Crude Oil Recovery from Oily Sludge Using Liquefied Dimethyl Ether Extraction: A Comparison with Conventional Extraction Methods

Oily sludge is an inevitable byproduct of the crude oil industry. The efficient recovery of oil contributes to economic improvement and pollution reduction. In this study, we investigated the recovery of oil from oily sludge using liquefied dimethyl ether (DME) extraction and explored the effects of the operational parameters on the oil recovery ratio. The results demonstrated that the DME/sludge ratio, extraction time, and stirring speed positively affected the oil recovery. In addition, the highest oil recovery ratio of 96.3 wt % was obtained under the optimal conditions of DME/sludge ratio 40 mL/g, extraction time 45 min, and stirring speed 40 rpm. The extraction pressure ranged between 0.5 to 0.9 MPa did not significantly affect the recovery ratio. Subsequently, the oil recovery ratio and the properties of the recovered oil and solid residue obtained by DME extraction were compared with those obtained by three traditional methods: mechanical shaking extraction, ultrasonic extraction, and Soxhlet extraction. The oil recovery ratio obtained by DME extraction (96.3 wt %) was higher than that obtained by mechanical shaking extraction (71.8 wt %) and ultrasonic extraction (90.5 wt %). The oil recovered by DME had a relatively higher H/C ratio and contained more saturated hydrocarbons and light compounds compared with the other three n-hexane extraction methods. Considering that heavy metals cannot be removed using DME extraction, solid residues rich in heavy metals necessitate appropriate disposal. In particular, DME extraction is a promising technology for effectively recovering crude oil from oily sludge and oil sands.