Colloidal stability, pyrolysis properties and kinetics studies of calcium-containing detergents

Demetallization pretreatment is of great significance for the re-refining of used lubricating oil (ULO) by catalytic hydrogenation. Calcium-containing detergents colloidal stability, pyrolysis properties and kinetics studies have great significance for the demetallization pretreatment, re-refining, and resource utilization of ULO. The present study is focused on the pyrolysis mechanism and determining an accurate pyrolysis kinetic model for the removal of calcium from ULO using vulcanized calcium alkylphenolate (T-115B) colloidal as a model compound. Colloidal stability, pyrolysis process and thermal decomposition products have been studied by DLS, TEM, FTIR spectroscopy and XPS. The reaction energy for primary and secondary dissociation is calculated using the B3LYP-D3(BJ)/6-31g* method. The pyrolysis characteristics at different heating rates have been investigated by TG/DTA, and based on iso-conversional and master plot methods, \(E\) $E$ and kinetic equation have been determined, which revealed that the process can be divided into two distinct phases and the pyrolysis mechanism and function are necessarily described by a two-step model. The colloid was relatively stable when the temperature is lower than 395 K. When the temperature rises, compounds occur thermal decomposition, alkyl-CH₂–S bond may be the trigger bond in the initiation process, and CaCO₃ is the main degradation product. Based on iso-conversional methods (KAS and FWO) and master plot methods, values of \(E\) $E$ are determined as 96.67 and 100.78 kJ mol⁻¹, respectively. And the pyrolysis reaction in stage 1 indicated that the most probable kinetic model followed an F_n mechanism with n = 1.39, and the second stage was also controlled by an F_n mechanism, but with n = 0.86.