Ethylene, catalytic oxidation process studies

The various hydrocarbon oxidation schemes discussed above were believed to proceed at the catalyst surface only. The present concepts accept the occurrence of complex heterogeneous-homogeneous reactions proceeding in part at the solid surface and in part in the gas or liquid phase. Many catalytic oxidation processes considered recently as purely heterogeneous appeared to proceed by the heterogeneous-homogeneous mechanism. Such are the oxidations of hydrogen, methane, ethane, ethylene, propene, and ammonia over platinum at elevated temperatures, as studied by Polyakov et al. (131-136). When hydrocarbons are oxidized over platinum the reaction sets in on the catalyst surface and terminates in the gas phase. 

The catalytic reactions of methane reforming to syngas, oxidative coupling of methane to ethane and ethylene, direct oxidation of methane to methanol and formaldehyde occur at relatively high temperatures, 400—1000 °C, i.e., can be qualified as high-temperature catalytic oxidation processes. Numerous studies of these reactions, different in many ways, showed, however, that they have a number of common features, the most important of which are ... 

Chromium zeolites are recognised to possess, at least at the laboratory scale, notable catalytic properties like in ethylene polymerization, oxidation of hydrocarbons, cracking of cumene, disproportionation of n-heptane, and thermolysis of H20 [ 1 ]. Several factors may have an effect on the catalytic activity of the chromium catalysts, such as the oxidation state, the structure (amorphous or crystalline, mono/di-chromate or polychromates, oxides, etc.) and the interaction of the chromium species with the support which depends essentially on the catalysts preparation method. They are ruled principally by several parameters such as the metal loading, the support characteristics, and the nature of the post-treatment (calcination, reduction, etc.). The nature of metal precursor is a parameter which can affect the predominance of chromium species in zeolite. In the case of solid-state exchange, the exchange process initially takes place at the solid- solid interface between the precursor salt and zeolite grains, and the success of the exchange depends on the type of interactions developed [2]. The aim of this work is to study the effect of the chromium precursor on the physicochemical properties of chromium loaded ZSM-5 catalysts and their catalytic performance in ethylene ammoxidation to acetonitrile. 

The first observation of a chemisorption process obeying Eq. (1) was probably reported by Zeldowitch in 1934 for the catalytic oxidation of CO on Mn02 [10] a later study of the chemisorption of CO and CO2 on Mn02 demonstrated that Eq. (1) was satisfied [11] but it was only after the discovery that Eq. (1) describes also the chemisorption of hydrogen and ethylene on a catalyst of reduced NiO [12] that this equation became of wide use. That Eq. (1) is indeed widely observed in chemisorption was confirmed by Taylor and Thon who analyzed previously published results for 10 systems and found that they were described by the time-logarithm law [53]. An extended list of adsorbent-adsorbate systems obeying the Elovich equation is given in Aharoni and Tompkins s review [14]. 

The production of higher hydrocarbons directly from methane by catalytic oxidative coupling is a novel methane conversion process which warrants further study. When combined with an ethylene oligomerisation step it is a potential alternative to conventional processes, based on synthesis gas, for producing liquid fuels from methane. However, further research is necessary to provide the information required to assess the commercial prospects for this route. 

Catalytic properties of complexes of multi-valenced metals with poly(ethylene glycol) (PEG) and polyurethane (PU) have been studied during liquid-phase oxidation processes such as the liquid-phase oxidation of hydrocarbons (phenanthrene, tetralin, cyclohexene), decomposition of hydroperoxides, hydrocarbons and decomposition of hydrogen peroxide [101 -106]. The kinetics of these reactions have been studied. The rate and selectivity of a particular reaction process depend not only on the properties... 

Very recently, Imamura and Wallace (1981) have used the decomposition tendency of rare earth and transition d metal intermetallics under oxygen atmosphere to prepare highly reactive supported catalysts. X-ray diffraction showed that they consist of mixtures of transition metal and rare earth oxide, the transition metal particle sizes ranging from 90 to 350 A. These catalysts exhibited superior catalytic activity compared to oxide-supported catalysts prepared by the conventional impregnation method for the hydrogenation of ethylene. Although further studies are necessary to elucidate the detailed structure of these catalysts, it appears that the oxidation process of rare earth intermetallics provides a novel means of producing active supported catalysts. 

Among such oxidations, note that liquid-phase oxidations of solid paraffins in the presence of heterogeneous and colloidal forms of manganese are accompanied by a substantial increase (compared with homogeneous catalysis) in acid yield [3]. The effectiveness of n-paraffin oxidations by Co(III) macrocomplexes is high, but the selectivity is low the ratio between fatty acids, esters, ketones and alcohols is 3 3 3 1. Liquid-phase oxidations of paraffins proceed in the presence of Cu(II) and Mn(II) complexes boimd with copolymers of vinyl ether, P-pinene and maleic anhydride (Amberlite IRS-50) [130]. Oxidations of both linear and cyclic olefins have been studied more intensively. Oxidations of linear olefins proceed by a free-radical mechanism the accumulation of epoxides, ROOH, RCHO, ketones and RCOOH in the course of the reaction testifies to the chain character of these reactions. The main requirement for these processes is selectivity non-catalytic oxidation of propylene (at 423 K) results in the formation of more than 20 products. Acrylic acid is obtained by oxidation of propylene (in water at 338 K) in the presence of catalyst by two steps at first to acrolein, then to the acid with a selectivity up to 91%. Oxidation of ethylene by oxygen at 383 K in acetic acid in... 

The use of liquid membranes for controlling chemical reactions such as that just discussed has been proposed for a number of other systems. This type of application, in which liquid membranes are used as heterogeneous catalysts or as reaction moderators, is an area that deserves more study. Ollis et al. and Wolytdc and Ollis studied liquid membranes as heterogeneous catalyst systems using the catalytic oxidation of ethylene to acetaldehyde (Wacker process) as a model. This process entails the following three... 

In the present work the catalytic activity, stracture, plysical and chemical properties of silver-containing zirconium phosphates, containing different amounts of silver, and synthesized using sol-gel, co-precipitation and ion exchange methods have been studied. It was shown that the method of phosphate synthesis determines the final composition, structure and catalytic properties. The phosphates, treated in reducing media, exhibit catalytic activity in the process of ethylene glycol oxidation into glyoxal. 

The aim of the present work is to study the influence of the methods of synthesis of silver-containing zirconium phosphates on the composition, stmcture and catalytic activity of materials in the process of ethylene glycol oxidation, and formation of active sites (Ag nanoparticles) on the surface of zirconium-phosphate matrix. 

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Ab initio molecular orbital studies on the whole catalytic cycle of hydroformylation of ethylene catalyzed by HRh(CO)2(PH3)2 has been performed [59,60], which points out the significance of the coordinating solvent—ethylene in this case—and identifies the oxidative addition of molecular hydrogen to the pentacoordinate acyl-Rh complex as the rate-determining step. In fact, this step is the only endothermic process in the catalytic cycle. 

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