Unraveling the catalytic pyrolysis of oil-based drill cuttings with diatomaceous earth: macroscopic kinetics, directed heteroatom migration, and DFT mechanisms.

This research looked into the catalytic impact of diatomite (DE) on the pyrolysis of oil-based drilling cuttings (OBDC) to achieve the high-value use and safe handling of OBDC. Thermogravimetric kinetic analysis revealed that the 20 wt% DE addition reduced the apparent energy of activation (Ea) of OBDC pyrolysis from 172.06 kJ/mol to 119.63 kJ/mol and transformed the reaction mechanism model from a 4th-order reaction model (F4) to a 2.5th-order reaction model (F2.5). Combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), gas chromatography-mass spectrometry (GC-MS), and density functional theory (DFT) analyses verified that DE narrowed the frontier orbital energy gap. The surface active sites of DE facilitated decarboxylation and olefin hydrogenation reactions, raising the alkane content by 28.81%. Furthermore, DE promoted the conversion of sulfur into gaseous H2S and solid sulfates/sulfones, while nitrogen-rich heterocycles were stably retained in solid coke. Environmental and ecological risk assessment demonstrates that DE exerted a prominent microscopic passivation effect on heavy metals. The proportions of acid-soluble fraction (F1) of Mn and Zn decreased from 68% and 30% to 1% and 14%, respectively. The final potential ecological risk index (RI) of pyrolytic solid residue was only 12.07, far below the threshold for slight ecological risk. This work provided detailed multi-scale theoretical guidance for the green thermal conversion of OBDC, directional upgrading of target products, and safe industrial disposal of residues.