Study of coke deposition phenomena on the SAPO_34 catalyst and its effects on light olefin selectivity during the methanol to olefin reaction
TL;DR: In this article, a combined measurement of product selectivity with coke deposition has been performed in order to study the deactivation of SAPO_34 during methanol conversion to light olefins, emphasizing the effects of coke formation on the product selectivities as well as investigating the parameters affecting coke forming.
Abstract: In the current contribution a combined measurement of product selectivity with coke deposition has been performed in order to study the deactivation of SAPO_34 during methanol conversion to light olefins, emphasizing the effects of coke formation on the product selectivities as well as investigating the parameters affecting coke formation. The shape selective effect of coke formation favors lighter hydrocarbon products and, depending on the reaction conditions, 14 wt% to 23 wt% coke content in a zeolite bed is suggested to be an appropriate range in terms of light olefin production. Comparing hydrogen transfer index (defined as [alkane/(alkene + alkane)] for Cn species) as an indicator of the aromatic formation with coke content of the catalyst led to a meaningful relationship in which the coke deposition behavior could be predicted through the hydrogen transfer index change during the methanol to olefin reaction. Analysis of the coke compounds revealed that, by increasing the temperature and as the time-on-stream went on, the relative distribution of soluble/insoluble coke shifted towards insoluble coke. Depending on the species formed at different reaction temperatures, the coke species removal by air treatment varies between the temperatures of 550–930 K. A mathematical relationship between the initial reaction conditions and time-on-stream with the average coke content is proposed as a deactivation model and verified.
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TL;DR: A strategy integrating advanced mass spectroscopy and isotope labeling to uncover a cage-passing molecular route of coking species in molecular sieve catalysts for aromatic hydrocarbon evolution is provided.
Abstract: Extension and clustering of polycyclic aromatic hydrocarbons (PAHs) are key mechanistic steps for coking and deactivation in catalysis reactions. However, no unambiguous mechanistic picture exists on molecule-resolved PAHs speciation and evolution, due to the immense experimental challenges in deciphering the complex PAHs structures. Herein, we report an effective strategy through integrating a high resolution MALDI FT-ICR mass spectrometry with isotope labeling technique. With this strategy, a complete route for aromatic hydrocarbon evolution is unveiled for SAPO-34-catalyzed, industrially relevant methanol-to-olefins (MTO) as a model reaction. Notable is the elucidation of an unusual, previously unrecognized mechanistic step: cage-passing growth forming cross-linked multi-core PAHs with graphene-like structure. This mechanistic concept proves general on other cage-based molecule sieves. This preliminary work would provide a versatile means to decipher the key mechanistic step of molecular mass growth for PAHs involved in catalysis and combustion chemistry. Coke-induced catalyst deactivation draws increasing concerns in industrially catalytic processes. Here the authors provide a strategy integrating advanced mass spectroscopy and isotope labeling to uncover a cage-passing molecular route of coking species in molecular sieve catalysts.
68 citations
TL;DR: In this article, the authors introduced oxygen vacancies into Nb2O5 via thermal treatment at 700°C under oxygen-deficient conditions for different lengths of time, and showed that increasing the number of oxygen vacancies was found to increase the catalytic activity.
66 citations
TL;DR: Sub-micrometric sized SAPO-34 crystallites were successfully synthesized by a facile surfactant-assisted hydrothermal synthesis route and cetyltrimethylammonium bromide (CTAB) was used as a crystal growth inhibitor (CGI) and it was found that the crystal size changes in the V shape with the increase in the amount of CTAB.
Abstract: SAPO-34 shows higher light olefin selectivity in the reaction of methanol to olefin (MTO), but its small pore system implies diffusion limitations to bigger molecular products and results in coking too. To inhibit these limitations, sub-micrometric sized SAPO-34 crystallites were successfully synthesized by a facile surfactant-assisted hydrothermal synthesis route, in which cetyltrimethylammonium bromide (CTAB) was used as a crystal growth inhibitor (CGI). It was found that the crystal size changes in the V shape with the increase in the amount of CTAB. The sub-micrometric sized sample (SP-0.02CTAB) was obtained when the molar ratio of CTAB to Al2O3 was 0.02 in a precursor gel. The SP-0.02CTAB catalyst presents excellent performance for the MTO reaction with 97.8% C2-C4 selectivity and 3 times longer lifetime than the conventional SAPO-34 sample (SP-Conv), which is attributed to its much higher surface area and enhanced acidity derived from the formation of the sub-micrometric sized crystallites. Further study about the appropriate time of CTAB addition demonstrates that CTAB can play its role as a crystal growth inhibitor effectively, only when it is added at the very initial stage of the crystallization process.
30 citations
TL;DR: In this paper, a review of catalytic pyrolysis of plastics, which has been identified as a promising process for waste revalorization, is given particular attention.
Abstract: In catalytic industrial processes, coke deposition remains a major drawback for solid catalysts use as it causes catalyst deactivation. Extensive study of this phenomenon over the last decades has provided a better understanding of coke behavior in a great number of processes. Among them, catalytic pyrolysis of plastics, which has been identified as a promising process for waste revalorization, is given particular attention in this paper. Combined economic and environmental concerns rose the necessity to restore catalytic activity by recovering deactivated catalysts. Consequently, various regeneration processes have been investigated over the years and development of an efficient
and sustainable process remains an industrial challenge. Coke removal can be achieved via several chemical processes, such as oxidation, gasification, and hydrogenation. This review focuses on oxidative treatments for catalyst regeneration, covering the current progress of oxidation treatments and presenting advantages and drawbacks for each method. Molecular oxidation with oxygen and ozone, as well as advanced oxidation processes with the formation of OH radicals, are detailed to provide a deep understanding of the mechanisms and kinetics involved (direct and indirect oxidation, reaction rates and selectivity, diffusion, and mass transfer). Finally, this paper summarizes all relevant
analytical techniques that can be used to characterize deactivated and regenerated solid catalysts: XRD, N2 adsorption-desorption, SEM, NH3-TPD, elemental analysis, IR. Analytical techniques are classified according to the type of information they provide, such as structural characteristics, elemental composition, or chemical properties. In function of the investigated property, this overall tool is useful and easy-to-use to determine the adequate analysis.
30 citations
TL;DR: In this paper, the deactivation of a SAPO-34 catalyst in the course of the methanol-to-olefin conversion has been studied in a slurry reactor in polydimethylsiloxane medium and compared with that in a fixed-bed reactor.
28 citations
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30 Jun 1972TL;DR: An overview of Chemical Reaction Engineering is presented, followed by an introduction to Reactor Design, and a discussion of the Dispersion Model.
Abstract: Partial table of contents: Overview of Chemical Reaction Engineering. HOMOGENEOUS REACTIONS IN IDEAL REACTORS. Introduction to Reactor Design. Design for Single Reactions. Design for Parallel Reactions. Potpourri of Multiple Reactions. NON IDEAL FLOW. Compartment Models. The Dispersion Model. The Tank--in--Series Model. REACTIONS CATALYZED BY SOLIDS. Solid Catalyzed Reactions. The Packed Bed Catalytic Reactor. Deactivating Catalysts. HETEROGENEOUS REACTIONS. Fluid--Fluid Reactions: Kinetics. Fluid--Particle Reactions: Design. BIOCHEMICAL REACTIONS. Enzyme Fermentation. Substrate Limiting Microbial Fermentation. Product Limiting Microbial Fermentation. Appendix. Index.
8,257 citations
TL;DR: This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.
Abstract: Liquid hydrocarbon fuels play an essential part in the global energy chain, owing to their high energy density and easy transportability. Olefins play a similar role in the production of consumer goods. In a post-oil society, fuel and olefin production will rely on alternative carbon sources, such as biomass, coal, natural gas, and CO(2). The methanol-to-hydrocarbons (MTH) process is a key step in such routes, and can be tuned into production of gasoline-rich (methanol to gasoline; MTG) or olefin-rich (methanol to olefins; MTO) product mixtures by proper choice of catalyst and reaction conditions. This Review presents several commercial MTH projects that have recently been realized, and also fundamental research into the synthesis of microporous materials for the targeted variation of selectivity and lifetime of the catalysts.
1,379 citations
TL;DR: The literature related to methanol-to-hydrocarbons (MTHC) technology over the past two decades has been reviewed, covering mainly the MTO and MTG reactions as mentioned in this paper.
1,283 citations
TL;DR: In this paper, a brief summary of the key issues for the methanol-to-olefins (MTO) reaction is given, including studies on the reaction mechanism, molecular sieve synthesis and crystallization mechanism, catalyst and its manufacturing scale-up, reactor selection and reactor scaleup, process demonstration, and commercialization.
Abstract: The methanol-to-olefins (MTO) reaction is an interesting and important reaction for both fundamental research and industrial application. The Dalian Institute of Chemical Physics (DICP) has developed a MTO technology that led to the successful construction and operation of the world’s first coal to olefin plant in 2010. This historical perspective gives a brief summary on the key issues for the process development, including studies on the reaction mechanism, molecular sieve synthesis and crystallization mechanism, catalyst and its manufacturing scale-up, reactor selection and reactor scale-up, process demonstration, and commercialization. Further challenges on the fundamental research and the directions for future catalyst improvement are also suggested.
1,174 citations
TL;DR: Using other microporous catalysts that are selective for light olefins, methanol-to-olefin (MTO) catalysis may soon become central to the conversion of natural gas to polyolefins.
Abstract: The process of converting methanol to hydrocarbons on the aluminosilicate zeolite HZSM-5 was originally developed as a route from natural gas to synthetic gasoline. Using other microporous catalysts that are selective for light olefins, methanol-to-olefin (MTO) catalysis may soon become central to the conversion of natural gas to polyolefins. The mechanism of methanol conversion proved to be an intellectually challenging problem; 25 years of fundamental study produced at least 20 distinct mechanisms, but most did not account for either the primary products or a kinetic induction period. Recent experimental and theoretical work has firmly established that methanol and dimethyl ether react on cyclic organic species contained in the cages or channels of the inorganic host. These organic reaction centers act as scaffolds for the assembly of light olefins so as to avoid the high high-energy intermediates required by all “direct” mechanisms. The rate of formation of the initial reaction centers, and hence the d...
844 citations