High-density polyethylene reactors

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

High-density polyethylene (HDPE) is produced by a low-pressure process in a fluid-bed reactor. Catalysts used for HDPE are either of the Zieglar-type (a complex of A1(C2H5)3 and a-TiCl4) or silica-alumina impregnated with a metal oxide such as chromium oxide or molybdenum oxide. 

Gas phase olefin polymerizations are becoming important as manufacturing processes for high density polyethylene (HOPE) and polypropylene (PP). An understanding of the kinetics of these gas-powder polymerization reactions using a highly active TiCi s catalyst is vital to the careful operation of these processes. Well-proven models for both the hexane slurry process and the bulk process have been published. This article describes an extension of these models to gas phase polymerization in semibatch and continuous backmix reactors. 

High pressures are required for many commercial chemical processes. For example, the synthesis of ammonia is carried out at reactor pressures of up to 1000 bar, and high-density polyethylene processes operate up to 1500 bar. 

Bimodal polymer, 20 165 Bimodal polymerization, 20 531 Bimodal reactor technology, for high density polyethylene, 20 170 Bimodal weight ratio, 70 17 Bimolecular reaction, 74 625 Bimolecular recombination coefficient, 74 833... 

High density extruded planks, 23 404 High density lipoproteins (HDLs), 5 135-137 10 829 niacin and, 25 798 High density polyethylene (HDPE), 10 596-595 11 225 16 21 17 724 20 149-179 24 267, 268. See also HDPE entries analysis of, 19 566 as barrier polymer, 3 377 bimodal reactor technology for, 20 170 blow molding of, 20 171-172 blown film applications, 20 173-174 catalysts used for, 20 152-155 chemical resistance of, 20 166 commercial applications of,... 

A similar technique is applied to low-density polyethylene reactors. Some of these systems operate in cooled tubular reactors at a very high pressure. Since the reactor has a thick tube wall, the temperature response to changes in the coolant is slow. Instead, the reaction rate (and thereby temperature.) is controlled by injecting initiator at select places along the length of the reactor tube (see Fig. 4.28). 

P. N. Sharratt, Y. H. Lin, A. A. Garforth, and J. Dwyer, Investigation of the Catalytic Pyrolysis of High-Density Polyethylene over a HZSM-5 Catalyst in a Laboratory Fluidized-Bed Reactor, Ind. Eng. Chem. Res.,36, 5118-5124 (1997). 

A. A. Garforth, Y-H Lin, P. N. Sharratt, and J. Dwyer, Production of hydrocarbons by catalytic degradation of high density polyethylene in a laboratory fiuidized-bed reactor, Appl Catal A, 169, 331-342 (1998). 

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