Study on production technology of styrene
Styrene is an important basic organic chemical raw material, which is mainly used to produce polystyrene resin (PS), acrylonitrile-butadiene-styrene terpolymer (ABS), styrene-acrylonitrile terpolymer (s an) resin, styrene-butadiene rubber (SBR) and styrene-butadiene latex (SBR latex), ion exchange resin, unsaturated polyester and styrene-based thermoplastic elastomer SBS. In addition, it can also be used in pharmaceutical, dye, pesticide and mineral processing industries, with a wide range of uses.
I. Introduction of Styrene Production Process
At present, the production methods of styrene in the world include ethylbenzene gas phase catalytic dehydrogenation method and propylene oxide method. Styrene co-production method, ethylbenzene dehydrogenation selective oxidation method, pyrolysis gasoline extraction distillation recovery method, ethylbenzene? Propylene oxidation, toluene-methanol synthesis, butadiene synthesis, etc. Among them, there are three commonly used methods: catalytic dehydrogenation, selective oxidative dehydrogenation of ethylbenzene (SMART) and ethylbenzene? Propylene * * * oxygen (POSM) method. The following focuses on these three methods.
1. Catalytic dehydrogenation
Dow Chemical Company, BASF Company and 1937 jointly developed the catalytic dehydrogenation method. In the long-term production, each company has its own characteristics in catalyst, reactor, process and energy saving, such as Fina/Badger method, Monsanto/Lummus/UOP method, DOW method, Cosden/Badger method and CdF method. Among them, Monsanto /Lummus/UOP process has been adopted by some styrene plants with the largest capacity in the world. Compared with other methods, 2t steam can be saved per ton of styrene, and the production cost can be reduced by 16%.
2. Selective oxidation of ethylbenzene by dehydrogenation
The oxidative dehydrogenation process of ethylbenzene adopts three-stage reactors: ethylbenzene and water vapor in the first-stage dehydrogenation reactor are dehydrogenated on the dehydrogenation catalyst layer, a certain amount of air or oxygen and water vapor are added into the second-stage reactor, and the second-stage reactor is equipped with highly selective oxidation catalyst and dehydrogenation catalyst. The heat generated by the reaction of oxygen and hydrogen heats the reactant stream, and all the oxygen is consumed without the loss of hydrocarbons. The outlet stream of the second stage reactor enters the third stage reactor to complete the dehydrogenation reaction. When the dehydrogenation temperature is 620 ~ 645℃, the pressure is 0.03 ~ 0. 13 MPa, and the mass ratio of steam to ethylbenzene is (1: 1)~ 2: 1, the ethylbenzene conversion is 85% and the styrene selectivity is 92% ~ 96.
3. propylene oxide? Co-production of styrene (PO/SM)
The co-production method of propylene oxide and styrene (PO/SM) is also called * * * oxidation method. At the temperature of 130 ~ 160℃ and the pressure of 0.3 ~ 4.05 MPa, ethylbenzene is firstly oxidized with oxygen in a liquid phase reactor to produce ethylbenzene peroxide. The generated ethylbenzene peroxide is concentrated to 17%, and then enters the epoxidation T sequence. The reaction temperature is 65438+. Epoxidation reaction liquid was distilled to obtain propylene oxide, and methyl benzyl alcohol was dehydrated at 260℃ and normal pressure to produce styrene. Benzene in the reaction product
The mass ratio of ethylene to propylene oxide is 2.5∶ 1. Combining the endothermic reaction of ethylbenzene dehydrogenation with the exothermic reaction of propylene oxidation not only saves energy, but also solves the problem of three wastes treatment in propylene oxide production. In addition, because the investment cost of the co-production plant is 25% lower than that of a single set of propylene oxide and styrene plant, and the operating cost is more than 50% lower, this method has more competitive advantages in building large-scale production plants. The disadvantages of this method are that it is greatly influenced by the product market, the reaction is complex, there are many by-products, the investment is large, and the ethylbenzene unit consumption and energy consumption of the device are higher than that of ethylbenzene dehydrogenation process.
4. Progress in localization of styrene production process
The negative pressure dehydrogenation reactor of ethylbenzene developed by East China University of Science and Technology adopts two key technologies: axial radial reactor technology and rapid gas-gas mixing. Axial radial reactor is a new type of radial reactor, which has a catalyst self-sealing structure at the top of the bed, so that the axial and radial two-dimensional flow occurs at the top of the radial bed. Compared with the traditional radial reactor, this catalyst self-sealing structure eliminates the mechanical sealing area on the upper part of the catalyst bed, simplifies the radial bed structure, effectively utilizes the catalyst in this part of the reactor space, eliminates the stagnant flow area of the catalyst bed, and is beneficial to improving the reaction conversion rate and facilitating the loading and unloading of the catalyst.
Second, the toxic mechanism of styrene
Although styrene is flammable and toxic, there are few explosion accidents of styrene due to the importance of explosion danger, but occupational poisoning is very common, so we should be alert to occupational poisoning of styrene. Styrene has both acute toxicity and chronic toxicity, which can cause damage to many systems of human body. Although its reproductive toxicity, blood toxicity and carcinogenicity are uncertain, it should be highly vigilant.
Effect of 1. on nervous system
Styrene has a strong neurasthenia effect, which can cause toxic encephalopathy after a large amount of inhalation. Studies have shown that lipid peroxidation and dystrophy fluctuation play an important role in toxic encephalopathy. A small amount of styrene inhalation will only cause slight dizziness and headache. In recent years, domestic studies have found that the abnormal rate of ECG in styrene long-term exposure group is significantly higher than that in control group, with arrhythmia in the majority and sinus bradycardia as the main factor.
2. Effect on digestive system
Short-term exposure to high concentration of styrene can cause nausea, vomiting, abdominal pain, diarrhea and other digestive tract symptoms. Long-term exposure to styrene can cause toxic liver disease, which has the characteristics of hidden attack. Clinically, digestive tract symptoms are the main symptoms, mostly hepatomegaly, but liver function tests are mostly normal.
3. Influence on urogenital system
Long-term low-concentration exposure to styrene can cause renal function damage, mainly by inhibiting the activity of enzymes in renal tissue, interfering with the cell tricarboxylic acid cycle and membrane absorption and transport, and damaging the proximal convoluted tubule epithelium. Short-term exposure can also affect glomerular function. In addition, styrene-7,8-oxide (SO), the main intermediate metabolite of styrene in vivo, has been proved to be a strong direct mutagen. Exposure of workers to styrene can lead to DNA damage in semen. Styrene is a small molecular compound with high fat solubility, which can be transported through placenta in vivo and directly contact with intrauterine fetus, thus causing toxic effects on developing embryos and interfering with organ formation and fetal development.
4. Effects on respiratory system
Inhaling a large amount of styrene at one time will cause corrosive damage to respiratory tract and lead to toxic pulmonary edema. In addition, styrene can produce free radicals through enzyme system or respiratory burst, start lipid peroxidation of biofilm, and cause diffuse lung injury together with inflammatory mediators. Short-term exposure to high concentration of styrene can cause respiratory irritation symptoms such as cough and sore throat, while long-term exposure to low concentration of styrene can obviously stimulate workers' respiratory tract, which can cause chronic rhinitis and chronic pharyngitis.
For safety professionals, the production process of styrene is very mature, but we need to find potential dangers in the process and eliminate or reduce the degree of harm as much as possible.
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Ren Yinjin, He, et al. Clinical and scientific research progress of occupational poisoning in China in the past 50 years [J]. China Journal of Occupational Diseases, 1999, 17 (5): 4 ~ 7.
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About the author: Wang Liansheng, male, from Yangzhou, Jiangsu Province,/kloc-0 was born in May, 1960, and is a member of Lianyungang Butterfly Dyeing and Chemical Co., Ltd.
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