Heterogeneous Isomerization of Ethylene Oxide to Acetaldehyde

Bernardini, O. O.; Cherniak, E. A.

doi:10.1139/v73-205

Cited by 5 publications

(13 citation statements)

References 4 publications

(6 reference statements)

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“…55 In the oxidative atmosphere, coke is readily removed 269,273 and the only side-products formed are acetaldehyde, carbon dioxide, and water, of which acetaldehyde is readily oxidized. 125,129,274,275 Attrition is expected to be less prevalent due to the strong, non-porous support material applied in industrial catalysts. 55,265 Leaching of silver is also expected to be negligible, as silver and silver oxides are not volatile, 56 but redistribution or loss of promotors is expected to significantly influence both the activity and selectivity of the catalyst.…”

Section: Introduction 411 Deactivation Mechanismsmentioning

confidence: 99%

“…322 Lee et al showed for a wide range of metal oxide support materials that the support material catalysed the ring opening of ethylene oxide to form acetaldehyde 196 . However, since acetaldehyde is rarely found under reaction conditions, it is thought that acetaldehyde is rapidly further oxidized to CO 2 in the presence of silver 125,177,274 . This led to a proposed scheme for the silver catalyzed ethylene epoxidation as displayed in Figure 5.1.…”

Section: Introductionmentioning

confidence: 99%

“…71,212,327 Industrial sources report a linear decrease of selectivity with increasing conversion, based on empirical observations, without offering insight into the origin of this relationship. [328][329][330][331] It was proposed that the isomerization of ethylene oxide would be a first order reaction in ethylene oxide and dependent on the support 274,323,332 . The isomerization rate of ethylene oxide in the absence of ethylene was determined, but either only on bare support materials or with catalysts prepared using a variety of preparation methods, with a wide range of silver particle sizes and in the presence of (potential) promotors.…”

Section: Introductionmentioning

confidence: 99%

“…The isomerization rate of ethylene oxide in the absence of ethylene was determined, but either only on bare support materials or with catalysts prepared using a variety of preparation methods, with a wide range of silver particle sizes and in the presence of (potential) promotors. 132,177,196,274,275,323,324,332 To address this important question, we set out to show the effect of the support properties and understand the empirical correlation between conversion and selectivity, by carefully excluding effects due to differences in particle size, metal loading or the presence of promotors. To this aim we prepared series of catalysts on supports with different specific surface areas and surface groups, but having similar silver particle size and weight loading, and being prepared using the same metal precursor.…”

Section: Introductionmentioning

confidence: 99%

“…The decreasing selectivity with increasing conversion, as shown in the middle frame, has been reported before, 306,329 stating a linear or first order correlation. 274,329,332,342 However, no chemical or physical explanation for this relation has been given. In the following section we try to describe and understand the dependence of selectivity on support properties and conversion.…”

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confidence: 99%

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Supported Silver Catalysts for Ethylene Epoxidation

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12or to increase the stability of the catalyst. [74][75][76] The activity of the catalyst is less important as high conversions decrease the ethylene oxide selectivity due to the secondary reaction (r 3 in Figure 1.2, the full oxidation of ethylene oxide).The presence of chlorine on the surface suppresses the full oxidation of ethylene, 74,77,78 as the presence of chlorine on the catalyst surface prevents the formation of certain surface species responsible for the unselective pathway, leading to an increase in the intrinsic selectivity. 75 The competitive adsorption of chlorine on the silver surface indiscriminately suppresses oxygen adsorption on the silver surface and therefore decreases the overall activity by suppressing both the selective (r 1 ) and unselective (r 2 ) pathways. 47,77,79,80 A secondary effect of chlorine promotion leads to a suppression of the secondary, unselective reaction (r 3 ); the decomposition of ethylene oxide to form carbon dioxide and water. 79,81 In a typical epoxidation reactor a feed containing oxygen, ethylene and ppm-levels of the chlorine moderator in an inert diluent gas is fed over the reactor at 200 -280 °C at 15 bar. 55,72 The reactor is designed to have good control over the temperature as to prevent hot-spots. 82 The oxygen content is important to maintain an oxide overlayer on the silver, which is required to obtain high selectivities. However, the oxygen content is kept below 10 % per volume to prevent the formation of explosive mixtures. 55,72,83 When the oxygen content is below this value, the ethylene concentration can be maintained at a relatively high value of 30 -40 vol% safely. 55,72,83 As selectivity decreases with conversion, the (ethylene) conversion is kept low to maintain a high yield. Commercially, a yield of 1 -3 vol% EO is viable. 55 Modern industrial catalysts obtain selectivities toward ethylene oxide of 90 % 77,84 compared to about 50-70 % for early epoxidation catalysts. 85,86 Besides (promoted) silver catalysts, also other catalytic systems are being investigated for this reaction. [87][88][89][90] High selectivities towards ethylene oxide are reported by Jankowiak and Barteau for CuAg bimetallic catalysts, 89,91 and later also for AgPd bimetallic catalysts. 87 Due to the bimetallic nature of these catalysts, the environment during reaction can greatly influence composition of the catalyst surface, as for example in the CuAg catalysts segregation of the metals occurs under reaction conditions. 92,93 Depending on the metal ratios and reaction conditions, alloying, but also promotion, additional metals can therefore be either beneficial or unfavorable for the catalytic performance of the silver catalyst. 88,92,93 As silver is capable of selectively oxidizing ethylene, the simplest olefin, it seems straightforward that this system is also an interesting candidate for the epoxidation of other olefins. However, silver appears to be unable to selectively oxidize higher olefins in gas phase, due to activation of the β-hydrogen (one of the hydrogen atoms b...

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