Ethylenes self-hydrogenation

He concludes that the first (associative) mechanism gives values nearest the observed heat of adsorption determined by Beeck (30), and is therefore accepted as nearest the truth (34) (Qo (calculated) = 42 kcal./ mole Qo (observed) = 58 kcal./mole). Experiments on tungsten and nickel films (Beeck (35), Trapnell (36), and more recent work in Rideal s laboratory) have shown that when ethylene is added to a clean metal surface ethane appears in the gas phase. A self hydrogenation mechanism must be operative and at least in these cases dissociation of ethylene must occur on the catalyst. It is suggested that the calculations might be complicated by the energy of bond strain in the adsorption of an ethylene molecule to the fixed lattice distances of the metal. 

It is well established that when ethylene is admitted to a freshly prepared evaporated metal film, self-hydrogenation resulting in the rapid production of ethane is observed [50—52]. A similar phenomenon is observed when ethylene is adsorbed on supported metal catalysts [49,53] (see Fig. 5). These observations have been interpreted as indicating that ethylene is first chemisorbed dissociatively, viz. 

These results are supported by volumetric studies [52,54]. With both nickel and palladium there is a slow self-hydrogenation at —78°C. This becomes increasingly important as the temperature is increased at 0°C the overall hydrogen/carbon ratio in the surface species is 1.5, falling to 1.0 at room temperature. Field emission microscopic (FEM) studies of ethylene adsorption on iridium [56] and tungsten [57] are also satisfactorily... 

Acetylene, when adsorbed on active nickel catalysts, undergoes self-hy-drogenation with the production of ethylene [91], although the extent of this process is less than with ethylene. Similar behaviour has been observed with alumina- and silica-supported palladium and rhodium [53], although with both of these metals ethane is the sole self-hydrogenation product some typical results for rhodium—silica are shown in Fig. 21. 

A comparison of the reactions of ethylene on three kinds of Ru-Y zeolites shows that the self-hydrogenation rate has the order Ru-H-Y > Ru-Ca-Y > Ru-Na-Y. The hydrogenation rate depends on the amount of coadsorbed hydrogen to roughly first order. The presence of polymerization products beyond butane is not observed. The reactions of ethylene are affected by reaction temperature with some rearrangement of butane to isobutane at intermediate temperatures. Carbon-carbon bond cleavage to methane predominates above 573K. 

Paraffins, of course, cannot have an associative mechanism and do not adsorb on hydrogen-covered nickel. When adsorbed on bare nickel they behave in a manner similar to ethylene. Acetylene, on the other hand, exhibits a unique behavior. Regardless of the pretreatment of the nickel, acetylene produces the spectrum assigned to chemisorbed ethyl radicals. This indicates extensive self-hydrogenation and the formation of a surface carbide. The idea of a surface carbide is supported by a very large increase in spectral intensity when hydrogen is added to chemisorbed acetylene. 

The results described in this section show clearly that surface hydrogen is involved in the process of adsorption of ethylene on sites II of alumina, in contrast to the conclusion of Lucchesi et al. (14), that chemisorbed ethyl radicals are formed by self-hydrogenation. In the polymerization of it was similarly found that the butenes formed... 

This conclusion was based on the result that when excess ethylene is admitted to a nickel film at room temperatures, ethane appears in the gas phase. Trapnell concluded that the initial chemisorption on tungsten films is a four-site process and the final adsorption self-hydrogenation is a two-site process. Jenkins and RideaP obtained results from self-hydrogenation of ethylene on nickel which fit the equation... 

Liquid ethylene oxide under adiabatic conditions requires about 200°C before a self-heating rate of 0.02°C/min is observed (190,191). However, in the presence of contaminants such as acids and bases, or reactants possessing a labile hydrogen atom, the self-heating temperature can be much lower (190). In large containers, mnaway reaction can occur from ambient temperature, and destmctive explosions may occur (268,269). 

The gases are again dried and then further compressed to about 550 psi. Separation of hydrogen and methane take place in the demethanizer and in its preflash system. Three successive Golder preflash steps are used in this separation, with propylene as refrigerant, then ethylene, and finally a self-generated methane refrigerant at -200 F. 

Elkins C, Viswanathan K, Long TE. Synthesis and characterization of star-shaped poly(ethylene-co-propylene) polymers bearing terminal self-complementary multiple hydrogen-bonding sites. Macromolecules 2006 39 3132-3139. 

A number of new processes exploiting metathesis have been developed by Phillips. A novel way to manufacture lubricating oils has been demonstrated.145 The basic reaction is self-metathesis of 1-octene or 1-decene to produce Ci4-C28 internal alkenes. The branched hydrocarbons formed after dimerization and hydrogenation may be utilized as lubricating oils. Metathetical cleavage of isobutylene with propylene or 2-butenes to isoamylenes has a potential in isoprene manufacture.136,146 High isoamylene yields can be achieved by further metathesis of C6+ byproducts with ethylene and propylene. Dehydrogenation to isoprene is already practiced in the transformation of isoamylenes of FCC C5 olefin cuts. 

The process of catalyst oxidation and reduction can be treated as a reversible phase transition [136]. It is to this process that the authors of recent investigations [37, 47-49, 85] ascribe critical effects. When studying kinetic self-oscillations in the oxidation of hydrogen over nickel [37] and measuring CPD, the authors established that the reaction performance oscillates between the states in which oxygen is adsorbed either on the reduced or on the oxidized nickel surface. Vayenas et al. [47-49], by using direct measurements of the electrochemical activity of 02 adsorbed on Pt, showed that the isothermal self-oscillations of the ethylene oxidation rate over Pt are due to the periodic formation and decomposition of subsurface Pt oxides. A mathemati-... 

Taking into consideration a) the specific properties of organoaluminum compounds, especially lower aluminumtrialkyls, and their hydride-, halo-gene- and alkoxy derivatives, which are highly flammable in air and explode at contact with water b) the use of hydrogen, ethylene, isobutene, ethylene, isobutene, ethylchloride, sodium and aluminum (finely dispersed and active, which can self-inflame in air), the production of organoaluminum compounds can be considered one of the most dangerous chemical productions. Therefore, safety measures and fire prevention are especially important. 

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