Low density polyethylene production

Table 5.8 lists propylene polymerization data for some of the complexes shown in Figure 5.12. Varieties of other polymer products have been prepared using the D/A-bridged complexes. For example the (Flu)(Cp)ZrCl2 complexes (22a-b) produce ultra-high molecular weight (UHMW) polyethylene with intrinsic viscosities as high as 13.5 d/g. The D/A metallocenes are also effective catalysts for the copolymerization of a-olefins with ethylene to produce medium to ultta-low density polyethylene products. ... 

Kiparissides, C., Krallis, A., and Meimaroglou, D. (2010) From molecular to plant-scale modeling of polymerization processes A digital high-pressure low-density polyethylene production paradigm. Chem. Eng. ej Techn., 33, 1754-1766. 

Purification of olefin-rich C4 cuts, particularly from FCC, is usually performed by selective hydrogenation of undesirable amounts of 1,3-butadiene and acetylene compounds. The use of butene-1 as a monomer in the production of polybutene and comonomer in low-density polyethylene production has high technological appeal and has been the object of recent studies in the literature [2-4], To this end a C4 stream needs to be rich in butene-1 and free from the presence of 1,3-butadiene and acetylenic compounds (content of < than 10 ppm). 

Figure is for low density polyethylene production for 1990 (est figure) and does not include 8 billion pounds d high density polyethylene produced as well Kiefer, D. M. Otem. Eng. News 1990,68(50), 26-28. 

Table 6 shows the sales estimates for principal film and sheet products for the year 1990 (14). Low density polyethylene films dominate the market in volume, followed by polystyrene and the vinyls. High density polyethylene, poly(ethylene terephthalate), and polypropylene are close in market share and complete the primary products. A number of specialty resins are used to produce 25,000—100,000 t of film or sheet, and then there are a large number of high priced, high performance materials that serve niche markets. The original clear film product, ceUophane, has faUen to about 25,000 t in the United States, with only one domestic producer. Table 7 Hsts some of the principal film and sheet material manufacturers in the United States.

There are three basic types of polyethylene foams of importance (/) extmded foams from low density polyethylene (LPDE) (2) foam products from high density polyethylene (HDPE) and (J) cross-linked polyethylene foams. Other polyolefin foams have an insignificant volume as compared to polyethylene foams and most of their uses are as resia extenders. 

Commodity chemical producers have varying records of performance in appHcations research. It is usually high on the priority Hst when the product is stiU evolving, eg, low density polyethylene in the late 1950s and early 1960s. In times of pinched profit margins, these services often have been dropped, sometimes to be reinstituted, especially if totally new uses appeared. 

The principal use of LDPE and LLDPE in building products is as a film water barrier under below-grade doors as a wall vapor barrier, though PVC is typically preferred and as temporary enclosure film during constmction. The film is made either by extmding a thin-waHed tube, which may be sHt or wound up direcdy, or by extmsion through a slot die and cast direcdy on to a cold roU, cooled, then wound up. The former method is more widely used. A much smaller use for low density polyethylene is in piping. 

In the Institut Fransais du Petrc le process (62), ethylene is dimerized into polymer-grade 1-butene (99.5% purity) suitable for the manufacture of linear low density polyethylene. It uses a homogeneous catalyst system that eliminates some of the drawbacks of heterogeneous catalysts. It also inhibits the isomerization of 1-butene to 2-butene, thus eliminating the need for superfractionation of the product (63,64). The process also uses low operating temperatures, 50—60°C, and pressures (65). 

Union Carbide Corp. also uses a siUca-supported chromium catalyst in their extremely low cost Unipol gas-phase linear low density ethylene copolymer process, which revolutionized the industry when it was introduced in 1977 (86—88). The productivity of this catalyst is 10 —10 kg polymer/kg transition metal contained in the catalyst. By 1990, the capacity of Unipol linear low density polyethylene reactors was sufficient to supply 25% of the world s total demand for polyethylene. 

Introduction of linear low density polyethylene in the 1970s and 1980s offered yet another design parameter, giving chlorosulfonated products with the advantages of linear types but with improved low temperature performance (8). 

There has been interest, particularly in Japan, in the production of cross-linked low-density polyethylene foam. Some processes, such as the Furukawa process and the Hitachi process, use chemical cross-linking techniques whilst others, such as the Sekisui process, involve radiation cross-linking. 

The three isomers constituting n-hutenes are 1-hutene, cis-2-hutene, and trans-2-hutene. This gas mixture is usually obtained from the olefinic C4 fraction of catalytic cracking and steam cracking processes after separation of isobutene (Chapter 2). The mixture of isomers may be used directly for reactions that are common for the three isomers and produce the same intermediates and hence the same products. Alternatively, the mixture may be separated into two streams, one constituted of 1-butene and the other of cis-and trans-2-butene mixture. Each stream produces specific chemicals. Approximately 70% of 1-butene is used as a comonomer with ethylene to produce linear low-density polyethylene (LLDPE). Another use of 1-butene is for the synthesis of butylene oxide. The rest is used with the 2-butenes to produce other chemicals. n-Butene could also be isomerized to isobutene. ... 

High-pressure polymerization of ethylene was introduced in the 1930s. The discovery of a new titanium catalyst hy Karl Ziegler in 1953 revolutionized the production of linear unhranched polyethylene at lower pressures. The two most widely used grades of polyethylene are low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Currently,... 

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