Chinese name: terephthalic acid mbth: p-phthalic acid abbreviation: PTA Chinese alias: purified terephthalic acid1,molecular formula of 4-terephthalic acid: C8H6O4；; HOOCC6H4COOH molecular weight: 166. 13 1 English alias: 1, 4-Dicarboxybenene CASNo.: 100-2 1-0 EINECSNo.: 202-830-0 Physical and chemical constants, environmental impact, health hazards, toxicological data and environmental behavior, environmental standards, emergency treatment, emergency treatment of leakage, protective measures, first-aid measures, technology, production methods, etc. Pure terephthalic acid; Phthalic acid; Terephthalic acid; Para-benzoic acid, para-phthalic acid CAS accession 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 in the benzene ring. Product characteristics: 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 300 °C, self-ignition point 680 C, ignition point 384~42 1℃, sublimation heat 98.4kJ/mol, combustion heat 3225.9kJ/mol, flash point > 1 10℃ density 1.55g/cm 3. 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 strong polar organic solvents such as DMF, DEF and DMSO. Terephthalic acid can be esterified; Under strong conditions, halogenation, nitration and sulfonation can 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); 3200mg/kg (oral) in rats; Hazard characteristics of 3550mg/kg (orally taken by mice): In case of high heat, naked flame or contact with oxidant, there is a danger of burning. Combustion (decomposition) products: carbon monoxide and carbon dioxide. Environmental standard: the maximum allowable concentration of harmful substances in the air of the workshop in the former Soviet Union is 0. 1mg/m3; the maximum allowable concentration of harmful substances in the water of the former Soviet Union (1975) is 0. 1mg/L; China workplace harmful factors occupational exposure limits: OELS (mg/m 3) PC-TWA: 8; PC-STEL： 15。 Emergency treatment leakage emergency treatment cut 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: safety mask can be used. Protective clothing: wear work clothes. Hand protection: Wear chemical-resistant gloves when necessary. Others: After work, take a shower and change clothes. Pay attention to personal hygiene. First-aid measures Skin contact: Take off contaminated clothes and rinse with flowing 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 fresh air. See a doctor. Ingestion: rinse your mouth by mistake, give milk or egg white, and see a doctor. Fire extinguishing methods: misty water, foam, carbon dioxide, dry powder and sand. Technology 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 crystallized, filtered and dried in turn to obtain crude product; Crude terephthalic acid is hydrogenated to remove impurities, then crystallized, centrifugally separated and dried to obtain PTA products. The purification method of crude terephthalic acid includes the following steps: drying crude terephthalic acid, ball milling, sieving to make the particle size reach1~ 5 μ m, soaking in water at 60-100℃, stirring, clarifying, skimming, and finally centrifugal separation at 80-/kloc-. The crude terephthalic acid is the precipitate of alkali deweighting wastewater after acid precipitation, and the dry weight content of impurities is15%-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, with their own characteristics and similar levels. The total production capacity of PTA plant using BP-Amoco process in the world is 7176,000 t/a, Dupont-ICI process is 3.495 million t/a, and Mitsui Oiling Process is1025,000 t/a.. ，4-C6H4（ COOH ）2。 Colorless crystal. Sublimation occurs above 300℃. Very little solubility 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 oxidation of p-xylene with nitric acid or air oxidation 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 (PTA) is one of the important bulk organic raw materials, and its main use is to produce polyester fiber (polyester), polyester film and polyester bottle, which is widely used in all aspects of national economy such as chemical fiber, light industry, electronics and construction, 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 widely produced until 1949 when Britain's Bremen Chemical Industry Company discovered that PTA (or its derivative dimethyl terephthalate) was the main raw material for manufacturing polyester. 198 1 year, the world PTA production has reached 3.485 mt. The first industrial production method is nitric acid oxidation. With the development of polyester industry, PTA production methods have been 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), which has high yield and short process. The low-temperature oxidation of p-xylene has mild reaction conditions and low corrosiveness, but the process is long and is only used in a few factories. It has also been suggested that p-xylene should be ammoniated and oxidized to produce terephthalonitrile, and then hydrolyzed to produce PTA, but this method has not been produced on a large scale. Because of 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, while others 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. Figure 1 The overall reaction formula is (Figure 1): However, the actual process is much more complicated, and some people think that it goes through the following steps (Figure 2): Because the second methyl group is not easy to oxidize, 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 high temperature and adding cocatalyst bromide (commonly used tetrabromoethane) to cobalt acetate-manganese acetate catalyst (see complex catalyst) (Figure 3). Bromine produced by bromide can trigger a chain oxidation reaction with free radicals. The oxidation reaction is generally carried out in a tower reactor. The reaction temperature is175 ~ 230℃, but most of them are higher than 200℃. Higher temperature can accelerate the reaction and reduce intermediate products, but the by-products obtained from decomposition also increase. Because the heat of reaction is removed by the water generated by evaporation reaction and the solvent acetic acid, the reaction pressure is related to evaporation, which is generally1.5 ~ 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. The yield of p-xylene in high temperature oxidation process can reach above 90%. Due to the high reaction temperature and the presence of bromine, it has a strong corrosive effect, so the reactor needs titanium or titanium-lined materials. Fig. 2 fig. 3 PTA has little solubility in acetic acid, and the oxidation product is in the form of slurry. After centrifugal separation and drying, solid crude TPA is obtained, in which the most harmful impurity is p-carboxybenzaldehyde (content1000 ~ 5000 ppm). Crude TPA can be used to produce polyester through dimethyl terephthalate, but a better method is purification, and refined TPA is 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 by 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. Low temperature oxidation of p-xylene The reaction temperature of this method is generally lower than 150℃. Although cobalt acetate is also used as the 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 * * * oxide which is easy to produce peroxide during oxidation reaction. For example, methyl ethyl ketone is used by American Mobile Chemical Company, acetaldehyde is used by American Hysmans-Kodak Company, and melamine is used by Japanese Toray Company. These substances also generate acetic acid after oxidation, and acetic acid is the solvent used in oxidation. The reaction conditions were as follows: temperature120 ~150℃, pressure 3MPa, and the yield was 96%. The low-temperature oxidation method does not contain bromide and the reaction temperature is low, so the reactor does not need titanium. The transposition method of phthalic anhydride is patented by henkel Company of the Federal Republic of Germany (1 1, 12, 13, 16 in Figure 4), also known as henkel I method. Industrialization was realized by Teijin Company of Japan. In this method, phthalic anhydride is first converted into dipotassium phthalate, dipotassium terephthalate can be obtained by transposition reaction, and PTA can be obtained by acidification (or acid precipitation). The most difficult of these steps is the transposition reaction, which uses cadmium or zinc catalyst, the reaction temperature is 350 ~ 450℃, the pressure is1~ 5 MPa, and the reactor structure is also very complicated. It is difficult to convert the potassium sulfate generated after acidification with sulfuric acid into potassium hydroxide for recycling, and it can only be used as potassium fertilizer. Henkel Ⅰ process is expensive in raw materials and complicated in technology, so it has been industrialized, but it has not been popularized. Fig. 4 The oxidative disproportionation method of toluene is also called henkel II method (i.e. 1, 12, 14, 16 in fig. 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 critical one 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 Corporation in Japan on 1963. Production was stopped in 1975 due to high cost. However, because the raw material toluene is much cheaper than p-xylene, companies in some countries are still studying and improving this method. Main uses PTA is mostly used to produce the most important polyester-polyethylene terephthalate. Before 1963, PTA was not easy to be refined, so all products were first made into dimethyl terephthalate. After refining and separating impurities, they reacted with ethylene glycol in kettle (intermittent operation) and tower (continuous operation) reactors to prepare a mixture of ethylene terephthalate and its oligomers, and then they were condensed to produce polyethylene terephthalate. 1963, PTA refining method was industrialized, especially in 1965, Amoco Chemical Company succeeded in refining method, 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. Because of the above advantages, direct esterification developed rapidly, and in the 1970 s, the output of refined PTA gradually approached that of dimethyl terephthalate. PTA can also react with ethylene oxide to produce ethylene terephthalate. This route not only saves the production step of hydration of ethylene oxide to produce ethylene glycol, but also has few oligomers in the reaction products. At the same time, ethylene terephthalate is soluble in water and easy to crystallize and refine. Therefore, the difficult refining process of crude PTA can be avoided by making crude polyethylene terephthalate from crude PTA 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 application of terephthalic acid is to produce plasticizers, including two types: the first type is dioctyl terephthalate (DOTP), which is the product of esterification reaction between terephthalic acid and industrial octanol (2-ethyl hexanol). It is a high-quality plasticizer with high flash point and high specific resistivity, and 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.), and its relative molecular weight is generally between 1000-4000 (the relative molecular weight of polyester as plasticizer is much smaller than that of polyester used for chemical fiber and plastic packaging). Storage and transportation conditions: products should be fireproof, moisture-proof and antistatic during transportation. Bagged products should be handled lightly to prevent packaging damage; When loading and unloading the tank car, 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 stored separately from oxidants, acids and alkalis. It should be protected from the sun and rain, and should not be piled up in the open air. Bagged products for packaging, storage and transportation shall be packed with plastic film, and the net weight of each bag shall be1000 2 kg. The name, address, trademark, product name, grade, batch number, net weight and standard code of the manufacturer shall be printed on the packaging bag. You can also use stainless steel tank car for shipment. Before loading, check whether the tank car is clean and dry. After loading, the inlet 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 can cause 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 material is easy to hydrolyze at high temperature, so drying treatment before processing is very important. It is suggested that the drying conditions in air are 120℃ for 6~8 hours, or 150℃ for 2~4 hours. Humidity must be less than 0.03%. If it is dried by a hygroscopic 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. The heat loss must be fast and even. It is suggested that the diameter of the mold cooling channel is 12mm. Injection pressure: medium (maximum 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 the pressure transmission (empirical formula: runner diameter = plastic thickness+1.5mm). Various types of gates can be used. Hot runner can also be used, but care should be taken to prevent leakage and degradation of materials. The gate diameter should be between 0.8~ 1.0*t, where t is the thickness of plastic parts. If it is a submerged gate, the recommended minimum diameter is 0.75 mm.