Experimental investigation of salt removal from medium-grade Zubir Mushref crude oil using ultrasonic and chemical methods: process optimisation and performance assessment

Crude-oil desalting limits the movement of inorganic salts into refinery equipment and therefore supports corrosion control and reliable operation. In this laboratory study, crude-oil demulsification was examined using RP6000, ultrasonic treatment, and a combined ultrasonic–chemical process. The material was medium-grade Zubair–Mishrif crude oil obtained through the South Refinery Company, Iraq. Its initial salt content was 98 ppm as NaCl equivalent, based on IP-77. Residual salt was measured by Mohr titration. For each treatment route, a three-factor Box–Behnken design was used to examine the effects of water-to-oil percentage and treatment-specific operating variables. Across the specified design ranges, the minimum measured residual salt contents were 4.7 ppm after chemical treatment, 3.6 ppm after ultrasonic treatment, and 2.4 ppm after the combined treatment. Relative to the confirmed 98 ppm starting value, these results correspond to apparent reductions of 95.20%, 96.33%, and 97.55%, respectively. The response-surface models predicted 4.453 ppm for the chemical process and 2.27 ppm for the combined process; the corresponding laboratory confirmation values were 4.90 and 3.13 ppm. The earlier ultrasonic prediction of 1.689 ppm was not used for optimization because its required treatment time was 399.2 min, outside the 25–55 min experimental interval.