Updated: Oct 21, 2018
Author: Bianca Goncalves
Excerpt from Bianca Gonçalves’ masters thesis, An Introduction to Less Toxic Approaches for the Cleaning of Paintings: The Particular Case of Acrylics. Presented July 2018, ENSAV La Cambre, Brussels, Belgium
Tools and techniques for solvent selection: Green solvent selection guides
Multiple programs, guides and organizations exist today to help concerned individuals develop a sustainable lifestyle. The importance of embracing these changes has been publicized on social media, in newspapers, and through politics. Today, even museums recognize climate change as reality, and as an unfortunate truth .
Guidelines  have been appearing all over the world, and it is past time for conservators to be part of this movement. There is no logic in preserving artwork at the cost of the planet. The production of waste and the use of solvents and toxic products has to be reduced and made aware before being expended. We can start with simple initiatives such as participation in the recycling programs of companies like Terracycle® , which recycles gloves, pens, metals and all sorts of materials used and discarded in conservation and restoration. We can also transform our studios into green labs by embracing energy savings plans in our workplaces. Universities all over the world have been using the Green labs  program , and they should be models for us.
The pharmaceutical industry, among others, has been driven by legislation and evolving attitudes towards environmental issues to focus on manufacturing green solvents  for extractions, separations, formulations and reactions of industrial products where solvents are needed. CR must now participate in this movement. The selection of alternative solvents with low toxicity, minimal safety concerns and little impact on the environment does not always require the user to perform calculations. In attempt to eliminate undesirable solvents, different replacement strategies have been presented by companies and organizations. Alternatives can simply be selected from visual aids such as  the one created by the European REACH  regulation, which controls and provides safety information on ‘industry’ chemicals and chemical products. Several general-purpose solvent selection guides have also been published, aiming to reduce the use of the most hazardous solvents. Even mobile phone apps  are now available for this purpose. An excellent starting point for incorporating these practices into CR are
the guides developed for medicinal chemistry by Pfizer , GSK  and Sanofi , which aid in selecting commercially available solvents in order to make synthesis “greener”. Byrne et al.  combined and compared three prominent guides from these three companies. Their table is organized by the universally-used ‘traffic light’ color system, where green indicates the “desirable solvents”, yellow indicates “acceptable solvents” and red indicates “undesirable solvents” (available in Annexes – Table 2). This classification is based on the criteria from the chart below:
Subsequently, more selection guides  have appeared with interesting new criteria like Recycle-ability, Bio-treatment, Volatile Organic Carbon (VOC), Environmental Impact in Water, Environmental Impact in Air, Health Hazard, Exposure Potential and Safety Hazard. These new guides further develop the classification system and provide even better information. The data collated from these companies showed that the number of
truly green solvents is very limited; only alcohols, esters, and water are recognized across the board as recommended solvents (green line in Table 1). Fortunately, the undesirable – if not already banned – solvents in Table 1’s red row, are not used in art conservation. However, the second-most toxic row is comprised of the most
frequently used solvents in conservation and restoration: hydrocarbons. We cannot really classify the toxicity of the solvents by their families, as inside each family there is always one or more very “dangerous” solvent. We can, however, analyze the data provided by the different pharmaceutical companies (e.g., if it is bio-based  or
not, if it can be renewable  , and if it is a potential biomass  feedstock) and classify them as being “recommended” or “highly hazardous”.
Solvent selection guides have become a vital component of the effort to enhance the greenness of the chemical industries, but a simpler way to choose solvents in CR would be to consider their sources and incorporate or give priority to solvents of a bio-based  origin. Advantages of a bio-based solvent include reduced toxicity, biodegradability, low volatile organic compounds (VOC), worker safety, and environmental friendliness .
The problems related to surfactants are fortunately already of concern among many art conservators and researchers. Chris Stavroudis, in some of his publications, addresses the impact of surfactants on the environment and mentions the importance of using those that are less dangerous, such as Ecosurf EH-3 . Unfortunately, the use of toxic agents is still widespread, and alternatives have been difficult to integrate into CR. However, the new products that have been introduced and accepted in art conservation over the last century have exhibited two main positive characteristics: efficacy and reduction in toxicity. For example, poly-functional polymer emulsifiers such as Pemulen TR-2 and Velvesil Plus, which appeared in the art conservation world not so long ago, have the ability to act as surfactants and to change the physical characteristic of the solvent by increasing its viscosity. Unfortunately, these types of products remain the second choice for cleaning materials in CR. Solvents remain the first option, as we have more knowledge about their long-term effects and can use them more easily.
ANNEX: Tools and techniques for solvent selection
A gathering of information from solvent guides made by Byrne et all in 2016 , and its adaptation to the solvents used in conservation and restoration. All the information in this chapter comes from their research.
SOLVENTS GUIDES MADE UNTIL 2016 AND ITS CONSULTING PLACES:
1. ACS GCI solvent selection guide : http://www.acs.org/content/acs/en/greenchemistry/research-innovation/research-topics/solvents.html
2. AstraZeneca solvent selection guide (within a presentation):
3. CHEM21 solvent selection guide DOI: 10.1039/C5GC01008J
4. GSK solvent selection guide DOI: 10.1039/C0GC00918K
5. Pfizer solvent selection guide DOI: 10.1039/B711717E
6. Sanofi solvent selection guide DOI: 10.1021/op4002565
7. Survey of solvent selection guides DOI: 10.1039/C4GC01149J
The classifications in the table above were made in reference to the properties from Table 2. Table 3 shows all the properties that we need to analyze in order to identify a green product.
Byrne, Fergal P., Saimeng Jin, Giulia Paggiola, Tabitha H. M. Petchey, James H. Clark, Thomas J. Farmer, and others, ‘Tools and Techniques for Solvent Selection: Green Solvent Selection Guides’, Sustainable Chemical Processes, 4 (2016), 7 <https://doi.org/10.1186/s40508-016-0051-z>
Clean Link, ‘What Are Biobased Solvents?’, 2018 <http://www.cleanlink.com/cleanlinkminute/details/What-Are-Biobased-Solvents-26781> [accessed 21 January 2018]
Curzons, a.D. D, D.C. C Constable, V.L. L Cunningham, and a.D. D Curzons, ‘Solvent Selection Guide: A Guide to the Integration of Environmental, Health and Safety Criteria into the Selection of Solvents’, Clean Products and Processes, 1 (1999), 82–90
Ekins, Sean, Alex M. Clark, and Antony J. Williams, ‘Incorporating Green Chemistry Concepts into Mobile Chemistry Applications and Their Potential Uses’, ACS Sustainable Chemistry & Engineering, 1 (2013), 8–13 <https://doi.org/10.1021/sc3000509>
GlaxoSmithKline, GSK Solvent Selection Guide, The Royal Society of Chemistry, 2009
<http://www.rsc.org/suppdata/gc/c0/c0gc00918k/c0gc00918k.pdf> [accessed 26
Prat, Denis, Olivier Pardigon, Hans Wolfram Flemming, Sylvie Letestu, Véronique Ducandas, Pascal Isnard, and others, ‘Sanofi’s Solvent Selection Guide: A Step Toward More Sustainable Processes’, Organic Process Research and Development, 17 (2013), 1517–25 <https://doi.org/10.1021/op4002565>
Prat, Denis, Andy Wells, John Hayler, Helen Sneddon, C. Robert McElroy, Sarah Abou-Shehada, and others, ‘CHEM21 Selection Guide of Classical- and Less Classical-Solvents’, Green Chem., 18 (2016), 288–96 <https://doi.org/10.1039/C5GC01008J>
Stavroudis, Chris, ‘More from CAPS3: Surfactants, Silicone-Based Solvents and Microemulsions’, Newsletter (Western Association for Art Conservation), 34 (2012), 24–27 <http://cool.conservation-us.org/waac/wn/wn34/wn34-3/wn34-306.pdf>[accessed 6 October 2017]
1 Examples : Museum and climate change network (https://mccnetwork.org/); Sara Sutton’s book Environmental Sustainability at Historic Sites and Museums (http://sustainablemuseums.net/051810/environmentalsustainability.html); UNESCO’s Education for Sustainable Development (https://en.unesco.org/themes/education-sustainable-development)
2 E.g.: Reduce, reuse, recycle; No more plastic bags or straws; Biodegradable packages; turn off your lights; share
4 My Green Lab is building a culture of sustainability through science: https://www.mygreenlab.org/
5 E.g.: Harvard Cardiff Universities, which have been exploring the role of green chemistry in their labs : https://green.harvard.edu/programs/green-labs
6 Green solvents are environmentally friendly solvents derived from the processing of agricultural crops.
7 Sean Ekins, Alex M. Clark, and Antony J. Williams, ‘Incorporating Green Chemistry Concepts into Mobile Chemistry Applications and Their Potential Uses’, ACS Sustainable Chemistry & Engineering, 1.1 (2013), 8–13 <https://doi.org/10.1021/sc3000509>.
8 REACH means « Registration, Evaluation, Authorization and Restriction of Chemicals » more information about it in p.
9 The American Chemical Society (ACS) and the Green Chemistry Institute (GCI) created an app for iPhones called “Green Solvents”, available at -https://itunes.apple.com/us/app/green-solvents/id446670983 [consulted 21-1-2018]
10 Pfizer were the first company to publish their colour-coded, hierarchical solvent selection guide for medicinal chemists. The tool is a simple document listing solvents as “preferred”, “usable”, or “undesirable”. In Byrne et al., “Tools and Techniques for Solvent Selection: Green Solvent Selection Guides.”
11 GlaxoSmithKline (GSK) then published a simplified solvent selection guide for medicinal chemistry laboratories themselves, derived from an updated and expanded solvent assessment. The methodology is more multi-faceted that the Pfizer tool, with a detailed breakdown of scores for different EHS categories freely available as supplementary information to the main article GlaxoSmithKline, “GSK Solvent Selection Guide”; Byrne et al., “Tools and Techniques for Solvent Selection: Green Solvent Selection Guides.”
12 More recently Sanofi have also offered an equivalent solvent selection guide. The tool has evolved from an early version of the company’s internal solvent selection guide, which divided solvents into a recommended list and a substitution list. The new tool provides reference cards for each solvent that contain useful property data. The Sanofi solvent selection guide contains many more solvents than feature in the Pfizer and GSK
medicinal chemistry tools Prat et al., “Sanofi’s Solvent Selection Guide: A Step Toward More Sustainable Processes.”
13 Byrne and others.
14 Image from: Byrne and others.
15 Like the GSK and the SmithKline Beecham (a.D. D Curzons and others, ‘Solvent Selection Guide: A Guide to the Integration of Environmental, Health and Safety Criteria into the Selection of Solvents’, Clean Products and Processes, 1.2 (1999), 82–90
<https://doi.org/10.1007/s100980050014>; The CHEM 21: Denis Prat, Andy Wells, and others, ‘CHEM21 Selection Guide of Classical- and Less Classical-Solvents’, Green Chem., 18.1 (2016), 288–96 <https://doi.org/10.1039/C5GC01008J>.
16 Bio-based material refers to a product or substance originally derived from living organisms. These substances may be natural or synthesized organic compounds that exist in nature (e.g. leather, wood). In Sustainability Dictionary
17 Renewable: Any material or energy that can be replenished in full without loss or degradation in quality. In Sustainability Dictionary
18 Biomass- Organic, non-fossil material that is available on a renewable basis. Biomass includes all biological organisms, dead or alive, and their metabolic by products, that have not been transformed by geological processes into substances such as coal or petroleum. E.g. : forest, agricultural crops, and wastes. In Sustainability Dictionary
19 Byrne and others available in https://sustainablechemicalprocesses.springeropen.com/articles/10.1186/s40508-016-0051-z#Tab5.
20 Bio-based products — those that are derived from plant or animal feedstock — includes cleaners, degreasers and solvents.
21 Clean Link, ‘What Are Biobased Solvents?’, 2018 <http://www.cleanlink.com/cleanlinkminute/details/What-Are-Biobased-Solvents--26781> [accessed 21 January 2018].
22 Chris Stavroudis, ‘More from CAPS3: Surfactants, Silicone-Based Solvents and Microemulsions’, Newsletter (Western Association for Art Conservation), 34.3 (2012), 24–27 <http://cool.conservation-us.org/waac/wn/wn34/wn34-3/wn34-306.pdf> [accessed 6 October 2017].
23 Byrne and others.