Union Carbide gas-phase process

Figure 12-2. The Union Carbide gas-phase process for producing polypropylene " (1) reactor, (2) centrifugal compressor, (3) heat exchanger, (4) product discharge tank (unreacted gas separated from product), (5) impact reactor, (6) compressor, (7) heat exchanger, (8) discharge tank (copolymer separated from reacted gas).

FIGURE 4.1 Union Carbide gas phase process for the production of polyethylene. 

Very-low-density polyethylene (VLDPE) n. Any polymer of ethylene with some higher-olefin content, in the density range from 0.90 to 0.915g/cm, produced by the Union Carbide gas-phase process (Flex-omer ). The materials have low moduli, with properties between those of low-density polyethylene and ethylene-propylene rubbers. They are useful for stretchable films. 

Scheme 13 Schematic diagram of the Union Carbide gas-phase process for manufacturing (a) fiuidized-bed reactor (b) cataiyst...

Application To produce homopolymer, random copolymer and impact copolymer polypropylene using the Union Carbide gas-phase UNIPOL PP process. 

K. C. H. Yi, and N. J. Maraschin, Bimodal HOPE Via Gas Phase Process, A New Frontier 1990, Union Carbide Chemicals Plastics Technology Corporation./ Mod. Plast. Int. January 1991, p. 12. 

Flexomer A gas-phase process for making ethylene-propylene co-polymers. Developed by Union Carbide Corporation and first commercialized in 1989. 

UNIPOL [Union Carbide Polymerization] A process for polymerizing ethylene to polyethylene, and propylene to polypropylene. It is a low-pressure, gas-phase, fluidized-bed process, in contrast to the Ziegler-Natta process, which is conducted in the liquid phase. The catalyst powder is continuously added to the bed and the granular product is continuously withdrawn. A co-monomer such as 1-butene is normally used. The polyethylene process was developed by F. J. Karol and his colleagues at Union Carbide Corporation the polypropylene process was developed jointly with the Shell Chemical Company. The development of the ethylene process started in the mid 1960s, the propylene process was first commercialized in 1983. It is currently used under license by 75 producers in 26 countries, in a total of 96 reactors with a combined capacity of over 12 million tonnes/y. It is now available through Univation, the joint licensing subsidiary of Union Carbide and Exxon Chemical. A supported metallocene catalyst is used today. 

Gas-phase processes commercialized in the late 1960s offer much simpler operation. Since they eliminate solvent, solvent separation, recovery, and purification are unnecessary. Polymerization is carried out in stirred-vessel reactors or in fluidized beds. A very successful fluidized-bed process is Union Carbide s UNIPOL technology444 designed originally for producing HDPE and extended later to LLDPE. Ethylene is polymerized by injecting the fine catalyst powder (organotitanium or... 

Unipol gas phase process for MDPE and HOPE commercialized by Union Carbide... 

Figure 5.5 Compounds used to produce supported chromium catalysts developed by Union Carbide for use in gas phase processes for LLDPE and HOPE. Catalysts must be supported, usually on silica, for optimal performance. Chromocene catalyst is used without a cocatalyst BTSC uses diethylaluminum ethoxide as cocatalyst.

Supported chromium catalysts were developed by Union Carbide Corporation in the 1970s using different chromium precursors than are used in standard Phillips catalysts (6,11). The most important of these are based on chromocene and bis(triphenylsilyl)chromate, depicted in Figure 5.5. These catalysts are used in the Unipol gas phase process for LLDPE and HOPE and are different from standard Phillips catalysts in several respects ... 

Union Carbide Corporation developed a gas-phase process to make HOPE. In the gas-phase process, ethylene is catalyzed into HOPE in a fluidized-bed reactor consisting of catalyst-polymer particles. The polymerization occurs at the interface between the solid catalyst and the polymer matrix, which is swollen with monomers during polymerization. Ethylene is then easily separated from the HOPE particles which are then converted into pellets using an extrusion step. The first commercial gas-phase polymerization plant for making HOPE using a fluidized-bed reactor was constructed by Union Carbide in 1968 at Seadrift, Texas. Union Carbide also developed the dual reactor UNIPOL-II gas phase process in the 1980s to make bi-modal HOPE resins with superior mechanical properties compared to UNIPOL single-reactor HOPE resins. A world scale UNIPOL-II plant was constructed in 1996 to make differentiated bi-modal HOPE resins. 

The gas-phase polyethylene plants introduced by Union Carbide in 1968 require only about half the capital investment of the high-pressure plants and far fewer workers to operate them. The wastage of ethylene during the polymerization process is also lower in the gas-phase process, reducing cost of the product and conserving the monomer resources. 

In 1968, Union Carbide introduced the gas-phase FBR low-pressure UNIPOL process. The first large-volume production unit started in 1970 in Sweden and later in the USA and 13 other countries. Initially the UNIPOL process used Z-N catalyst and after 1980 the metallocene single-site catalyst. In the early 1990s LLDPE constituted 25 % of the world production of PEs (Fraser et al. 1997 Univation Technol. 2007). A summary of conditions used in the solution- and gas-phase processes is presented in Table 18.2. 

Gas-Phase Processes. Unlike solution or slurry processes, the original gas-phase polymerization processes employed no hydrocarbon diluent. Union Carbide introduced the first gas-phase technology in 1968, and other firms soon developed the approach still further, such as Naphtachimie, British Petroleum, BASF, and Amoco (110-114). In this technology, solid catalysts are used for ethylene polymerization or its copolymerization with light comonomers in the... 

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