Products distribution and heavy metals migration during catalytic pyrolysis of refinery oily sludge

The reclamation disposal of oily sludge, which is a hazardous waste from the extraction, transportation, storage, and refining of crude oil, is a paramount challenge for environmental protection and resource recycle. Herein, a catalytic pyrolysis approach with the participation of CaO was adopted for oil resource recovery. The results show that the optimal pyrolysis temperature for recovering oil was 500 °C, in which the pyrolysis oil yield was 44.37%. CaO could act as a catalyst during the pyrolysis process, thus promoting the formation of light components in the pyrolysis oil. The light components in pyrolysis oil increased from 5.08% to 16.67% with the participation of CaO. Meanwhile, the addition of CaO immobilized As, Cr, Pb and Zn into the pyrolysis slag, thus decreasing their migration into pyrolysis oil and gas. The migration of Ni displayed a different trend, and part of Ni entered into the pyrolysis oil and gas. The BCR continuous extraction experiments display that the highly biological-activity heavy metals (i.e., F1, F2 and F3 form) was transformed to a more stable state (i.e., F4 form). These results demonstrate that the catalytic pyrolysis approach with the participation of CaO not only improve the yield and quality of pyrolysis oil, but also reduce the emission and mobility of heavy metals.