Polymerization ethylene to polyethylene

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 The catalyst powder is continuously added to the bed and the granular product is continuously withdrawn.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. 

Silica supported chromium catalysts that polymerize ethylene to polyethylene with as many as 12 methyl branches/1000 carbon atoms have been reported. The small amount of branching observed in the ethylene homopolymers prepared by these supported chromocene catalysts was attributed to a chain isomerization process (a) Karol, F. J. Karapinka, G. L. Wu,... 

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 The catalyst powder is continuously added to the bed, and the granular product is continuously withdrawn.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 comonomer, such as 1-butene, is normally used. 

UNIPOL process A process used for polymerizing ethylene to polyethylene and also for polymerizing propylene to polypropylene. Unlike the Ziegler-Natta process, it uses a gas phase process at low pressure. The catalyst is continuously added to the process and the granular product withdrawn. A co-monomer is also usually used in the process. 

Addition or chain-growth polymerization involves the opening of a double bond to form new bonds with adjacent monomers, as typified by the polymerization of ethylene to polyethylene ... 

Polymerization reactions. Polymerization of ethylene to polyethylene has been conducted at pilot-plant scales reaching a target of 1500 tons per year. Some reactions, including polymerization and copolymerization of polymers for grafting on textile fibers, have been successfully performed. Similarly, cross-linking of polyethylene to improve thermal properties has also been achieved. 

Radical chain polymerization of ethylene to polyethylene is carried out at high pressures of 120-300 MPa (17,000-43,000 psi) and at temperatures above the Tm of polyethylene (Fig. 3-18) [Doak, 1986]. Batch processes are not useful since the long residence time gives relatively poor control of product properties. Long-chain branching due to intermolecular chain transfer becomes excessive with deleterious effects on the physical properties. Continuous processes allow better control of the polymerization. 

High-Density Polyethylene (HDPE). Polymerization of ethylene to polyethylenes is most often carried out at low temperature and pressure, using either the Ziegler aluminum triethyl plus titanium tetrachloride catalyst system, the Phillips chromic oxide plus silica plus alumina system, or more recently the newer metallocene single-site catalyst systems. 

A free radical is usually generated by the decomposition of a relatively unstable material called a radical initiator. This process includes initiation, chain propagation, and termination. Examples of this kind of polymerization include polymerization of ethylene to polyethylene, vinyl chloride to poly(vinyl chloride), and vinyl acetate to poly(vinyl acetate). 

Utilizing a related complex, Coates and coworkers reported that 30b/MAO at 50 °C polymerized ethylene to produce polyethylene with MJM = 1.10 and M = 44 500 g/mol (Reinartz et al, 2003). Additionally, Ivanchev et al reported a near-linear increase in M with time for the polymerization of ethylene with 30a/MAO at 30 °C (Ivanchev et al, 2004). In later work on the same system, Fujita and coworkers found that molecular-weight distributions were low at a reaction time of one minute M /M = 1.12, = 52 000 g/mol) while the PDl... 

Medium pressure and temperature polyethylene production facilities have much in common with Ziegler-Natta type polymerization plants. The reaction can be carried out in the gas phase, in a slurry, or in solution. There is a fair degree of overlap between the ranges of temperature and pressure employed in the two processes, but on the whole the Phillips and Indiana processes are run slightly hotter and under greater pressure. Removal of excess heat produced by polymerization is also accomplished in similar ways. Conversion of ethylene to polyethylene can reach 98% in some solvent-diluted processes. Unless otherwise stated, the following description of operating conditions relates primarily to the Phillips process, which dominates this type of production. 

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