CH-06-14-4 (RP-1211) - Mechanism for Reaction between Polyolester Lubricant and Ferrous Metals, Part II: Research Phase ✓ Most Recent

This paper summarizes the results of the research performed to evaluate the reaction mechanism proposed in Part 1 of the project (Kauffman 2004) to explain the catalytic effects of ferrous metals on the thermal degradation of polyolesters. The research investigates the effects of metal oxidation state, temperature, time, contaminants (air, carboxylic acid, and water), refrigerant, additives, and ester molecular structure on the ferrous-polyolester reactions. The research indicates that the rate of the ferrous-polyolester reactions is dependent on the hydrolytic stability, not the thermal stability, of the polyolester and that the initiating step of the reactions is independent of temperature. The research indicates that soluble metal species are responsible for the catalysis of the polyolester hydrolytic reactions and that the presence of water or carboxylic acids accelerates the reaction in the presence of metal, especially iron, steel, or tin. Based on the research, a reaction mechanism is proposed to describe the multiple ferrous-polyolester reactions and to recommend practices and lubricant compositions to inhibit polyolester hydrolysis/ degradation in operating refrigeration systems.

Units: Dual