Steric hindrance effect on miscibility and properties of palm oil derived pentaerythritol ester lubricants

Abstract

The miscibility and solubility between refrigerant and lubricant is a prerequisite in any refrigeration system. Polyol is known to have good miscibility with refrigerant and can be synthesized from methyl ester of vegetable oils via transesterification reaction. Pentaerythritol (PE) ester is the best biolubricant in hydrofluorocarbons (HFCs) refrigerant system due to its high viscosity. PE ester was analyzed for its physicochemical properties and was compared with commercial refrigeration polyol ester (POE) RL 68H. The kinematic viscosity and density of PE ester were comparable with commercial POE. The pour point was obtained at −24 °C which is slightly higher than commercial POE. Nevertheless, the PE ester was not completely miscible in refrigerant, HFC R134a. The miscibility with refrigerant decreases as the number of ester functional group increases and the number of fatty acids carbon chain increases because of the neopentyl structure of esters hindered the ester functional group to interact with polar group of HFC refrigerant. An appropriate surfactant is needed to improve the miscibility and solubility of PE ester with HFC refrigerant.