A graphene oxide-polyamide conductive composite membrane, its preparation method and application

Abstract

The present invention discloses a graphene oxide-polyamide conductive composite membrane, its preparation method and application. The structure of the prepared graphene oxide-polyamide conductive composite membrane is composed of a stainless-steel substrate, a polypyrrole intermediate layer, and a polyamide doped with graphene oxide. The polypyrrole intermediate layer adjusts the conductivity of the substrate and the structure and distribution of the pores; the functional layer selects polyamide doped with graphene oxide, which greatly improves the hydrophilicity of its overall structure, and the slit structure formed by the stacking of graphene oxide is conducive to the transport of water and increases the difficulty of micelle transmembrane, thereby enhancing selectivity. The efficient separation of complex emulsions is achieved by using the ultrafiltration membrane separation technology with low energy consumption. When the existing wastewater passes through the surface of the conductive membrane, the emulsion droplets and inorganic salt ions in the wastewater are intercepted through "size sieving" and "charge effect" to remove pollutants. When treating complex emulsions, the operation is convenient, the energy consumption is low, and the treatment efficiency is high.

Description

Technical Field

[0001] The present invention belongs to the field of oil-water emulsion treatment, and particularly relates to a graphene oxide-polyamide conductive composite membrane, a preparation method thereof and an application thereof. Background Art

[0002] Oil-water emulsion (<10 μm) is an environmental pollutant in industrial processing wastewater with a wide range of sources. A large amount of emulsions are generated in oil extraction, electronic, mechanical processing industries, pharmaceutical industries and microelectronics manufacturing industries. It usually accompanies inorganic ions, surfactants and high-molecular substances such as demulsifiers; treating emulsions with complex components often requires a large amount of chemicals. Conventional treatment technologies such as physical sedimentation / adsorption, chemical flocculation / coagulation, and microbial decomposition have unsatisfactory treatment effects on oil-water emulsions (<10 μm), and there are problems such as high energy consumption and large initial equipment investment. The discharge of unqualified wastewater has a certain impact on the surrounding environmental water bodies and the physical and mental health of the surrounding residents. Therefore, a suitable and efficient treatment technology should be sought for emulsions with complex and stable components.

[0003] Membrane technology is a new type of water treatment technology in the 21st century. For the treatment of different types of oily wastewater, not only is the removal rate much higher than that of traditional methods, but also the energy consumption is low, and the treatment process and scale are flexible and variable. However, there are still some problems in the actual separation process of emulsions by membrane technology: on the one hand, the particle size of the emulsion will deform under the action of shear force, resulting in the deformation of micelles originally larger than the membrane pores and entering the pores, blocking the filtration channels and fouling; on the other hand, during the transmembrane transport process, the demulsification and aggregation of micelles accumulate on the membrane surface to form a filter cake pollution, increasing the transmembrane resistance, resulting in a decrease in flux, increasing the filtration energy consumption, shortening the service life of the membrane, and restricting the practicability and economy of membrane separation technology.

[0004] In view of the above problems, the present invention provides a graphene oxide-polyamide conductive composite membrane, a preparation method thereof and an application thereof. The structure of the graphene oxide-polyamide conductive composite membrane is composed of a stainless steel substrate, a polypyrrole intermediate layer and a polyamide doped with graphene oxide. The polypyrrole intermediate layer adjusts the conductivity of the substrate and the structure and distribution of the pores; the functional layer is made of polyamide doped with graphene oxide, which greatly improves the hydrophilicity of its overall structure, and the slit structure formed by the stacking of graphene oxide is beneficial to the transmission of water and increases the transmembrane difficulty of micelles, improving the selectivity. Summary of the Invention

[0005] The purpose of the present invention is to provide a graphene oxide-polyamide conductive composite membrane, a preparation method thereof and an application thereof, which solves the problem of unqualified emulsion treatment efficiency and alleviates membrane pollution and reduces energy consumption.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A preparation method of a graphene oxide - polyamide conductive composite film, comprising the following steps:

[0008] Step 1, pretreatment of the metal substrate. Press and sinter stainless steel substrates with a pore size of 0.1 μm into 1 - mm - thick substrates, repeatedly polish one side of the stainless steel substrate with water - sandpaper for polishing treatment, and use nano - tape to seal the unpolished side. The polished side is the front side of the stainless steel substrate, and the unpolished side is the back side of the stainless steel substrate;

[0009] Step 2, preparation of the conductive intermediate layer of polypyrrole. Take pyrrole monomer and 98% sulfuric acid to prepare 1 L of polymerization solution, and use the cyclic voltammetry method of the three - electrode system of an electrochemical workstation for electrochemical polymerization. Use silver chloride as the reference electrode, the stainless steel substrate as the working electrode, and a platinum sheet as the counter electrode. Set the working voltage range to - 0.2 - 1.1 V, the scanning speed to 0.05 V / s, and the number of scanning cycles to 90; Place the stainless steel substrate treated in Step 1 into the polymerization solution with the front side of the stainless steel substrate facing the platinum sheet for electrochemical polymerization of pyrrole to form a polypyrrole intermediate layer firmly attached to the front side of the stainless steel substrate. After taking it out, remove the sealed nano - tape on the back side of the substrate, rinse the surface of the stainless steel substrate with deionized water to remove unreacted polymer particles, and place it in an oven to dry;

[0010] Step 3, preparation of the modified polyamide functional layer. The specific method is as follows:

[0011] Step 3.1, dissolve 4 g of piperazine and 3 g of inorganic salt in 100 ml of deionized water as the aqueous solution for interfacial polymerization, dissolve 0.8 g of trimesoyl chloride in 100 ml of n - hexane as the organic solution for interfacial polymerization, and prepare a 0.1 mg / mL graphene oxide dispersion for standby;

[0012] Step 3.2, immerse the stainless steel substrate treated in Step 2 in the aqueous solution, ultrasonicate for 10 min to remove internal air bubbles so that its interior is filled with the aqueous solution. After taking it out, place the stainless steel substrate with the front side facing up on a flat plate, and use a rubber roller to remove the moisture on the surface of the stainless steel substrate;

[0013] Step 3.3, take 10 ml of the 0.1 mg / mL graphene oxide dispersion and load it into an electric nano - sprayer to spray it directly on the front side of the stainless steel substrate. Spray it repeatedly from top to bottom and from left to right for two cycles. One single stainless steel substrate consumes 10 ml of graphene oxide solution;

[0014] Step 3.4, take 15 ml of the organic solution and load it into the electric nano - sprayer to continue spraying and covering the front side of the stainless steel substrate. Spray it in a cyclic manner in the order from top to bottom and from left to right. One single stainless steel substrate consumes 15 ml of the organic solution;

[0015] Step 3.5: Place the stainless-steel substrate on a rack, conduct interfacial polymerization for 1 minute, rinse the front surface of the stainless-steel substrate with a n-hexane solution, and then put it into an oven at a temperature of 80 °C for curing to obtain a graphene oxide-polyamide conductive composite film.

[0016] Further, in Step 1, the stainless-steel substrate is polished unidirectionally with 1500 grit sandpaper for 30 times.

[0017] Further, in Step 2, the molar ratio of the pyrrole monomer to 98% sulfuric acid is 0.1 mol / L:0.3 mol / L.

[0018] Further, in Step 2, the size of the stainless-steel substrate is 8×10 cm, the size of the platinum sheet is 8×13 cm, the temperature of the oven is 60 °C, and drying is carried out for 30 minutes.

[0019] Further, in Step 3.5, the curing duration is 1 hour.

[0020] A graphene oxide-polyamide conductive composite film prepared according to the above method.

[0021] Application of the graphene oxide-polyamide conductive composite film in treating oil-water emulsions.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The efficient separation of stable emulsions is achieved by using the ultrafiltration membrane separation technology with low energy consumption. When the existing wastewater passes through the surface of the conductive membrane, emulsion droplets and inorganic salt ions in the wastewater are intercepted through "size screening" and "charge effect" to remove pollutants. When treating complex emulsions, the operation is convenient, the energy consumption is low, and the treatment efficiency is high. The treatment process only consumes extremely low electric energy, and no additional chemical treatment agents are required to achieve the efficient purification of sewage. Not only does it meet the strict standards for discharging wastewater, but it also improves the utilization rate of wastewater and creates a good water circulation system. Specific Embodiments

[0024] The present invention will be described in detail below in conjunction with specific embodiments.

[0025] This device demulsifies and separates emulsions, with convenient operation, simple device, and low energy consumption requirements. It not only meets more stringent water treatment standards but also realizes the efficient recycling and reuse of water resources.

[0026] By preparing a functional layer with appropriate pore sizes, the screening of emulsion droplets and salt ions is achieved. On this basis, the composite membrane is given an electric property and used as a cathode to repel the charged oil droplets and anions wrapped by anionic surfactants. Under the dual selection, a cross-flow filtration method is adopted to achieve an extremely high removal rate.

[0027] The present invention prepares a metal conductive film applicable to ultrafiltration equipment. The graphene oxide-polyamide conductive composite film can be divided into three layers, which are, from bottom to top, a stainless steel substrate (with a pore size of 0.1 μm) pressed from powder, a polypyrrole intermediate layer, and a polyamide functional layer (doped with graphene oxide). The functions of the three layers are as follows: the stainless steel substrate provides strong support and conductivity; the polypyrrole intermediate layer reduces the voids of the substrate and has excellent conductivity itself, which can optimize the conductivity of the substrate; the polyamide functional layer mainly plays a role of selective retention. Among them, doping graphene oxide can enhance the hydrophilicity of the film on the one hand, and on the other hand, it can form slit-shaped channels to strengthen the retention of micelles.

[0028] A preparation method of a graphene oxide-polyamide conductive composite film includes the following steps:

[0029] Step 1, pretreatment of the metal substrate. Sinter a stainless steel substrate with a pore size of 0.1 μm pressed from powder into a 1-mm-thick substrate. Use 1500-grit sandpaper to polish one side of the stainless steel substrate repeatedly 30 times for polishing treatment. Use nano tape to seal the unpolished side. The polished side is the front side of the stainless steel substrate, and the unpolished side is the back side of the stainless steel substrate;

[0030] Step 2, preparation of the conductive intermediate layer of polypyrrole. Take pyrrole monomer and 98% sulfuric acid to prepare 1 L of polymerization solution. The molar ratio of pyrrole monomer to 98% sulfuric acid is 0.1 mol / L:0.3 mol / L. Use the cyclic voltammetry method in a three-electrode system of an electrochemical workstation for electrochemical polymerization. Use silver chloride as the reference electrode, the stainless steel substrate as the working electrode, and a platinum sheet as the counter electrode. The size of the stainless steel substrate is 8×10 cm, and the size of the platinum sheet is 8×13 cm. Set the working voltage range to -0.2 - 1.1 V, the scanning speed to 0.05 V / s, and the number of scanning cycles to 90; Put the stainless steel substrate treated in Step 1 into the polymerization solution for electrochemical polymerization of pyrrole to form a polypyrrole intermediate layer firmly attached to the front side of the stainless steel substrate. After taking it out, remove the sealing nano tape on one side, rinse the surface of the stainless steel substrate with deionized water to remove unreacted polymer particles, and place it in an oven for drying. The oven temperature is set to 60 °C and dried for 30 min;

[0031] Step 3, preparation of the modified polyamide functional layer. The specific method is as follows:

[0032] Step 3.1, Dissolve 4 g of piperazine (PIP) and 3 g of inorganic salt (NaHCO3) in 100 ml of deionized water as the aqueous solution for interfacial polymerization. Dissolve 0.8 g of trimesoyl chloride in 100 ml of n-hexane as the organic solution for interfacial polymerization. Prepare a 0.1 mg / mL graphene oxide dispersion for standby;

[0033] Step 3.2: Immerse the stainless-steel substrate processed in Step 2 in an aqueous solution, and ultrasonically treat it for 10 min to remove internal air bubbles, so that its interior is filled with the aqueous solution. After taking it out, place the front side of the stainless-steel substrate upward on a flat plate, and use a rubber roller to remove the moisture on the surface of the stainless-steel substrate.

[0034] Step 3.3: Take 10 ml of 0.1 mg / mL graphene oxide dispersion and load it into an electric nano-sprayer, and spray it directly on the front side of the stainless-steel substrate. Spray it repeatedly from top to bottom and from left to right for two cycles. 10 ml of graphene oxide solution is consumed for a single stainless-steel substrate.

[0035] Step 3.4: Take 15 ml of organic phase solvent and load it into the electric nano-sprayer to continue spraying and covering the front side of the stainless-steel substrate. Spray it in a cycle according to the order from top to bottom and from left to right. 15 ml of organic phase solution is consumed for a single stainless-steel substrate.

[0036] Step 3.5: Place the stainless-steel substrate on a rack, carry out interfacial polymerization for 1 min, rinse the front side surface of the stainless-steel substrate with n-hexane solution, and then put it into an oven. The oven temperature is 80 °C, and it is cured for 1 h to obtain a graphene oxide-polyamide conductive composite film.

[0037] Application of the graphene oxide-polyamide conductive composite film in treating oil-water emulsions.

[0038] First, prepare an emulsion by using edible corn oil and two different surfactants, anionic sodium dodecyl sulfate (SDS) and Triton X-100. According to the oil:water ratio of 1:99 and the surfactant content of 10 mg / g, use a homogenizer to emulsify evenly, and prepare two liters of emulsion for standby. TM X-100). According to the oil: water ratio of 1:99 and the surfactant content of 10 mg / g, use a homogenizer to emulsify evenly, and prepare two liters of emulsion for standby.

[0039] Secondly, assemble an ultrafiltration module:

[0040] Put the prepared graphene oxide-polyamide conductive composite membrane into the ultrafiltration module and assemble it layer by layer. From top to bottom, it is the upper side of the ultrafiltration external module - graphene oxide-polyamide conductive composite membrane (cathode) - graphite rod (anode) - the lower side of the ultrafiltration external module, and seal it with a rubber gasket. Connect the water inlet end to the emulsion and start the equipment; according to "size sieving" and "charge effect", the emulsion and inorganic salt ions larger than the pores of polyamide cannot pass through the membrane, and the inorganic salt ions and emulsion smaller than the pore size will penetrate to the other side; combined with charge repulsion, when the graphene oxide-polyamide conductive composite membrane is used as the positive cathode, the anions in the solution will generate charge repulsion and cannot pass through the graphene oxide-polyamide conductive composite membrane. When the ionic radius is small and beyond the controllable range of the electric field, the anions will pass through the graphene oxide-polyamide conductive composite membrane. The outlet water is divided into two paths. The upper side is the retained effluent (waste water), which can be re-introduced into the water inlet end for secondary filtration, and the lower side is the permeated effluent (purified water).

[0041] When the above device is used to treat emulsified liquid wastewater with complex components, the following technical methods are adopted for treatment:

[0042] First, connect the wastewater to the water inlet end of the ultrafiltration equipment.

[0043] Secondly, turn on the ultrafiltration equipment, assemble the ultrafiltration external module, place the graphene oxide-polyamide conductive composite membrane and the graphite electrode in it, open the water inlet pipe, the retained effluent and the permeated effluent pipelines, set the flow rate to 2 L / h, set the voltage of the mobile power supply to 2 V, connect the negative pole to the conductive membrane, and the positive pole to the graphite electrode. When the solution fills the inside of the module, a circuit is formed. The emulsion and the anions in it generate a repulsive effect on the membrane under the action of the electric field and cannot pass through the membrane. As the filtration progresses, concentration polarization occurs on the water inlet side of the membrane, and the concentration of the retained substances will increase. However, due to the cross-flow filtration method, local turbulence will be generated according to the change of the flow rate, scouring the retained substances, moderately alleviating membrane fouling, so that the running time is extended, and the number of times and the service life of the membrane are prolonged.

[0044] Finally, judge whether to perform cyclic filtration according to the concentration of the retained effluent to improve the treatment efficiency. If cyclic filtration is carried out, the retained effluent pipeline can be connected to the water inlet end to achieve efficient separation of the emulsion.

[0045] The treatment efficiency of the conventional membrane technology generally remains at a removal rate of 95 - 99%, but the transmembrane pressure difference increases rapidly in a short time, and the membrane fouling is serious. After applying an external electric field, the cake fouling is significantly alleviated, and the use time of the filter membrane is prolonged.

[0046] Example 1

[0047] Step 1, pretreatment of the metal substrate

[0048] Use a 316L braided stainless steel mesh / copper mesh with a wire diameter of 4 μm (8×10 cm), and seal one side with nano tape. The sealed side is the back side of the stainless steel substrate, and the other side is the front side of the stainless steel substrate.

[0049] Step 2, prepare the conductive interlayer polypyrrole

[0050] Step 2.1, take pyrrole monomer: sulfuric acid (98%) at a ratio of 0.1 mol / L: 0.3 mol / L, prepare 1 L of polymerization solution, and carry out electrochemical polymerization using the cyclic voltammetry method of the three-electrode system in an electrochemical workstation. Use silver chloride as the reference electrode, a stainless steel substrate (8×10 cm) as the working electrode, and a platinum sheet (8×13 cm) as the counter electrode. Set the working voltage range to -0.2 - 1.1 V, the scanning speed to 0.05 V / s, and the number of scanning cycles to 90. Carry out electrochemical polymerization of pyrrole to form a polypyrrole intermediate layer firmly attached to the front side of the stainless steel substrate. After taking it out, remove the sealed nano tape on the back side of the stainless steel substrate, rinse the unreacted pyrrole monomer with deionized water, and place it in an oven at 60 °C for drying for 30 min.

[0051] Step 3, prepare the modified polyamide functional layer

[0052] Step 3.1, dissolve 4 g of piperazine (PIP) and 3 g of inorganic salt (NaHCO3) in 100 ml of deionized water, and dissolve 0.8 g of trimesoyl chloride in 100 ml of n-hexane, respectively, as the aqueous solution and organic solution for interfacial polymerization. Prepare a 0.1 mg / ml graphene oxide dispersion for standby.

[0053] Step 3.2, immerse the stainless steel substrate in the aqueous solution, ultrasonically remove the internal bubbles to make it fully filled with the aqueous solution inside, take it out and place the side covered with polypyrrole upwards, and use a rubber roller to remove the surface moisture.

[0054] Step 3.3, take 10 ml (0.1 mg / mL) of graphene oxide solution and load it into an electric nano sprayer to spray on the front side of the stainless steel substrate. Spray repeatedly from top to bottom and from left to right for two cycles. One single stainless steel substrate consumes 10 ml of graphene oxide solution.

[0055] Step 3.4, take 15 ml of the organic phase solvent and load it into the electric nano sprayer to continue spraying and covering the front side of the stainless steel substrate. Spray in a cyclic manner in the order of from top to bottom and from left to right. One single stainless steel substrate consumes 15 ml of the organic phase solution.

[0056] Step 3.5, place the stainless steel substrate on a rack, carry out interfacial polymerization for 1 min, rinse the front side surface of the stainless steel substrate with n-hexane solution, and then put it into an oven at 80 °C for curing for 1 h.

[0057] Prepare an emulsion by using hexadecane and two different surfactants, namely anionic sodium dodecyl sulfate (SDS) and Triton TM X-100). According to the oil:water ratio of 1:99 and the surfactant content of 30 mg / g, use a homogenizer to emulsify evenly and prepare 2 L of emulsion for standby.

[0058] Assemble the ultrafiltration module. Put the prepared graphene oxide-polyamide conductive composite membrane into the ultrafiltration module and assemble it layer by layer. From top to bottom, it is the upper side of the ultrafiltration external module - graphene oxide-polyamide conductive composite membrane (cathode) - graphite rod (anode) - the lower side of the ultrafiltration external module, and seal it with a rubber gasket. Connect the inlet end to the emulsion and start the equipment; according to the "size sieving" and "charge effect", the emulsion and inorganic salt ions larger than the pores of polyamide cannot pass through the membrane, and the inorganic salt ions and emulsion smaller than the pore size will penetrate to the other side; combined with charge repulsion, when the graphene oxide-polyamide conductive composite membrane acts as the cathode, the anionic ions in the solution generate charge repulsion and cannot pass through the membrane. When the ionic radius is small and beyond the controllable range of the electric field, the anions will pass through the membrane. The outlet water is divided into two paths. The upper side is the retained effluent (waste water), which can be re-introduced into the inlet end for secondary filtration, and the lower side is the permeated effluent (purified water).

[0059] For the cutting fluid generated by machining, it has a high degree of emulsification, contains a large amount of surfactants, and has a high COD value. The specific implementation method is as follows:

[0060] First, pre-treat the waste water to remove large particle processing waste to prevent damage to the instrument, and then connect it to the inlet end of the ultrafiltration equipment.

[0061] Secondly, turn on the ultrafiltration equipment, assemble the ultrafiltration external module, place the graphite electrode in it, open the inlet pipe, the retained effluent and the permeated effluent pipelines, set the flow rate to 2 L / h, set the voltage of the mobile power supply to 2 V, connect the cathode to the conductive membrane, and connect the anode to the graphite electrode. When the solution fills the inside of the module, a circuit is formed. The emulsion and the anions in it generate a repulsive effect on the membrane under the action of the electric field and are intercepted. As the filtration progresses, concentration polarization occurs on the inlet side of the membrane, and the retained substances accumulate and compress. However, due to the cross-flow filtration method, the filter cake layer is relatively loose and easy to remove, and the local turbulence generated by the cross-flow strips and breaks the pollutants, alleviating membrane fouling, making the transmembrane pressure difference increase slowly, and extending the service life of the composite membrane. The graphene oxide-polyamide functional layer has a pore size one order of magnitude smaller than that of the emulsion and has excellent removal effects; in summary, the composite membrane has better filtration performance and a longer service life compared to common commercial membranes.

[0062] Finally, determine whether to perform cyclic filtration based on the concentration of the retained effluent to improve the treatment efficiency. If cyclic filtration is to be carried out, the retained effluent pipeline can be connected to the inlet end. The separation efficiency of this technology for emulsions is >99%, which is much higher than that of traditional membrane technology for separating emulsions.

[0063] Example 2

[0064] Step 1, pretreatment of the metal substrate

[0065] Pretreat a 1-mm-thick stainless steel substrate sintered by pressing 0.1-μm-pore-size powder / a copper substrate sintered by pressing copper powder; repeatedly polish one side of the stainless steel substrate 30 times with 1500 water sandpaper for polishing treatment, and use nano tape to seal the unpolished side. The polished side is the front side of the stainless steel substrate, and the unpolished side is the back side of the stainless steel substrate.

[0066] Step 2, preparation of the conductive interlayer polypyrrole

[0067] Step 2.1, take pyrrole monomer: sulfuric acid (98%) at 0.1 mol / L: 0.3 mol / L, prepare 1 L of polymerization solution, and carry out electrochemical polymerization using the cyclic voltammetry method of the three-electrode system in an electrochemical workstation. Use silver chloride as the reference electrode, a stainless steel substrate (8×10 cm) as the working electrode, and a platinum sheet (8×13 cm) as the counter electrode. Set the working voltage range to -0.2 - 1.1 V, the scanning speed to 0.05 V / s, and the number of scanning cycles to 90. Carry out electrochemical polymerization of pyrrole. The generated polypyrrole interlayer firmly adheres to the front side of the stainless steel substrate. After taking it out, remove the single-sided sealing nano tape, rinse the polymer particles that have not fully reacted on the surface with deionized water, and place it in an oven at 60 °C for drying for 30 min.

[0068] Step 3, preparation of the modified polyamide functional layer

[0069] Step 3.1, dissolve 4 g of piperazine (PIP) and 3 g of inorganic salt (NaHCO3) in 100 ml of deionized water, and dissolve 0.8 g of trimesoyl chloride in 100 ml of n-hexane, respectively, as the aqueous phase and organic phase of interfacial polymerization, and prepare a 0.1 mg / mL graphene oxide dispersion for standby.

[0070] Step 3.2, immerse the stainless steel substrate in the aqueous solution, ultrasonically remove the internal bubbles for 10 min to make its interior filled with the aqueous solution, take it out, place the front side of the substrate upwards on a flat plate, and use a rubber roller to remove the moisture on the surface of the substrate.

[0071] Step 3.3: Take 10 ml of graphene oxide solution (0.1 mg / mL) and fill it into an electric nano-sprayer. Spray it directly onto the front side of the stainless-steel substrate. Spray from top to bottom and from left to right repeatedly for two cycles. Each single stainless-steel substrate consumes 10 ml of graphene oxide solution.

[0072] Step 3.4: Take 15 ml of organic phase solvent and fill it into the electric nano-sprayer. Continue to spray and cover the front side of the stainless-steel substrate. Spray in a cycle according to the order from top to bottom and from left to right. Each single stainless-steel substrate consumes 15 ml of organic phase solution.

[0073] Step 3.5: Place the stainless-steel substrate on a rack and conduct interfacial polymerization for 1 min. Rinse the front side of the stainless-steel substrate with n-hexane solution, and then put it into an oven at 80 °C for 1 h of curing.

[0074] Prepare an emulsion. Use hexadecane and sodium dodecyl sulfate (SDS) as the surfactant (anionic type). According to the oil:water ratio of 1:99 and the surfactant content of 30 mg / g, use a stirring device to stir evenly and prepare two liters of emulsion for standby.

[0075] Assemble the ultrafiltration module. Put the prepared graphene oxide-polyamide conductive composite membrane into the ultrafiltration module and assemble it layer by layer. From top to bottom, it is the upper side of the ultrafiltration external module - graphene oxide-polyamide conductive composite membrane (cathode) - graphite rod (anode) - the lower side of the ultrafiltration external module, and seal it with a rubber gasket. Connect the water inlet end to the emulsion and start the equipment; according to the "size screening" and "charge effect", the emulsion and inorganic salt ions larger than the polyamide pore size cannot pass through the membrane, and the inorganic salt ions and emulsion smaller than the pore size will penetrate through the membrane; combined with charge repulsion, when the conductive composite membrane is used as the cathode, the anionic ions in the solution will generate charge repulsion and cannot pass through the membrane. When the ionic radius is small and beyond the controllable range of the electric field, the anions will pass through the membrane. The filtered water of the filtration system is divided into two paths. The upper side is the retained effluent (waste water), which can be recycled and filtered by being re-introduced into the water inlet end. The lower side is the permeated effluent (clean water).

[0076] During the oilfield exploitation process, a large amount of demulsifiers and surfactants and other polymer oil recovery aids are usually used for dehydrating crude oil. And the produced water usually contains a high salt content. The current methods such as sedimentation, filtration, and centrifugation consume a large amount of energy and manpower. Now, a new type of conductive composite membrane is used to conduct ultrafiltration treatment on the waste water. The oil-water separation efficiency can reach more than 99%, the retention rate of divalent salt ions is higher than 98%, and the retention rate of monovalent salt ions is above 90%. The specific implementation method is as follows:

[0077] First, connect the waste water to the water inlet end of the ultrafiltration equipment.

[0078] Secondly, turn on the ultrafiltration equipment, assemble the external components of ultrafiltration, place the graphene oxide-polyamide conductive composite membrane and graphite electrodes therein, open the water inlet pipe, retain the outlet water and the permeate water pipeline, set the flow rate to 4 L / h, set the voltage of the mobile power supply to 2 V, connect the negative electrode to the conductive membrane, and connect the positive electrode to the graphite electrode. When the solution fills the inside of the component, a circuit is formed. The emulsion and the anions in it exert a repulsive force on the membrane under the action of the electric field and do not pass through the membrane. As the filtration progresses, concentration polarization occurs on the water inlet side of the membrane, and the concentration of the retained substances will increase. However, due to the cross-flow filtration method, local turbulence will be generated according to the change of the flow rate, scouring the retained substances. The filter cake layer is relatively loose and easy to remove, and the local turbulence generated by the cross-flow strips and breaks the pollutants, alleviating membrane fouling, making the transmembrane pressure difference increase slowly, and extending the service life of the composite membrane. The graphene oxide-polyamide functional layer has a pore size one order of magnitude smaller than that of the emulsion and has excellent removal effects. In summary, the composite membrane has better filtration performance and a longer service life compared with common commercial membranes.

[0079] During the actual operation of the graphene oxide-polyamide conductive composite membrane, the conductive membrane not only acts as a cathode to generate microbubbles through the hydrogen evolution reaction, breaking and peeling off the accumulated pollutants from the membrane surface, alleviating membrane fouling; but also as the charge-carrying ability of the membrane increases, according to the Donnan effect, the membrane electrode repels the charged pollutants, making it difficult for them to approach the membrane surface to form a fouling layer, improving the selectivity for pollutants, and thus enhancing the selective separation ability of the membrane. On the one hand, the applied electric field can regulate the transport behavior of charged pollutants and accelerate the migration of pollutants; on the other hand, it can adjust the electric potential between the liquid and the solid, change the surface tension between the solid and the liquid, and thus change the contact angle between the two, improving the hydrophilicity. The above membrane filtration coupled with electrochemical functions breaks through the limitation of the single function (size sieving) of the membrane, obtains better separation effects and a longer service time, and proposes a new strategy for alleviating membrane fouling problems.

[0080] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only for illustration purposes. The protection scope of the present invention is defined by the appended claims. Without departing from the principles and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A preparation method of a graphene oxide-polyamide conductive composite membrane, characterized in that, It includes the following steps: Step 1: Pretreatment of the metal substrate. Press and sinter the powder with a pore size of 0.1 μm into a 1-mm-thick stainless-steel substrate. Use water sandpaper to repeatedly polish one side of the stainless-steel substrate, and perform polishing treatment. Use nano tape to seal the unpolished side. The polished side is the front side of the stainless-steel substrate, and the unpolished side is the back side of the stainless-steel substrate. Step 2: Preparation of the conductive intermediate layer of polypyrrole. Take pyrrole monomer and 98% sulfuric acid to prepare 1 L of polymerization solution. Use the cyclic voltammetry method of the three-electrode system of an electrochemical workstation for electrochemical polymerization. Use silver chloride as the reference electrode, the stainless-steel substrate as the working electrode, and a platinum sheet as the counter electrode. Set the working voltage range to -0.2 - 1.1 V, the scanning speed to 0.05 V / s, and the number of scanning cycles to 90. Place the stainless-steel substrate treated in Step 1 into the polymerization solution with the front side of the stainless-steel substrate facing the platinum sheet, and perform electrochemical polymerization of pyrrole to form a polypyrrole intermediate layer firmly attached to the front side of the stainless-steel substrate. After taking it out, remove the sealed nano tape on the back side of the substrate, rinse the polymer particles that have not fully reacted on the surface of the stainless-steel substrate with deionized water, and place it in an oven to dry. Step 3: Preparation of the modified polyamide functional layer. The specific method is as follows: Step 3.1: Dissolve 4 g of piperazine and 3 g of inorganic salt in 100 ml of deionized water to form an aqueous solution for interfacial polymerization. Dissolve 0.8 g of trimesoyl chloride in 100 ml of n-hexane to form an organic solution for interfacial polymerization. Prepare a 0.1 mg / mL graphene oxide dispersion solution for standby. Step 3.2: Immerse the stainless-steel substrate treated in Step 2 in the aqueous solution, and ultrasonicate for 10 min to remove internal bubbles so that its interior is filled with the aqueous solution. After taking it out, place the front side of the stainless-steel substrate facing up on a flat plate, and use a rubber roller to remove the moisture on the surface of the stainless-steel substrate. Step 3.3: Take 10 ml of the 0.1 mg / mL graphene oxide dispersion solution and load it into an electric nano sprayer to spray it directly on the front side of the stainless-steel substrate. Spray it repeatedly from top to bottom and from left to right for two cycles. Each single stainless-steel substrate consumes 10 ml of graphene oxide solution. Step 3.4: Take 15 ml of the organic solution and load it into the electric nano sprayer to continue spraying and covering the front side of the stainless-steel substrate. Spray it in a cycle according to the order from top to bottom and from left to right. Each single stainless-steel substrate consumes 15 ml of the organic solution. Step 3.5: Place the stainless-steel substrate on a rack and perform interfacial polymerization for 1 min. Use n-hexane solution to rinse the front side surface of the stainless-steel substrate, and then put it into an oven. The oven temperature is 80 °C for curing to obtain a graphene oxide-polyamide conductive composite film.

2. The preparation method of a graphene oxide-polyamide conductive composite membrane according to claim 1, characterized in that, In Step 1, use 1500 water sandpaper to repeatedly polish one side of the stainless-steel substrate 30 times.

3. The preparation method of a graphene oxide-polyamide conductive composite film according to claim 1, characterized in that, In Step 2, the molar ratio of the pyrrole monomer to 98% sulfuric acid is 0.1 mol / L:0.3 mol / L.

4. The preparation method of a graphene oxide - polyamide conductive composite film according to claim 1, characterized in that, In Step 2, the size of the stainless-steel substrate is 8×10 cm, the size of the platinum sheet is 8×13 cm, the oven temperature is 60 °C, and it is dried for 30 min.

5. The preparation method of a graphene oxide - polyamide conductive composite membrane according to claim 1, wherein In Step 3.5, the curing duration is 1 h.

6. The graphene oxide-polyamide conductive composite membrane prepared by the method according to any one of claims 1-5.

7. The application of the graphene oxide-polyamide conductive composite membrane according to claim 6 in treating oil-water emulsion.