A method for extracting lithium from oil and gas field produced water based on a full membrane method

Abstract

This invention belongs to the field of oil and gas field produced water treatment technology. It provides a method for lithium extraction from oil and gas field produced water based on a full-membrane process. The produced water is pretreated to obtain pretreated produced water; this pretreated produced water is then treated by a nanofiltration membrane device to obtain a high-valence ion concentrate and nanofiltration produced water; the nanofiltration produced water is then treated by a reverse osmosis membrane device to obtain a monovalent ion concentrate and purified water; the monovalent ion concentrate is then treated by a membrane distillation device equipped with a fluorinated polytetrafluoroethylene (PTFE) filter membrane. A heat source is provided on the feed side to heat the monovalent ion concentrate into water vapor, which passes through the PTFE filter membrane and is condensed into purified water by a cold source; the monovalent ions are further concentrated to obtain a lithium-rich concentrate; this lithium-rich concentrate is then transported to a lithium precipitation device, heated and stirred, and Na₂CO₃ or Na₃PO₄ is added. After lithium precipitation, the solution is filtered, washed, and dried to obtain Li₂CO₃ or Li₃PO₄. This invention enables the extraction of high-value lithium salts.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field produced water treatment technology, specifically relating to a method for lithium extraction from oil and gas field produced water based on a full-membrane method. Background Technology

[0002] Produced water from oil and gas fields typically contains large amounts of suspended solids and organic matter, and is characterized by high mineralization. Existing engineering operations usually employ a pretreatment method of "flocculation-softening to remove hardness-advanced oxidation-filtration" to remove suspended solids, organic matter, and most of the calcium. 2+ Mg 2+ Scaling ions. The pretreated effluent still contains a large amount of Li. + K + Na + Monovalent ions and some Ca 2+ Mg 2+ Deep desalination of pretreated effluent and extraction of high-value lithium salts can not only treat high-salt wastewater but also create huge economic benefits.

[0003] Therefore, it is of great significance to develop an efficient, economical, and environmentally friendly method for extracting high-value lithium salts. Summary of the Invention

[0004] To address the problems existing in the background technology, this invention provides a lithium extraction method for oil and gas field produced water based on a full-membrane method. This method removes suspended solids, organic matter, and most of the calcium from the produced water after pretreatment processes such as flocculation, softening and hardening removal, advanced oxidation, and filtration. 2+ Mg 2+ The effluent after scaling and ion formation undergoes further treatment to achieve the extraction of high-value lithium salts.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for lithium extraction from produced water in oil and gas fields based on a full-membrane process, wherein the produced water is pretreated to obtain pretreated produced water, comprising the following steps: S1. The pretreated effluent is treated with a nanofiltration membrane device to remove residual Ca. 2+ Mg 2+ High-valence ions reduce the hardness of the produced water and decrease calcium content. 2+ Mg 2+ This reduces interference with subsequent lithium precipitation processes and minimizes the risk of scaling in the entire membrane system piping, resulting in high-valence ion concentrate and nanofiltration permeate. S2. The nanofiltration effluent obtained in S1 is treated by a reverse osmosis membrane device to remove monovalent ions, resulting in a Li-rich solution. + K + Na +The solution contains monovalent ions, a concentrated solution of monovalent ions, and purified water. The purified water can be used to wash the lithium precipitate in the subsequent lithium precipitation step.

[0006] S3. The monovalent ion concentrate obtained in S2 is processed by a membrane distillation device. The membrane distillation device is equipped with a fluorine-modified polytetrafluoroethylene filter membrane. The feed side is equipped with a heat source for heating the monovalent ion concentrate into water vapor. The water vapor passes through the fluorine-modified polytetrafluoroethylene filter membrane and is condensed into purified water by a cold source set on the permeate side. The monovalent ions are further concentrated to obtain a lithium-rich concentrate. S4. The lithium-rich concentrate obtained in S3 is transferred to a lithium precipitation device. While heating and stirring, Na2CO3 or Na3PO4 and Li are added. + After the reaction, lithium precipitates and is then filtered, washed, and dried to obtain Li2CO3 or Li3PO4.

[0007] Preferably, the preparation method of the fluorine-modified polytetrafluoroethylene filter membrane is as follows: A1. Clean the surface of the polytetrafluoroethylene filter membrane with acetone, dry it, and set it aside. A2. Place the dried membrane obtained in A1 in a reaction chamber, evacuate, introduce fluorocarbon gas, and apply radio frequency glow discharge treatment for 50-80 minutes to obtain the final product.

[0008] Preferably, in A1, the drying temperature is 55-60℃ and the drying time is 23-25h.

[0009] Preferably, in A2, a vacuum is drawn to 5-20 Pa, and fluorocarbon gas is introduced to a concentration of 25-35%.

[0010] Preferably, the high-valence ion concentrate obtained in S1 is transported to a nanofiltration concentrate treatment tank for precipitation treatment.

[0011] Preferably, NaOH and Na₂CO₃ are added to the nanofiltration concentrate treatment tank to remove Ca. 2+ Mg 2+ They are converted into Mg(OH)2 precipitate and CaCO3 precipitate, respectively.

[0012] Preferably, in S3, the water temperature on the raw material side is controlled at 80°C by a heat source, and the water temperature on the permeation side is controlled at 20°C by a cold source.

[0013] Preferably, in the lithium-rich concentrate, Li + ≥5000mg / L.

[0014] Preferably, the lithium precipitate is rich in K. + Na + The concentrated liquid was crystallized stepwise into potassium chloride and sodium chloride using a cooling crystallization method.

[0015] This application has the following beneficial effects: This invention integrates and couples multiple membrane separation methods and processes to develop a highly efficient, economical, and environmentally friendly all-membrane staged desalination and lithium extraction technology for the pretreatment of produced water from oil and gas fields. Through the synergistic effect of the all-membrane process—nanofiltration membrane, reverse osmosis membrane, and membrane distillation—Li is gradually extracted. + The enrichment of lithium yields a concentrated lithium precipitation solution. The main focus is on optimizing the desalination process and modularizing the technology to achieve purified and reused produced water, extract high-value lithium salts, and generate significant economic benefits. This provides technical support for produced water treatment and lithium extraction in oil and gas fields and is of great importance for achieving energy conservation, emission reduction, cost reduction, and efficiency improvement.

[0016] In this invention, the polytetrafluoroethylene (PTFE) filter membrane is hydrophobic; its surface tension prevents water molecules from directly passing through the membrane pores, but water vapor can pass through freely. The microporous structure of the PTFE filter membrane (pore size 0.2-1 μm, porosity 35%-80%) effectively blocks liquid water and ions, allowing only water vapor to pass through, thereby achieving Li + Enrichment of Li; Water on the feed side (heat source side) evaporates at 80°C to form steam, and steam molecules diffuse through the membrane pores to the permeate side (cold source side). A significant temperature difference exists between the heat source side (80°C) and the cold source side (20°C), creating a vapor pressure difference that drives water vapor to transfer from the high-temperature side to the low-temperature side and through the membrane pores. + The concentration was increased to ≥5000 mg / L in the concentrate. The cold-side steam condensed to form purified water, while Li... + K + Na + Plasma is trapped in the concentrate because it is not easily volatile.

[0017] In the preparation of fluorinated polytetrafluoroethylene (PTFE) filter membranes, fluorination introduces fluorine atoms (with the highest electronegativity), resulting in a significant negative shift in the zeta potential of the membrane surface. The negatively charged membrane surface hinders the flow of Li through electrostatic repulsion. + The permeation of positively charged molecules increases its rejection rate. Furthermore, the hydrophobicity of the fluorinated polytetrafluoroethylene (PTFE) filter membrane is further enhanced. This enhanced hydrophobicity reduces the wettability of water on the membrane, decreases the formation of aqueous channels, and forces Li... + The pathway through the membrane, which relies on hydration, is blocked. Attached Figure Description

[0018] Figure 1 A schematic diagram of the lithium extraction system for produced water in oil and gas fields based on the all-membrane method of this invention.

[0019] Explanation of reference numerals in the attached figures: 1. Nanofiltration membrane unit; 2. Nanofiltration concentrate treatment tank; 3. Reverse osmosis membrane unit; 4. Reverse osmosis concentrate tank; 5. Membrane distillation unit; 6. Lithium precipitation unit. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0021] Example 1: (a) The preparation method of fluorine-modified polytetrafluoroethylene filter membrane is as follows: A1. Clean the surface of the polytetrafluoroethylene (PTFE) filter membrane with acetone and dry it at 60°C for 24 hours. The PTFE filter membrane used is a commercially available hydrophobic PTFE membrane purchased from Tianjin Luohua Technology Co., Ltd.

[0022] A2. Place the dried membrane obtained in A1 in a special fluorination reaction chamber, evacuate to 10 Pa, introduce fluorocarbon gas to a concentration of 30%, and apply radio frequency glow discharge treatment for 60 min to obtain fluorine-modified polytetrafluoroethylene filter membrane.

[0023] (II) A lithium extraction method for oil and gas field produced water based on a full-membrane process. This method removes suspended solids, organic matter, and most of the calcium from oil and gas field produced water through pretreatment methods such as flocculation, softening and hardening removal, advanced oxidation, and filtration. 2+ Mg 2+ After the scale ions have settled, the produced water undergoes advanced treatment to extract high-value lithium salts, thereby realizing the resource utilization and compliant discharge of produced water from oil and gas fields.

[0024] Specifically, produced water from oil and gas fields is pretreated to obtain pretreated produced water, which is then used... Figure 1 The lithium extraction system for produced water from oil and gas fields, based on the all-membrane method, is shown for lithium extraction operations. The system includes, via pipelines, a nanofiltration concentrate treatment tank 2, a nanofiltration membrane unit 1, a reverse osmosis membrane unit 3, a reverse osmosis concentrate tank 4, a membrane distillation unit 5, and a lithium precipitation unit 6. The steps are as follows: S1, Ca 2+ =500 mg / L, Mg 2+ =500 mg / L, Li + =100mg / L, K + =500 mg / L, Na + Pretreated effluent with a concentration of 500 mg / L is pumped into a nanofiltration membrane unit via a booster pump to remove Ca from the water. 2+ Mg 2+ High-valence ions reduce the hardness of the produced water and decrease Ca2+. 2+ Mg2+ This reduces the risk of interference with subsequent lithium deposition processes and minimizes the risk of fouling in the entire membrane system's piping.

[0025] Ca in nanofiltration membrane product water 2+ =5mg / L, Mg 2+ =4.3mg / L, Li + =98mg / L, K + =483mg / L, Na + =489mg / L, permeate flux controlled at 25L·m -2 ·h -1 The high-valence ion concentrate from the nanofiltration membrane device is fed into the nanofiltration concentrate treatment tank, where NaOH and Na₂CO₃ are added to remove Ca²⁺ ions. 2+ Mg 2+ They are converted into Mg(OH)2 precipitate and CaCO3 precipitate, respectively.

[0026] S2. The nanofiltration membrane effluent is pumped into the reverse osmosis membrane unit for deep desalination to produce purified water, while simultaneously obtaining Li-rich water. + K + Na + The concentrate contains monovalent ions, and the purified water is used for washing the lithium precipitate in the subsequent lithium precipitation step. The permeate flux is controlled at 8 L·m³. -2 ·h -1 Monovalent ion concentrate is fed into the reverse osmosis concentrate tank. The concentrate contains Li... + =511mg / L, K + =2470mg / L, Na + =2437mg / L.

[0027] S3. The monovalent ion concentrate in the reverse osmosis concentrate tank is fed into the membrane distillation unit via a centrifugal pump. The unit operates at atmospheric pressure, and the membrane material is a fluorinated polytetrafluoroethylene (PTFE) filter membrane. The water temperature on the feed side of the membrane distillation is controlled at 80°C by adjusting the heat source. After evaporation, the water permeates through the membrane as steam. The temperature on the permeate side of the membrane distillation is controlled at 20°C by a cold source. The permeated water vapor condenses to obtain purified water, containing non-volatile Li. + K + Na + Further concentration yields a lithium-rich concentrate that meets the requirements for lithium precipitation. The Li in the lithium-rich concentrate... + =5136mg / L.

[0028] Polytetrafluoroethylene (PTFE) filter membranes are hydrophobic; their surface tension prevents water molecules from directly passing through the membrane pores, but water vapor can pass through freely. The microporous structure of PTFE filter membranes (pore size 0.2-1 μm, porosity 35%-80%) effectively blocks liquid water and ions, allowing only water vapor to pass through, thus achieving Li…+ Enrichment of Li; Water on the feed side (heat source side) evaporates at 80°C to form steam, and steam molecules diffuse through the membrane pores to the permeate side (cold source side). A significant temperature difference exists between the heat source side (80°C) and the cold source side (20°C), creating a vapor pressure difference that drives water vapor to transfer from the high-temperature side to the low-temperature side and through the membrane pores. + The concentration was increased to ≥5000 mg / L in the concentrate. The cold-side steam condensed to form purified water, while Li... + K + Na + Plasma is trapped in the concentrate because it is not easily volatile.

[0029] In the preparation of fluorinated polytetrafluoroethylene (PTFE) filter membranes, fluorination introduces fluorine atoms (with the highest electronegativity), resulting in a significant negative shift in the zeta potential of the membrane surface. The negatively charged membrane surface hinders the flow of Li through electrostatic repulsion. + The permeation of positively charged molecules increases its rejection rate. Furthermore, the hydrophobicity of the fluorinated polytetrafluoroethylene (PTFE) filter membrane is further enhanced. This enhanced hydrophobicity reduces the wettability of water on the membrane, decreases the formation of aqueous channels, and forces Li... + The pathway through the membrane, which relies on hydration, is blocked.

[0030] S4. Input the lithium-rich concentrate into the lithium precipitation device, maintain the overall temperature of the device at 90℃, and then add Na2CO3 or Na3PO4 and Li during stirring. + The reaction, followed by filtration, washing, and drying, yields Li₂CO₃ or Li₃PO₄. The lithium precipitate is rich in potassium (K). + Na + The temperature of the concentrated solution was maintained at approximately 90°C. Based on the difference in solubility of potassium chloride and sodium chloride at different temperatures, a cooling crystallization method was used to crystallize them stepwise into potassium chloride and sodium chloride.

[0031] In this embodiment, the final purified water Li + =0.12mg / L.

[0032] This invention integrates and couples multiple membrane separation methods and processes to develop a highly efficient, economical, and environmentally friendly all-membrane staged desalination and lithium extraction technology for the pretreatment of produced water from oil and gas fields. Through the synergistic effect of the all-membrane process—nanofiltration membrane, reverse osmosis membrane, and membrane distillation—Li is gradually extracted. + The enrichment of lithium yields a concentrated lithium precipitation solution. The main focus is on optimizing the desalination process and modularizing the technology to achieve purified and reused produced water, extract high-value lithium salts, and generate significant economic benefits. This provides technical support for produced water treatment and lithium extraction in oil and gas fields and is of great importance for achieving energy conservation, emission reduction, cost reduction, and efficiency improvement.

[0033] Comparative Example 1: The only difference between this comparative example and Example 1 is that the fluorine-modified polytetrafluoroethylene filter membrane is replaced with a commercially available hydrophobic polytetrafluoroethylene filter membrane.

[0034] In this comparative example, the final purified water Li was obtained + =0.51mg / L.

[0035] A comparison between Example 1 and Comparative Example 1 shows that, compared to Comparative Example 1 which used a commercially available hydrophobic polytetrafluoroethylene filter membrane, the purified water Li + =0.51 mg / L, Example 1 uses the fluorine-modified polytetrafluoroethylene filter membrane of the present invention to obtain purified water Li + =0.12mg / L, Li + The significantly lower content indicates that the fluorine-modified polytetrafluoroethylene filter membrane of this invention is more conducive to lithium extraction, thereby reducing the Li content in purified water. + content.

[0036] This is mainly because the polytetrafluoroethylene (PTFE) filter membrane in this invention is hydrophobic, and its surface tension prevents water molecules from directly passing through the membrane pores, while allowing water vapor to pass freely. The microporous structure of the PTFE filter membrane (pore size 0.2-1 μm, porosity 35%-80%) effectively blocks liquid water and ions, allowing only water vapor to pass through, thereby achieving Li + Enrichment of Li; Water on the feed side (heat source side) evaporates at 80°C to form steam, and steam molecules diffuse through the membrane pores to the permeate side (cold source side). A significant temperature difference exists between the heat source side (80°C) and the cold source side (20°C), creating a vapor pressure difference that drives water vapor to transfer from the high-temperature side to the low-temperature side and through the membrane pores. + The concentration was increased to ≥5000 mg / L in the concentrate. The cold-side steam condensed to form purified water, while Li... + K + Na + Plasma is retained in the concentrate due to its low volatility. In the preparation of fluorinated polytetrafluoroethylene (PTFE) filter membranes, fluorination introduces fluorine atoms (with the highest electronegativity), significantly shifting the zeta potential of the membrane surface negatively. The negatively charged membrane surface hinders Li+ flow through electrostatic repulsion. + The permeation of positively charged molecules increases its rejection rate. Furthermore, the hydrophobicity of the fluorinated polytetrafluoroethylene (PTFE) filter membrane is further enhanced. This enhanced hydrophobicity reduces the wettability of water on the membrane, decreases the formation of aqueous channels, and forces Li... + The pathway through the membrane, which relies on hydration, is blocked.

[0037] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0038] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for lithium extraction from produced water in oil and gas fields based on a full-membrane process, wherein the produced water from the oil and gas field is pretreated to obtain pretreated produced water, characterized in that, Includes the following steps: S1, treating the pretreated effluent water through a nanofiltration membrane device to retain residual Ca 2+ , Mg 2+ high valence ions to obtain a high valence ion concentrate and nanofiltration effluent water; S2. The nanofiltration effluent obtained in S1 is processed through a reverse osmosis membrane device to remove monovalent ions, resulting in monovalent ion concentrate and purified water. S3. The monovalent ion concentrate obtained in S2 is processed by a membrane distillation device. The membrane distillation device is equipped with a fluorine-modified polytetrafluoroethylene filter membrane. The feed side is equipped with a heat source for heating the monovalent ion concentrate into water vapor. The water vapor passes through the fluorine-modified polytetrafluoroethylene filter membrane and is condensed into purified water by a cold source set on the permeate side. The monovalent ions are further concentrated to obtain a lithium-rich concentrate. S4, the lithium-rich concentrated solution obtained in S3 is transported to a lithium precipitation device, while being heated and stirred, Na2CO3 or Na3PO4 and Li + After lithium precipitation, the solution is filtered, washed, and dried to obtain Li2CO3 or Li3PO4.

2. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 1, characterized in that, The preparation method of the fluorine-modified polytetrafluoroethylene filter membrane is as follows: A1. Clean the surface of the polytetrafluoroethylene filter membrane with acetone, dry it, and set it aside. A2. Place the dried membrane obtained in A1 in a reaction chamber, evacuate, introduce fluorocarbon gas, and apply radio frequency glow discharge treatment for 50-80 minutes to obtain the final product.

3. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 2, characterized in that, In A1, the drying temperature is 55-60℃ and the drying time is 23-25h.

4. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 2, characterized in that, In A2, a vacuum is drawn to 5-20 Pa, and fluorocarbon gas is introduced until the concentration is 25-35%.

5. The method for lithium extraction from produced water in oil and gas fields based on the full-film method according to claim 1, characterized in that, The high-valence ion concentrate obtained from S1 is transported to a nanofiltration concentrate treatment tank for precipitation treatment.

6. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 5, characterized in that, NaOH and Na2CO3 were added to the nanofiltration concentrate treatment tank to convert Ca 2+ , Mg 2+ to Mg(OH)2 precipitate and CaCO3 precipitate, respectively.

7. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 1, characterized in that, In S3, the water temperature on the raw material side is controlled at 80℃ by a heat source, and the water temperature on the permeation side is controlled at 20℃ by a cold source.

8. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 1, characterized in that, In the lithium-rich concentrate, Li + ≥5000mg / L.

9. The method for lithium extraction from produced water in oil and gas fields based on the full-membrane method according to claim 1, characterized in that, The K-rich area after lithium precipitation + Na + The concentrated liquid was crystallized stepwise into potassium chloride and sodium chloride using a cooling crystallization method.

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