Coke formation in high-silica zeolites

Bibby, D.M.; Howe, Russell F.; Mclellan, G.D.

doi:10.1016/0926-860x(92)80291-j

Cited by 236 publications

(118 citation statements)

References 114 publications

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“…In addition, a range of factors will affect the composition of coke, including the nature of the reactants, time on-stream, temperature, acid site concentration and the location of the coke deposit [15,22,34,38]. Therefore, coke will have a broad range of compositions, determined by these different factors.…”

Section: Hydrothermal Stability Of Zsm-5mentioning

confidence: 99%

Maximizing propylene production via FCC technology

2015

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This review looks at the main processes available for the production of light olefins with a focus on maximizing the production of propylene. Maximization of propylene production has become the focus of most refineries because it is in high demand and there is a supply shortage from modern steam crackers, which now produce relatively less propylene. The flexibility of the fluid catalytic cracking (FCC) to various reaction conditions makes it possible as one of the means to close the gap between supply and demand. The appropriate modification of the FCC process is accomplished by the synergistic integration of the catalyst, temperature, reaction-residence time, coke make, and hydrocarbon partial pressure. The main constraints for maximum propylene yield are based on having a suitable catalyst, suitable reactor configuration and reaction conditions.

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Section: Hydrothermal Stability Of Zsm-5mentioning

confidence: 99%

Maximizing propylene production via FCC technology

2015

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“…This reaction is involved in the propagation of the catalytic cycle of cracking 1,2 and alkylation 3 of hydrocarbons, as well as in the formation of aromatic hydrocarbons 4 in gasoline and coke, 5,6 which are carbonaceous materials deposit over the catalyst surface that may lead to loss of activity. Conceptually, HT involves the bimolecular transfer of a hydride from an alkane to a carbenium ion (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

A theoretical study of the hydride transfer between 1-Adamantyl cation and isopentane

Oliveira¹,

Rosenbach²,

Santos³

et al. 2010

J. Braz. Chem. Soc.

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Foi realizado um estudo teórico da transferência de hidreto entre o cátion 1-adamantila e isopentano, usando a teoria do funcional da densidade em nível PBE1PBE/6-31G (d,p). Os resultados indicaram que há formação de um íon carbônio como intermediário, que é mais estável que os complexos de van der Waals entre os íons carbênios e os alcanos. Os fatores entrópicos são bastante importantes e sobrepujam o termo entálpico à temperatura ambiente.A density functional teory study of the hydride transfer between 1-adamantyl cation and isopentane has been performed at the PBE1PBE/6-31G(d,p) theoretical level. The results indicate that a carbonium ion is involved as intermediate and is more stable than the van der Waals complexes between the carbenium ions and the alkanes. Entropic factors are important and overcome the enthalpic term at room temperature. Keywords: hydride transfer, carbocations, adamantane, isopentane IntroductionIntermolecular or bimolecular hydride transfer (HT) is a crucial step in acid-catalyzed hydrocarbon transformations. This reaction is involved in the propagation of the catalytic cycle of cracking 1,2 and alkylation 3 of hydrocarbons, as well as in the formation of aromatic hydrocarbons 4 in gasoline and coke, 5,6 which are carbonaceous materials deposit over the catalyst surface that may lead to loss of activity. Conceptually, HT involves the bimolecular transfer of a hydride from an alkane to a carbenium ion (Scheme 1). R⊕ + R'-H → R-H + R'⊕ Scheme 1. Schematic representation of hydride transfer reactions.In the gas phase, HT is much slower than proton transfer 7 and shows a negative temperature dependence. [8][9][10] The reaction is believed to occur via formation of a "tight" complex, 11,12 whose structure may resemble a carbonium ion, 13 formed by the interaction of the empty p-orbital of a carbenium ion with the C-H bond of the alkane. The reaction is used 14,15 to assess the carbenium ion stability in the gas phase.In condensed phase, especially on zeolites and other solid acid catalysts, there are few studies regarding hydride transfer. 16,17 Product distribution obtained from bimolecular alkane reactions is potentially interesting for the evaluation of the HT capability of solid acids. However, the validity of the results depends on the system chosen as model reaction. Indeed, variation of the hydride acceptor seems to affect the rates of hydride transfer to a considerably greater extent, than an equal change of the thermodynamic driving force caused by variation of the hydride donor. 18 In addition, some systems involve simultaneous reactions competing with HT, and may significantly affect the interpretation of the results.The 1-adamantyl cation is a stable species 19 and can be synthesized from the 1-adamantanol and fluorosulfonic acid-antimony pentafluoride. 20 On the zeolite surface, this species can be also generated from its halide. 21 In addition de Oliveira et al. 2181 Vol. 21, No. 12, 2010 to the stabilization by sC-C bond hyperconjugation, the 1-adamantyl cation has a cage ...

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“…The selective preparation of para substituted for benzene derivatives by means of various modified zeolite catalysts has been reported [7][8][9]. In particular, ZSM-5 class zeolites have been of considerable interest because the channel dimensions are approximately the same as the molecular dimensions of many aromatic molecules.…”

Section: Introductionmentioning

confidence: 99%

Development of Alkylation Toluene with Methanol for Fuel on Modified ZSM-5 Zeolites by Amphoteric Surfactant

Morsi¹,

Omar²,

Almehbad³

2014

JSEMAT

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Methylation of toluene over ZSM-5 zeolites modified by the introduction of Sr of 2.5%, 5%, and 10% by weight was studied. Experiments were performed in a fixed bed under the conditions of reaction temperatures between 300˚C -500˚C, liquid hour space velocity of 4 g toluene/h.g catalyst, methanol to toluene ratio 4:1, and 0.01% of N-Octyl-N-benzyl-N-methylglycine as emulsifier. Data for conversion of toluene and selectivity towards xylene isomers showed that 2.5% Sr/ZSM-5 catalyst has the highest conversion of toluene at 500˚C, and the lowest p-xylene selectivity, while 10% Sr/ZSM-5 catalyst has the highest selectivity for p-xylene production. Nevertheless, the catalyst 2.5% Sr/ZSM-5 has the highest selectivity for m-xylene. The two catalysts 2.5% and 5% Sr/ZSM-5 give nearly the same selectivity for the three xylene isomers at all conversions obtained at the reaction conditions under study.

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Coke formation in high-silica zeolites

Cited by 236 publications

References 114 publications

Maximizing propylene production via FCC technology

Maximizing propylene production via FCC technology

A theoretical study of the hydride transfer between 1-Adamantyl cation and isopentane

Development of Alkylation Toluene with Methanol for Fuel on Modified ZSM-5 Zeolites by Amphoteric Surfactant

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