What are Green Solvents?
Over the past few decades, Analytical chemistry has struggled to align the latest advancements with the sustainable goals of the world. And why not? Since the constantly changing climatic conditions as a repercussion of the industrial revolution no longer remain a topic of debate, taking serious initiatives in this regard has become imperative. No wonder the concept of “Green chemistry has taken all over, aiming to outpace the existing harmful chemical usages in numerous industries.
One of the crucial assets of green chemistry is Green Solvents, which are set to extend their penetration in numerous applications such as paint & coatings, industrial & domestic cleaning, printing inks, cosmetics, pharmaceutical, agriculture, adhesive sealant, and textile, among others. Keeping the green protocol as the priority, numerous attempts, in the form of extensive research, have already been made to come up with environmentally friendly substances, cites Markntel Advisors in its recent report named, Global Green Solvent Market.
As a result, supercritical fluids, ionic liquids, and deep eutectic solvents have been investigated for numerous applications as green solvents. Since awareness regarding their applications in various fields is in its infancy, a lot more focused investigation is still required.
Reasons Why Green Solvents Are Crucial to Industries
- Regulatory Compliance with Rising Environmental Concern: As regulations related to the environment continue to heap on, industries are being compelled to turn to sustainable practices and watch out for their carbon emissions. Thankfully, maximizing green solvent usage can significantly assist companies in keeping up with compliance requirements while avoiding potential fines, penalties, and reputational damage.
- Financial Constraints: Green solvents are often more efficient, requiring lower quantities for the same process, and their reuse or recycling potential reduces the need for frequent purchasing. Although the initial adoption of such solvents may require some investment, they can lead to cost savings in the long run. Besides, companies embracing sustainability practices may easily extend their consumer base by gaining attention from environmentally conscious consumers and investors.
- Health and Safety Concerns: Conventional Solvents are usually flammable, volatile, and toxic, resulting in potential exposure risks and adverse health effects for workers who handle them. Green solvents, on the other hand, are meant to ensure a safer working environment with their non-toxic and low-volatile nature.
- Sustainability and Resource Efficiency: With the use of green solvents, the dependency on fossil fuels can be brought down to a bare minimum as they are derived from renewable resources. Also, it can be recycled or reused, leading to minimum waste generation and efficient utilization of resources in industrial processes.
Supercritical CO2 and Its Properties as A Solvent
In recent years, the efficacy of supercritical fluids, especially CO2, in replacing the existing chemical-based solvents has been doing the rounds on the internet. Digging deeper, let us shift our focus to supercritical CO2 and explore how it may revolutionize solvent usage.
CO2, employed as a solvent, can be obtained as a by-product from various industrial operations like fermentation, cement production, and fertilizer manufacturing. After purification, compression, and cooling to a liquid state at 20 bar and -20°C, it can be stored or transported in insulated containers for reuse in numerous liquid and supercritical CO2 processes. The properties of CO2 are well-documented and can be harnessed for various scientific and industrial purposes.
For instance, slight adjustments in pressure or temperature around the critical point can significantly alter the density of supercritical CO2. Its viscosity is extremely low, and it exhibits no surface tension in its supercritical state. Moreover, high diffusivity, combined with low viscosity, induces significant changes in condensed phases.
Supercritical CO2 also influences the properties of substances it is mixed with. It has the ability to dissolve non-polar compounds to a far greater extent than its vapor pressure would suggest. Furthermore, it can dissolve substantially into condensed phases, thereby reducing surface tension and viscosity, simplifying the processing of viscous materials.
With its unique characteristics of variable density, low viscosity, and high diffusivity, supercritical CO2 serves as an exceptional solvent. The manipulation of these properties has led to a wide range of applications for this green solvent in various fields, including extractions, impregnations, particle formation, and cleaning.
What The Studies Have to Say About Supercritical CO2 (ScCO2)
Supercritical CO2 (ScCO2) serves as a cost-effective, non-toxic, and non-flammable solvent in material synthesis and processing. It has gained significant attention as the most extensively studied environmentally friendly medium for organic transformations and polymerization reactions.
Studies have demonstrated that sugar acetates exhibit high solubility in CO2 and have been suggested as renewable “CO2-philic” building blocks. Theoretically, these materials could serve as inexpensive ligands and surfactants, but their full potential remains untapped, primarily due to practical hurdles that need to be overcome.
Similarly, affordable poly (ether carbonate) (PEC) copolymers can dissolve in CO2 under moderate conditions, offering potential as economic surfactant building blocks. However, several practical challenges need to be addressed. Likewise, Poly (vinyl acetate) (PVAc) has also shown remarkable solubility in CO2 compared to other vinyl hydrocarbon polymers. However, this polymer’s solubility is limited to relatively low molecular weights under conditions that are practically applicable.
A Quick Recap
Minimizing reagents and excipients, in general, is of utmost importance, focusing on eliminating hazardous solvents or substituting them with safer alternatives. However, simultaneously, the development of analytical procedures places significant emphasis on key validation parameters, including sensitivity, selectivity, accuracy, precision, and robustness. As a result, analytical chemists worldwide strive to balance these conflicting demands in the current era.
To achieve this balance, the advancement of green analytical procedures has been propelled by automation, acceleration, miniaturization, simplification, and the utilization of environmentally friendly chemicals and innovative materials. Many of these procedures have achieved notable levels of “greenness.”
The use of organic solvents in chemical processes carries substantial environmental and economic burdens, contributing to health issues, environmental degradation, flammability risks, smog formation, and Eco toxicity. Consequently, the pursuit of green chemistry aims to eliminate hazardous organic solvents and explore safer alternatives. Among these alternatives, CO2, when in a liquid or supercritical state, possesses many qualities of an ideal green solvent.
