Polypropylene manufacturing

Erom 1955—1975, the Ziegler-Natta catalyst (91), which is titanium trichloride used in combination with diethylaluminum chloride, was the catalyst system for propylene polymerization. However, its low activity, which is less than 1000 g polymer/g catalyst in most cases, and low selectivity (ca 90% to isotactic polymer) required polypropylene manufacturers to purify the reactor product by washing out spent catalyst residues and removing unwanted atactic polymer by solvent extraction. These operations added significantly to the cost of pre-1980 polypropylene. 

Figure 11.]. Typical flow sheet for polypropylene manufacture...

Polymer films can be made antistatic with a-sulfonated fatty acid salts and esters [94]. For example, an antistatic additive for polypropylene manufacture can be prepared from potassium methyl a-sulfopalmitate, styrene oligomer, and 2-propanol [95]. The treatment of synthetic fibers and fabrics with a-sulfo-... 

Some applications, particularly polypropylene manufacture, require very pure propylene feed. Polymer grade propylene is made by simple fractionation of one of the less pure propylene streams, refinery or chemical grade. 

The slurry process is the oldest and still widely used method for manufacturing polymers of ethylene, propylene and higher a-olefins. In this process, the monomer dissolves in the polymerisation medium (hydrocarbon diluent) and forms a solid polymer as a suspension containing ca 40 wt-% of the polymer the polymerisation occurs below the melting point of the polymer. In slurry polymerisation, the temperature ranges from 70 to 90 °C, with the ethylene pressure varying between 7 and 30 atm. The polymerisation time is 1-4 h and the polymer yield is 95-98 %. The polymer is obtained in the form of fine particles in the diluent and can be separated by filtration. Removal of the catalyst residues from the polymer can be achieved by the addition of alcohol (isopropanol, methanol), followed by recovery and extraction of the catalyst residues. The polymer is freed from diluent by centrifuging and then dried. In the case of polypropylene manufacture, the atactic fraction remains in the diluent [28,37]. 

In this chapter we first discuss the salient features of polyethylene and polypropylene manufacture by heterogeneous catalytic processes. We also discuss the structural features of metallocene complexes that are used as homogeneous catalysts and the relationship between the structure of these catalysts and the structures of the resultant polymers. 

Integration with polypropylene manufacture can occur in those cases when production is very large, or there is some cracking of heavier material or else additional propylene can be sourced from a local refinery or a propylene specific production operation. 

Propylene exiting the gas plant is suitable for many refinery and chemical operations. For polypropylene manufacturing further purification is required to protect downstream units from traces of acetylenes and allene which may be produced. 

A colorectal cancer cluster was reported in a polypropylene manufacturing plantJ15 The chemicals used included... 

Discovery of Linear (High-Density) Polyethylene Use of Comonomers Linear Low-Density Polyethylene Stereospecific Polymerization Discovery of Polypropylene Manufacturing Processes High-Pressure LDPE Low-Pressure, Linear HOPE LLDPE... 

Figure 15-2 shows the global market for polymerization catalysts, the main sectors are for polyethylene and polypropylene manufacture. 

As we saw previously, polypropylene was first made in June 1951, unintentionally as a solid polymer, by Phillips Petroleum, who were at that time seeking to convert excess refinery gases, ethylene and propylene, to high-octane fuel. Phillips developed their chromium olefin polymerization catalyst for linear polyethylene, but in fact, Phillips never entered the polypropylene manufacturing business. Paul Hogan and Robert Banks recorded the invention of the process by which they produced crystalline polypropylene about an hour after their discovery. As we shall see in more detail below, their January 1953 patent application was issued in March 1983 (32 years after their discovery) [11]. 

Propylene is to be considered as a monomer under REACH when it is used for the purpose of a polymerisation process such as polypropylene manufacture, as illustrated in (Figure 2.2). 

The Unipol process, initially developed for polyethylene production, was later extended to polypropylene manufacture. The process consists of a large fluidized-bed gas-phase reactor for homopolymer and random copolymer production, and a second smaller reactor for impact copolymer production. The second reactor is smaller than the first one because only 20% of the production comes from the second reactor. This reactor typically has a lower pressure rating as copolymerization is usually carried out at lower temperatures and pressures. Condensed mode operation is used in the homopolymer reactor but an inert diluent is not required because propylene is partially fed as a liquid. The copolymerization reactor is operated purely in the gas phase. The Unipol process has a unique and complex product discharge system that allows for very efficient recovery of unreacted monomer, but this does add complexity and capital cost to the process. 

Table 2.17 Comparison of different polypropylene manufacture processes ...

Polypropylene manufactured by the low pressure route gives a polymer which is largely isotactic (pendant methyl groups all on same side of carbon backbone). The crystallinity of low pressure polypropylene at 65 to 70% is somewhat lower than that of HOPE. 

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