Ethylene promotor

A Langmuir—Hinshelwood type of mechanism is also supported by the work of Klugherz and Harriott [178] and Spath and Handel [300], These authors, and several others, advocate 02 (and O2-) as the active oxygen species. Carberry et al. [74] and Forzatti et al. [118] contributed to the evidence for Oj with their results on the effect of promotors. 7-Irradiation of a calcium-promoted silver catalyst enhanced the yield of ethylene oxide. It could be shown that, during irradiation, calcium migrated to the surface, increasing the 02 concentration there. 

A third group contains those metal catalysts which do not form specific crystal phases in an oxidized state. The common types of oxygen on the surface are then 02 (adsorbed) and O (adsorbed) which generally do not lead to selective oxidation. One of the exceptions is silver, which very probably catalyses the selective oxidation of ethylene by providing 02 on the surface. However, an active role of surface oxides, which may be formed particularly by the action of promotors, is not excluded. 

The industrially important acetoxylation consists of the aerobic oxidation of ethylene into vinyl acetate in the presence of acetic acid and acetate. The catalytic cycle can be closed in the same way as with the homogeneous Wacker acetaldehyde catalyst, at least in the older liquid-phase processes (320). Current gas-phase processes invariably use promoted supported palladium particles. Related fundamental work describes the use of palladium with additional activators on a wide variety of supports, such as silica, alumina, aluminosilicates, or activated carbon (321-324). In the presence of promotors, the catalysts are stable for several years (320), but they deactivate when the palladium particles sinter and gradually lose their metal surface area. To compensate for the loss of acetate, it is continuously added to the feed. The commercially used catalysts are Pd/Cd on acid-treated bentonite (montmorillonite) and Pd/Au on silica (320). 

A limited kinetic investigation has been carried out on promotors for vanadium catalysts (VO(Ot-Bu)3/Al2Et3Cl3) in ethylene polymerization [234]. It was shown that esters of trichloroacetic acid, added continuously during the polymerization, reactivated the catalyst and permitted polymerization to be carried out at 120°C. Under these circumstances over 250 polymer chains were produced per vanadium atom and the polymers had /Mn ratios close to 2.0, which would be anticipated for a single catalytic entity. 

Examples of synergistic effects are now very numerous in catalysis. We shall restrict ourselves to metallic oxide-type catalysts for selective (amm)oxidation and oxidative dehydrogenation of hydrocarbons, and to supported metals, in the case of the three-way catalysts for abatement of automotive pollutants. A complementary example can be found with Ziegler-Natta polymerization of ethylene on transition metal chlorides [1]. To our opinion, an actual synergistic effect can be claimed only when the following conditions are filled (i), when the catalytic system is, thermodynamically speaking, biphasic (or multiphasic), (ii), when the catalytic properties are drastically enhanced for a particular composition, while they are (comparatively) poor for each single component. Therefore, neither promotors in solid solution in the main phase nor solid solutions themselves are directly concerned. Multicomponent catalysts, as the well known multimetallic molybdates used in ammoxidation of propene to acrylonitrile [2, 3], and supported oxide-type catalysts [4-10], provide the most numerous cases to be considered. Supported monolayer catalysts now widely used in selective oxidation can be considered as the limit of a two-phase system. 

Recent patent disclosures by the Standard Oil Co. of Indiana indicate that their process for the polymerization of ethylene is also a relatively low-pressure process, and the following process information is based on these disclosures. The polymerization process is a fixed-bed process employing a prereduced catalyst, ethylene pressures of 809-1,000 psi, and temperatures somewhat greater than 200°C. The metal oxides (such as nickel, cobalt, and molybdenum) can be supported on either charcoal or alumina, and materials such as lithium aluminum hydride, boron, alkali metals, and alkaline-earth hydrides may be used as promotors. Variations of this process are reported to produce polyethylene resins with densities from 0.94-0.97. 

Special Uses. High molecular mass copolyester resins are used in the manufacture of flexible packaging. Terephthalate resins are particularly suitable as adhesion promotors for printing inks, lacquers, and adhesives on poly(ethylene terephthalate) films. Some polyester printing inks adhere directly to these sheets. Lacquers that can be heat sealed at relatively low temperature can be produced from high molecular mass, soft copolyester resins. Special linear copolyester resins are used for magnetic tape coatings [2.97]. 

While alkylation of aromatics with olefins or alcohols occurs at the aromatic ring over acid catalysts, alkylation of the alkyl groups proceeds over basic catalysts. Pines and coworkers reported that the side-chain alkylation of toluene with ethylene is effectively catalyzed by the use of a mixture of sodium and a promotor such as anthracene or o-chlorotoluene. ... 

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