A method for desulfurization of oil and gas field wastewater

Abstract

The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas field sewage desulfurization method, it is related to oil and gas field sulfur-containing sewage treatment field.The application discloses a kind of oil and gas

Description

Technical Field

[0001] This invention relates to the field of sulfur-containing wastewater treatment technology in oil and gas fields, and specifically to a method for desulfurizing wastewater from oil and gas fields. Background Technology

[0002] The large amounts of sulfur-containing wastewater generated during oil and gas field development pose a significant environmental challenge to the industry. This wastewater contains high concentrations of harmful substances such as hydrogen sulfide and sulfides, which not only severely corrode pipelines, storage tanks, and treatment equipment, shortening facility lifespan and increasing maintenance costs, but also pose a significant threat to the ecological environment and human health if improperly treated and directly discharged. Therefore, developing efficient and economical desulfurization technologies to achieve compliant wastewater discharge or reuse has become a critical issue urgently needing to be addressed for the safe production and green development of oil and gas fields.

[0003] Currently, the main technologies used in the industry for treating sulfur-containing wastewater fall into three categories: physical, chemical, and biological methods. While steam stripping, as a traditional physical method, is widely used, it suffers from inherent drawbacks such as high energy consumption and a tendency to cause secondary air pollution. Chemical oxidation methods (such as the Fenton process and ozone oxidation) offer rapid reactions, but require large amounts of reagents, have high operating costs, and easily generate chemical sludge, causing secondary pollution. Biological methods, while having lower treatment costs, suffer from slow reaction rates, sensitivity to environmental conditions (such as temperature, pH, and toxic substances), and weak resistance to shock loads, making it difficult to meet the stable treatment requirements for continuous production in oil and gas fields.

[0004] The complexed iron method, a promising chemical desulfurization technology, utilizes the redox properties of complexed iron ions to oxidize H2S in water into elemental sulfur for recovery, theoretically enabling the recycling of sulfur resources. However, traditional complexed iron methods still face three prominent technical bottlenecks in practical engineering applications: First, the iron complexes are unstable. In complex oil and gas field wastewater systems, especially under high temperature and high salinity conditions, the iron complexes are prone to decomposition or ligand degradation, leading to the precipitation and deactivation of iron ions in the form of ferric hydroxide, resulting in a rapid decline in catalytic efficiency and requiring frequent reagent replenishment, thus increasing operating costs. Second, sulfur separation is difficult and prone to causing equipment blockage. The elemental sulfur particles generated in the reaction are small, highly hydrophilic, and difficult to aggregate, resulting in low separation efficiency using traditional sedimentation or filtration methods. Large amounts of sulfur particles deposit in reactors, pipelines, and pumps, causing severe equipment blockage and forcing frequent system shutdowns for cleaning, affecting continuous and stable operation. Third, the process route is incomplete, lacking a closed-loop resource recovery system. Most processes focus only on the removal of sulfides, failing to achieve efficient recycling of catalysts and standardized recovery of sulfur resources, thus failing to truly "turn waste into treasure" and achieve near-zero wastewater discharge, and failing to maximize environmental and economic benefits.

[0005] In traditional processes, sulfur recovery from sulfur-containing foam or slurry typically employs the following methods: High-temperature melting method: This requires heating the sulfur to its melting point (~115℃), resulting in high energy consumption. Molten sulfur is also highly viscous and flammable, posing a high operational hazard and potentially causing carbonization of encapsulated organic matter, affecting product purity. Steam distillation method: This method involves complex equipment and consumes significantly more energy. Single solvent extraction method: While carbon disulfide (CS2) has good sulfur solubility, it is highly volatile, flammable, explosive, and toxic, posing extremely high safety risks for industrial applications.

[0006] In summary, existing technologies struggle to simultaneously ensure efficient and stable desulfurization while also achieving low-cost operation, avoiding secondary pollution, and realizing resource recovery. Therefore, the industry urgently needs to develop a novel integrated deep desulfurization process that can systematically address issues such as catalyst stability, sulfur blockage, and process closed-loop operation. Summary of the Invention

[0007] The purpose of this invention is to provide a desulfurization method for oil and gas field wastewater. By establishing a bifunctional complex iron catalytic system, the method utilizes organic acid ligands to stabilize iron ions and form a hydrophobic microenvironment; creates free radical chain reaction conditions to achieve staged oxidation of sulfides; introduces an in-situ regeneration mechanism to maintain continuous and efficient catalytic activity; and systematically solves the problems of catalyst stability, sulfur blockage, and process closed-looping.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for desulfurization of wastewater from oil and gas fields includes the following steps:

[0010] S100. Adjust the pH of sulfur-containing wastewater to 8.0~9.0 and add sulfur granules as a regulator;

[0011] S200: Add a composite complex iron catalyst to the wastewater treated in step S100 and carry out a catalytic oxidation reaction under the condition that the dissolved oxygen concentration is controlled at 2~8 mg / L.

[0012] S300, by adding an air flotation separator, separates the generated sulfur particles from the aqueous phase to obtain sulfur-enriched foam and desulfurized wastewater;

[0013] S400: Add an oxidation-reduction regulator to the separated desulfurization wastewater and restore catalyst activity by controlling the oxidation-reduction potential within the range of 150~250mV.

[0014] S500, with the addition of flocculants and pH adjusters, ensures that the treated water meets discharge standards.

[0015] Traditional complexed iron processes are limited by three major problems: poor stability of the complexes, sulfur blockage, and equipment corrosion, making long-term stable industrial operation difficult. This invention takes a holistic approach, constructing a multi-step synergistic system: In step S100, a sulfur particle regulator is added within the optimal pH range (8.0~9.0) to pre-regulate the morphology of subsequently generated sulfur, making it easier to separate from the source, shifting from passive treatment to active regulation. The composite complexed iron catalyst used in step S200, through molecular design, significantly enhances chemical stability and antioxidant degradation resistance in high-temperature, high-salt, and oily environments, fundamentally inhibiting iron precipitation and deactivation, ensuring the persistence of reaction efficiency. Step S200 employs an air flotation separator to efficiently capture and separate the regulated hydrophobic sulfur particles, allowing sulfur to be quickly removed from the system immediately after generation, avoiding deposition in reactors and pipelines, ensuring long-term continuous and stable operation of the unit, eliminating the maintenance burden and production loss associated with frequent shutdowns for cleaning, and solving the core problem of sulfur blockage in pipelines and equipment.

[0016] In traditional methods, catalyst deactivation is either irreversible or requires complex external treatment. This invention employs an online monitoring-dynamic adjustment regeneration strategy. By monitoring the system's redox potential (ORP) in real time as a control parameter and precisely adding redox modifiers such as hydrogen peroxide and sodium bisulfite, the ORP is stabilized at 150-250 mV. This achieves in-situ, real-time, and intelligent recovery of catalyst activity, significantly extending catalyst lifespan and reducing reagent consumption.

[0017] Further, in step S100, the sulfur particle control agent is a compound of sodium dodecyl sulfate and polyethylene glycol, the mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:2~4, and the amount of sulfur particle control agent added is 10~50 mg / L.

[0018] Traditional desulfurization processes typically focus only on oxidizing sulfides, neglecting the crucial influence of the physical form of the reaction product—sulfur—on subsequent separation and the overall system stability. This invention innovatively intervenes before the oxidation reaction occurs (S100 step) by adding a regulator composed of sodium dodecyl sulfate (SDS, an anionic surfactant) and polyethylene glycol (PEG, a nonionic polymer) in a specific mass ratio (1:(2~4)) to actively control the form of sulfur formation.

[0019] SDS, as a surfactant, adsorbs onto the surface of sulfur microcrystals, significantly reducing their surface energy and inhibiting excessive aggregation and scale formation. Meanwhile, PEG long-chain molecules, through steric stabilization, guide sulfur particles to form easily separable flocs with uniform size, loose structure, and enhanced hydrophobicity. The resulting sulfur particles, after regulation, become loose, hydrophobic, and easily separable, fundamentally preventing their adhesion and deposition in reactors, pipes, pumps, and valves, greatly reducing the risk of equipment blockage. The regulated sulfur particle properties (increased size, enhanced hydrophobicity) make them more easily captured and floated by air bubbles during the air flotation separation process in step S300, thus significantly improving the separation efficiency and recovery rate of sulfur.

[0020] Furthermore, the composite complexed iron catalyst is prepared by the following method: first, the main complexing agent, auxiliary stabilizer and antioxidant are dissolved in water to form a mixture, and stirring is maintained. Under the conditions of pH 4.0~6.0 and system temperature below 40℃, ferrous sulfate aqueous solution is added dropwise to the mixture to carry out the complexation reaction, and then it is matured for 30~60 min to obtain a homogeneous catalyst solution.

[0021] The molar ratio of ferrous sulfate to the main complexing agent is 1:1.5~2.5, and the molar ratio of the main complexing agent, auxiliary stabilizer and antioxidant is 1:0.2~0.5:0.05~0.15.

[0022] First, the main complexing agent, auxiliary stabilizer, and antioxidant are pre-formed into a stable mixed ligand environment. Then, iron ions are slowly introduced, effectively preventing the instantaneous hydrolysis of iron ions at localized high concentrations to form ferric hydroxide precipitate. This ensures that each iron ion is fully complexed, improving the catalyst's uniformity and stability from the source. Under weakly acidic conditions (pH 4.0-6.0) and low temperatures (<40℃), the efficient coordination reaction between iron ions and the complexing agent is guaranteed, while maximally suppressing Fe... 2+ oxidation and Fe 3+ Hydrolysis forms a stable, homogeneous, and highly active catalytic solution.

[0023] The primary complexing agent provides the main coordination bonds with iron ions. The auxiliary stabilizer further enhances the steric stability of the complex through steric hindrance and additional coordination sites. The antioxidant preferentially captures free radicals in the system, effectively preventing the complexing agent molecular chains from being oxidized and degraded, thus maintaining the catalyst's activity over a long period. The multi-component, specifically proportioned compound design constitutes a triple structural barrier protecting the active centers of iron ions.

[0024] Furthermore, the primary complexing agent is selected from at least two of citrate, tartrate, or gluconate; the secondary stabilizer is selected from triethanolamine or ethylenediamine; and the antioxidant is selected from catechol or hydroquinone.

[0025] Citrates include sodium citrate, potassium citrate, or ammonium citrate; tartrates include sodium tartrate, potassium tartrate, or sodium tartrate potassium; and gluconates include sodium gluconate, potassium gluconate, or calcium gluconate. When the main complexing agent is composed of two compounds, the citrate:tartrate ratio is 1:(0.5~1.5); citrate:gluconate ratio is 1:(0.8~2); and tartrate:gluconate ratio is 1:(1~2). When the main complexing agent is composed of two compounds, the molar ratio of citrate:tartrate:gluconate is (0.3~0.6):(0.2~0.4):(0.2~0.4), and the sum of the three is 1.

[0026] Furthermore, in step S200, the conditions for the catalytic oxidation reaction are: temperature 40~60℃, reaction time 30~90min.

[0027] Further, in step S300, the air flotation separator is a compound of cationic and anionic surfactants, with a mass ratio of cationic to anionic surfactant of 1:1~3 and an addition amount of 5~20 mg / L; the anionic surfactant is selected from sodium dodecylbenzenesulfonate or sodium dodecyl sulfate; the cationic surfactant is selected from hexadecyltrimethylammonium chloride or dialkyldimethylammonium bromide.

[0028] Further, in step S400, the redox regulator is a composite system of hydrogen peroxide and sodium bisulfite, with hydrogen peroxide and sodium bisulfite added at a redox equivalent ratio of 1:0.8~1.2. The redox potential is maintained in the range of 150~250mV by controlling the amount of redox regulator added at one time.

[0029] In the complexed iron desulfurization system, the catalyst activity depends on Fe. 3+ / Fe 2+ The equilibrium ratio of Fe. 3+ It is in the oxidized state and is responsible for oxidizing H2S. The higher its proportion, the stronger the oxidizing power of the system and the higher the ORP value. Fe 2+ It is in a reduced state and needs to be regenerated into Fe. 3 + The higher the proportion of , the stronger the reducibility of the system and the lower the ORP value.

[0030] Set a lower limit of 150 mV: below this value, it indicates that Fe 2+ Too high a concentration of Fe 3+ Insufficient oxygen content leads to a decrease in the system's oxidation capacity, necessitating the addition of hydrogen peroxide as an oxidant. An upper limit of 250 mV is set: values ​​exceeding this indicate insufficient Fe... 3+Excessive concentration may lead to decreased stability of the complex or other side reactions, requiring the addition of sodium bisulfite as a reducing agent. The total amount of oxidant and reducing agent added should follow the redox equivalent ratio, that is, the equivalent ratio of hydrogen peroxide to sodium bisulfite should be controlled within the range of 1:0.8~1.2 to ensure that the system is neither over-oxidized nor over-reduced, thereby achieving optimal recovery and stability of catalyst activity.

[0031] Further, in step S500, the flocculant is a composite flocculation system of polyaluminum chloride and polyacrylamide, with the dosage of polyaluminum chloride being 20~100 mg / L and the dosage of polyacrylamide being 0.5~5 mg / L.

[0032] This invention employs a compound of polyaluminum chloride (PAC, an inorganic polymeric flocculant) and polyacrylamide (PAM, an organic polymeric flocculant). The two have clearly defined roles: PAC first neutralizes the negative charge on the surface of colloidal particles through electrical properties and physical interactions, destabilizing them to form micro-flocs; subsequently, PAM, with its long molecular chains, adsorbs and bridges the micro-flocs, forming large and dense flocs. Through this highly efficient synergistic effect, it can deeply remove various suspended and colloidal pollutants from water, significantly reducing effluent turbidity and ensuring that the final water quality consistently meets stringent discharge or reuse standards.

[0033] Furthermore, it also includes a catalyst recovery step: the effluent purified in step S500 is separated by a nanofiltration membrane, and the retained catalyst concentrate is returned to step S200 for recycling.

[0034] After purification in step S500, the effluent is first subjected to fine filtration to remove suspended solids and colloids, and then separated by nanofiltration membrane. The nanofiltration membrane material includes polyamide or cellulose acetate, with a pore size of 1~2nm, a pressure of 0.4~5.0 MPa, and a filtration temperature below 45℃.

[0035] Furthermore, it also includes a sulfur purification step: the sulfur-enriched foam obtained in step S300 is added to a melting agent and melted and separated at 80~120℃ to obtain a sulfur product with a purity ≥99.5%; the melting agent is a mixed solvent of carbon disulfide and toluene, and the volume ratio of carbon disulfide to toluene is 1:1~3.

[0036] This invention proposes a melt-extraction composite process for treating sulfur foam using a mixed solvent at 80-120°C. This temperature is significantly lower than the operating temperature of traditional melt methods, greatly reducing energy consumption and the risk of overheating and decomposition. This step utilizes heat to disrupt the foam structure and reduce sulfur viscosity, while simultaneously leveraging the selective solubility of the solvent to achieve phase separation and purification at low temperatures.

[0037] This invention does not use a single solvent, but instead employs a mixed system of carbon disulfide (CS2) and toluene. Carbon disulfide provides excellent solubility for sulfur and is the core of efficient extraction. Toluene, as a high-boiling-point, mild diluent and extractant, can significantly reduce the overall volatility and vapor pressure of the mixed solvent, greatly improving operational safety and overcoming the fatal drawback of CS2 being flammable and explosive. Toluene itself has a certain solubility for sulfur and can effectively dissolve organic impurities (such as residual surfactants, oils, etc.) carried in sulfur foam, thus playing a role in washing and removing impurities during the purification process. This is also the key to improving purity and can stably obtain sulfur products with a purity of ≥99.5%.

[0038] This step directly processes the sulfur-enriched foam from S300, eliminating the need for complex pretreatment steps such as foam bursting, sulfur paste collection, and drying. It achieves direct conversion from foam to product, simplifies the process, and improves overall recycling efficiency.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. This invention, through the high stability of the composite catalyst and the catalyst regeneration system, enables continuous and efficient operation over a wide range of water quality fluctuations. It can stably reduce sulfide levels in high-concentration sulfur-containing wastewater to below 0.5 mg / L, with a desulfurization efficiency far exceeding 99.9%. It converts hydrogen sulfide into sulfur products with a purity of ≥99.5%, and the treatment effect is stable and reliable, with a sulfur recovery rate of ≥93.2%. The final products of this invention are clean and compliant effluent, high-purity sulfur resources, and recyclable catalyst. It does not produce difficult-to-treat chemical sludge or other secondary pollution, truly achieving an organic combination of pollution control and resource recovery, resulting in significant environmental and social benefits.

[0041] 2. The entire process can be completed simply by adding chemical agents and simple solid-liquid separation, without relying on complex and expensive high-temperature and high-pressure equipment (such as gas stripping towers) or biological systems that require demanding environmental conditions. This makes the method low in equipment investment, easy to operate, requires little space, and is easy to modularize and skid-mount, making it particularly suitable for field applications in remote and dispersed oil and gas fields, demonstrating significant practicality and wide adaptability.

[0042] 3. This invention recovers high-purity sulfur byproducts through an air flotation separation step; and recovers the catalyst through a subsequent nanofiltration membrane separation step, achieving efficient retention and recycling of valuable catalyst molecules; the final effluent can meet discharge standards or be reused.

[0043] Polyaluminium chloride (PAC) is not a single pure substance, but an inorganic polymer. Its chemical composition is complex, consisting of a mixture of different forms of aluminum hydroxyl complexes. Its general chemical formula can be represented as: [Al₂(OH)₂] n Cl 6-n ] m Where n = 1~5, m ≤ 10. Its core effective components are various polymeric cationic compounds, the most important of which is the Al species with the best flocculation effect, usually referring to [AlO4Al]. 12 (OH) 24 (H2O) 12 ] 7+ Al (abbreviated as Al) 13 Aggregates. Detailed Implementation

[0044] Example 1

[0045] A method for on-site preparation of a composite complex iron catalyst includes the following steps:

[0046] 1. Preparation of complexing agent solution: Under normal temperature conditions, add 6.5 kg of purified water to the reaction vessel, and add the main complexing agent, triethanolamine and catechol in sequence according to the ratio, and stir until completely dissolved to form a mixed complexing agent solution; the molar ratio of the main complexing agent, triethanolamine and catechol is 1:0.35:0.1; the main complexing agent includes sodium citrate and potassium tartrate in a molar ratio of 1:1.

[0047] 2. Dissolving iron salts: In another container, completely dissolve 1 kg of FeSO4·7H2O in 2.5 kg of purified water to prepare an iron salt solution; the molar ratio of ferrous sulfate to the main complexing agent is 1:2.

[0048] 3. Complexation reaction: At a rotation speed of 220 rpm, ferrous sulfate solution is added dropwise to the mixed complexing agent solution obtained in step 1. The time for all ferrous sulfate solution to be added is controlled within 45 minutes, and the system temperature is maintained below 35℃ to prevent local overconcentration or excessive temperature from causing hydrolysis of iron ions or decomposition of the complex.

[0049] 4. pH adjustment: During the complexation reaction, the pH value of the system is maintained in the range of 4.0 to 6.0 by using a 15% dilute sodium hydroxide solution.

[0050] 5. Maturation: After the iron salt solution is added, continue stirring the reaction solution for 45 minutes to ensure that the complexation reaction is sufficient and complete, resulting in a uniform and stable dark green composite complex iron catalyst solution.

[0051] Example 2

[0052] A method for on-site preparation of a composite complex iron catalyst includes the following steps:

[0053] 1. Preparation of complexing agent solution: Under normal temperature conditions, add 6 kg of purified water to the reaction vessel, and add the main complexing agent, ethylenediamine and catechol in sequence according to the ratio, and stir until completely dissolved to form a mixed complexing agent solution; the molar ratio of the main complexing agent, ethylenediamine and catechol is 1:0.2:0.05; the main complexing agent includes sodium citrate and sodium gluconate in a molar ratio of 1:1.2.

[0054] 2. Dissolving iron salts: In another container, completely dissolve 1 kg of FeSO4·7H2O in 2 kg of purified water to prepare an iron salt solution; the molar ratio of ferrous sulfate to the main complexing agent is 1:1.5.

[0055] 3. Complexation reaction: At a rotation speed of 120 rpm, the iron salt solution is added dropwise to the mixed complexing agent solution obtained in step (1). The time for all the ferrous sulfate solution to be added is controlled within 30 minutes, and the system temperature is maintained below 35℃ to prevent local overconcentration or excessive temperature from causing iron ion hydrolysis or complex decomposition.

[0056] 4. pH adjustment: During the complexation reaction, the pH value of the system is maintained in the range of 4.0~6.0 by using a 10% dilute sodium hydroxide solution.

[0057] 5. Maturation: After the iron salt solution is added, continue stirring the reaction solution for 30 minutes to ensure that the complexation reaction is sufficient and complete, resulting in a uniform and stable dark green composite complex iron catalyst solution.

[0058] Example 3

[0059] A method for on-site preparation of a composite complex iron catalyst includes the following steps:

[0060] 1. Preparation of complexing agent solution: Under normal temperature conditions, add 7 kg of purified water to the reaction vessel, and add the main complexing agent, ethylenediamine and hydroquinone in sequence according to the ratio, and stir until completely dissolved to form a mixed complexing agent solution; the molar ratio of the main complexing agent, ethylenediamine and hydroquinone is 1:0.5:0.15; the main complexing agent includes potassium tartrate and sodium gluconate in a molar ratio of 1:1.5.

[0061] 2. Dissolving iron salts: In another container, completely dissolve 1 kg of FeSO4·7H2O in 3 kg of purified water to prepare an iron salt solution; the molar ratio of ferrous sulfate to the main complexing agent is 1:2.5.

[0062] 3. Complexation reaction: At a rotation speed of 320 RPM, the iron salt solution is added dropwise to the mixed complexing agent solution obtained in step (1). The time for all the ferrous sulfate solution to be added is controlled within 60 minutes, and the system temperature is maintained below 35℃ to prevent local overconcentration or excessive temperature from causing iron ion hydrolysis or complex decomposition.

[0063] 4. pH adjustment: During the complexation reaction, the pH value of the system is maintained in the range of 4.0~6.0 by using a 20% dilute sodium hydroxide solution.

[0064] 5. Maturation: After the iron salt solution is added, continue stirring the reaction solution for 60 minutes to ensure that the complexation reaction is sufficient and complete, resulting in a uniform and stable dark green composite complex iron catalyst solution.

[0065] Example 4

[0066] A method for on-site preparation of a composite complex iron catalyst includes the following steps:

[0067] 1. Preparation of complexing agent solution: Under normal temperature conditions, add 6.5 kg of purified water to the reaction vessel, and add the main complexing agent, triethanolamine and hydroquinone in sequence according to the ratio, and stir until completely dissolved to form a mixed complexing agent solution; the molar ratio of the main complexing agent, triethanolamine and hydroquinone is 1:0.3:0.12; the main complexing agent includes ammonium citrate, sodium tartrate and potassium gluconate in a molar ratio of 0.4:0.3:0.3.

[0068] The remaining steps are the same as in Example 1.

[0069] Example 5

[0070] A method for on-site preparation of a composite complex iron catalyst includes the following steps:

[0071] 1. Preparation of complexing agent solution: Under normal temperature conditions, add 6-7 kg of purified water to the reaction vessel, and add the main complexing agent, triethanolamine and catechol in sequence according to the ratio, and stir until completely dissolved to form a mixed complexing agent solution; the molar ratio of the main complexing agent, auxiliary stabilizer and antioxidant is 1:0.2-0.5:0.05-0.15; the main complexing agent includes potassium citrate, potassium sodium tartrate and calcium gluconate in a molar ratio of 0.5:0.2:0.3.

[0072] Comparative Example 1

[0073] In step 3, the system temperature is maintained at 50~55℃. All other parameters and steps are the same as in Example 1.

[0074] Comparative Example 2

[0075] In step 3, the time for completely adding the ferrous sulfate solution is controlled within 2 minutes. All other parameters and steps are the same as in Example 1.

[0076] Comparative Example 3

[0077] No auxiliary stabilizers or antioxidants were used; only the main chelating agent, sodium citrate:potassium tartrate, was used in a 1:1 ratio. All other parameters and procedures were the same as in Example 1.

[0078] Comparative Example 4

[0079] In step 4, the pH of the system is maintained within the range of 2.0 to 3.0. All other parameters and steps are the same as in Example 1.

[0080] The performance parameters of the composite complex iron catalysts prepared by the methods of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0081] 500 mL of simulated wastewater with a sulfide concentration of 500 mg / L was placed in the reactor, and the temperature was controlled at 40℃ and the dissolved oxygen concentration at 5 mg / L. A catalyst was added to bring the Fe³⁺ concentration in the system to 100 mg / L, and the timer was started while stirring continuously. Samples were taken 60 minutes after the start of the reaction, and the residual sulfide concentration was determined using the methylene blue spectrophotometric method (GB / T 16489-1996), and the desulfurization efficiency was calculated. The desulfurization efficiency results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0082] Table 1 Performance parameters of the composite complex iron catalysts prepared by the methods of Examples 1-5 and Comparative Examples 1-4

[0083] Group Complexation time (min) Settling (24h, %) Simulated desulfurization efficiency (%) Example 1 <5 <1 >99 Example 2 <10 <3 98.5 Example 3 <5 <1 >99 Example 4 <5 <1 >99 Example 5 <5 <2 98.8 Comparative Example 1 >30 >20 (Reddish-brown) <90 Comparative Example 2 >60 >15 (Yellowish-green flocculent) 92 Comparative Example 3 <5 >10 (pale yellow) 95 (rapid decay) Comparative Example 4 >30 >25 (mostly reddish-brown) <85

[0084] Table 1 shows that in Examples 1-5, the complexation time was less than 10 min, the precipitation rate after 24 h of standing was less than 3%, and the desulfurization efficiency was ≥98%. In Comparative Example 1, the reaction temperature of 50-55℃ was too high, and the high temperature greatly accelerated the desulfurization of Fe. 2+ Oxidized by dissolved oxygen in water to Fe 3+ The rate of Fe. 3+ Under non-strongly acidic conditions, it readily undergoes hydrolysis to form ferric hydroxide precipitate (reddish-brown). Simultaneously, high temperatures may also cause some organic complexing agents to decompose, collectively leading to catalyst deactivation, prolonged complexation time, and a sharp drop in desulfurization efficiency.

[0085] In Comparative Example 2, the rapid introduction of ferrous sulfate solution within 2 minutes resulted in localized overconcentration. In areas where the ferrous salt solution was concentrated, the pH dropped sharply and instantaneously, Fe... 2+When the concentration far exceeds that of the complexing agent, it cannot be complexed in time, resulting in localized hydrolysis and the formation of ferrous or ferric basic salt colloids (yellow-green flocculent substances). These colloids are difficult to dissolve and complex again, thus disrupting the homogeneity of the solution.

[0086] In Comparative Example 3, no auxiliary stabilizers or antioxidants were added. The absence of triethanolamine resulted in the complex lacking steric hindrance protection, making it prone to intermolecular aggregation and precipitation. The absence of catechol meant that free radicals in the system could not be eliminated, continuously attacking and degrading the main complexing agents such as citrate and tartrate, leading to a decrease in their complexing ability. Iron ions were gradually released and eventually precipitated, resulting in a rapid decline in activity.

[0087] In Comparative Example 4, the reaction environment was excessively acidic, with a pH of 2.0–3.0. Under such a strongly acidic environment, H… + Too high a concentration, with Fe 2 + Competing complexing agents have strong coordination sites, which severely inhibits the complexation reaction. At the same time, strong acidity also means that OH... - The concentration is extremely low, which is unfavorable for Fe. 2+ The complex forms a stable hydroxyl-bridged structure with the complexing agent, which makes the complex unstable and the iron ions eventually hydrolyze and precipitate.

[0088] Example 6

[0089] A method for desulfurizing wastewater from oil and gas fields, characterized by comprising the following steps:

[0090] S100. Adjust the pH of 1000L of sulfur-containing wastewater to 8.5 and add sulfur granules; the sulfur granules are a compound of sodium dodecyl sulfate and polyethylene glycol, with a mass ratio of sodium dodecyl sulfate to polyethylene glycol of 1:3; the amount of sulfur granules added is 30mg / L.

[0091] S200. Add the composite complex iron catalyst (prepared by the method in Example 1) to the wastewater treated in step S100, and carry out the catalytic oxidation reaction under the condition that the dissolved oxygen concentration is controlled at 5 mg / L; the conditions for the catalytic oxidation reaction are: temperature 50℃, reaction time 60 min.

[0092] S300, add an air flotation separator to separate the generated sulfur particles from the aqueous phase, and obtain sulfur-enriched foam and desulfurized wastewater; the air flotation separator is a compound of hexadecyltrimethylammonium chloride and sodium dodecylbenzenesulfonate with a mass ratio of 1:2, and the addition amount of the two air flotation separators is 13 mg / L.

[0093] Sulfur purification step: The sulfur-enriched foam obtained in step S300 is added to a melting agent and melted and separated at 100°C to obtain a sulfur product with a purity ≥99.5%; the melting agent is a mixed solvent of carbon disulfide and toluene, with a volume ratio of carbon disulfide to toluene of 1:2.

[0094] S400. Add an oxidation-reduction regulator to the separated desulfurization wastewater to restore catalyst activity by controlling the oxidation-reduction potential within the range of 150~250mV. The oxidation-reduction regulator is a composite system of hydrogen peroxide and sodium bisulfite, with hydrogen peroxide and sodium bisulfite added at an oxidation-reduction equivalent ratio of 1:1. Control the single addition amount of the oxidation-reduction regulator to maintain the oxidation-reduction potential within the range of 150~250mV.

[0095] S500, with the addition of flocculant and pH adjuster, ensures that the treated water meets discharge standards; the flocculant is a composite flocculation system of polyaluminum chloride and polyacrylamide, with a dosage of 60 mg / L for polyaluminum chloride and 2.8 mg / L for polyacrylamide.

[0096] Catalyst recovery step: The effluent purified in step S500 is separated by a nanofiltration membrane, and the retained catalyst concentrate is returned to step S200 for recycling. The nanofiltration membrane is made of polyamide, with a pore size of 1.5 nm, a pressure of 2.5 MPa, and a filtration temperature of 40°C.

[0097] Example 7

[0098] A method for desulfurizing wastewater from oil and gas fields, characterized by comprising the following steps:

[0099] S100. Adjust the pH of 1000L of sulfur-containing wastewater to 8.0 and add sulfur granules; the sulfur granules are a compound of sodium dodecyl sulfate and polyethylene glycol, with a mass ratio of sodium dodecyl sulfate to polyethylene glycol of 1:4; the amount of sulfur granules added is 50mg / L.

[0100] S200. Add a composite complex iron catalyst (prepared by the method in Example 1) to the wastewater treated in step S100, and carry out a catalytic oxidation reaction under the condition that the dissolved oxygen concentration is controlled at 8 mg / L. The conditions for the catalytic oxidation reaction are: temperature 60℃ and reaction time 90 min.

[0101] S300, adding an air flotation separator to separate the generated sulfur particles from the aqueous phase, obtaining sulfur-enriched foam and desulfurized wastewater; the air flotation separator is a compound of dialkyl dimethyl ammonium bromide and sodium dodecyl sulfate, with a mass ratio of 1:3 and an addition amount of 20 mg / L.

[0102] Sulfur purification step: The sulfur-enriched foam obtained in step S300 is added to a melting agent and melted and separated at 120°C to obtain a sulfur product with a purity ≥99.5%; the melting agent is a mixed solvent of carbon disulfide and toluene, with a volume ratio of carbon disulfide to toluene of 1:3.

[0103] S400. Add an oxidation-reduction regulator to the separated desulfurization wastewater to restore catalyst activity by controlling the oxidation-reduction potential within the range of 150~250mV. The oxidation-reduction regulator is a composite system of hydrogen peroxide and sodium bisulfite, with hydrogen peroxide and sodium bisulfite added at an oxidation-reduction equivalent ratio of 1:1.2. Control the single addition amount of the oxidation-reduction regulator to maintain the oxidation-reduction potential within the range of 150~250mV.

[0104] S500, with the addition of flocculant and pH adjuster, ensures that the treated water meets discharge standards; the flocculant is a composite flocculation system of polyaluminum chloride and polyacrylamide, with a dosage of 100 mg / L for polyaluminum chloride and 5 mg / L for polyacrylamide.

[0105] Catalyst recovery step: The effluent purified in step S500 is separated by a nanofiltration membrane, and the retained catalyst concentrate is returned to step S200 for recycling. The nanofiltration membrane material includes polyamide or cellulose acetate, with a pore size of 1 nm, a pressure of 4.0 MPa, and a filtration temperature of 35°C.

[0106] Example 8

[0107] A method for desulfurization of wastewater from oil and gas fields includes the following steps:

[0108] S100. Adjust the pH of 1000L of sulfur-containing wastewater to 9.0 and add sulfur granules; the sulfur granules are a compound of sodium dodecyl sulfate and polyethylene glycol, with a mass ratio of sodium dodecyl sulfate to polyethylene glycol of 1:2; the amount of sulfur granules added is 10mg / L.

[0109] S200. Add the composite complex iron catalyst (prepared by the method in Example 1) to the wastewater treated in step S100, and carry out the catalytic oxidation reaction under the condition that the dissolved oxygen concentration is controlled at 2 mg / L. The conditions for the catalytic oxidation reaction are: temperature 40℃, reaction time 30 min.

[0110] S300, adding an air flotation separator to separate the generated sulfur particles from the aqueous phase, obtaining sulfur-enriched foam and desulfurized wastewater; the air flotation separator is a compound of dialkyl dimethyl ammonium bromide and sodium dodecylbenzene sulfonate in a mass ratio of 1:1, and the amount of air flotation separator added is 5 mg / L;

[0111] Sulfur purification step: The sulfur-enriched foam obtained in step S300 is added to a melting agent and melted and separated at 80°C to obtain a sulfur product with a purity ≥99.5%; the melting agent is a mixed solvent of carbon disulfide and toluene, with a volume ratio of carbon disulfide to toluene of 1:1.

[0112] S400. Add an oxidation-reduction regulator to the separated desulfurization wastewater to restore catalyst activity by controlling the oxidation-reduction potential within the range of 150~250mV. The oxidation-reduction regulator is a composite system of hydrogen peroxide and sodium bisulfite, with hydrogen peroxide and sodium bisulfite added at an oxidation-reduction equivalent ratio of 1:0.8. Control the single addition amount of the oxidation-reduction regulator to maintain the oxidation-reduction potential within the range of 150~250mV.

[0113] S500, with the addition of flocculant and pH adjuster, ensures that the treated water meets discharge standards; the flocculant is a composite flocculation system of polyaluminum chloride and polyacrylamide, with a polyaluminum chloride dosage of 20 mg / L and a polyacrylamide dosage of 0.5 mg / L.

[0114] Catalyst recovery step: The effluent purified in step S500 is separated by a nanofiltration membrane, and the retained catalyst concentrate is returned to step S200 for recycling. The nanofiltration membrane material includes polyamide or cellulose acetate, with a pore size of 1 nm, a pressure of 0.4 MPa, and a filtration temperature of 44 °C.

[0115] Comparative Example 5

[0116] In S100, no sodium dodecyl sulfate-polyethylene glycol complex is added. In S300, a single component, sodium dodecyl sulfate (20 mg / L), is used as the flotation separator. The remaining steps are exactly the same as in Example 6.

[0117] Comparative Example 6

[0118] The S400 (catalyst regeneration) and catalyst recovery steps are omitted. After a single pass in S200, the catalyst flows with the water into S500 and is removed by flocculant precipitation. The remaining steps are exactly the same as in Example 6.

[0119] Comparative Example 7

[0120] The catalyst used in S200 was prepared using the method described in Comparative Example 3. The remaining steps were exactly the same as in Example 6.

[0121] Table 2 shows a comparison of the desulfurization effects of the desulfurization methods used in Examples 6-8 and Comparative Examples 5-7 for oil and gas field wastewater.

[0122] Table 2 Comparison of desulfurization effects of oil and gas field wastewater desulfurization methods in Examples 6-8 and Comparative Examples 5-7

[0123] Test Project Desulfurization efficiency (%) Sulfur recovery rate (%) Sulfur purity (%) Catalyst replenishment rate (per cycle) Effluent turbidity (NTU) Continuous operation stability Example 6 ＞99.9 96.5 99.6 <5% (after 10 cycles) <5 Excellent (no clogging, stable water output) Example 7 99.5 95.0 99.5 <8% (after 10 cycles) <8 Excellent (no clogging, stable water output) Example 8 98.8 93.2 99.5 <10% (after 10 cycles) <10 Excellent (no clogging, stable water output) Comparative Example 5 85.0 65.0 90.0 >50% (after 3 cycles) >50 Poor (severe sulfur blockage, frequent shutdowns) Comparative Example 6 92.0 Ineffective recycling - 100% (One-way use) >20 Poor (system paralysis) Comparative Example 7 94.0 88.0 95.0 30% (after 5 cycles) >15 Medium (efficiency continues to decline)

[0124] As shown in Table 2, Examples 6-8 achieved a desulfurization efficiency of over 99.9%, a sulfur recovery rate of ≥93.2%, a sulfur purity of ≥99.5%, a catalyst replenishment rate of <10% after 10 catalyst cycles, and a turbidity of <10 NTU in the desulfurized effluent. The effluent operated continuously without clogging and was stable.

[0125] Comparative Example 5 lacked pre-treatment of sulfur particles, resulting in small, highly hydrophilic sulfur particles that were difficult to aggregate. A single surfactant could not simultaneously address charge neutralization and foam stability issues, and the flotation process could not effectively capture and entrain small sulfur particles, leading to a large amount of sulfur remaining in the system and causing severe equipment blockage (sulfur blockage). The sulfur recovery rate dropped sharply to only 65.0%. Residual sulfur interfered with subsequent catalytic reactions and effluent quality, resulting in low overall system efficiency, unstable operation, and effluent turbidity > 50 NUT.

[0126] Comparative Example 6: Even though the catalyst itself is very stable, Fe in the reaction 3+ It will be reduced to Fe 2+ Without the ORP-controlled regeneration step of S400, the catalyst's oxidation activity rapidly declines as the reaction proceeds. The catalyst's activity cannot be maintained, resulting in low desulfurization efficiency of only 92%. A large amount of iron ions enters the subsequent flocculation unit, increasing the burden on sludge treatment.

[0127] Comparative Example 7 lacked the steric hindrance protection of triethanolamine and the antioxidant protection of catechol. Under high-temperature, oxygen-rich reaction conditions, the catalyst rapidly deactivated, and iron ions underwent hydrolysis and precipitation. The catalyst was not only unstable during storage but also experienced continuous performance degradation during the reaction, leading to a gradual decrease in desulfurization efficiency to only 94%. Frequent and large-scale replenishment of fresh catalyst was required to maintain efficiency, resulting in a high replenishment rate. After five cycles, the replenishment rate reached 30%, increasing operating costs.

[0128] The desulfurization method for oil and gas field wastewater of the present invention can be used directly for desulfurization of raw wastewater from oil and gas fields, or it can be used in conjunction with a gas stripping device.

[0129] Example 9

[0130] A method for desulfurization of wastewater from oil and gas fields includes the following steps:

[0131] S50, Air Stripping Pretreatment: The sulfur-containing wastewater is transported to a vacuum degassing unit (or air stripping tower) where, under a vacuum of -0.06 MPa and a temperature of 50°C, most of the free hydrogen sulfide (H2S) gas is removed. The removed H2S gas is then transported to the subsequent sulfur recovery unit (Claus furnace) for further treatment. After air stripping pretreatment, the sulfide concentration in the wastewater is significantly reduced, and it then proceeds to the subsequent chemical desulfurization steps S100~S500.

[0132] Steps S100 to S500 are the same as in Example 1.

[0133] Step S50, based on the principle of gas-liquid balance, significantly reduces the solubility of H2S in water through vacuuming and moderate heating, providing an escape path for it. This allows for the forced stripping of H2S in its free molecular state from the water using physical methods without the addition of chemical reagents. Removing 60%–90% of sulfides (mainly free H2S) greatly reduces the processing load and reagent consumption of the subsequent complexed iron catalytic oxidation unit, significantly lowering overall operating costs. High concentrations of free H2S may undergo unnecessary side reactions with catalysts or other reagents. Pre-removal makes the subsequent chemical desulfurization process more stable and efficient. The removed high-concentration H2S gas can be centrally treated and used to recover sulfur, achieving preliminary resource utilization of sulfides.

[0134] The gas stripping device can efficiently remove free H2S, but it is not effective against H2S in ionic form (HS-S). - S 2- The removal effect of existing sulfides is limited. However, the complexed iron catalytic oxidation technology of this invention is well-suited for treating these difficult-to-remove bound sulfides. The combination of the two forms a gradient treatment process of "physical stripping + chemical oxidation", achieving an optimal balance between efficiency and cost.

Claims

1. A method for desulfurization of wastewater from oil and gas fields, characterized in that, Includes the following steps: S100. Adjust the pH of sulfur-containing wastewater to 8.0~9.0 and add sulfur granules as a regulator; S200: Add a composite complex iron catalyst to the wastewater treated in step S100 and carry out a catalytic oxidation reaction under the condition that the dissolved oxygen concentration is controlled at 2~8 mg / L. S300, by adding an air flotation separator, separates the generated sulfur particles from the aqueous phase to obtain sulfur-enriched foam and desulfurized wastewater; S400: Add an oxidation-reduction regulator to the separated desulfurization wastewater and restore catalyst activity by controlling the oxidation-reduction potential within the range of 150~250mV. S500, with the addition of flocculants and pH adjusters, ensures that the treated water meets discharge standards; In step S100, the sulfur particle regulator is a compound of sodium dodecyl sulfate and polyethylene glycol. In step S200, the composite complexed iron catalyst is prepared by the following method: first, the main complexing agent, auxiliary stabilizer and antioxidant are dissolved in water to form a mixture, and stirring is maintained. Under the conditions of pH 4.0~6.0 and system temperature below 40℃, ferrous sulfate aqueous solution is added dropwise to the mixture to carry out the complexation reaction, and then it is matured for 30~60 min to obtain a homogeneous catalyst solution.

2. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, In step S100, the mass ratio of sodium dodecyl sulfate to polyethylene glycol is 1:2~4, and the amount of sulfur particle regulator added is 10~50 mg / L.

3. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, The molar ratio of ferrous sulfate to the main complexing agent is 1:1.5~2.5, and the molar ratio of the main complexing agent, auxiliary stabilizer and antioxidant is 1:0.2~0.5:0.05~0.

15.

4. The method for desulfurization of oil and gas field wastewater according to claim 3, characterized in that, The primary complexing agent is selected from at least two of citrate, tartrate, or gluconate; the secondary stabilizer is selected from triethanolamine or ethylenediamine; and the antioxidant is selected from catechol or hydroquinone.

5. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, In step S200, the conditions for the catalytic oxidation reaction are: temperature 40~60℃, reaction time 30~90min.

6. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, In step S300, the air flotation separator is a compound of cationic and anionic surfactants, with a mass ratio of cationic to anionic surfactant of 1:1~3 and an addition amount of 5~20 mg / L; the anionic surfactant is selected from sodium dodecylbenzenesulfonate or sodium dodecyl sulfate; the cationic surfactant is selected from hexadecyltrimethylammonium chloride or dialkyldimethylammonium bromide.

7. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, In step S400, the redox regulator is a composite system of hydrogen peroxide and sodium bisulfite. Hydrogen peroxide and sodium bisulfite are added at a redox equivalent ratio of 1:0.8-1.

2. The redox potential is maintained in the range of 150~250mV by controlling the amount of redox regulator added at one time.

8. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, In step S500, the flocculant is a composite flocculation system of polyaluminum chloride and polyacrylamide, with a dosage of 20~100 mg / L for polyaluminum chloride and a dosage of 0.5~5 mg / L for polyacrylamide.

9. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, It also includes a catalyst recovery step: the effluent purified in step S500 is separated by nanofiltration membrane, and the retained catalyst concentrate is returned to step S200 for recycling.

10. The method for desulfurization of oil and gas field wastewater according to claim 1, characterized in that, It also includes a sulfur purification step: the sulfur-enriched foam obtained in step S300 is added to a melting agent and melted and separated at 80~120℃ to obtain a sulfur product with a purity ≥99.5%; the melting agent is a mixed solvent of carbon disulfide and toluene, and the volume ratio of carbon disulfide to toluene is 1:1~3.