Pyrolysis and combustion kinetics and emissions of waste lube oils

Abstract

The present work studies first the kinetics of the global primary thermal decomposition of raw waste lubricant oils in helium atmosphere conditions and with different proportions of helium:oxygen by TGA. In addition, pyrolysis and partial oxidation runs were carried out in a tubular reactor at 723 and 1123 K, where the volatiles and semivolatiles evolved were quantified by gas chromatography. TGA analysis shows nearly no difference between helium and helium/oxygen atmosphere, yielding no appreciable residue. Primary decomposition, which takes place between 450 and 700 K, can be modeled with two different processes: the main one (92.6% of the initial material) is an evaporation of the motor oil (with apparent zero order and a kinetic constant dependent on the mass and heating rate) and a small contribution of a typical solid carbonoceous pyrolysis. In the tubular reactor, gases evolved in pyrolysis at 773 K corroborate TG findings that the process is mainly an evaporation, with little changes with respect to the original chemical structure of the oil. Nevertheless, the gas composition changes completely in the presence of air, where the partial oxidation in the gas phase after evaporation yields lower chain paraffins and olefines. Gas evolution at 1123 K is completely different, yielding showing typical cracked flue gas composition: light gases with abundant olefins and poly-condensed aromatics.