The CHEM21 Solvent Selection Guide

In this video, Denis Prat explains the work of the CHEM21 consortium in developing its own solvent selection guide of classical and less-classical (including bio-derived) solvents, including its formulation and scope.

This work is also published as an open access article [1] alongside an associated Excel spreadsheet (in the supplementary data) that will enable the user to rank a solvent not included in the list according to the guidelines outlined in the publication.

Furthermore, the spreadsheet has now been adapted into an interactive tool for the platform.

After the survey of existing solvent guides[1], the CHEM21 solvent team elaborated a methodology, based on easily available physical properties and GHS statements, permitting anyone to establish safety, health and environment criteria of any solvent, even if full data on the solvents are not yet available.[2] A simple way to obtain a preliminary ranking of the solvent (so-called “ranking by default”) was also proposed, based on a combination of these SHE criteria. The methodology was tested on the classical solvents having a clear ranking according to the survey, with a fair predictivity of 81%.

The SHE criteria are scored from 1 to 10, the highest figure representing the highest hazard level. A colour code is associated with these scores: 1 to 3: green, 4 to 6: yellow, 7 to 10: red.

The safety score derives mainly from the flash point, with contributions of the auto-ignition temperature (AIT), the resistivity and the ability to form explosive peroxides (statement EUH019 in GHS/CLP) (Table 1).

As an example, the safety score of diethyl ether, with a FP of – 45°C, an AIT of 160°C, a resistivity of 3.10 11 ohm.m and an EUH019 statement is 7+1+1+1=10.

The health score derives mainly from the most stringent GHS H3xx statements, with a contribution of the boiling point, according to Table 2.

If, after full REACH registration, there is no H3xx statement, the health score is 1. The score of newer solvents for which the REACH registration is not complete is 5 if the boiling point is 85°C or higher, otherwise, 6, unless a more stringent H3xx is attributed by the supplier.

The environment score takes into account both the volatility of the solvent (ability to form Volatile Organic Compounds) and the energy demand for recycling. Both are linked to the boiling point. The GHS H4xx statements are also important (Table 3). The environment score is based on the most stringent of these factors. For example, the score of 7 for heptane is due to its H410 statement, whereas the score of 7 for dichloromethane is as a result of its low boiling point.

If the REACH registration is not full and no H4xx has been attributed by the supplier, the environment score is 5 by default.

These S, H & E scores are combined according to Table 4 to give an overall scoring of the solvent. The ranking is imposed by the most stringent combination.

The ranking by default does not make the distinction between “hazardous” and “highly hazardous”. The decision to “ban” a solvent necessitates discussion at an organisational level. It is important to remember that the ranking methodology is only a model that gives a ranking by default and this should be critically assessed by occupational hygienists and other experts of any institution using it. For example, the scoring of chloroform as only “problematic” or of pyridine as “recommended” are not acceptable. This illustrates the limits of a health scoring system only based on GHS hazard statements. As the Occupational Threshold Limits of these solvents are available and very low (ppm range), CHEM21 finally ranked them as “highly hazardous” and “hazardous” respectively. Other decisions are more the result of the policy of the institution. CHEM21 finally decided to rank methanol and acetone as “recommended”, and on the contrary, cyclohexanone as “problematic”, for reasons which will not be debated here.

For the solvent you are assessing, complete the information one question at a time below.  When you get to the end, the tool will calculate the scores and overall ranking by default for the solvent. 

As a reminder, to rank the solvent you will need access to the following information:

• Boiling point, flash point, auto-ignition temperature, resistivity;
• Whether or not it is an ether that forms explosive peroxides;
• GHS statements and symbols;
• Whether or not it is hazardous to the ozone layer; and
• Whether or not it is fully registered for REACH.