Silica-alumina polymerization catalyst

Silicates which have been calcined may show an acid reaction when placed in an aqueous medium. Gayer (14) reported, many years ago, that his silica-alumina polymerization catalyst, when tested with an indicator in an aqueous medium, was acid in reaction. He reported no connection between this observation and catalyst activity. Such a catalyst if placed in water can be titrated with a base. Long periods (18 hours) may be allowed for reaction with a base, and the results can... 

In the early 1950s there was the quite contemporary discovery—in three different laboratories—of processes for the polymerization of ethene at low pressure using solid catalysts The catalyst used by the Standard Oil of Indiana was Mo(VI) oxide supported on aluminum oxide the one by Phyllips Petroleum was Cr(VI) oxide still supported on silica/alumina the catalyst studied by Ziegler and his co-workers at the Max Planck Institute at Miihlheim... 

Other chromium catalysts for ethylene polymerization employ chromo-cene [246] and bis(triphenylsilyl) chromate [247] deposited on silica-alumina. The catalyst support is essential for high activity at moderate ethylene pressures (200—600 p.s.i.). The former catalyst is activated further by organo-aluminium compounds. Polymerization rates are proportional to ethylene pressure and molecular weight is lowered by raising the temperature or with hydrogen (0.1—0.5 mole fraction) in the monomer feed wide molecular weight distributions were observed. 

Figure 6 illustrates the usefulness of the apparatus in tracer research. It has long been known from data in the literature that ethylene, propylene, and other olefins are capable of polymerizing over standard silica-alumina cracking catalysts to form a mixture of hydrocarbon polymers. Figure 6... 

The surfaces of some types of silica and alumina freed from adsorbed water contain acidic -OH groups. Ballard et al. (15) showed that these -OH groups react readily with transition metal alkyls giving stable compounds that are highly active polymerization catalysts for olefins. These systems are best described with reference to silica. 

Phillips (1) A process for polymerizing ethylene and other linear olefins and di-olefins to make linear polymers. This is a liquid-phase process, operated in a hydrocarbon solvent at an intermediate pressure, using a heterogeneous oxide catalyst such as chromia on silica/ alumina. Developed in the 1950s by the Phillips Petroleum Company, Bartlesville, OK, and first commercialized at its plant in Pasadena, TX. In 1991, 77 reaction fines were either operating or under construction worldwide, accounting for 34 percent of worldwide capacity for linear polyethylene. 

Silica-alumina mixtures are of great technological importance in the oil industry as catalysts for petroleum processing. The cracking activity is closely linked to surface acidity. Other typical reactions catalyzed by silica-alumina are the dehydration of alcohols and the polymerization of olefins. 

Certain oxides, particularly clays and synthetic silica-alumina composites, are very active polymerization catalysts. They probably owe their activity to the presence of acidic hydrogen. 

The reactor equipment used for solution polymerizations is typically glass-lined stainless steel. An example of solution polymerization is the reaction of ethylene in isooctane with a chromia silica alumina catalyst initiator (see Figure 3.23) to form polyethylene. Typical reaction conditions for this polymerization are 150-180°C and 2.1-4.8 MPa (300-700 psi). 

It was later found that stable organometallic compounds of transition metals exhibiting very low polymerization activity could be transformed into high-activity catalysts when deposited on silica, alumina, or silica-alumina.287-289 Interaction of surface hydroxyl groups with the organometallic compounds such as chromocenes, benzyl, and Tt-allyl complexes results in the formation of surface-bound organometallic complexes (41-43) 289-291... 

We report here a study of Zr, Nb, Cr, and Mo hydrocarbyl compounds grafted onto oxide supports as potential olefin polymerization catalysts and oxide-supported Mo and W 7r-allyl derivatives in olefin disproportionation catalyses. The interaction of these compounds with silica and alumina supports has been examined using ESR and IR, analyses to define the catalytic materials that result. Finally, we consider why chemical support of these organometallic compounds confers on them an enhanced catalytic activity. 

It is curious that during 30 years of interminable debate about valence, almost no mention has been made of organochromium compounds that also make active catalysts. As early as 1961 Walker and Czenkusch at Phillips showed that diarene-Cr(O) compounds polymerize ethylene when deposited on silica or silica-alumina (51). We now suspect that the Cr(0) is oxidized by silanol groups to Cr(I), implying that Cr(I) is also an active valence. Such catalysts, however, do not resemble Cr(VI)/silica. The kinetics and polymer obtained are entirely different. 

Silica and aluminum phosphate have much in common. They are isoelec-tronic and isostructural, the phase diagrams being nearly identical even down to the transition temperatures. Therefore, aluminum phosphate can replace silica as a support to form an active polymerization catalyst (79,80). However, their catalytic properties are quite different, because on the surface the two supports exhibit quite different chemistries. Hydroxyl groups on A1P04 are more varied (P—OH and A1—OH) and more acidic, and of course the P=0 species has no equivalent on silica. The presence of this third species seems to reduce the hydroxyl population, as can be seen in Fig. 21, so that Cr/AP04 is somewhat more active than Cr/silica at the low calcining temperatures, and it is considerably more active than Cr/alumina. 

A silica-alumina catalyst also has been used in several commercial units. It has the disadvantage of polymerizing only a relatively small percentage of the olefins charged. 

In only a few polymerization processes are metallocene catalysts used in a soluble form. Supported metallocene catalysts are preferred for the production of polyethylene or isotactic polypropylene on an industrial scale, especially in the slurry and gas-phase processes. To use them in existing technological processes (drop-in technology) as replacements for the conventional Ziegler-Natta catalysts, the metallocenes have to be anchored to an insoluble powder support, including silica, alumina, and magnesium dichloride (208-217). Various methods of anchoring catalysts to supports are possible (Fig. 25) ... 

Among the supports that have been used in the preparation of supported transition metal nanoparticles are carbon, silica, alumina, titanium dioxide, and polymeric supports [57], and the most frequently used support is alumina [56], These supports normally produce an effect on the catalytic activity of the metallic nanoparticles supported on the amorphous material [60], In Chapter 3, different methods for the preparation of metallic catalysts supported on amorphous solids were described [61-71],... 

Polymerization with Complex Catalysts. High density polyethylene reached a domestic production of 1.25 billion pounds in 1968. It is made either with a stereospecific Ziegler-Natta catalyst or on a supported chromium oxide catalyst. The latter forms a complex with the silica-alumina and is activated by treatment with air and steam at elevated temperature. The mechanism is such that electrons are donated to the catalyst in order to be returned under polymerizational-promoting conditions, consequently lowering the energy of the system ... 

It is, however, more complex than this because the silica-alumina support affects also the polymerization. A. Clark describes the correlation between the chromium trioxide and the silica-aluminum support. He also shows the effect of the catalyst activation temperature on the molecular weight of the polyethylene formed. 

The idea that complex formation may be important in the catalytic process can be carried further. It has been found, for example, that bis-arene chromium complexes supported on silica-alumina are active for ethylene polymerization. These catalysts are prepared by activating the support alone in the usual manner and then impregnating with a hydrocarbon solution of the bis-arene compound at room temperature in the absence of air or other oxidizing agent. 

The present paper describes the phenomena of shape-selective polymerization involved in converting C--C olefins over HZSM-5 to higher boiling olefins and the similarities and differences compared to amorphous silica-alumina. The channel systems of ZSM-5 (8), Figure 1, impose shape-selective constraints on the shape of the large molecules accounting for the differences with amorphous catalysts. 

V. Dufaud and J.-M. Basset, Catalytic hydrogenolysis at low temperature and pressure of polyethylene and polypropylene to diesels or lower alkanes by silica-alumina a step toward polyolefin degradation by the microscopic reverse of Ziegler-Natta polymerization, Angew. Chem. Int.Ed., (1998) 37(6) 806-810. I. Nakamura and K. Fujimoto, Development of new disposable catalyst for waste plastics treatment for high quality transportation fuel. Catalysis Today, 27,175-179 (1996)... 

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