Investigation on the Composition and Extraction Mechanism of the Soluble Species from Oily Sludge by Solvent Extraction.

Oily sludge (OS) was extracted with petroleum ether (PE), methanol, carbon disulfide (CDS), acetone, and isometric CDS/acetone mixture (IMCDSAM), respectively, to obtain soluble species (E1-E5) and extraction residues (R1-R5). The soluble species were analyzed by gas chromatography/mass spectrometry (GC/MS), and the extraction residues were characterized by Fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA). Results showed that the extract yield of the soluble species from OS using CDS and IMCDSAM as the solvent was 61.0 and 67.3%, respectively. GC/MS results exhibited that the compounds detected in E1-E5 are mainly hydrocarbons and oxygen-containing compounds. E1-E5 are rich in alkanes, alkenes, ketones, alcohols, and other oxygen-containing compounds. Double-bond equivalence (DBE) and carbon numbers (CNs) of the compounds detected in E1, E2, and E4 are distributed in 0-4 (DBE) and 10-20 (CNs), respectively, while the DBE and CNs of the detected compounds in E3 and E5 are concentrated in 0-6 and 15-35, respectively. Thermogravimetry-differential thermogravimetry (TG-DTG) profiles presented that pyrolysis of OS occurred mainly in the temperature range of 150-750 °C, while pyrolysis of R1-R5 took place in the range of 350-750 °C. In the temperature range of 150-550 °C, the weight losses of OS and each extraction residue differ significantly, with OS having a much higher weight loss than the extraction residues. Meanwhile, the possible mechanism of oily sludge extraction was considered. Results revealed that selecting a low-polar or nonpolar solvent capable of selectively destroying hydrogen bonds and/or aromatic interactions is critical for improving the extract yield of OS.