Development of New Nanofiber-Based Composite Membranes for the Opportunity of Oily Water Treatment

Qatar is world number one natural gas exporter; and Qatar economy heavily relies on oil/gas industry. Large quantity of oil-containing wastewater is being produced on daily basis from various industries, such as, oil/gas exploration and production, as well as oil product refinery. The removal of emulsified oil from such wastewater is challenging, due to the tiny sizes of oil droplets. These oil-polluted wastewater need to be properly treated before disposal and discharge to the environment. The oily wastewater is treated using the conventional treatment technologies. Following that, the treated wastewater is disposed in two way. One way is to inject the water to reinject it to oil/gas well. Another way is to inject the wastewater underground water reservoir. The challenge in oil/gas industry in Qatar is to reduce produced water volumes injected in disposal wells by 50% to maintain long-term reservoir sustainability. However, the issue is that treated produced water in Qatar is not qualified to be discharged to the environment. In this study, new nanofiber-based composited membranes with three-dimensional (3D) architecture, were designed and developed, with the goal to achieve fast, efficient and low-fouling separation of emulsified oil from oily water. Two types of membranes were synthesized to remove emulsified oil from water. The first membrane is composed of titanate nanofibers and silicon dioxide noanospheres (TNFS). The nanoporous and interconnected network structure constructed with titanate nanofibers is the key to ensure the high separation efficiency and high water flux of the new membrane. The SiO₂ gel is used as a binder to offer mechanical flexibility and integrity for this type of all-inorganic membrane. The second membrane is composed of titanate nanofibers and carbon nanofibers (TNFCNF). The intertwined structure of titanate and carbon nanofibers is critical to ensuring a high mechanical strength and durability for the new membrane. The carbon nanofiber works as a scaffold in this membrane to maintain mechanical integrity during multiple cycles of reuses, which is an important merit for its practical applications. The ultralong titanate nanofibers work as functional component to provide high hydrophilicity of the membrane. The physical and chemical properties of the fabricated membranes were studied using different characterization techniques such as SEM, FTIR, AFM, XRD, water/oil contact angles, and microscopy. The separation performance tests were investigated with lab simulated emulsified oil/water solution. The emulsified oil was characterized with ViPA. The oil/water separation efficiency of the fabricated new membranes was evaluated by a filtration device with its effective membrane area of 11.3 cm². The oil content in permeate was measured using TOC analyzer.The oil (in water) contact angles for TNFS and TNFCNF membranes were above 150 °, while the water contact angle of both membranes were 0°. In other words, the two fabricated membranes were super hydro-phylic and supr oleo-phobic, which suggest excellent fouling resistance by oil. The prepared emulsion used in the performance test has mean oil size of 3.35 µm with d10, d50, and d90 of 2.04, 2.83, and 5.27 respectively. The new membranes have an oil/water separation efficiency of more than 99%, an oil content in treated effluent that is lower than US environmental discharge standards (42 ppm), and a high water flux, due to its excellent superhydrophilicity and inter-connected pore structure. The water permeation flux were 1600 LMH/bar and 1520 LMH/bar for TNFSI membranes and TNFCNF membranes, respectively. The new membranes exhibits outstanding durability in a variety of salinity environments, as well as good resistance to oil fouling. This new type of membrane has a high potential for industrial application in treating oily wastewater due to its excellent environmental durability, oil-fouling resistance, and high separation efficiency.