Introduction:
Green chemistry is the concept of developing chemical products and processes that reduce the use and generation of hazardous materials, minimize waste and decrease demand on diminishing resources. Paul Anastas and John Warner developed the 12 Principles of Green Chemistry— the global framework that has served as the foundation for green chemistry(1). That framework proposes 12 complementary principles around resource efficiency and risk (human health and environmental) minimization, targeting a life-cycle perspective (e.g., raw materials extraction, chemical production, and end-of-life bioaccumulation and biodegradation). These 12 principles were also adopted by the American Chemical Society’s Green Chemistry Institute (GCI). While various approaches to quantifying greener processes and products have been proposed, there was no unifying set of metrics in place. After a review of the current state of green chemistry methods, MilliporeSigma developed the DOZN™ quantitative green chemistry evaluator and leveraged generally accepted industry practices. In review of the literature, MilliporeSigma found that while a few methods had been proposed to evaluate greener chemistry, there were hindrances to their implementation. Primary limitations included a required high level of effort (2-4) and a lack of readily available data and access to specialized or proprietary data sets. Additional limitations included results that lack transparency and are difficult to communicate.
One example of a method used to evaluate 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 bio-based 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 wasn’t completely comprehensive yet for tabulating scores to determine which chemical characteristics are less harmful to the environment. MilliporeSigma saw an opportunity to build on their efforts by evaluating the missing gaps including chemical use and end-of-life stages along with the specific principles: reduce derivatives, use of catalysis, design for degradation, and real-time analysis for pollution prevention.
The DOZN™ 2.0 approach and Life Cycle Assessment (LCA) serve as complementary approaches. While the DOZN™ 2.0 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 12 principles. The ability to capitalize on readily available data for green chemistry evaluation, as incorporated into this DOZN™ 2.0 approach, is a relatively recent phenomenon. This availability of data is tied to the timely development, use and adoption of the GHS, a classification system that provides an influx of information on the physical, health and environmental hazards of individual chemicals.
Additionally, the DOZN™ 2.0 approach leverages other product-specific information to address the full complement of the 12 principles. This approach and scoring method are described herein and demonstrated with a case study.
Figure 1: The DOZN Scale
Method:
The design objectives for the DOZN™ 2.0 system, developed by MilliporeSigma scientists, included the following:
- 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.
- Allow transparent comparison against each of the 12 Principles of Green Chemistry, and for each of the three major stewardship categories: resource efficiency, human health and environmental hazard, and energy use.
- Allow customers to score their own products/processes.
- Provide enough flexibility to apply to a diverse product portfolio.
- Be inexpensive to implement by utilizing readily available data.
- Be based on generally accepted industry practices, when available.
- Be easy to communicate the method and results to customers.
Considering these guiding elements, MilliporeSigma investigated and designed an approach to evaluate and score chemical products and processes against each of the 12 Principles of Green Chemistry.
The DOZN™ 2.0 system groups the 12 Principles of Green Chemistry into like categories, allowing for a focus on overarching green chemistry categories of hazard, resource use and energy efficiency.
- Improved resource use
- Increased energy efficiency
- Reduced human and environmental hazards
Results — A Case Study
MilliporeSigma industrial chemists trialed the DOZN ™2.0 system in a case study and found that it provided users with the ability to evaluate and score chemical products and processes against each of the 12 Principles of Green Chemistry while meeting 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 DOZN™ 2.0 approach. The original process to synthesize 1-aminobenzotriazole includes four steps. The second step includes hazardous hydrogenation at atmospheric pressure, using 10% palladium/carbon in methanol. The final product is purified by a silica gel column using kilograms of silica gel and additional liters of organic solvents. The re-engineered process solves this problem as it does not need column purification and hydrogenation.
The new re-engineered process to synthesize 1-aminobenzotriazole is a one-step process. The nucleophilic reaction of benzotriazole with hydroxylamine-O-sulfonic acid in alkaline aqueous solution gives 1-aminobenzotriazole. The final product is purified by multiple extractions, washings and recrystallization. Some of the improvements of the re-engineered process include the following: eliminating the hazardous hydrogenation procedure; using 40% less organic solvents; removing palladium/carbon catalyst use and waste disposal, and using lesser auxiliaries. Additionally, product yield was increased by about 60%.
The category groupings and scores are shown in Table 1 for 1-aminobenzotriazole (original and re-engineered processes).
Conclusions:
As a free, web-based tool, the DOZN™ 2.0 system moves the quantitative approach to green chemistry forward through accessibility, with a goal of continuing discussions with key stakeholders about improvements to the methodology. Sustainability programs that implement the proposed approach should anticipate the following benefits:
- Inexpensive to implement with readily available data
- Based on generally accepted industry practices, when available
- Easy to communicate the method and results to customers
- Offers data privacy; users can evaluate their processes and products in a secure manner
- Enables customers to choose more environmentally friendly approaches for their research/manufacturing projects to promote overall sustainability
Table 1: DOZN™ 2.0 Scores for 1-Aminobenzotriazole
*Aggregate Score is calculated by averaging each category score and summing three category scores to get the single score. Then, this will be further normalized (divided by 50) to get an aggregate score from 0 to 100 (0 being the most desired).
References:
- Anastas PT and Warner JC, Green Chemistry: Theory and Practice; Oxford University Press: New York 1998; p 30.
- NSF/GCI/ANSI 355-2011. Greener Chemical and Processes Information. Gate-to-Gate Information on Chemical Products and Their Manufacturing Processes, Standard; NSF International: Ann Arbor, MI, 2011.
- Department of Toxic Substances Control Safer Products and Workplaces Program. Draft Stage 1 Alternatives Analysis Guide. Safer Consumer Products. [Online] September (2015).
- Baitz M, Partl J, Braube A and Brauner E, Whitepaper—Improving the Environmental Performance of Chemical Products, 2011.