Chinese name: mbth terephthalic acid: PTA abbreviation: PTA Chinese alias: purified terephthalic acid 1, 4- terephthalic acid molecular formula: c8h6o4; ; HOOCC6H4COOH molecular weight: 166. 13 1 English alias: 1, 4- dicarboxylbenzene casNo. :100-21-0 enechino. : 202-830-0 Physical and chemical constants. Toxicological data and environmental behavior, environmental standards, emergency treatment, leakage emergency treatment, protective measures, emergency measures, technology, production methods, phthalic anhydride transposition method, toluene oxidation disproportionation method, main uses, storage and transportation conditions, processing technology, physical and chemical constants Chinese alias: terephthalic acid, terpenoid terephthalic acid; Pure terephthalic acid; Phthalic acid; Terephthalic acid; Terephthalic acid, terephthalic acid CAS registration number: 100-2 1-0 EINECS number: 202-830-0 Terephthalic acid is a binary aromatic carboxylic acid formed by connecting two carboxyl groups with two opposite carbon atoms on the benzene ring. Product features: this product is white crystal or powder, with low toxicity and flammability. If it is mixed with air, it will burn or even explode in case of fire within a certain limit. Melting point is 300℃, auto-ignition point is 680℃, ignition point is 384 ~ 42 1℃, sublimation heat is 98.4kJ/mol, combustion heat is 3225.9kJ/mol, and flash point is >; 1 10℃ density1.55g/cm3. Soluble in alkali solution, slightly soluble in hot ethanol, insoluble in most organic solvents such as water, ether, glacial acetic acid, ethyl acetate, dichloromethane, toluene, chloroform, etc. But soluble in strongly polar organic solvents, such as DMF, DEF and DMSO. Terephthalic acid can be esterified; Under strong conditions, halogenation, nitration and sulfonation will also occur. Invasive ways of environmental impact on health hazards: inhalation, ingestion and percutaneous absorption. Health hazards: it has * * effects on eyes, skin, mucous membrane and upper respiratory tract, and no occupational poisoning has been reported. Toxicological data and environmental behavioral toxicity: low toxicity. Acute toxicity: LD 50 1670mg/kg (abdominal cavity of mice); Rats 3200mg/kg (oral); Hazard characteristics of 3550mg/kg (taken orally by mice): In case of high fever, naked flame or contact with oxidant, there is a risk of burns. Combustion (decomposition) products: carbon monoxide and carbon dioxide. Environmental standard: the maximum allowable concentration of harmful substances in the air of workshops in the former Soviet Union is 0.1mg/m3; In the former Soviet Union (1975), the maximum allowable concentration of harmful substances in water was 0.1mg/L; Occupational exposure limits: OELS (mg/m3) PC-TWA: 8; Personal computer -STEL: 15. Emergency treatment for leakage. Emergency treatment for cutting off the fire source. Wear a gas mask and gloves. Collect it and transport it to an open place for burning. Such as a large number of leaks, collected and recycled or discarded after harmless treatment. Protective measures Respiratory system protection: Wear a gas mask when the concentration in the air is high. Eye protection: You can use a safety mask. Protective clothing: wear work clothes. Hand protection: Wear chemical resistant gloves when necessary. Others: Take a shower and change clothes after work. Pay attention to personal hygiene. First aid measures for skin contact: take off contaminated clothes and rinse with running water. Eye contact: immediately open the upper and lower eyelids and rinse with flowing water 15 minutes. See a doctor. Inhalation: Leave the site and go to a place with fresh air. See a doctor. Miseating: gargle by mistake, give milk or egg white, and see a doctor. Fire extinguishing methods: misty water, foam, carbon dioxide, dry powder and sand. The PTA production process can be divided into two parts: oxidation unit and hydrofining unit. Using acetic acid as solvent, raw material p-xylene is oxidized into crude terephthalic acid by air under the action of catalyst, and then the crude product is obtained by crystallization, filtration and drying in turn. Crude terephthalic acid is hydrogenated to remove impurities, then crystallized, centrifugally separated and dried to obtain PTA products. A method for purifying crude terephthalic acid includes the following steps: drying crude terephthalic acid, ball milling, sieving to make the particle size reach 65438 0-5 microns, soaking in water at 60-65438 000 DEG C, stirring, clarifying, skimming off impurities, and finally centrifuging at 80-65438 000 DEG C.. Crude terephthalic acid (TPA) is the precipitate of alkali decrement wastewater after acid precipitation, and the dry weight content of impurities is 15%- 18%. The main patent manufacturers of PTA process are BP-Amoco, DuPont -ICI and Mitsui Petrochemical Company. After years of development, the technologies of the above three companies are similar, each with its own characteristics and similar level. The total production capacity of PTA plant using BP-Amoco process in the world is 765,438+760,000 t/a, DuPont -ICI process is 3,495,000 t/a, and Mitsui oil refining process is 6,543.8+250,000 t/a.4-C6H4 (COOH) 2. Colorless crystals. Sublimation occurs above 300℃. Very slightly soluble in water, soluble in dimethyl sulfoxide, dimethylformamide and hexamethylphosphoryl triamine. Because of its low solubility and high melting point, it is difficult to purify. Terephthalic acid is industrially prepared by oxidizing paraxylene with nitric acid or air under the catalysis of cobalt salt. Terephthalic acid can also be produced by rearrangement of potassium benzoate or potassium phthalate in the presence of cadmium or zinc catalyst and carbon dioxide. Uses: Terephthalic acid and its dimethyl ester are mainly used for polycondensation with ethylene glycol to form polyester, and the synthetic fiber made from it is called polyester. Polyester can also be made into film or injection molding, which is widely used in electronics and automobile manufacturing. Terephthalic acid can also be used to make herbicides and adhesives. Purified terephthalic acid is one of the important bulk organic raw materials, which is mainly used to produce polyester fiber (polyester), polyester film and polyester bottles. It is widely used in chemical fiber, light industry, electronics, construction and other aspects of the national economy, and is closely related to people's living standards. The application of PTA is concentrated. More than 90% of PTA in the world is used to produce polyethylene terephthalate (PET), and the rest is used as raw materials for polypropylene terephthalate (PTT), polybutylene terephthalate (PBT) and other products. Production method PTA was discovered in19th century, and it was not until 1949 that British Bremen Chemical Industry Company discovered that PTA (or its derivative dimethyl terephthalate) was the main raw material for polyester production that large-scale production began. 198 1 year, the world PTA output has reached 3.485 mt, and the first industrial production method is nitric acid oxidation. With the development of polyester industry, PTA production methods have also developed from various raw materials and through various channels (Figure 1). The most economical and widely used method is high-temperature liquid phase oxidation with p-xylene as raw material (see color chart), with high yield and short process. The low-temperature oxidation reaction of p-xylene has mild conditions and low corrosiveness, but the process is long, which is only used in a few factories. It has also been suggested that p-xylene can be ammoniated and oxidized to produce terephthalonitrile, and then hydrolyzed to produce PTA, but this method has not been produced on a large scale. Due to the high cost of separating p-xylene from mixed xylene, some methods based on other raw materials have been developed. Although some of these methods have long been industrialized, they have not developed, and some are only in the intermediate experimental stage. Liquid phase oxidation of p-xylene at high temperature was first proposed by American Medieval Company and British Bremen Chemical Industry Company in 1955, and was industrialized by American Amoco Chemical Company in 1958. The general reaction formula of figure 1 is (figure 1): but the actual process is much more complicated, and some people think that it has gone through the following steps (figure 2): because the second methyl group is not easy to be oxidized, the reaction process is easy to stop in the stage of p-toluic acid or p-carboxybenzaldehyde. In order to continue the oxidation reaction, Amoco Chemical Company adopted the process of adding high temperature and cocatalyst bromide (usually tetrabromoethane) to cobalt acetate-manganese acetate catalyst (see complex catalyst) (Figure 3). Bromine produced by bromide can initiate a chain oxidation reaction with free radicals. The oxidation reaction is usually carried out in a tower reactor. The reaction temperature is 175 ~ 230℃, but most of them are higher than 200℃. Higher temperature can accelerate the reaction and reduce the intermediate products, but the by-products obtained by decomposition also increase. Because the heat of the reaction is taken away by the water generated by the evaporation reaction and the solvent acetic acid, the reaction pressure is related to evaporation, which is generally 1.5 ~ 3.0 MPa. The residence time is 0.5 ~ 3h. Increasing the concentration of cobalt acetate and manganese acetate can shorten the residence time or reduce the reaction temperature. In the process of high temperature oxidation, the yield of p-xylene can reach above 90%. Due to the high reaction temperature and the existence of bromine, it has a strong corrosive effect, so the reactor needs titanium or titanium-lined materials. Figure 2 Figure 3 The solubility of PTA in acetic acid is very small, and the oxidation products are slurry. After centrifugal separation and drying, solid crude TPA was obtained, in which the most harmful impurity was p-carboxybenzaldehyde (content 1000 ~ 5000 ppm). Crude TPA can be used to produce polyester through dimethyl terephthalate, but a better method is purification, and refined TPA can be directly used as the raw material of polyester. The commonly used refining method is hydrogenation method adopted by Amoco Company, that is, crude TPA is dissolved in water at high temperature and high pressure, then impurities are hydrogenated in the presence of palladium catalyst, and then fiber-grade PTA (purity specification suitable for spinning) is obtained through crystallization and filtration, and the content of p-carboxybenzaldehyde in the product can be less than 25ppm. The yield of terephthalic acid in the refining process is more than 97%. Besides hydrogenation, there are other refining methods, such as sublimation. The low-temperature oxidation of p-xylene generally has a reaction temperature lower than 150℃. Although cobalt acetate is also used as a catalyst, bromide is not used. At this time, in order to convert the second methyl group into carboxyl group, it is generally necessary to add an oxide which is easy to generate peroxide during oxidation reaction. For example, methyl ethyl ketone used by American Mobile Chemical Company, acetaldehyde used by American Heismann Kodak Company and melamine used by Japanese Toray Company. These substances will also produce acetic acid after oxidation, and acetic acid is the solvent used in oxidation. Taking Toray method as an example, the reaction conditions are: temperature 120 ~ 150℃, pressure 3MPa, and the yield is 96%. The low temperature oxidation method does not contain bromide, the reaction temperature is low, and the reactor does not need titanium. The patents of Henkel Company of the Federal Republic of Germany (processes of 1 1 2, 13 and 16 in Figure 4) are also called Henkel I method. Teijin Company of Japan has realized industrialization. Firstly, phthalic anhydride was converted into dipotassium phthalate, and dipotassium terephthalate was obtained by transposition reaction, and PTA was obtained by acidification (or acid precipitation). The most difficult of these steps is the metathesis reaction, using cadmium or zinc catalyst, the reaction temperature is 350 ~ 450℃, the pressure is 1 ~ 5 MPa, and the reactor structure is also very complicated. Potassium sulfate produced after sulfuric acid acidification is difficult to be converted into potassium hydroxide for recycling and can only be used as potassium fertilizer. Henkel Ⅰ process is industrialized because of its expensive raw materials and complicated process, but it has not been popularized. The oxidative disproportionation method of toluene in Figure 4 is also called Henkel Ⅱ method (i.e. the processes of 1, 12, 14 and 16 in Figure 4). That is, toluene is oxidized to benzoic acid, and its potassium salt is disproportionated to produce benzene and dipotassium terephthalate, and PTA is obtained by acidification. The most important thing is disproportionation reaction, which is carried out at 400℃, 2MPa and in the presence of carbon dioxide. This method was industrialized by Mitsubishi Chemical Industry Company of Japan in 1963. 1975 discontinued due to high cost. However, because the raw material toluene is much cheaper than p-xylene, companies in some countries are still studying to improve this method. Main uses PTA is mainly used to produce the most important polyester-polyethylene terephthalate. Before 1963, PTA was not easy to refine, so all products were made into dimethyl terephthalate first. After refining and separating impurities, they react with ethylene glycol in kettle (batch operation) and tower (continuous operation) reactors to prepare a mixture of ethylene terephthalate and its oligomers, and then they are condensed to produce polyethylene terephthalate. 1963, industrialization of PTA refining method, especially 1965, the refining method of Amoco chemical company was successful, and more PTA was directly esterified with ethylene glycol in one or more series kettle reactors. Direct esterification has higher requirements for the reactor, but it can save the process of manufacturing dimethyl terephthalate and recovering methanol, and the product quality is also high. Due to the above advantages, direct esterification developed rapidly, and by the 1970s, the output of purified terephthalic acid was gradually close to dimethyl terephthalate. PTA can also react with ethylene oxide to produce ethylene terephthalate. This route not only saves the production step of ethylene glycol by hydration of ethylene oxide, but also has less oligomer in the reaction product. At the same time, ethylene terephthalate is easily soluble in water and easy to crystallize and refine. Therefore, the difficulty of refining crude PTA can be avoided by making crude PTA into crude polyethylene terephthalate and then producing polyethylene terephthalate after refining. Many companies have studied and developed this method. The application of terephthalic acid is relatively concentrated. More than 90% of terephthalic acid in the world is used to produce polyethylene terephthalate. Another important use of terephthalic acid is to produce plasticizers, including two kinds: the first one is dioctyl terephthalate (DOTP), which is the product of esterification of terephthalic acid with industrial octanol (2-ethyl hexanol). It is a high-quality plasticizer with high flash point and high resistivity, which is especially suitable. The second is polyester plasticizer, which is the product of esterification and polycondensation of terephthalic acid with polyols (such as diethylene glycol, triethylene glycol, glycerol, propylene glycol, butanediol, etc.). ), its relative molecular weight is generally between 1000-4000 (the relative molecular weight of polyester as plasticizer is much smaller than that of polyester for chemical fiber and plastic packaging). Storage and transportation conditions: the products should be fireproof, moisture-proof and antistatic during transportation. Bagged products should be handled with care to prevent packaging damage; When loading and unloading tank cars, attention should be paid to controlling the loading and unloading speed to prevent static electricity. It should be stored in a cool, ventilated and dry warehouse, away from fire and heat sources, and separated from oxidants, acids and alkalis. Should avoid the sun and rain, should not be stacked in the open air. Bagged products for packaging, storage and transportation are packed with plastic film, and the net weight of each bag is 1000 2kg. The name, address, trademark, product name, grade, batch number, net weight and standard code of the manufacturer shall be printed on the packaging bag. It can also be shipped by stainless steel tank car. Check whether the tank car is clean and dry before loading. After loading, the entrance should be sealed and sealed with lead. Precautions for use are low-toxic substances, which have certain effects on skin and mucosa. For allergic people, contact with this product may lead to rash and bronchitis. The maximum allowable concentration in the air is 0. 1mg/m 3. Operators should wear protective equipment. Drying treatment of processing technology: this substance is easy to hydrolyze at high temperature, so drying treatment before processing is very important. It is suggested that the drying conditions in air are120℃ for 6 ~ 8h, or150℃ for 2 ~ 4h. Humidity must be less than 0.03%. If it is dried by a moisture absorption dryer, the recommended conditions are 150℃ for 2.5 hours. [2] Melting temperature: 225~275℃, suggested temperature: 250℃. Mold temperature: 40~60℃ for unreinforced materials. The cooling cavity of the mold should be well designed to reduce the bending of plastic parts. Heat loss must be rapid and uniform. It is suggested that the diameter of the mold cooling cavity is 12 mm and the injection pressure is medium (up to 1500bar). Injection speed: the injection speed should be as fast as possible (because PBT solidifies quickly). Runner and gate: circular runner is recommended to increase pressure transmission (empirical formula: runner diameter = plastic thickness+1.5mm). Various types of doors can be used. Hot runner can also be used, but attention should be paid to prevent leakage and material degradation. The gate diameter should be between 0.8~ 1.0*t, where t is the thickness of plastic parts. If it is an underwater gate, the recommended minimum diameter is 0.75mm..