Aromatization of Light Alkanes

O’Connor, C.T.

doi:10.1002/9783527610044.hetcat0157

Cited by 4 publications

(4 citation statements)

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“…Increasing shale gas production in the United States has incentivized the conversion of light alkanes derived from shale gas to alkenes and aromatics, primarily benzene, toluene, and xylenes (BTX). BTX are traditionally produced via catalytic reforming of naphtha and are important feedstocks for the production of plastics, fibers, resins, and films. − Prior work has shown that dehydroaromatization involves initial alkane dehydrogenation to form alkenes, which then undergo oligomerization, cyclization, and further dehydrogenation to form the final aromatic products. Lewis acidic metal cations exchanged into zeolites are used industrially to catalyze the dehydrogenation and subsequent aromatization of light alkanes.…”

Section: Introductionmentioning

confidence: 99%

“…Lewis acidic metal cations exchanged into zeolites are used industrially to catalyze the dehydrogenation and subsequent aromatization of light alkanes. In particular, BP/UOP’s Cyclar process utilizes Ga/H-MFI zeolites for the dehydroaromatization of C 3 –C 4 alkanes. − While Ga/H-MFI has been explored extensively for this purpose, the Ga hydride species contained in this catalyst ([GaH] 2+ and [Ga(H) 2 ] + cations) are active for alkane cracking as well as dehydrogenation. − For this reason, and because Ga is a relatively expensive element, efforts have been undertaken to find a more earth-abundant element and one that would exhibit low selectivity to alkane cracking.…”

Section: Introductionmentioning

confidence: 99%

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Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl₂

2021

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Light alkanes in shale gas are an attractive source of carbon for the production of alkenes and aromatics compared to petroleum-derived naphtha. Zinc-exchanged zeolite H-MFI (Zn/ H-MFI) is active and selective for light alkane dehydrogenation and dehydroaromatization. In this study, Zn/H-MFI with varying Zn/Al ratios was prepared via solid-state ion exchange (SSIE) of ZnCl 2 and characterized by various methods. As-prepared Zn/H-MFI with Zn/Al ≤ 0.52 contains isolated [ZnCl] + and [ZnCl-(HCl)] + species; Zn/H-MFI with higher Zn loadings also contains ZnAl 2 O 4 /ZnAl 2 O 4−x Cl 2x nanoclusters. Postsynthetic treatment in He and subsequently in 2.5% H 2 in He at 773 K removes Cl and adsorbed HCl, resulting in the formation of [ZnH] + cations. Studies of C 3 H 8 dehydrogenation and cracking suggest that in the absence of cofed H 2 , [ZnH] + cations are transformed to bridging Zn 2+ cations, which exhibit higher C 3 H 8 dehydrogenation activity and selectivity relative to [ZnH] + cations. The kinetics of dehydrogenation and cracking over Zn/H-MFI were investigated as a function of Zn loading, C 3 H 8 partial pressure, and temperature. The turnover frequency for propane dehydrogenation and cracking increases with Zn loading, which we propose is due to localization of Zn 2+ cations either at increasingly distant pairs of Al atoms or at the β-site in the MFI framework. The selectivity to dehydrogenation over cracking over Zn 2+ is independent of C 3 H 8 partial pressure and temperature, consistent with dehydrogenation and cracking pathways that proceed via a common surface intermediate and have similar enthalpies of activation. The product distribution is thus determined by the entropy of activation for each pathway, which is less negative in the case of C 3 H 8 dehydrogenation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl₂

2021

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“…Ethane and propane present in the condensable part of shale gas are important feedstocks for the production of aromatics, namely, benzene, toluene, and xylenes, which serve as raw materials for the production of plastics and pharmaceuticals. − Industrial processes, such as Aromax (Chevron), Aroforming (IFP/Salutec), Cyclar (BP/UOP), and Z-Forming (Mitsubishi Oil and Chiyoda), typically utilize zeolite catalysts for alkane dehydroaromatization . In particular, gallium-exchanged H-MFI zeolites (Ga/H-MFI), employed in the Cyclar process, are active and selective for light alkane dehydroaromatization.…”

Section: Introductionmentioning

confidence: 99%

“…1−4 Industrial processes, such as Aromax (Chevron), Aroforming (IFP/Salutec), Cyclar (BP/UOP), and Z-Forming (Mitsubishi Oil and Chiyoda), typically utilize zeolite catalysts for alkane dehydroaromatization. 3 In particular, galliumexchanged H-MFI zeolites (Ga/H-MFI), employed in the Cyclar process, 3 are active and selective for light alkane dehydroaromatization.…”

Section: Introductionmentioning

confidence: 99%

Role of Ga³⁺Sites in Ethene Oligomerization over Ga/H-MFI

Nozik

Bell

2022

ACS Catal.

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Because of their relatively low cost, ethane and propane derived from shale gas are the currently preferred feedstocks for the production of aromatics. Ga-exchanged H-MFI zeolite (Ga/H-MFI) exhibits high activity and selectivity for light alkane dehydroaromatization, a process that involves alkane dehydrogenation to form alkenes, followed by alkene oligomerization and cyclization, and further dehydrogenation of the resulting products. Recent work has shown (Phadke et al. Characterization of Isolated Ga3+ Cations in Ga/H-MFI Prepared by Vapor-Phase Exchange of H-MFI Zeolite with GaCl3. ACS Catal. 2018, 8, 6106–6126; Phadke et al. Mechanism and Kinetics of Propane Dehydrogenation and Cracking over Ga/H-MFI Prepared via Vapor-Phase Exchange of H-MFI with GaCl3. J. Am. Chem. Soc. 2019, 141, 1614–1627; Phadke et al. Mechanism and Kinetics of Light Alkane Dehydrogenation and Cracking over Isolated Ga Species in Ga/H-MFI. ACS Catal. 2021, 11, 2062–2075; Mansoor et al. ACS Catal. 2018, 8, 2146–6162) that Ga3+ ([GaH]2+ and [Ga(H)2]+) sites catalyze the initial dehydrogenation of alkanes; however, the role of Ga3+ sites in the subsequent alkene oligomerization step requires clarification. In this work, the kinetics of ethene oligomerization over Ga/H-MFI were investigated as a function of Ga loading, feed space time, temperature, and ethene partial pressure. The presence of Ga3+ sites gives rise to enhanced rates of ethene oligomerization and higher selectivities to butene and hexene relative to H-MFI. However, selective titration of Brønsted acid sites with NH3 reveals that, in the absence of Brønsted acid sites, [GaH]2+ and [Ga(H)2]+ cations do not contribute appreciably to the higher activity of Ga/H-MFI. Similarly, in situ Fourier-transform infrared spectroscopy shows that the reaction pathway for ethene oligomerization over Ga/H-MFI involves the same intermediates as that over H-MFI. The higher ethene oligomerization activity and selectivity to even-carbon-numbered alkenes of Ga/H-MFI stems from cooperative effects between Ga3+ sites and Brønsted acid protons.

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Aromatization of C₅‐rich Light Naphtha Feedstock over Tailored Zeolite Catalysts: Comparison with Model Compounds (n‐C₅ ‐ n‐C₇)

et al. 2016

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In this work, aromatization of C 5 -rich light naphtha as feedstock obtained from the refinery of Hindustan Petroleum Corporation Ltd. (HPCL) was studied along with n-hexane (model compound for light naphtha) over non-noble metal oxide based catalyst; ZnGa/ZSM-5. Zeolite ZSM-5 was modified with zinc and gallium by co-impregnation method. High aromatic yields were obtained over modified ZSM-5 catalysts due to dissociative chemisorption of alkanes resulting in dehydrogenation/ aromatization. The effect of acid sites on aromatization was studied by varying SiO 2 /Al 2 O 3 ratio (SAR) of ZSM-5 and correlated with the temperature programmed desorption of am-monia (NH 3 -TPD) studies. Optimized catalyst composition was further used for aromatization of n-pentane, n-heptane and light naphtha from a refinery. The Zn-GaÀH-ZSM-5 catalyst produced aromatics in high yields (64.8 % for light naphtha), especially high quantities of toluene with toluene/benzene ratio (T/ B)~2. From the aromatization studies, it could be envisaged that a proper balance of acid sites with dehydrogenation function is required to achieve maximum aromatic yield. Nitrogen was found to be a better carrier gas compared to hydrogen for aromatization of light naphtha.

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Aromatization of Light Alkanes

Abstract: The sections in this article are Introduction Thermodynamics of Alkane Aromatization Catalysts Ga / HZSM ‐5 Pt / KL Other Catalysts for Alkane Aromatization … Show more

Cited by 4 publications

References 70 publications

Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl₂

Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl₂

Role of Ga³⁺Sites in Ethene Oligomerization over Ga/H-MFI

Aromatization of C₅‐rich Light Naphtha Feedstock over Tailored Zeolite Catalysts: Comparison with Model Compounds (n‐C₅ ‐ n‐C₇)

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Aromatization of Light Alkanes

Abstract: The sections in this article are Introduction Thermodynamics of Alkane Aromatization Catalysts Ga / HZSM ‐5 Pt / KL Other Catalysts for Alkane Aromatization … Show more

Cited by 4 publications

References 70 publications

Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl2

Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl2

Role of Ga3+Sites in Ethene Oligomerization over Ga/H-MFI

Aromatization of C5‐rich Light Naphtha Feedstock over Tailored Zeolite Catalysts: Comparison with Model Compounds (n‐C5 ‐ n‐C7)

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Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl₂

Propane Dehydrogenation and Cracking over Zn/H-MFI Prepared by Solid-State Ion Exchange of ZnCl₂

Role of Ga³⁺Sites in Ethene Oligomerization over Ga/H-MFI

Aromatization of C₅‐rich Light Naphtha Feedstock over Tailored Zeolite Catalysts: Comparison with Model Compounds (n‐C₅ ‐ n‐C₇)