Ziegler catalyst ethylene

Ziegler catalysts Complex catalysts prepared by interaction between an organometallic derivative and a transition metal derivative. A typical catalyst is the product of the interaction of TiCU and AIBU3. These catalysts polymerize olefins, particularly ethylene, to polyolefins, the polymerization generally being in a siereoregular manner. 

Most Kaminsky catalysts contain only one type of active center. They produce ethylene—a-olefin copolymers with uniform compositional distributions and quite narrow MWDs which, at their limit, can be characterized by M.Jratios of about 2.0 and MFR of about 15. These features of the catalysts determine their first appHcations in the specialty resin area, to be used in the synthesis of either uniformly branched VLDPE resins or completely amorphous PE plastomers. Kaminsky catalysts have been gradually replacing Ziegler catalysts in the manufacture of certain commodity LLDPE products. They also faciUtate the copolymerization of ethylene with cycHc dienes such as cyclopentene and norhornene (33,34). These copolymers are compositionaHy uniform and can be used as LLDPE resins with special properties. Ethylene—norhornene copolymers are resistant to chemicals and heat, have high glass transitions, and very high transparency which makes them suitable for polymer optical fibers (34). 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

The discovery by Ziegler that ethylene and propylene can be polymerized with transition-metal salts reduced with trialkyl aluminum gave impetus to investigations of the polymerization of conjugated dienes (7—9). In 1955, synthetic polyisoprene (90—97% tij -l,4) was prepared using two new catalysts. A transition-metal catalyst was developed at B. E. Goodrich (10) and an alkaU metal catalyst was developed at the Ekestone Tke Rubber Co. (11). Both catalysts were used to prepare tij -l,4-polyisoprene on a commercial scale (9—19). 

Linear alcohols used for the production of ethoxylates are produced by the oligomerization of ethylene using Ziegler catalysts or by the Oxo reaction using alpha olefins. 

Oligomerization of ethylene using a Ziegler catalyst produces unbranched alpha olefins in the C12-C16 range by an insertion mechanism. A similar reaction using triethylaluminum produces linear alcohols for the production of biodegradable detergents. 

Linear alcohols (C12-C26) are important chemicals for producing various compounds such as plasticizers, detergents, and solvents. The production of linear alcohols by the hydroformylation (Oxo reaction) of alpha olefins followed by hydrogenation is discussed in Chapter 5. They are also produced by the oligomerization of ethylene using aluminum alkyls (Ziegler catalysts). 

In contrast to the processes of Ethyl and of Chevron/Gulf, which use Ziegler catalyst in the oligomerization of the ethylenes, Shell uses a self-developed catalyst system consisting of, for example, a nickel salt, a rm-organophosphine group, and a polar solvent such as 1,4-butanediol (3) [34,35] ... 

Figure 19 (a) Peak melting temperature as a function of the branch content in ethylene-octene copolymers (labelled -O, and symbol —B (symbol, ) and -P (symbol, A) are for ethylene-butene and ethylene-propylene copolymers, respectively) and obtained from homogeneous metallocene catalysts show a linear profile, (b) Ziegler-Natta ethylene-octene copolymers do not show a linear relationship between peak melting point and branch content [125]. Reproduced from Kim and Phillips [125]. Reprinted with permission of John Wiley Sons, Inc. 

The mechanism of the polymerisation of ethylene by Ziegler catalyst may be put as follows. (C2H5)3Al+TiCl 4 —> (C2H5)2A1C1+C 2H5 TiCl3... 

Ethylene-propylene (30-60 mole per cent) copolymers produce substances which are rubbery in nature. They are prepared by using Ziegler catalysts based on vanadium oxychloride/aluminium trihexyl by solution process at 40°C using chlorobenzene or pentane as a solvent. These can be vulcanised with peroxides. Ethylene-propylene-hexa 1, 4-diene terpolymers are rubbers which can be vulcanised with sulphur. 

Figure 2 shows the profile of the 27-29 ppm spectral region of three polymers which served as models (1J ) for ethylene propylene rubber. The better agreement between the observed spectrum and the five-parameter model strongly suggests the three-parameter model is less realistic as an explanation for the polymerization mechanism. Table VII compares the observed profiles of EPDM rubbers made with a Ziegler catalyst system. The ratio of... 

Linear hydrocarbons with a double bond at the end of the chain are made by oligomerization of ethylene. Compounds with 6-18 carbons are the most popular. Ziegler catalysts are used in this process. Note that certain olefins... 

Alternatively, linear a-olefins can be made from ethylene using Ziegler catalysts to give the ethylene oligomer with a double-bonded end group. 

Also, it can be prepared by the reaction of lead with ethylene and hydrogen in the presence of Ziegler catalyst, triethylaluminum ... 

Obviously, the polymerization of ethylene does not involve isotactic steric control, since no isomers are possible in the linear polyethylene polymer. However, as the simpliest member of the vinyl monomer series, ethylene should be considered along with the substituted ethylenes. Where does the Ziegler catalyst, which produces polyethylene, lie in relation to the polypropylene catalysts ... 

It is known that the polymerization of ethylene by trialkyl aluminum is not a rapid reaction at normal pressures and temperatures. Ziegler, Gellert, Holzkamp, Wilke, Duck and Kroll (72) have found that ethylene was polymerized to higher trialkylaluminums only at elevated temperatures and pressures. Anionic hydride transfer commonly occured under these conditions. However, the addition of a transition metal halide such as titanium tetrachloride, the classical Ziegler catalyst, polymerized ethylene rapidly under mild conditions. 

There is considerable information that points to the cationic nature of the Ziegler ethylene polymerization. Tabata, Shibano, Sobue and Hara (76) have found that the polymerization of ethylene at —78° with cobalt —60 irradiation shows the characteristics of cationic polymerization. Roha, Kreider, Frederick and Beears (77) found that an active Ziegler catalyst for polyethylene from a non-reduced trialkyl-aluminum-titanium tetrachloride system requires an electrophilic com-... 

Tracer studies have been used in an attempt to determine the nature of the ends of the chain but these were as unsatisfactory as for propylene. Feldman and Perry (83) used triterated methanol to react the polyethylene from a titanium tetrachloridetrialkylaluminum catalyst. They found a continual increase in the number of polymeric chain ends which react with the tritium. This agrees with the results of Roha and Beears (84) who showed the very rapid exchange of alkyls which took place when ethylene was grown on a Ziegler catalyst in the presence of excess alkylaluminum chloride. In these experiments only an extremely small... 

Typical heterogeneous Ziegler catalysts operate at temperatures of 70 100°C and pressures of 0.1 2 MPa (15 300 psi). The polymerization reactions are carried out in an inert liquid medium (e.g, hexane, isobutane) or in the gas phase. Molecular weights of LLDPE resins are controlled by using hydrogen as a chain-transfer agent. Reactivities of a-olefins in copolymerization with ethylene depend on two factors the size of the alkyl groups attached to their double bonds and the type of catalyst,... 

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