Selection of equipment for phosphorus trichloride oxidation
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I would like to ask the experts here about the selection of equipment for phosphorus trichloride use. After searching for relevant information online, it was found that the equipment used in the oxygen oxidation method for producing phosphorus trichloride is all made of enamel (including the intermediate metering tanks for the finished phosphorus trichloride product)! However, after checking corrosion data and material selection manuals, it was found that for dry phosphorus oxychloride, carbon steel is sufficient. Regarding the corrosiveness of phosphorus trichloride, does dry phosphorus trichloride lack corrosiveness? So in a system where phosphorus trichloride is used as a reactant, if other substances are not corrosive, can carbon steel equipment be chosen for the devices? I earnestly ask all the experts to help clarify this!
According to corrosion data and material selection manuals, carbon steel can be used for dry phosphorus oxychloride. However, wet phosphorus trichloride cannot be handled with carbon steel (or 304 stainless steel). Upon searching relevant literature, it is found that for the reactors used in the reaction of oxidizing phosphorus trichloride with oxygen to produce phosphorus oxytrichloride, enamel-coated equipment is always selected.
For inorganic materials, except for hydrogen fluoride, hydrofluoric acid, and hot concentrated phosphoric acid for which enamel cannot be used, common inorganic materials can all be used
Phosphorus trichloride oxide should be obtained by chlorination of phosphorus trichloride. Enameled steel equipment is generally chosen.
In a dry, anhydrous environment, materials such as stainless steel can be used; it is essential to ensure there is no water present, otherwise corrosion will occur immediately.
Carbon steel should not be used for reaction vessels. In actual production, leaks can occur in such equipment; therefore, the pressure inside the vessel is usually kept at a slight negative level, of about 2 cm of water column. If air enters the vessel, it can cause corrosion of the iron components as well as hydrolysis of the product, leading to damage. After production stops, cleaning the vessel also presents corrosion-related issues.
Phosphorus trichloride storage tanks can be made of carbon steel, including the pipes; yellow phosphorus will adhere to their interior. However, the sealing surfaces of the equipment and pipes must be properly protected to prevent leaks. In the event of a leak, the area must not come into contact with air or water.
The production processes for phosphorus trichloride are divided into the “oxygen oxidation process” and the “chlorination process with dripping chlorine.” In the latter process, by-products such as hydrochloric acid and phosphoric acid are generated. Sometimes, these two processes are switched back and forth, and the raw material phosphorus trichloride may contain trace amounts of water. Therefore, the chlorination reactors used for producing phosphorus trichloride, as well as the oxidation reactors used for producing phosphorus oxychloride, usually employ acid-resistant enamel reactors.
Phosphorus trichloride oxide and phosphorus trichloride undergo decomposition reactions when in contact with water. For dry forms, both carbon steel and ordinary austenitic stainless steel can be used; the choice depends on the process requirements. Reactors are often lined with enamel