Hydrothermal treatment of petrochemical sludge in subcritical and supercritical water: Oil phase degradation and syngas production

Abstract

The reaction process of petrochemical sludge under hydrothermal conditions was investigated to explore the feasibility of its disposal using hydrothermal treatment. Experiments were conducted in an autoclave for 30 min at 350–450 °C. During the hydrothermal treat of petrochemical sludge, 44.98%–59.64% of the oil (organic matter) in the sludge was decomposed into aqueous and gas products. The gas yield reached 1.37 mol/kg of organic matter at reaction temperature of 450 °C. The H2 yield was 0.26 mol/kg of organic matter. The primary product was still in the aqueous phase. The TOC concentration of the aqueous product was in the range of 14,960–19,050 mg/L. The concentration of COD, total phenol, and total nitrogen of product were in the ranges of 9029–10,870, 13.83–20.10, and 497.5–599.0 mg/L, respectively. The group analysis and GC-MS analysis of the residual oil indicated that the saturated long chain hydrocarbons (C18–C21) in petrochemical sludge had decomposed to form saturated short chain hydrocarbons (C11–C17); however, the short chain saturated hydrocarbons in the sludge had decomposed thoroughly. The removal rate of asphaltenes, resins and aromatic hydrocarbons were low. Finally, a mechanism for treating petrochemical sludge under hydrothermal conditions was proposed. The study provides an experimental basis for the hydrothermal treatment of petrochemical sludge.