A permeation membrane for high-efficiency oil-gas separation, its preparation method and application

Abstract

This invention relates to the field of permeate membrane preparation, specifically disclosing a method for preparing and applying a permeate membrane for high-efficiency oil-gas separation, comprising the following steps: (1) preparation of primary modified polytetrafluoroethylene; (2) preparation of secondary modified polytetrafluoroethylene; and (3) preparation of the permeate membrane. The permeate membrane disclosed in this invention can be used for dissolved gas analysis in transformer oil, achieving high-efficiency oil-gas separation, and significantly improving both permeability and mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of permeate membrane preparation, and specifically discloses a permeate membrane for high-efficiency oil-gas separation, its preparation method, and its application. Background Technology

[0002] Transformers are crucial operating equipment in power systems, and their proper functioning significantly impacts the safe operation of the power grid. Under the influence of heat and electricity, the insulating oil inside a transformer decomposes, producing seven characteristic gases: H2, CO, CO2, CH4, C2H2, C2H4, and C2H6, which dissolve in the oil. The presence of latent overheating or discharge faults accelerates the production of these gases. By detecting the dissolved gas content in the insulating oil, the type and severity of transformer faults can be analyzed promptly. Oil-gas separation is a vital step in the analysis of dissolved gases in transformer oil, and permeate membrane degassing is one of the most commonly used methods for this process.

[0003] Membrane material is the most critical factor affecting the performance of gas separation membranes. An ideal gas separation membrane should have excellent thermochemical stability, high mechanical strength, and good permeation selectivity. More commonly used membrane materials are organic polymer membranes, such as polyvinyl chloride, polyvinylidene fluoride, and polyether block amide membranes.

[0004] Patent application number 202310297489.2 discloses an oil-gas separation membrane for online transformer testing and its preparation method, comprising: Step 1, spreading liquid fluorosilicone rubber on a flat plate and curing it to form a thin film; Step 2, mixing and dispersing Hyflon AD60 with perfluoropolyether thermally conductive liquid evenly, adding α-phase nano-alumina powder, dispersing evenly to obtain a casting solution; Step 3, coating the casting solution onto the thin film, allowing it to stand, covering it with a pressure plate, and heating it to 180-220℃ in a drying oven for 3-10 hours; Step 4, allowing it to stand under high pressure for 24-48 hours, then placing it again in a preheated drying oven for 6-12 hours, and cooling to obtain the final product. The preparation method of this invention is mild, resulting in an oil-gas separation membrane with high mechanical strength and a short oil-gas separation time. The short oil-gas separation time of the oil-gas separation membrane disclosed in this invention can significantly improve the efficiency of online transformer testing and shorten the testing cycle.

[0005] However, the main component of the disclosed oil-gas separation membrane, fluorosilicone rubber, is not resistant to hot air aging, and its stability and durability are insufficient. Furthermore, the gas separation capacity of this membrane still has room for improvement. Meanwhile, existing permeate membrane materials suffer from low permeability and poor mechanical properties, directly leading to long gas analysis times, low efficiency, and problems such as membrane rupture and oil leakage during prolonged operation. Therefore, a degassing membrane with superior permeability and mechanical properties is urgently needed in the oil-gas separation stage of dissolved gas analysis in transformer oil.

[0006] In view of this, the present invention discloses a permeation membrane for efficient oil and gas separation, which is of particular importance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention discloses a permeation membrane for efficient oil-gas separation, its preparation method, and its applications. The permeation membrane disclosed in this invention can be used for dissolved gas analysis in transformer oil, achieving highly efficient oil-gas separation, and its permeability and mechanical strength are significantly improved.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for preparing a permeation membrane for efficient oil-gas separation, comprising the following steps:

[0010] (1) Preparation of primary modified polytetrafluoroethylene: Polytetrafluoroethylene is pretreated by plasma to obtain primary modified polytetrafluoroethylene.

[0011] (2) Preparation of secondary modified polytetrafluoroethylene: primary modified polytetrafluoroethylene and organic solvent are mixed, graft modifier, crosslinking agent and initiator are added, the temperature is raised to 50-70℃, the reaction is carried out for 2-5 hours, and after washing and drying, secondary modified polytetrafluoroethylene is obtained.

[0012] (3) Preparation of permeation membrane: Add secondary modified polytetrafluoroethylene and organic solvent to the reactor and stir for 1-3 hours. Then add modified fumed silica and stir for 2-4 hours to obtain a mixture. Place the mixture in an oven to remove bubbles and spin-coat it onto a dry and smooth substrate to form a membrane. Dry it at room temperature to obtain the permeation membrane.

[0013] Preferably, in step (3), the spin coating film is formed by dispensing adhesive while rotating at a speed of 200 to 800 r / min. After completion, the speed is increased to 1000 to 2000 r / min and rotated for 30 seconds to 1 minute.

[0014] In some embodiments of the present invention, in step (1), the plasma pretreatment is performed with a discharge spacing of 8 mm, a discharge power of 10000 Hz, a voltage of 30-50 V, a current of 1-3 A, and a treatment time of 2-10 min.

[0015] In some embodiments of the present invention, in step (2), the grafting modifier is polysilazane.

[0016] In some embodiments of the present invention, in step (2), the mass ratio of the primary modified polytetrafluoroethylene to the graft modifier is 10:(2-3).

[0017] Preferably, in step (2), the mass ratio of the primary modified polytetrafluoroethylene to the graft modifier is 10:2.5.

[0018] In some embodiments of the present invention, in step (3), the amount of modified fumed silica added is 0.3 to 1% of the mass of the secondary modified polytetrafluoroethylene.

[0019] Preferably, in step (3), the amount of modified fumed silica added is 0.6% of the mass of the secondary modified polytetrafluoroethylene.

[0020] In some embodiments of the present invention, the preparation steps of the modified fumed silica are as follows:

[0021] 1) Add water, ethanol and modifier to the reactor, adjust the pH to 5-7, stir for 20-30 min, then add fumed silica, stir at room temperature for 1-3 h, centrifuge, wash and dry to obtain pretreated fumed silica.

[0022] 2) Add fumed silica and the pretreated fumed silica from step 1) to the reactor and stir to obtain modified fumed silica.

[0023] In some embodiments of the present invention, in step 1), the modifier is a composite of KH-570 and hexamethyldisilazane.

[0024] Preferably, in step 1), the mass ratio of KH-570 to hexamethyldisilazane is (1-3):1.

[0025] More preferably, in step 1), the mass ratio of KH-570 to hexamethyldisilazane is 2:1.

[0026] In some embodiments of the present invention, in step 1), the mass ratio of the modifier to fumed silica is (1-1.5):1.

[0027] Preferably, in step 1), the mass ratio of the modifier to fumed silica is 1.3:1.

[0028] In some embodiments of the present invention, in step 2), the mass ratio of the fumed silica to the pretreated fumed silica is 1:(0.5-1).

[0029] Preferably, in step 2), the mass ratio of the fumed silica to the pretreated fumed silica is 1:0.75.

[0030] Preferably, in step 2), the average particle size of the fumed silica is 100–300 nm.

[0031] More preferably, in step 2), the average particle size of the fumed silica is 200 nm.

[0032] Among many polymers, polytetrafluoroethylene (PTFE) has strong comprehensive properties and is an ideal organic substrate for preparing high-performance permeation membranes. However, it has a high thermal expansion coefficient and poor resistance to overheating. When heated, its fiber-knot structure will shrink, leading to a decrease in the overall performance of the permeation membrane. When used as a permeation membrane for transformer diagnostic analysis, its fatigue strength is significantly insufficient, and it is prone to failure.

[0033] This invention first pretreats polytetrafluoroethylene (PTFE) with plasma, then grafts it with a grafting modifier, and finally blends it with modified fumed silica to obtain a mixture, which is then spin-coated to obtain a permeate membrane. The introduction of a grafting modifier in this invention further improves the hydrophobicity of the permeate membrane, accelerating the dissolution rate of gas within the membrane during oil-gas separation. Simultaneously, the durability and dimensional stability of the PTFE membrane after formation are effectively improved, effectively delaying the thermal shrinkage phenomenon of the permeate membrane under high-pressure and overheating conditions. This may be because the specific modified fumed silica deposits and fills the fiber-knot structure of the PTFE, synergistically preventing shrinkage with the grafted hydrophobic segments.

[0034] In the field of permeable membranes, there is always an upper limit effect between the permeability and selectivity of permeable membranes. Inorganic matrices are often incorporated into the preparation process of organic membranes, serving as the dispersed phase. This aims to leverage the unique advantages of inorganic particles in gas adsorption and separation, such as high flux and good mechanical strength, to address the shortcomings of existing organic polymer permeable membranes in this regard. However, current technologies mostly employ physical blending, where the inorganic matrix is ​​merely coated by the polymer, resulting in weak interaction forces and insufficient utilization. There is still room for improvement in the utilization efficiency of inorganic matrices.

[0035] Based on this, the present invention first adds a composite modifier to hydrophobically modify fumed silica, then blends it with fumed silica of the same nanoscale, and finally composites it with polytetrafluoroethylene (PTFE). On the one hand, this solves the problem of poor modification effect of commonly used modifiers on fumed silica, where uneven dispersion still occurs in the polymer system when the amount added increases. In this case, the mixed fumed silica and PTFE are used to prepare a permeation membrane for oil-gas separation. When subjected to external stress impact, the fumed silica migrates, absorbing or buffering the impact energy. On the other hand, the fumed silica modified by the composite of KH-570 and hexamethyldisilazane to a certain extent hinders the movement of PTFE chains, jointly playing a role in toughening and enhancing the mechanical strength of the permeation membrane. Furthermore, it further increases the specific surface area of ​​the fumed silica, increases the volume of the amorphous region between it and the polymer, and further increases the gas flux.

[0036] In another aspect, the present invention provides a permeation membrane for efficient oil-gas separation obtained by the above preparation method, wherein the thickness of the permeation membrane is 40-70 μm.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The present invention pre-treats polytetrafluoroethylene with plasma, then grafts it with a grafting modifier, and finally mixes it with modified fumed silica to obtain a mixture. The mixture is then spin-coated to obtain a permeable membrane. When used for dissolved gas analysis in transformer oil, it can achieve efficient oil-gas separation, and its permeability and mechanical strength are significantly improved.

[0039] (2) The present invention introduces a grafting modifier to further improve the hydrophobicity of the permeation membrane, which promotes the gas dissolution rate in the membrane during oil-gas separation; at the same time, the tolerance and dimensional stability of the polytetrafluoroethylene membrane after formation are also effectively improved, effectively delaying the thermal shrinkage phenomenon of the permeation membrane under high pressure and overheating environment.

[0040] (3) The present invention uses a composite modifier to hydrophobically modify a specific fumed silica, blends it with fumed silica of the same nanoscale, and then composites it with polytetrafluoroethylene. On the one hand, it solves the problem that commonly used modifiers have poor modification effect on fumed silica and that it still has uneven dispersion in the polymer system when the amount added is increased; on the other hand, it plays a role in toughening and enhancing the mechanical strength of the permeable membrane; and on the other hand, it increases the volume of the amorphous region between fumed silica and polymer, further increasing the gas flux. Detailed Implementation

[0041] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0042] Unless otherwise specified, all reagents used below are readily available from commercial companies. Polysilazane was purchased from Perry Technology Co., Ltd., and polytetrafluoroethylene was purchased from Dongguan Hongyu Plastics Co., Ltd.

[0043] Unless otherwise specified, the average particle size of the fumed silica used below is 200 nm.

[0044] Preparation Example 1

[0045] The preparation steps of modified fumed silica are as follows:

[0046] 1) Add 20 mL of water, 80 mL of ethanol, 4.35 g of KH-570 and 2.15 g of hexamethyldisilazane to the reactor, adjust the pH to 6, stir for 25 min, then add 5 g of fumed silica, stir at room temperature for 2 h, centrifuge, wash and dry to obtain pretreated fumed silica.

[0047] 2) Mix 10g of fumed silica and 7.5g of the pretreated fumed silica from step 1) to obtain modified fumed silica.

[0048] Preparation Example 2

[0049] The preparation steps for modified fumed silica are the same as in Preparation Example 1, except that 6.5g of KH-570 is added in step 1).

[0050] Preparation Example 3

[0051] The preparation steps for modified fumed silica are the same as in Preparation Example 1, except that 4g of fumed silica is added in step 1).

[0052] Preparation Example 4

[0053] The preparation steps for modified fumed silica are the same as in Preparation Example 1, except that 11g of pretreated fumed silica is added in step 2).

[0054] Example 1

[0055] A method for preparing a permeate membrane for efficient oil-gas separation includes the following steps:

[0056] (1) Preparation of primary modified polytetrafluoroethylene: Polytetrafluoroethylene was treated with a discharge gap of 8 mm, a discharge power of 10000 Hz, a voltage of 40 V, and a current of 2 A for 6 min to obtain primary modified polytetrafluoroethylene.

[0057] (2) Preparation of secondary modified polytetrafluoroethylene: 10g of primary modified polytetrafluoroethylene and 30mL of n-butanol were mixed, and 2.5g of polysilazane, 1g of ethylene glycol and 0.013g of potassium persulfate were added. The mixture was heated to 60℃ and reacted for 3.5h. After washing and drying, secondary modified polytetrafluoroethylene was obtained.

[0058] (3) Preparation of permeation membrane: 50g of secondary modified polytetrafluoroethylene and 100mL of n-butanol were added to the reactor and stirred for 2h. Then 0.3g of modified fumed silica was added and stirred for 3h to obtain a mixture. The mixture was placed in an oven to remove bubbles and then dripped onto a dry and smooth substrate at a speed of 500r / min. After completion, the speed was increased to 1500r / min and rotated for 50s to form a film. The film was dried at room temperature for 1d to obtain a permeation membrane with a thickness of 55μm.

[0059] The modified fumed silica used in step (3) was obtained from preparation example 1.

[0060] Example 2

[0061] A method for preparing a permeate membrane for efficient oil-gas separation includes the following steps:

[0062] (1) Preparation of primary modified polytetrafluoroethylene: Polytetrafluoroethylene was treated with a discharge gap of 8 mm, a discharge power of 10000 Hz, a voltage of 30 V, and a current of 3 A for 2 min to obtain primary modified polytetrafluoroethylene.

[0063] (2) Preparation of secondary modified polytetrafluoroethylene: 10g of primary modified polytetrafluoroethylene and n-butanol were mixed, 2g of polysilazane, 1g of ethylene glycol and 0.01g of potassium persulfate were added, the temperature was raised to 50℃, and the reaction was carried out for 5h. After washing and drying, secondary modified polytetrafluoroethylene was obtained.

[0064] (3) Preparation of permeation membrane: 50g of secondary modified polytetrafluoroethylene and 100mL of n-butanol were added to the reactor and stirred for 1h. Then 0.15g of modified fumed silica was added and stirred for 2h to obtain a mixture. The mixture was placed in an oven to remove bubbles and then dripped onto a dry and smooth substrate at a speed of 200r / min. After completion, the speed was increased to 2000r / min and rotated for 30s to form a film. The film was dried at room temperature for 1d to obtain a permeation membrane with a thickness of 40μm.

[0065] The modified fumed silica used in step (3) was obtained from preparation example 1.

[0066] Example 3

[0067] A method for preparing a permeate membrane for efficient oil-gas separation includes the following steps:

[0068] (1) Preparation of primary modified polytetrafluoroethylene: Polytetrafluoroethylene was treated with a discharge gap of 8 mm, a discharge power of 10000 Hz, a voltage of 50 V, and a current of 1 A for 10 min to obtain primary modified polytetrafluoroethylene.

[0069] (2) Preparation of secondary modified polytetrafluoroethylene: 10g of primary modified polytetrafluoroethylene and n-butanol were mixed, 3g of polysilazane, 1g of ethylene glycol and 0.015g of potassium persulfate were added, the temperature was raised to 60℃ and the reaction was carried out for 3.5h. After washing and drying, secondary modified polytetrafluoroethylene was obtained.

[0070] (3) Preparation of permeation membrane: 50g of secondary modified polytetrafluoroethylene and 100mL of n-butanol were added to the reactor and stirred for 2h. Then 0.5g of modified fumed silica was added and stirred for 3h to obtain a mixture. The mixture was placed in an oven to remove bubbles and then dripped onto a dry and smooth substrate at a speed of 800r / min. After completion, the speed was increased to 1000r / min and the film was formed by rotation for 1min. The film was dried at room temperature for 1d to obtain a permeation membrane with a thickness of 70μm.

[0071] The modified fumed silica used in step (3) was obtained from preparation example 1.

[0072] Example 4

[0073] A method for preparing a permeation membrane for efficient oil and gas separation is described in the same way as in Example 1, except that the modified fumed silica used in step (3) is obtained from Preparation Example 2.

[0074] Example 5

[0075] A method for preparing a permeation membrane for efficient oil and gas separation is described in the same way as in Example 1, except that the modified fumed silica used in step (3) is obtained from Preparation Example 3.

[0076] Example 6

[0077] A method for preparing a permeation membrane for efficient oil and gas separation is described in the same way as in Example 1, except that the modified fumed silica used in step (3) is obtained from Preparation Example 4.

[0078] Example 7

[0079] A method for preparing a permeation membrane for efficient oil and gas separation, the specific implementation method is the same as in Example 1, except that the amount of polysilazane added in step (2) is 3.5g.

[0080] Example 8

[0081] A method for preparing a permeation membrane for efficient oil and gas separation, the specific implementation method is the same as in Example 1, the difference being that the amount of modified fumed silica added in step (3) is 0.6g.

[0082] Comparative Example 1

[0083] A method for preparing a permeation membrane for efficient oil and gas separation, the specific implementation method is the same as in Example 1, the difference being that 0.3g of fumed silica is added in step (3) to replace 0.3g of modified fumed silica.

[0084] Comparative Example 2

[0085] A method for preparing a permeate membrane for efficient oil-gas separation includes the following steps:

[0086] Add 50g of polytetrafluoroethylene and 100mL of n-butanol to the reactor and stir for 2 hours. Then add 0.3g of modified fumed silica and stir for 3 hours to obtain a mixture. Place the mixture in an oven to remove bubbles, and then apply it to a dry and smooth substrate while rotating at 500r / min to form a film. After completion, increase the speed to 1500r / min and rotate for 50s to form a film. Dry at room temperature for 1 day to obtain a permeation membrane with a thickness of 55μm.

[0087] The modified fumed silica used was obtained from Preparation Example 1.

[0088] Performance testing:

[0089] The permeation membranes prepared in Examples 1-8 and Comparative Examples 1-2 were subjected to the following performance tests:

[0090] (1) Mechanical strength performance test-1: Each permeation membrane was fixed with a metal perforated frame and sealed circumferentially on the top wall of the oil chamber. Each permeation membrane and the top of the oil chamber formed a gas chamber. Insulating oil was filled into the oil chamber below the metal perforated frame. The front port of the oil chamber was sealed to a gas cylinder. The pressure valve of the gas cylinder was adjusted to 500 kPa and maintained for 48 hours. The permeation membrane was tested for rupture, oil leakage or layer separation. The specific test results are shown in Table 1.

[0091] (2) Mechanical strength performance test-2: According to standard GB / T 1040, each permeation membrane was cut into strips of 5cm×1cm and tensile strength was tested using a CMT6104 electronic universal testing machine, with the tensile rate set to 10mm / min.

[0092] (3) Air permeability test: The air permeability of the permeation membrane was tested by the differential pressure method. Nitrogen and liquefied gas were mixed in a mixing tank at a volume ratio of 80:20 as the inlet gas and passed through the membrane module containing each permeation membrane at room temperature. The inlet gas pressure in the mixing tank was set to be maintained at 0.4 MPa. A soap bubble flow meter was connected to the other side of the membrane module to test the gas flow rate to characterize the air permeability of the permeation membrane.

[0093] Table 1

[0094]

[0095]

[0096] As shown in Table 1, the permeable membranes disclosed in Examples 1-3 of this invention have excellent performance in terms of air permeability and mechanical strength.

[0097] As can be seen from the comparison between Examples 4 and 5 and Example 1, when the amount of KH-570 and fumed silica added in step 1) is changed during the preparation of modified fumed silica, the mechanical strength of the permeation membrane will decrease significantly.

[0098] As can be seen from the comparison between Example 6 and Example 1, when the amount of pretreated fumed silica added in step 2) is changed during the preparation of modified fumed silica, the permeability and mechanical strength of the permeation membrane will deteriorate to varying degrees.

[0099] As can be seen from the comparison between Example 7 and Example 1, when the amount of polysilazane added in step (2) of the preparation method is changed, the permeability of the permeation membrane will become worse, which may be caused by the weakening of the dissolution and diffusion effect.

[0100] As can be seen from the comparison between Example 8 and Example 1, when the amount of modified fumed silica added in step (3) of the preparation method is changed, the mechanical strength of the permeation membrane will decrease due to the agglomeration effect.

[0101] As can be seen from the comparison between Comparative Example 1 and Example 1, when the modified fumed silica is replaced by an equal amount of fumed silica in step (3) of the preparation method, the mechanical strength of the permeation membrane is greatly affected, its brittleness increases and the interaction force between the components of the system decreases, resulting in poorer air permeability.

[0102] As can be seen from the comparison between Comparative Example 2 and Example 1, when unmodified polytetrafluoroethylene is added directly during the preparation of the permeation membrane, the mechanical strength of the permeation membrane will decrease, and oil leakage and layer separation will occur.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a high-efficiency oil-gas separation permeation membrane, characterized in that, Includes the following steps: (1) Preparation of primary modified polytetrafluoroethylene: Polytetrafluoroethylene is pretreated by plasma to obtain primary modified polytetrafluoroethylene. (2) Preparation of secondary modified polytetrafluoroethylene: primary modified polytetrafluoroethylene and organic solvent are mixed, graft modifier, crosslinking agent and initiator are added, the temperature is raised to 50-70℃, the reaction is carried out for 2-5 hours, and after washing and drying, secondary modified polytetrafluoroethylene is obtained. (3) Preparation of permeation membrane: Add secondary modified polytetrafluoroethylene and organic solvent to the reactor, stir and mix for 1-3 hours, then add modified fumed silica, stir and mix for 2-4 hours to obtain a mixture, place the mixture in an oven to degas, then spin-coat it onto a dry and smooth substrate to form a membrane, and dry it at room temperature to obtain the permeation membrane. The grafting modifier is polysilazane; The amount of modified fumed silica added is 0.3% to 1% of the mass of the secondary modified polytetrafluoroethylene; The preparation steps of the modified fumed silica are as follows: 1) Add water, ethanol and modifier to the reactor, adjust the pH to 5-7, stir for 20-30 min, then add fumed silica, stir at room temperature for 1-3 h, centrifuge, wash and dry to obtain pretreated fumed silica. 2) Stir and mix the fumed silica and the pretreated fumed silica from step 1) to obtain modified fumed silica; The modifier is a composite of KH-570 and hexamethyldisilazane.

2. The method for preparing a high-efficiency oil-gas separation permeation membrane according to claim 1, characterized in that, In step (1), the plasma pretreatment is performed with a discharge spacing of 8 mm, a discharge power of 10000 Hz, a voltage of 30-50 V, a current of 1-3 A, and a treatment time of 2-10 min.

3. The method for preparing a high-efficiency oil-gas separation permeation membrane according to claim 1, characterized in that, In step (2), the mass ratio of the primary modified polytetrafluoroethylene to the graft modifier is 10:(2-3).

4. The method for preparing a high-efficiency oil-gas separation permeation membrane according to claim 1, characterized in that, In step 1), the mass ratio of the modifier to fumed silica is (1-1.5):

1.

5. A permeation membrane for efficient oil-gas separation obtained by the preparation method according to any one of claims 1-4, characterized in that, The thickness of the permeation membrane is 40–70 μm.

6. The application of a permeation membrane obtained by the preparation method according to any one of claims 1-4 or the permeation membrane according to claim 5 in the field of dissolved gas analysis in transformer oil.

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