Heterogeneous titanium catalyst

Polystyrene (PS) is the fourth big-volume thermoplastic. Styrene can be polymerized alone or copolymerized with other monomers. It can be polymerized by free radical initiators or using coordination catalysts. Recent work using group 4 metallocene combined with methylalumi-noxane produce stereoregular polymer. When homogeneous titanium catalyst is used, the polymer was predominantly syndiotactic. The heterogeneous titanium catalyst gave predominantly the isotactic. Copolymers with butadiene in a ratio of approximately 1 3 produces SBR, the most important synthetic rubber. 

As an example of the use of MIXCO.TRIAD, an analysis of comonomer triad distribution of several ethylene-propylene copolymer samples will be delineated. The theoretical triad Intensities corresponding to the 2-state B/B and 3-state B/B/B mixture models are given In Table VI. Abls, et al (19) had earlier published the HMR triad data on ethylene-propylene samples made through continuous polymerization with heterogeneous titanium catalysts. The data can be readily fitted to the two-state B/B model. The results for samples 2 and 5 are shown In Table VII. The mean deviation (R) between the observed and the calculated Intensities Is less than 1% absolute, and certainly less than the experimental error In the HMR Intensity determination. 

Note that the catalyst of Figure 10.6 contains the same titanium part as that of Figure 10.5, but that they differ in the aluminium Lewis acid and anions formed. The use of diethylaluminium chloride (DEAC, the common initiator for heterogeneous titanium catalysts) gave propene dimerisation only. This... 

Fig. 1. Illustrative molecular weight distributions of polyethylene prepared by soluble vanadium and heterogeneous titanium catalysts...

The first industrial production of EPM from heterogeneous titanium catalysts was in 1983 four commercial grades were initially available. Prom 1986 on, CO053TX was the only grade on the market. Production was then stopped in the late 1980s. 

The polymerization of 4-MPD to give 1,2-isotactic polymer has been performed with various heterogeneous titanium catalysts The product in this case contains a portion (20-30%) of soluble, amorphous 1,4 polymer. The insoluble polymer material is highly crystalline with a Tm of... 

Reaction of titanium compounds with surface hydroxyls of inorganic gels, their strong adsorption on the inorganic salts or oxides, and their reaction with active functional groups of polymers lead to heterogenized titanium catalysts, which after modification with alkyl metal derivatives are active in the olefin oligomerization reactions [99-102]. 

Enichem made one of the most important steps forward in the development of general heterogeneous oxidation catalysts in the early 1990s with the commercialization of titanium silicate (TS-1) catalysts. TS-1 has a structure similar to ZSM-5 in which the aluminium has been replaced by titanium it is prepared by reaction of tetraethylorthosilicate and tetra-ethylorthotitanate in the presence of an organic base such as tetrapropy-lammonium hydroxide. This catalyst is especially useful for oxidation reactions using hydrogen peroxide (Scheme 4.11), from which the only byproduct is water, clean production of hydroquinone being one of the possibilities. 

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. 

Among the large bulk of work regarding titanium(IV) silsesquioxanes, specific studies have been focused on synthesizing close molecular models of the active sites of titanium heterogeneous epoxidation catalysts in siUcaUte and in mesostruc-tured MCM-41 silica (Figure 14.3 gives some selected examples) [54, 61-66]. 

Therefore, in such heterogeneous polymerizations, almost all industrial catalysts are supported, for example on silica, whereas the typical Ziegler s titanium catalysts are by definition supported on magnesium chloride. These catalysts are adsorbed at the surface or incorporated into the crystal structure of the support. Other catalysts, such as Phillips chromium catalysts, can be coupled at the support surface by a chemical bond. 

Ziegler-Natta Catalysts. All isotactic polymers of higher a-olefins are produced with the same type of heterogeneous, titanium-based Ziegler-Natta catalyst systems as that used for the manufacture of isotactic PP. 

Rrijnen, S., Mojet, B. L., Abbenhuis, H. C. L., Van Hooff, J. H. C. and Van Santen, R. A. MCM-41 heterogenized titanium silsesquioxane epoxidation catalysts a spectroscopic investigation ofthe adsorption characteristics, Phys. Chem. Chem. Phys., 1999,1,361-365. 

Table 4.3 Polymerisation of styrene using various heterogeneous titanium-based catalysts activated with methylaluminoxane 1...

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