Recovering hydrocarbon from oily sludge using supercritical CO2: Experiments and a new method for predicting optimal conditions

A novel methodology considering phase behavior and hydrogen bonding association between asphaltene and water was developed to predict the optimal conditions during hydrocarbon recovery from oily sludge (OS) using supercritical CO2 (SCCO2). The predicted optimal extraction temperature and pressure for Fuling OS are 23 MPa and 333.15 K, respectively. After performing systematic experimental studies, time was found to positively affect extraction efficiency, whereas temperature and pressure had negative effects beyond 25 MPa and 323.15 K (i.e., the measured optimal conditions of Fuling OS). The extraction efficiency under these conditions reached 11.02%. Compared with unprocessed OS, processed OS had a different crystalline structure, more homogeneous particle size, and lower spectral peak intensity. Additionally, sixteen-carbon chains (C16) or shorter were recovered more easily than heavier components. The distribution of carbon number in OS was unaffected by the extraction process, indicating that SCCO2 extraction did not change the hydrocarbon composition.