Feasibility of Using Ionic Liquids as Additives for HVAC Compressor Oils

Lubricants are essential for minimizing energy losses and enhancing system reliability for compressors. The adoption of next-generation refrigerants in a heating, ventilation, and air conditioning (HVAC) system introduces additional compatibility challenges to compressor lubricants for maintaining stability and performance in the new chemical environments. This study assessed the technical feasibility of applying ionic liquids (ILs) as lubricant additives for HVAC compressors. Candidate ILs showed 1–5 wt% oil solubility in compressor polyolester (POE) oils and demonstrated superior tribological performance at both room and elevated temperatures. Specifically, a 1 wt% addition of ILs to a POE base oil led to 3–30% friction reduction and 45–80% wear reduction. On the other hand, chemical instability and corrosivity were revealed when mixing IL-containing POE oils and fluorine-containing refrigerants at 175 °C, releasing corrosive refrigerant breakdown compounds. Phosphonium-based ILs caused more significant refrigerant decomposition, leading to a more severe corrosion of copper and aluminum, while ammonium-based ILs together with refrigerants resulted in stronger corrosive attacks against iron. Quantum chemical calculations were conducted to further understand the IL–refrigerant incompatibilities in correlation with the experimental observations.