Conversion of methanol to hydrocarbons over zeolite H-ZSM-5: On the origin of the olefinic species

Bjørgen, Morten; Svelle, Stian; Joensen, Finn; Nerlov, Jesper; Kolboe, Stein; Bonino, Francesca; Palumbo, Luisa; Bordiga, Silvia; Olsbye, Unni

doi:10.1016/j.jcat.2007.04.006

Cited by 941 publications

(846 citation statements)

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“…During steady state MTH conversion, the operation of a hydrocarbon pool mechanism which regulates product distribution over zeolite catalysts is dominant [14,15]. Within this hydrocarbon pool framework, two catalytic cycles have been readily distinguished: an alkene cycle and an aromatic cycle.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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The desorption of methanol and dimethyl ether has been studied over fresh and hydrocarbon-occluded ZSM-5 catalysts with Si/Al ratios of 25, 36 and 135 using a temporal analysis of products reactor. The catalysts were characterized by XRD, SEM, N 2 physisorption and pyridine FT-IR. The crystal size increases with Si/Al ratio from 0.10 to 0.78 µm. The kinetic parameters were obtained using the Redhead method and a plug flow reactor model with coupled convection, adsorption and desorption steps. ZSM-5 catalysts with Si/Al ratios of 25 and 36 exhibit three adsorption sites (low, medium, and high temperature sites), while there is no difference between medium and high temperature sites at a Si/Al ratio of 135. Molecular adsorption on the low temperature site and dissociative adsorption on the medium and high temperature sites give a good match between experiment and the plug flow reactor model. The DME desorption activation energy was systematically higher than that of methanol. Adsorption stoichiometry shows that methanol and DME form clusters onto the binding sites. When non-activated re-adsorption is accounted for, a local equilibrium is reached only on the low and medium temperature binding sites. No differences were observed, other than in site densities, when extracting the kinetic parameters for fresh and activated ZSM-5 catalysts at full coverage. Graphical AbstractElectronic supplementary material The online version of this article (https://doi

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Section: Introductionmentioning

confidence: 99%

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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“…3a-c) obtained in each reaction, showing formation of olefins is not thermodynamically favoured under the applied conditions. In the temperature range of 300-500°C, which was indicated to donate large portions of C 2 -C 4 olefins in the previous researches, [3,5,12,19], ethylene selectivity is higher than other two olefin types, and shows a gradually increasing trend. It seems C 4 H 8 (1-butene) is greatly supressed in each case, as reflected by the observed data.…”

Section: Computer-aided Simulations For Three Reactions Of Differentmentioning

confidence: 79%

“…Although the MTH mechanism is in a great complexity, thermodynamics are not affected by the reaction routes. The selected 25 reactions have covered all the directions from methanol to the major MTH products (C 1 -C 9 ) with essential product intra-conversions, and are supposed to happen in a real MTH system proceeding in timeon-stream [11,12]. Particularly, we have further separated the isomers of xylene and tri-methylbenzene, for a more comprehensive study than the previous works, and a consideration that para-xylene might be the most favourable product in the methanol to aromatics process via H-ZSM-5 zeolite [4,8,9].…”

Section: Initial Work-thermodynamic Calculations On Selected Sub Reacmentioning

confidence: 99%

“…However, our assumption is based on the 'hydrocarbon-pool' cycle, which has been considered as the origin of series of MTH reactions and gives C 2 -C 4 olefins and methyl-aromatics as the primary products [4]. Further consideration is given to the fact that latter stage hydrogen transfer may convert these primary products into either saturated hydrocarbons (alkanes) or graphite species (deeply dehydrogenated cokes), and these intra-conversions indeed play an important role in deciding the following catalytic process, and the final product yields [3,4,11,12]. This simulation also takes the advantage that all of these 'hydrocarbon-pool' primary products (C 2 -C 4 olefins and C 6 -C 9 aromatics) take a large portion in the product yield of short time (a few minutes to several hours) lab reactions and industrial applications [4,5].…”

Section: Computer-aided Simulations For Three Reactions Of Differentmentioning

confidence: 99%

“…According to the hydrocarbon pool theory, olefins are earlier formed in the system where aromatics (some of them are also formed in an early time as the hydrocarbon pools) and alkanes can be obtained in later H 2 transfers (intra-conversion between products, via H 2 loss/addition) [12]. It seems that the longer the olefins stay in the system, the more they are consumed.…”

Section: Introductionmentioning

confidence: 99%

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A research into the thermodynamics of methanol to hydrocarbon (MTH): conflictions between simulated product distribution and experimental results

et al. 2017

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Thermodynamic calculations and analysis were carried out for a rational understanding of the results from selected laboratory MTH reactions. Simulations without solid carbons (coke), CO, CO 2 and light alkanes target on the yield of olefin and aromatic products, which has been found better referenced to the real experimental observations that occur in time-on-stream (TOS). The confliction between simulated data and real experimental results is presumably ascribed to the limited dwelling time of products in the reaction system. Hydrocarbon pool based reactions donate olefins and methyl-benzenes as primary products in a continuous-flow MTH reaction; when the dwelling time of product extends intra-conversions (H 2 transfers) between products would further adjust the composition of MTH yield, in which case alkanes and aromatic products (cokes precursors) increase. In the case of intraconversions are ignored due to limited product dwelling time, thermodynamic calculation on Gibbs free energy change of selected sub reactions shows fairly close results to the real experimental data, which well supports the above explanations. This work highlights the importance of proper choosing target products and/or sub reactions for a rational thermodynamic prediction of MTH product distribution obtained in time-on-stream.Keywords Methanol to hydrocarbon Á Hydrocarbon pool mechanism Á Thermodynamic Á Intra-conversion Á Dwelling time IntroductionAt present, the pathways of methanol to hydrocarbon reaction especially the formation of first C-C bond are still in debate. The most acceptable hypothesis by far relies on the mechanism based on a 'hydrocarbon pool' [1]. In this theory, limited trace amount of hydrocarbons introduced as impurities in the methanol feedstock formed the initial aromatics (some benzene ring structures), which play a key role as the 'scaffold' in later process [2]. Methyl groups are added onto the hydrocarbon pool molecules in alkylation steps and light olefins are subsequently formed by the corresponding de-alkylation steps. The initial olefins can be converted into alkanes by occupying H 2 , whereas continuous loss of H 2 , followed by the cyclization steps forms more aromatics [3][4][5]. In a mature MTH system, series of the above reactions proceed in a parallel way and, therefore, bring in a complexity to the products and orders of their formation; however, thermodynamics always say coke (extremely dehydrogenated products, or solid carbons) is the dominating product in MTH and most other hydrocarbon transformations [6]. Before the reaction reaches a final format of solid carbons [C (s) ], Electronic supplementary material The online version of this article

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Methanol to Lower Olefins and Methanol to Propylene

Wang

Wei

2017

Multiphase Reactor Engineering for Clean and Low‐Carbon Energy Applications

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Conversion of methanol to hydrocarbons over zeolite H-ZSM-5: On the origin of the olefinic species

Cited by 941 publications

References 42 publications

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

A research into the thermodynamics of methanol to hydrocarbon (MTH): conflictions between simulated product distribution and experimental results

Methanol to Lower Olefins and Methanol to Propylene

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