System and method for realizing Kr / CF4 separation by utilizing rectification-membrane separation coupling

Abstract

The invention relates to a chemical separation system and method, in particular to a system and method for achieving Kr / CF4 separation through rectification-membrane separation coupling. The molecular sieve membrane is used as a key separation membrane material, a whole set of Kr / CF4 separation and purification process is designed according to the molecular sieve membrane, and the problems of Kr / CF4 purification and consumption of a large amount of heat are well solved.

Description

Technical Field

[0001] The present invention relates to a chemical separation system and method, and in particular to a system and method for realizing Kr / CF4 separation by utilizing distillation-membrane separation coupling. Background Art

[0002] Electronic specialty gases refer to ultra-pure and ultra-clean specialty gases that can be used in the production of the electronics industry. Kr, as an important electronic gas, is widely used in industries such as integrated circuits, display panels, and photovoltaics. However, during the concentration process, fluorocarbons will be enriched in Kr. As the amount of fluorocarbons in the air increases, the difficulty of purifying Kr increases, and the purity of its products is seriously affected. How to efficiently remove CF4 is the key issue in achieving the purification and preparation of high-purity krypton.

[0003] Existing distillation technology presents significant challenges in the purification process of high-purity krypton. Relying solely on distillation towers to separate high-purity krypton often requires a multi-stage series connection, such as three towers or even more distillation units, which not only increases the complexity of the process flow, but also leads to huge energy consumption. In addition, although getter technology is used in the purification process of krypton, it is not economical in actual applications due to the large loss of metal materials. At the same time, due to the reaction between the getter surface and krypton to generate solid products such as zirconium carbide (ZrC) and zirconium fluoride (ZrF4), these by-products will gradually cover the getter surface, seriously affecting its adsorption efficiency and service life. In addition, traditional adsorbents such as 13X molecular sieves have limited capture capabilities for trace carbon tetrafluoride (CF4) and cannot meet the needs of deep removal of such impurities in high-purity krypton.

[0004] Membrane separation technology is an emerging technology for separation and purification. It can be used together with distillation to improve the purification effect. However, for Kr / CF4 separation, the temperature of the material flow after preliminary purification in the distillation tower is extremely low. It needs to be heated to a higher temperature to ensure the normal application of the membrane material, which will undoubtedly consume a lot of heat. Therefore, it is urgent to transform the existing Kr / CF4 separation and purification process to solve the above problems. Summary of the invention

[0005] In view of the above problems, the present invention utilizes molecular sieve membrane as the key separation membrane material, and designs a complete set of Kr / CF4 separation and purification processes accordingly, which effectively solves the problems of Kr / CF4 purification and large amount of heat consumption.

[0006] As the first contribution of the present invention, the present invention provides a system for achieving Kr / CF4 separation by utilizing distillation-membrane separation coupling, which includes a preliminary distillation tower and a membrane separation device connected in sequence, wherein the feed side of the membrane separation device is connected to the bottom of the preliminary distillation tower, the permeate side of the membrane separation device is connected to the secondary distillation tower or the permeate side of the membrane separation device is connected to the feed side of the preliminary distillation tower again via 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 module or a plurality of membrane modules. When the membrane separation device comprises a plurality of membrane modules, the plurality of membrane modules are arranged in series, in parallel, or in both series and parallel configurations.

[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°C and 0.2-1MPaG.

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

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

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

[0012] Preferably, the secondary distillation tower has a plate number of 5-20 and a reflux ratio of 5-10.

[0013] The present invention also provides a method for realizing Kr / CF4 separation by utilizing distillation-membrane separation coupling, comprising the following steps: 1) A liquid material containing Kr and CF4 is passed into a preliminary distillation tower, and the distillate from the top of the preliminary distillation tower is used as a product. The feed temperature of the liquid material is -160°C to -127°C, and the CF4 concentration in the liquid material is 20-1000ppm; 2) The materials in the bottom of the preliminary distillation tower are heated to -100~-120℃ through a heat exchanger and then introduced into the feed end of the membrane separation device to achieve CF4 retention on the retentate side through membrane separation; 3) The material obtained from the permeation side of the membrane separation device is further passed into a secondary distillation tower for further separation and purification, or the material obtained from the permeation side of the membrane separation device is further passed into a buffer tank and further passed into a preliminary distillation tower.

[0014] Preferably, in step 1), the CF4 concentration in the overhead distillate after preliminary distillation in the preliminary distillation tower is 0.05-1 ppm, and the CF4 concentration in the material obtained in the bottom of the tower is 500 ppm - 20000 ppm.

[0015] Preferably, after the secondary distillation in the secondary distillation tower in step 3), the CF4 concentration in the overhead distillate is less than 1 ppm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: First, the CHA molecular sieve membrane used in the present invention can maintain stable separation performance at a relatively low temperature, so efficient membrane separation can be achieved by only moderately heating the ultra-low temperature liquid phase material in the reactor of the preliminary distillation tower to a gas phase. 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 production costs.

[0017] Secondly, the present invention can achieve efficient separation and purification of Kr and CF4 through the coupling process of distillation and membrane separation. This specific separation design ensures the high purity of the product and meets the strict requirements of the electronics industry for high-purity krypton. The purity of the Kr product treated by the present invention 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 electronics industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : The Kr / CF4 separation system of Example 1 of the present invention, wherein 1-preliminary distillation tower, 2-membrane separation device, 3-secondary distillation tower, 4-heat exchanger, 5-condenser.

[0019] Figure 2 : The Kr / CF4 separation system of Example 3 of the present invention, wherein 1-preliminary distillation tower, 2-membrane separation device, 4-heat exchanger, 5-condenser, 6-buffer tank.

[0020] Figure 3 : An enlarged view of the single-stage membrane separation device of Example 1 of the present invention.

[0021] Figure 4 : An enlarged view of the double-stage series membrane separation device of Example 1 of the present invention.

[0022] Figure 5 : Kr / CF4 separation effect of the membrane used in Example 1 of the present invention under different feed pressures. DETAILED DESCRIPTION

[0023] The following descriptions are merely preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention.

[0024] Example 1 Figure 1 This is a system for realizing Kr / CF4 separation by distillation-membrane separation coupling in this embodiment, which includes a primary distillation tower 1, a membrane separation device 2 and a secondary distillation tower 3 connected in sequence, the feed side W1 of the membrane separation device 2 is connected to the tower kettle of the primary distillation tower 1, the permeate side F2 of the membrane separation device 2 is connected to the secondary distillation tower 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 provided on the pipeline connecting the feed side of the membrane separation device 2 to the tower kettle of the primary distillation tower to convert the liquid phase material into a gas phase material, and a condenser 5 is provided on the pipeline connecting the permeate side of the membrane separation device 2 to the secondary distillation tower 3 to convert the gas phase material into a liquid phase material.

[0025] Example 2 Figure 2 This is a system for realizing Kr / CF4 separation by distillation-membrane separation coupling in this embodiment, which includes a buffer tank 6, a preliminary distillation tower 1 and a membrane separation device 2 connected once, the discharge side of the buffer tank 6 is connected to the feed side of the preliminary distillation tower 1, the feed side W1 of the membrane separation device 2 is connected to the tower bottom of the preliminary distillation tower 1, and the permeate side F2 of the membrane separation device 2 is connected to 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 provided on the pipeline connecting the feed side of the membrane separation device 2 and the tower bottom of the preliminary distillation tower to convert the liquid phase material into a gas phase material, and a condenser 5 is provided on the pipeline connecting the permeate side of the membrane separation device 2 and the buffer tank 6 to convert the gas phase material into a liquid phase material.

[0026] The membrane separation device in Examples 1 and 2 is a single-stage membrane device, and its enlarged diagram is shown in FIG. Figure 3 In other cases, such as Figure 4 As shown, the middle membrane separation device in Examples 1 and 2 can be replaced by a two-stage series type.

[0027] Example 3 Taking a membrane separation device using a single-stage membrane as an example, the method for realizing Kr / CF4 separation using the distillation-membrane separation coupling system of Example 1 is described: This technology adopts a separation method of distillation-membrane separation coupling, including preliminary distillation, membrane separation and secondary distillation. The feed raw material F1 includes Kr and CF4, of which the CF4 concentration is 100 ppm, the feed pressure is 0.2 MPa, the feed temperature is -143.7℃, the feed is all liquid phase, and the feed flow rate is 11.67 L / min. The number of plates of the distillation tower T1 is 9, the feed position is the feed above the 6th plate, the reflux ratio is 3-6.4, the top condenser temperature is -145.3℃, and the tower bottom reboiler temperature is -143.3℃. After separation in distillation tower T1, the distillate D1 at the top of the distillation tower is used as the product, and the CF4 concentration in its stream is between 0.1 ppm and 1 ppm, with a flow rate of 9.57 L / min; the CF4 concentration in the stream W1 in the distillation tower kettle varies from 500 ppm to 20000 ppm, with a flow rate of 2.1L / min. At this time, the stream needs to be recovered for secondary purification. The W1 stream is heated to -120 ℃ through a heat exchanger to make the stream a pure gas phase, and then passed into a membrane separation device. The membrane separation technology is used to retain CF4 on the retentate side, and then the stream P1 on the permeate side is pressurized and condensed to stream F2 and passed into distillation tower 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 number of plates of distillation tower T2 is 8, the feed position is above the 5th plate, the reflux ratio is 7.8, the top condenser temperature is -125.1 ℃, and the bottom reboiler temperature is -124.3 ℃. After separation in distillation tower T2, the top distillate D2 of the distillation tower is used as the product. When the CF4 concentration in the feed F2 is below 1000 ppm, the CF4 concentration in the top 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%.

[0028] Example 4 Taking a membrane separation device using a single-stage membrane as an example, the method of realizing Kr / CF4 separation using the distillation-membrane separation coupling system of Example 2 is described: This technology adopts a separation method of distillation-membrane separation coupling, including two parts: preliminary distillation and membrane separation. The permeate side stream of membrane separation is circulated to the preliminary distillation tower for further separation and purification. The feed raw material F1 includes Kr and CF4, of which the CF4 concentration is 100 ppm, the feed pressure is 0.2 MPa, the feed temperature is -143.7 ℃, the feed is all liquid phase, and the feed flow rate is 11.67 L / min; the circulating stream F2 is the permeate side stream of the membrane separation device, with a flow rate of 1.71 L / min. The number of plates of the preliminary distillation tower T1 is 9, the feed position is the feed above the 6th plate, the reflux ratio is 2.6-5.2, the top condenser temperature is -145.3 ℃, and the tower bottom reboiler temperature is -143.3 ℃. After separation in the preliminary distillation tower T1, the distillate D1 from the top of the preliminary distillation tower is used as the product, and the CF4 concentration in the stream is between 0.1 ppm and 1 ppm, with a flow rate of 11.18 L / min; the CF4 concentration in the stream W1 in the bottom of the preliminary distillation tower varies from 500 ppm to 20000 ppm, with a flow rate of 2.2 L / min. The W1 stream is heated to -120 °C through a heat exchanger to make the stream a pure gas phase, and is passed into the membrane separation device at a pressure of 0.6 MPa through a pressure conversion device. The membrane separation technology is used to isolate CF4 on the retentate side, and then the stream P1 on the permeate side is pressurized and condensed to stream F2, which is mixed with F1 and passed into the distillation tower T1 to realize the circulation of the stream. The flow rate of stream F2 is 1.71 L / min, the pressure is 0.2 MPa, and the temperature is -143.7 °C.

[0029] Example 5 The molecular sieve membrane used in the above-mentioned Examples 1 and 2 is a CHA molecular sieve membrane, and the specific preparation steps thereof are as follows: First, the synthesis solution was 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 was weighed, mixed, heated and stirred until the solution was transparent. Subsequently, the transparent synthesis solution was transferred to a stainless steel reactor and aged at 95 °C for 3 days. Next, the porous α-Al2O3 carrier was immersed in 0.5 wt% seed solution for crystal coating and dried at 60 °C. After that, the carrier was transferred to a reactor for hydrothermal synthesis at 180 °C for 1 day. Finally, the prepared membrane was placed in an ozone atmosphere and calcined at 200 °C for 4 days to obtain a high-performance CHA molecular sieve membrane.

[0030] The performance of the CHA molecular sieve membrane prepared above was characterized. The membrane tube was installed in the membrane assembly and sealed. The mixed gas used for the test entered from the membrane surface. After the pressure was adjusted by the back pressure valve, the pressure difference on both sides of the membrane was used as the driving force for the permeation of gas molecules to drive the gas permeation. The flow rate on the permeation side was read by the flow meter, and the concentration of each component on the permeation side was obtained by the gas chromatograph. The permeability of each component in the gas can be calculated by the following formula, expressed as: in, It represents the permeability of component i under this condition, in units of , It represents the volume flow rate of component i on the permeate side, in units of , Indicates the test temperature in °C. Represents the effective membrane area in units of .

[0031] The separation selectivity of different components is expressed as: in, and Represents the permeability of component i and component j respectively, in units of .

[0032] The Kr / CF4 separation performance under different feed pressures was studied. Under the conditions of feed flow rate of 500 mL / min and mixed gas CF4 concentration of 3000 ppm, the feed pressure (0.2 MPaG – 1.0 MPaG) was changed by adjusting the back pressure valve and the gas composition on the permeate side was analyzed. The results are shown in Figure 5. It can be found that with the increase of feed pressure, the separation selectivity of Kr / CF4 is greater than 30, and the permeability of Kr remains stable at 2×10 -8 , and CF4 permeability increases with the increase of pressure. When the feed pressure is 1 MPaG, the CF4 content in the permeate side drops to 185 ppm. The stream after membrane separation enters the distillation tower for further purification, and the CF4 concentration in the obtained Kr can reach below 1 ppm.

Claims

1. A system for realizing Kr / CF4 separation by coupling distillation-membrane separation, characterized in that: It comprises a primary distillation tower and a membrane separation device which are connected in sequence, wherein the feed side of the membrane separation device is connected to the kettle of the primary distillation tower, the permeate side of the membrane separation device is connected to the secondary distillation tower or the permeate side of the membrane separation device is connected to the feed side of the primary distillation tower again via a buffer tank, and the separation membrane material in the membrane separation device is a molecular sieve membrane.

2. The system according to claim 1, characterized in that The membrane separation device comprises a single membrane component or a plurality of membrane components. When the membrane separation device comprises a plurality of membrane components, the plurality of membrane components are arranged in series or in parallel, or are arranged in series and in parallel at the same time.

3. The system according to claim 1, characterized in that 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°C and 0.2-1MPaG.

4. The system according to claim 1, characterized in that A heat exchanger is arranged on the pipeline connecting the feed side of the membrane separation device and the bottom of the preliminary distillation tower to convert the liquid phase material into the gas phase material.

5. The system according to claim 1, characterized in that A condenser is provided on the pipeline connecting the permeation side of the membrane separation device and the secondary distillation tower, or on the pipeline connecting the permeation side of the membrane separation device and the buffer tank to convert the gas phase material into the liquid phase material.

6. The system according to claim 1, characterized in that The number of plates of the preliminary distillation tower is 5-20, and the reflux ratio is 2-6.

4.

7. The system according to claim 1, characterized in that The secondary distillation tower has a plate number of 5-20 and a reflux ratio of 5-10.

8. A method for separating Kr / CF4 by coupling distillation and membrane separation, characterized in that: The method adopts the system for realizing Kr / CF4 separation by distillation-membrane separation coupling as described in any one of claims 1 to 7, and the method comprises the following steps: 1) Passing a liquid material containing Kr and CF4 into a preliminary distillation tower, and using the distillate from the top of the preliminary distillation tower as a product, wherein the feed temperature of the liquid material is -160°C to -127°C, and the concentration of CF4 in the liquid material is 20-1000ppm; 2) The materials in the bottom of the preliminary distillation tower are heated to -100~-120℃ through a heat exchanger and then introduced into the feed end of the membrane separation device to isolate CF4 on the retentate side through membrane separation; 3) The material obtained from the permeate side of the membrane separation device is further passed into a secondary distillation tower for further separation and purification, or the material obtained from the permeate side of the membrane separation device is further passed into a buffer tank and further passed into a preliminary distillation tower.

9. The method according to claim 8, characterized in that In step 1), after preliminary distillation in a preliminary distillation tower, the CF4 concentration in the top distillate is 0.05-1ppm, and the CF4 concentration in the material obtained in the bottom of the tower is 500 ppm - 20000 ppm.

10. The method according to claim 8, characterized in that After the secondary distillation in the secondary distillation tower in step 3), the CF4 concentration in the top distillate is less than 1 ppm.

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