5 large polypropylene production process (1)

At present, the production process of polypropylene can be divided into five categories according to the type of polymerization: solution method, slurry method, bulk method, gas-phase method and bulk-gas-phase combination technology. 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's Borstar Process and so on.

1 slurry process Slurry process (Slurry Process), also known as slurry or solvent process, is the world's earliest used in the production of polypropylene technology. From the first industrial installation in 1957 to the mid-to-late 1980s, the slurry process has been the most important polypropylene production process for up to 30 years. Typical processes include the Montedison process in Italy, the Hercules process in the United States, the Mitsui East-Pressure chemical process in Japan, the Amoco process in the United States, the Mitsui oilification process in Japan, and the Sowell process. The development of these processes was based on the first-generation catalysts of the time, and the use of a vertical stirred tank reactor required the removal of ash and the removal of irregularities. Due to the different solvents used, the process flow and operating conditions were different. In recent years, the proportion of traditional slurry process in production has been significantly reduced. The retained slurry products are mainly used in some high-value areas such as specialty BOPP films, high molecular weight blown film, and high-strength pipe materials. In recent years, the method has been improved. The improved slurry production process uses a highly active second-generation catalyst, which can remove the catalyst deliming step, reduce the production of atactic polymers, and can be used to produce homopolymers. , random copolymers and impact copolymer products. At present, the production capacity of the world's slurry process PP accounts for about 13% of the global PP's total production capacity.

2, solution process
The solution process production process is an early process route used to produce crystalline polypropylene and is unique to Eastman. The process uses a specially modified catalyst system - a lithium compound (such as lithium aluminum hydride) to accommodate high solution polymerization temperatures. The catalyst components, monomers and solvents are continuously fed to the polymerization reactor, and the unreacted monomers are separated and recycled by depressurizing the solvent. Additional solvent was added to lower the viscosity of the solution and the remaining catalyst was removed by filtration. The solvent is concentrated by a plurality of evaporators and a solid polymer is formed by an extruder capable of removing volatiles. The solid polymer is further purified with heptane or similar hydrocarbon extraction, while the amorphous polypropylene is also removed, the use of ethanol and the multi-step distillation process are eliminated, mainly for the production of some lower modulus than the slurry process product, Higher toughness for special grades. The process is complex, the cost is high, the polymerization temperature is high, and due to the limited application range of the product due to the use of a special high-temperature catalyst, it is no longer used to produce crystalline polypropylene.

3, bulk process

The research and development of the bulk process began in the 1960s. In 1964, Dart Corporation of the United States used a tank reactor to build the world's first industrialized bulk polypropylene production plant. After 1970, Japan's Sumitomo, Phillips, and EI Psao of the United States all achieved industrial production of liquid-phase bulk polypropylene technology. Compared with the slurry method using a solvent, the liquid phase propylene polymerization method does not use an inert solvent, the monomer concentration in the reaction system is high, the polymerization rate is fast, the activity of the catalyst is high, the polymerization conversion rate is high, and the time-space of the reactor is high. Larger production capacity, low energy consumption, simple process flow, less equipment, low production cost, low “three wastes”, easy removal of heat of polymerization, simplified evacuation control, and increased polymerization of unit reactors. Low-molecular-weight atactic polymers and catalyst residues that have an adverse effect on product properties can provide high-quality products and the like. The disadvantage is that the reaction gas needs to be gasified 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. In addition, 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 copolymer product will not be too high.
The difference between the different process routes of the bulk process is mainly the difference of reactors. The reactors can be divided into tank reactors and loop reactors. The tank reactor uses the latent heat of liquid evaporation to remove the heat of reaction. Most of the vaporized gas is condensed and returned to the reactor. The uncondensed gas is repressurized by the compressor and recycled back to the reactor. The loop reactor utilizes an axial flow pump to circulate the slurry at a high speed, cooling and removing the heat through the jacket. Due to the large heat transfer area and good heat removal effect, the unit reactor has a high volumetric yield and low energy consumption.

Bulk process production process according to polymerization process, can be divided into batch polymerization process and continuous polymerization process two. (1) Batch bulk process. The batch bulk polypropylene polymerization technology is a self-developed and successful production technology in China. It has reliable production technology, low quality of raw material propylene, required domestic catalyst, simple process, low investment, rapid efficiency, simple operation, flexible product grade conversion, less waste, suitable for China's national conditions, etc. The reason is that the production scale is small, it is difficult to produce scale benefits, the equipment is operated more manually, the production is intermittent, the level of automation is low, the quality of the product is unstable, the consumption of raw materials is higher, the grade of the product is less, the grade is not high, and the use is comparatively low. narrow. At present, China's polypropylene production capacity using this method accounts for about 24.0% of the country's total production capacity; (2) continuous bulk process technology. The process mainly includes the United States Rexall process, the United States Phillips process and Japan Sumitimo process. (a) Rexall process. The Rexall bulk polymerization process is a production process between a solvent process and a bulk process. It was developed by Rexall, a US company that uses a vertical stirred reactor with propane content of 10%-30%.

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