Development of Polyol Ester Refrigeration Oils for HFO Refrigerants

Recently, R32 refrigerant, which has low global warming potential (GWP), attracts much attention as an alternative one instead of R410A and has started to be used in practical systems of room air conditioners (RAC), but compared with natural refrigerants, its GWP of 675 is still high and it is required to use refrigerants with much lower GWP. In addition, although R134a (GWP=1300) is widely used for mobile air conditioner systems (MAC), it has been decided by MAC directive in Europe that refrigerants whose GWP is over 150 can no longer be available in future. In such a situation, HFO refrigerants like R1234yf, R1234ze (E) and an HFO-1123+R32 mixture are considered as the candidates for next-generation refrigerants because of their much lower GWP. Therefore, at the same time, it is required to develop refrigeration oils which have good compatibility with HFO refrigerants for RAC. One of the characteristics of HFO refrigerants is that their miscibility with refrigeration oils is equal to or greater than that of HFCs. However, a problem is that HFOs have a double bond in their molecular structure, resulting in their lower chemical stability than that of HFCs. We developed polyol ester (POE) refrigeration oils with high chemical stability under HFO atmospheres by improving the formulation of additives. In this study, we will report the method and the characteristics of lubricity under HFOs.