Key Factors in Solvent Selection: Balancing Performance, Safety, and Sustainability
Solvents play a critical role in countless industrial processes, from coatings and adhesives to pharmaceuticals and cleaning agents. They are essential for dissolving, dispersing, or extracting substances, enabling reactions and formulations that would otherwise be impossible. However, choosing the right solvent is not just a matter of technical performance, it also impacts safety, environmental compliance, and sustainability.
The selection process has become increasingly complex in recent years. Regulatory pressures, such as restrictions on Volatile Organic Compounds (VOCs) and hazardous substances, have pushed industries to rethink traditional solvent choices. At the same time, customers and stakeholders demand reduced environmental impact solutions that minimize carbon footprint and align with circular economy principles. This means that solvent selection today requires a holistic approach, considering not only chemical properties but also life-cycle impact and regulatory status.
This article explores the essential criteria for solvent selection, balancing technical properties with ecological and regulatory considerations.
Environmental and Safety Considerations
When selecting a solvent, environmental and safety factors are often the first priority. Volatile Organic Compounds (VOCs) are a major concern because they contribute to air pollution and smog formation. Regulations worldwide increasingly limit VOC emissions, which makes low-VOC or VOC-free solvents the preferred choice for many industries.
Hazardous classification is another critical aspect. Solvents can be flammable, toxic, or even carcinogenic, so it is essential to review their classification under systems such as the Globally Harmonized System (GHS). Whenever possible, safer substitutes should be considered to reduce risks for workers and the environment.
Finally, the carbon footprint of a solvent should not be overlooked. Beyond immediate hazards, the environmental impact of a solvent’s entire life cycle—from production to disposal—matters. Choosing bio-based or circular solvents can significantly reduce greenhouse gas emissions and align with sustainability goals.
Physical and Chemical Properties
The physical and chemical characteristics of a solvent determine its performance in specific applications. Molecular weight, for example, influences volatility and solubility. Lower molecular weight solvents tend to evaporate faster, which can be advantageous for quick-drying processes but problematic for controlled applications.
Vapour pressure is closely related to evaporation. A solvent with high vapour pressure will evaporate rapidly, which may increase inhalation risks. Additionally, for processes requiring precise drying times, vapour pressure must be carefully considered.
Viscosity affects how the solvent flows and spreads. Low-viscosity solvents are ideal for applications requiring easy spreading and penetration, whilst a higher viscosity can improve hold up and sag resistance in coatings, for example. Density also plays a role, particularly in mixing and phase separation, as differences in density can influence compatibility in multi-component systems.
Evaporation rate is another key factor, especially in coatings and printing inks. A balanced evaporation rate prevents defects, such as blushing or poor adhesion. Surface tension determines how well the solvent wets and spreads on a substrate; lower surface tension generally improves penetration and coverage.
Safety-related properties such as flash point and boiling point are equally important. A low flash point indicates a higher flammability risk, requiring strict handling and storage precautions. Boiling point influences distillation and recovery processes—high boiling points reduce evaporation losses but may complicate recycling.Beyond basic physical properties, performance parameters help predict how a solvent will behave in a formulation. Hansen Solubility Parameters are widely used to estimate compatibility between solvents and solutes or polymers. Matching these parameters ensures optimal dissolution and performance.
Refractive index is another useful indicator, particularly for applications requiring optical clarity, such as coatings, adhesives, and films. It can also serve as a measure of purity and concentration in certain processes.
Sustainability and Circular Economy
Whilst it is recognized that performance characteristics are key, modern solvent selection is becoming increasingly influenced by the need to make the correct sustainable choice. There are now many reduced environmental impact options that both have the correct performance characteristics and help achieve sustainability goals. Many companies now use scoring systems that weigh technical performance against environmental impact, ensuring that solvents are selected using both technical and sustainable factors. In doing so consideration can be given to, for example, product carbon footprint, how biodegradable the solvent is, health and safety classification and the formation of low level ozone.
There are an increasing number of circular solvents. Historically these may have been considered to be poor technical choices, however production technologies have improved, and it is now possible to achieve highly pure grades that offer both a strong technical performance AND, given these solvents are a byproduct or recovered from waste streams, a significantly lower product carbon footprint,
>> Discover SEQENS sustainable solvents portfolio
Summary
Selecting the correct solvent requires balancing multiple factors: safety, environmental responsibility, and technical performance. In practice, adopting a structured approach—such as using a decision matrix—can simplify complex evaluations and provide transparency in solvent selection. It enables teams to balance performance with environmental and safety considerations, ensuring that every choice supports both technical goals, operational goals and long-term sustainability.
As industries move toward lower environmental impact practices, solvent choice will continue to evolve, favoring solutions that combine technical excellence with ecological responsibility. The future of solvent selection lies in innovation, collaboration, and a commitment to reducing environmental impact without compromising performance.
