Risk of chemical reduction reaction and preventive measures
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.
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