Liquid propylene polymerization

Compare and contrast the slurry, gas phase, solution and liquid propylene polymerization methods. 

An important phenomenon occurs in ethylene-propylene co-polymerization, especially in liquid propylene polymerization addition of small amounts (< 30 mol%) of ethylene causes a strong decrease in PP molecular masses. This... 

Table 10 Influence of the bridge and indenyl C(3) substituents on PP structure. Liquid propylene polymerization results at 50 °c222,776...

FIGURE 7.14 Distal ligand elaboration impacts catalyst performance for the production of syndiotactic polypropylene. Shown are precatalysts diphenylmethylene(9-fluorenyl)(cyclopentadienyl)zirconium dichloride (4) and diphenylmethylene(octamethyloctahydrodibenzofluorenyl)(cyclopentadienyl)zirconium dichloride (5). (Liquid propylene polymerization at 20 °C, Zr Al 1 1000 and 1 2000, methylaluminoxane cocatalyst. 

Table 12 Performance Data of Metallocenes in Polymerization of Liquid Propylene...

We have a choice of four major polymerization techniques by which to manufacture polypropylene using Ziegler-Natta catalysts slurry, liquid propylene, solution, and gas phase. Regardless of which technique is employed, all polymerization plants must accomplish the same basic goals they must... 

Another method of manufacturing polypropylene employs the liquid monomer as the polymerization solvent. This process, known as the liquid propylene or bulk-phase process, has a major advantage over the slurry method in that the concentration of the monomer is extremely high. The high concentration increases the rate of the reaction relative to that seen... 

The catalyst 4b/borate was tested under similar conditions as in the case of 4a (toluene solution and liquid propylene) in propylene polymerization experiments after preactivation with TIBA (Table 1). According to the data from Table 1, the catalytic properties of 4b are inferior to those of 4a. The behavior of 4b is similar to that of asymmetric catalysts with a forward orientation of the 4-substituted indene unit [10]. The effect of the substitution position is remarkable. While the 5,7-substituted hafnocene 4a shows higher activities (up to 3.2 x 105 kg PP mol 1 Hf h 1 at 40 °C) with increasing temperatures, substantially lower or almost no activities were found for the 4,6-substituted hafnocene 4b at the same temperature (Fig. 13). 

In heterogeneous polymerizations in bulk, the formed polymer is insoluble in its monomer and the polyreaction is performed below the softening point of the polymer. On an industrial scale, this type of process is especially utilized for chain polymerizations, for example, the radical polymerization of liquid vinyl chloride, the polymerization of liquid propylene with Ziegler-Natta or with metallocene catalysts, and the polymerization of molten trioxane. 

Polymerization in liquid monomer was pioneered by Rexall Drug and Chemical and Phillips Petroleum (United States). Gas-phase polymerization of propylene was pioneered by BASF, who developed the Novolen process which uses stirred-bed reactors, Eastman Chemical has utilized a unique, high temperature solution process for propylene polymerization. In the 1970s, Solvay introduced an advanced TiCl3 catalyst with high activity and stereoregularity. 

After an induction period, the polymerization rate reaches a maximum and then becomes almost constant for over 20 hours. The constant rate of polymerization of the homogeneous system indicates that living polymers are present in this case. Indeed, block copolymers of propylene and ethylene could be obtained with this homogeneous system when ethylene was dissolved in liquid propylene [see also, related experiments with the heterogeneous system (3/)]. 

Liquid monomer Polymer swollen with monomer Precipitation or slurry polymerization Polypropylene in a pool of liquid propylene... 

Conditions bulk polymerization in 1 liter of liquid propylene at 70°C, Al/Zr molar ratio = 15000. The results illustrate the broad range of attainable product properties (155). 

In 1963, liquid polymerization was introduced in which liquid propylene, catalysts, and hydrogen were pumped continuously into the reactor while polypropylene slurry was transferred to a cyclone separator. The unconverted... 

Description In the Spheripol process, homopolymer and random copolymer polymerization takes place in liquid propylene within a tubular loop reactor (1). Heterophasic impact copolymerization can be achieved by adding a gas-phase reactor (3) in series. 

Investigations of the bis(benzamidinate) dichloride or dialkyl complexes of Group 4 metals show that these complexes, obtained as a racemic mixture of c/s-octahedral compounds with C2 symmetry, are active catalysts for the polymerization of a-olefins when activated with MAO or perfluoroborane cocatalysts [29-41]. As was demonstrated above, polymerization of propylene with these complexes at atmospheric pressure results in the formation of an oily atactic product, instead of the expected isotactic polymer. The isotactic polypropylene (mmmm>95%, m.p.=153 °C) is formed when the polymerization is carried out at high concentration of olefin (in liquid propylene), which allows faster insertion of the monomer and almost completely suppresses the epimerization reaction. 

The polymerization of propylene using complex 14 activated by MAO (Al Zr ratio=500, solvent toluene, 25 °C) yielded 80 g polymer-mol Zrl-hrl with a molecular weight Mw= 115,000 and polydispersity=2.4 [119]. The reaction was carried out in liquid propylene to avoid, as much as possible, the epimerization of the last inserted monomer unit and to allow rational design of the elastomeric polymer. The formation of elastomeric polypropylene is consistent with the proposed equilibrium between ds-octahedral cationic complexes with C2 symmetry inducing the formation of the isotactic domain, and tetrahedral complexes with C2v symmetry responsible for the formation of the atactic domain (Scheme 7). The narrow polydispersity of the polypropylene obtained supports the polymerization mechanism in which the single-site catalyst is responsible for the formation of the elastomeric polymer. 

Description In the Spheripol process, homopolymer and random copolymer polymerization takes place in liquid propylene within a loop tubular reactor (1). Heterophasic impact copolymerization is done by adding a gas-phase reactor (3) operated in series. Removal of catalyst residue and amorphous polymer is not required. Unreacted monomer is flashed in a two-stage pressure system (2, 4) and recycled back to the reactors. This improves yield and minimizes energy... 

Metallocenes immobilized on solid support materials have been successfully introduced in industry as polymerization catalysts for the production of new application-oriented polymer materials. Industrial polymerizations, which are carried out either as a slurry process in liquid propylene or as a gas-phase process (Section 7.2.3), require that catalysts are in the form of solid grains or pellets soluble metallocene catalysts thus have to be supported on a solid carrier. 

The results mentioned above, referring to polymerization in a slurry, can be further improved by polymerizing in liquid propylene (Figs. 55, 56, 57). 

Fig. 55. Super active 3rd generation catalyst activity vs. polymerization time. Polymerization in liquid propylene at 70 °C...

Polymerization occurs at pressures usually less than 50 atm and at temperatures below 110°C (to avoid dissolving the polymer) to form a slurry of about 20% polymer in an aliphatic liquid diluent. The diluent can be liquid propylene itself in the manufacture of polypropylene. 

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