factor (SFP)

critical pressure of water (218 atm) standard or atmospheric pressure at sea level (1 atm) absolute vacuum pressure (0 atm)

7 1 3

n

∑i (H score × mass of solvent (kg))

Table 5. Example Temperature Table temperature ranges (°C)

severity factor (SFT)

Ice absorbs heat (−20 to 0) water freezes (0) liquid water absorbs heat (0 to 20) room temperature (20 to 30) liquid water absorbs heat (30 to 100) liquid water boils (100) steam absorbs heat (>100)

7 5 3 1 3 5 7


where H score is the hazard score determined from evaluation and assessment of chemical specific E scores for all solvents i. Principle 10: Design for Degradation Focuses on Environmental Hazard Criteria. This principle states “chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.”2 The GCM for this principle is derived from the GHS environmental hazard criteria for parent and degradation products. To score environmental hazards, the GCM uses GHS-derived information on biodegradation, chronic aquatic toxicity, log octanol− water partitioning coefficient (Log Kow), and bioconcentration factor (BCF) in addition to acute aquatic toxicity data. A score for degradation and bioaccumulation (B) is assigned based on GHS hazard classification values (Supporting Information Tables S18 and S19). The P10-GCM can be calculated from

Reduced Human and Environmental Hazard Category. The reduced human and environmental hazards category includes the green chemistry principles that address potential impacts to human health and safety and the environment (Table 1). Metrics for this category are derived from the numerical category (or modified category) assigned to each hazard class based on GHS criteria.20 The GCMs for principles 3−5 (P3-GCM to P5-GCM) are based on acute and chronic toxicity end points (E) for human health (H; Supporting Information Tables S3−S16). P10-GCM draws on GHS environmental hazard criteria for degradation and bioaccumulation (B; Supporting Information Tables S18 and S19), and P12-GCM is based on end points (Z) for physical hazards (P; Supporting Information Tables S20−S35). Several principles in this category are derived from the same GHS health hazard end points.20 P3-GCM, P4-GCM, and P5GCM all use a similar GHS-based approach to assessing toxicity. The key differences are that P3-GCM focuses on input materials, P4-GCM focuses on the produced product, and P5GCM focuses on solvents and separation agents. For principles 3−5, chemicals are evaluated in a two-step process. First, a score for each toxicity end point (E score) is assigned based on GHS hazard classifications values (Supporting Information Tables S3−S16). Next, an overall hazard score (H score) is determined from the maximum E score (Supporting Information Table S17). Principle 3: Less Hazardous Chemical Synthesis. “Wherever practical, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.”2 The equation for the P3-GCM is

[B score of highest ranked parent product or degradation product × mass of highest ranked parent product or degradation product (kg)]/(mass of product (kg)) (10)

where B score is the biodegradation score determined from the GHS environmental hazards criteria. Principle 12: Inherently Safer Chemistry for Accident Prevention. This principle states “substances and their form used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.”2 The P12-GCM is derived from the GHS hazard classification values for the physical properties of a given chemical substance across the range of hazard types including explosivity, flammability, oxidizing capabilities, reactivity, and corrosivity. Similarly to principles 3−5, a Z score for each end point (e.g., flammability, reactivity) is assigned based on GHS hazard classifications values (Supporting Information Tables S20−S35). Then the overall physical properties score (P score) is determined by selecting the maximum Z score for any physical property or other comparisons as warranted by the investigator (Supporting Information Table S36). The equation for P12-GCM is

n

∑i (H score × mass of raw material (kg)) mass of product (kg)

(7)

n

∑i (P score × mass of raw material (kg))

where H score is the hazard score determined from evaluation and assessment of chemical specific E scores for all raw materials i. Principle 4: Designing Safer Chemicals. “Chemical products should be designed to affect their desired function while minimizing their toxicity.”2 The P4-GCM can be calculated from n ∑i (H score


(11)

where P score is the physical score determined from evaluation and assessment of chemical specific Z scores for all raw materials i.

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APPLICATION OF THE GCM The GCM approach allows transparent comparison between chemicals based on each of the 12 principles. The GCM scoring method was designed to optimize transparency and clarity of

× mass of product (kg))


(9)

(8) F


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ACS Sustainable Chemistry & Engineering communication. Fundamental to the scoring method is that, first, companies define equivalent boundaries of comparison and, second, the scoring method defines a hierarchy of metricsincluding principle score rank (PSR), category rank (CR), and summary rank (SR)to allow multiple chemical products or synthetic manufacturing processes to be compared. As the GCMs have been designed such that a lower PS represents a greener option, the principle with a lowest PS will be assigned a PSR of 1 and the principle with a higher PS will be assigned a PSR of 2 etc. If the PSR averages are tied, then the two alternatives receive the same rank. The mean of PSRs by category are then ranked to determine CR, category rank, and the mean of PSRs for all 12 principles are then ranked to determine SR, summary rank. Ranking each chemical for each PS allows users to transparently see in what manner chemicals or chemical processes improve green chemistry over alternatives, as well as where there are trade-offs between green chemistry principles. Case Study. Millipore Sigma industrial chemists trialed the GCM in a case study and found that the GCM provided for the ability to evaluate and score chemical products and processes on each of the 12 principles and met the key design objectives delineated above. This case study compares two alternative processesan original and a re-engineered processto synthesize 1-aminobenzotriazole to evaluate and score the greener alternative using the GCM approach. The original process to synthesize 1-aminobenzotriazole includes four steps illustrated in Figure 1. The second step includes a hazardous hydrogenation step at atmospheric pressure using 10% palladium/carbon in methanol (20 L flask). The final product

is purified by silica gel column using kilograms of silica gel and additional tens of liters of organic solvents. The re-engineered process solves this problem as it does not need column purification. The new process to synthesize 1-aminobenzotriazole is a one step process illustrated in Figure 2. The nucleophilic reaction of

Figure 2. Re-engineered process to synthesize 1-aminobenzotriazole.

benzotriazole with hydroxylamine-O-sulfonic acid in alkaline aqueous solution gives 1-aminobenzotriazole. The final product is purified by extractions, washings, and recrystallization. Some of the improvements of the re-engineered process include the following: the hazardous hydrogenation procedure at atmospheric pressure using 10% palladium/carbon in methanol (20 L flask) was eliminated from the process, 40% less organic solvents, eliminated about 6 L of concentrated hydrochloric acid and 150 g of 10% palladium/carbon catalyst waste disposal, used 6 kg less auxiliaries (e.g., sodium acetate/ carbonate/sulfate), reduced 22 days (73%) process time, and product yield was increased by about 60%. On the basis of the improvements, the original and redesigned alternatives were compared based on each of the 12 P-GCM. They were then scored by ranks by principle and by category. The alternatives were compared with the following boundary setting assumptions: The lifecycle stage included in the case study boundaries is chemical manufacturing. The case study excludes raw materials extraction, raw materials preprocessing, and disposal. These lifecycle stages are excluded to provide a simplified example. The case study boundaries did not include any raw material inputs or intermediates. Table 8 provides the results of the greener alternative example. The results table is organized to compare chemicals scores and ranks by principle and by category. In this example, the re-engineered 1-aminobenzotriazole process only ranks better (has a lower PSR) than the original 1-aminobenzotriazole process for principles 1−3, 5−7, and 12. The reengineered 1-aminobenzotriazole process ranks better (has lower CRs) in all three categories, and the re-engineered 1aminobenzotriazole process is better overall (has an improved SR) compared to the original 1-aminobenzotriazole process. The GCM provides directional evidence that the re-engineered process is better or the same in 11 out of 12 principles (only worse for principle 9), all three categories, and overall. Ultimately, the end user will decide if they will prioritize chemical selection based on individual principles, categories, or an overall rank. This case study and the GCM method were not peer reviewed by other industrial chemists outside of MilliporeSigma, which is a potential limitation of this research. The GCM is advantageous over existing approaches, because it provides metrics that are (1) inexpensive to implement with readily available data, (2) based on generally accepted industry practices when available, and (3) an easy way to communicate the method equations and results to customers. Sustainability

Figure 1. Original process to synthesize 1-aminobenzotriazole. G


Research Article

ACS Sustainable Chemistry & Engineering Notes

Table 8. Greener Alternatives Example Results original 1aminobenzotriazole process category and related principles

PS

PSR

improved resource use principle 1: prevention 2701 2 principle 2: atom economy 933 2 principle 7: use of renewable feedstock 933 2 principle 8: reduce derivatives 0.0 1 principle 9: catalysis 0.5 1 principle 11: real-time analysis for pollution 1.0 1 prevention category PSR average 1.5 category rank (CR) 2 increased energy efficiency principle 6: design for energy efficiency 3282 2 category PSR average 2 category rank (CR) 2 reduced human and environmental hazards principle 3: less hazardous chemical 3358 2 synthesis principle 4: designing safer chemicals 5 1 principle 5: safer solvents and auxiliaries 2245 2 principle 10: design for degradation 0 1 principle 12: inherently safer chemistry for 2516 2 accident prevention category PSR average 1.6 category rank (CR) 2 summary PSR average 1.6 summary rank (SR) 2

The authors declare the following competing financial interest(s): MilliporeSigma retained Ramboll Environ to review the scientific methodology of and improve their Greener Alternatives Scoring Matrix.

re-engineered 1aminobenzotriazole process PS 1042 345 345 0.0 1.0 1.0

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PSR

ACKNOWLEDGMENTS Ramboll Environ acknowledges MilliporeSigma for financial support of this work.

1 1 1 1 2 1

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ABBREVIATIONS ACS, American Chemical Society; ANSI, American National Standards Institute; BCF, bioaccumulation factor; CR, category rank; GCI, Green Chemistry Institute; GCM, green chemistry metrics; GHS, Globally Harmonized System of Classification and Labeling of Chemicals; NSF, NSF International; P-GCM, principle-specific green chemistry metric; PME, process mass efficiency; PS, principle score; PSR, principle score rank; SR, summary rank; SCP regulations, Safer Consumer Products regulations

1.2 1 1322

1 1 1

1455

1

5.0 1252 0.0 220

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1 1 1 1 1.0 1 1.1 1

programs that implement the proposed approach should anticipate the following benefits: • Measurement: ability to use on-hand data sources or establish straightforward data collection programs • Calculations: ability to utilize well-defined metrics to calculate the benefits of the 12 principles of green chemistry • Communication: ability to transparently communicate greener alternatives to customers As with all methods, including those as established as LCA, there are limitations. We propose the following next steps to improve upon this research: • engage a green chemistry working group to pilot and review the method • conduct an LCA to compare the GCM results with LCA results

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02399. Detailed calculations, tables, and equations (PDF)

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*Tel.: 1-303-382-5483. Fax: 1-303-382-5499. E-mail: [email protected]. ORCID

Ashley DeVierno Kreuder: 0000-0002-4973-4959 H


Research Article

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