Oil recovery and characterization of storage tank bottom oily sludge via solvent extraction

Oily sludge is one of the most hazardous wastes generated by the petroleum industry due to its high hydrocarbon content and associated environmental risks. In this study, solvent extraction was employed to recover hydrocarbon oil from sludge collected at the base of a crude oil tank in an Algerian refinery. Cyclohexane and xylene were selected as solvents due to their efficiency in extracting oil from aliphatic, cyclic, and aromatic fractions. Residual solids were collected to assess the environmental impact. To optimize oil recovery from the sludge, the effects of physicochemical parameters, including stirring time, solvent volume, and temperature, were studied. The extracted oil was characterized using gas chromatography-mass spectrometry (GC-MS) and Fourier-transform infrared (FTIR) spectroscopy, while the residual solids were analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and FTIR spectroscopy. Xylene demonstrated superior extraction performance, achieving an oil recovery rate of 96.11% from crude oil sludge. Elemental analysis of the residues revealed the presence of iron, sulfur, aluminum, silicon, and calcium, with calcium being the predominant element. XRD analysis identified calcium carbonate and silicon dioxide as the main mineral phases in the solid residues.