Pyrolysis characteristics of oil in oily sludge from experiments and simulation by model compounds

Pyrolysis of oily sludge (OS) possesses dual advantages of oil recovery and harmless treatment. Exploring the reaction pathway for petroleum hydrocarbons during pyrolysis in the presence of minerals is critical for optimizing pyrolysis parameters. This study selected six pure soil minerals and five typical oil compounds as representative to simulate OS samples. Model compounds are more helpful deriving and clarifying the internal mechanism. The mixed oil compounds were continuously loading fed into reactor loaded with varied minerals, which was facilitated the detection of pyrolytic products. Meanwhile, the pyrolysis reaction pathways of oil compounds at different temperature and pressure were simulated by ReaxFF MD. According to the experimental results, high temperature increased the content of light hydrocarbons and gas products (i.e., C3H4, C4H8, CH4, and H-2). Montmorillonite (MT) and illite (IT) exhibited catalytic ring-opening and cracking effects as alkaline minerals, while the kaolin (KL) presented catalytic aromatization effects. The catalytic ring-opening effect of calcite (CA) and hematite (MA) was equally evident, but quartz (QA) possessed a weak catalytic effect and even promoted condensation. n-Dodecane (ND) and 1-dodecene (1-DE) had more complicated pathways compared to other com-pounds with stable rings. The main cracking reaction pathway of ND was the breakage of beta-C-C bond, and the C-C bond at both ends was easier to break than the one in the middle. The pyrolysis reaction pathway of 1-DE not only included the breakage of beta-C-C bond, and the generation of ethyl radicals. The methyl groups in methylcyclohexane (MC), methylbenzene (MB), and 1-methylnaphthalene (1-ME) could be detached, while ring-opening reactions generated free radicals. This work provides detailed explanation of pyrolysis reaction pathway of oil compounds and the catalytic mechanism of soil minerals, which helps us understand OS pyrolysis process.