Overview【1】【2】
Red phosphorus, also known as red phosphorus (Phosphourus), is more stable than yellow phosphorus and does not emit phosphorescence in the dark. Red phosphorus can only interact with other substances at high temperatures, at 290. When C is distilled off, it becomes yellow phosphorus. It does not spontaneously ignite in air. It will catch fire when heated to about 200°C and burn to form phosphorus pentoxide. It will also burn when heated in chlorine gas and encounter KCl0. , KMnO. Peroxides and other oxidizing agents are explosive.
In light industry, it is mainly used to make matches. A mixture of red phosphorus, antimony sulfide and glue is applied to the side of the matchbox. When the match head (potassium chlorate, antimony sulfide, glass powder and glue, etc.) rubs on it, it produces Under the influence of heat, a small amount of red phosphorus is converted into yellow phosphorus, and then the burning of yellow phosphorus causes a chemical reaction in the match head to burn. In the chemical industry, it is used to produce raw materials for phosphorus-containing compounds such as phosphoric acid, phosphorus anhydride, phosphorus pentoxide, and phosphorus trioxide, as well as organophosphorus pesticides, fertilizers and other organic synthetic products. Used in the metallurgical industry to make phosphor bronze sheets.
Production process【4】
(1) Phosphorus trichloride reduction method
Since the vapor pressures of arsenic trichloride and phosphorus trichloride are relatively close, appropriate separation conditions and distillation equipment must be selected during separation. The balancer used is a packed or glass distillation column, diameter. 20 mm, the filling is glass balls with a diameter of 3-4 mm, and the filling height is 750 mm. The fractionating head uses a timing relay to control the opening and closing of the electromagnetic switch. The distillation outlet at the upper part of the packing layer is equipped with a flow metering device. The distillation column is insulated with a vacuum jacket, and the inner wall of the jacket is silver-plated. The distillation flask at the bottom of the distillation column has a capacity of 1000 mL: it is heated by an electric furnace.
The distillation and purification of phosphorus trichloride is carried out in the above-mentioned packed distillation column, using analytically pure reagents as raw materials. The distillate is collected in three parts. According to PCI. AsCl. The following proportions are selected for the actual separation capacity of the system and the impurity content in the raw materials: the first part takes 15% of the total distillate, the second part takes 60% of the total distillate, and the remaining residual liquid is 25% of the total distillate. The distillation rate is 0.17·mL/min. The reflux ratio is 1 to 28. For each distillation, add 750 mL of the feed liquid into the distillation bottle, heat to boiling, then reduce the heating current to maintain the maximum reflux flow, and start distillation at the specified speed after full reflux for 2 hours. If necessary, the phosphorus trichloride obtained for the first time is rectified again.
The hydrogen reduction of phosphorus trichloride is carried out in a vertically placed transparent quartz tube. The diameter of the quartz tube is 25 mm, and the outside is heated by a resistance furnace. The heating is divided into upper and lower sections, each of which is 350 mm long. The hydrogen in the cylinder is purified by pyrogallic acid-platinum asbestos (℃)-solid potassium hydroxide. The purified hydrogen enters the reaction tube through the flow meter in two ways: one way leads to the phosphorus trichloride storage container to bring the phosphorus trichloride gas into the reaction tube; the other way directly enters the reaction tube. Before starting the operation, hydrogen is introduced to purge the air in the system, and then the reaction tube is heated to the required temperature, and a mixed gas of phosphorus trichloride and hydrogen is introduced. The reaction waste gas is discharged through a bubbler. The generated phosphorus drips into the collector along the tube wall, and part of the uncondensed phosphorus vapor condenses when the exhaust gas passes through the collector. When phosphorus drips along the tube wall, a small amount is converted into red phosphorus at the end of the reaction tube and adheres to the tube wall.
Reduction is based on the second part of the primary distillation, which is at ℃ (both the upper and lower sections are ℃), 600℃ (both the upper and lower sections are 600℃), and 800℃ (the upper end is 800℃, the lower section is 500℃) Hydrogen reduction is carried out below. At ℃, it can be observed that the reaction is proceeding, but the speed is very slow, and only a thin layer of sediment is precipitated at the end of the reaction tube. At 600°C, the reaction speed is still relatively slow and not much product is obtained. At 800℃, when H. /PCI. When the molecular ratio is 3.5, the precipitation rate of phosphorus is 3 to 4 g/h. The recovery rate is 95%.
In order to facilitate storage or meet the needs of use, the obtained white phosphorus can be converted into red phosphorus. As long as the white phosphorus is transferred to another glass tube, sealed under vacuum and gradually heated to 300-350°C, it will be completely converted into red phosphorus in about a week.
(2) Direct distillation method
Put 5 kg of 99% industrial phosphorus into a 10 L distillation flask, move it to a sand bath, install a fractionator, connect the condenser tube, heat it with a sealed electric furnace, and control it with a voltage regulating transformer Temperature, the temperature should rise slowlySlowly, when all the phosphorus melts into liquid, increase the temperature to 300°C and start distillation. Operation should be carried out in a fume hood. First, put 200 mL of the initial distillate separately as the next raw material; 4 kg of the middle distillate as the intermediate product (semi-finished product); and 800 mL of the residual liquid. , can be used as raw materials, but can only be reused three times, otherwise the product quality will be affected. The above operation is the first distillation.
Distill the 4 kg of semi-finished product obtained above in exactly the same manner as above. After two distillations, approximately 3 kg of phosphorus will be obtained. After chemical and instrumental analysis, the purity reached 99.999%. Since the storage and storage of white phosphorus is not as safe as red phosphorus, white phosphorus must be converted into red phosphorus. The operation method is as follows:
Put 3 kg of high-purity phosphorus into a hard glass tube, move it to a tubular electric furnace, heat it under nitrogen, control the temperature at 300-350 OC, keep it for several hours, and then cool it to obtain high-purity phosphorus. red phosphorus.
Toxic effects【3】
For animals: it causes a decrease in the amount of hemoglobin, red blood cells and autologous cells and pathological changes in the liver and kidneys (Heimann).
For humans: When red phosphorus dust enters the respiratory tract, it causes a phenomenon similar to chronic poisoning by white phosphorus vapor. It is known that a worker engaged in red phosphorus sublimation work developed atypical acute pneumonia, and the concentration of red phosphorus aerosol in his working environment reached o. 104 mg/L (Delhamn, 140lma). It was reported that a worker developed cervical osteonecrosis after only coming into contact with red phosphorus (Heimann). It has been pointed out that red phosphorus may be converted into autophosphorus in the body. Some authors believe that the toxic effects of red phosphorus are due to its doping with white phosphorus.
Effects on the skin: Serious cases of skin diseases have been reported, as well as skin diseases caused by experiments.
References
[1]Han Changri, editor-in-chief Song Xiaoping, Chemical Commodity Production Method (Episode 17), Hunan Science and Technology Press, August 1996, first edition, page 615
[2] Han Changri, editor-in-chief Song Xiaoping, Fine Inorganic Chemical Manufacturing Technology, Science and Technology Literature Press, 2008.8, page 21
[3] Translated by Jin Feng, Zhou Shusen and others, Handbook of Hazardous Substances in Industrial Production Volume 3 (Revised Seventh Edition) Inorganic and Elemental Organic Compounds, Chemical Industry Press, May 1986, 1st edition, page 206
[4] Han Changri, editor-in-chief Song Xiaoping, Fine Inorganic Chemical Manufacturing Technology, Science and Technology Literature Press, 2008.8, page 21
