Synthetic base oils are classified under API Group V and include synthetic esters and polyalkylene glycols. Synthetic esters are made by reacting carboxylic acids with alcohols to form molecules that offer thermal resistance oxidation stability, low volatility and biodegradability. These fluids are used in hydraulic systems aviation greases compression systems and environmentally acceptable lubricants where residue control fire resistance or biodegradability are required.
Polyalkylene glycols (PAGs) are another major Group V category. PAGs are produced by polymerizing ethylene oxide or propylene oxide with alcohols or water to form glycol chains. They provide high viscosity index excellent lubricity polarity and temperature stability. These properties make them suitable for food‑grade lubricants quenching fluids compressor oils gear and chain lubricants and HFC hydraulic fluids.
The synthetic base oil market is niche. Demand for ester base stocks is growing in sectors where biodegradability or nonflammable characteristics are prioritized. In 2019 esters accounted for more than two‑thirds of base stocks used for biobased lubricants. Volume remains small but grows mostly in environmentally regulated sectors. Ester technology is evolving to address previous limitations such as hydrolytic instability through molecular design that enhances stability and performance.
Emerging ester chemistries offer new functional benefits. VBASE Oil Company has developed secondary polyol ester base oils that retain biodegradability while improving deposit control friction reduction and thermal stability. These products span ISO viscosity grades 32 to 460 and provide hydrolytic resistance superior to traditional esters due to their ester and ether bond architecture and branched backbone. Other fluid innovations include estolides produced by Biosynthetic Technologies derived from castor and soy that deliver oxidative and wear performance comparable to petroleum base oils.
PAGs continue to be used mainly in industrial applications where their polarity and lubricity excel in extreme environments. Dow Chemical’s Ucon fluids are widely used in compressors and refrigeration systems. Dow operates multiple PAG plants including Tarragona Spain Freeport Texas South Charleston West Virginia and a joint venture in Malaysia. Combined output reaches nearly 246,000 tons annually. PAG demand persists in industrial markets especially in India China Europe and North America where compressor warranties or low temperature operations drive performance requirements.
Cost and compatibility remain challenges for non‑PAO synthetics. Esters typically cost more than Group III or PAO base oils. PAGs are incompatible with many seal materials and cannot be blended easily with mineral or other synthetic oils which limits application flexibility. Ester hydrolysis may cause acid formation seal corrosion sludge or varnish if not formulated correctly.
Applications where non‑PAO synthetic base stocks dominate include aerospace gear oils metalworking fluids environmentally acceptable lubricants and electric vehicle coolant fluids. Ester technology supports lubricant formulation in sectors pursuing thermal and environmental performance. PAGs offer performance in conditions unsuitable for mineral oils such as low temperature compressors and food machinery scenarios. Together these fluids support equipment reliability regulatory compliance and reduced environmental impact while filling gaps that mineral and PAO fluids cannot address.
Growth for non‑PAO synthetic base stocks is expected to continue where performance requirements intersect with regulatory or sustainability mandates. Capacity expansion by specialist ester producers and continued PAG investment by major industrial suppliers will shape the future of these products. Despite limited volume compared with other base stocks non‑PAO synthetics provide essential functional value in niche but expanding markets.
Producers
Savita Oil Technologies Ltd (synthetic esters)
VBASE Oil Company (secondary polyol ester base oils)
Biosynthetic Technologies (estolide and ester base oils)
Perstorp (saturated synthetic polyol esters)