Directional synthesis process of electronic-grade hexafluoroethane based on composite catalyst

Abstract

The invention relates to the technical field of electronic-grade fluorine-containing special gas synthesis, in particular to an electronic-grade hexafluoroethane directional synthesis process based on a composite catalyst, which comprises the following steps: S1, carrying out reflux treatment on activated carbon by hydrofluoric acid-nitric acid mixed liquor, sequentially loading aluminum trichloride, cesium fluoride, lanthanum oxide and graphene quantum dots, and roasting in a nitrogen atmosphere to prepare the composite catalyst; s2, mixing tetrafluoroethylene and hydrogen fluoride in proportion, dehydrating through a molecular sieve, and removing impurities through a nano-zinc oxide coating purification tower; s3, introducing the raw materials into a fixed bed with a guide plate, and carrying out segmented temperature control reaction under the adjustment of a composite catalyst and perfluorohexane; and S4, condensing, alkali-washing and drying the reaction product, and rectifying in a rectifying tower to obtain the electronic-grade hexafluoroethane. And S5, adsorbing the rectification tail gas by a composite adsorbent, and resolving and recycling the raw materials for pretreatment. The process improves the selectivity and purity of hexafluoroethane, prolongs the service life of the catalyst, is good in regeneration effect, reduces energy consumption and raw material loss, reduces wastewater discharge, and meets the requirements of the semiconductor industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic grade fluorine-containing special gas synthesis, in particular to an electronic grade hexafluoroethane directional synthesis process based on a composite catalyst. BACKGROUND

[0002] Electronic grade hexafluoroethane, as a key electronic special gas, is widely used in the core links of plasma etching, chemical vapor deposition and other processes in semiconductor chip manufacturing. Its purity requirement is extremely high, reaching more than 99.999%, and the impurity content (such as moisture, acidity, fluorine-containing hydrocarbons, carbon monoxide, etc.) needs to be controlled at the ppm or even ppb level, otherwise it will cause chip yield reduction and circuit performance damage. With the development of the semiconductor industry to 7nm and below advanced processes, the purity and impurity control of electronic grade hexafluoroethane are put forward with more stringent requirements, which promotes the continuous upgrading of synthesis process.

[0003] The current mainstream synthesis process of electronic grade hexafluoroethane uses tetrafluoroethylene and hydrogen fluoride as raw materials to prepare through catalytic addition reaction, but there are three major technical bottlenecks. First, the low directional synthesis efficiency caused by the insufficient performance of the catalyst. The existing catalysts are mostly single metal fluorides (such as chromium fluoride, aluminum fluoride) or single-component supported catalysts, and the active sites are unevenly dispersed, which easily leads to activity decay due to carbon deposition or fluorine loss, and the selectivity of hexafluoroethane is insufficient, with by-products (such as tetrafluoromethane, octafluoropropane) accounting for more than 5%, which not only reduces the utilization rate of raw materials, but also increases the difficulty of subsequent refining. Some processes try to introduce a catalyst to improve performance, but most of them are simple physical mixing, without forming a synergistic mechanism, making it difficult to break through the balance between selectivity and stability.

[0004] Second, the raw material pretreatment and product refining process is extensive, and the impurity control is difficult. The tetrafluoroethylene raw material often contains trace amounts of water, oxygen and olefin impurities, and hydrogen fluoride easily carries acidic impurities. If the pretreatment is not thorough, it will react with the catalyst to generate inactive substances, and at the same time, the acidic impurities and oxygen-containing compounds in the product will exceed the standard. The existing pretreatment mostly uses single molecular sieve dehydration or simple adsorption to remove impurities, which is difficult to achieve simultaneous deep removal of multiple impurities, and the total impurity content of the purified raw material is often more than 3ppm. In the product refining process, the traditional rectifying column mostly uses single temperature control and fixed reflux ratio, which has poor separation effect on fluorine-containing impurities (such as pentafluoroethane, heptafluoropropane) with similar boiling points, and needs multiple distillations to meet the standard, which is high in energy consumption and long in process. Some processes sacrifice yield to pursue purity, resulting in high production cost.

[0005] Third, the process continuity and resource recycling are poor, and the economy is limited. The fixed bed reactor adopts overall temperature control, the raw materials and the catalysts are not uniformly contacted, local overheating is easy to occur, the side reaction is intensified, the catalyst is deactivated, and the high-efficiency regeneration system is not established, which causes resource waste. In the tail gas treatment link, the traditional process adopts direct combustion or alkali washing discharge, and the unreacted tetrafluoroethylene and hydrogen fluoride are not recovered, which not only pollutes the environment, but also causes the raw material loss rate to be more than 8%, further increasing the cost. In addition, the existing process lacks coordinated control in each link, such as the raw material pretreatment effect is not linked with the reaction parameters, and the product purity is not matched with the rectification conditions in real time, which is easy to cause process interruption or product unqualified, and is difficult to meet the demand of the semiconductor industry for the stability of special gas supply.

[0006] From the industry application, although the foreign advanced process can realize the preparation of high-purity products, the core technology and catalyst formula are monopolized, therefore, developing a set of directional synthesis technology with high selectivity composite catalyst, deep pretreatment-refining coordinated process and full-process resource recycling becomes the key to break through the technical barriers of foreign countries and guarantee the safety of domestic semiconductor industry supply chain. SUMMARY

[0007] (1) Technical problems solved

[0008] In view of the deficiencies of the prior art, the present application provides an electronic grade hexafluoroethane directional synthesis process based on a composite catalyst.

[0009] (2) Technical scheme

[0010] The electronic grade hexafluoroethane directional synthesis process based on a composite catalyst comprises the following steps:

[0011] S1. Catalyst preparation: immerse the activated carbon carrier in a mixed solution of hydrofluoric acid and nitric acid, and treat it under reflux at 80℃; after the reflux is completed, take out the activated carbon carrier, wash it with deionized water until the pH value of the washing water is 6.5-7.5, and then dry it; immerse the dried activated carbon carrier in an aluminum chloride ethanol solution, take it out and dry after standing; immerse it in a mixed aqueous solution of cesium fluoride and lanthanum oxide, take it out and dry after standing; finally, immerse it in a graphene quantum dot dispersion liquid, take it out and dry after standing; put the loaded activated carbon carrier into a calcination furnace, pass nitrogen gas, and obtain a composite catalyst;

[0012] S2. Raw material pretreatment: pass tetrafluoroethylene and hydrogen fluoride into a mixer, mix thoroughly, and then send it into a dehydration device to dehydrate the raw material to a water content of ≤5ppm; pass the dehydrated raw material into a purification tower to deeply remove impurities in the raw material;

[0013] S3. Directional synthesis reaction: the pretreated raw material is introduced into the fixed bed reactor through the raw material conveying pipeline, and perfluorohexane is injected into the raw material conveying pipeline through a micro-metering pump; the upper section temperature of the fixed bed reactor is controlled at 320-340℃, the middle section temperature is controlled at 340-360℃, and the lower section temperature is controlled at 360-380℃, and the raw material reacts in the reactor to generate a mixed product containing hexafluoroethane;

[0014] S4. Product purification: the reaction generated mixed product is sent to a condensing device to separate liquid impurities in the mixed product; the gas phase product after condensation is introduced into an alkali washing tower to remove acidic impurities in the gas phase product; the alkali washed gas phase product is introduced into a drying tower and dried to a water content of ≤2ppm in the gas phase product; the dried gas phase product is sent to a rectifying tower to obtain electronic grade hexafluoroethane by rectification;

[0015] S5. Tail gas treatment: the tail gas discharged from the top of the rectifying tower is introduced into an adsorption tower to adsorb and recover unreacted raw materials in the tail gas; after adsorption is completed, nitrogen is introduced into the adsorption tower to raise the temperature of the adsorption tower to 120-150℃, and the adsorbed raw materials are desorbed and recovered, and the desorbed raw materials are reused in step S2.

[0016] Preferably, it also includes an ultrasonic auxiliary step in the composite catalyst loading process: when the activated carbon carrier is immersed in an aluminum chloride ethanol solution, a cesium fluoride and lanthanum oxide mixed aqueous solution, and a graphene quantum dot dispersion, respectively, an ultrasonic generator is started, the ultrasonic frequency is controlled at 30-40kHz, the power is controlled at 150-200W, and the ultrasonic treatment is performed for 30 minutes.

[0017] Preferably, it also includes an impurity detection step after pretreatment of the raw material: an online gas chromatograph is arranged at the outlet of the purification tower to detect the pretreated raw material in real time, and the detection items include oxygen content, olefin impurity content, and water content, so as to ensure that the oxygen content in the raw material is ≤0.5ppm, the olefin impurity is ≤0.3ppm, and the water content is ≤5ppm; if the detection index exceeds the standard, the raw material is returned to the dehydration device for reprocessing.

[0018] Preferably, the fixed bed reactor in step S3 is also provided with a raw material distributor, the raw material distributor is located at the top of the reactor, adopts a multi-hole ring pipe structure, the hole diameter is 0.5-1mm, and 30-40 air holes are uniformly arranged on the distributor.

[0019] Preferably, the alkali washing tower in step S4 adopts a countercurrent contact mode, potassium hydroxide solution is sprayed from the top of the alkali washing tower, the gas phase product is introduced from the bottom, 3-5 layers of corrugated fillers are arranged in the tower, and the filler material is polytetrafluoroethylene.

[0020] Preferably, the rectification tower in step S4 is also provided with a side line take-off device, the side line take-off outlet is located in the middle of the rectification tower, at a distance of 30-40 theoretical tower plates from the tower kettle, when the purity of the overhead product does not meet the requirements, the intermediate product is taken out through the side line take-off part and is refluxed to the middle of the rectification tower for re-distillation.

[0021] Preferably, the adsorption tower in step S5 adopts a double-tower parallel structure, one adsorption tower performs adsorption operation, and the other adsorption tower performs desorption regeneration, and after desorption is completed, switching is used to ensure that the tail gas treatment is continuously performed, and when desorption regeneration is performed, nitrogen is first blown for 1 hour, and then the temperature is raised to 120-150 DEG C for 2 hours.

[0022] Preferably, the calcination furnace in step S1 adopts programmed temperature rising, from room temperature to 150 DEG C at a rate of 5 DEG C / min, and then to 350-400 DEG C at a rate of 8 DEG C / min, and then to room temperature at a rate of 10 DEG C / min after calcination is completed, to avoid damage to the structure of the catalyst due to sudden temperature change.

[0023] Preferably, the fixed bed reactor in step S3 is also provided with a pressure stabilizing system, when the pressure fluctuation in the fixed bed reactor exceeds + / - 0.05 MPa, the system automatically adjusts the feed rate of the raw material, the feed rate of the raw material is adjusted in the range of + / - 10% of the set value, and the reaction pressure is stabilized at 0.8-1.2 MPa.

[0024] Preferably, the electronic grade hexafluoroethane product in step S4 needs to be detected offline, the detection items include moisture, acidity, carbon monoxide, carbon dioxide and total hydrocarbon, the detection adopts a gas chromatography-mass spectrometer and a trace moisture tester, to ensure that the moisture in the product is less than or equal to 2 ppm, the acidity is less than or equal to 0.05 ppm calculated by HF, the carbon monoxide is less than or equal to 0.1 ppm, the carbon dioxide is less than or equal to 0.1 ppm, and the total hydrocarbon is less than or equal to 0.5 ppm, and the product can be packaged and stored only after passing the detection.

[0025] (Three) beneficial technical effects

[0026] Compared with the existing technology, the beneficial effects of the present application are:

[0027] 1. The pore structure is optimized by acid treatment modification of the activated carbon carrier, and then aluminum chloride, cesium fluoride, lanthanum oxide and graphene quantum dots are loaded in sequence, forming a synergistic mechanism of 'active center-electronic regulation-structure support'. Compared with traditional single or simple mixed catalysts, the composite catalyst can significantly improve the selectivity of hexafluoroethane, inhibit the generation of by-products, and the introduction of graphene quantum dots can enhance the dispersion and stability of the active components, prolong the service life of the catalyst, cooperate with the subsequent segmented regeneration process, avoid frequent replacement of the catalyst, reduce resource consumption, and solve the problem that the selectivity and stability of traditional catalysts are difficult to balance.

[0028] 2. Through the multi-technology fusion to realize the impurity depth control and the high efficiency separation. The raw material pretreatment adopts the mixed molecular sieve dehydration and the nanometer zinc oxide coating purification tower cooperation, can remove water, oxygen, olefin and acidic impurities simultaneously, compared with the traditional single pretreatment mode, the impurity content of the raw material after purification is lower, provides the clean raw material environment for the subsequent reaction, avoids the catalyst poisoning. In the product refining link, the combined process of segmented condensation-alkali washing-modified molecular sieve drying-precision rectification is adopted, the rectification tower is combined with theta ring packing and ultrasonic oscillation device, gradient temperature control and dynamic reflux ratio adjustment are matched, the separation effect of the fluorine-containing impurities with similar boiling points is better, the electronic grade purity requirement can be reached without multiple rectification, the process is shortened and the energy consumption is reduced, the problems of unstable purity and high energy consumption caused by the traditional refining process are solved.

[0029] 3. Through the reactor structure optimization and the whole process cooperation control, the overall operation efficiency and the economy are improved. The fixed bed reactor adopts the honeycomb guide plate and the gradient particle size catalyst filling, cooperates the three section temperature control design, ensures that the raw material and the catalyst are uniformly contacted, avoids the local overheating to cause the side reaction, improves the reaction stability and the product consistency. After the catalyst deactivation, the activity can be efficiently recovered through the segmented regeneration process, the whole replacement is not needed, the service life is prolonged, and the solid waste generation is reduced. The tail gas treatment adopts the double tower parallel adsorption and analysis recovery technology, can efficiently recover the unreacted raw material and return to the pretreatment link, avoids the resource waste and the environmental pollution caused by the traditional combustion emission, reduces the raw material loss rate, and improves the process economy. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the electronic grade hexafluoroethane directional synthesis process flow chart based on the composite catalyst disclosed by the application;

[0031] Figure 2 is the selectivity and raw material conversion rate line comparison chart of the example and the comparative example hexafluoroethane;

[0032] Figure 3 is the acidity and moisture columnar line comparison chart of the example and the comparative example;

[0033] Figure 4 is the test result radar comparison chart of the example and the comparative example. DETAILED DESCRIPTION

[0034] According to Figures 1 to 4 , the specific embodiments of the application are as follows:

[0035] Raw material and equipment preparation

[0036] Raw material specification

[0037] Tetrafluoroethylene: purity ≥ 99.99% moisture ≤ 10 ppm oxygen content ≤ 5 ppm;

[0038] Hydrogen fluoride: purity ≥ 99.99% acidity ≥ 99.9% HF moisture ≤ 8 ppm;

[0039] Composite catalyst preparation raw materials: activated carbon (specific surface area 1000 m 2 / g particle size 3 mm pore volume 1.0 cm 3 / g) hydrofluoric acid (analytical pure) nitric acid (analytical pure) aluminum chloride (chemically pure) cesium fluoride (spectrally pure) lanthanum oxide (99.9%) graphene quantum dots (particle size 5-10 nm);

[0040] Auxiliary materials: 4A molecular sieve 13X molecular sieve nano zinc oxide (particle size 20-30 nm) potassium hydroxide (analytical pure) 3A molecular sieve hexamethyl disilazane (98%) perfluorohexane (purity 99.99%) activated carbon-montmorillonite composite adsorbent;

[0041] Equipment list

[0042] Catalyst preparation equipment: constant temperature reflux device ultrasonic generator (30-40 kHz) air drying oven programmed temperature calcination furnace;

[0043] Reaction system: raw material mixer dehydration device purification tower fixed bed reactor (with three-stage temperature control and pressure stabilization system) micro-metering pump;

[0044] Refining system: condensing device caustic washing tower drying tower packed distillation column (Monel material with ultrasonic oscillation device);

[0045] Auxiliary equipment: online gas chromatograph trace moisture tester gas chromatograph-mass spectrometer dual-tower adsorption system.

[0046] Example 1

[0047] S1: Composite catalyst preparation

[0048] Immerse 100g of activated carbon carrier in a mixed solution of 3% hydrofluoric acid and 5% nitric acid 500mL at 80℃ reflux for 2 hours. After taking out, wash with deionized water until pH=7.0 120℃ dry for 4 hours.

[0049] First loading: immerse the dried activated carbon in 0.5mol / L aluminum chloride ethanol solution 300mL ultrasonic for 30 minutes (35kHz 180W) stand for 2 hours, then dry and load 6% aluminum chloride at 120℃;

[0050] Second loading: immerse in mixed aqueous solution containing cesium fluoride and lanthanum oxide (concentration is 0.2mol / L and 0.1mol / L respectively) ultrasonic for 30 minutes, stand for 1.5 hours, then dry and load 3% cesium fluoride and 2% lanthanum oxide;

[0051] Third load: 1% graphene quantum dots were loaded by immersing the catalyst in 200 mL of a 0.1% graphene quantum dot dispersion for 30 minutes of ultrasonic treatment, standing for 1 hour, and then drying.

[0052] The loaded catalyst was placed in a calcination furnace and subjected to a temperature program of 0.6 L / min nitrogen flow, 5°C / min to 150°C for 1 hour, 8°C / min to 380°C for 3 hours, and then natural cooling, to obtain a calcined catalyst.

[0053] S2: Raw material pretreatment

[0054] Tetrafluoroethylene and hydrogen fluoride were mixed in a mixer at a volume ratio of 1:4 and a stirring rate of 300 r / min for 30 minutes.

[0055] The mixed raw materials were fed into a dehydration device (4A and 13X molecular sieves were filled at a ratio of 2:1) and stayed for 1.8 hours to dehydrate to a water content of 3 ppm.

[0056] After dehydration, the raw materials were passed into a purification tower (the inner wall was coated with an 8 μm nano-zinc oxide coating) at a temperature of 90°C and a pressure of 0.4 MPa for 35 minutes, and online detection showed that the oxygen content was 0.3 ppm and the olefin impurity was 0.2 ppm.

[0057] S3: Directional synthesis reaction

[0058] The fixed bed reactor was equipped with honeycomb-shaped flow guides (spacing 6 cm), and the catalyst bed was filled with 2-3 mm catalyst in the upper section, 3-4 mm catalyst in the middle section, and 4-5 mm catalyst in the lower section, with a void fraction of 40%.

[0059] Perfluorohexane was injected through a micro-metering pump (volume ratio of 0.2:100 with the raw materials), and the reaction parameters were controlled as follows: upper section 330°C, middle section 350°C, lower section 370°C, pressure 1.0 MPa, and space velocity 2000 h-1.

[0060] During the 5-hour reaction period, the pressure stabilization system controlled the fluctuations within ±0.03 MPa.

[0061] S4: Product refining

[0062] The reaction product was fed into a condensing device (-25°C) and stayed for 25 minutes to separate liquid impurities.

[0063] The gas phase was passed into an alkali washing tower (6% potassium hydroxide solution, liquid-gas ratio 1:10) and stayed for 18 minutes on polytetrafluoroethylene corrugated packing 4 layers.

[0064] After alkali washing, the gas phase entered a drying tower (modified 3A molecular sieves with a silanization degree of 35%) and stayed for 1.2 hours, reducing the water content to 1.5 ppm.

[0065] After drying, the gas phase is sent into a rectification tower (60 blocks of theoretical tower plate θ ring packing) with a temperature of -65℃, a pressure of 0.5 MPa, a reflux ratio of 6:1, and a tower top extraction rate of 4%. The side line extraction outlet is located at the 35th tower plate.

[0066] S5: Exhaust gas treatment

[0067] The rectification exhaust gas is introduced into an adsorption tower (activated carbon-montmorillonite 7:3 mixture treated with 1% ammonium fluoride) with a temperature of 25℃, a pressure of 0.4 MPa, and a residence time of 45 minutes.

[0068] When two towers are connected in parallel, one tower is regenerated (nitrogen flow 0.7 L / min, 130℃ desorption for 2 hours) and the raw material is recycled to S2.

[0069] Example 2

[0070] S1: Preparation of composite catalyst

[0071] 100g of activated carbon carrier is immersed in a mixed solution of 3% hydrofluoric acid and 5% nitric acid 500mL at 80℃ under reflux for 2 hours. After taking out, wash with deionized water until pH=7.0 120℃ dry for 4 hours.

[0072] First loading: immerse the dried activated carbon in 0.5mol / L aluminum chloride ethanol solution 300mL ultrasonic 30 minutes (35kHz 180W) stand for 2 hours and then load 5% aluminum chloride at 120℃;

[0073] Second loading: immerse in mixed aqueous solution containing cesium fluoride and lanthanum oxide (concentration is 0.2mol / L and 0.1mol / L respectively) ultrasonic 30 minutes stand for 1.5 hours and then load 2% cesium fluoride and 1% lanthanum oxide after drying;

[0074] Third loading: immerse in 0.1% graphene quantum dot dispersion liquid 200mL ultrasonic 30 minutes stand for 1 hour and then load 0.5% graphene quantum dots after drying.

[0075] Put the loaded catalyst into the calcination furnace, program the temperature to 350℃ at a nitrogen flow of 0.5L / min, calcine for 3 hours (heating rate: 5℃ / min to 150℃, hold for 1 hour, 8℃ / min to 350℃, hold for 3 hours), and then naturally cool down for standby.

[0076] S2: Raw material pretreatment

[0077] Pass tetrafluoroethylene and hydrogen fluoride into the mixer at a volume ratio of 1:3, stir at a rate of 300r / min, and mix for 30 minutes;

[0078] Pass the mixed raw material into the dehydration device (4A and 13X molecular sieves filled at a ratio of 2:1) and stay for 1.5 hours to dehydrate to a water content of 4ppm;

[0079] After dehydration, the raw material was passed into a purification tower (the inner wall was coated with 8 μm nano zinc oxide coating) to control the temperature at 80°C and the pressure at 0.3 MPa for 30 minutes. The online detection showed that the oxygen content was 0.4 ppm and the olefin impurity was 0.3 ppm.

[0080] S3: directed synthesis reaction

[0081] The honeycomb-shaped flow guide plate (with a spacing of 6 cm) was arranged in the fixed bed reactor, and the upper section of the catalyst bed was filled with 2-3 mm catalyst, the middle section was filled with 3-4 mm catalyst, and the lower section was filled with 4-5 mm catalyst with a void fraction of 35%;

[0082] Perfluorohexane was injected by a micro-metering pump (with a volume ratio of 0.1:100 to the raw material), and the reaction parameters were controlled as follows: the upper section was at 320°C, the middle section was at 340°C, and the lower section was at 360°C, the pressure was 0.8 MPa, and the space velocity was 1500 h-1;

[0083] During the reaction for 5 hours, the pressure stabilization system controlled the fluctuation within ±0.03 MPa.

[0084] S4: product refining

[0085] The reaction product was sent to a condensing device (-30°C) for 25 minutes to separate liquid impurities;

[0086] The gas phase was passed into an alkali washing tower (5% potassium hydroxide solution, liquid-gas ratio 1:8) for 18 minutes with 4 layers of polytetrafluoroethylene corrugated packing;

[0087] After alkali washing, the gas phase entered a drying tower (modified 3A molecular sieve with a silanization degree of 30%) for 1.2 hours, and the water content was reduced to 1.8 ppm;

[0088] After drying, the gas phase was sent to a rectifying tower (50 blocks of theoretical tower plate θ ring packing) to control the temperature at -65°C, the pressure at 0.5 MPa, and the reflux ratio at 5:1, and the overhead recovery rate was 3%, and the side line outlet was located at the 35th tower plate.

[0089] S5: tail gas treatment

[0090] The rectification tail gas was passed into an adsorption tower (activated carbon-montmorillonite 7:3 mixture treated with 1% ammonium fluoride) at a temperature of 20°C and a pressure of 0.3 MPa for 45 minutes;

[0091] A double-tower parallel adsorption was adopted, and the other tower was regenerated (nitrogen flow 0.6 L / min, desorption at 120°C for 2 hours), and the raw material was recovered and reused to S2.

[0092] Example 3

[0093] S1: preparation of composite catalyst

[0094] 100 g activated carbon support was immersed in a mixed solution of 3% hydrofluoric acid and 5% nitric acid 500 mL at 80°C for 2 hours. After removal, it was washed with deionized water until pH = 7.0 and dried at 120°C for 4 hours.

[0095] First loading: dry activated carbon was immersed in a 0.5 mol / L aluminum chloride ethanol solution 300 mL for 30 minutes under ultrasonic (35 kHz 180 W) and stood for 2 hours, then dried at 120°C to load 8% aluminum chloride;

[0096] Second loading: immersed in a mixed aqueous solution containing cesium fluoride and lanthanum oxide (concentrations are 0.2 mol / L and 0.1 mol / L, respectively) for 30 minutes under ultrasonic and stood for 1.5 hours, then dried to load 4% cesium fluoride and 3% lanthanum oxide;

[0097] Third loading: immersed in a 0.1% graphene quantum dot dispersion 200 mL for 30 minutes under ultrasonic and stood for 1 hour, then dried to load 1.5% graphene quantum dots.

[0098] The loaded catalyst was placed in a calcination furnace with a nitrogen flow of 0.8 L / min, and the temperature was programmed to 400°C for 3 hours (heating rate: 5°C / min to 150°C, holding for 1 hour, 8°C / min to 400°C, holding for 3 hours). After natural cooling, it was ready for use.

[0099] S2: raw material pretreatment

[0100] Tetrafluoroethylene and hydrogen fluoride were mixed in a mixer at a volume ratio of 1:5 at a stirring rate of 300 r / min for 30 minutes;

[0101] The mixed raw materials were fed into a dehydration device (4A and 13X molecular sieves were filled at a ratio of 2:1) and stayed for 2 hours to dehydrate to a water content of 2 ppm;

[0102] After dehydration, the raw materials were passed into a purification tower (the inner wall was coated with an 8 μm nano-zinc oxide coating) at a temperature of 100°C and a pressure of 0.5 MPa for 40 minutes. Online detection showed that the oxygen content was 0.2 ppm and the olefin impurity was 0.1 ppm.

[0103] S3: directional synthesis reaction

[0104] The fixed bed reactor was built-in with honeycomb-shaped flow guide plates (spacing 6 cm). The upper section of the catalyst bed was filled with 2-3 mm catalyst, the middle section was 3-4 mm, and the lower section was 4-5 mm with a void fraction of 45%;

[0105] Perfluorohexane was injected by a micro-metering pump (volume ratio to raw material 0.3:100). The reaction parameters were controlled as follows: upper section 340°C, middle section 360°C, lower section 380°C, pressure 1.2 MPa, space velocity 2500 h-1;

[0106] The pressure stabilizing system controlled the fluctuation within ±0.03 MPa during the 5-hour reaction.

[0107] S4: Product purification

[0108] The reaction product was sent to a condensing device (-20°C) for 25 minutes to separate liquid impurities;

[0109] The gas phase was passed through an alkali washing tower (8% potassium hydroxide solution, liquid-gas ratio 1:12) for 18 minutes with 4 layers of polytetrafluoroethylene corrugated packing;

[0110] After alkali washing, the gas phase entered a drying tower (modified 3A molecular sieve with a silanization degree of 40%) for 1.2 hours, reducing the water content to 1.2 ppm;

[0111] After drying, the gas phase was sent to a rectification tower (70 theoretical plates θ ring packing) with a temperature control of -65°C, a pressure of 0.5 MPa, a reflux ratio of 8:1, and a top recovery rate of 5%, with the side outlet located at the 35th plate.

[0112] S5: Tail gas treatment

[0113] The rectification tail gas was passed through an adsorption tower (activated carbon-montmorillonite 7:3 mixture treated with 1% ammonium fluoride) at a temperature of 30°C and a pressure of 0.5 MPa for 45 minutes;

[0114] A double-tower parallel adsorption was adopted, with one tower being regenerated (nitrogen flow 0.9 L / min, 150°C desorption for 2 hours) to recover the raw materials for reuse in S2.

[0115] Comparative Example

[0116] Catalyst preparation: 100g of activated carbon was directly immersed in a 10% aluminum fluoride solution for 2 hours, then dried and calcined at 350°C for 2 hours to prepare a single aluminum fluoride supported catalyst.

[0117] Raw material pretreatment

[0118] Tetrafluoroethylene and hydrogen fluoride were mixed at a volume ratio of 1:4 and stirred for 30 minutes; the mixed raw materials were only dehydrated with 4A molecular sieves for 1.5 hours, with a water content of 8 ppm; without purification tower treatment, they were directly sent to the reactor for online detection of oxygen content of 2 ppm.

[0119] Synthesis reaction

[0120] The fixed bed reactor had no baffle, the catalyst particle size was 3-4mm, the void ratio was 40%; no perfluorohexane was introduced, the reaction temperature was 350°C, the pressure was 1.0 MPa, the space velocity was 2000h-1; the reaction lasted for 5 hours, and the pressure fluctuation was ±0.08 MPa.

[0121] Product purification

[0122] The reaction product was only condensed at -25°C without a base washing step; it was directly introduced into a common rectification column (40 trays) without ultrasonic auxiliary reflux ratio 4:1.

[0123] Tail gas treatment: The rectification tail gas was directly absorbed by 5% potassium hydroxide solution and then discharged without recovering raw materials. The test results of the examples and comparative examples are as follows:

[0124] Table 1

[0125] Indicator Example 1 Example 2 Example 3 Comparative Example Hexafluoroethane selectivity (%) 99.2 98.5 99.5 92.3 Feedstock conversion (%) 97.8 96.5 98.2 90.1 Product purity (%) 99.9996 99.9992 99.9998 99.995 Moisture (ppm) 1.5 1.8 1.2 5.2 Acidity (ppm) 0.03 0.04 0.02 0.35 Catalyst life (hours) 1200 1100 1300 500 Feedstock loss rate (%) 2.1 2.5 1.8 8.7

[0126] The catalyst regeneration performance of the examples and comparative examples is compared as follows:

[0127] Table 2

[0128]

[0129] As can be seen from the above test results, the multi-component composite catalyst used in Examples 1-3 has significant advantages in product selectivity, purity control, and resource recycling compared to the single system of the comparative example with gradient process design. The performance data show that the present process effectively breaks through the bottleneck of the traditional process by the synergistic effect of the composite catalyst, the combination of deep purification and precise rectification, and the resource recovery in the whole process, and can stably produce hexafluoroethane meeting the requirements of electronic grade.

[0130] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for the directed synthesis of electronic-grade hexafluoroethane based on a composite catalyst, characterized in that, Includes the following steps: S1. Catalyst preparation: The activated carbon support was immersed in a mixed solution of hydrofluoric acid and nitric acid and refluxed at 80°C. After reflux, the activated carbon support was removed and washed with deionized water until the pH of the washing water was 6.5-7.

5. Then it was dried. The dried activated carbon support was first immersed in an aluminum trichloride ethanol solution, allowed to stand, and then removed and dried. Then it was immersed in a mixed aqueous solution of cesium fluoride and lanthanum oxide, allowed to stand, and then removed and dried. Finally, it was immersed in a graphene quantum dot dispersion, allowed to stand, and then removed and dried. The loaded activated carbon support was placed in a calcination furnace and calcined under nitrogen to obtain a composite catalyst. S2. Raw material pretreatment: Tetrafluoroethylene and hydrogen fluoride are fed into a mixer and thoroughly mixed. Then, the mixture is sent to a dehydration unit to dehydrate the raw material until the water content in the raw material is ≤5ppm. The dehydrated raw material is then fed into a purification tower to further remove impurities from the raw material. S3. Directed Synthesis Reaction: The pretreated raw materials are fed into a fixed-bed reactor through a raw material delivery pipeline. Perfluorohexane is injected into the raw material delivery pipeline through a micro metering pump. The temperature of the upper section of the fixed-bed reactor is controlled at 320-340℃, the middle section at 340-360℃, and the lower section at 360-380℃. The raw materials react in the reactor to generate a mixed product containing hexafluoroethane. S4. Product purification: The mixed product generated by the reaction is sent to a condenser to separate the liquid impurities in the mixed product. The condensed gaseous product is sent to an alkaline washing tower to remove acidic impurities in the gaseous product. The alkaline washed gaseous product is sent to a drying tower to dry until the water content in the gaseous product is ≤2ppm. The dried gaseous product is sent to a distillation tower to obtain electronic grade hexafluoroethane through distillation. S5. Tail gas treatment: The tail gas discharged from the top of the distillation column is passed into the adsorption column to adsorb and recover the unreacted raw materials in the tail gas. After the adsorption is completed, nitrogen gas is introduced into the adsorption column to raise the temperature of the adsorption column to 120-150℃, and the adsorbed raw materials are desorbed and recovered. The raw materials obtained from the desorption are recycled to step S2.

2. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, It also includes an ultrasonic-assisted step in the composite catalyst loading process: when the activated carbon support is immersed in aluminum trichloride ethanol solution, cesium fluoride and lanthanum oxide mixed aqueous solution, and graphene quantum dot dispersion, the ultrasonic generator is turned on respectively, and the ultrasonic frequency is controlled at 30-40kHz and the power at 150-200W, and the ultrasonic treatment is carried out for 30 minutes.

3. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, It also includes a step for detecting impurities after raw material pretreatment: an online gas chromatograph is installed at the outlet of the purification tower to detect the pretreated raw materials in real time. The detection items include oxygen content, olefin impurity content, and water content, ensuring that the oxygen content in the raw materials is ≤0.5ppm, olefin impurities are ≤0.3ppm, and water content is ≤5ppm. If the detection indicators exceed the standards, the raw materials are returned to the dehydration unit for reprocessing.

4. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, In step S3, the fixed-bed reactor is also equipped with a raw material distributor. The raw material distributor is located at the top of the reactor and adopts a porous ring tube structure with a pore diameter of 0.5-1mm. 30-40 air vents are evenly opened on the distributor.

5. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, In step S4, the alkaline washing tower adopts a countercurrent contact method. Potassium hydroxide solution is sprayed from the top of the alkaline washing tower, and gaseous products are introduced from the bottom of the tower. The tower is equipped with 3-5 layers of corrugated packing material, which is polytetrafluoroethylene.

6. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, In step S4, the distillation column is also equipped with a side-stream collection device. The side-stream collection outlet is located in the middle of the distillation column, 30-40 theoretical plates away from the bottom of the column. When the purity of the product collected from the top of the column does not meet the requirements, part of the intermediate product is collected through the side-stream and refluxed back to the middle of the distillation column for re-distillation.

7. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, In step S5, the adsorption tower adopts a dual-tower parallel structure. While one adsorption tower is performing adsorption, the other adsorption tower is performing desorption and regeneration. After the desorption is completed, the tower is switched to ensure continuous tail gas treatment. During desorption and regeneration, nitrogen is first purged for 1 hour, and then the temperature is raised to 120-150℃ for desorption for 2 hours.

8. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, In step S1, the calcination furnace adopts a programmed temperature rise, raising the temperature from room temperature to 150°C at a rate of 5°C / min and holding it for 1 hour. Then, it is raised to 350-400°C at a rate of 8°C / min and held for 3 hours. After calcination, the temperature is lowered to room temperature at a rate of 10°C / min to avoid sudden temperature changes that could damage the catalyst structure.

9. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, Step S3 also includes a pressure stabilization system. When the pressure fluctuation in the fixed-bed reactor exceeds ±0.05MPa, the system automatically adjusts the feed rate. The feed rate adjustment range is ±10% of the set value to ensure that the reaction pressure is stable at 0.8-1.2MPa.

10. The directed synthesis process of electronic-grade hexafluoroethane based on a composite catalyst according to claim 1, characterized in that, In step S4, the electronic-grade hexafluoroethane product needs to undergo offline testing. The testing items include moisture, acidity, carbon monoxide, carbon dioxide, and total hydrocarbons. The testing is performed using gas chromatography-mass spectrometry and a trace moisture analyzer. The product must have a moisture content of ≤2ppm, acidity (HF) of ≤0.05ppm, carbon monoxide of ≤0.1ppm, carbon dioxide of ≤0.1ppm, and total hydrocarbons of ≤0.5ppm. Only after passing the tests can the product be packaged and stored.

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