Synergic Effect Of Oleophilic & Hydrophilic Membranes For Oil-water Separation In Refining Processes

At present,the oil-water separation sedimentation tank used in the refinery takes a long time to separate the small droplets with the size of micron,so the volume of the separation tank should be increased to meet the requirements of higher quality naphtha.Membrane separation method has the property of size screening,which can effectively screen smaller water droplets.In the refinery,the original production equipment is directly modified,and the membrane separation equipment is added to further remove micron-level water droplets in naphtha,which is easy to be modified and has low input cost.In order to improve the technology of separating micron-level water from naphtha in refinery,this paper studied the efficient separation method of naphtha containing micron-level water from three aspects:the deficiency of separation of existing sedimentation equipment,the effect of membrane separation,the design and model calculation of double-membrane separation module.Firstly,the shortcomings of gravity separation of aqueous naphtha by the existing sedimentation equipment in the refinery were studied,namely,the separation of micron-sized droplets（60μm）requires a long separation time（5.6 h）,and the volume of gravity sedime-ntation tank（644.0 m³）is large.In this case,the required safe distance is greater than 500 m.The separation of small droplets with micrometer size（below 60μm）by settling tank is difficult to be modified,the transportation cost of settling tank is high,it is difficult to replace the equipment and occupies a large area,etc.An optimal solution is to install a high efficiency separator on the original production facility.Then a membrane separation method with screening performance was introduced,which can effectively separate water droplets below 60μm.However,in the process of polyvinylidene fluoride（PVDF）membrane separation,it is obvious that water is concentrated on the surface of the membrane,which hinders the further separation of oil.When the PVDF membrane is coated with PDMS,the water contact angle increases from 95?to 117?,and the oil penetration rate is 15598 L·m^-2·h^-1·bar^-1.The separation of modified PDMS/PVDF membrane was also accompanied by the phenomenon of water enrichment.It is suggested that improving the properties of microporous membrane alone can not significantly alleviate the water enrichment,so other separation methods should be explored.Finally,a hydrophilic membrane was introduced on the opposite side of the oleophilic membrane to realize the bidirectional enrichment of oil and water.A dual-membrane separation module was designed to improve the efficiency of oil-water separation.The relationship between oil permeation rate and transmembrane pressure difference,flow rate and oil content of oil-water mixture in dual-membrane separation module was investigated.The water contact angle of the modified PA6 fiber film is 47?,and the water permeation rate is 7652 L·m^-2·h^-1·bar^-1.The separation model of double membrane modules was established,and the membrane area needed for separation could be calculated by the model.The membrane area needed for treating naphtha with an annual output of 5.4×10⁶ t was 546 m².Under the condition that the original refinery equipment remains unchanged,a pair of outer membrane components can be installed to remove micron-level water in naphtha,laying a solid foundation for industrialization.