By Ashley Baker, Scientific Content Manager (Contractor) at ACS GCI
Calculating Process Mass Intensity (PMI) is straightforward: divide the mass of raw materials used by the mass of the final product. In practice, however, chemical processes are complex, often involving many steps and inputs, making it challenging to determine which steps are the most resource-intensive. It may hardly be obvious, for example, that reducing materials in an early step could lead to an unintended increase in materials in later steps.
To accelerate the development of more sustainable synthetic processes for pharmaceutical manufacturing, the ACS GCI Pharmaceutical Roundtable members developed and launched the first-of-its-kind Process Mass Intensity (PMI) Calculator over a decade ago. This innovative tool allowed synthetic chemists to measure, set goals for, and decrease the amount of material used and disposed of during syntheses.
Since then, many new sustainability metrics have been proposed for various applications, but there are no streamlined tools to evaluate them. In addition, looking only at the mass of materials used does not adequately indicate potential environmental and human health impacts. To help chemists and engineers consider processes more holistically, the Roundtable developed an expanded version of the PMI Calculator. Rather than evaluating all available metrics, the Roundtable members selected those that would be both the most informative and least complex for fast decision-making. The new combined PMI and Life Cycle Assessment (LCA) Tool made its debut at the annual Green Chemistry and Engineering Conference in 2023. It is now freely downloadable with a quick-start guide.
Features of the PMI-LCA Tool
In addition to including life cycle impacts, the new tool addresses challenges faced by earlier versions, such as simplifying user input, adding automated data-entry-error detection, and removing Excel Macros which could affect the ability to transfer the tool between organizations.
Fast LCA Calculations
The incorporation of pre-loaded LCA data, sourced from the Ecoinvent life cycle inventory database, enables users to bypass the lengthy timelines required for full assessments. Instead, the tool uses average values for classes of compounds, like solvents, while accounting for six environmental impact indicators: mass net, energy, global warming potential (GWP), acidification, eutrophication, and water depletion. While there is more robust LCA software that accounts for additional impacts, the simplicity and efficiency of this tool for approximating impact makes it more practical for timely decision-making. Simplifying assumptions are therefore embedded in the PMI-LCA Tool to generate results quickly enough for process designers to implement changes. With that in mind, users should remain aware that calculator outputs are representative rather than absolute values.
The PMI-LCA Tool is designed to be used by chemists and engineers, rather than experts in Excel or LCA. The workbook format makes it transferable across organizations and allows users to compare multiple synthetic routes simply by creating copies of the workbook.
To make it easier to keep track of data, all materials for a particular step are grouped together and then automatically carried throughout the workbook. Once the process steps and materials are entered, a series of automatic calculations generates customizable charts with both the PMI and LCA results (see Figure 1). These visuals make it easy for users to identify and prioritize steps that are less efficient or have greater life cycle impacts.
Figure 1: Example output from the streamlined PMI-LCA tool. The tool enables users to break down PMI and six life cycle indicators by raw material or processing step. Materials shared across multiple steps can be grouped or assigned to “complex” raw materials such as stock solutions or organometallic compounds. The example chemistry shown here is drawn from J. Chem. Educ. 2019, 96, 8, 1738-1744 for illustrative purposes.
Design for Iterative Assessment
The developers of the tool recommend that chemists and engineers apply it iteratively during process development, starting when a chemical route has been established. This workflow can quickly identify hot spots and enable early-phase action. In each phase up to commercialization, users can quickly check that PMI and LCA results are trending in the right direction.
With plans for a web-based version in the pipeline, the ACS GCI Pharmaceutical Roundtable envisions further improvements to the ease of use to enable broader adoption. A web version would allow for regular updates with the most recent LCA data and a common database of benchmark information from Roundtable members.
While many organizations have already incorporated the tool into their process development workflows, increasing training opportunities for industry researchers will speed its adoption. Academic institutions can also benefit from teaching the tool to better prepare students for the workforce and encourage the development of innovative, sustainable processes that are commercially viable.
The Roundtable and ACS GCI invite project managers, research chemists, and engineers who impact process development to share this tool with their networks. With continued industry commitment, tools like this will remain at the forefront of “green-by-design" chemistry, aligning and improving sustainability metrics along the way.
About the ACS GCI Pharmaceutical Roundtable
The ACS GCI Pharmaceutical Roundtable (GCIPR) is the leading organization dedicated to catalyzing the integration of green chemistry and engineering in the pharmaceutical industry. Established in 2005 by the American Chemical Society’s Green Chemistry Institute, the Roundtable’s activities are driven by the shared belief that green chemistry and engineering is imperative for business and environmental sustainability. Learn more on the ACS GCIPR website.
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