Using the Right Green Yardstick: Why Process Mass Intensity Is Used in the Pharmaceutical Industry To Drive More Sustainable Processes

Abstract

There have been a many publications and much discussion about green metrics. While many have been proposed, The American Chemical Society Green Chemistry Institute's Pharmaceutical Roundtable has chosen process mass intensity (PMI) as the key, high-level metric for evaluating and benchmarking progress towards more sustainable manufacturing. This paper provides the philosophical and technical arguments on why PMI was chosen above other related metrics such as E factor or atom economy.

Application of environmental and economic metrics to guide the development of biocatalytic processes

“…The use of more complete and complex performance assessment tools (such as LCA and/or full costing) during the early stages is definitely not a suitable strategy, as many of the process details are not yet defined, nor is the process optimized and thus, the output of these evaluations are highly sensitive to the quality and quantity of the input information. Nevertheless, several relevant mass metrics such as green chemistry metrics and process metrics are a necessary step to perform an LCA and determine process footprints [43]. Hence, it is necessary to select a suite of appropriate and relevant metrics that can well foresee the performance evaluation and relate with the environmental impacts and costs at a later stage (Table 5).…”

“…PMI is the metric chosen by the American Chemical Society Green Chemistry Institute's Pharmaceutical Roundtable as a high-level metric to evaluate the extent to which a given manufacturing process is sustainable [43]. PMI is defined as the total mass of materials used to produce a specified mass of product [43], Eq.…”

“…PMI is defined as the total mass of materials used to produce a specified mass of product [43], Eq. (9).…”

“…(9). When calculating PMI the starting point is the commonly available materials [43]. Hence, the metric accounts for all the steps in the chemical synthesis including the catalyst production and all reagents (including water) that are used directly in the process [44].…”

“…For bio-based raw materials, a high Y reaction might lead to lower nutrient enrichment potential (NEP) (due to reduced use of fertilizers during the growing of crops) and other land use aspects [34]. Due to the high selectivity of enzymes, when highly functionalized molecules or those Figure 3 Typical relative contribution of raw material, biocatalyst production and downstream on the operating costs of a chemical (adapted from [5], [22], [43], [46], [65]). with several chiral centers are aimed at, the biocatalytic route might appear to be a suitable alternative to avoid protection and de-protection steps (with an overall reduction of the process steps) and thus, the theoretical yield can be greatly improved and the amount of waste minimized [34].…”