Pollution characteristics of polycyclic aromatic hydrocarbons in common used mineral oils and their transformation during oil regeneration

The pollution characteristic of polycyclic aromatic hydrocarbons (PAHs) in common used mineral oils, semi-refined oils, refined oils and solid wastes produced during the used mineral oil regeneration process was analyzed. The results showed that total PAHs content in six common used mineral oils was as follows: used engine oil > used quenching oil > used casting oil > used hydraulic oil > used antirust oil > used industrial lubricating oil. Furthermore, this order was dependent on the source of PAHs and oil working temperatures. Additionally, total PAHs content in regenerated oils was as follows: semi-refined oil > refined oil > crude oil, which was related to the catalytic cracking process of crude oil and adsorption refining process of semi-refined oil. The ranking of total PAHs content in regenerated wastes varied depending on the regeneration technology used as follows: waste adsorption sand > acid sludge > waste clay > precipitation sludge > cracked residue. In all types of used mineral oils and regenerated wastes, the maximum and minimum proportions of the total PAHs content were composed of 2–3 ring-PAHs and 5–6 ring-PAHs, respectively. The majority of PAHs in the used mineral oils entered into regenerated wastes during regeneration process, while a small number remained in the regenerated oil.