EXPERIMENTAL AND MODELING STUDY OF KINETICS AND SELECTIVITY IN THE OXIDATION OF A POLY(ALPHA-OLEFIN) LUBRICANT

A major means of lubricant oil degradation is by oxidation in the presence of metal surfaces that can have catalytic activity. In this work an experimental and modeling study has been carried out on the oxidation kinetics and selectivity of a typical poly(alpha-olefin) (PAO) lubricant in the presence of both inert (glass) and active (brass, steel) surfaces in the temperature range 170-240 degrees C. Inhibition of the reaction by zinc dialkyl dithiophosphate (ZDP) has been investigated. A batch recycling trickle-bed reactor system has been developed which provides reliable data on intrinsic chemical kinetics. Reaction rates are a strong function of temperature, with products appearing in the order of water, carbon dioxide, aldehydes, ketones, acids, and alcohols in both gas and liquid phases. Significant changes in viscosity and molecular weight were observed for T > 200 degrees C. A four-lump (PAO, carbonyl-containing compounds in the liquid phase, gaseous products, and deposits) kinetic model has been developed that gives good agreement with experimental results, including oxidation rate promotion by metals and inhibition by ZDP.