Phosphorus trichloride production safety related matters
Time：2019-6-28 17:49:22 Clicks：437
Phosphorus trichloride must be fused first in production. Melt yellow phosphorus into a melting pot. Yellow phosphorus is spontaneous combustion articles, need to be stored in water, leaving the water surface is easy to spontaneous combustion, so before feeding phosphorus tank must be filled with nitrogen or carbon dioxide, drive clean air. When feeding, the action should be fast to prevent spontaneous combustion. Yellow phosphorus melting point is very low, heating temperature need not be too high, can be heated with interlayer hot water.
Reaction: yellow phosphorus reacts with chlorine gas in the reactor to form phosphorus trichloride. It reacts quickly and releases a lot of heat, which is dangerous.
Reaction must first add an appropriate amount of phosphorus trichloride, production known as "bottom phosphorus", make yellow phosphorus and phosphorus trichloride mixed, and then through chlorine gas reaction, so it is safer. The content of "bottom phosphorus" must be measured regularly in production, not too little.
The ratio of yellow phosphorus to chlorine gas must be appropriate, if the amount of yellow phosphorus is insufficient, chlorine gas and phosphorus trichloride, will produce phosphorus pentachloride. The latter is a white solid that tends to sublimate and often clogs pipes, leading to accidents. If the amount of phosphorus pentachloride has been more, when the yellow phosphorus is put in, it immediately reacts violently with the yellow phosphorus and reduces to a large amount of phosphorus trichloride. The reaction is as follows:
3 pcl5 + 2 p - > 5 pcl3
(phosphorus pentachloride) (phosphorus trichloride)
In the reaction process, due to the generation of high temperature, phosphorus trichloride large amount of gasification, resulting in increased pressure, easy to blanch. After flushing, will make the yellow phosphorus ejected together, yellow phosphorus encounter air spontaneous combustion, easy to cause fire. Sometimes there is no time to flush material explosion, the consequences are very serious. There have been lessons learned from accidents in production and we must be fully vigilant. So the use of special liquid reciprocating pump to transport molten yellow phosphorus. Using this pump to transport yellow phosphorus, so that the amount of phosphorus added will not be too much, can prevent the violent reaction with phosphorus pentachloride and cause explosion or impact.
The reaction generates a lot of heat and must be cooled in time. Cooling method should spray cold water all around the reactor wall, and should not use the method of interlayer cooling water, in case of wall leakage, the pressure of interlayer cooling water makes the water enter the reactor, react violently with phosphorus trichloride and cause explosion.
PCl3 + 3H2O → H3PO3+3HCl↑
Phosphorous acid (hydrogen chloride)
Even the use of spray method, but also to frequently overhaul the reactor, strictly prevent leakage. Same thing with the condenser.
The chlorine pipe must be inserted into the bottom of the reactor. If the pipe breaks, chlorine gas reacts with phosphorus trichloride on the surface to form phosphorus pentachloride:
PCl3 + Cl2 - PCl5
It is easy to explode or flush when molten phosphorus is added.
The bottom phosphorus buoy, or "bottom phosphorus buoy", can be used to control the liquid level of the reactor. "Bottom phosphorus buoy" can generally be made according to the reaction tank at a certain temperature of yellow phosphorus and phosphorus trichloride mixture proportion. An iron rod is installed on the upper end of the buoy, and a spiral tube transformer is fitted on it, and then the instrument indicator is connected. Depending on the height of the buoy and the current generated, the height of the bottom phosphorus level can be determined.
Rectification: the hot gasified phosphorus trichloride from the reactor is rectified in the column to obtain the condensate of phosphorus trichloride and enter the storage tank.
If phosphorus trichloride contains high free phosphorus, it will cause combustion and explosion due to spontaneous combustion of yellow phosphorus in deacidification and next chemical reaction, so the quality of phosphorus trichloride should be strictly controlled.
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