At present, the production process of polypropylene can be divided into five major categories: solution method, slurry method, bulk method and gas phase method and bulk method-gas phase method. The specific processes include BP's gas phase Innovene process, Chisso's gas phase process, Dow's Unipol process, Novolene gas phase process, Sumitomo gas phase process, Basell's bulk process, Mitsui's Hypol process, and Borealis' Borstar process. Process, etc.
1 Slurry Process The Slurry Process, also known as the Slurry Process or the Solvent Process, is the world's first process technology for the production of polypropylene. From the first industrial plant in 1957 until the mid-to-late 1980s, the slurry process has been the most important polypropylene production process for 30 years. Typical processes include the Montedison process in Italy, the Hercules process in the United States, the Mitsui Chemical Process in Japan, the Amoco process in the United States, the Mitsui Oiling Process in Japan, and the Sowell Process. The development of these processes was based on the first generation of catalysts at the time, using vertical stirred tank reactors, requiring deashing and de-purification, depending on the solvent used, the process flow and operating conditions were different. In recent years, the proportion of the traditional slurry process in production has been significantly reduced, and the retained slurry products are mainly used in some high-value fields, such as special BOPP film, high molecular weight blown film and high-strength pipe. In recent years, the method has been improved. The improved slurry process uses a highly active second-generation catalyst, which removes the catalyst deashing step, reduces the generation of random polymers, and can be used to produce homopolymers. , random copolymers and impact copolymer products. At present, the world's slurry method PP production capacity accounts for about 13% of the global PP production capacity.
2, the solution process
The solution process is an early process route for the production of crystalline polypropylene, unique to Eastman. The process employs a specially modified catalyst system - a lithium compound such as lithium aluminum hydride to accommodate high solution polymerization temperatures. The catalyst component, the monomer and the solvent are continuously fed to the polymerization reactor, and the unreacted monomer is separated and circulated by depressurizing the solvent. Additional solvent is added to reduce the viscosity of the solution and the residual catalyst is removed by filtration. The solvent is concentrated by a plurality of evaporators and formed into a solid polymer by an extruder capable of removing volatiles. The solid polymer is further purified by extraction with heptane or a similar hydrocarbon, while also removing the amorphous polypropylene, eliminating the use of ethanol and multi-step distillation, mainly for producing some of the lower modulus than the slurry product. Special grade products with higher toughness. The method has complicated process flow, high cost, high polymerization temperature, and limited application range due to the use of special high-temperature catalyst, and is no longer used for producing crystalline polypropylene.
3, the body process
The research and development of the bulk process began in the 1960s. In 1964, Dart Company of the United States built the world's first industrialized bulk polypropylene production plant using a kettle reactor. After 1970, Sumitomo, Phillips, and EI Psao of the United States realized the industrial production of the liquid phase bulk polypropylene process. Compared with the slurry method using solvent, the polymerization using the liquid phase propylene bulk method does not use an inert solvent, the monomer concentration in the reaction system is high, the polymerization rate is fast, the catalyst activity is high, the conversion rate of the polymerization reaction is high, and the time-space of the reactor is high. Larger production capacity, low energy consumption, simple process, less equipment, low production cost, less "three wastes"; easy to remove polymerization heat, and simple control of heat removal Low molecular weight random polymers and catalyst residues that adversely affect the properties of the product provide advantages such as high quality products. The disadvantage is that the reaction gas needs to be vaporized and condensed before it can be recycled back to the reactor. The high pressure liquid hydrocarbon material in the reactor has a large capacity and is potentially dangerous. Further, the concentration of ethylene in the reactor should not be too high, otherwise a separate gas phase is formed in the reactor, making the reactor difficult to handle, and thus the ethylene content in the resulting copolymerized product is not too high.
The difference between the different process routes of the bulk method is mainly the difference of the reactor. The reactor can be divided into two types: a tank reactor and a loop reactor. The kettle reactor uses the latent heat of liquid evaporation to remove the heat of reaction. Most of the vaporized gas is condensed by circulation and returned to the reactor. The uncondensed gas is pumped back to the reactor after being pressurized by the compressor. The loop reactor uses the axial flow pump to circulate the slurry at a high speed, and the heat is removed by the jacket. Since the heat transfer area is large, the heat removal effect is good, so the unit reactor has a high volumetric yield and low energy consumption.
The bulk production process can be divided into two types: a batch polymerization process and a continuous polymerization process according to a polymerization process. (1) Batch bulk process. The batch bulk polypropylene polymerization technology is a successful production technology developed by China. It has reliable production technology and low quality requirements for raw material propylene. The required catalysts are guaranteed domestically, the process is simple, the investment is saved, the effect is fast, the operation is simple, the product grade is flexible, the three wastes are small, and it is suitable for China's national conditions. The production scale is small, it is difficult to produce scale benefits; the device has many manual operations, intermittent production, low level of automation control, unstable product quality, high consumption of raw materials; less variety of products, low grade, and use narrow. At present, the production capacity of polypropylene produced by this method in China accounts for about 24.0% of the total production capacity of the country; (2) continuous bulk process. The process mainly includes the American Rexall process, the American Phillips process, and the Japanese Sumitimo process. (a) Rexall process. The Rexall bulk polymerization process is a production process between the solvent process and the bulk process, developed by Rexall Corporation of the United States, which employs a vertical stirred reactor with a propane content of 10% to 30%.
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