A mechanistic basis for the effects of crystallite size on light olefin selectivity in methanol-to-hydrocarbons conversion on MFI

Rachit Khare; Dean Millar; Aditya Bhan

doi:10.1016/j.jcat.2014.10.016

A mechanistic basis for the effects of crystallite size on light olefin selectivity in methanol-to-hydrocarbons conversion on MFI

Rachit Khare
, Dean Millar
, Aditya Bhan

Chemical Engineering and Materials Science

Research output: Contribution to journal › Article › peer-review

171 Scopus citations

Abstract

Light olefin selectivity in methanol-to-hydrocarbons conversion on MFI increases with an increase in crystallite size because intra-crystalline residence time of methylbenzenes increases as a consequence of increased transport restrictions, which enables these methylbenzenes to undergo multiple methylation/dealkylation reactions before exiting the crystal. Selectivity toward light olefins, for the reaction of dimethyl ether (DME) at 623 K, increased monotonically from 22% in 2 nm-MFI (∼2 nm crystallites) to 47% in 17 μm-MFI (∼17 μm crystallites) at 46-59% net DME conversion. Transport restrictions were introduced externally in a conventional MFI sample (500 nm-MFI) by single-/multi-cycle silylation using tetraethyl orthosilicate. Light olefin selectivity, for the reaction of DME at 623 K and at 46-59% net DME conversion, increased from 33% in the conventional MFI sample to 49% in a sample that had undergone three silylation treatments. Adsorption uptake measurements of 2,2-dimethylbutane were used to estimate the "effective" crystallite size of the silylated MFI samples. Total light olefin selectivity and ethene/(2-methyl-2-butene + 2-methylbutane) increased monotonically with the effective crystallite size for all zeolite samples used in this study, irrespective of their provenance, thereby suggesting that the mechanistic basis for increase in light olefin selectivity with increasing crystallite size is the enhanced propagation of aromatics-based catalytic cycle.

Original language	English (US)
Pages (from-to)	23-31
Number of pages	9
Journal	Journal of Catalysis
Volume	321
DOIs	https://doi.org/10.1016/j.jcat.2014.10.016
State	Published - Jan 1 2015

Bibliographical note

Funding Information:
The authors acknowledge financial support from The Dow Chemical Company and National Science Foundation (CBET 1055846). The authors also acknowledge Prof. Dongxia Liu, University of Maryland, for the synthesis and characterization of 40 nm-MFI and 17 μm-MFI samples, and Ms. Dandan Xu, University of Minnesota, for the synthesis of 2 nm-MFI sample. The authors also acknowledge Mr. Neel Rangnekar, University of Minnesota, for help with the SEM analysis of zeolites, which was carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.

Keywords

Crystallite size
Ethene selectivity
Light olefin selectivity
MFI
Methanol-to-hydrocarbons
Methanol-to-olefins
Zeolites

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10.1016/j.jcat.2014.10.016

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title = "A mechanistic basis for the effects of crystallite size on light olefin selectivity in methanol-to-hydrocarbons conversion on MFI",

abstract = "Light olefin selectivity in methanol-to-hydrocarbons conversion on MFI increases with an increase in crystallite size because intra-crystalline residence time of methylbenzenes increases as a consequence of increased transport restrictions, which enables these methylbenzenes to undergo multiple methylation/dealkylation reactions before exiting the crystal. Selectivity toward light olefins, for the reaction of dimethyl ether (DME) at 623 K, increased monotonically from 22\% in 2 nm-MFI (∼2 nm crystallites) to 47\% in 17 μm-MFI (∼17 μm crystallites) at 46-59\% net DME conversion. Transport restrictions were introduced externally in a conventional MFI sample (500 nm-MFI) by single-/multi-cycle silylation using tetraethyl orthosilicate. Light olefin selectivity, for the reaction of DME at 623 K and at 46-59\% net DME conversion, increased from 33\% in the conventional MFI sample to 49\% in a sample that had undergone three silylation treatments. Adsorption uptake measurements of 2,2-dimethylbutane were used to estimate the {"}effective{"} crystallite size of the silylated MFI samples. Total light olefin selectivity and ethene/(2-methyl-2-butene + 2-methylbutane) increased monotonically with the effective crystallite size for all zeolite samples used in this study, irrespective of their provenance, thereby suggesting that the mechanistic basis for increase in light olefin selectivity with increasing crystallite size is the enhanced propagation of aromatics-based catalytic cycle.",

keywords = "Crystallite size, Ethene selectivity, Light olefin selectivity, MFI, Methanol-to-hydrocarbons, Methanol-to-olefins, Zeolites",

author = "Rachit Khare and Dean Millar and Aditya Bhan",

note = "Funding Information: The authors acknowledge financial support from The Dow Chemical Company and National Science Foundation (CBET 1055846). The authors also acknowledge Prof. Dongxia Liu, University of Maryland, for the synthesis and characterization of 40 nm-MFI and 17 μm-MFI samples, and Ms. Dandan Xu, University of Minnesota, for the synthesis of 2 nm-MFI sample. The authors also acknowledge Mr. Neel Rangnekar, University of Minnesota, for help with the SEM analysis of zeolites, which was carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. ",

year = "2015",

month = jan,

day = "1",

doi = "10.1016/j.jcat.2014.10.016",

language = "English (US)",

volume = "321",

pages = "23--31",

journal = "Journal of Catalysis",

issn = "0021-9517",

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AU - Khare, Rachit

AU - Millar, Dean

AU - Bhan, Aditya

N1 - Funding Information: The authors acknowledge financial support from The Dow Chemical Company and National Science Foundation (CBET 1055846). The authors also acknowledge Prof. Dongxia Liu, University of Maryland, for the synthesis and characterization of 40 nm-MFI and 17 μm-MFI samples, and Ms. Dandan Xu, University of Minnesota, for the synthesis of 2 nm-MFI sample. The authors also acknowledge Mr. Neel Rangnekar, University of Minnesota, for help with the SEM analysis of zeolites, which was carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program.

PY - 2015/1/1

Y1 - 2015/1/1

N2 - Light olefin selectivity in methanol-to-hydrocarbons conversion on MFI increases with an increase in crystallite size because intra-crystalline residence time of methylbenzenes increases as a consequence of increased transport restrictions, which enables these methylbenzenes to undergo multiple methylation/dealkylation reactions before exiting the crystal. Selectivity toward light olefins, for the reaction of dimethyl ether (DME) at 623 K, increased monotonically from 22% in 2 nm-MFI (∼2 nm crystallites) to 47% in 17 μm-MFI (∼17 μm crystallites) at 46-59% net DME conversion. Transport restrictions were introduced externally in a conventional MFI sample (500 nm-MFI) by single-/multi-cycle silylation using tetraethyl orthosilicate. Light olefin selectivity, for the reaction of DME at 623 K and at 46-59% net DME conversion, increased from 33% in the conventional MFI sample to 49% in a sample that had undergone three silylation treatments. Adsorption uptake measurements of 2,2-dimethylbutane were used to estimate the "effective" crystallite size of the silylated MFI samples. Total light olefin selectivity and ethene/(2-methyl-2-butene + 2-methylbutane) increased monotonically with the effective crystallite size for all zeolite samples used in this study, irrespective of their provenance, thereby suggesting that the mechanistic basis for increase in light olefin selectivity with increasing crystallite size is the enhanced propagation of aromatics-based catalytic cycle.

AB - Light olefin selectivity in methanol-to-hydrocarbons conversion on MFI increases with an increase in crystallite size because intra-crystalline residence time of methylbenzenes increases as a consequence of increased transport restrictions, which enables these methylbenzenes to undergo multiple methylation/dealkylation reactions before exiting the crystal. Selectivity toward light olefins, for the reaction of dimethyl ether (DME) at 623 K, increased monotonically from 22% in 2 nm-MFI (∼2 nm crystallites) to 47% in 17 μm-MFI (∼17 μm crystallites) at 46-59% net DME conversion. Transport restrictions were introduced externally in a conventional MFI sample (500 nm-MFI) by single-/multi-cycle silylation using tetraethyl orthosilicate. Light olefin selectivity, for the reaction of DME at 623 K and at 46-59% net DME conversion, increased from 33% in the conventional MFI sample to 49% in a sample that had undergone three silylation treatments. Adsorption uptake measurements of 2,2-dimethylbutane were used to estimate the "effective" crystallite size of the silylated MFI samples. Total light olefin selectivity and ethene/(2-methyl-2-butene + 2-methylbutane) increased monotonically with the effective crystallite size for all zeolite samples used in this study, irrespective of their provenance, thereby suggesting that the mechanistic basis for increase in light olefin selectivity with increasing crystallite size is the enhanced propagation of aromatics-based catalytic cycle.

KW - Crystallite size

KW - Ethene selectivity

KW - Light olefin selectivity

KW - MFI

KW - Methanol-to-hydrocarbons

KW - Methanol-to-olefins

KW - Zeolites

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UR - https://www.scopus.com/pages/publications/84912561341#tab=citedBy

U2 - 10.1016/j.jcat.2014.10.016

DO - 10.1016/j.jcat.2014.10.016

M3 - Article

AN - SCOPUS:84912561341

SN - 0021-9517

VL - 321

SP - 23

EP - 31

JO - Journal of Catalysis

JF - Journal of Catalysis

ER -

A mechanistic basis for the effects of crystallite size on light olefin selectivity in methanol-to-hydrocarbons conversion on MFI

Abstract

Bibliographical note

Keywords

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