Decontamination of petroleum-contaminated soil via pyrolysis under carbon dioxide atmosphere

Accidental leakage and/or spillage of crude oil contaminates soil occurring during petroleum extraction, which can have harmful effects both on the environment and human beings. Therefore, petroleum-contaminated soil needs to be effectively decontaminated. As a study of thermal remediation of petroleum-contaminated soil, a real soil sample contaminated with petroleum was pyrolyzed at different pyrolysis conditions. In particular, carbon dioxide (CO₂) was used as the pyrolysis medium for effective thermal remediation of the petroleum-contaminated soil. At temperatures above 620 °C, pyrolytic gas evolution patterns obtained in CO₂ condition were distinguishable from those obtained in N₂ condition; the generation of carbon monoxide (CO) was observed. The formation of CO at temperatures higher than 620 °C might be a clue about the role of CO₂ in pyrolysis of the petroleum-contaminated soil in that CO₂ helps form CO via reactions between CO₂ and volatile species evolved from the petroleum hydrocarbons deposited on the soil during the pyrolysis. For further investigating the effect of CO₂ on the pyrolysis, two-stage pyrolysis of the petroleum-contaminated soil was conducted. The CO evolution also occurred in the CO₂ condition during the two-stage pyrolysis at >210 °C. The different compositions of pyrolytic oil obtained from the pyrolysis in N₂ and CO₂ were identified in that the formation of polycyclic aromatic hydrocarbons was restricted by the consuming the source of carbon. The pyrolysis operated under CO₂ atmosphere would be an effective decontamination method to treat petroleum-contaminated soil.