Green Solvents

The term "green solvents" covers everything from truly green, fully bio-based, fully certified solvents to pure greenwash, solvents that provably are worse for the planet but great for marketing.

However green the solvent is, it is useless if it cannot dissolve your target solute, either on its own or as a rational mixture with other green solvents. You will not be surprised when we say that HSP is an excellent general-purpose tool for assessing this. Perhaps more surprising is that the EU agrees and in CEN/TS 16766:2015 – Bio-based solvents there is a requirement to provide the HSP of your solvent to achieve bio-based solvent certification.

In HSPiP we have worked with a number of key institutes/organisations to allow us to include their lists of green(er) solvents.

The U. York Green Chemistry Centre of Excellence, GCCE, led by Prof Clark, has produced a very small group of green-but-also-useful solvents which users can load into the Solvent Optimizer in order to find rational replacements for current solvents.

The GCCE was also a key member of the Chem21 group which set out to produce a pragmatic set of "greener" solvents to be used in industries such as pharma or agrochem. Their view is that it is better for the planet, and for human health, to use a "better" solvent today rather than wait for a perfectly green solvent which may never appear. Again, the Chem21 list is included in the Solvent Optimizer

The U Lille team under Prof Aubry has adopted a different, complementary approach, producing two lists of greener solvents based on a set of scientific criteria, using a computational chemistry approach. The first list contains all their interesting molecules. The second list has been trimmed to focus on a range of solvents that span HSP space without unnecessary duplication. Both lists are included with HSPiP

A group of chemists/engineers at INP-ENSIACET in Toulouse led by Professors Thiebaud-Roux and Gerbaud are working extensively with industry (and with the EU standards committees) to introduce greener solvents via a computational science approach linked to expertise in Life Cycle Analysis (LCA). The LCAs of many green solvents show that it can be difficult to decide if they are good for the planet. The problem revealed in the LCAs is nicely described in a German expression "Tank oder Teller": "Do we use crops for the Tank (fuel tank) or the Teller (plate)?" Even if waste products are used, sometimes the carbon footprint can be worse if, for example, the process involves lots of evaporation of water.

Saving the planet is hard

All these groups are aware that it is hard to save the planet. So those who want to do so need all the help they can get - because resources spent on ideas that have no chance of success (many projects could have been avoided via a quick HSP check), are resources that could have been used on more productive activities. HSPiP is used extensively by the teams because it not only handles the "solubility" aspects but also can generate excellent key parameters such as vapour pressure, boiling point, relative evaporation rates.

The HSPiP team are proud that the package of software and datasets is now making many positive contributions to saving the planet.