Sulfur hexafluoride can be used in circuit breakers, transformers, power transmission pipelines, lightning arresters and other fields, as well as refrigerants and anti-oxidants. It has a wide range of uses. Therefore, the preparation process of sulfur hexafluoride has attracted much attention. Today, Shuncheng Chemical Industry Institute will introduce you to the preparation process of sulfur hexafluoride, and it is easy to make sulfur hexafluoride gas.
The industrial production of sulfur hexafluoride mainly adopts the method of direct reaction between gaseous or molten sulfur and fluorine. There are also a few household pyrolysis methods and electrolysis methods.
, pyrolysis method pyrolysis method is to heat sulfur tetrafluoride to 500, 2000C into sulfur hexafluoride.
Second, the electrolysis method the electrolysis method is 20,10. Sulfur hexafluoride is obtained by electrolyzing liquid sulfur tetrafluoride and hydrofluoric acid at C. When the direct reaction method of elemental fluorine and sulfur is adopted, fluorine is produced by electrolysis first, and then the elemental fluorine and sulfur are directly synthesized and purified. The preparation process of sulfur hexafluoride is constantly improving. 1. Fluorine production by electrolysis The preparation of elemental fluorine is carried out only by electrochemical methods. Fluorine production by electrolysis is a technology that is related to various uses of fluorine, such as the production of uranium hexafluoride, sulfur hexafluoride, fluorine halides, and various fluorocarbons. Electrolysis of fluorine is a step in the industrial production of sulfur hexafluoride, and it is also a very critical step. The synthesis of sulfur hexafluoride is often interrupted due to the failure of the electric cell. Synthetic sulfur hexafluoride often contains impurities such as sulfur low-valent fluorides, oxyfluorides, sulfur oxides and fluorine, among which impurities (HF, OF2, CF4, C2F6, N2, OD) may also be entrained with the raw material fluorine. Therefore, Electrolysis of fluorine directly affects the quality and yield of SF6 products.
Fluorine production by electrolysis is divided into high temperature method, medium temperature method and low temperature method according to the operating temperature of the electric cell. The high-temperature method uses KHF2 as the electrolyte, graphite cation, and electrolysis at 240 and 280C. The tank body, the cathode, the partition, and the diaphragm are all made of copper-magnesium alloy or Monel alloy. The advantage is that the HF vapor pressure is low at the operating temperature, and the fluorine purity produced can be as high as 98 ‰. The disadvantage is that as the electrolysis progresses, HF is continuously consumed, causing the melting point of the electrolyte to rise sharply, the composition of the electrolyte needs to be adjusted continuously, and the corrosion of the electric cell, especially the corrosion of the male parts, is serious. Due to the high operating temperature, it brings difficulties to continuous operation. These shortcomings hinder the widespread adoption of high-temperature methods. The low-temperature method is to electrolyze KF 8 and IOHF at room temperature. Due to the high vapor pressure of hydrogen fluoride during low-temperature electrolysis, the corrosion of various parts of the cell is serious, and the current rate is also low, so it is not suitable for popularization.
2. The fluorine electrolyte produced by the medium temperature method is mainly KF • 2HFCHF with a content of 40• 8% (mass) and a melting point of 71 • 7 ℃]. The electrolysis is carried out at 80 and 110 ℃. Low corrosiveness, not easy to change, high critical current density. The tank body, partition, diaphragm, cathode and other materials can be made of mild steel, preferably Monel alloy, especially for electrolytic cells above 2500A, which not only resists corrosion, but also has a significant effect on reducing the phenomenon. In modern industrial fluorine production, a medium-temperature fluorine cell is widely used. Nowadays, large-scale fluorine cells are operating in North America, Europe and Japan, such as 5000 and 7500A fluorine cells, 11000A fluorine cells, etc. At the same time, larger fluorine cells such as 15000A fluorine cells are being developed.
3. Direct reaction of sulfur and fluorine in gaseous or molten state. Industrial sulfur hexafluoride gas is usually prepared by the reaction of fluorine produced by electrolysis with sulfur at medium and high temperatures. In addition to sulfur hexafluoride, a small amount of tetrahydrofuran is also produced. Sulfur fluoride (SF4) and other by-products. The method of directly synthesizing sulfur hexafluoride from fluorine-sulfur can be divided into three methods: fluorine gas and solid sulfur, molten sulfur, and sulfur vapor: fluorine gas reacts with solid sulfur, because the fluorine-sulfur reaction is a very intense exothermic reaction. The reaction temperature is not easy to control, resulting in increased by-products and increased post-processing burden. In addition, it is difficult to continuously add solid sulfur to a sealed reactor, so this method is not suitable for industrial production.
The reaction of fluorine gas with sulfur vapor is to heat the sulfur to above 445 ℃ (boiling point), so that the sulfur becomes vapor and is sent to the reactor to react with fluorine. There is also the defect that the reaction temperature is difficult to control, and the reaction temperature can reach 600 Above ℃, special reactor materials must be used, and this method is not suitable for industrial production. The reaction of fluorine gas with molten sulfur is to keep the sulfur in the reactor in a molten state at 85-105 ℃ to react with the introduced fluorine gas. This method is easier to control the reaction temperature.
Sulfur hexafluoride gas is a colorless, odorless, non-toxic, non-flammable, non-corrosive gas at room temperature and pressure. The gas density is 61139 g/L, and its chemical stability is strong. It does not decompose at 500-600 ℃, and Acid, alkali, salt, ammonia, water, etc. do not react, and decompose into atomic gas of S and F under the action of an arc (thousands of degrees), but once the arc is released, it will recombine into SF6 within 0-5 ～10-6 s. .
Sulfur hexafluoride has good electrical properties and excellent arc extinguishing performance. Its electric strength is 215 times that of nitrogen under the same pressure, its breakdown voltage is 215 times that of air, and its arc extinguishing ability is 100 times that of air. A new-generation ultra-high-edge media material superior to air and oil.
High purity sulfur hexafluoride has stable chemical properties. Slightly soluble in water, alcohol and ether, soluble in potassium hydroxide. Does not react chemically with sodium hydroxide, liquid ammonia, hydrochloric acid and water. It does not react with copper, silver, iron, and aluminum in a dry environment below 300°C. Below 500℃, it has no effect on quartz. It reacts with metallic sodium at 250°C, and reacts in liquid ammonia at -64°C. It will be decomposed when mixed with hydrogen sulfide and heated. At 200℃, in the presence of certain metals such as steel and silicon steel, it can promote its slow decomposition.
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