A system and method for separating Kr / CF4 by coupling rectification and membrane separation

Abstract

The present application relates to a kind of chemical separation system and method, specifically to a kind of system and method for realizing Kr / CF4 separation using rectification-membrane separation coupling.The present application uses molecular sieve membrane as the key separation membrane material, and designs a whole set of Kr / CF4 separation and purification process, which solves the problems of Kr / CF4 purification and large amount of heat consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to a chemical separation system and method, in particular to a system and method for separating Kr / CF4 by using distillation-membrane separation coupling. BACKGROUND

[0002] Electronic special gas refers to ultra-pure and ultra-clean special gas used in electronic industry. Kr is widely used in integrated circuits, display panels and photovoltaic industries as an important electronic gas. However, fluorocarbons are enriched in Kr during the concentration process. With the increase of fluorocarbons in the air, the purification of Kr becomes more difficult, and the purity of the product is seriously affected. Therefore, how to efficiently remove CF4 is a key problem in the purification and preparation of high-purity Kr.

[0003] The existing distillation technology has significant challenges in the purification process of high-purity Kr. Purely relying on a distillation column to separate high-purity Kr often requires a multi-stage series method, such as three columns or even more distillation units. This not only increases the complexity of the process, but also leads to huge energy consumption. In addition, although the getter technology is used in the purification process of Kr, it is not economical due to the large amount of metal material loss in practical application. At the same time, due to the reaction between the surface of the getter and Kr to generate solid products such as zirconium carbide (ZrC) and zirconium fluoride (ZrF4), these by-products will gradually cover the surface of the getter, seriously affecting its adsorption efficiency and service life. In addition, traditional adsorbents such as 13X molecular sieve have limited ability to capture trace amounts of carbon tetrafluoride (CF4), which cannot meet the deep removal needs of such impurities in high-purity Kr.

[0004] Membrane separation technology is a new technology for separation and purification, which can be used together with distillation to improve the purification effect. However, for Kr / CF4 separation, the material stream after preliminary purification by the distillation column is extremely low in temperature, which needs to be heated to a higher temperature to ensure the normal application of membrane materials, which undoubtedly consumes a large amount of heat. Therefore, it is urgent to reform the existing Kr / CF4 separation and purification process to solve the above problems. SUMMARY

[0005] To solve the above problems, the present application uses molecular sieve membrane as the key separation membrane material, and designs a complete set of Kr / CF4 separation and purification process, which solves the problems of Kr / CF4 purification and large heat consumption.

[0006] As the first contribution of the present application, the present application provides a system for realizing Kr / CF4 separation by coupling rectification-membrane separation, which comprises a preliminary rectification tower, a membrane separation device connected in sequence, the feed side of the membrane separation device is connected with the tower bottom of the preliminary rectification tower, the permeation side of the membrane separation device is connected with a secondary rectification tower or the permeation side of the membrane separation device is connected with the feed side of the preliminary rectification tower again through a buffer tank, and the separation membrane material in the membrane separation device is a molecular sieve membrane.

[0007] Preferably, the membrane separation device comprises a single membrane assembly or a plurality of membrane assemblies, when comprising a plurality of membrane assemblies, the plurality of membrane assemblies are one of series connection, parallel connection or both series connection and parallel connection.

[0008] Preferably, the molecular sieve membrane is a CHA molecular sieve membrane, and the separation selectivity of the CHA molecular sieve membrane for Kr / CF4 is greater than 30 at 25 ℃, 0.2-1 MPaG.

[0009] Preferably, a heat exchanger is arranged on the pipeline connecting the feed side of the membrane separation device with the tower bottom of the preliminary rectification tower to convert liquid-phase material into gas-phase material.

[0010] Preferably, a condenser is arranged on the pipeline connecting the permeation side of the membrane separation device with the secondary rectification tower or the pipeline connecting the permeation side of the membrane separation device with the buffer tank to convert gas-phase material into liquid-phase material.

[0011] Preferably, the number of plates of the preliminary rectification tower is 5-20, and the reflux ratio is 2-6.4.

[0012] Preferably, the number of plates of the secondary rectification tower is 5-20, and the reflux ratio is 5-10.

[0013] The present application also provides a method for realizing Kr / CF4 separation by coupling rectification-membrane separation, which comprises the following steps:

[0014] 1) passing liquid-phase material containing Kr and CF4 into a preliminary rectification tower, taking the overhead distillate of the preliminary rectification tower as a product, the feeding temperature of the liquid-phase material is-160 ℃--127 ℃, and the CF4 concentration in the liquid-phase material is 20-1000 ppm;

[0015] 2) passing the tower bottom material of the preliminary rectification tower into the feed end of a membrane separation device after being warmed to-100--120 ℃ by a heat exchanger to realize CF4 retention on the retentate side by membrane separation;

[0016] 3) further passing the material obtained from the permeation side of the membrane separation device into a secondary rectification tower for further separation and purification, or further passing the material obtained from the permeation side of the membrane separation device into a buffer tank and then into the preliminary rectification tower.

[0017] Preferably, the concentration of CF4 in the overhead of the primary rectification column in step 1) is 0.05-1 ppm, and the concentration of CF4 in the material obtained from the column bottom is 500 ppm - 20000 ppm.

[0018] Preferably, the concentration of CF4 in the overhead of the secondary rectification column in step 3) is less than 1 ppm.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] Firstly, the CHA molecular sieve membrane used in the present application can maintain stable separation performance at a relatively low temperature, so that the ultra-low temperature liquid material in the column bottom of the primary rectification column can be moderately heated to a gas phase state to achieve efficient membrane separation. This design avoids the energy consumption problem caused by the need to heat the material significantly in the traditional process, significantly improves the energy utilization efficiency of the system, and reduces the production cost.

[0021] Secondly, the coupling process of rectification and membrane separation in the present application can realize efficient separation and purification of Kr and CF4. This specific separation design ensures high purity of the product and meets the strict requirements of the electronic industry for high-purity krypton. The purity of the Kr product treated by the present application is significantly improved, and the CF4 content is greatly reduced, reaching the industry-leading level, providing high-quality and reliable raw material guarantee for the electronic industry. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 : Kr / CF4 separation system of Example 1 of the present application, wherein 1-primary rectification column, 2-membrane separation device, 3-secondary rectification column, 4-heat exchanger, 5-condenser.

[0023] Figure 2 : Kr / CF4 separation system of Example 3 of the present application, wherein 1-primary rectification column, 2-membrane separation device, 4-heat exchanger, 5-condenser, 6-buffer tank.

[0024] Figure 3 : Enlarged view of the single-stage membrane separation device of Example 1 of the present application.

[0025] Figure 4 : Enlarged view of the two-stage series membrane separation device of Example 1 of the present application.

[0026] Figure 5 : Kr / CF4 separation effect of the membrane used in Example 1 of the present application under different feed pressures. DETAILED DESCRIPTION

[0027] The following description is only preferred embodiments of the present application and does not limit the protection scope of the present application.

[0028] Embodiment 1

[0029] Figure 1 The system for realizing Kr / CF4 separation by distillation-membrane separation coupling in this embodiment includes a preliminary distillation column 1, a membrane separation device 2 and a secondary distillation column 3 connected in sequence, the feed side W1 of the membrane separation device 2 is connected with the column bottom of the preliminary distillation column 1, the permeation side F2 of the membrane separation device 2 is connected with the secondary distillation column 3, and the separation membrane material in the membrane separation device 2 is a molecular sieve membrane. The molecular sieve membrane is a CHA molecular sieve membrane. A heat exchanger 4 is arranged on the pipeline connecting the feed side of the membrane separation device 2 with the column bottom of the preliminary distillation column to convert the liquid-phase material into a gas-phase material, and a condenser 5 is arranged on the pipeline connecting the permeation side of the membrane separation device 2 with the secondary distillation column 3 to convert the gas-phase material into a liquid-phase material.

[0030] Embodiment 2

[0031] Figure 2 The system for realizing Kr / CF4 separation by distillation-membrane separation coupling in this embodiment includes a buffer tank 6, a preliminary distillation column 1 and a membrane separation device 2 connected in sequence, the discharge side of the buffer tank 6 is connected with the feed side of the preliminary distillation column 1, the feed side W1 of the membrane separation device 2 is connected with the column bottom of the preliminary distillation column 1, and the permeation side F2 of the membrane separation device 2 is connected with the feed side of the buffer tank 1. The separation membrane material in the membrane separation device 2 is a molecular sieve membrane. The molecular sieve membrane is a CHA molecular sieve membrane. A heat exchanger 4 is arranged on the pipeline connecting the feed side of the membrane separation device 2 with the column bottom of the preliminary distillation column to convert the liquid-phase material into a gas-phase material, and a condenser 5 is arranged on the pipeline connecting the permeation side of the membrane separation device 2 with the buffer tank 6 to convert the gas-phase material into a liquid-phase material.

[0032] The membrane separation device in Embodiments 1 and 2 is a single-stage membrane device, and an enlarged view thereof is shown in Figure 3 In other cases, the membrane separation device in Embodiments 1 and 2 can be replaced by a two-stage series type, as shown in Figure 4

[0033] Embodiment 3

[0034] Taking the membrane separation device with a single-stage membrane as an example, the method for realizing Kr / CF4 separation by the distillation-membrane separation coupling system in Embodiment 1 is described as follows:

[0035] ​The present technology adopts a separation method coupling rectification and membrane separation, including preliminary rectification, membrane separation and secondary rectification. The feedstock F1 includes Kr and CF4, wherein the concentration of CF4 is 100 ppm, the feed pressure is 0.2 MPa, the feed temperature is -143.7 ℃, the feed is in full liquid phase, and the feed flow rate is 11.67 L / min. The rectification column T1 has 9 plates, the feed position is above the 6th plate, the reflux ratio is 3-6.4, the column top condenser temperature is -145.3 ℃, and the column bottom reboiler temperature is -143.3 ℃. After separation by the rectification column T1, the rectification column overhead distillate D1 is taken as the product, the flow rate of which is 9.57 L / min, and the concentration of CF4 in the flow rate is 0.1 ppm-1 ppm; the CF4 concentration in the rectification column bottom stream W1 is 500 ppm-20,000 ppm, and the flow rate is 2.1 L / min, which needs to be recycled for secondary purification. The stream W1 is warmed to -120 ℃ by a heat exchanger to make the stream in pure gas phase, and is introduced into a membrane separation device, wherein the membrane separation technology is used to retain CF4 on the retentate side, and the permeate side stream P1 is pressurized and condensed to stream F2 and introduced into the rectification column T2. The flow rate of stream F2 is 1.8 L / min, the pressure is 0.6 MPa, and the temperature is -124.9 ℃. The rectification column T2 has 8 plates, the feed position is above the 5th plate, the reflux ratio is 7.8, the column top condenser temperature is -125.1 ℃, and the column bottom reboiler temperature is -124.3 ℃. After separation by the rectification column T2, the rectification column overhead distillate D2 is taken as the product, and when the CF4 concentration in the feed F2 is below 1000 ppm, the CF4 concentration in the overhead distillate stream D2 is below 1 ppm, the flow rate of stream D2 is 1.69 L / min, and the Kr recovery rate is above 94%.

[0036] Example 4

[0037] Taking a membrane separation device using a single-stage membrane as an example, the method for separating Kr / CF4 by the rectification-membrane separation coupling system of Example 2 is described.

[0038] The present technology adopts a separation method coupling distillation and membrane separation, including two parts of preliminary distillation and membrane separation, and the permeate side stream of the membrane separation is recycled to the preliminary distillation column for further separation and purification. The feedstock F1 includes Kr and CF4, wherein the concentration of CF4 is 100 ppm, the feed pressure is 0.2 MPa, the feed temperature is -143.7 ℃, the feed is full liquid phase, and the feed flow rate is 11.67 L / min; the recycle stream F2 is the permeate side stream of the membrane separation device, and the flow rate is 1.71 L / min. The preliminary distillation column T1 has 9 trays, the feed position is above the 6th tray, the reflux ratio is 2.6-5.2, the overhead condenser temperature is -145.3 ℃, and the bottom reboiler temperature is -143.3 ℃. After the separation of the preliminary distillation column T1, the preliminary distillation column overheads D1 is taken as the product, the CF4 concentration in the stream is 0.1 ppm-1 ppm, and the flow rate is 11.18 L / min; the CF4 concentration in the preliminary distillation column bottom stream W1 is 500 ppm-20,000 ppm, and the flow rate is 2.2 L / min. The stream W1 is warmed to -120 ℃ by a heat exchanger, so that the stream is in pure gas phase, and is introduced into the membrane separation device at a pressure of 0.6 MPa by a pressure changer, CF4 is isolated in the retentate side by using the membrane separation technology, and the permeate side stream P1 is condensed to the stream F2 and mixed with F1 to be introduced into the distillation column T1 to realize the circulation of the stream, the flow rate of F2 is 1.71 L / min, the pressure is 0.2 MPa, and the temperature is -143.7 ℃.

[0039] Example 5

[0040] The molecular sieve membrane used in the above examples 1 and 2 is a CHA molecular sieve membrane, and the specific preparation steps are as follows:

[0041] First, a synthesis solution is prepared according to the stoichiometric ratio of Al(OH)3:NaOH:TMAdaOH:SiO2:H2O = 1:23:22:116:4800, and the corresponding amount of raw materials is mixed and heated and stirred until the solution is transparent. Subsequently, the transparent synthesis solution is transferred to a stainless steel reaction kettle, and aging is carried out at 95 ℃ for 3 days. Then, the porous α-Al2O3 carrier is immersed in a 0.5 wt% seed solution for crystal coating treatment and dried at 60 ℃. After that, the carrier is transferred to the reaction kettle for hydrothermal synthesis at 180 ℃ for 1 day. Finally, the prepared membrane is placed in an ozone atmosphere and calcined at 200 ℃ for 4 days to obtain a high-performance CHA molecular sieve membrane.

[0042] The CHA molecular sieve membrane prepared above was characterized for performance. The membrane tube was installed into a membrane module and sealed, and a mixed gas was tested to enter from the membrane surface, and after the pressure was adjusted by a back pressure valve, the pressure difference between the two sides of the membrane was used as the driving force for the gas molecules to permeate, and the flow rate on the permeation side was read by a flow meter, and the concentration of each component on the permeation side was obtained by a gas chromatograph. The permeability of each component in the gas can be calculated by the following formula, which is expressed as:

[0043]

[0044] wherein, represents the permeability of the i component under the condition, and the unit is , represents the volume flow rate of the i component on the permeation side, and the unit is , represents the test temperature, and the unit is ℃, represents the effective membrane area, and the unit is .

[0045] The separation selectivity of different components is expressed as:

[0046]

[0047] wherein, and represent the permeability of the i component and the j component, respectively, and the unit is .

[0048] The Kr / CF4 separation performance under different feed pressures was studied. Under the conditions of a feed flow rate of 500 mL / min and a mixed gas CF4 concentration of 3000 ppm, the feed pressure was changed by adjusting the back pressure valve (0.2 MPaG - 1.0 MPaG), and the composition of the gas on the permeation side was analyzed, and the results are shown in FIG. 5. It can be found that as the feed pressure rises, the separation selectivity of Kr / CF4 is greater than 30, the permeability of Kr remains stable at 2 x 10 -8 , and the permeability of CF4 increases with the rise of the pressure. When the feed pressure is 1 MPaG, the CF4 content in the permeation side decreases to 185 ppm. After the membrane separation, the stream is further purified in a rectifying column, and the CF4 concentration in the obtained Kr can be below 1 ppm.

Claims

1. A method for separating Kr / CF4 by coupling rectification-membrane separation, characterized in that, The system used in the method comprises a preliminary rectification tower (1), a membrane separation device (2) connected in sequence, the feed side of the membrane separation device (2) is connected with the tower kettle of the preliminary rectification tower (1), the permeation side of the membrane separation device (2) is connected with a secondary rectification tower (3), the separation membrane material in the membrane separation device is a molecular sieve membrane; the molecular sieve membrane is a CHA molecular sieve membrane, the separation selectivity of the CHA molecular sieve membrane for Kr / CF4 is greater than 30 at 25 ℃, 0.2-1 MPaG; The method comprises the following steps: 1) passing a liquid phase material containing Kr and CF4 into the preliminary rectification tower (1), the overhead distillate of the preliminary rectification tower (1) is used as a product, the feed temperature of the liquid phase material is -160 ℃ to -127 ℃, and the CF4 concentration in the liquid phase material is 20-1000 ppm; 2) passing the tower kettle material of the preliminary rectification tower (1) into the feed end of the membrane separation device (2) after being warmed to -100 to -120 ℃ by a heat exchanger to realize the isolation of CF4 on the retentate side by membrane separation; 3) further passing the material obtained from the permeation side of the membrane separation device (2) into the secondary rectification tower (3) to further separate and purify; after the secondary rectification of the secondary rectification tower (3) in step 3), the CF4 concentration in the overhead distillate is less than 1 ppm.

2. The method of claim 1, wherein, The membrane separation device (2) comprises a single membrane assembly or a plurality of membrane assemblies, when comprising a plurality of membrane assemblies, the plurality of membrane assemblies are one of series connection or parallel connection or simultaneously comprise series connection and parallel connection.

3. The method of claim 1, wherein, A heat exchanger is arranged on the pipeline connecting the feed side of the membrane separation device (2) with the tower kettle of the preliminary rectification tower (1) to convert the liquid phase material into a gas phase material.

4. The method of claim 1, wherein, A condenser is arranged on the pipeline connecting the permeation side of the membrane separation device (2) with the secondary rectification tower (3) to convert the gas phase material into a liquid phase material.

5. The method of claim 1, wherein, The number of plates of the preliminary rectification tower (1) is 5-20, and the reflux ratio is 2-6.

4.

6. The method of claim 1, wherein, The number of plates of the secondary rectification tower (3) is 5-20, and the reflux ratio is 5-10.

7. The method of claim 1, wherein, After the preliminary rectification of the preliminary rectification tower (1) in step 1), the CF4 concentration in the overhead distillate is 0.05-1 ppm, and the CF4 concentration in the material obtained from the tower kettle is 500 ppm-20000 ppm.

Images