Method and production system for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride

Abstract

The invention belongs to the field of chemical production, and provides a method and a production system for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride, and the method comprises the following steps: S1, reaction: introducing silicon tetrafluoride gas, ammonia gas and water vapor into a closed gas-phase reaction kettle in proportion for reaction; the reaction temperature is 120-280 DEG C, the reaction time is 20-80 minutes, and the molar ratio of the reaction raw materials is as follows: SiF4: NH3: H2O = 1: (2-3): (2-3); after the reaction is finished, cooling to less than 140 DEG C to obtain a solid mixture; s2, separation: separating the solid mixture in the step S1 to obtain high-purity ammonium bifluoride and high-purity white carbon black. The method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride provided by the invention can realize the preparation of high-purity ammonium bifluoride with high economic benefit.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method and a production system for preparing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black. Background Art

[0002] Ammonium bifluoride is a widely used compound in the fluorine chemical industry. It is widely used in chemical industry, metallurgy, food and other aspects. High-purity electronic grade ammonium bifluoride can also be used in the semiconductor industry and pharmaceutical industry.

[0003] At present, several production processes of ammonium bifluoride that are widely used at home and abroad can be summarized as follows:

[0004] (1) Hydrogen fluoride-liquid ammonia method: According to the different phases of the raw material hydrogen fluoride, it can be divided into gas phase method and liquid phase method. Patent CN102115095A discloses the liquid phase method. The process is to first pass liquid ammonia into hydrofluoric acid solution to obtain ammonium fluoride paste crystals, then synthesize ammonium bifluoride dilute solution with hydrofluoric acid, and finally obtain ammonium bifluoride by concentration, cooling, and crystallization. The reaction equation is as follows: HF+NH3→NH4F, NH4F+HF→NH4HF2; The liquid phase method has problems such as excessive water content in the product and difficulty in drying. The principle of the gas phase method is to control the molar ratio of HF and NH3 to 2:1 for reaction, and the obtained ammonium bifluoride gas is quickly cooled and separated by a cyclone separator to obtain the product. The reaction equation is as follows: NH4F+2HF→NH4HF2. The gas phase method has disadvantages such as large equipment investment and high raw material cost.

[0005] (2) Fluorosilicic acid-liquid ammonia method: This process is already mature. Duofuduo applied for the corresponding patent CN101028931A in 2006. The production process mainly uses the fluosilicic acid solution obtained by absorbing the fluorine-containing gas discharged during the production of phosphate fertilizers into water as raw material, which reacts with ammonia water to produce ammonium fluoride and silicon dioxide. The ammonium fluoride solution is concentrated and decomposed at high temperature to obtain ammonium bifluoride. The reaction equation is as follows: H2SiF6+6NH3H2O→6NH4F+SiO2+4H2O, 2NH4F→NH4HF2+NH3. This process uses an indirect liquid phase production method. The process flow is cumbersome. The prepared silicon dioxide easily absorbs fluoride ions and has low purity. In addition, there is a problem that the water content of ammonium bifluoride synthesized by the liquid phase method is high, which is not suitable for large-scale long-term storage.

[0006] (3) Fluorine-containing waste residue-liquid ammonia method: This method is disclosed in CN102491370A. Its principle is to dissolve fluorine-containing waste residue in ammonium fluoride solution to obtain ammonium fluorosilicate solution. After cooling, liquid ammonia is introduced to precipitate silicon dioxide. The obtained ammonium fluoride solution is then added with hydrofluoric acid to produce ammonium bifluoride product. The reaction equation is: (NH4)2SiF6+4NH3+2H2O→SiO2+NH4F, NH4F+HF→NH4HF2. This process is relatively long, the purity of the produced white carbon black is low, the concentration of fluorine-containing impurities is high, and the produced ammonium bifluoride also has the problem of high water content.

[0007] In summary, the synthesis process of ammonium bifluoride in the prior art can be divided into three methods: liquid phase synthesis, gas phase synthesis, and indirect synthesis. The liquid phase synthesis method is widely used in China due to its simple equipment and mild process conditions. About 90% of ammonium bifluoride is produced by the liquid phase method. However, the product produced has problems such as high water content, low purity, and many impurities. Long-term storage will cause moisture absorption and caking. Moreover, since ammonium bifluoride is easily decomposed upon heating, it cannot be dehydrated using ordinary high-temperature drying processes, which limits the application range of ammonium bifluoride produced by the liquid phase method. The gas phase method does not contact liquid water throughout the process, and the product has low water content, high purity, and fine particle size, which can meet the high quality requirements of the semiconductor and pharmaceutical industries. However, the raw materials used in the production of ammonium bifluoride by the gas phase method are anhydrous hydrogen fluoride and liquid ammonia, which has high requirements for raw material purity and a single product, resulting in low profits for ammonium bifluoride and difficulty in industrial promotion.

[0008] Based on this, there is an urgent need in the art to develop a method for preparing high-purity ammonium bifluoride with high economic benefits. Summary of the Invention

[0009] The first object of the present invention is to provide a method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride, which can achieve high-purity ammonium bifluoride preparation with high economic benefits.

[0010] The second object of the present invention is to provide a production system for preparing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black, which can achieve industrial production of high-purity ammonium bifluoride with high economic benefits.

[0011] In order to achieve the above object, the present invention provides the following specific solutions:

[0012] The present invention first provides a method for preparing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black, comprising the following steps:

[0013] S1 reaction: silicon tetrafluoride gas, ammonia gas and water vapor are introduced into a sealed gas phase reactor in proportion to react; the reaction temperature is 120-280°C, the reaction time is 20-80 minutes, and the molar ratio of the reaction materials satisfies: SiF4:NH3:H2O=1:2-3:2-3;

[0014] After the reaction is completed, the temperature is lowered to less than 140° C. to obtain a solid mixture;

[0015] S2 separation: separating the solid mixture in step S1 to obtain high-purity ammonium bifluoride and high-purity white carbon black.

[0016] The core process principle of the present invention is: SiF4(g)+2H2O(g)+2NH3(g)→2NH4HF2(s)+SiO2(s). In view of the problems of poor product quality of the liquid phase method and high raw material cost and low product yield of the hydrogen fluoride gas phase method, the present invention creatively adopts this principle as the basis for the production of high-purity ammonium bifluoride, so as to achieve the purpose of preparing high-purity ammonium bifluoride by using silicon tetrafluoride as a gas raw material and reacting it with ammonia and water vapor in the gas phase, and specifically designs the reaction conditions of the reaction.

[0017] First, the inventors demonstrated that the reaction could proceed through thermodynamic calculations.

[0018] Secondly, it has been calculated that the reaction can proceed smoothly in the forward direction only if the temperature is below 146.39°C, and a reversible reaction occurs above this temperature. However, in the actual reaction, although the reaction can proceed in the forward direction if the temperature is lower than this, considering that the reaction system is under high pressure, the boiling point of water will increase under high pressure. If the temperature is too low, part of the water vapor in the system will liquefy and trigger other side reactions. In practice, in order to ensure product purity, the reaction temperature should be designed to be higher than 120°C. At the same time, for gas-phase reactions, the reaction temperature is too low, the molecular motion rate between gas materials is low, the mixing uniformity is poor, and it is easy to produce the by-product ammonium fluorosilicate, which affects the product purity. Therefore, the reaction temperature should be designed to be higher. Moreover, the inventors consider that for this reaction, even if the temperature exceeds 146.39°C, a reversible reaction occurs, which will only affect the yield of the product to a certain extent and will not affect the purity of the product. In summary, in order to ensure product purity, the inventors designed the reaction temperature to be 120-280°C. Preferably, the reaction temperature is 150-250°C.

[0019] In addition, to better avoid the production of byproducts such as ammonium fluorosilicate and ammonium fluoride, the inventors designed the molar ratio of the reaction raw materials to meet the following requirements: SiF4:NH3:H2O=1:2-3:2-3, so as to ensure that the reaction is carried out under conditions of excess ammonia and water vapor, thereby avoiding the production of byproducts such as ammonium fluorosilicate and ammonium fluoride. Further preferably, the molar ratio of the reaction raw materials designed by the present invention meets the following requirements: SiF4:NH3:H2O=1:2-2.5:2-2.5.

[0020] In actual production, product yield has a direct impact on the economic benefits of the product. To further improve product yield while ensuring purity, the present invention cools the gas phase reactor to less than 140°C after the reaction in step S1. During this process, as the temperature decreases, the reaction in the reactor proceeds forward. The desublimation temperature of ammonium bifluoride is 140°C. Below this temperature, the ammonium bifluoride gas generated in the reactor will desublimate into a solid, thereby reducing the product concentration in the reaction system and allowing the reaction to continue forward. By cooling, the product is converted into a solid mixture, while the forward reaction is ensured, thereby improving the yield.

[0021] Preferably, step S2 is specifically as follows: the solid mixture obtained in step S1 is subjected to high-temperature gasification and gas-solid separation to obtain a high-temperature gas phase and a high-temperature solid phase; the solid obtained after cooling the high-temperature gas phase is high-purity ammonium bifluoride; the high-temperature solid phase is high-purity white carbon black; the temperature of the high-temperature gasification is 150°C to 250°C, and the high-temperature gasification is completed until the solid mixture reaches a constant weight.

[0022] After the reaction in step S1 is completed, the resulting solid mixture is primarily composed of white carbon black and ammonium bifluoride, as well as very small amounts of by-products ammonium fluorosilicate and ammonium fluoride. This solid mixture is subjected to high-temperature gasification separation. Since the vaporization points of ammonium bifluoride, ammonium fluorosilicate, and ammonium fluoride are 140°C, 109°C, and 98°C, at a high-temperature gasification temperature above 140°C, ammonium bifluoride, ammonium fluorosilicate, and ammonium fluoride can all be gasified and separated from the white carbon black, thereby obtaining high-purity white carbon black.

[0023] On the one hand, to ensure product yield, the temperature should not be too high to prevent ammonium bifluoride from decomposing at high temperatures. On the other hand, to reduce the energy consumption of heating the solid mixture during the high-temperature gas phase and the cooling energy consumption during the subsequent high-temperature gas phase cooling process, the temperature should not be too high to avoid excessive gas generation rate leading to excessive subsequent cooling capacity requirements. Therefore, the temperature of the high-temperature gasification of the present invention is preferably 150°C to 250°C, and more preferably 180°C to 220°C.

[0024] Moreover, within the preferred temperature range of the present invention, ammonium fluoride undergoes a decomposition reaction to generate ammonium bifluoride, which is then cooled in a subsequent cooling process to form an ammonium bifluoride product, while ammonium fluorosilicate decomposes into ammonia and silicon tetrafluoride gas, which can be reused as reaction raw gas.

[0025] In step S1, after the reaction is completed, the temperature is preferably cooled to room temperature. The reaction product is given sufficient cooling time to ensure that the raw materials in the reactor continue to react in the forward direction. At the same time, cooling the temperature to room temperature can also better promote the forward reaction and thus improve the reaction yield.

[0026] In step S1, the reaction is cooled naturally or by heat exchange with a refrigerant after completion. Natural cooling or cooling with cooling water or other refrigerants can be selected based on actual conditions to ensure that the generated ammonium bifluoride can be converted into a solid and to promote the forward progress of the reaction.

[0027] In the present invention, in step S1, the purity of the silicon tetrafluoride gas, the ammonia gas, and the water vapor is greater than 99%. Preferably, in step S1, the purity of the silicon tetrafluoride gas, the ammonia gas, and the water vapor is greater than 99.99%. The product purity is high, thereby ensuring high product purity.

[0028] Preferably, in step S1, the ammonia gas and the water vapor are first added to the gas phase reactor in proportion, and then the silicon tetrafluoride gas is added to the gas phase reactor. Since ammonium fluorosilicate or ammonium fluoride will be preferentially generated as a byproduct in the reaction system when silicon tetrafluoride is in excess, during the reaction, ammonia gas and water vapor should be added to the gas phase reactor first, and then silicon tetrafluoride should be added to ensure that the reaction can always be carried out under the conditions of excess ammonia gas and water vapor, thereby avoiding the generation of byproducts.

[0029] The present invention also provides a production system for use with the above-mentioned reaction method, comprising a gas-phase reactor, a silicon tetrafluoride gas storage device, a liquid ammonia storage device, and a water vapor generator, each connected to the gas inlet of the gas-phase reactor, and a solid mixture separation device connected to the discharge end of the gas-phase reactor. Specifically, the silicon tetrafluoride gas storage device can be a silicon tetrafluoride steel cylinder, and the liquid ammonia storage device can be a liquid ammonia steel cylinder.

[0030] Silicon tetrafluoride gas is added to the gas phase reactor through a silicon tetrafluoride gas storage device, ammonia is added to the gas phase reactor through a liquid ammonia storage device, and water vapor is added to the reactor through a water vapor generator. The three react in the gas phase reactor to generate ammonium bifluoride and white carbon black. The generated solid mixture enters the solid mixture separation device through the discharge end for separation.

[0031] Preferably, the solid-liquid mixture separation device of the present invention is a high-temperature gasification device, and the gas outlet of the high-temperature gasification device is connected to a cooling and drying device. Specifically, the high-temperature gasification device can be a vacuum drying oven. By heating the solid mixture in the vacuum drying oven to a specified temperature (150°C to 250°C), the ammonium bifluoride in the solid mixture is vaporized at this temperature, and the ammonium fluoride undergoes a decomposition reaction to form ammonium bifluoride, while ammonium fluorosilicate decomposes into ammonia and silicon tetrafluoride gas. These gases enter the cooling and drying device connected to the high-temperature gasification device, and after the temperature is reduced, they condense to form ammonium bifluoride solid. The uncondensed ammonia and silicon tetrafluoride are also separated from the ammonium bifluoride solid. The solid that fails to vaporize in the high-temperature gasification device is high-purity white carbon black. By using the high-temperature gasification device and the cooling and drying device, the separation of ammonium bifluoride and white carbon black is well achieved, and high-purity white carbon black and high-purity ammonium bifluoride are prepared.

[0032] Preferably, the cooling and drying device of the present invention is further connected to the gas phase reactor. Gas that fails to cool in the cooling and drying device (i.e., ammonia and silicon tetrafluoride gas obtained by decomposition of ammonium fluorosilicate) is returned to the gas phase reactor for reaction. Specifically, the gas can first be returned to the gas absorption and concentration device, and then returned to the gas phase reactor for reaction after reaching a certain concentration.

[0033] Preferably, the production system of the present invention further includes a nitrogen storage device and a gas absorption and concentration device; the nitrogen storage device is respectively connected to the silicon tetrafluoride gas storage device, the liquid ammonia storage device, and the water vapor generator; the gas absorption and concentration device is connected to the gas outlet of the gas phase reactor, and the gas absorption and concentration device is connected to the gas inlet of the gas phase reactor. Specifically, the nitrogen storage device can be a nitrogen cylinder.

[0034] The nitrogen storage device is used to purge the reaction pipelines before and after the reaction. After the reaction is completed, the nitrogen is used to purge the residual gas in the gas phase reactor into a gas absorption and concentration device connected to the gas phase reactor. Once the gas concentration in the concentration device exceeds 20%, it can be returned to the gas phase reactor and reused as a reaction raw material to ensure the overall reaction yield.

[0035] The beneficial effects of the present invention are:

[0036] (1) The present invention uses silicon tetrafluoride gas as a raw material to produce high-purity ammonium bifluoride and high-purity white carbon black, wherein the purity of ammonium bifluoride can reach more than 95%, and the purity of white carbon black can reach more than 96%, which can effectively improve the economic benefits of the entire reaction.

[0037] (2) The present invention also designs specific reaction conditions for preparing high-purity ammonium bifluoride using silicon tetrafluoride gas as a raw material. By designing the reaction temperature and the ratio of each raw material, as well as controlling the reaction process, the purity and yield of the prepared product are effectively guaranteed.

[0038] (3) The present invention also designs a method for separating the solid mixture after the reaction, and the solid mixture is separated by high-temperature gasification to obtain high-purity white carbon black and high-purity ammonium bifluoride.

[0039] (4) The present invention also designs specific gasification conditions for high-temperature gasification to further promote the improvement of product purity and yield.

[0040] (5) The present invention also designs a production system for preparing ammonium bifluoride and white carbon black from silicon tetrafluoride to make the industrialization of the process feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a production system diagram for preparing ammonium bifluoride and white carbon black from silicon tetrafluoride in Example 1 of the present application.

[0042] In the figure: 10-silicon tetrafluoride gas cylinder, 11-silicon tetrafluoride pipeline, 12-valve one, 13-flow meter one, 14-silicon tetrafluoride branch, 15-valve four, 20-liquid ammonia cylinder, 21-liquid ammonia pipeline, 22-valve two, 23-flow meter two, 24-liquid ammonia branch, 25-valve five, 30-water vapor generator, 31-water vapor pipeline, 32-valve three, 33-flow meter three, 34-water vapor branch, 35-valve six, 40-nitrogen cylinder, 41-nitrogen main valve, 42-nitrogen flow meter, 43-nitrogen pipeline, 50-gas phase reactor, 60-gas absorption and concentration device, 61-recovery pipeline one, 62-valve seven, 63-recovery pipeline two, 64-valve eight, 70-vacuum drying oven, 80-cooling and drying device. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the present invention is further described below with reference to specific examples. Where specific conditions are not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. The example embodiments can be implemented in various forms and should not be construed as being limited to the examples set forth herein; on the contrary, these embodiments are provided so that the present invention will be more comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art.

[0044] Example 1

[0045] This embodiment provides a production system for preparing ammonium bifluoride and white carbon black from silicon tetrafluoride, as shown in the attached figure. Figure 1As shown, it includes a gas phase reactor 50, a silicon tetrafluoride gas cylinder 10, a liquid ammonia cylinder 20 and a water vapor generator 30 respectively connected to the gas inlet of the gas phase reactor 50, and a high-temperature gasification device connected to the discharge end of the gas phase reactor 50, and the gas outlet of the high-temperature gasification device is connected to a cooling and drying device 80.

[0046] In this embodiment, the cooling and drying device 80 is also connected to the gas phase reactor 50 .

[0047] This embodiment further includes a nitrogen cylinder 40 and a gas absorption and concentration device 60; the nitrogen cylinder 40 is connected to the silicon tetrafluoride gas cylinder 10, the liquid ammonia cylinder 20 and the water vapor generator 30 respectively; the gas absorption and concentration device 60 is connected to the gas outlet of the gas phase reactor 50, and the gas absorption and concentration device 60 is connected to the gas inlet of the gas phase reactor 50.

[0048] Specifically, in this embodiment, it also includes a silicon tetrafluoride pipeline 11, a liquid ammonia pipeline 21, a water vapor pipeline 31 and a nitrogen pipeline 43; one end of the silicon tetrafluoride pipeline 11 is connected to the silicon tetrafluoride gas cylinder 10, and the other end is connected to the air inlet at the top of the gas phase reactor 50, and a valve 12 and a flow meter 13 are provided on the silicon tetrafluoride pipeline 11; one end of the liquid ammonia pipeline 21 is connected to the liquid ammonia cylinder 20, and the other end is connected to the air inlet at the bottom of the gas phase reactor 50, and a valve 22 and a flow meter 23 are provided on the liquid ammonia pipeline 21; one end of the water vapor pipeline 31 is connected to the water vapor generator 30, and the other end is connected to the gas phase reactor 50. The air inlet at the bottom of the reactor 50 is connected, and a valve three 32 and a flowmeter three 33 are provided on the water vapor pipeline 31; one end of the nitrogen pipeline 43 is connected to the nitrogen cylinder 40, and the other end is connected to the silicon tetrafluoride gas cylinder 10 through the silicon tetrafluoride branch 14, and is connected to the liquid ammonia cylinder 20 through the liquid ammonia branch 24, and is connected to the water vapor generator 30 through the water vapor branch 34. The nitrogen pipeline 43 is provided with a nitrogen main valve 41 and a nitrogen flowmeter 42, the silicon tetrafluoride branch 14 is provided with a valve four 15, the liquid ammonia branch 24 is provided with a valve five 25, and the water vapor branch 34 is provided with a valve six 35.

[0049] More specifically, the gas phase reactor 50 is provided with a pressure gauge, a stirring device is provided inside the gas phase reactor 50 , and the gas phase reactor 50 is also equipped with an electric heating device and a temperature control facility.

[0050] More specifically, the gas absorption and concentration device 60 is connected to the gas inlet of the gas phase reactor 50 through a recovery line 1 61 , and a valve 7 62 is provided on the recovery line 1 61 .

[0051] To be more specific, the high-temperature gasification device of this embodiment is a vacuum drying oven 70, the air outlet of the vacuum drying oven 70 is connected to the cooling and drying device 80, and the cooling and drying device 80 is connected to the air inlet at the top of the gas phase reactor 50 through the recovery line 2 63, and a valve 8 64 is provided on the recovery line 2 63.

[0052] The cooling and drying device 80 of this embodiment is a water-cooled heat exchanger equipped with a coil-type cooling pipe. The cooling and drying device 80 is connected to the gas absorption and concentration device 60. The uncooled gas phase in the cooling and drying device 80 is absorbed by the gas absorption and concentration device 60. After the concentration reaches greater than 20%, it is heated and returned to the gas phase reactor 50.

[0053] The production system for preparing ammonium bifluoride and white carbon black from silicon tetrafluoride provided in this embodiment has closely connected devices and a reasonable layout, and can be well applied to the reaction of the present invention.

[0054] Example 2 to Example 8

[0055] Examples 2 to 8 each provide a method for preparing ammonium bifluoride and white carbon black from silicon tetrafluoride.

[0056] Examples 2 to 8 were all produced using the production system of Example 1, and the production processes were as follows:

[0057] (1) Preparation before reaction: Since the system is a closed gas phase reaction, preparation work must be done before the reaction. The specific operation steps are as follows: ① Check whether the equipment and pipelines are damaged or leaking, and whether the stirring device is working properly. After confirming that everything is correct, follow the instructions in the attached Figure 1 Set up the experimental setup as shown, ensuring the pipelines are unobstructed and unblocked. Open the gas phase reactor outlet. ② Close all valves, leaving only the nitrogen main valve and valve 6 of the water vapor branch open. Adjust the nitrogen main valve to a gas flow rate of 10 mL / s and aerate for 1 minute. Once the flow rate stabilizes, observe and compare the nitrogen flowmeter and flowmeter 3 to ensure flow rates are consistent. If not, replace the flowmeters immediately. If no abnormalities are observed, proceed to the next step. ③ Open valve 5 of the liquid ammonia branch and close valve 6. After a minute of aeration, observe and compare the nitrogen flowmeter and flowmeter 2 to ensure flow rates are consistent. If not, replace the flowmeters immediately. If no abnormalities are observed, proceed to the next step. ④ Open valve 4 of the silicon tetrafluoride branch and close valve 5. After a minute of aeration, observe and compare the nitrogen flowmeter and flowmeter 1 to ensure flow rates are consistent. If not, replace the flowmeters immediately. If no abnormalities are observed, proceed to the next step. ⑤ Close the nitrogen main valve and valve 4. Observe the pressure gauge of the gas phase reactor to see if it increases with the increase in gas flow rate in the previous steps. If no change occurs, replace the pressure gauge. If no abnormalities are observed, complete the pre-reaction preparation phase.

[0058] (2) Reaction stage: After completing the inspection of the pre-reaction preparation stage, start the reaction according to the following steps: ① Confirm that the nitrogen main valve of the nitrogen cylinder is in the closed state and the gas outlet of the gas phase reactor is in the slightly open state to avoid overpressure inside the gas phase reactor. Open the temperature control device of the gas phase reactor and set the temperature inside the gas phase reactor to the reaction temperature. At the same time, pay attention to the changes in the pressure gauge. ② After the temperature stabilizes, start the steam generator, open valve 3 of the steam pipeline and valve 2 of the liquid ammonia pipeline, control the water vapor flow rate (flow meter 3) and the ammonia flow rate (flow meter 2) to the set flow rate. After the ammonia volume reaches the set value, close valve 2 of the liquid ammonia pipeline, open the stirring device, continue to ventilate until the water vapor volume reaches the set value, close valve 3 of the steam pipeline, and then close the steam generator. ③ Open valve 1 of the silicon tetrafluoride pipeline, introduce silicon tetrafluoride gas, control the flow rate to the set value (flow meter 1), and start the reaction. After the silicon tetrafluoride gas volume reaches the set value, close the valve of the silicon tetrafluoride pipeline and start the reaction. Since the nature of this reaction is an exothermic reaction of acid-base gas neutralization, the temperature in the reactor will fluctuate. It is necessary to adjust the heating frequency in time to stabilize the reaction temperature during the reaction within the set reaction temperature ±5°C. ④ After reaching the set reaction time, stop heating, cool naturally to room temperature, open the gas phase reactor, collect the solid mixture, and collect the gas in the reactor into the gas absorption and concentration device. ⑤ After the collection is completed, open the nitrogen main valve, valve six of the water vapor branch, valve five of the liquid ammonia branch, and valve four of the silicon tetrafluoride branch, adjust the nitrogen flow rate to 10mL / s, blow out the residual gas into the gas absorption and concentration device through nitrogen, and after detecting that the ammonia concentration in the gas absorption and concentration device is greater than 20%, heat the gas concentration device, and the ammonia and water can be recycled; at the same time, ensure that the surrounding environment is well ventilated, there is no obvious fire source, and personnel are away from the equipment.

[0059] (3) Product collection and separation stage: The solid mixture obtained after the reaction is placed in a vacuum drying oven for high-temperature gasification. It is heated to a constant solid weight at the set gasification temperature. The volatile gas (high-temperature gas phase) is collected and placed in a cooling dryer. Cooling water is passed through the heat exchange coil in the cooling dryer to cool and condense the collected gas to form a solid product of ammonium bifluoride. The remaining solid (high-temperature solid phase) in the vacuum drying oven is the white carbon black product. The residual gas in the cooling dryer enters the gas absorption and concentration device and is recovered in the gas absorption and concentration device together with the residual gas in the gas phase reactor. After the ammonia concentration in the gas absorption and concentration device is detected to be greater than 20%, the gas concentration device is heated to allow the gas to be reused.

[0060] The specific reaction conditions of Examples 2 to 8 are shown in Table 1:

[0061] Table 1 Reaction conditions of Examples 2 to 8

[0062]

[0063] Experimental example

[0064] The white carbon black and ammonium bifluoride products collected in Examples 2 to 8 were subjected to purity testing and yield calculation, and the testing method was as follows:

[0065] ① Ammonium bifluoride detection: According to the method shown in GB28655-2012, weigh about 0.8g of ammonium bifluoride product sample and white carbon black product sample after drying in a silica gel dryer for 8 hours, accurate to ±0.0002g, and transfer the ammonium bifluoride product sample with a small amount of cold water to a polyethylene beaker pre-filled with 20ml of saturated potassium nitrate solution and 50g of crushed ice, and stir until the sample is dissolved. Add 5 drops of bromothymol blue-neutral red mixed indicator solution and titrate with sodium hydroxide standard titration solution until dark green. Shake for 30s without fading as the titration end point. Keep the solution in an ice-water mixing state after titration and immediately use it for the determination of ammonium fluorosilicate content. The ammonium bifluoride content is expressed as mass fraction w1 and calculated according to formula (1):

[0066]

[0067] Where:

[0068] V—the volume of sodium hydroxide standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0069] c—The exact value of the concentration of the sodium hydroxide standard titration solution, in moles per liter (moL / L);

[0070] m—weight of the test product sample, in grams (g);

[0071] M—the numerical value of the molar mass of ammonium bifluoride, in grams per mole (g / moL) (M is taken as 57.04).

[0072] The arithmetic mean of the parallel determination results was taken as the determination result, and the absolute difference between the two parallel determination results was not greater than 0.1%.

[0073] ② Ammonium fluorosilicate test: According to the method shown in GB28655-2012, filter the above-mentioned solution with a polyethylene funnel and slow filter paper, and keep it at a temperature close to 0°C for suction filtration. Wash the precipitate thoroughly with a pre-cooled potassium chloride-ethanol solution, transfer the precipitate and the filter paper into the original beaker, add about 100mL of warm water, heat to 80°C in a constant temperature water bath, add 5 drops of phenolphthalein indicator solution, and titrate with sodium hydroxide standard titrant until the solution turns light red. Shake for 30 seconds without fading, which is the titration end point. The ammonium fluorosilicate content is expressed as mass fraction w2 and calculated according to formula (2):

[0074]

[0075] Where:

[0076] V—the volume of sodium hydroxide standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0077] c—The exact value of the concentration of the sodium hydroxide standard titration solution, in moles per liter (moL / L);

[0078] m—weight of the test product sample, in grams (g);

[0079] M—the numerical value of the molar mass of ammonium fluorosilicate The unit is gram per mole (g / moL) (M is taken as 44.54).

[0080] The arithmetic mean of the parallel determination results was taken as the determination result, and the absolute difference between the two parallel determination results was not greater than 0.1%.

[0081] ③ Silica Testing: According to the method outlined in HG / T 3062, weigh m0, an empty platinum crucible calcined at (1000 ± 25)°C to constant weight, to the nearest 0.1 mg. Weigh approximately 2 g of the ammonium bifluoride product sample and the silica product sample, dried at 105°C for 30 minutes, into the crucible. Calcined at 1000 ± 25°C for 2 hours until constant mass is achieved. Weigh this mass, m1, to the nearest 0.1 mg. Wet the calcined sample with a small amount of water. Add 15 mL of hydrofluoric acid and 1 mL of sulfuric acid to the platinum crucible containing the calcined residue. Heat on an electric furnace in a fume hood to evaporate until a slurry forms, avoiding splashing. Cool the crucible and rinse the material off the crucible walls with a small amount of water. Add 10 mL of hydrofluoric acid and evaporate to dryness. Continue heating the residue on the electric furnace until white smoke ceases. Then, place the crucible in a high-temperature furnace at (1000 ± 25)°C and calcine for 15 minutes. Remove the crucible from the high-temperature furnace and cool it to room temperature in a desiccator. Weigh and record the mass m2 of the slag and platinum crucible after calcination to the nearest 0.1 mg. The silica content is expressed as mass fraction w3 and calculated according to formula (3):

[0082]

[0083] Where:

[0084] m0—the mass of the empty platinum crucible, in grams (g);

[0085] m1—The mass of the sample and the platinum crucible after burning to a constant mass, in grams (g);

[0086] m2—The mass of the residue and platinum crucible after hydrofluoric acid treatment and burning, in grams (g);

[0087] The arithmetic mean of the parallel determination results was taken as the determination result, and the absolute difference between the two parallel determination results was not greater than 0.1%.

[0088] ④ Free acid test: According to the method specified in GB28653-2012, weigh approximately 1g of ammonium bifluoride product sample and white carbon black product sample to the nearest 0.001g, place them in a plastic cup, add 50mL of carbon dioxide-free water to dissolve, add 2 drops of bromocresol purple indicator solution, and titrate with sodium hydroxide standard solution until the solution turns purple. The free acid content is calculated as the mass fraction of hydrogen fluoride (HF) w4 according to formula (4):

[0089]

[0090] Where:

[0091] V—the volume of sodium hydroxide standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0092] c—The exact value of the concentration of the standard sodium hydroxide titration solution, in moles per liter (mol / L);

[0093] m—mass of product sample, in grams (g);

[0094] M—molar mass of hydrogen fluoride (HF) in grams per mole (g / mol) (M=20.01).

[0095] The arithmetic mean of the parallel determination results was taken as the determination result, and the absolute difference between the two parallel determination results was not greater than 0.15%.

[0096] ⑤ Ammonium fluoride test: According to the method shown in GB28653-2012, weigh approximately 0.5g of ammonium bifluoride product sample and white carbon black product sample, accurate to 0.002g, place them in a plastic cup, add 20mL of water to dissolve, add 40mL of neutral formaldehyde solution, shake well and let it stand for 30 minutes. Add 2 drops of phenolphthalein indicator solution and titrate with sodium hydroxide standard titration solution until the solution turns pink and remains unchanged for 30 seconds. The white carbon black content is expressed as mass fraction w5 and calculated according to formula (5):

[0097]

[0098] Where:

[0099] V—the volume of sodium hydroxide standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0100] c—The exact value of the concentration of the standard sodium hydroxide titration solution, in moles per liter (mol / L);

[0101] m—mass of product sample, in grams (g);

[0102] M—molar mass of ammonium fluoride in grams per mole (g / mol) (M=37.04);

[0103] w2—the value of ammonium fluorosilicate content, in %;

[0104] w4—the value of free acid content, in %;

[0105] 1.851—Coefficient for converting hydrogen fluoride to ammonium fluoride:

[0106] 0.4158—The coefficient for converting ammonium fluorosilicate to ammonium fluoride;

[0107] The arithmetic mean of the parallel determination results was taken as the determination result, and the absolute difference between the two parallel determination results was not greater than 0.3%.

[0108] ⑥ Yield calculation: After the reaction in step S1 is completed and the mixture is fully cooled, all solids in the gas phase reactor are collected and weighed. The weight is recorded as m1. The flow meter reading of the silicon tetrafluoride pipeline is V1. The yield of fluorine is measured as F%, and the yield of silicon is measured as Si%. They are calculated according to (Equation 6) and (Equation 7), respectively.

[0109]

[0110] Where:

[0111] m1—total weight of collected products, in grams (g);

[0112] w1—mass percentage of ammonium bifluoride, in percentage (%);

[0113] w3—mass percentage of white carbon black, in percentage (%);

[0114] V1—total gas flow rate of silicon tetrafluoride, in milliliters (mL);

[0115] 0.667—the percentage of fluorine in ammonium bifluoride;

[0116] 1.213—Percentage of fluorine in silicon tetrafluoride gas;

[0117] 0.467—the proportion of silicon in white carbon black;

[0118] 0.447—The proportion of silicon in silicon tetrafluoride gas.

[0119] The results of the determination of the product purity and yield obtained in Examples 2 to 8 are shown in Table 2:

[0120] Table 2 Purity and yield of the products obtained in Examples 2 to 8

[0121]

[0122]

[0123] From the results in Table 2, it can be concluded that the purity of ammonium bifluoride prepared by the method of the present invention can reach up to 97.19%, the purity of the prepared white carbon black can reach up to 98.55%, and the fluorine and silicon yields are both greater than 90%. It can be seen that the method of the present invention can prepare high-purity ammonium bifluoride, has high economic benefits, and has industrial promotion value.

[0124] The present invention is not limited to the above-mentioned embodiments. Anyone should be aware that any structural changes made under the guidance of the present invention, and any technical solutions that are the same or similar to those of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for preparing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black, characterized in that: The steps include: S1 reaction: silicon tetrafluoride gas, ammonia gas and water vapor are introduced into a closed gas phase reactor in proportion for reaction; the reaction temperature is 120-280°C, the reaction time is 20-80min, and the molar ratio of the reaction raw materials satisfies: SiF4:NH3:H2O=1:2-3:2-3; After the reaction is completed, the temperature is lowered to less than 140° C. to obtain a solid mixture; S2 separation: separating the solid mixture of step S1 to obtain high-purity ammonium bifluoride and high-purity white carbon black.

2. The method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride according to claim 1, characterized in that: Step S2 specifically comprises: performing high-temperature gasification on the solid mixture obtained in step S1 and performing gas-solid separation to obtain a high-temperature gas phase and a high-temperature solid phase; the solid obtained after cooling the high-temperature gas phase is high-purity ammonium bifluoride; the high-temperature solid phase is high-purity white carbon black; the temperature of the high-temperature gasification is 150° C. to 250° C., and the high-temperature gasification is completed until the solid mixture reaches a constant weight.

3. The method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride according to claim 1, characterized in that: In step S1, the temperature is lowered to room temperature after the reaction is completed.

4. The method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride according to claim 3, characterized in that: In step S1, natural cooling is adopted after the reaction is completed, or refrigerant heat exchange cooling is adopted after the reaction is completed.

5. The method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride according to claim 1, characterized in that: In step S1, the purity of the silicon tetrafluoride gas, the ammonia gas and the water vapor is greater than 99%.

6. The method for preparing ammonium bifluoride and co-producing white carbon black from silicon tetrafluoride according to claim 1, characterized in that: In step S1, the ammonia gas and the water vapor are first added into the gas phase reaction kettle in proportion, and then the silicon tetrafluoride gas is added into the gas phase reaction kettle.

7. The system for producing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black according to any one of claims 1 to 6, characterized in that: The invention comprises a gas phase reactor, a silicon tetrafluoride gas storage device, a liquid ammonia storage device and a water vapor generator respectively connected to the gas inlet of the gas phase reactor, and a solid mixture separation device connected to the discharge end of the gas phase reactor.

8. The system for producing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black according to claim 7, characterized in that: The solid-liquid mixture separation device is a high-temperature gasification device, and the gas outlet of the high-temperature gasification device is connected to a cooling and drying device.

9. The system for producing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black according to claim 8, characterized in that: The cooling and drying device is also communicated with the gas phase reaction kettle.

10. The system for producing ammonium bifluoride from silicon tetrafluoride and co-producing white carbon black according to claim 7, characterized in that: It also includes a nitrogen storage device and a gas absorption and concentration device; The nitrogen storage device is respectively connected to the silicon tetrafluoride gas storage device, the liquid ammonia storage device and the water vapor generator; The gas absorption and concentration device is communicated with the gas outlet of the gas phase reactor, and the gas absorption and concentration device is communicated with the gas inlet of the gas phase reactor.

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