阅读说明：本技术 电子级chf3的三级精馏方法 (Electronic grade CHF3Three-stage rectification method ) 是由 张奎 华祥斌 黄雨迪 杨青 黄荣保 阙祥育 于 2021-01-27 设计创作，主要内容包括：本发明提供了一种电子级CHF-3的新型制备方法,包括：S1,在催化剂列管(105)由上而下通入HF与二氟一氯甲烷混合的反应气体,其中,所述HF与所述二氟一氯甲烷的比例为1.05～1.1:1；所述催化剂列管(105)包括活化催化剂颗粒,所述催化剂颗粒由8～10份重量的三氯化铬/活性炭复合物、50～70份重量的三氯化铝、2～5分重量的氯化镍、2～5份重量的氯化镁混合而成,且三氯化铬在所述三氯化铬/活性炭复合物中的含量为15～25wt％；S2,控制所述催化剂列管(105)上部温度220～230℃,中部温度245～255℃,下部温度230～240℃,反应压力0.05～0.2Mpa,停留时间40～80s,从而获得纯度98％以上的三氟甲烷粗产品；S3,将所述三氟甲烷粗产品经过水洗、碱洗、干燥以及精馏后,得到纯度99.9999％的电子级CHF-3。(The invention provides an electronic grade CHF 3 The novel preparation method of (1), comprising: s1, introducing reaction gas mixed by HF and chlorodifluoromethane into the catalyst tube (105) from top to bottom, wherein the ratio of HF to chlorodifluoromethane is 1.05-1.1: 1; the catalyst tube (105) comprises activated catalyst particles, the catalyst particles are formed by mixing 8-10 parts by weight of chromium trichloride/activated carbon compound, 50-70 parts by weight of aluminum trichloride, 2-5 parts by weight of nickel chloride and 2-5 parts by weight of magnesium chloride, and the content of the chromium trichloride in the chromium trichloride/activated carbon compound is 15-25 wt%; s2, controlling the upper temperature of the catalyst tube (105) to be 220-230 ℃, the middle temperature to be 245-255 ℃, the lower temperature to be 230-240 ℃, the reaction pressure to be 0.05-0.2 Mpa and the retention time to be 40-80S, thereby obtaining a crude trifluoromethane product with the purity of more than 98%; s3, washing, alkali washing, drying and rectifying the crude trifluoromethane productThen, the electronic grade CHF with the purity of 99.9999 percent is obtained 3 。)

1. Electronic grade CHF using novel three-stage rectification device₃The novel three-stage rectification device comprises a first-stage rectification tower (20), a second-stage rectification tower (21) and a third-stage rectification tower (22), and is characterized by comprising: the method comprises the following steps:

s10, controlling the temperature of the first tower kettle (203) to be 5-10 ℃, the temperature of the first tower middle (202) to be-2-5 ℃, and the temperature of the first tower top (201) to be-5-3 ℃; the temperature of the second tower kettle (213) is 0-5 ℃, the temperature of the second tower middle (212) is-5-0 ℃, and the temperature of the second tower top (211) is-6-1 ℃; the temperature of the third tower kettle (213) is-5-0 ℃, the temperature of the third tower middle (212) is-8-2 ℃, the temperature of the third tower top (211) is-8-2 ℃, and dried trifluoromethane gas is introduced;

s11, controlling the emptying amount of the first collector (214) to be 12-20% V in the rectification process₁(ii) a And controlling the emptying rate of the first collector (214) to be 2-5% V₂Wherein V is₁Is the input volume of the second-stage rectifying tower (21), V₂The input amount of the three-stage rectifying tower (22).

2. An electronic grade CHF as claimed in claim 1₃The three-stage rectification method is characterized in that in the step S10, the temperature of the first tower bottom (203) is 7 ℃, the temperature of the first tower (202) is 1 ℃, and the temperature of the first tower top (201) is-1 ℃; the temperature of the second tower kettle (213) is 3 ℃, the temperature of the second tower middle (212) is-2 ℃, and the temperature of the second tower top (211) is-4 ℃; the temperature of the third tower kettle (213) is-2 ℃, the temperature of the third tower middle (212) is-5 ℃, and the temperature of the third tower top (211) is-5 ℃.

3. An electronic grade CHF as claimed in claim 2₃The three-stage rectification method of (1), characterized in that, in step S11, the first collector (214) is emptied at 15% V₁(ii) a The first collector (214) is emptied by 5% V₂。

4. An electronic grade CHF as claimed in claim 1₃The three-stage rectification method is characterized in that the first-stage rectification tower (20) and the second-stage rectification tower (21) are of an integrated structure.

5. An electronic grade CHF as claimed in claim 1₃The three-stage rectification method is characterized in that the three-stage rectification tower (22) is of a split structure, the third tower top (211) and the third tower middle (212) are arranged in a separated mode, and the third tower kettle (213) is arranged at the bottom of the third tower middle (212).

6. An electronic grade CHF as claimed in claim 5₃The three-stage rectification method is characterized in that the three-stage rectification tower (22) further comprises a sample collector (224), and the sample collector (224) is connected to the top of the third tower top (211).

7. An electronic grade CHF as claimed in claim 5₃The tertiary rectification method of (2), characterized in that the tertiary rectification apparatus further comprises a storage tank (23), the storage tank (23) being connected to the bottom of the third column top (211).

Technical Field

The invention relates to an electronic grade CHF₃The three-stage rectification method.

Background

Trifluoromethane is a widely used and chemically stable fluoroalkane. In semiconductor processing, the demand for high purity trifluoromethane as an etchant in the fabrication of 8-12 inch chips is increasing with the rapid development of the semiconductor industry.

The purity of the electronic-grade trifluoromethane is generally 99.9999%, and the purification of the electronic-grade trifluoromethane involves the difficulty in deep removal technology separation of various impurities. At present, the purity of the existing industrialized trifluoromethane in China is low, reports are few, and the patent 201110423419.4 adopts a low-temperature batch rectification process to prepare the high-purity trifluoromethane, the purity reaches 99.99 percent, and the use requirement of the semiconductor industry (electronic grade) is not met.

Disclosure of Invention

The invention provides an electronic grade CHF₃The three-stage rectification method can effectively solve the problems.

The invention is realized by the following steps:

electronic grade CHF using novel three-stage rectification device₃The novel three-stage rectification device comprises a first-stage rectification tower, a second-stage rectification tower and a third-stage rectification tower, and comprises: the method comprises the following steps:

s10, controlling the temperature of the first tower kettle to be 5-10 ℃, the temperature in the first tower to be-2-5 ℃ and the temperature at the top of the first tower to be-5-3 ℃; the temperature of the kettle of the second tower is 0-5 ℃, the temperature in the second tower is-5-0 ℃, and the temperature at the top of the second tower is-6 to-1 ℃; the temperature of the kettle of the third tower is-5-0 ℃, the temperature in the third tower is-8 to-2 ℃, the temperature at the top of the third tower is-8 to-2 ℃, and the dried trifluoromethane gas is introduced;

s11, controlling the emptying amount of the first collector to be 12-20% V in the rectification process₁(ii) a And controlling the emptying rate of the first collector to be 2-5% V₂Wherein V is₁Is the input volume of the second-stage rectifying tower, V₂The input amount of the three-stage rectifying tower.

The invention has the beneficial effects that: the rectification method can rectify the crude trifluoromethane product with the purity of more than 98 percent to obtain the electronic grade CHF with the purity of 99.9999 percent₃。

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is an electronic grade CHF provided by an embodiment of the present invention₃Schematic structural diagram of the novel preparation device.

FIG. 2 is an electronic grade CHF provided by an embodiment of the invention₃The structure of part of the components in the novel preparation device is shown schematically.

FIG. 3 is an electronic grade CHF provided by an embodiment of the invention₃The flow chart of the preheating activation method of the novel preparation device.

FIG. 4 is a graph of CHF prepared using a novel catalyst as provided by an embodiment of the invention₃Is shown in the method flow chart.

FIG. 5 is CHF₃The structure of the three-stage rectifying device is shown schematically.

FIG. 6 is CHF₃A process flow diagram of the three-stage rectification process.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

Referring to FIG. 1, an embodiment of the present invention provides an electronic grade CHF₃The novel preparation device of (1), comprising:

the reaction tank 10 includes: the device comprises a hollow tank body 101, a top cover 102 detachably arranged at the top of the hollow tank body 101, a bottom cover 103 detachably arranged at the bottom of the hollow tank body 101, partition plates 109 respectively arranged between the hollow tank body 101 and the top cover 102 and between the hollow tank body 101 and the bottom cover 103, a catalyst array pipe 105 penetrating and arranged between the partition plates 109, a gas material inlet 104 arranged at the top cover 102 and a material outlet 106 arranged at the bottom cover 103;

a heating unit 11 including a heat medium pipe inlet 111 provided at the bottom of the hollow tank 101, a heat medium pipe outlet 112 provided at the top of the hollow tank 101, and a heat medium exhaust port 114 provided at the top of the hollow tank 101;

the temperature measuring unit 12 comprises a first temperature sensor 121, a second temperature sensor 122 and a third temperature sensor 123 which are used for measuring the top, the middle and the bottom of the hollow tank body 101;

and a load cell 13 disposed in the top cover 102 for measuring a pressure of the reaction gas in the top cover 102.

The outer layer of the hollow tank body 101 can be made of carbon steel, and the inner layer is made of stainless steel 304. The top cover 102 may be made of stainless steel 304, and the bottom cover 103 may be made of monel. Because the bottom part can generate part of water, HF is dissolved in the water to form water acid, and Monel material is selected to prevent high temperature corrosion and prolong the service life of the equipment. The bottom of the bottom cover 103 is further provided with a sewage draining outlet 107. In addition, since the top cover 102 and the bottom cover 103 are both detachable structures, replacement of the catalyst tubes 105 is facilitated.

Referring to fig. 2, as a further improvement, the reaction tank 10 includes a further gas outlet cover 108 covering the gas material inlet 104, wherein the gas outlet cover 108 is of an inverted trapezoidal structure, and two side edges thereof are uniformly provided with a plurality of openings 1082. Correspondingly, the catalyst tubes 105 are uniformly distributed in the middle of the hollow tank 101. It is understood that the above configuration allows sufficient mixing of the reaction gas in the top cover 102.

As a further improvement, the catalyst tube 105 comprises catalyst particles filled in the catalyst tube, the catalyst particles are formed by mixing 8-10 parts by weight of chromium trichloride/activated carbon compound, 50-70 parts by weight of aluminum trichloride, 2-5 parts by weight of nickel chloride and 2-5 parts by weight of magnesium chloride, and the content of the chromium trichloride in the chromium trichloride/activated carbon compound is 15-25 wt%. In one embodiment, the catalyst particles are prepared by mixing 8 parts by weight of chromium trichloride/activated carbon composite, 60 parts by weight of aluminum trichloride, 3 parts by weight of nickel chloride and 5 parts by weight of magnesium chloride, and the content of chromium trichloride in the chromium trichloride/activated carbon composite is 20 wt%. The chromium trichloride/activated carbon composite can be used for loading the chromium trichloride on the activated carbon by an impregnation method or other methods. Further, the chromium trichloride/active carbon compound is mixed with other chloride to form the chromium trichloride/active carbon compound.

As a further modification, the heating unit 11 further includes a heat medium drain port 111 provided at the bottom of the hollow tank 101. When the heating unit 11 is used, heating medium is firstly introduced through the heating medium pipeline inlet 111, the heating medium pipeline outlet 112 and the heating medium exhaust port 114 are opened, and the heating medium exhaust port 114 is higher than the heating medium pipeline outlet 112, so that when the heating medium flows out from the heating medium pipeline outlet 112, the heating medium exhaust port 114 is closed. When the heat medium needs to be discharged, the heat medium exhaust port 114 and the heat medium discharge port 111 need to be opened, so that the heat medium can be discharged.

The first temperature sensor 121 and the third temperature sensor 123 may be directly provided with corresponding holes at the top and the bottom of the hollow tank 101. The second temperature sensor 122 is formed by opening a hole from the top cover 102 and the partition 109, respectively, so as to extend into the middle of the hollow can 101, which is advantageous in that the height of measurement can be adjusted. When the temperature is too high or too low in the reaction process, the reaction temperature can be controlled by adjusting the air input or the heating medium flow.

Referring to fig. 3, an embodiment of the invention further provides the electronic-grade CHF₃The preheating activation method of the novel preparation device comprises the following steps:

s1, introducing N into the catalyst tube nest 105₂Heating to 200 ℃ and drying for 5-15 h;

s2, drying, keeping N₂Introducing HF for fluorination at the temperature of 200 ℃, gradually increasing the flow of the HF from 5-10 ml/min to 300ml/min, simultaneously monitoring the temperature of a catalyst tube array 105 through a temperature measurement unit 12, controlling the temperature of the catalyst tube array 105 to be 200 +/-5 ℃, and keeping the flow of the HF for 1-3 hours after the flow is stable;

s3, under the temperature of 200 ℃, the HF flow is unchanged, and N is gradually reduced₂The flow rate is 0ml/min, meanwhile, the temperature of the catalyst tube array 105 is monitored through the temperature measuring unit 12, the temperature of the catalyst tube array 105 is controlled to be 200 +/-5 ℃, and the temperature is kept for 3-5 hours after stabilization;

s4, heating to raise the temperature of the catalyst tube 105 from 200 ℃ to 260 ℃, and keeping for 3-5 hours after stabilization;

s5, heating to raise the temperature of the catalyst tube 105 from 260 ℃ to 300 ℃, and keeping for 3-5 hours after stabilization;

and S6, heating to raise the temperature of the catalyst tube 105 from 300 ℃ to 350 ℃, keeping the temperature for 20-28 h after stabilization, and reducing the temperature to the reaction temperature to complete preheating and activation.

As a further improvement, in step S1, N is introduced into the catalyst tubes 105₂And heating to 200 ℃ and drying for 5-15 h, wherein the steps comprise:

s11, holding N₂The flow rate is 200-400 ml/min, the temperature of the catalyst tube array 105 is increased to 100 ℃ at the temperature increase rate of 5-10 ℃/min, and the catalyst tube array is dried for 2-6 h at constant temperature;

and S12, raising the temperature of the catalyst tube array 105 to 200 ℃ at a temperature raising rate of 5-10 ℃/min, and drying for 3-9 h at constant temperature.

As a further modification, in step S2, the HF flow rate is reduced when the temperature of the catalyst tubes 105 is too high. Step S2 is mainly to reduce the activity of HF and prevent reaction runaway during activation.

As a further modification, in step S3, N is increased when the temperature of the catalyst tubes 105 is too high₂And (4) flow rate. It will be appreciated that the selectivity and efficiency of the catalyst may be improved by the above-described warm-up activation method.

Referring to fig. 4, the present invention further provides a novel method for preparing electronic grade CHF3, comprising: the method comprises the following steps:

s7, introducing reaction gas mixed by HF and chlorodifluoromethane into the catalyst tube 105 from top to bottom, wherein the ratio of HF to chlorodifluoromethane is 1.05-1.1: 1, HF can be partially dissolved in formed water and has no reaction activity, so that excessive HF is needed; the catalyst tubes 105 comprise activated catalyst particles;

s8, controlling the upper temperature of the catalyst tube 105 to be 220-230 ℃, the middle temperature to be 245-255 ℃, the lower temperature to be 230-240 ℃, the reaction pressure to be 0.05-0.2 Mpa and the retention time to be 40-80S, thereby obtaining a crude trifluoromethane product with the purity of more than 98%;

s9, washing, alkali washing, drying and rectifying the crude trifluoromethane product to obtain electronic grade CHF with the purity of 99.9999%₃。

In step S8, it is more preferable that the upper temperature of the catalyst tubes 105 is controlled to 225 ± 2 ℃, the middle temperature is controlled to 250 ± 2 ℃, the lower temperature is controlled to 235 ± 2 ℃, the reaction pressure is controlled to 0.07Mpa, and the residence time is controlled to 60S.

In step S9, the water washing, the alkali washing, and the drying are common steps, and will not be described again. Referring also to fig. 5, fig. 5 is a three-stage rectification apparatus for trifluoromethane.

The three-stage rectifying device comprises a first-stage rectifying tower 20, a second-stage rectifying tower 21 and a third-stage rectifying tower 22, wherein the first-stage rectifying tower 20 is of an integrated structure and comprises a first tower top 201, a first tower middle 202 and a first tower kettle 203 which are sequentially arranged below the first tower top 201, and the first-stage rectifying tower 20 is used for rectifying heavy components; the second-stage rectification tower 21 is of an integral structure and comprises a second tower top 211, a second tower middle 212 and a second tower kettle 213, wherein the second tower middle 212 and the second tower bottom 213 are sequentially arranged below the second tower top 211, the second-stage rectification tower 21 is used for rectifying light components, and the top of the first tower top 201 is connected with the middle part of the second tower middle 212; the third-stage rectifying tower 22 is of a split structure and comprises a third tower top 211, a third tower middle 212 separated from the third tower top 211, and a third tower kettle 213 arranged at the bottom of the third tower middle 212, wherein the bottom of the second tower kettle 213 is connected with the middle part of the third tower middle 212, and the third-stage rectifying tower 22 is used for rectifying the distillate again.

As a further improvement, the second rectification column 21 further comprises a first collector 214, one end of the first collector 214 is connected to the top of the second column top 211, and the other end is arranged to be evacuated. The three-stage rectifying tower 22 further comprises a second collector 224, one end of the second collector 224 is connected with the top of the third tower top 211, and the other end is arranged to be evacuated. By providing one end of the first and second collectors 214, 224 for evacuation, the effectiveness of the rectification can be increased by providing the amount of evacuation. The evacuation of the first and second accumulators 214, 224 is selected according to the amount of feed to the second and third rectification columns 21, 22. Defining the introduction amount of the second-stage rectifying tower 21 as V₁The evacuation amount of the first collector 214 is preferably 12-20% V₁(ii) a The introduction amount of the three-stage rectifying tower 22 is defined as V₂Said first collector 2The evacuation amount of 14 is preferably 2-5% V₂。

As a further improvement, since the three-stage rectification column 22 is a split structure, the three-stage rectification column 22 may further include a sample collector 224, and the sample collector 224 is connected to the top of the third column top 211.

The tertiary rectification apparatus further comprises a storage tank 23, and the storage tank 23 is connected to the bottom of the third tower top 211.

In order to obtain a good rectification effect, the temperatures of the first-stage rectification column 20, the second-stage rectification column 21 and the third-stage rectification column 22 need to be strictly controlled. Specifically, the temperature of the first tower kettle 203 is 5-10 ℃, the temperature of the first tower middle 202 is-2-5 ℃, and the temperature of the first tower top 201 is-5-3 ℃; the temperature of the second tower kettle 213 is 0-5 ℃, the temperature of the second tower 212 is-5-0 ℃, and the temperature of the second tower top 211 is-6 to-1 ℃; the temperature of the third tower kettle 213 is-5 to 0 ℃, the temperature of the third tower 212 is-8 to-2 ℃, and the temperature of the third tower top 211 is-8 to-2 ℃.

Referring to fig. 6, the present invention further provides a three-stage rectification method of trifluoromethane, comprising the following steps:

s10, controlling the temperature of the first tower kettle 203 to be 5-10 ℃, the temperature of the first tower 202 to be-2-5 ℃ and the temperature of the first tower top 201 to be-5-3 ℃; the temperature of the second tower kettle 213 is 0-5 ℃, the temperature of the second tower 212 is-5-0 ℃, and the temperature of the second tower top 211 is-6 to-1 ℃; the temperature of the third tower kettle 213 is-5 to 0 ℃, the temperature of the third tower 212 is-8 to-2 ℃, the temperature of the third tower top 211 is-8 to-2 ℃, and dried trifluoromethane gas is introduced;

s11, controlling the emptying amount of the first collector 214 to be 12-20% V in the rectification process₁(ii) a And controlling the emptying rate of the first collector 214 to be 2-5% V₂Wherein V is₁Is the amount of introduction, V, of the secondary rectification column 21₂The input amount of the three-stage rectifying tower 22.

In step S10, more preferably, the temperature of the first column bottom 203 is 7 ℃, the temperature of the first column bottom 202 is 1 ℃, and the temperature of the first column top 201 is-1 ℃; the temperature of the second tower kettle 213 is 3 ℃, the temperature of the second tower 212 is-2 ℃, and the temperature of the second tower top 211 is-4 ℃; the temperature of the third tower kettle 213 is-2 ℃, the temperature of the third tower 212 is-5 ℃, and the temperature of the third tower top 211 is-5 ℃.

In step S11, it is more preferable that the first collector 214 is emptied by 15% V₁(ii) a The first collector 214 has a drain of 5% V₂。

Example 1:

mixing 8 parts by weight of chromium trichloride/activated carbon compound, 60 parts by weight of aluminum trichloride, 3 parts by weight of nickel chloride and 5 parts by weight of magnesium chloride, wherein the content of chromium trichloride in the chromium trichloride/activated carbon compound is 20 wt%, filling the chromium trichloride/activated carbon compound into the catalyst tube 105, and assembling the catalyst tube to a device for activation; n is a radical of₂The flow rate is 300ml/min, the temperature of the catalyst bed layer is increased to 100 ℃ at the heating rate of 10 ℃/min, and the catalyst bed layer is dried for 4 hours at constant temperature; heating the catalyst tube 105 to 200 ℃ at a heating rate of 10 ℃/min, and drying for 6h at constant temperature; after drying at 200 ℃, starting HF fluorination at the temperature; n is a radical of₂The flow rate is kept at 300ml/min, the HF flow rate is gradually increased from 10ml/min to 300ml/min, 20ml/min can be adjusted every time, the HF flow rate is adjusted every 1 hour, meanwhile, the temperature of the catalyst tube array 105 is monitored, the reaction hot point of the catalyst tube array 105 is enabled to be less than 5 ℃, the HF flow rate is reduced when necessary, and the HF flow rate is kept for 2 hours after being stabilized; keeping the temperature at 200 ℃, keeping the HF flow constant, gradually reducing the nitrogen flow to 0ml/min, adjusting the nitrogen flow to 50ml/min every time, adjusting the nitrogen flow once every 1 hour, monitoring the temperature of the catalyst tube 105, ensuring that the reaction hot spot of the catalyst tube 105 is less than 5 ℃, and increasing N when necessary₂The flow is kept for 4 hours after being stabilized; the temperature of the catalyst tube 105 is increased from 200 ℃ to 260 ℃, the temperature increase rate is 5 ℃/min and then the temperature is kept for 4 h; the temperature of the catalyst tube 105 is increased from 260 ℃ to 300 ℃, the temperature increase rate is 5 ℃/min and then the temperature is kept for 4 h; the temperature of the catalyst tube 105 is increased from 300 ℃ to 350 ℃, the temperature rising rate is 5 ℃/min, the reaction temperature is kept for 24h after the temperature rising rate is stabilized, and the activation is finished. After the activation is completed, introducing HF and the chlorodifluoromethane in a molar ratio of 1.08:1, controlling the upper temperature of the catalyst tube array 105 to be 195 +/-2 ℃, the middle temperature to be 255 +/-2 ℃, the lower temperature to be 245 +/-2 ℃, the reaction pressure to be 0.07Mpa and the retention time to be 60-70 s, thereby obtaining a crude trifluoromethane product with the purity of more than 98%; washing, alkaline washing, drying and rectifying the crude trifluoromethane product to obtain the electronic grade CHF with the purity of 99.99999%₃Wherein the first collector 214 is emptied by 15% V during the rectification₁(ii) a The first collector 214 has a drain of 5% V₂(ii) a The temperature of the first tower kettle 203 is 7 ℃, the temperature of the first tower 202 is 1 ℃, and the temperature of the first tower top 201 is-1 ℃; the temperature of the second tower kettle 213 is 3 ℃, the temperature of the second tower 212 is-2 ℃, and the temperature of the second tower top 211 is-4 ℃; the temperature of the third tower kettle 213 is-2 ℃, the temperature of the third tower 212 is-5 ℃, and the temperature of the third tower top 211 is-5 ℃.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.