CHEM21 Metrics Toolkit

The CHEM21 project has developed a unified metrics toolkit to comprehensively evaluate the sustainability of chemical and bio-chemical reactions based on a series of key parameters (see Figure 1 below).  Moving beyond the use of ‘mass based metrics’ alone, the Toolkit uses a blend of both qualitative and quantitative criteria to assess how green a reaction is, as well as considering factors both upstream and downstream of the reaction itself.  This ensures a truly holistic approach.

Key parameters

Fig. 1: Summary of the Key Parameters covered by the metrics toolkit [R. McElroy et al.  Green Chem., 2015, 17 (5), 3111 – 3121. Reproduced under license: Creative Commons Attribution 3.0 http://creativecommons.org/licenses/by/3.0/]

The Toolkit allows the user to:

  • Assess/demonstrate the ‘green credentials’ of their research – highlighting where research is performing well in terms of its ‘greenness’ and clearly identify hot-spots or areas of concern in current methodologies (in order to focus research to areas where it will have greatest effect).
  • Benchmark against current state of the art for a particular reaction or pathway by giving a baseline against which new discoveries can be compared.
  • Monitor, measure and evaluate new methodologies to ensure that solving one problem does not give rise to others elsewhere in the process.

The Toolkit is specifically structured with a series of ‘passes’ to cover everything from bench top research right through to industrial scale with increasing level of complexity (see Figure 2):

  • Zero Pass’ – an initial light tough appraisal for screening reactions (few mg scale)
  • First Pass’ – a more comprehensive evaluation of research that has shown potential at Zero Pass and has been further optimised and scaled up (ca. hundreds mg/g scale).
  • Second Pass’ & ‘Third Pass’ thorough analyses of data gathered from pilot scale research and beyond (kg/multi kg scale)

Metrics toolkit structure

Fig. 2: Structure of the metrics toolkit showing the parameters covered at each Pass. [R. McElroy et al.  Green Chem., 2015, 17 (5), 3111 – 3121. Reproduced under license: Creative Commons Attribution 3.0 http://creativecommons.org/licenses/by/3.0/]

The acceptability of a particular process or reaction step is shown by a system of flags.  For each of the assessed criteria a green, amber or red ‘flag’ is assigned, where green denotes ‘preferred’, amber is ‘acceptable – some issues’ and red is ‘undesirable’.  Whilst amber or red flags in the metrics analysis draw the user’s attention to issues or concerns, this does not necessarily indicate an outright ‘ban’.  Rather that the user should seek further information, considering why the flag has been produced and what means can be taken to improve the issue.

The purpose of the toolkit is to ensure a holistic approach is taken so that no parameter is looked at in isolation. As such the impact of changing one parameter on the overall metrics is always investigated, particularly to see whether any detrimental effects have occurred elsewhere.  CHEM21’s aim is that this Toolkit will encourage continuous improvement whilst training researchers to think critically about sustainability and environmental acceptability, making analysis of their synthetic routes and the use of greener and more sustainable techniques part of everyday practice.

For CHEM21 consortium members this Toolkit has been incorporated into a Reaction Database (developed by the University of Leeds) to allow routine use and interpretation of data.  For all others the Toolkit is available in the form of a user friendly excel spreadsheet in the supplementary information of the publication.

You can also download a free quick to use guide of the CHEM21 first pass metrics toolkit that could be printed and displayed in your laboratory.

Reference: Green Chem., 2015, 17 (5), 3111 – 3121