Risk analysis of typical chemical reactions

1 oxidation

For example, ammoxidation to nitric acid, toluene oxidation to benzoic acid, ethylene oxidation to ethylene oxide, and the like.

(1) Fire hazard of oxidation

1 The oxidation reaction requires heating, but the reaction process is an exothermic reaction, especially the catalytic gas phase reaction, which is generally carried out at a high temperature of 250-600 ° C. If the heat of reaction is not removed in time, the temperature will rise rapidly. There was even an explosion.

2 Some oxidation, such as ammonia, ethylene and methanol vapor oxidation in the air, the material ratio is close to the lower explosion limit, if the ratio is out of balance, temperature control is improper, it is easy to explode and ignite.

3 Most of the oxidized substances are flammable and explosive substances. For example, in the oxidation of ethylene to ethylene oxide, ethylene is a flammable gas with an explosion limit of 2.7% to 34% and an autoignition temperature of 450 ° C. Toluene is oxidized to produce benzoic acid. Toluene is a flammable liquid. It is easy to form an explosive mixture with air, the explosion limit is 1.2% to 7%; methanol is a flammable liquid in the oxidation of formaldehyde, and the explosion limit of steam and air is 6% to 36.5%.

4 oxidants have a great fire risk. Such as potassium chlorate, potassium permanganate, chromic anhydride, etc. are all oxidants, such as high temperature or impact, friction and contact with organic matter, acids, can cause fire and explosion; organic peroxides not only have strong oxidative properties, but also Most are flammable substances, some are particularly sensitive to temperature and explode when exposed to high temperatures.

5 Some oxidation products are also dangerous to fire. For example, ethylene oxide is a combustible gas; although nitric acid is a corrosive substance, it is also a strong oxidant; 36.7% of the aqueous formaldehyde solution is a flammable liquid, and the explosion limit of the vapor is 7.7% to 73%. In addition, some oxidation processes may also generate more dangerous peroxides, such as the formation of acetic acid during the oxidation of acetic acid to produce acetic acid, peracetic acid is an organic peroxide, the properties are extremely unstable, subject to high temperature, friction Or the impact will break down or burn.

(2) Fire prevention measures for oxidation process

1 When air or oxygen is used as the oxidant in the oxidation process, the ratio of the reaction materials (mixing ratio of combustible gas and air) should be strictly controlled outside the explosion range. Before entering the reactor, the air should pass through a gas purification device to eliminate dust, water vapor, oil and impurities that can reduce or poison the catalyst to maintain the activity of the catalyst and reduce the risk of fire and explosion.

2 Oxidation reaction contactors are available in both horizontal and vertical types, and are internally filled with a catalyst. Vertical is generally used because this type of catalyst is convenient and safe to handle. In the catalytic oxidation process, for the exothermic reaction, the appropriate temperature and flow rate should be controlled to prevent the over-temperature, over-pressure and mixed gas from being in the explosion range.

3 In order to prevent the contactor from jeopardizing the safety of people and equipment in the event of an explosion or fire, a flame arrester should be installed in front of the reactor and on the pipeline to prevent the flame from spreading and prevent tempering, so that the fire does not affect other systems. In order to prevent the contactor from exploding, the contactor should have a pressure relief device and use automatic control or adjustment and alarm interlocking devices whenever possible.

4 When using oxidizing agents such as nitric acid and potassium permanganate, it is necessary to strictly control the feeding rate to prevent excessive addition and mis-addition. The solid oxidant should be used after pulverization, preferably in the form of a solution. The reaction should be continuously stirred and the reaction temperature should be strictly controlled. Never exceed the spontaneous ignition point of the oxidized material.

5 When using an oxidizing agent to oxidize inorganic substances, if the use of potassium chlorate is oxidized to form iron blue pigment, the drying temperature of the product should be controlled not to exceed its ignition point. The product should be washed with water before drying to completely remove the oxidizing agent to prevent the potassium chlorate from being completely reacted. Causes the dried material to catch fire. Oxidation of some organic compounds, especially at high temperatures, may produce char in equipment and piping and should be removed in time to prevent spontaneous combustion.

6 Raw materials and products used in the oxidation reaction shall be fire-fighting measures according to the relevant regulations on dangerous goods, such as isolation and storage, away from fire, avoiding high temperature and sun exposure, and preventing friction and impact. In the case of a flammable liquid or gas of a dielectric, a grounding device that removes static electricity should be installed.

7 Nitrogen and steam fire extinguishing devices should be installed in the equipment system so that the fire can be extinguished in time.

2 restore

For example, nitrobenzene is reduced by iron powder into aniline in hydrochloric acid solution, o-nitroanisole is reduced to anthranilic ether by alkaline powder in alkaline solution, and it is reduced by using insurance powder, potassium borohydride or lithium aluminum hydride. The agent is subjected to reduction or the like.

Risk analysis and fire protection requirements for the reduction process:

(1) Whether using primary ecological reduction or hydrogenation after catalyst activation, hydrogen is present (hydrogen explosion limit is 4%-75%), especially catalytic hydrogenation reduction, mostly under heating and pressurization conditions. Under the operation, if there is an operation error or a hydrogen leak due to equipment defects, it is easy to form an explosive mixture with air, and it will explode if it encounters a fire source. Therefore, the temperature, pressure and flow should be strictly controlled during the operation; the electrical equipment in the workshop must meet the explosion-proof requirements. Wire and wire junction boxes should not be laid on the top of the workshop; the ventilation of the plant should be good, light roof should be used, skylights or hoods should be installed to allow hydrogen to escape in time; the hydrogen generated in the reaction can be exported to the workshop house by the exhaust pipe. Above the ridge of 2m, it will be discharged through the flame arrester; the equipment for pressure reaction should be equipped with a safety valve, and the equipment that generates pressure in the reaction should be equipped with a rupture disc; the hydrogen detection and alarm device should be installed.

(2) Catalyst used in the reduction reaction After the moisture absorption of Reynolds nickel, there is a danger of spontaneous combustion in the air. Even if there is no ignition source, the mixture of hydrogen and air can be ignited to form a fire explosion. Therefore, when they are used to activate hydrogen for reduction, it is necessary to replace all the air in the reactor with nitrogen, and after the measurement confirms that the oxygen content falls to the standard, the hydrogen can be passed through; after the reaction, nitrogen should be used first. The hydrogen in the reactor is replaced and the hole cover can be opened to prevent the outside air from colliding with the hydrogen in the reactor. In the case of self-ignition of the Reynolds nickel, a fire explosion occurs, and the Reynolds nickel should be stored in the alcohol, palladium. When carbon is recycled, it should be washed thoroughly with alcohol and water. When vacuuming, it should not be pumped too dry to avoid oxidative ignition.

(3) Solid reducing agent insurance powder, potassium borohydride, lithium aluminum hydride, etc. are all wet and flammable dangerous goods, in which the insurance powder is heated by water, and the sulfur can be separated out in humid air, and the sulfur vapor is heated and has the danger of spontaneous combustion. And the insurance powder itself is heated to 190 °C, there is also the danger of decomposing and exploding; potassium borohydride (sodium) can spontaneously ignite in humid air, liberating a large amount of hydrogen in the presence of water or acid, and generating high heat, which can cause hydrogen to ignite and cause an explosion accident. Lithium aluminum hydride is a reducing agent for the risk of moisture, so be sure to keep it safe to prevent moisture. When the powder is used for dissolution, the temperature should be strictly controlled. The powder can be added to the water in batches with stirring, and then reacted with the organic matter after dissolution; when sodium borohydride (potassium) is used as the reducing agent When adjusting the acidity and alkalinity during the process, special attention should be paid to prevent the acid from being added too quickly and too much. When using lithium aluminum hydride as the reducing agent, special care must be taken. It must be used under the protection of nitrogen, usually immersed in kerosene. Store. The reducing agent mentioned above reacts violently with the oxidant, generates a large amount of heat, and is in danger of being exposed to fire and explosion, so it must not be mixed with the oxidant.

(4) The intermediate of the reduction reaction, especially the intermediate of the reduction reaction of the nitro compound, also has a certain fire hazard. For example, in the process of reducing o-nitroanisole to anthranilic acid, an oxidative couple is generated. Azain, the intermediate is self-igniting when heated to 150 °C. In the production of aniline, if the reaction conditions are not well controlled, cyclohexylamine, which is highly explosive, can be produced. Therefore, various reaction parameters and reaction conditions must be strictly controlled in the reaction operation.

(5) Carry out technological innovations and study the use of new reducing agents with low risk and high reduction efficiency to replace reducing agents with high fire risk. For example, the use of sodium sulfide instead of iron powder reduction can avoid hydrogen generation and also eliminate the problem of iron mud accumulation.

3 nitrification

Nitrification generally refers to a reaction in which a nitro group (—NO 2 ) is introduced into an organic compound molecule to replace a hydrogen atom to form a nitro compound. For example, toluene nitration to produce TNT, benzene nitration to obtain nitrobenzene, glycerol nitration to obtain nitroglycerin.

The fire hazard of the nitrification process is mainly:

(1) Nitrification is an exothermic reaction. The introduction of a nitro group requires an exotherm of 152.2 to 153 kJ/mol, so the nitrification needs to be carried out under cooling conditions. In the nitrification reaction, if there is slight negligence, such as stop stirring in the middle, poor supply of cooling water, too fast feeding rate, etc., the temperature will increase sharply, the acid oxidation ability will be strengthened, and the formation of polynitrogen will cause fire and explosion. accident.

(2) The nitrating agent has oxidizing properties. The commonly used nitrating agent concentrated nitric acid, nitric acid, concentrated sulfuric acid, fuming sulfuric acid, mixed acid, etc. all have strong oxidizing, water absorbing and corrosive properties. When they are in contact with oils and fats, especially unsaturated organic compounds, they can cause combustion. If the temperature is too high or a small amount of water is dropped during the preparation of the nitrating agent, it will promote the decomposition and evaporation of nitric acid, which will not only cause strong equipment. Corrosion can also cause an explosion.

(3) Most of the substances that are nitrated are flammable, such as benzene, toluene, glycerin (glycerol), de-esterified cotton, etc., which are not only flammable, but also have toxicity. If used or improperly stored, it is easy to cause fire. .

(4) Nitrification products are mostly exposed to fire and explosion hazards, especially polynitro compounds and nitrate esters, which are subject to heat, friction, impact or contact with fire sources, and are prone to explosion or fire.

4 Electrolysis

When a current passes through an electrolyte solution or a molten electrolyte, the chemical change caused on the two poles is called electrolysis. Electrolysis has a wide range of functions in the industry. Many non-ferrous metals (sodium, potassium, magnesium, lead, etc.) and rare metals (zirconium, hafnium, etc.) smelting, metal copper, zinc, aluminum and other refining; many basic chemical industrial products (hydrogen, oxygen, chlorine, caustic soda, potassium chlorate, The preparation of hydrogen peroxide, etc., as well as electroplating, electropolishing, anodizing, etc., are all achieved by electrolysis.

Such as salt water electrolysis production of sodium hydroxide, hydrogen, chlorine, electrolysis of water to produce hydrogen. Risk analysis and fire prevention points in the brine electrolysis process:

(1) The brine should ensure that the mass of brine contains iron impurities, which can produce a second cathode to release hydrogen; the brine is mixed with ammonium salt. Under suitable conditions (pH<4.5), ammonium salt and chlorine can be used. Ammonium chloride is formed, and chlorine acts on the concentrated ammonium chloride solution to form nitrogen trichloride in the form of a yellow oil.

3C12+NH4Cl——4HCl+NCl3

Nitrogen trichloride is an explosive substance that is in contact with many organic substances or heated above 90 ° C and is struck, that is, a violent decomposition explosion occurs. The explosion decomposition is as follows:

2NCl3——N2+3C12

Therefore, salt water preparation must strictly control the quality, especially the content of iron, calcium, magnesium and inorganic ammonium salts. Generally, Mg2+<2 mg/L, Ca2+<6 mg/L, and SO42-<5 mg/L are required. An automatic analyzer for salt water purity should be used as much as possible to observe changes in brine composition and adjust the amount of sodium carbonate, caustic soda, barium chloride or acrylamide at any time.

(2) The salt addition height should be appropriately added to the anode chamber of the electrolysis cell during operation. If the brine level is too low, hydrogen may be infiltrated into the anode chamber through the cathode network and mixed with chlorine gas; if the electrolyzer brine is overfilled, The salt water will rise under pressure. Therefore, the salt water should not be added too little or too much, and should maintain a certain safe height. The brine feeder should be intermittently supplied with brine to avoid the loss of current and prevent the brine conduit from being corroded by current (there is currently a hose).

(3) Prevent hydrogen and chlorine from mixing. Hydrogen is a highly flammable gas. Chlorine is a highly toxic toxic gas. Once the two gases are mixed, they are prone to explosion. When the chlorine content in the chlorine gas reaches 5% or more, it may be Explosion in the event of light or heat. The main reason for the mixing of hydrogen and chlorine gas is that the brine liquid level in the anode chamber is too low; the hydrogen outlet of the electrolytic cell is blocked, causing the pressure in the cathode chamber to rise; the adsorption capacity of the diaphragm of the electrolytic cell is poor; the quality of the asbestos is not good, when the electrolytic cell is installed. If the diaphragm is damaged, causing the diaphragm to partially fall off or the amount of salt water injected before power transmission to break the diaphragm, and the pressure in the cathode chamber is equal to or exceeds the pressure in the anode chamber, hydrogen may enter the anode chamber, etc., which may cause The amount of hydrogen in the chlorine gas increases. At this time, the electrolytic cell should be thoroughly inspected to control the hydrogen concentration of the single-channel chlorine to be less than 2%, and the hydrogen concentration of the main-tube chlorine is controlled to be less than 0.4%.

(4) Strict installation requirements of electrolytic equipment Because of the existence of hydrogen in the electrolysis process, there is a danger of fire explosion. Therefore, the electrolysis cell should be installed in a single-storey building with good natural ventilation. The plant should have sufficient explosion-proof pressure relief area.

(5) Mastering the correct emergency treatment method In the production, when the sudden power failure or other reasons suddenly stop, the high pressure valve can not be closed immediately, so as to avoid the chlorine gas flowing back in the electrolytic tank and explode. The venting tube should be installed behind the electrolyzer, decompressed at the same time, and a check valve should be installed on the high pressure valve to effectively prevent chlorine from running, avoiding environmental pollution and fire hazard.

5 aggregation

The reaction process in which several molecules are combined into one larger compound having the same molecular weight and higher molecular weight is polymerization.

For example, vinyl chloride polymerizes to produce polyvinyl chloride plastics, and butadiene polymerizes to produce butadiene rubber and styrene-butadiene rubber.

According to the reaction type, the polymerization can be divided into two types: addition polymerization and condensation polymerization; according to the polymerization method, it can be divided into five types: bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization and condensation polymerization.

(1) Bulk polymerization

Bulk polymerization is carried out in the absence of other media (such as high pressure polymerization of ethylene, polymerization of formaldehyde, etc.), using a tubular polymerization vessel immersed in a coolant (or coiling in a polymerization vessel, cooling of the tubes) A polymerization method. This polymerization method is often dangerous due to the fact that the heat of polymerization is not easily conducted and discharged. For example, in the production of high-pressure polyethylene, 3.8 MJ of heat is released per 1 kg of ethylene. If the heat is not removed in time, the temperature in the autoclave can be increased by 12 to 13 ° C per 1% of ethylene. When it is raised to a certain temperature, ethylene will be decomposed, strongly exothermic, and there is a danger of occurrence of agglomeration. In the event of a catastrophe, the equipment is clogged, the pressure is suddenly increased, and the explosion is highly prone.

(2) Solution polymerization

Solution polymerization is a polymerization method in which a solvent is selected to dissolve a monomer into a homogeneous system, and a catalyst or an initiator is added to form a polymer. In this polymerization process, the flammable solvent is easily volatilized and generates a static spark during polymerization and separation.

(3) Suspension polymerization

Suspension polymerization is a polymerization method in which water is used as a dispersion medium. It utilizes an organic dispersant or an inorganic dispersant, and the water-insoluble liquid monomer together with the initiator dissolved in the monomer is strongly stirred, broken into beads, dispersed in water to form a suspension, and is extremely fine. The unit droplets (0.1 um in diameter) are polymerized, so it is also called bead polymerization. In the polymerization process, if the process conditions are not strictly controlled, the equipment is not functioning properly, and the flash material is prone to occur. If the material is flashed, the unpolymerized monomer and the initiator are easily exposed to the fire source after the water is evaporated. Causes a fire or explosion.

(4) Emulsion polymerization

Emulsion polymerization is a method in which an emulsifier is used to disperse a liquid monomer in water (bead diameter 0.001 to 0.01 um) under mechanical strong stirring or ultrasonic vibration, and the initiator is dissolved in water to carry out polymerization. This polymerization method usually uses an inorganic peroxide (such as hydrogen peroxide) as an initiator. If the peroxide is improperly mixed in the medium (water), the temperature is too high, the reaction rate is too fast, and the charging occurs, and at the same time, the polymerization occurs. Combustible gases are also produced during the process.

(5) Condensation polymerization

Condensation polymerization, also called polycondensation, is a polymerization in which monomers having two or more functional groups are condensed with each other and a small molecular by-product is precipitated to form a polymer. Condensation polymerization is an endothermic reaction, but because of the high temperature, it will also cause the pressure of the system to increase, or even cause a burst, leaking flammable and explosive monomers.

6 Catalytic

The catalytic reaction is a chemical reaction carried out under the action of a catalyst. For example, the synthesis of ammonia from nitrogen and hydrogen, the synthesis of sulfur trioxide from sulfur dioxide and oxygen, and the synthesis of ethylene oxide from ethane and oxygen are all catalytic reactions.

Catalytic fire hazard:

(1) Reaction operation In the catalytic process, if the catalyst is selected incorrectly or the amount of discomfort is added, the local reaction is likely to be intense; in addition, since the catalysis is mostly carried out at a certain temperature, if the heat dissipation is poor and the temperature control is not good, it is easy. An over-temperature explosion or a fire accident has occurred.

(2) Catalytic products in the catalytic process some hydrogen chloride, hydrogen chloride is corrosive and poisoning hazard; some produce hydrogen sulfide, the risk of poisoning is greater, and the explosion limit of hydrogen sulfide in the air is wider (4.3% ~ 45.5%), there is also an explosion hazard in the production process; some catalytic processes produce hydrogen, and the danger of fire and explosion is greater, especially under high pressure, the corrosion of hydrogen can make the metal high-pressure container embrittlement, thus causing destructive accidents. .

(3) The amount of impurities in the raw material gas feed gas that can react with the catalyst increases, which may become an explosion hazard, which is very dangerous. For example, in the reaction of catalytic oxidation of ethylene to acetaldehyde, since the catalyst system often contains a large amount of cuprous salt, if the acetylene in the raw material gas is too high, acetylene reacts with the cuprous salt to form acetylene copper. Acetylene copper is a red precipitate. It is an extremely sensitive explosive. The self-ignition point is between 260 and 270 °C. It is very easy to explode in the dry state. It is easily oxidized to dark black under the action of air and is prone to fire.

7 cracking

Cracking, sometimes called cracking, refers to the reaction process in which organic compounds decompose at high temperatures. Cracking can be divided into three types: thermal cracking, catalytic cracking, and hydrocracking.

(1) Thermal cracking

Thermal cracking is carried out under high temperature and high pressure. The temperature of the oil in the device generally exceeds its self-ignition point. If the oil leaks, it will immediately ignite; in the process of thermal cracking, a large amount of cracked gas will be generated, and there will be a large amount of gas fractionation equipment. The formation of explosive gas mixtures, in the case of open flames such as furnaces, there is a risk of explosion. In the refinery units, the number of fires occurring in the thermal cracking unit is high.

(2) Catalytic cracking

Catalytic cracking is generally carried out at higher temperatures (460 to 520 ° C) and pressures of 0.1 to 0.2 MPa, which poses a greater risk of fire. If not handled properly, the air and flame in the regenerator will enter the reactor and cause a vicious explosion. There are many small equipments and small valves on the U-shaped tube, which are easy to leak oil and catch fire. Flammable cracked gas is also produced during the catalytic cracking process, and flammable carbon monoxide gas may also be present when the scorch activation catalyst is abnormal.

(3) Hydrocracking

Since hydrocracking uses a large amount of hydrogen, and the reaction temperature and pressure are high, the steel is in contact with hydrogen under high pressure, and the carbon molecules in the steel are easily taken by the hydrogen gas, so that the hardness of the carbon steel is increased to lower the strength and hydrogen embrittlement is generated. If equipment or pipelines are not inspected or replaced in time, equipment explosion will occur under high pressure (10 ~ 15MPa). In addition, hydrogenation is a strong exothermic reaction and the reactor must be cooled with hydrogen to control the temperature. Therefore, it is necessary to strengthen the inspection of equipment, regularly replace pipes and equipment, and prevent accidents caused by hydrogen embrittlement; the furnace should be operated smoothly to prevent local overheating of the equipment, prevent the furnace tube of the heating furnace from burning or the high temperature pipeline and the reactor leaking. on fire.

8 Chlorination

The process of replacing a hydrogen atom in an organic compound with a chlorine atom is called chlorination. Such as methane chloride from methane, chlorinated benzene to benzene, and the like. Commonly used chlorinating agents are: liquid or gaseous chlorine, gaseous hydrogen chloride and various concentrations of hydrochloric acid, phosphoric acid chloride (phosphorus oxychloride), phosphorus trichloride (acid chloride used to make organic acids), sulfuryl chloride (dichlorosulfur Acyl), hypochlorite, and the like.

Chlorination process hazard analysis and fire prevention points:

(1) The fire hazard of the chlorination reaction is mainly determined by the nature of the chlorinated material and the conditions of the reaction process. Most of the raw materials used in the reaction process are organic flammable materials and strong oxidants such as methane, ethane, benzene, alcohol, natural gas, toluene, liquid chlorine and the like. For example, the production of 1t methane chloride requires 2006m3 methane and 6960kg liquid chlorine, which also poses a fire and explosion hazard during the production process. Therefore, all kinds of ignition sources should be strictly controlled, and electrical equipment should meet the requirements of fire and explosion protection.

(2) The most commonly used chlorinating agent in the chlorination reaction is liquid or gaseous chlorine. Chlorine gas itself is highly toxic, highly oxidizing, and has a high storage pressure. Once leaked, it is very dangerous. Therefore, the liquid chlorine in the tank must be vaporized by an advanced evaporator before entering the chlorinator. Under normal circumstances, it is not allowed to use a gas cylinder or tank truck that stores chlorine as a storage tank, because it is possible to cause the chlorinated organic matter to flow back into the intake bottle or tank truck to cause an explosion. For general chlorinators, chlorine buffer tanks should be installed to prevent backflow when chlorine gas is shut off or pressure is reduced.

(3) The chlorination reaction is an exothermic process, especially at higher temperatures, and the reaction is more severe. For example, in the production of epichlorohydrin, propylene needs to be preheated to about 3000 ° C for chlorination, and the reaction temperature can be raised to 500 ° C. At such a high temperature, if the material leaks, it may cause fire or cause an explosion. Therefore, the general chlorination reaction equipment must have a good cooling system, and strictly control the flow of chlorine gas, so as to avoid accidents due to excessive flow rate and temperature rise.

(4) Since almost all hydrogen chloride gas is formed in the chlorination reaction, the equipment used must be corrosion-proof and the equipment should be kept tight. Since hydrogen chloride gas is easily soluble in water, most of the hydrogen chloride in the exhaust gas can be removed by adding an absorption and cooling device.

9 diazotization

Diazotization is a reaction that converts an aromatic primary amine into a diazonium salt. It is usually a chemical reaction in which an aromatic amine-containing organic compound is reacted with sodium nitrite in an acidic medium to convert an amine group (-NH2) into a diazo group (-N=N-). Such as the preparation of dinitrodiazophenols.

Fire risk analysis of diazotization:

(1) The main fire hazard of the diazotization reaction is the diazonium salt produced, such as diazonium hydrochloride (C6H5N2Cl), diazosulfate (C6H5N2H504), especially the diazonium salt containing nitro group, such as heavy Nitrodinitrophenol [(NO2) 2N2C6H2OH], etc., which are easily decomposed under the action of a slightly higher temperature or light, and some can be decomposed even at room temperature. Generally, for every 10 °C increase, the decomposition rate is doubled. In the dry state, some diazonium salts are unstable, have high vigor, and can be decomposed and exploded by heat or friction or impact. If the solution containing diazonium salt is spilled on the ground or steam pipe, it can cause fire or explosion after drying. In acidic media, some metals such as iron, copper, zinc, etc. can cause the diazo compounds to decompose violently and even cause an explosion.

(2) Aromatic amine compounds as diazo agents are all combustible organic substances, and there is a danger of fire and explosion under certain conditions.

(3) The sodium nitrite used in the diazotization production process is an inorganic oxidant, which decomposes at 175 ° C to react with organic matter to cause fire or explosion. Sodium nitrite is not an oxidizing agent, so when it encounters an oxidizing agent which is more oxidizing than it, it is reductive. Therefore, when a strong oxidizing agent such as potassium chlorate, potassium permanganate or ammonium nitrate is encountered, there is a possibility of fire or explosion.

(4) In the production process of diazotization, if the reaction temperature is too high and the sodium nitrite is fed too fast or excessively, the concentration of nitrous acid will increase, the decomposition of the material will be accelerated, and a large amount of nitrous oxide gas will be generated. The danger of a fire explosion.

10 alkylation

Alkylation (also known as alkylation) is a chemical reaction in which an alkyl group R is introduced into an atom of nitrogen, oxygen, carbon or the like in an organic compound. The alkyl group to be introduced is a methyl group (-CH3), an ethyl group (-C2H5), a propyl group (-C3H7), a butyl group (-C4H9) or the like.

Alkylation is generally used as an alkylating agent for introducing an alkyl group into an atom such as carbon, oxygen or nitrogen in an organic compound molecule, such as an olefin, a halogenated hydrocarbon or an alcohol. For example, aniline and methanol are used to prepare dimethylaniline.

Fire risk of alkylation:

(1) Most of the alkylated substances are in danger of fire and explosion. For example, benzene is a liquid of class A, with a flash point of -11 ° C and an explosion limit of 1.5% to 9.5%. The aniline is a liquid of type C, with a flash point of 71 ° C and an explosion limit of 1.3% to 4.2%.

(2) The alkylating agent is generally more dangerous than the fire of the alkylated material. For example, propylene is a flammable gas with an explosion limit of 2% to 11%; methanol is a liquid of class A with a flash point of 7 ° C and an explosion limit of 6% to 36.5%; dodecene is a liquid of class B with a flash point of 35 ° C and spontaneous combustion. Point 220 ° C.

(3) The catalyst used in the alkylation process is highly reactive. For example, aluminum trichloride is a wet substance, which is strongly corrosive. It is liberated by water or water vapor, and hydrogen chloride gas is released, which sometimes causes an explosion. If it is in contact with combustible materials, it is easy to catch fire; phosphorus trichloride is corrosive. Avoid wet liquid, violently decompose with water or ethanol, release a lot of heat and hydrogen chloride gas, have strong corrosive and irritating, toxic, water and acid (mainly nitric acid, acetic acid), heat, smoke, fire The danger of explosion.

(4) The alkylation reaction is carried out under heating conditions. If the order of addition of raw materials, catalysts, alkylating agents, etc. is reversed, the speed is too fast, or the stirring is stopped, a violent reaction occurs, causing the material to run, causing a fire or Explosion accident.

(5) Alkylation products also have a certain fire hazard. For example, cumene is a liquid of class B, with a flash point of 35.5 ° C, a self-ignition point of 434 ° C, and an explosion limit of 0.68% to 4.2%; dimethylaniline is a class C liquid with a flash point of 61 ° C and self-ignition point 371 °C; alkylbenzene is a liquid C, with a flash point of 127 ° C.

11 sulfonation

Sulfonation is a reaction in which a sulfo (acid) group (-SO3H) is introduced into an organic compound molecule. Commonly used sulfonating agents are fuming sulfuric acid, sodium sulfite, potassium sulfite, sulfur trioxide, and the like. For example, the production of sodium m-aminobenzenesulfonate with nitrobenzene and fuming sulfuric acid, the formation of a sulfonate by a halogenated alkane and sodium sulfite under high temperature and pressure conditions are all sulfonation reactions.

Sulfuration process hazard analysis:

(1) Sulfur trioxide is an oxidant, which will cause fire quickly when it is more flammable than nitrobenzene. In addition, sulfur trioxide is very corrosive, but when it meets water, it produces sulfuric acid and emits a lot of heat. Increasing the reaction temperature not only causes boiling or causing the sulfonation reaction to cause a combustion reaction to cause fire or explosion, but also has strong corrosiveness due to sulfuric acid, which increases corrosion damage to the equipment.

(2) Since benzene, nitrobenzene and chlorobenzene are all combustible materials, the sulfonating agent concentrated sulfuric acid, fuming sulfuric acid (sulfur trioxide) and chlorosulfonic acid are all oxidizing substances, and some are strong oxidizing agents. Therefore, it is very dangerous to carry out the sulfonation reaction under the condition of interaction between the two, because the combustion condition of the exothermic reaction of the combustible and the oxidant is already available. If the sulfonation reaction is reversed in the order of feeding, the feeding speed is too fast, the stirring is poor, and the cooling effect is not good, the reaction temperature may rise, and the sulfonation reaction may become a combustion reaction, causing a fire or explosion accident.

(3) The sulfonation reaction is an exothermic reaction. If effective cooling and good agitation are not obtained during the reaction, the reaction temperature may be too high, and a combustion reaction may occur, causing an explosion or a fire accident.