Efficient demulsification of water-in-crude oil emulsions using CTAB-modified bentonite: structure alteration, interfacial behavior, and performance evaluation

Abstract

Water-in-crude oil emulsions are a major challenge in petroleum production due to increased viscosity, pipeline corrosion, and higher processing costs. Conventional demulsifiers are often expensive or environmentally harmful, motivating the development of low-cost and recyclable alternatives. In this study, natural bentonite was modified with the cationic surfactant cetyltrimethylammonium bromide (CTAB) to produce a heterogeneous demulsifier (CTAB/Be). The material was characterized by XRD, FTIR, SEM, zeta potential, IFT, contact angle, and DLS. Demulsification performance was evaluated using bottle tests under varying dosage, temperature, settling time, and salinity, and recyclability was assessed over five cycles. Modification increased the basal spacing from 14.70 Å to 21.94 Å, changed the water contact angle from 0° to 48.3°, and reversed the zeta potential from − 4.8 mV to + 45.7 mV. CTAB/Be reduced the oil–water interfacial tension from 26.7 mN/m to 6.5 mN/m. Under selected conditions (5 g/L CTAB/Be, 60 °C, 24 h), 89.95% water separation was achieved; adding 2 wt% NaCl increased this to 99.43%, and 70 °C gave 94.71%. At the optimal dosage, more than 80% of water separation occurred within the first 20 min. After five reuse cycles, the efficiency decreased from 95.75 % to 84.63%, indicating reasonable reusability. The results demonstrate that CTAB-modified bentonite is a cost-effective and recyclable demulsifier for water-in-crude oil emulsions, with performance comparable to more complex nanomaterials. The main limitation is that the proposed interfacial mechanism remains indirect and requires further validation.