Catalysts titanium chloride-based

Zieglor Catalysts. Titanium chloride based Ziegler catalysts are also widely used throughout the HDPE industry. These catalysts generally produce a narrower molecular weight distribution than that obtained from chromium oxide catalysts. Figure 3 shows this typical distinction. Because of this, the Ziegler catalysts are often used for different applications compared to chromium oxide. 

Since for various catalytic systems only the relative content of different fractions changes (e.g. from 25 to 98.5% for a fraction insoluble in boiling n-heptane without changing their stereoregularity, the composition of catalytic systems influences the relative amount of isospecific and non-stereospecific centers. The reactivities of these centers (rate constants of propagation of isotactic and atactic polymers) for the titanium chloride-based catalysts are similar (Table 2 and Ref >). 

The activation energy of the insertion of coordinated ethylene estimated by the ab initio method was found to be 15 kcal/mol Despite the application of a more advanced calculation technique these results are less compatible with the experimental data on solid titanium chloride-based catalysts, when the activation energy of the propagation step is 3-6 kcal/mol (Table 10). Probably, this incompatability is due to the model used in ref. which describes the AC as a bimetallic complex CljTiCHj with A1(CH3)3. However, it is important to note that the calculations performed by means of the nonempirical method confirm the concept implying that in the active center the alkyl group occupies an intermediate position between the octahedral sites and that in olefin coordination the AC structure is reconstructed. 

Other Early Developments. In addition to the breakthrough by Ziegler, two other discoveries of ethylene polymerization catalysts were made in the early 1950s. A patent by Standard Oil of Indiana, filed in 1951, disclosed reduced molybdenum oxide or cobalt molybdate on alumina (13). At the same time, Phillips discovered supported chromium oxide catalysts, prepared by impregnation of a silica-alumina support with Cr03 (14 16). Both the Phillips catalyst and titanium chloride based Ziegler catalysts are widely used in the production of high density polyethylene (HDPE). 

This process uses sodium ethylaluminate- and titanium chloride-based catalysts and isopropanol or butanol washing to eliminate the catalysts. 

The metal catalyzed production of polyolefins such as high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and polypropylene (PP) has grown into an enormous industry. Heterogeneous transition metal catalysts are used for the vast majority of PE and all of the PP production. These catalysts fall generally within two broad classes. Most commercial PP is isotactic and is produced with a catalyst based on a combination of titanium chloride and alkylaluminum chlorides. HDPE and LLDPE are produced with either a titanium catalyst or one based on chromium supported on silica. Most commercial titanium-based PE catalysts are supported on MgCl2. 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

Based on the number of radioactive tags in the polymer being at short ( 10 min) contact with CO the following values of for the polymerization of ethylene on titanium chloride catalysts were found (go °C, bulk and supported... 

However, the comparative data on (Table 1) and the stereoregularity of polymer fractions (Table 6) for one- and two-component catalysts based on titanium chlorides indicate that the cocatalyst does not influence the reactivity and stereospecificity of the propagation centers. Its effect on the overall polymerization rate is apparently due to the change in the total number of active centers and the ratio of isospecific and non-stereospecific centers. 

It was shown in [249] on the base of quantum-chemical calculations and experimental data that acidic force of electrophilic catalysts is the measure of activity and stereospecificity of their action under cationic polymerization. Increase of acidic force of electrophilic polymerizations catalysts promotes increase of their activity but decreases process selectivity. For example, in [250] piperylene oligomerization initiated by etherates of titanium chloride and aluminum is studied. AlCl3 0(C6Hs)2 gives high yield and molecular mass of product and received oligopiperylene however has low unsaturation. 

The high-pressure process relied on large and complex plants that required careful process control. Therefore, the discovery in 1953 of the appropriate catalysts that allowed the process to be carried under low pressure ( 500 psi) was welcomed by the industry [7]. Three types of catalysts were developed about that time the Ziegler-type catalysts typically obtained by reacting alkyl aluminum compounds with titanium chloride metal oxide catalyst systems, developed by Phillips Petroleum in the United States, typically made of chromium oxide supported on a silicaceous carrier [8]) and a different type of oxide catalyst developed by Standard Oil Company. The first plants based on the Ziegler catalyst went on line in Germany by 1955 and a plant based on the Phillips catalyst in Texas opened in 1957. The third catalyst system developed much slower and was picked up by the Japanese plastics industry in a plant opened in 1961. 

Cugini, C. Rombola, O. A. Giarrusso, A. Poni, L. Ricci, G. Polymerization of 4-methyl-l,3-pentadiene with catalysts based on cyclopentadienyl titanium chlorides Effect of anti/syn isomerism of the allyUc group on the chemoselectivity and the role of backbiting coordination in 1,3-diene polymerization. Macromol. Chem. Phys. 2005, 206, 1684-1690. 

Commercial Ziegler polyethylene processes are generally operated at pressures only slightly above atmospheric, namely 2-4 atmospheres and at temperatures of 50—75°C. Polymerization is conducted in the presence of Ziegler-Natta catalysts, the nature of which is discussed in Chapter 1. For the polymerization of ethylene the catalyst is usually based on titanium tetrachloride/aluminium alkyl (e.g., diethylaluminium chloride). The catalyst may be prepared in situ by adding the components separately to the reactor as solutions in diluents such as diesel oil, heptane or toluene or the components may be pre-reacted and the catalyst added as a slurry in a liquid diluent. These operations must be conducted in an inert atmosphere (usually of nitrogen) since oxygen and water reduce the effectiveness of the catalyst and may even cause explosive decomposition. In a typical process, ethylene and the catalyst and diluent are... 

The most investigated homogeneous catalyst systems are based on bis(cyclopenta-dienyl)titanium(lV), bis(cyclopentadienyl)zirconium(rV), tetrabenzyltitanium, vanadium chloride, and trialkylaluminum or alkylaluminum halides as cocatalysts. Subsequent research on these and other systems with various alkyl groups has been conducted by Patat and Sinn [4], Shilov [5], Hemici-Olive and Olive [6], Reichert and Schoetter [7], and Fink et al. [8]. 

The structures of a wide variety of additional crystalline complexes based on titanium chlorides were discussed in a detailed publication by Greco and coworkers [57]. Complexes containing anions such as (TijCl ) TiClg and TiCyOPCCgHjlcy were isolated and evaluated as ethylene polymerization catalysts. 

Many other catalysts capable of polymerizing olefins have become available since the original Ziegler-Natta catalyst based on crystalline titanium chloride was introduced. More recently, the discovery of soluble metallocene/aluminoxane catalysts opened the doors to a new revolution in the production of polyolefins. These catalyst systems are able to make polyolefins in very high yields and with a degree of microstructural control not possible to achieve using conventional Ziegler-Natta catalysts. 

The catalyst is based on a titanium chloride and an organic compound based on aluminium, Al. When you look closely at the surface of the solid (Figure 13.4), you see that a CH3CH2 group has transferred from an Al atom to a titanium atom, Ti. Crucially, the Ti atom also has an exposed face, a site capable of forming a bond but as yet unoccupied by other atoms. 

The earliest Ziegler-Natta catalysts were combinations of titanium tetrachloride (T1CI4) and diethylalummum chloride [(CH3CH2)2A1C1] but these have given way to more effective zirconium based metallocenes the simplest of which is bis(cyclopentadi enyl)zirconmm dichlonde (Section 14 14)... 

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