Titanium magnesium catalysts

MPC [Mitsui Petrochemical] A continuous process for polymerizing propylene, based on the Ziegler-Natta process, but using a much more active catalyst so that de-ashing (catalyst removal) is not required. The catalyst contains magnesium in addition to titanium successive versions of it have been known as HY-HS (high yield, high stereospecifity), HY-HS II, and T-catalyst. Developed jointly by Mitsui Petrochemical Industries, Japan, and Montedison SpA, Italy, in 1975, and now licensed in 56 plants worldwide. 

This reaction can be carried out with numerous variations to give a broad range of catalysts. It is a heterogeneous high-surface TiCIs material of which the active sites contain titanium in an unknown valence state. It is quite likely that alkyltitanium groups at the surface are responsible for the co-ordination polymerisation. In more recent catalysts titanium supported on magnesium salts are used [4,5],... 

Research Focus Development of Ziegler-Natta polymerization catalysts containing magnesium and titanium for polymerizing ethylene. 

Groups I IE metal, it is the unique ratio of magnesium and titanium that defines the catalyst efficacy. In earlier studies Ziegler-Natta catalysts containing varying titanium/magnesium ratios were prepared and then used to polymerize ethylene. 

If polymerization catalysts, for instance for alkenc polymerization (Zicglcr-Natta-type catalysts), are prepared by precipitation methods, they can be formed by precipitation from organic solvents, as claimed in several patents [22], In these patents the precipitation of titanium-magnesium compounds in THF with hexane as precipitating agent is used for the formation of the catalyst. Many important Zicgler-Natta initiators are solids, and heterogeneous initiator systems seem to be necessary for the production of isotactic polyalkenes [23]. However, not much information on the details of catalyst preparation is available in the open literature. 

Table 4. EPR data on Ti3+ ions formed in titanium-magnesium catalysts of various composition 80) By permission of Hiithig Wepf Verlag...

The maximum number of AQ in propylene polymerization by supported titanium-magnesium catalysts may be estimated on the basis of the maximum activity of catalysts and kp values ( 10 l/(mol x s). The initial activity of this catalytic system was as high as 80 kg C3H6/(g Ti x h x atm) (in the presence of Al(i-Bu)3 and ethyl /7-methoxybenzoate), not less than 90% of isotactic polymer being formed. One can conclude that is 0.07 mol/mol Ti. Taking into account Cp, the total number of active centers for this catalyst is 10 % of the content of titanium in the catalyst. These data are close to those obtained in ref (see Table 2). 

Traditional ZN Catalysts and Supported Titanium-Magnesium Catalysts. 121... 

A new and more effective and reliable variant of the kinetic method is the stopped flow method (SF method), which has been offered by Keii and Terano [153] for determination of the number of active centers and the propagation rate constant in olefin polymerization on ZN catalysts. The main feature of this method is determination of Cp and k values in conditions of quasi-living polymerization, when transfer reactions of a polymer chain practically do not proceed and linear dependences of molecular weight of formed polymer and yield of polymer on polymerization time are observed. It has been shown that these conditions are obtained for propylene polymerization on supported titanium-magnesium catalysts (TMC) at low temperature (30°C) and at times of polymerization less than 0.2 s in these cases, values of Cp and can be calculated from Eqs. (14) and (15) ... 

Similarly, Arnold found that NHCs with tethered nucleophilic chelating ligands (42-44 Figure 31.9) possessed the ability to catalyze the ROP of lactide as a bifunctional catalyst [63]. The juxtaposition of an alkoxy or amino group with a labile NHC-transition metal (metal = yttrium, titanium, magnesium, zinc) complex allowed the labilized NHC to activate the metal-coordinated monomer (Scheme 31.15). Additionally, a metal-free analog (38), in which an alkoxy ligand was tethered to the NHC, was found to promote similar catalytic activity. These catalyst... 

Modelling of the polymer particle growth process [82] has resulted in the conclusion that diffusion limitations are the single reason for the wide polydispersity of synthesised polymers. The model has demonstrated that the main transport limitations localise on the level of macroparticles. Modelling results are confirmed by data obtained in gas and liquid polymerisation experiments on titanium-magnesium catalysts. Authors also consider that the wide polydispersity of polymers can be explained by the existence of more than one type of active centre. Each specific type is responsible for a certain portion of polymer with a different MWD. However, the authors did not succeed in characterising the active centre [82] because it required the optimisation of many kinetic parameters. 

Heterogeneous catalysts, which are obtained by deposition of cluster-type metal complexes on inorganic substances such as aluminum, titanium, magnesium, zinc, silicon, tin, and tungsten or on polymers,have also been... 

Dialkylaminoethyl acryhc esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyitin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

There are other methods of preparation that iavolve estabhshing an active phase on a support phase, such as ion exchange, chemical reactions, vapor deposition, and diffusion coating (26). For example, of the two primary types of propylene polymerization catalysts containing titanium supported on a magnesium haUde, one is manufactured usiag wet-chemical methods (27) and the other is manufactured by ball milling the components (28). 

Supported Catalysts for Propylene Polymerization. Although magnesium haUde supported titanium catalysts for propylene... 

Ethyl chloride can be dehydrochlorinated to ethylene using alcohoHc potash. Condensation of alcohol with ethyl chloride in this reaction also produces some diethyl ether. Heating to 625°C and subsequent contact with calcium oxide and water at 400—450°C gives ethyl alcohol as the chief product of decomposition. Ethyl chloride yields butane, ethylene, water, and a soHd of unknown composition when heated with metallic magnesium for about six hours in a sealed tube. Ethyl chloride forms regular crystals of a hydrate with water at 0°C (5). Dry ethyl chloride can be used in contact with most common metals in the absence of air up to 200°C. Its oxidation and hydrolysis are slow at ordinary temperatures. Ethyl chloride yields ethyl alcohol, acetaldehyde, and some ethylene in the presence of steam with various catalysts, eg, titanium dioxide and barium chloride. 

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