Development of polyethylene production process in

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Development of polyethylene production process in the world since the early 20th century, the output of polyethylene, the largest tonnage of commodity plastic in the world, has increased rapidly. At present, the global output of polyethylene has reached 56million tons/year, which is expected to grow with the economic recovery of North America and Europe, and the demand in Asia will continue to increase rapidly. Scientific invention and technological progress have become the characteristics of polyethylene industry. There are a wide range of process series to meet the choice of polyethylene manufacturers. The development of polyethylene process technology has been well known to people. There are five leading process technologies in industrial practice, namely, high pressure method, slurry or suspension method, solution method, gas phase method and step slurry/gas phase method

in the late 1930s, ICI developed the high-pressure LDPE process. The LDPE products produced by this process have excellent properties such as transparency, softness and toughness, which makes it the most suitable for manufacturing films. Its consumption accounts for about 30% of the global film market, such as canon, Nikon, Sony and 3-star. The recently announced increase in high-pressure polyethylene production capacity, including plant expansion and new construction, reflects that the process technology continues to be competitive, and its economy is further improved by expanding production scale

the second milestone in history is the emergence of polyethylene coordination catalysts based on transition metals. The industrialization of HDPE produced by Phillips slurry process and LLDPE produced by sclairtech process of DuPont Canada reached its peak

in the early 1950s, hogan of Phillips oil company invented a catalyst made of chromium oxide loaded on Diatomite for ethylene polymerization, and produced HDPE industrially under conditions that were more relaxed than LDPE manufacturing requirements. This density is 0 97g/cm3 crystalline polymer is currently produced by the slurry process of inert, low boiling hydrocarbon diluent when the temperature change cannot reach the experimental temperature value with the operating pressure MPa and the temperature as high as 100 ℃. The operating conditions are mild, allowing the use of reactors with large volumes, reducing the investment of the device, and the variable cost of production is also low. Due to its excellent tensile strength and melting flow characteristics, HDPE can be used as hard materials, such as large and small industrial containers, household utensils and pipes

almost at the same time, Hearst company in Germany began industrial production of HDPE by using a multi-stage continuous stirred tank reactor loaded with titanium catalyst. With the continuous progress of Phillips particle process and Hearst process, HDPE products with a wide variety, excellent quality and predictable properties are provided to users, while meeting the requirements of continuously reducing the total investment of the device and variable production costs

DuPont first industrialized the solution polyethylene process with Ziegler catalyst in 1960 to produce low-density ethylene copolymers, adding linear polymers such as 1-butene or (and) 1-octene? Cut olefin. The new polyethylene type was later called LLDPE, with a density range of 0.905-0.935 g/cm3 based on the success of this study, and a melt index of less than 0 G/10min, providing excellent puncture strength, tensile strength and impact strength, and excellent optical properties and melt rheological properties during blow molding. Subsequently, Dow Chemical and United carbon applied Ziegler catalyst in the solution and gas phase process platform, which greatly expanded the production base of LLDPE

the third important event in the progress of polyethylene process is the low-pressure gas phase process developed by United carbon in the late 1960s and early 1970s. It was first used to manufacture HDPE in 1968, and proved to be able to produce LLDPE economically in 1977. Due to the active technology transfer plan, Unipol process has greatly expanded the global polyethylene production capacity. The gas-phase fluidized bed process is also implemented by BP chemical company and Basel company. The special process design is adopted. The monomer is introduced through the outer circulation loop pipe, and the comonomer and hydrogen enter the particle polymer bed, which is fluidized with the help of circulating gas flow

the fourth and recent milestone in the development of polyethylene technology is a new metallocene, namely, a single center catalyst system. This route strengthens the control of the microstructure of the polymer and ultimately improves the end use performance of polyethylene. At present, the goal of polyethylene producers is to simply retrofit the existing process technology with this catalyst system in order to limit capital expenditure and maintain the wide flexibility of catalyst use and the grade of polymer in the reactor chain. After considerable cost and effort, metallocene catalyst technology has been industrialized on five major process platforms in the past 10 years. At present, the industrial production and sales of metallocene polymers have targeted ultra-low density LDPE (VLDPE) and LLDPE grades, with a density of 0 93 g/cm3, melt index 0 G/10min of other polymers, this kind of catalyst has played a unique role in controlling the molecular weight distribution and short branch chain distribution of polymers. The success of this revolutionary step in the polymerization process technology only requires the technical transformation of the existing process mode at a low cost. A representative overview of polyethylene technologies currently available is shown in Table 1

in the early 1990s, the second generation sclairtech process completed the development and engineering development of high activity Ziegler Natta catalyst (now known as advanced sclairtech process), completed the process design in 1998, and began to build industrial units in the same year. From the point of view of process design and operation, there are several important differences between the advanced sclairtech process and the first generation sclairtech process: (1) C6 mixed hydrocarbon replaces cyclohexane as the polymerization solvent, which improves the process situation in several aspects. First, it is no longer necessary to monitor the low-pressure solvent system for devices in cold climates. Second, because the new solvent is volatile, it is more effective to remove volatiles from the products before packaging; (2) The removed catalyst residue will not adsorb the solvent. Save investment and variable costs; (3) The reactor series consists of two reactors with appropriate internal mixing elements. The molecular weight distribution and branching distribution range of polymer are widened, and this configuration makes the production of polymer with single center catalyst particularly beneficial; (4) The advanced sclairtech process works well at low reaction temperature, and various metallocene catalysts or Ziegler Natta Catalysts can be used; (5) The comonomer used in the first sclairtech process unit that has been established is 1-octene, which is located in ruofur, Canada

from the development process of polyethylene process in the world, it can be seen that the development trend of polyethylene production process in the world at present is that the share of high-pressure method will gradually decrease, while the share of low-pressure method will gradually increase, especially the gas-phase fluidized bed process technology, which is becoming the mainstream of polyethylene production process technology at present. Bimodal technology and new production process technology based on single center catalyst will continue to develop and eventually occupy an important position in industrial production

this year's goal: 70% of the days with good air Author: Wen liyufang source: foreign plastics

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