Propylene carbonate: properties, production and applications / Articles

Propylene carbonate (PC, 4-methyl-1,3-dioxolan-2-one, 1,2-propylene glycol carbonate) is a cyclic ester of carbonic acid and propylene glycol, one of the most important representatives of the organic carbonate class. Under normal conditions, it is a clear, colourless, slightly viscous liquid with a mild ethereal odour. Its molecular formula is C₄H₆O₃, with a molecular mass of 102.09 g/mol. The unique combination of a high dielectric constant, a wide liquid range, low toxicity and the ability to dissolve a wide range of polar and non-polar compounds makes propylene carbonate an indispensable component in the production of modern electrochemical power sources, a high-performance solvent in organic synthesis, an absorbent for gas treatment and a sought-after ingredient in the cosmetics industry.

Chemical Nature and Physicochemical Properties

Propylene carbonate is a five-membered heterocycle containing a carbonate group. The presence of polar C=O and C–O bonds, as well as a methyl radical, determines the high polarity of the molecule (dipole moment about 4.9 D) and its aprotic nature. Unlike water and alcohols, propylene carbonate contains no mobile hydrogen atoms and is incapable of acting as a proton donor, which prevents undesirable side reactions in electrochemical and cosmetic systems.

The key physical characteristics of propylene carbonate determine its industrial value:

Melting point: about minus 49 °C. The wide liquid range (from minus 49 to plus 241 °C) allows the product to be used in extreme climatic conditions.
Boiling point: 240–242 °C at atmospheric pressure. The high boiling point ensures low volatility and fire safety compared to traditional solvents.
Density: 1.20–1.21 g/cm³ at 20 °C.
Dielectric constant: 64.4–69 at 23–25 °C — an exceptionally high value for organic solvents, ensuring efficient dissociation of lithium salts and other electrolytes.
Viscosity: 1.67 cSt at 23 °C (or 2.53 cP at 25 °C).
Flash point: about 132 °C (in a closed cup). Propylene carbonate is classified as a combustible liquid, but its high flash point makes it significantly safer than many other organic solvents.
Solubility: miscible with water, alcohols, acetone, chloroform and most organic solvents; insoluble in aliphatic hydrocarbons.

Classification and Grades

Depending on the application and depth of purification, propylene carbonate is supplied in several grades that differ in requirements for impurity, moisture and acidity content:

Industrial grade: purity 99.0–99.5%, water content up to 1000 ppm. Used for gas treatment, as a plasticiser, in foundry production and as a general-purpose solvent.
High purity (HP, chemical grade): purity not less than 99.5–99.7%, water content typically not more than 1000 ppm. Used in organic synthesis, polymer and paint production.
Battery grade: purity not less than 99.9%, water content less than 10–50 ppm, acidity less than 10 ppm, metal content specified at ppb levels. Intended for electrolytes of lithium-ion and sodium batteries. This grade is the most in-demand in the modern market.
Electronic grade (4N): purity 99.99%, ultra-low impurity content. Used in microelectronics and special electrochemical applications.
Cosmetic grade: meets safety requirements for use in personal care products, supported by the Cosmetic Ingredient Review (CIR) conclusion that it is safe in present practices of use.

Production Technology

The main industrial method for producing propylene carbonate is the cycloaddition reaction of carbon dioxide (CO₂) with propylene oxide. This process is known as carboxylation and is one of the most promising ways of chemical CO₂ fixation. The reaction proceeds in the presence of catalysts, which may include phthalocyanine complexes of aluminium, zinc, cobalt, as well as heterogeneous catalysts on inert supports. The process is carried out at elevated temperature (150–200 °C) and pressure (40 atm and above), which allows high selectivity and conversion to be achieved.

Modern research is aimed at developing more environmentally friendly and cost-effective catalytic systems, including metal- and halogen-free catalysts based on natural amino acids, which allow the reaction to be carried out under milder conditions. From an economic and environmental point of view, an important advantage of this method is the use of CO₂ as a feedstock, which aligns with sustainable development goals and reducing the carbon footprint.

Applications

Electrolytes for electrochemical power sources. This is the largest and most dynamically growing consumption area for high-purity propylene carbonate. PC is used as a high-polarity aprotic co-solvent in lithium-ion battery electrolytes. Its high dielectric constant promotes the dissociation of lithium salts (LiPF₆, LiBF₄), and its wide temperature range ensures battery operability at low temperatures. The low moisture and metal content of the battery grade is critically important for forming a stable solid electrolyte interphase (SEI) and preventing battery degradation.

Feedstock for organic synthesis. Propylene carbonate serves as a key intermediate for the production of dimethyl carbonate (DMC), an environmentally friendly solvent and electrolyte component. The transesterification of PC with methanol allows DMC to be produced with high selectivity. In addition, PC is used in the synthesis of polycarbonates (via diphenyl carbonate), polyols, plasticisers and pharmaceutical substances.

Solvent for polymers and in the paint and coatings industry. Propylene carbonate effectively dissolves a wide range of polymers, including polyacrylonitrile, polyvinyl chloride (PVC), cellulose nitrate and acetate, polyethylene terephthalate and polyester resins. This makes it in demand in the production of paints and coatings, adhesives, sealants and composite materials. As a high-polarity aprotic solvent with low volatility, PC is an attractive alternative to traditional VOCs (volatile organic compounds) and helps comply with environmental regulations.

Gas treatment and absorption. Propylene carbonate has a high selectivity for the absorption of carbon dioxide (CO₂) and hydrogen sulphide (H₂S). It is used in the treatment of natural gas, synthesis gas and refinery gases to remove acid components. Thanks to its low volatility and thermal stability, PC enables economical cyclic absorption and regeneration processes.

Applications in cosmetics and personal care. Propylene carbonate finds wide application in modern cosmetic formulations due to its ability to act as a polar solvent and co-solvent. In cosmetic products, it performs several key functions:

Polar solvent and co-solvent: PC helps dissolve or suspend other ingredients without altering their chemical properties. It is particularly effective for incorporating polar active substances into formulations.
Clay activator and thickener: Propylene carbonate is used as a polar additive to activate the thickening properties of montmorillonite, bentonite and hectorite clays. This enables the creation of stable gels widely used as bases for antiperspirants, deodorants and other cosmetic products.
Viscosity control: The inclusion of PC in a formulation helps regulate product viscosity, improving spreadability and distribution on skin and hair.
Penetration enhancement: Due to its chemical structure, PC readily penetrates the skin, which can help increase the efficacy of active ingredients by enhancing their absorption.

According to CosIng and CIR reports, propylene carbonate is registered as a cosmetic ingredient (INCI: Propylene Carbonate) with solvent and viscosity-controlling functions. It is most commonly found in the following product categories:

Decorative cosmetics: lipstick, eye shadow, mascara, foundations.
Skincare products: creams, lotions, gels, serums.
Skin cleansing products: facial washes and cleansers.
Sunscreens: mineral sunscreens with titanium dioxide (TiO₂) and zinc oxide (ZnO).
Hair care products: conditioners and masks.

Typical concentrations of propylene carbonate in cosmetic products range from 0.1% to 5%, although in some products (such as decorative cosmetics or clay-based gels) it may be used at concentrations up to 10–20%.

Cosmetic Safety. The safety of propylene carbonate as a cosmetic ingredient is confirmed by the authoritative Cosmetic Ingredient Review (CIR) Expert Panel. According to the CIR conclusion, propylene carbonate is safe for use in cosmetics in the present practices and concentrations when formulated to be non-irritating. The substance does not significantly penetrate the epidermis, systemic absorption through the skin is minimal, and the risk of contact dermatitis is assessed as low. It is also considered safe during pregnancy and lactation at usual cosmetic concentrations.

Other applications. Propylene carbonate is used as a component of moulding sands in foundry production, as a coolant in laser technology and electronics, as a solvent in the textile industry for dyeing and finishing, and as an extractant for aromatic hydrocarbons.

Safety and Storage

Propylene carbonate belongs to moderately hazardous substances (hazard class 3 according to GOST 12.1.007). It has an irritating effect on the skin and mucous membranes, and vapours can irritate the respiratory tract. When working with the product, personal protective equipment is recommended: rubber gloves, safety goggles, protective clothing, and a respirator when handling large volumes.

Propylene carbonate is combustible (flash point 132–135 °C), so fire safety measures must be observed. The substance is hygroscopic, so it should be stored in tightly closed containers in a cool, dry, well-ventilated area protected from direct sunlight and heat sources. The optimal storage temperature is below plus 30 °C. Contact with moist air and water must be prevented, which is especially critical for the battery grade.

Market and Trends

The global propylene carbonate market demonstrates steady growth, which is largely driven by the development of lithium-ion battery production for electric vehicles and energy storage systems, as well as the expanding use in the cosmetics and pharmaceutical industries. According to industry estimates, the compound annual growth rate (CAGR) of the market in the coming years will be in the range of 5–11% depending on the segment.

Key market trends include:

Growing demand for battery grade: the battery-grade propylene carbonate segment is growing at an outstripping pace, driven by tightening requirements for electrolyte purity.
Growing popularity in cosmetics: there is a steady trend toward using PC as a safe and effective co-solvent in premium cosmetic formulas, especially in mineral sunscreens and decorative cosmetics.
Localisation of production: there is a trend towards building new propylene carbonate production capacities in regions with developing battery industries, especially in the Asia-Pacific region.
Development of green technologies: there is growing interest in producing propylene carbonate using captured CO₂, which helps reduce the carbon footprint of products.
Expansion of applications in specialty areas: propylene carbonate is increasingly used as a replacement for more toxic solvents in the paint, electronics and pharmaceutical industries.

Conclusion

High-purity propylene carbonate is a multifunctional product combining the properties of a high-performance solvent, reagent, absorbent and cosmetic ingredient. Its unique physicochemical characteristics — high dielectric constant, wide temperature range and low toxicity — make it an indispensable component in the production of lithium-ion batteries, polymers, pharmaceuticals and cosmetics.