A composite permeation membrane structure, permeation tube and application for volatile hydrazine compounds

Abstract

The application belongs to the technical field of permeation membrane, and discloses a composite permeation membrane structure, a permeation tube and application for volatile hydrazine compounds. The composite permeation membrane structure has at least two layers of permeation membranes, which include: a contact permeation membrane, which is the first layer of permeation membrane contacted by hydrazine compounds along the permeation direction. The contact permeation membrane is a material resistant to corrosion of liquid hydrazine compounds and has a first permeation coefficient for hydrazine compounds. A slow-release permeation membrane is arranged on the back side of the contact permeation membrane along the permeation direction of hydrazine compounds, and at least one layer is arranged. The slow-release permeation membrane has a second permeation coefficient for hydrazine compounds, and the second permeation coefficient is smaller than the first permeation coefficient. The composite permeation membrane structure of the application can realize stable and low-speed permeation of hydrazine compounds, and the permeation tube can be prepared to be used for preparation of low-concentration hydrazine compound standard gas.

Description

Technical Field

[0001] This invention belongs to the field of permeation membrane technology, specifically, it relates to a composite permeation membrane structure, permeation tube and application for volatile hydrazine compounds. Background Technology

[0002] Hydrazine, methylhydrazine, unsymmetrical dimethylhydrazine, and other hydrazine compounds are widely used liquid fuels in aerospace propellants. However, these hydrazine compounds are highly toxic, corrosive, and volatile. Long-term exposure to hydrazine vapor can cause liver and kidney damage, while short-term exposure to high concentrations of hydrazine vapor can lead to pulmonary edema, respiratory failure, and even death. Therefore, it is necessary to monitor the concentration of hydrazine compounds in the air of relevant workplaces to ensure the personal safety and health of operators.

[0003] Currently, rapid real-time monitoring of hydrazine concentrations in workplace air primarily relies on hydrazine gas sensors. These sensors utilize the changes in electrical signals induced by gaseous hydrazine compounds to detect these changes in the sensor's sensitive element. To establish a quantitative relationship between the response electrical signal and the hydrazine gas concentration, the hydrazine gas sensor needs to be calibrated or standardized using a standard hydrazine gas of accurate concentration.

[0004] Permeation is a common method for dynamically preparing standard gases. This method utilizes a permeation tube with a stable permeation rate to release a calibration component into a carrier gas at a constant flow rate, thereby obtaining a standard gas with a stable concentration of the calibration component. The permeation tube typically consists of a volatile liquid calibration component, an outer shell, and a permeation membrane. After the liquid calibration component volatilizes, it forms a high-concentration vapor inside the permeation tube, creating a partial pressure difference of the calibration component across the permeation membrane. Under the influence of this partial pressure difference, the calibration component inside the permeation tube diffuses through the permeation membrane to the outside. Under the condition of constant temperature and permeation membrane structure, the permeation rate of the permeation tube is stable, and therefore, the permeation rate can be calculated by observing the mass change of the permeation tube over a time interval.

[0005] However, when applying the permeation method to the preparation of standard gases for hydrazine compound calibration, a problem arises where the stability of the permeation membrane material and the permeation rate are difficult to balance. According to the national occupational health standard GBZ 2.1-2019 "Occupational Exposure Limits for Hazardous Factors in Industrial Workplaces Part 1: Chemical Hazardous Factors," the time-weighted average permissible concentration of hydrazine is only 0.06 mg / m³. 3 The permissible concentration for short-term exposure is only 0.13 mg / m³. 3 The maximum permissible concentration of methylhydrazine is only 0.08 mg / m³. 3 The time-weighted average permissible concentration of unsymmetrical dimethylhydrazine is only 0.5 mg / m³.3 Based on a commonly used gas mixing rate of 1 L / min, the corresponding permeation rate is only 0.06–0.5 μg / min. At such a low permeation rate, it is impossible to use a plastic membrane with good corrosion resistance but a high permeation rate; only rubber materials with a relatively slow permeation rate can be used. However, in the permeation tube, hydrazine compounds volatilize to form nearly saturated vapor. When the permeation membrane is weighed or otherwise subjected to other operations, this nearly saturated hydrazine vapor easily condenses on the inner surface of the membrane due to changes in ambient temperature, forming liquid hydrazine compounds adhering to the inner surface. Liquid hydrazine compounds are highly corrosive to rubber materials, causing changes in the macroscopic / microscopic structure and chemical composition of the rubber permeation membrane, leading to changes in the permeation rate and affecting the normal use of the permeation tube.

[0006] Therefore, in order to meet the needs of preparing and using standard gases for hydrazine compounds, it is necessary to design and develop a permeation membrane suitable for stable and low-speed permeation of hydrazine compounds.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a composite permeation membrane structure, permeation tube and application for volatile hydrazine compounds, which can realize stable low-speed permeation of hydrazine compounds, and thus meet the needs of preparing standard gases of low concentration hydrazine compounds.

[0009] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0010] A composite permeation membrane structure for volatile hydrazine compounds, comprising at least two permeation membrane layers, including:

[0011] The contact permeation membrane is the first permeation membrane that hydrazine compounds come into contact with along the permeation direction. The contact permeation membrane is made of a material resistant to corrosion by liquid hydrazine compounds and has a first permeation coefficient for hydrazine compounds.

[0012] A slow-release permeation membrane is disposed on the rear side of the contact permeation membrane along the permeation direction of the hydrazine compound, and has at least one layer. The slow-release permeation membrane has a second permeation coefficient for the hydrazine compound, the second permeation coefficient being smaller than the first permeation coefficient.

[0013] In the above scheme, the permeability coefficient refers to the ratio of the amount of target compound passing through the permeation membrane per unit time to the partial pressure difference of the target compound gas on both sides of the permeation membrane. The higher the permeability coefficient, the easier it is for the target compound to pass through the permeation membrane, that is, the permeation rate of the target compound through the permeation membrane is relatively higher. In this invention, the target compound corresponding to the permeability coefficient is a hydrazine compound. The hydrazine compound mentioned in this invention can be hydrazine, methylhydrazine, or unsymmetrical dimethylhydrazine, or other hydrazine compounds.

[0014] The term "rear side" is defined relative to the permeation direction of hydrazine compounds; that is, hydrazine compounds need to permeate through the contact permeation membrane to come into contact with the sustained-release permeation membrane on the rear side. Correspondingly, the contact permeation membrane is equivalent to being positioned on the front side of the sustained-release permeation membrane.

[0015] In this invention, the composite permeation membrane structure can consist of two or more layers of permeation membranes. A material with good resistance to liquid hydrazine compounds is placed in the first layer of the composite permeation membrane structure that contacts the hydrazine compound; that is, it is in direct contact with the liquid hydrazine compound or in direct contact with nearly saturated hydrazine compound vapor. When the contact permeation membrane is in direct contact with the liquid hydrazine compound, the liquid hydrazine compound does not affect the permeation stability of the contact permeation membrane. Similarly, when it is in direct contact with nearly saturated hydrazine compound vapor, even if the hydrazine compound vapor condenses on its surface, it will not affect the permeation stability of the contact permeation membrane.

[0016] By placing a slow-release permeation membrane with a low permeability coefficient behind the contact permeation membrane, the overall permeation rate can be effectively reduced, allowing the permeation rate of the composite permeation membrane structure to match the target concentration. Simultaneously, because the vapor pressure of hydrazine compounds in the region behind the contact permeation membrane is significantly lower than the saturated vapor pressure after being blocked by the contact permeation membrane, condensation is less likely to occur on the surface of the permeation membrane behind the contact permeation membrane. Furthermore, gaseous hydrazine compounds are less corrosive, and some materials easily corroded by liquid hydrazine compounds can remain stable in hydrazine vapor for extended periods. Even though the slow-release permeation membrane has only moderate resistance to liquid hydrazine compounds, it can maintain a long-term stable permeation rate, thus ensuring the overall permeation rate of the composite permeation membrane structure remains stable.

[0017] Specifically, the first-layer contact osmotic membrane, due to its need for resistance to corrosion by liquid hydrazine compounds, has a relatively limited range of material options. Common materials suitable for use as osmotic membranes are mainly certain types of plastic films. However, plastic films have good permeability to hydrazine compounds. When a single-layer plastic film is used as the osmotic membrane on the osmotic tube, the permeation rate of the osmotic tube is high, and the concentration of the prepared hydrazine standard gas cannot match the concentration range required for sensor calibration. Therefore, by setting a slow-release osmotic membrane with a lower permeability coefficient behind the contact osmotic membrane, the overall permeation rate can be effectively reduced. At the same time, the contact osmotic membrane's shielding effect against saturated hydrazine vapor and liquid hydrazine protects the downstream osmotic membrane from corrosion by condensed liquid hydrazine compounds.

[0018] Furthermore, the contact permeation membrane is provided with a certain gap between it and the adjacent permeation membrane.

[0019] Furthermore, the gap between the contact permeation membrane and its adjacent permeation membrane is ≥1mm, preferably 2 to 20mm.

[0020] Furthermore, the thickness of the contact permeation membrane is 0.005–2 mm.

[0021] In the above scheme, the contact membrane and its adjacent downstream membrane layer are not in direct contact; instead, a gap exists between the two membrane layers. Even if the contact membrane is wetted by liquid hydrazine compounds that come into contact with its surface, the adjacent membrane layer will not directly contact the liquid hydrazine compounds due to the existence of the gap. This avoids the situation where the membrane layer downstream of the contact membrane comes into contact with the liquid hydrazine compounds, especially when the membrane layer adjacent to the contact membrane is a slow-release membrane, thus preventing the slow-release membrane from being corroded by the liquid hydrazine compounds contained in the contact membrane.

[0022] Specifically, in this invention, a support is provided between the contact permeation membrane and its adjacent permeation membrane layer, and the support supports the permeation membranes on both sides to form the gap. The support is preferably located near the outer periphery of the permeation membrane and surrounds it, thereby forming a gap between the contact permeation membrane and the adjacent permeation membrane within the area surrounded by the support.

[0023] Experiments have shown that when the gap is controlled to be greater than or equal to 1 mm, it can effectively prevent liquid hydrazine compounds from permeating through the contact membrane and contacting the adjacent membrane layer. Preferably, the gap is controlled to be between 2 and 20 mm, making it easier to maintain a stable gap between the two membrane layers with a support structure.

[0024] Furthermore, it also includes other permeation membranes disposed on the rear side of the contact permeation membrane along the permeation direction of the hydrazine compound; the material of the other permeation membranes is different from that of the sustained-release permeation membrane.

[0025] Furthermore, at least one layer of the other permeation membrane is provided; in the composite permeation membrane structure, at least the last permeation membrane along the permeation direction of the hydrazine compound is the other permeation membrane;

[0026] Preferably, the other permeable membrane is a material resistant to corrosion by liquid hydrazine compounds.

[0027] When the composite permeation membrane structure of this invention is applied to a permeation tube, the liquid hydrazine compounds in the permeation tube volatilize and form hydrazine vapor inside the tube, which may also directly contact a portion of the composite permeation membrane. When the permeation tube is used for standard gas preparation, under the influence of the vapor pressure difference, the hydrazine compounds permeate layer by layer through the composite permeation membrane structure and diffuse into the carrier gas. After a period of equilibrium, a gradually decreasing partial pressure gradient of hydrazine gas is formed in the internal space of the permeation tube, the intermembrane space between adjacent layers of the composite permeation membrane structure, and the external space of the permeation tube.

[0028] Specifically, the partial pressure of hydrazine compounds in the internal space of the permeate tube is approximately equal to its saturated vapor pressure at its operating temperature; the partial pressure of hydrazine compounds in the intermembrane space is significantly lower than its saturated vapor pressure. Furthermore, when three or more permeate membranes are present, if each membrane is spaced apart, the partial pressure of the gas in the intermembrane space closer to the outer side of the permeate tube (i.e., closer to the rear side along the permeation direction) is lower than the partial pressure of the gas in the intermembrane space closer to the inner side of the permeate tube (i.e., closer to the front side along the permeation direction). The partial pressure of hydrazine compounds in the external space of the permeate tube is approximately zero due to the continuous flow of carrier gas carrying away the permeated hydrazine compounds. Thus, when the composite permeate membrane structure is applied to the permeate tube, only the permeate membrane is in contact with approximately saturated hydrazine vapor and liquid hydrazine compounds.

[0029] The contact osmosis membrane is an inert material resistant to corrosion by liquid hydrazine compounds. When the nearly saturated hydrazine vapor inside the permeation tube condenses into liquid hydrazine on the surface of the contact osmosis membrane due to temperature changes or other reasons, or when the contact osmosis membrane directly contacts the liquid hydrazine filling the permeation tube, the contact osmosis membrane will not be corroded. In the space between the membranes and outside the permeation tube, because the partial pressure of the hydrazine gas is significantly lower than its saturated vapor pressure, the gaseous hydrazine compounds therein are unlikely to condense into liquid hydrazine, thus preventing corrosion of other layers of the permeation membrane.

[0030] In this invention, the sustained-release permeation membrane can be disposed between the contact permeation membrane and other permeation membranes, or other permeation membranes can be disposed between the contact permeation membrane and the sustained-release permeation membrane. Furthermore, when multiple layers of the sustained-release permeation membrane and other permeation membranes are disposed, the multiple layers of the sustained-release permeation membrane can be disposed adjacent to each other, and the multiple layers of other permeation membranes can also be disposed adjacent to each other; alternatively, the sustained-release permeation membrane and other permeation membranes can be alternately disposed behind the contact permeation membrane.

[0031] Preferably, the last layer of the composite permeate membrane structure is made of another permeate membrane material resistant to corrosion by liquid hydrazine compounds, so that the slow-release permeate membrane does not come into direct contact with the external space. In this way, when assembling the composite permeate membrane structure into a permeate tube, especially when filling the permeate tube with liquid hydrazine compounds, the problem of the slow-release permeate membrane accidentally coming into contact with the liquid hydrazine compounds is avoided, and even if the other permeate membranes in the last layer come into contact with liquid hydrazine compounds, they will not be corroded or damaged.

[0032] Furthermore, the contact permeation membrane is a fluoroplastic film.

[0033] Furthermore, the fluoroplastic film is made of one or a combination of several of the following: polytetrafluoroethylene, perfluoroethylene propylene, polyvinylidene fluoride, and perfluoroalkoxy resin.

[0034] In the above scheme, the contact osmosis membrane is a fluoroplastic film with good chemical stability and good resistance to liquid hydrazine compounds. Preferred fluoroplastics are polytetrafluoroethylene (PTFE), perfluoroethylene propylene (PFEP), polyvinylidene fluoride (PVDF), and perfluoroalkoxy resins. These materials exhibit good resistance to hydrazine compounds and maintain chemical composition and structural stability even after long-term immersion in liquid hydrazine compounds. Furthermore, fluoroplastics are easily processed into membrane materials, making them suitable for use as contact osmosis membranes.

[0035] Furthermore, the slow-release permeation membrane is made of synthetic rubber material.

[0036] Furthermore, the synthetic rubber material is one or more of fluororubber, fluorosilicone rubber, EPDM rubber, styrene-butadiene rubber, chloroprene rubber, and butyl rubber.

[0037] In the above scheme, synthetic rubber is chosen as the material for the slow-release permeation membrane. Compared with plastic film, synthetic rubber has a denser microstructure, which can effectively slow down the permeation of gaseous hydrazine compounds, thereby reducing the overall permeation rate to meet the requirements for preparing low-concentration standard gases. Simultaneously, synthetic rubber has good elasticity, allowing it to fit tightly against other structural surfaces of the permeation tube after processing into a permeation membrane. Even if it is processed into a thicker layer to reduce the permeation rate, the sealing of the membrane edges can be guaranteed, preventing hydrazine vapor from seeping out from the gaps between the membrane and other structural surfaces of the permeation tube.

[0038] The synthetic rubber material is preferably one or more of fluororubber, fluorosilicone rubber, EPDM rubber, styrene-butadiene rubber, chloroprene rubber, and butyl rubber. Among them, fluororubber, fluorosilicone rubber, EPDM rubber, styrene-butadiene rubber, and chloroprene rubber have relatively good resistance to all or some types of gaseous hydrazine compounds and can maintain stable permeation performance even when exposed to hydrazine compound vapors for a long time; while butyl rubber, in addition to having a certain resistance to hydrazine compound vapors, also has lower gas permeability, which can significantly reduce the permeation rate of hydrazine compounds in the permeation tube without increasing the thickness of the permeation membrane.

[0039] The present invention also provides a permeation tube for volatile hydrazine compounds, comprising the composite permeation membrane structure for volatile hydrazine compounds described above, wherein the contact permeation membrane is disposed on the side of the composite permeation membrane structure that directly contacts the hydrazine compound inside the permeation tube.

[0040] Furthermore, the permeation rate of the permeation tube to hydrazine compounds is 0.01–2 μg / min, preferably 0.01–0.5 μg / min.

[0041] In the above scheme, the composite permeation membrane structure can be applied in the permeation tube, and the contact permeation membrane is disposed on the side of the composite permeation membrane structure that directly contacts the hydrazine compound inside the permeation tube, thus serving as the first permeation membrane in contact with the hydrazine compound inside the tube. In this way, while ensuring that the composite permeation membrane structure is not corroded by the hydrazine compound, the permeation rate of the permeation tube to the hydrazine compound can be reduced to 0.01–2 μg / min. For example, the permeation rate of the permeation tube of the present invention to hydrazine is 0.01–0.5 μg / min, preferably 0.01–0.3 μg / min; the permeation rate to methylhydrazine is 0.02–0.8 μg / min, preferably 0.02–0.4 μg / min; and the permeation rate to unsymmetrical dimethylhydrazine is 0.02–2 μg / min, preferably 0.02–0.5 μg / min. At a gas mixing rate of 0.2–2 L / min, the permeation tube of the present invention can achieve a concentration of 0.005–10 mg / m³. 3 The preparation of hydrazine compound standard gases meets the requirements for calibrating or standardizing hydrazine compound gas sensors.

[0042] Furthermore, the composite permeation membrane structure forms the sidewall of the permeation tube, and a sealing structure is provided at the two ends of the sidewall opening.

[0043] In the above scheme, the sidewall of the permeation tube can be directly rolled into a composite permeation membrane structure, and then an additional sealing structure can be used to seal the openings at both ends. The contact permeation membrane forms the inner sidewall of the permeation tube, and the sealing structure is impermeable to hydrazine compounds. To create a gap between adjacent permeation membrane layers, a support needs to be placed between them. Specifically, the support is at least located near both ends of the permeation tube and can be a gasket fitted onto the cylindrical surface formed by the inner permeation membrane. Preferably, one or more gaskets can be placed between the gaskets at both ends for more stable support and to create a gap between adjacent permeation membrane layers.

[0044] Alternatively, the permeation tube may include the aforementioned composite permeation membrane structure and a housing, the housing forming the sidewall of the permeation tube; at least one end of the housing is an open end, and the composite permeation membrane structure is sealed over the open end.

[0045] Specifically, the sidewall of the permeation tube is formed by a separate outer shell. This outer shell can be open at only one end or at both ends, and then a composite permeation membrane structure covers the open end. The contact permeation membrane faces inwards and covers the open end. In this scheme, the support used to create the gap between the two permeation membrane layers can also be a gasket. Specifically, the contact permeation membrane of the first layer of the composite permeation membrane structure is sealed and covered at the open end of the outer shell. Then, a gasket is placed on the outward-facing surface of the contact permeation membrane, and the next layer of permeation membrane is placed over the gasket, thus forming a gap between the contact permeation membrane and the adjacent permeation membrane layer.

[0046] Alternatively, the permeation tube includes a shell, the interior of which has a space for holding hydrazine compounds; the composite permeation membrane structure forms a permeation pipeline, the main body of which is located inside the shell, and the inlet and outlet ends of the permeation pipeline are respectively connected to the outside of the shell.

[0047] Specifically, the permeation tube contains hydrazine compounds within a closed shell. A composite permeation membrane structure forms the permeation channel within the shell, with the contact permeation membrane located on the outermost side of the permeation channel enclosed by the composite permeation membrane structure. The inlet end of the permeation channel is connected to a carrier gas source, allowing a constant flow rate of carrier gas to enter the permeation channel. The hydrazine compounds inside the shell pass through the composite permeation membrane structure into the permeation channel, and the outlet end of the permeation channel outputs a gas flow containing a certain concentration of hydrazine compounds. In this scheme, the method of forming the gap between adjacent permeation membrane layers using supports is similar to the scheme where the composite permeation membrane structure is directly rolled into the sidewall of the permeation tube. Multiple gaskets can be spaced at intervals on the inner permeation membrane along the extension direction of the permeation channel, thus ensuring that adjacent permeation membrane layers do not contact each other.

[0048] The present invention also provides an application of the above-described permeation tube for volatile hydrazine compounds in the preparation of standard gases for hydrazine compound calibration.

[0049] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art.

[0050] 1. This invention employs a composite permeation membrane structure composed of double or multiple layers of permeation membranes. The contact permeation membrane, i.e., the first permeation membrane that hydrazine compounds come into contact with during permeation, is made of a material resistant to corrosion by liquid hydrazine compounds. It directly contacts the nearly saturated hydrazine vapor and may also come into contact with liquid hydrazine compounds. The slow-release permeation membrane with a lower permeability coefficient is placed behind the contact permeation membrane. By utilizing the shielding effect of the contact permeation membrane on the saturated hydrazine vapor and liquid hydrazine compounds, the partial pressure of the hydrazine gas that the slow-release permeation membrane comes into contact with is significantly lower than its saturated vapor pressure. As a result, the hydrazine compounds will not condense on the surface of the slow-release permeation membrane and cause corrosion, thereby achieving a stable and low-speed permeation effect for the composite permeation membrane structure.

[0051] 2. The permeation tube of the present invention utilizes the aforementioned composite permeation membrane structure, achieving a permeation rate as low as 0.01–2 μg / min for hydrazine compounds, and thus, at commonly used gas mixing rates, can achieve a permeation rate of 0.005–10 mg / m³. 3 The preparation of low-concentration hydrazine compound standard gases can meet the requirements for calibration or standardization of hydrazine compound gas sensors.

[0052] The specific embodiments of the present invention will be described in further detail below. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0054] Example 1

[0055] This embodiment provides a permeation tube for methylhydrazine, comprising a shell and a composite permeation membrane structure, wherein the composite permeation membrane structure is composed of two layers of permeation membranes. Specifically, the contact permeation membrane facing the inner side of the permeation tube is a polytetrafluoroethylene film, and the slow-release permeation membrane on the outer side is an EPDM rubber membrane, with a 2mm gap between the two permeation membranes. The permeation area of ​​the permeation tube is 28mm². 2 .

[0056] After injecting methylhydrazine into the permeation tube of this embodiment, it was placed in a 45°C constant temperature chamber, and nitrogen gas was continuously introduced into the chamber. The initial mass of the permeation tube was recorded, and then its mass was weighed every 14 days. The weight loss in the five intervals was measured to be 4.5 mg, 4.4 mg, 4.4 mg, 4.3 mg, and 4.4 mg, respectively, indicating that the permeation rate remained basically stable. The calculated permeation rate of methylhydrazine in the permeation tube of this embodiment was 0.218 μg / min, achieving a low-speed and stable permeation effect.

[0057] Example 2

[0058] This embodiment provides a permeation tube for unsymmetrical dimethylhydrazine (UDMH), comprising a shell and a composite permeation membrane structure, wherein the composite permeation membrane structure consists of three layers. Specifically, the contact permeation membrane facing the inner side of the permeation tube is a polytetrafluoroethylene (PTFE) film, the middle layer is a slow-release permeation membrane made of butyl rubber, a 5mm gap is placed between the contact permeation membrane and the slow-release permeation membrane, and the outermost permeation membrane is a PTFE film. The permeation area of ​​the permeation tube is 13mm². 2 .

[0059] After injecting unsymmetrical dimethylhydrazine into the permeation tube of this embodiment, it was placed in a 35°C constant temperature chamber, and nitrogen gas was continuously introduced into the chamber. The initial mass of the permeation tube was recorded, and then its mass was weighed every 35 days. The weight loss in the five intervals was measured to be 1.62 mg, 1.67 mg, 1.59 mg, 1.59 mg, and 1.65 mg, respectively. The permeation rate of unsymmetrical dimethylhydrazine in the permeation tube of this embodiment was calculated to be 0.0322 μg / min.

[0060] Comparative Example 1

[0061] This comparative example provides a permeation tube using only a single-layer polytetrafluoroethylene (PTFE) film, comprising a shell and a single-layer PTFE film, with the same permeation area as in Example 1. After injecting the same amount of methylhydrazine as in Example 1 into its interior, it is placed in a 45°C constant temperature chamber under the same conditions as in Example 1, and nitrogen gas is continuously introduced into the constant temperature chamber.

[0062] The initial mass of the permeation tube was recorded, and then weighed again after 14 days. The total weight loss was measured to be 71.2 mg, and the permeation rate was calculated to be 3.53 μg / min. It is evident that in this comparative example, the single-layer polytetrafluoroethylene film, due to its excellent permeability to methylhydrazine, resulted in a higher permeation rate of methylhydrazine through the permeation tube, making it unsuitable for preparing low-concentration methylhydrazine standard gas.

[0063] Comparative Example 2

[0064] This comparative example provides a permeation tube using only a single-layer EPDM rubber membrane, comprising a shell and a single-layer EPDM rubber membrane, with the same permeation area as in Example 1. After injecting the same amount of methylhydrazine as in Example 1 into its interior, it is placed in a 45°C constant temperature chamber under the same conditions as in Example 1, and nitrogen gas is continuously introduced into the constant temperature chamber.

[0065] After 14 days, it was clearly observed that the rubber membrane bulged and that liquid condensed on its inner surface. Simultaneously, the methylhydrazine in the permeation tube turned yellow, indicating that the EPDM rubber membrane was corroded by methylhydrazine. Therefore, it is evident that the permeation tube provided in this comparative example showed corrosion of the EPDM rubber membrane after 14 days of testing, thus failing to achieve a long-term stable low-rate permeation effect.

[0066] Comparative Example 3

[0067] This comparative example provides a permeation tube for methylhydrazine, comprising a shell and a composite permeation membrane structure, wherein the composite permeation membrane structure is composed of a double-layer permeation membrane, and the permeation area of ​​the permeation tube is the same as that in Example 1. Specifically, the composite permeation membrane structure in this comparative example is a double-layer polytetrafluoroethylene film.

[0068] After injecting the same amount of methylhydrazine as in Example 1 into the permeation tube, it was placed in a 45°C constant temperature chamber under the same conditions as in Example 1, and nitrogen gas was continuously introduced into the chamber. The initial mass of the permeation tube was recorded, and then weighed after 14 days. The total weight loss was measured to be 52.8 mg, and the permeation rate was calculated to be 2.62 μg / min. Although the permeation tube with a double-layer polytetrafluoroethylene (PTFE) film in this comparative example achieved a slight decrease in permeation rate compared to the permeation tube with a single-layer PTFE film in Comparative Example 1, its permeation rate was still significantly higher than that of the permeation tube in Example 1. Therefore, simply increasing the number of PTFE film layers is insufficient to meet the permeation rate requirements for preparing low-concentration methylhydrazine standard gas.

[0069] Comparative Example 4

[0070] This comparative example provides a permeation tube for methylhydrazine, comprising a shell and a composite permeation membrane structure, wherein the composite permeation membrane structure is composed of a double-layer permeation membrane, and the permeation area of ​​the permeation tube is the same as that in Example 1. Specifically, the composite permeation membrane structure in this comparative example is a double-layer EPDM rubber membrane, and the two rubber membranes have the same gap as the two permeation membranes in Example 1.

[0071] After injecting the same amount of methylhydrazine as in Example 1 into the permeation tube, it was placed in a 45°C constant temperature chamber under the same conditions as in Example 1, and nitrogen gas was continuously introduced into the chamber. The initial mass of the permeation tube was recorded, and then its mass was weighed every 14 days. The weight loss in the three intervals was measured to be 1.8 mg, 2.5 mg, and 3.8 mg, respectively, and the corresponding permeation rates in the three intervals were 0.089 μg / min, 0.12 μg / min, and 0.19 μg / min, respectively. It can be seen that the permeation rate is not stable and gradually increases with time. After disassembling the permeation tube, it was found that the inner rubber membrane was severely corroded and could no longer effectively block the permeation of methylhydrazine vapor. At the same time, the methylhydrazine inside the permeation tube was brownish-yellow, and its composition had been partially changed.

[0072] Comparative Example 5

[0073] The difference between this comparative example and Example 1 above is that the polytetrafluoroethylene film facing the inside of the permeation tube is bonded to the EPDM rubber film on the outside to form a composite permeation membrane structure.

[0074] After injecting the same amount of methylhydrazine as in Example 1 into the permeation tube of this comparative example, it was placed in a 45°C constant temperature chamber under the same conditions as in Example 1, and nitrogen gas was continuously introduced into the chamber. The initial mass of the permeation tube was recorded, and then its mass was weighed every 14 days. The weight loss in the five intervals was measured to be 5.2 mg, 5.1 mg, 5.5 mg, 5.6 mg, and 5.8 mg, respectively, and the corresponding permeation rates in the five intervals were 0.26 μg / min, 0.25 μg / min, 0.27 μg / min, 0.28 μg / min, and 0.29 μg / min, respectively. Although no obvious signs of corrosion were observed on the outer rubber membrane of the permeation tube of this comparative example, it can be seen that its permeation rate for methylhydrazine tends to gradually increase over time, indicating that it cannot guarantee a stable permeation rate over a long period of time.

[0075] 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-described 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 composite permeation membrane structure for volatile hydrazine compounds, characterized in that, It has at least two permeable membranes, including: The contact permeation membrane is the first permeation membrane that hydrazine compounds come into contact with along the permeation direction. The contact permeation membrane is made of a material resistant to corrosion by liquid hydrazine compounds and has a first permeation coefficient for hydrazine compounds. A slow-release permeation membrane is disposed on the rear side of the contact permeation membrane along the permeation direction of the hydrazine compound, and at least one layer is disposed thereon. The slow-release permeation membrane has a second permeation coefficient for the hydrazine compound, and the second permeation coefficient is smaller than the first permeation coefficient. The contact permeation membrane is separated from its adjacent permeation membrane by a certain gap, which is ≥1 mm.

2. The composite permeation membrane structure for volatile hydrazine compounds according to claim 1, characterized in that, The thickness of the contact permeation membrane is 0.005–2 mm.

3. The composite permeation membrane structure for volatile hydrazine compounds according to claim 1 or 2, characterized in that, The contact permeation membrane is a fluoroplastic film.

4. The composite permeation membrane structure for volatile hydrazine compounds according to claim 3, characterized in that, The fluoroplastic film is made of one or a combination of several of the following: polytetrafluoroethylene, perfluoroethylene propylene, polyvinylidene fluoride, and perfluoroalkoxy resin.

5. The composite permeation membrane structure for volatile hydrazine compounds according to claim 1 or 2, characterized in that, The slow-release permeation membrane is made of synthetic rubber.

6. The composite permeation membrane structure for volatile hydrazine compounds according to claim 5, characterized in that, The synthetic rubber material is one or more of fluororubber, fluorosilicone rubber, EPDM rubber, styrene-butadiene rubber, chloroprene rubber, and butyl rubber.

7. A permeation tube for volatile hydrazine compounds, characterized in that, The composite permeation membrane structure for volatile hydrazine compounds as described in any one of claims 1-6, wherein the contact permeation membrane is disposed on the side of the composite permeation membrane structure that directly contacts the hydrazine compound inside the permeation tube.

8. The permeation tube for volatile hydrazine compounds according to claim 7, characterized in that, The permeation rate of the permeation tube for hydrazine compounds is 0.01–2 μg / min.

9. The permeation tube for volatile hydrazine compounds according to claim 7, characterized in that, A support is provided between the contact permeation membrane and its adjacent permeation membrane layer to form the gap.

10. The use of the permeation tube for volatile hydrazine compounds as described in any one of claims 7-9 in the preparation of standard gases for hydrazine compound calibration.