Gas phase LLDPE

Table 5 Properties of Gas Phase LLDPE (Hexene-1 Comonomer) Using Supported Metallocenes...

PE catalysts supported on inorganic magnesium compounds commercialized Unipol gas-phase LLDPE emerges as potential replacement for LDPE... 

Effects of Comonomer and Compositional Uniformity. Table 4 shows blown film mechanical properties for an LDPE, two gas-phase LLDPEs, and one gas-phase mLLDPE, all at the same nominal melt index and density. 

Property ASTM test method Gas-phase LLDPE Gas-phase LLDPE... 

Typical heterogeneous Ziegler catalysts operate at temperatures of 70— 100°C and pressures of 0.1—2 MPa (15—300 psi). The polymerization reactions are carried out ia an iaert Hquid medium (eg, hexane, isobutane) or ia the gas phase. Molecular weights of LLDPE resias are coatroUed by usiag hydrogea as a chain-transfer ageat. 

The technologies suitable for LLDPE manufacture include gas-phase fluidised-bed polymerisation, polymerisation in solution, polymerisation in a polymer melt under high ethylene pressure, and slurry polymerisation. Most catalysts are fine-tuned for each particular process. 

Eluidized-bed reactors are highly versatile and can accommodate many types of polymerization catalysts. Most of the catalysts used for LLDPE production are heterogeneous Ziegler catalysts, in both supported and unsupported forms. The gas-phase process can also accommodate supported metallocene catalysts that produce compositionaHy uniform LLDPE resins (49—51). 

Reaction conditions are generally mild, but they differ from one process to another. In the newer Unipol process (Eigure 12-1) used to produce both HDPE and LLDPE, the reaction occurs in the gas phase. Ethylene and the comonomers (propene, 1-butene, etc.) are fed to the reactor containing a fluidized bed of growing polymer particles. Operation temperature and pressure are approximately 100°C and 20 atmospheres. A single-stage centrifugal compressor circulates unreacted ethylene. The circulated gas fluidizes the bed and removes some of the exothermic reaction heat. The product from the reactor is mixed with additives and then pelletized. New modifications for gas-phase processes have been reviewed by Sinclair. ... 

Linear low-density polyethylene (LLDPE) is produced in the gas phase under low pressure. Catalysts used are either Ziegler type or new generation metallocenes. The Union Carbide process used to produce HDPE could be used to produce the two polymer grades. Terminal olefins (C4-C6) are the usual comonomers to effect branching. 

Gas phase process. This most widely used process yields both HDPE and LLDPE with a wide range of copolymers. Its simplicity begets its popularity. In addition, it accommodates a broad range of interesting property combinations used in both HDPE and LLDPE markets. 

Coordination copolymerization of ethylene with small amounts of an a-olefin such as 1-butene, 1-hexene, or 1-octene results in the equivalent of the branched, low-density polyethylene produced by radical polymerization. The polyethylene, referred to as linear low-density polyethylene (LLDPE), has controlled amounts of ethyl, n-butyl, and n-hexyl branches, respectively. Copolymerization with propene, 4-methyl-1-pentene, and cycloalk-enes is also practiced. There was little effort to commercialize linear low-density polyethylene (LLDPE) until 1978, when gas-phase technology made the economics of the process very competitive with the high-pressure radical polymerization process [James, 1986]. The expansion of this technology was rapid. The utility of the LLDPE process Emits the need to build new high-pressure plants. New capacity for LDPE has usually involved new plants for the low-pressure gas-phase process, which allows the production of HDPE and LLDPE as well as polypropene. The production of LLDPE in the United States in 2001 was about 8 billion pounds, the same as the production of LDPE. Overall, HDPE and LLDPE, produced by coordination polymerization, comprise two-thirds of all polyethylenes. 

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... 

In principle, PE gas phase plants are so-called swing units which are able to produce both HDPE, MDPE and LLDPE, even if cost-wise it is better to avoid frequent switches between the PE grades with different densities. The gas phase process is the most commonly used technology for the production of LLDPE with 1-butene or 1-hexene as a comonomer. Fluidised bed gas phase process technology is licensed by Univation (Unipol) and BP (Innovene), stirred bed gas phase technology by Basell (Lupotech G). 

Gas-phase polymerization processes, as mentioned earlier, are also used. In this section, we will discuss a plant geared toward the production of LLDPE. A simplified version of the flow diagram is given in Figure 11.3 [1]. 

Application The Innovene G (gas phase) process produces linear-low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) using either Ziegler-Natta, chromium or metallocene catalysts. 

Application The Borstar polyethylene (PE) process is used when producing bimodal and unimodal linear low density (LLDPE), medium density (MDPE) and high density (HDPE) polyethylene using loop and gas-phase low pressure reactors in series. All products can be produced in one cycle. 

Borealis A/S Polyethylene Ethylene, butene Slurry-loop process uses supercritical propane and a series gas-phase reactor produce tailor-made MW, enhanced LLDPEs, MDPEs, HDPEs 4 2000... 

Gas phase processes, LLDPE and supported catalysts emerged in the late 1960s and 1970s. 

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.

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