During the extraction of fossil fuels, a complex waste stream is produced simultaneously, also known as produced water (PW). Membrane filtration is a promising technology that can successfully enable the treatment and reuse of PW. Silicon carbide (SiC) membranes are preferred for PW treatment, due to their low (ir)reversible fouling compared to other ceramic membranes. However, full SiC membrane is expensive and thus economically less feasible. Therefore, we established a method for coating SiC on alumina (Al₂O₃) ultrafiltration membranes, based on low-pressure chemical vapor deposition at 860 °C. In the presented study the fouling resistance and behavior of these novel membranes, with various pore sizes and under different operating conditions, including flux and crossflow velocity, were evaluated. We also used Al₂O₃ membranes and SiC-coated Al₂O₃ membranes in constant flux mode to treat real oilfield PW with high salinity (142 mS/cm) and COD (22670 mg/L). Additionally, the fouling mechanisms in the SiC-coated and Al₂O₃ membranes were analyzed with the help of Focused Ion Beam-Scanning Electron Microscopy imaging. The major findings were that pore blockage served as the initial (irreversible) fouling mechanism and that the (reversible) cake layer, a mixture of organic and inorganic components, dominated the rest of the filtration cycle, where the SiC coated membrane performed better than the original alumina membrane. In addition, it was found that the application of the SiC coating, and the selection of the appropriate pore size (62 nm) and crossflow velocity (0.8 m/s) increased the fouling mitigation, potentially advancing the utilization of ultrafiltration in treating saline PW for reuse purposes.

Worldwide, a considerable amount of oily wastewater is generated, with oil droplets from 2 to 200 nm that are difficult to separate because of their size and colloidal stability. This study presents a novel approach for effectively separating microemulsions via cubic silicon carbide (3C-SiC)-coated alumina (Al ₂O ₃) membranes fabricated based on low pressure chemical vapor deposition (LPCVD). SiC was deposited at a relatively low temperature at 860 °C on 100 nm Al ₂O ₃ membranes using two precursors: SiH ₂Cl ₂ and C ₂H ₂. With the increase in deposition time, up to 25 min, the pore size decreased from 41 nm to 33 nm, which is a smaller pore size of a SiC membrane than previously used for oil/water separation. The polycrystalline 3C-SiC-coated membranes showed improved hydrophilicity (water contact angle of 15°) and highly negatively charged surfaces (−65 mV). Microemulsion filtration experiments were carried out at a constant permeate flux (80 Lm ⁻² h ⁻¹) for six cycles with varying deposition time, pH, surfactant types, and pore sizes. The fouling of the SiC-coated membrane was, compared to the Al ₂O ₃ membrane, effectively mitigated due to the enhanced electrostatic repulsion and hydrophilicity. Surfactant adsorption mainly occurred when the surface charge of the microemulsion and the membranes were opposite. Therefore, the surface charge of the alumina membrane changed from positive to negative when soaked in negatively charged microemulsions, whereas SiC-coated membranes remained negatively charged regardless of surfactant type. The membrane fouling was alleviated when the membrane and oil droplets had the same charge. Lastly, the 62 nm SiC-coated membrane with 20 min coating time was the best choice for the filtration of the microemulsion, because of the high rejection of the oil droplets and low fouling tendency.