scholarly journals The mechanism of the catalytic oxidation of ethylene - I. Experiments using a flow system

1946 ◽  
Vol 188 (1012) ◽  
pp. 92-104 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Ethylene Oxide ◽  
Catalytic Oxidation ◽  
Flow System ◽  
Oxidation Reactions ◽  
Direct Oxidation ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Products Of Reaction ◽  
Kinetics Of

Experiments have been made using a flow system to determine the mechanism of the catalytic oxidation of ethylene on a silver catalyst. The effects of time of contact of the gases with the catalyst, gas concentration, and temperature have been investigated. The products of reaction are ethylene oxide, and carbon dioxide and water. There appear to be two processes whereby the carbon dioxide is formed: (1) by direct oxidation of the ethylene not via ethylene oxide, and (2) by the further oxidation of the ethylene oxide. The isomerization of ethylene oxide to acetaldehyde by the catalyst in the absence of any oxygen has also been examined. By comparison with the oxidation of ethylene oxide, it has been shown that this latter reaction proceeds to a large extent, and possibly entirely, through a preliminary isomerization of the ethylene oxide to acetaldehyde. The rate of oxidation of acetaldehyde is extremely rapid and no trace of acetaldehyde is found during the oxidation of ethylene or of ethylene oxide. Ethylene oxide forms on the catalyst an involatile deposit, which is oxidized away by oxygen, so that during oxidation reactions the quantity of it on the catalyst is kept low. The kinetics of the oxidation of ethylene, i.e. rate of reaction proportional to the oxygen concentration and slightly dependent on the ethylene pressure, are consistent with the view that ethylene reacts with oxygen adsorbed on the catalyst and that the slowest step in the whole series of reactions is the rate of adsorption of the oxygen. An energy of activation of about 27 kcal. was found for the production of ethylene oxide, and slightly less for the production of carbon dioxide and consumption of oxygen.

Gas phase interaction with catalytic oxidation reactions

1972 ◽  
Vol 326 (1565) ◽  
pp. 215-227 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Maleic Anhydride ◽  
Catalytic Oxidation ◽  
Gas Phase ◽  
Major Part ◽  
Oxidation Reactions ◽  
Mixed Gas ◽  
Kinetics Of ◽  
Oxidation Of Benzene ◽  
Homogeneous Decomposition

Studies of the catalytic oxidation of benzene to maleic anhydride and carbon dioxide over vanadia/molybdena catalysts show that the major part of the reaction involves interacting gas and gas-solid processes. The results are consistent with a mechanism in which a benzeneoxygen adduct is formed catalytically, desorbs and then reacts to give maleic anhydride entirely in the gas phase. On the basis of this proposed mechanism, the kinetics of individual reactions have been investigated in some depth. The over-oxidation of maleic anhydride has been found to be not significant under the conditions of reaction. The kinetic relationships governing the homogeneous decomposition of the adduct and the oxidation of the adduct to maleic anhydride and to carbon dioxide have been established. The results show that essentially all of the anhydride originates from mixed gas-solid/gas reaction while substantial amounts of carbon dioxide are produced entirely catalytically.

THE ROLE OF REACTION PRODUCTS IN THE SILVER-CATALYZED OXIDATION OF ETHYLENE

1960 ◽  
Vol 38 (11) ◽  
pp. 2256-2268 ◽  
Author(s):  
Kenneth E. Hayes
Keyword(s):  
Carbon Dioxide ◽  
Ethylene Oxide ◽  
Initial Rate ◽  
Flow System ◽  
Oxygen Exchange ◽  
Reaction Products ◽  
Exchange Reactions ◽  
Kinetics Of ◽  
Catalyzed Oxidation

Initial-rate studies of the kinetics of the silver-catalyzed oxidation of ethylene oxide and carbon dioxide in a flow system have been made. It was found that, using carefully purified reactants, the effect of added carbon dioxide was to suppress the formation of ethylene oxide only. The initial rate of the formation of ethylene oxide is given by the equation[Formula: see text]where r0 is the initial rate in the absence of CO2; m, n, and k are constants with m + n = 1.These results together with the results of oxygen exchange reactions between O18 and C2H4O16, CO216 and H2O16 are interpreted mechanistically.

scholarly journals The thermal decomposition of nitrogen pentoxide at low pressures

1925 ◽  
Vol 109 (751) ◽  
pp. 526-540 ◽  
Keyword(s):  
Thermal Decomposition ◽  
The Other ◽  
Nitrogen Tetroxide ◽  
Nitrogen Pentoxide ◽  
Other Hand ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Products Of Reaction ◽  
Glass Surfaces ◽  
Low Pressures

Unimolecular reactions possess a unique interest in that, as Perrin (‘Ann. Physique,’ vol. 11, p. 5, 1919) first pointed out, for the occurrence of such, some type of interaction between radiation and matter must take place. Although such reactions appear to be extremely rare, many physical processes such as evaporation, ionisation in gases at high temperatures and radio-active decay, proceed at rates conforming to a unimolecular law; true chemical reactions which are definitely unimolecular and not pseudo-unimolecular in character are, on the other hand, stated by many ( e. g ., Lowry, ‘Trans. Farad. Soc.,’ vol. 17, p. 596 (1922) ) to be non-existent. In order to substantiate this statement, it is clearly necessary to prove the more complex character of any reaction which satisfies the usual criteria of unimolecular change. The thermal decomposition of gaseous nitrogen pentoxide apparently fulfils these conditions, for Daniels and Johnston (‘J. Am. C. S.,’ vol. 43, p. 53 (1921)) showed that the reaction proceeded according to a unimolecular law over wide ranges of variation of pressure, and Lueck ( ibid ., vol. 44, p. 757 (1922)) obtained practically identical unimolecular constants for the decomposition in solution in carbon tetrachloride and chloroform. On the other hand, Daniels, Wulf and Karrer ( ibid ., vol. 44, p. 2402 (1922) ) suspected the reaction to be autocatalytic, owing to the apparent retardation of the reaction velocity in the presence of ozone, but the experiments of one of us (Hirst, ‘J. C. S.,’ vol. 127, p. 657 (1925), and of White and Tolman (‘J. Am. C. S.’ vol. 47, p. 1,240 (1925)) proved this to be erroneous. In addition, it has been shown that the reaction proceeds uniformly according to the unimolecular law even in the presence of extensive glass surfaces, or of gases which may be either indifferent, such as argon and nitrogen, or the products of reaction, such as nitrogen tetroxide or dioxide or oxygen. The rate of reaction may be expressed in the form - d C/ dt = 4·98 × 10 13 e -24.700/RT . C. Attempts have been made to interpret the experimental results on the hypothesis that the reaction is in reality bimolecular, and only apparently unimolecular in character; but owing to the abnormally large value of the energy of activation, namely, 24,700 calories per gram. molecule, the number of molecules which could be activated per second by inelastic collision, calculated according to the kinetic theory, falls far short of the observed reaction rate, being, in fact, some 10 5 times smaller.

scholarly journals Further investigations on the kinetics of gaseous oxidation reactions

1930 ◽  
Vol 129 (810) ◽  
pp. 284-299 ◽  
Keyword(s):  
Rate Of Change ◽  
Chain Mechanism ◽  
Oxidation Reactions ◽  
Chain Reactions ◽  
Oxidation Of Methane ◽  
Simple Order ◽  
Oxidation Of Hydrocarbons ◽  
Rate Of Reaction ◽  
A Chain ◽  
Kinetics Of

Investigation of the kinetics of the oxidation of ethylene and of benzene showed that these reactions are peculiar in the following respects. First, the relation between the rate of reaction and concentration is such that the reactions possess no simple “order,” though the nearest integral value for the order is about the third of fourth. The rate increases very rapidly with increasing hydrocarbon concentration, but is relatively little influenced by oxygen; under some conditions oxygen may have a retarding influence. Secondly, the reactions can be slowed down by increasing the surface exposed to the gases. This indicates that the oxidation occurs by a chain mechanism. Thirdly, the rate of change of pressure accompanying the oxidation only attains its full value after an induction period, during which evidently intermediate products are accumulating. Accepting the fact that the oxidations are probably chain reactions, the relation between rate and concentration shown that the chains are much more easily propagated when the intermediate active molecules encounter more hydrocarbon than when they encounter oxygen. Following the view of Egerton, and consistently with previous work on the combination of hydrogen and oxygen, the working hypothesis adopted is that some intermediate peroxidised substance is responsible for the propagation of the chains. This being so, the question arises whether the peculiarities found in the oxidation of hydrocarbons will also be found with substances already containing oxygen. To investigate, therefore, the influence of chemical configuration on the mechanism of oxidation reactions the following series of compounds has been studied CH 4 CH 3 OH HCHO which represent the stages through which Bone and others have shown the oxidation of methane to occur.

THE KINETICS OF THE FORMATION OF ETHANOLAMINES

1947 ◽  
Vol 25b (4) ◽  
pp. 405-414 ◽  
Author(s):  
C. Potter ◽  
R. R. McLaughlin
Keyword(s):  
Ethylene Oxide ◽  
Maximum Yield ◽  
Ammonium Hydroxide ◽  
Second Order ◽  
Energy Of Activation ◽  
Reaction Proceeds ◽  
Kinetics Of

The formation of ethanolamines from ethylene oxide and ammonia is a case of simultaneous, consecutive, competitive second order reactions. The results obtained show the time at which to stop a reaction for a maximum yield of any one of the three products. It is shown that as the reaction proceeds from ammonia to monoethanolamine to diethanolamine to triethanolamine the velocity constants are in the ratio of 1:6:4 for the three reactions. The values of the velocity constants are determined graphically. From these values an energy of activation of 16,600 cal. is calculated and is the same for each step. There is an indication that a tetraethanol – ammonium hydroxide is slowly formed.

THE SILVER CATALYZED OXIDATION OF ETHYLENE: III. KINETICS OF ETHYLENE OXIDE OXIDATION

1954 ◽  
Vol 32 (4) ◽  
pp. 432-442 ◽  
Author(s):  
A. Orzechowski ◽  
K. E. MacCormack
Keyword(s):  
Ethylene Oxide ◽  
Initial Rate ◽  
Oxidation Mechanism ◽  
Kinetic Studies ◽  
Main Step ◽  
Direct Oxidation ◽  
Flow Rates ◽  
Rate Determining Step ◽  
Kinetics Of ◽  
Catalyzed Oxidation

A flow type apparatus was used for kinetic studies of the silver catalyzed oxidation of ethylene oxide (EtO) by oxygen at 274 °C. Using N2 as diluent the concentrations of O2 and ethylene oxide were varied independently from 9.9 to 79% and 2.35 to 9.4% respectively while a total pressure of 1 atmosphere was maintained. Flow rates were varied to give a range of contact times varying from 0.06 to 0.25 sec. It was shown that EtO is oxidized without previous dissociation into C2H4 and O2. The dependence of the initial rate of oxidation of EtO on reactant concentrations excludes isomerization of EtO (to acetalde hyde) as a main step in its oxidation, and a direct oxidation mechanism is suggested. The results of a few experiments to determine the extent of isomerization of EtO to acetaldehyde in the absence of oxygen are presented. No steady state could be achieved but the results may be used semiquantitatively to support the belief that isomerization is not the rate determining step in the oxidation of ethylene oxide.

Kinetics of the oxidation of ethane by nitric oxide over manganese(III) oxide

1981 ◽  
Vol 59 (14) ◽  
pp. 2232-2238
Author(s):  
R. A. Ross ◽  
C. Fairbridge
Keyword(s):  
Nitric Oxide ◽  
Carbon Dioxide ◽  
Nitrous Oxide ◽  
Atmospheric Pressure ◽  
Flow System ◽  
Oxide Formation ◽  
Catalyst Structure ◽  
X Ray ◽  
Apparent Activation Energies ◽  
Kinetics Of

The catalytic reaction between ethane and nitric oxide over manganese(III) oxide has been investigated in a continuous flow system from 673 to 573 K at atmospheric pressure. The products of catalysis were nitrogen, carbon dioxide, nitrous oxide, and water. The rate of nitrous oxide formation was constant over this temperature region, while the apparent activation energies for nitrogen and carbon dioxide formation increased from 32 ± 4 and 22 ± 4 kJ mol−1, respectively, at 573 to 613 K, to 78 ± 4 and 63 ± 4 kJ mol−1 between 613 and 673 K. The kinetic results were best described by the rate equation:[Formula: see text]The surface mechanism appears to be complex and has been interpreted by a scheme involving interaction of the reactants in an absorbed layer. Both nitric oxide and ethane are believed to be involved further in subsequent steps. Infrared evidence indicates the possibility of a surface nitrate intermediate consistent with the mechanistic proposal. Scanning electron microscopy and X-ray powder diffraction techniques were used to assess the catalyst structure.

scholarly journals The mechanism of the catalytic oxidation of ethylene - II. Reactions between ethylene, etc. and chemisorbed oxygen monolayers

1946 ◽  
Vol 188 (1012) ◽  
pp. 105-122 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Ethylene Oxide ◽  
Low Temperatures ◽  
Adsorbed Oxygen ◽  
Silver Catalyst ◽  
Time Curve ◽  
Chemisorbed Oxygen ◽  
Pressure Time ◽  
Adsorbed Oxygen Atom ◽  
Kinetics Of

Experiments have been carried out at temperatures of 263° C and higher between oxygen adsorbed as atoms on the silver catalyst, and ethylene, ethylene oxide and acetaldehyde. The course of reaction was followed by measuring the change in pressure, and analyses of the products were made by micro-fractionation of the gases at low temperatures. In the reaction of ethylene with an oxygen-covered catalyst, the absence of an induction period in the pressure-time curve showed that oxidation of ethylene to carbon dioxide and water by a route not through ethylene oxide is possible. The reaction of acetaldehyde with the oxygenated catalyst was too fast to measure. The reactions of ethylene oxide were found to be complex, and reaction occurred both with the oxygenated and the clean catalyst. On a clean catalyst, ethylene oxide was simultaneously isomerized to acetaldehyde and converted back to ethylene and adsorbed oxygen; the acetaldehyde and adsorbed oxygen then reacted to form carbon dioxide and water. Both ethylene oxide and acetaldehyde, but not ethylene, were adsorbed with decomposition to form a non-volatile layer on the catalyst. This was composed of carbon, hydrogen and possibly oxygen, combined in indefinite and varying proportions. The kinetics of the reaction between ethylene and the adsorbed oxygen layer were measured. Throughout the course of any one reaction, the rate of oxidation to carbon dioxide was proportional to the square of the concentration of adsorbed oxygen, but the velocity constant depended on the initial concentration. The apparent energy of activation was 10 kcal. It is thought that when ethylene reacts with a single adsorbed oxygen atom, ethylene oxide is produced, and that with a pair of adsorbed oxygen atoms, intermediates such as formaldehyde are produced which react rapidly to form carbon dioxide and water.

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