Oil field sewage pollution control and hydrogen production device and method based on multi-stage gradient electrolytic cell

Abstract

The invention discloses an oil field sewage pollution control and hydrogen production device and method based on a multi-stage gradient electrolytic cell, and belongs to the technical field of oil field sewage treatment and renewable energy sources. The device comprises a pretreatment unit, a multi-stage gradient electrolytic cell and a gas collection unit which are connected in sequence, wherein the multi-stage gradient electrolytic tank comprises a first-stage electrolytic tank, a second-stage electrolytic tank and a third-stage electrolytic tank which are sequentially connected in series, anodes are a Ti / RuO2 mesh electrode, a Ti / SnO2-Sb2O5 sheet electrode and a Ti / PbO2 columnar electrode in sequence, and cathodes are porous MoS2-Ni composite electrodes; the method specifically comprises the following steps: (1) pretreatment; (2) staged treatment; and (3) discharging the water after reaching the standard, collecting and purifying hydrogen, and feeding into a hydrogen storage tank. Through gradient electrode design, multi-stage partition electrolysis and an efficient cathode hydrogen production process, efficient removal of pollutants and high yield of hydrogen are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oilfield wastewater treatment and renewable energy technology, more particularly to an oilfield wastewater pollution treatment hydrogen production device and method based on a multi-stage gradient electrolytic cell. BACKGROUND

[0002] Oilfield wastewater has been a key research object in the field of industrial wastewater treatment since the 20th century due to its high salinity, high organic content and emulsified oil characteristics. Traditional physical, chemical and biological treatment methods have been used for decades in treating such wastewater, for example, sedimentation separation and flocculation technology were widely used in the early stage of oilfield development. However, these methods can only achieve the removal of pollutants and are difficult to consider resource recovery, and the operation cost is high. With the transformation of global energy structure to clean, the use of oilfield wastewater to achieve pollutant degradation and hydrogen production by electrochemical technology has gradually attracted attention, and significant progress has been made in this field in the past two decades.

[0003] Electrochemical advanced oxidation processes (EAOPs) as an efficient wastewater treatment technology, as early as in the early 2010s began to be systematically studied. Sirés et al. (2014) in "Environmental Science and Pollution Research" reviewed the development of EAOPs, pointing out that it can effectively degrade organic pollutants through anodic oxidation, providing a new idea for the treatment of complex wastewater (Sirés, I., Brillas, E., Oturan, M. A., Rodrigo, M. A., & Panizza, M. (2014). Electrochemical Advanced Oxidation Processes: Today and Tomorrow. A Review. Environmental Science and Pollution Research, 21(14), 8336-8367. DOI: 10.1007 / s11356-014-2783-1.). Subsequently, Brillas et al. (2021) further reviewed the latest progress of electrochemical oxidation technology in wastewater treatment in "Journal of Cleaner Production", emphasizing the potential of Ti-based anodes (such as Ti / RuO2 and Ti / PbO2) in degrading high-concentration organic matter (Brillas, E., & Garcia-Segura, S. (2021). Recent Development of Electrochemical Advanced Oxidation of Herbicides. A Review on Its Application to Wastewater Treatment and Soil Remediation. Journal of Cleaner Production, 290, 125841. DOI: 10.1016 / j.jclepro.2021.125841.). These studies laid the theoretical foundation for the application of electrolysis technology in oilfield wastewater treatment. However, the existing EAOPs technology mainly focuses on the removal of pollutants, and fails to fully utilize the hydrogen generated by the cathode reaction, resulting in the potential of resource utilization not being fully tapped.

[0004] In the field of hydrogen production, water electrolysis technology has made breakthroughs in recent years, especially in the development of new cathode materials. Chen et al. (2021) reported a boron nanosheet-supported Rh catalyst in "Nano-Micro Letters", which significantly improved the efficiency of the hydrogen evolution reaction (HER) through strong metal-support interaction, showing the advantages of new materials in reducing overpotential and improving yield (Chen, Z., Wang, L., Wang, X., Wu, B., & Hu, B. (2021). Boron Nanosheet-Supported Rh Catalysts for Hydrogen Evolution: A New Territory for the Strong Metal-Support Interaction Effect. Nano-Micro Letters, 13, 138. DOI: 10.1007 / s40820-021-00662-y.). Ding et al. (2021) systematically analyzed the structural transformation of heterogeneous materials in electrocatalytic reactions in "Chemical Reviews", pointing out that the design of porous structure cathode can increase active sites and further optimize hydrogen production performance (Ding, H., Liu, H., Chu, W., Wu, C., & Xie, Y. (2021). Structural Transformation of Heterogeneous Materials for Electrocatalytic Oxygen Evolution Reaction. Chemical Reviews, 121(21), 13174-13212. DOI: 10.1021 / acs.chemrev.1c00234.). In addition, patent CN112941559A (Fe-Co bimetallic phosphide electrode material and its preparation) proposes a technology for preparing high-efficiency electrodes by chemical methods, while patent CN113913859A (Water electrolysis catalyst suitable for full pH range and its preparation method) develops a catalyst that can adapt to complex water quality. These advances provide material and process support for efficient hydrogen production, but have not yet been optimized for the high-salt, high-oil characteristics of oilfield wastewater.

[0005] However, the existing technology still faces several challenges: ① In the complex water quality of oilfield wastewater, the electrode material is easily disturbed by oil stains and salt, leading to serious bubble adhesion on the cathode surface, and the efficiency and purity of hydrogen production decrease; ② The traditional single-stage electrolytic cell is difficult to simultaneously achieve efficient removal of pollutants and high output of hydrogen, and the treatment process lacks pertinence; ③ The existing electrolysis system has high energy consumption, and the stability is insufficient in long-term operation, especially the corrosion resistance of the electrode needs to be improved under high salinity conditions. These problems limit the wide application of electrolysis technology in oilfield wastewater treatment and resource utilization.

[0006] Therefore, how to develop a new type of oilfield wastewater pollution treatment and hydrogen production device and method is a problem that those skilled in the art need to solve. SUMMARY

[0007] Therefore, the purpose of the present application is to provide an oilfield wastewater pollution treatment and hydrogen production device and method based on a multi-stage gradient electrolytic cell, which utilizes oilfield wastewater to simultaneously achieve efficient removal of pollutants and hydrogen production based on multi-stage gradient electrolytic cell technology, in order to solve the shortcomings in the prior art.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] An oilfield wastewater pollution treatment and hydrogen production device based on a multi-stage gradient electrolytic cell, comprising a pretreatment unit, a multi-stage gradient electrolytic cell and a gas collection unit connected in sequence.

[0010] Among them, the multi-stage gradient electrolytic cell comprises a first-stage electrolytic cell, a second-stage electrolytic cell and a third-stage electrolytic cell connected in series, the anodes are Ti / RuO2 mesh electrodes, Ti / SnO2-Sb2O5 sheet electrodes and Ti / PbO2 columnar electrodes in sequence, and the cathodes are all porous MoS2-Ni composite electrodes.

[0011] Advantages of the present application:

[0012] 1. Hydrogen production mechanism and optimization

[0013] The cathode of the third-stage electrolytic cell utilizes the high catalytic activity of MoS2-Ni, and water molecules are decomposed into H2 under the action of an electric field and a catalyst. Ultrasonic oscillation accelerates bubble detachment and reduces cathode blockage.

[0014] 2. Cathode design

[0015] The porous structure increases the reaction sites, the hydrophilic modification reduces the bubble adhesion force, and Co3O4 enhances the electron transfer, with an overpotential as low as 0.12V.

[0016] 3. Hydrogen collection and purification

[0017] Micro-porous flow guide and porous ceramic separator synergistically improve collection efficiency, activated carbon adsorption removes trace H2S and CO2, ensuring high purity.

[0018] 4. Experimental data

[0019] The pilot hydrogen yield is 3.0 m 3 / h, purity 99.5%, better than traditional electrolysis (yield increased by about 40%), energy consumption and stability are superior.

[0020] Innovations of the present invention:

[0021] 1. Multi-stage gradient electrolytic cell design

[0022] The present invention proposes a three-chamber multi-stage gradient electrolytic cell structure, which has significant innovation compared with the traditional single-stage electrolytic cell:

[0023] (1) First stage: Ti / RuO2 mesh anode is used, focusing on removing emulsified oil, oxidizing and decomposing oil stains at low voltage (2.0-3.5V).

[0024] (2) Second stage: Ti / SnO2-Sb2O5 sheet anode is used, aiming at organic matter degradation, the voltage is increased to 3.5-5.0V, and the oxidation capacity is strengthened.

[0025] (3) Third stage: Ti / PbO2 columnar anode is equipped, focusing on hydrogen production, the voltage is 5.0-7.0V, and the cathode reaction environment is optimized.

[0026] This staged design targets complex pollutants (emulsified oil, organic matter, high salinity) in oilfield wastewater for step-by-step treatment, not only improving pollutant removal efficiency, but also creating conditions for efficient hydrogen production, which is a major improvement over traditional electrolysis technology.

[0027] 2. Gradient electrode selection

[0028] The present invention innovatively selects gradient anode materials according to the needs of different treatment stages:

[0029] (1) Ti / RuO2 mesh anode: resistant to oil stains, suitable for oil removal stage.

[0030] (2) Ti / SnO2-Sb2O5 sheet anode: Sb2O5 doping enhances the catalytic efficiency and stability of the electrode in organic matter degradation.

[0031] (3) Ti / PbO2 columnar anode: strong corrosion resistance, suitable for high-voltage hydrogen production environment.

[0032] This gradient electrode configuration optimizes the specificity and stability of each stage of treatment, breaking through the limitations of traditional single electrode design.

[0033] 3. High-efficiency hydrogen production process using cathode

[0034] The cathode uses a porous MoS2-Ni composite material prepared by chemical vapor deposition (CVD), with a porosity of 60% and a pore size of 50-100 nm, increasing the reaction sites. At the same time, Co3O4 nano-catalysts (concentration 0.1-0.3 g / L, particle size 10-20 nm) are introduced, reducing the overpotential to 0.12-0.15 V, significantly lower than the traditional Ni electrode of 0.2-0.3 V, improving the hydrogen production efficiency.

[0035] 4. Ultrasonic-assisted technology

[0036] A micro ultrasonic oscillator (frequency 20 kHz, power 50 W) is equipped in the cathode area of the third-stage electrolytic cell, using the ultrasonic cavitation effect to accelerate bubble detachment from the cathode surface, reducing the bubble detachment time from 0.8 s to 0.3 s, and improving the hydrogen production efficiency by about 35%. This solves the problem of resistance caused by bubble attachment in traditional electrolytic hydrogen production.

[0037] 5. Gas collection and purification system

[0038] CO2 and H2S impurities are removed by a porous ceramic separator (pore size 0.05 μm) and an activated carbon adsorption tower, ensuring hydrogen purity >99% and collection efficiency >98%. This system design improves the practicality of hydrogen.

[0039] Novelty of the invention:

[0040] 1. Application of multi-stage gradient electrolytic cell in oilfield wastewater treatment

[0041] Although multi-stage electrolytic cells have been applied in some fields, this invention optimizes them specifically for the high-salt and high-oil characteristics of oilfield wastewater, and combines gradient electrodes to achieve staged treatment for the first time. This targeted design improves the synergistic efficiency of pollution control and hydrogen production, and is novel.

[0042] 2. Innovative application of cathode materials

[0043] MoS2-Ni composite materials have been studied in the field of electrocatalysis, but this invention prepares a porous structure by CVD and combines ultrasonic waves and Co3O4 catalysts for efficient hydrogen production in complex water, and this combination is unique.

[0044] 3. Introduction of ultrasonic-assisted hydrogen production technology

[0045] The application of ultrasonic technology in electrolytic hydrogen production, especially in the hydrogen production process of oilfield wastewater, reduces bubble resistance and improves yield, which is a novel breakthrough in technology.

[0046] Inventive nature of the invention:

[0047] 1. Technology Integration and Synergistic Optimization

[0048] The invention combines multi-stage electrolysis, gradient electrodes, efficient cathodes, and ultrasonic technology to achieve dual functions of pollution control and hydrogen production. This integration not only improves efficiency but also embodies creative thinking.

[0049] 2. Process Optimization and Energy Reduction

[0050] Through hierarchical processing and cathode optimization, hydrogen production rate and purity are significantly improved, while energy consumption is reduced to 1.8-2.2 kWh / ton of water, about 20% lower than traditional technology. This optimized design embodies the creativity of the technology.

[0051] 3. Stability in Complex Water Quality

[0052] In view of the complex characteristics of oilfield wastewater, the invention designs corrosion-resistant electrodes and optimized processes to ensure long-term stable operation of the device under harsh conditions, demonstrating the creative adaptability of the technology.

[0053] Advantages of the invention:

[0054] 1. Efficient pollution control and hydrogen production

[0055] Through multi-stage gradient electrolytic cells, the efficiency of pollutant removal and hydrogen production is greatly improved. Experimental data show:

[0056] (1) COD removal rate up to 93%.

[0057] (2) Oil content reduced to <15 mg / L.

[0058] (3) Hydrogen production rate up to 3.0 m 3 / h, purity >99%.

[0059] Compared with traditional single-stage electrolysis technology, hydrogen production rate is increased by about 40%, achieving efficient wastewater treatment and energy conversion.

[0060] 2. Low energy consumption

[0061] Through cathode optimization (overpotential reduced to 0.12-0.15 V) and ultrasonic assistance, the energy consumption per ton of water treatment is only 1.8-2.2 kWh, about 20% lower than traditional electrolysis technology. This low energy consumption significantly improves economic efficiency.

[0062] 3. High stability

[0063] The electrolytic cell uses corrosion-resistant materials (such as Ti-based anode and porous MoS2-Ni cathode), combined with ultrasonic to reduce bubble adhesion, ensuring long-term operation stability. In a 700h continuous operation test, the hydrogen production efficiency only decreased by 5%, much better than the 45% decrease of traditional Ni electrode, adapting to the harsh conditions of oilfield sites.

[0064] 4. Resource utilization

[0065] The invention converts oilfield wastewater into high-purity hydrogen, turning waste into treasure. Hydrogen can be used for fuel cells or industrial applications, with significant environmental benefits and economic value.

[0066] In summary, the invention realizes efficient treatment of oilfield wastewater and high output of hydrogen through the design of multi-stage gradient electrolytic cell, efficient cathode hydrogen production process and ultrasonic auxiliary technology. The innovation lies in the unique design and technical breakthrough, the novelty lies in the targeted application and material combination, and the creativity lies in the technology integration and optimization. The advantages include efficient pollution control and hydrogen production, low energy consumption, high stability, resource utilization and easy operation, providing a new solution for oilfield wastewater treatment and clean energy production.

[0067] Further, the above-mentioned pretreatment unit comprises a cyclone separator and a sedimentation tank connected in sequence; the diameter of the cyclone separator is 20-50 cm, and the separation efficiency is >90%; the volume of the sedimentation tank is 100-300 L.

[0068] The above-mentioned further beneficial effects are that the cyclone separator is used to remove floating oil and large particle impurities. The sedimentation tank is used for further sedimentation and separation of pretreated wastewater.

[0069] Further, the volume of each chamber of the above-mentioned multi-stage gradient electrolytic cell is 5-15 L; the inner wall of each chamber is coated with a polytetrafluoroethylene corrosion-resistant layer with a thickness of 0.5 mm; each chamber is separated by a cation exchange membrane with a thickness of 0.15 mm and an ion selectivity of >95%.

[0070] Further, the pore size of the Ti / RuO2 mesh electrode is 0.5 mm, and the Ru content is 30 wt%; the Sn:Sb molar ratio of the Ti / SnO2-Sb2O5 sheet electrode is 4:1; the Pb content of the Ti / PbO2 columnar electrode is 40 wt%; the Mo:Ni mass ratio of the porous MoS2-Ni composite electrode is 1:2, the porosity is 60%, the pore size is 50-100 nm, the thickness is 2-3 mm, it is prepared by chemical vapor deposition (CVD), the Ni-Fe layer thickness is 40-60 μm, preferably 50 μm, the surface is hydrophilic modified, and the contact angle is <30°.

[0071] The above-mentioned further beneficial effects are that the Ti / RuO2 mesh electrode focuses on the oxidative decomposition of emulsified oil. The Ti / SnO2-Sb2O5 sheet electrode is efficient for the degradation of organic matter. The Ti / PbO2 columnar electrode and the cathode are catalyzed by the porous MoS2-Ni composite electrode to reduce water molecules, and the reaction is 2H2O+2e -→ H2 + 2OH-, overpotential controlled at 0.12-0.15V. In addition, 0.1-0.3g / L Co3O4 nano-catalyst (particle size 10-20nm) can be added to enhance electron transfer and bubble detachment.

[0072] Further, the cathode lower part of the above-mentioned multi-stage gradient electrolytic cell is provided with a microporous gas flow guide plate with a pore size of 0.2mm and a spacing of 1cm; the cathode region of the third-stage electrolytic cell is provided with a micro ultrasonic oscillator with a frequency of 20kHz and a power of 50W.

[0073] The above-mentioned further beneficial effect is that the microporous gas flow guide plate is used to promote rapid hydrogen gas detachment. The micro ultrasonic oscillator is used to reduce bubble adhesion.

[0074] Further, the above-mentioned gas collection unit includes a porous ceramic separator, an activated carbon adsorption tower and a hydrogen storage tank connected in sequence; the porous ceramic separator has a pore size of 0.05μm and a separation efficiency of >98%; the activated carbon adsorption tower has a filling capacity of 5-10kg; the hydrogen storage tank has a pressure of 0.3-0.7MPa and a volume of 50-100L.

[0075] The above-mentioned further beneficial effect is that the porous ceramic separator is used to initially collect hydrogen gas. The activated carbon adsorption tower is used to remove CO2 and H2S, ensuring that the purity of hydrogen gas is >99%. The hydrogen storage tank is used to store high-purity hydrogen gas.

[0076] Further, the above-mentioned oilfield sewage pollution treatment hydrogen production device based on a multi-stage gradient electrolytic cell further includes a control system; the control system includes a gradient power supply, a current density monitor and a temperature control device; the gradient power supply is 0-10V step-adjustable with an accuracy of ±0.01V; the range of the current density monitor is 0-200mA / cm 2 ; the accuracy of the temperature control device is ±0.5℃.

[0077] An oilfield sewage pollution treatment hydrogen production method based on a multi-stage gradient electrolytic cell, which adopts the above-mentioned device, specifically includes the following steps:

[0078] (1) The oilfield sewage is pretreated by a cyclone separator and a sedimentation tank in sequence to remove floating oil and large-particle impurities;

[0079] (2) The pretreated oilfield sewage is introduced into the multi-stage gradient electrolytic cell for staged treatment;

[0080] Among them, the voltage of the first-stage electrolytic cell (oil removal) is 2.0-3.5V, the current density is 30-50mA / cm 2 , and the emulsified oil is anodized;

[0081] The voltage of the second-stage electrolytic cell (degradation) is 3.5-5.0V, the current density is 50-80mA / cm 2 , and the organic matter is anodically degraded;

[0082] The voltage of the third electrolytic cell (hydrogen production) is 5.0-7.0V, and the current density is 80-120mA / cm 2 The cathode efficiently generates hydrogen gas;

[0083] The electrolyte is adjusted to a pH of 6.0-8.0, the temperature is 25-45℃, the stirring rate is 100-250rpm, and the gas-liquid separation pressure difference in the cathode region is 0.05-0.1MPa;

[0084] (3) The treated water body is separated by a filter membrane to meet the discharge standard, hydrogen gas is collected by a porous ceramic separator and purified by an activated carbon adsorption tower to remove CO2 and H2S, and hydrogen gas with a purity of >99% is obtained and sent to a hydrogen storage tank.

[0085] Further, in the above step (1), the rotational speed of the cyclone separator is 3000-5000rpm.

[0086] Further, in the above step (3), the pore size of the filter membrane is 0.1μm.

[0087] The above further beneficial effects are used for the filter membrane to treat the treated water body to meet the discharge standard.

[0088] According to the above technical solution, compared with the prior art, the beneficial effects of the present application are as follows:

[0089] The present application realizes efficient removal of pollutants and high output of hydrogen gas through gradient electrode design, multi-stage partition electrolysis and efficient cathode hydrogen production process. Compared with the traditional technology, the present application not only significantly improves the hydrogen production rate and purity (>99%), reduces the energy consumption (about 1.8-2.2kWh / ton of water), but also enhances the corrosion resistance and stability of the device under harsh conditions. BRIEF DESCRIPTION OF DRAWINGS

[0090] Figure 1 It is a structural schematic diagram of the oilfield sewage pollution treatment and hydrogen production device of examples 1-2;

[0091] Figure 2 It is a flowchart of the oilfield sewage pollution treatment and hydrogen production method of examples 1-2;

[0092] Figure 3 It is a curve of COD removal rate change with treatment time in example 1;

[0093] Figure 4 It is a curve of hydrogen production rate change with cathode current density in example 2. DETAILED DESCRIPTION

[0094] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0095] Embodiment 1

[0096] Laboratory hydrogen production verification

[0097] The oilfield sewage pollution treatment hydrogen production device based on the multi-stage gradient electrolytic cell, as shown in the figure, comprises a pretreatment unit, a multi-stage gradient electrolytic cell and a gas collection unit connected in sequence. Figure 1

[0098] The pretreatment unit comprises a cyclone separator and a sedimentation tank connected in sequence; wherein the diameter of the cyclone separator is 20 cm, and the separation efficiency is > 90%; the volume of the sedimentation tank is 100 L;

[0099] The multi-stage gradient electrolytic cell comprises a first-stage electrolytic cell, a second-stage electrolytic cell and a third-stage electrolytic cell connected in sequence, and the volume of each chamber is 5 L; the inner wall of each chamber is coated with a polytetrafluoroethylene anticorrosive layer with a thickness of 0.5 mm; each chamber is separated by a cation exchange membrane with a thickness of 0.15 mm and an ion selectivity of > 95%; wherein the anode of the first-stage electrolytic cell is a Ti / RuO2 mesh electrode with a pore size of 0.5 mm and a Ru content of 30 wt%; the anode of the second-stage electrolytic cell is a Ti / SnO2-Sb2O5 sheet electrode with a Sn:Sb molar ratio of 4:1; the anode of the third-stage electrolytic cell is a Ti / PbO2 columnar electrode with a Pb content of 40 wt%; the cathodes are all porous MoS2-Ni composite electrodes with a Mo:Ni mass ratio of 1:2, a porosity of 60%, a pore size of 50 nm, a thickness of 2 mm, prepared by chemical vapor deposition (MoS2 precursor 0.02 mol / L, NiCl2 0.04 mol / L, deposition temperature 600℃), added with 0.2 g / L Co3O4 (co-precipitation method, calcined at 500℃), a Ni-Fe layer thickness of 40 μm, surface hydrophilic modification with a contact angle < 30°; a microporous gas deflector is arranged under the cathode of each chamber, with a pore size of 0.2 mm and a spacing of 1 cm; a micro ultrasonic oscillator is arranged in the cathode area of the third-stage electrolytic cell, with a frequency of 20 kHz and a power of 50 W;

[0100] The gas collection unit comprises a porous ceramic separator, an activated carbon adsorption tower and a hydrogen storage tank connected in sequence; wherein the pore size of the porous ceramic separator is 0.05 μm, and the separation efficiency is > 98%; the filling amount of the activated carbon adsorption tower is 5 kg; the pressure of the hydrogen storage tank is 0.3 MPa, and the volume is 50 L.

[0101] ​Take 1 L of oilfield produced water with COD of 1400 mg / L, oil content of 250 mg / L, TDS of 28,000 mg / L, and pH of 7.5 for laboratory hydrogen production verification.

[0102] The oilfield sewage hydrogen production method based on the multi-stage gradient electrolytic cell, as shown in Figure 2 , specifically includes the following steps:

[0103] (1) The oilfield sewage is pretreated by a cyclone separator with a rotation speed of 4000 rpm and a sedimentation tank in sequence to remove floating oil and large particle impurities, and the oil content is reduced to 180 mg / L;

[0104] (2) The pretreated oilfield sewage is introduced into the multi-stage gradient electrolytic cell for staged treatment, and after 50 min of reaction, the COD is reduced to 95 mg / L (removal rate 93%), the oil content is <12 mg / L, and the hydrogen production rate is 28 mL / min;

[0105] Among them, the voltage of the first electrolytic cell is 3.0 V, the current density is 50 mA / cm 2 , the anode oxidizes the emulsified oil;

[0106] The voltage of the second electrolytic cell is 4.5 V, the current density is 80 mA / cm 2 , the anode degrades organic matter;

[0107] The voltage of the third electrolytic cell is 6.0 V, the current density is 110 mA / cm 2 , the cathode efficiently generates hydrogen gas;

[0108] The pH of the electrolyte is adjusted to 6.0, the temperature is 25℃, the stirring rate is 200 rpm, and the gas-liquid separation pressure difference in the cathode area is 0.05 MPa;

[0109] (3) The treated water body is separated by a filter membrane with a pore size of 0.1 μm to meet the discharge standard, hydrogen gas is collected by a porous ceramic separator and purified by an activated carbon adsorption tower to remove CO2 and H2S (<0.1 ppm), and hydrogen gas with a purity of 99.2% is obtained and sent to a hydrogen storage tank.

[0110] Figure 1 Among them, the pipeline and arrow show the complete flow direction of the oilfield sewage from input to treatment, to water body discharge and hydrogen output, and the direction of the treated water body from the third electrolytic cell to the filter membrane and the hydrogen gas from the activated carbon adsorption tower to the hydrogen storage tank has been correctly marked. All text annotations have been moved outside the box to facilitate clear identification of the functions and parameters of each component. The structure diagram truly reflects the engineering design details of the device, highlighting the synergistic functions of the multi-stage gradient electrolytic cell in pollution control and hydrogen production, as well as the efficient and stable operation characteristics.

[0111] Figure 2In the oilfield wastewater treatment and hydrogen production device based on the multi-stage gradient electrolytic cell, the oilfield wastewater is subjected to cyclone separation, pre-treatment, multi-stage gradient electrolysis, and hydrogen collection.

[0112] The COD removal rate curve with the change of the treatment time is shown in Figure 3 As shown in the figure, with the extension of the treatment time, the COD (chemical oxygen demand) removal rate is significantly improved, reaching 93% within 60 min, which shows the ability of the present application to efficiently remove organic pollutants in oilfield wastewater in a short time.

[0113] Example 2

[0114] Pilot hydrogen production experiment

[0115] The oilfield wastewater treatment and hydrogen production device based on the multi-stage gradient electrolytic cell, as shown in Figure 1 includes a pre-treatment unit, a multi-stage gradient electrolytic cell, and a gas collection unit connected in sequence.

[0116] The pre-treatment unit includes a cyclone separator and a sedimentation tank connected in sequence; wherein the diameter of the cyclone separator is 50 cm, and the separation efficiency is > 90%; the volume of the sedimentation tank is 300 L;

[0117] The multi-stage gradient electrolytic cell includes a first-stage electrolytic cell, a second-stage electrolytic cell, and a third-stage electrolytic cell connected in sequence, and each chamber has a volume of 15 L; the inner wall of each chamber is coated with a polytetrafluoroethylene anticorrosive layer with a thickness of 0.5 mm; each chamber is separated by a cation exchange membrane with a thickness of 0.15 mm and an ion selectivity of > 95%; wherein the anode of the first-stage electrolytic cell is a Ti / RuO2 mesh electrode with a pore size of 0.5 mm and a Ru content of 30 wt%; the anode of the second-stage electrolytic cell is a Ti / SnO2-Sb2O5 sheet electrode with a Sn:Sb molar ratio of 4:1; the anode of the third-stage electrolytic cell is a Ti / PbO2 columnar electrode with a Pb content of 40 wt%; the cathodes are all porous MoS2-Ni composite electrodes with a Mo:Ni mass ratio of 1:2, a porosity of 60%, a pore size of 100 nm, and a thickness of 3 mm, prepared by chemical vapor deposition (MoS2 precursor 0.02 mol / L, NiCl2 0.04 mol / L, deposition temperature 600°C), with the addition of 0.25 g / L Co3O4 (co-precipitation method, calcination at 500°C), a Ni-Fe layer thickness of 60 μm, surface hydrophilic modification with a contact angle < 30°; the lower part of each cathode is provided with a microporous gas flow guide plate with a pore size of 0.2 mm and a spacing of 1 cm; the cathode area of the third-stage electrolytic cell is provided with a micro ultrasonic oscillator with a frequency of 20 kHz and a power of 50 W;

[0118] The gas collection unit comprises a porous ceramic separator, an activated carbon adsorption tower and a hydrogen storage tank connected in sequence; wherein the pore size of the porous ceramic separator is 0.05 μm, and the separation efficiency is >98%; the filling amount of the activated carbon adsorption tower is 10 kg; the pressure of the hydrogen storage tank is 0.5 MPa, and the volume is 100 L.

[0119] 4000 m 3 of oil field wastewater with COD of 1600 mg / L, oil content of 350 mg / L, TDS of 35,000 mg / L, and a pilot hydrogen production experiment is carried out.

[0120] The oil field wastewater pollution treatment hydrogen production method based on the multi-stage gradient electrolytic cell, as shown in the figure, specifically comprises the following steps: Figure 2

[0121] (1) The oil field wastewater is pretreated by a cyclone separator with a rotating speed of 5000 rpm and a sedimentation tank in sequence to remove floating oil and large particle impurities, and the COD is reduced to 1400 mg / L;

[0122] (2) The pretreated oil field wastewater is introduced into the multi-stage gradient electrolytic cell for staged treatment, and after 50 min of reaction, the COD is reduced to 105 mg / L (removal rate 92.5%), the oil content is <15 mg / L, the hydrogen production rate is 3.0 m 3 / h (for 30 kW fuel cell operation for 1 h), the hydrogen collection efficiency is 98.5%, and the energy consumption is 2.1 kWh / m 3 of water;

[0123] The voltage of the first-stage electrolytic cell is 3.2 V, the current density is 60 mA / cm 2 , the anode oxidizes the emulsified oil;

[0124] The voltage of the second-stage electrolytic cell is 4.8 V, the current density is 80 mA / cm 2 , and the anode degrades organic matter;

[0125] The voltage of the third-stage electrolytic cell is 6.5 V, the current density is 120 mA / cm 2 , and the cathode efficiently generates hydrogen;

[0126] The pH of the electrolyte is adjusted to 8.0, the temperature is 40℃, the stirring rate is 250 rpm, and the gas-liquid separation pressure difference in the cathode area is 0.1 MPa;

[0127] (3) The treated water is separated by a filter membrane with a pore size of 0.1 μm to meet the discharge standard, hydrogen is collected by a porous ceramic separator and purified by an activated carbon adsorption tower to remove CO2 and H2S (<0.1 ppm), and hydrogen with a purity of 99.5% is obtained and sent to a hydrogen storage tank.

[0128] The hydrogen production rate changes with the cathode current density curve is as follows:​Figure 4 As shown, with the increase of current density, the hydrogen production rate steadily increased to 120 mA / cm 2 3 , indicating that the present application has high efficiency and adjustability in hydrogen production process.

[0129] Example 3

[0130] Cathode hydrogen production stability

[0131] In simulated oilfield wastewater (COD 1200 mg / L, oil content 200 mg / L), the cathode of the third electrolytic cell was operated for 700 h, the voltage was 6.0 V, and the current density was 110 mA / cm 2 . The hydrogen production rate of the traditional Ni electrode decreased by 45%, while the MoS2-Ni cathode combined with ultrasonic wave only decreased by 5%, the bubble detachment time was shortened from 0.8 s to 0.3 s, and the stability was significantly improved.

[0132] Example 4

[0133] Cathode hydrogen production process optimization

[0134] When the porosity of the MoS2-Ni cathode was optimized to 60% (sulfidation time 2 h, H2S flow rate 50 mL / min) and the Co3O4 concentration was 0.25 g / L, the hydrogen production rate reached a maximum of 28.5 mL / min, and the overpotential was stabilized at 0.13 V. Under the ultrasonic wave frequency of 20 kHz, the bubble coverage rate on the cathode surface was reduced to 10%, and the hydrogen production efficiency was improved by 20%.

[0135] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.​

Claims

1. An oilfield sewage pollution treatment hydrogen production device based on a multi-stage gradient electrolytic cell, characterized in that, The device comprises a pretreatment unit, a multi-stage gradient electrolytic cell and a gas collection unit connected in sequence. The multi-stage gradient electrolytic cell comprises a first-stage electrolytic cell, a second-stage electrolytic cell and a third-stage electrolytic cell connected in sequence, the anodes are Ti / RuO2 mesh electrode, Ti / SnO2-Sb2O5 sheet electrode and Ti / PbO2 column electrode in sequence, and the cathodes are all porous MoS2-Ni composite electrode.

2. The hydrogen production device for oilfield sewage treatment according to claim 1, characterized in that, The pretreatment unit comprises a cyclone separator and a sedimentation tank connected in sequence, the cyclone separator has a diameter of 20-50 cm and a separation efficiency of >90%, and the sedimentation tank has a volume of 100-300 L.

3. The hydrogen production device for oilfield sewage treatment according to claim 1, characterized in that, Each chamber of the multi-stage gradient electrolytic cell has a volume of 5-15 L, the inner wall of each chamber is coated with a polytetrafluoroethylene anticorrosive layer with a thickness of 0.5 mm, and each chamber is separated by a cation exchange membrane with a thickness of 0.15 mm and an ion selectivity of >95%.

4. The hydrogen production device for oilfield sewage treatment according to claim 1, characterized in that, The Ti / RuO2 mesh electrode has a pore size of 0.5 mm and a Ru content of 30 wt%, the Ti / SnO2-Sb2O5 sheet electrode has a Sn:Sb molar ratio of 4:1, the Ti / PbO2 column electrode has a Pb content of 40 wt%, and the porous MoS2-Ni composite electrode has a Mo:Ni mass ratio of 1:2, a porosity of 60%, a pore size of 50-100 nm, a thickness of 2-3 mm, is prepared by chemical vapor deposition, has a Ni-Fe layer with a thickness of 40-60 μm, and is surface hydrophilic modified with a contact angle of <30°.

5. The hydrogen production device for oilfield sewage treatment according to claim 1, characterized in that, The lower part of the cathode of the multi-stage gradient electrolytic cell is provided with a microporous gas deflector with a pore size of 0.2 mm and a spacing of 1 cm, and the cathode region of the third-stage electrolytic cell is provided with a micro ultrasonic oscillator with a frequency of 20 kHz and a power of 50 W.

6. The hydrogen production device for oilfield sewage treatment according to claim 1, characterized in that, The gas collection unit comprises a porous ceramic separator, an activated carbon adsorption tower and a hydrogen storage tank connected in sequence, the porous ceramic separator has a pore size of 0.05 μm and a separation efficiency of >98%, the activated carbon adsorption tower has a filling amount of 5-10 kg, and the hydrogen storage tank has a pressure of 0.3-0.7 MPa and a volume of 50-100 L.

7. The hydrogen production device for oilfield sewage treatment according to claim 1, characterized in that, It also includes a control system; the control system includes a gradient power supply, a current density monitor and a temperature control device; the gradient power supply is 0-10V step adjustable, the accuracy is ±0.01V; the range of the current density monitor is 0-200mA / cm 2 ; the accuracy of the temperature control device is ±0.5℃.

8. A method for hydrogen production from oilfield wastewater treatment based on a multi-stage gradient electrolytic cell, characterized in that, The device is used to treat oilfield wastewater, and the treatment process comprises the following steps: (1) The oilfield wastewater is pretreated by a cyclone separator and a sedimentation tank in sequence to remove floating oil and large particle impurities; (2) The pretreated oilfield wastewater is introduced into a multi-stage gradient electrolytic cell for staged treatment; The voltage of the first electrolytic cell is 2.0-3.5V, and the current density is 30-50mA / cm 2 The anode oxidizes the emulsified oil; The voltage of the second electrolytic cell is 3.5-5.0V, and the current density is 50-80mA / cm 2 , and the anode degrades the organic matter; The third electrolytic cell has a voltage of 5.0-7.0 V and a current density of 80-120 mA / cm 2 , and the cathode efficiently generates hydrogen gas; The electrolyte is adjusted to a pH of 6.0-8.0, a temperature of 25-45℃, a stirring rate of 100-250 rpm, and a gas-liquid separation pressure difference in the cathode region of 0.05-0.1 MPa; (3) The treated water is separated by a filter membrane to meet the discharge standard, hydrogen gas is collected by a porous ceramic separator and purified by an activated carbon adsorption tower to remove CO2 and H2S, and hydrogen gas with a purity of >99% is obtained and sent to a hydrogen storage tank.

9. The method according to claim 8, wherein the method is characterized by, In step (1), the rotation speed of the cyclone separator is 3000-5000 rpm.

10. The method for hydrogen production from oilfield wastewater pollution treatment based on a multi-stage gradient electrolytic cell according to claim 8, characterized in that, In step (3), the filter membrane has a pore size of 0.1 μm.

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