Commercial High-Density Polyethylene, Properties, and Manufacture

3 Commercial High-Density Polyethylene, Properties, and Manufacture 

High-density polyethylene (0.94-0.97 g/cm ) is produced commercially with two types of catalysts  

The two catalytic systems are used at different conditions. Both types have undergone evolution from earlier development. The original practices are summarized in Table 6.1. 

The Ziegler process yields polyethylene as low as 0.94/cm in density, but process modifications can result in products with a density of 0.965 g/cm. The transition metal oxide catalysts on support, on the other hand, yield products in the density range of 0.960-0.970 g/cm.  

The continuous solution processes are usually carried out between 120 and 160 C at 400-500 Ib/in. pressure. The diluents may be cyclohexane or isooctane. In one zone reactors, the solid catalyst is evenly dispersed throughout the reactor. In the two zrme reactors (specially constructed), the polymerizations are conducted with stirring in the lower zmie where the catalysts are present in concentrations of 0.2-0.6% of the diluent. Purified ethylene is fed into the bottom portions of the reactors. The polymers that form are carried with small portions of the catalyst to the top and removed. To compensate for the loss, additirmal catalysts are added intermittently to the upper quiescent zones. 

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