Micro-kinetic Modeling as a Tool Towards Better Understanding of Hydrocarbon Cracking Chemistry Over Zeolite Catalysts PDF Download
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Author: Nitin Agarwal
Publisher:
ISBN:
Category : Actors
Languages : en
Pages : 354
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Author: Nitin Agarwal
Publisher:
ISBN:
Category : Actors
Languages : en
Pages : 354
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Author: J. A. Dumesic
Publisher: Wiley-VCH
ISBN:
Category : Language Arts & Disciplines
Languages : en
Pages : 340
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Book Description
Defines the emerging field of catalytic reaction synthesis in the search for new catalysts and catalytic processes. Illustrates how experimental data from diverse sources can be consolidated to form a quantitative description of the essential chemistry taking place on the catalyst surface. Elucidates the possible relationships between catalyst kinetic properties and surface chemical bonding properties. Offers examples of microkinetic analysis and catalytic reaction synthesis for a variety of catalytic reactions over metals, oxides, and zeolite catalysts. Illustrates the underlying strategy used to formulate a microkinetic model, calibrate the model to the existing experimental data, and assess the critical aspects of the essential surface chemistry involved in the catalytic process.
Author: Pascal Granger
Publisher: MDPI
ISBN: 303921179X
Category : Technology & Engineering
Languages : en
Pages : 214
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Book Description
Kinetics and reactor modeling for heterogeneous catalytic reactions are prominent tools for investigating and understanding catalyst functionalities at nanoscale and the related rates of complex reaction networks. This book illustrates some examples related to the transformation of simple to more complex feedstocks, including different types of reactor designs, i.e., steady-state, transient plug flow reactors, and TAP reactors for which there is sometimes a strong gap in the operating conditions from ultra-high-vacuum to high-pressure conditions. In conjunction, new methodologies have emerged, giving rise to more robust microkinetics models. As exemplified, they include the kinetics and the dynamics of the reactors and span a large range of length and time scales. The objective of this Special Issue is to provide contributions that can illustrate recent advances and novel methodologies for elucidating the kinetics of heterogeneous reactions and the necessary multiscale approach for optimizing the reactor design. This book is dedicated to postgraduate and scientific researchers, and experts in heterogeneous catalysis. It may also serve as a source of original information for the elaboration of lessons on catalysis for Master students.
Author: Mingxia Zhou
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Efficient and selective catalysis lies at the heart of many chemical reactions, enabling the synthesis of chemicals and fuels with enormous societal and technological impact. A fundamental understanding of intrinsic catalyst properties for effective manipulation of the reactivity and selectivity of industrial catalysts is essential to select proper catalysts to catalyze the reactions we want and hinder the reactions we do not want. The progress in density functional theory (DFT) makes it possible to describe interfacial catalytic reactions and predict catalytic activities from one catalyst to another. In this study, water-gas shift reaction (WGSR) was used as a model reaction. First-principles based micro-kinetic modeling has been performed to deeply understand interactions between competing reaction mechanisms, and the relationship with various factors such as catalyst materials, structures, promoters, and interactions between intermediates (e.g., CO self-interaction) that govern the observed catalytic behaviors. Overall, in this thesis, all relevant reaction mechanisms in the model reaction on well-defined active sites were developed with first-principles calculations. With the established mechanism, the promotional effect of K adatom on Ni(111) on WGSR compared to the competing methanation was understood. Moreover, the WGSR kinetic trend, with the hydrogen production rate decreasing with increasing Ni particle diameters (due to the decreasing fractions of low-coordinated surface Ni site), was reproduced conveniently from micro-kinetic modeling techniques. Empirical correlations such as Brønsted-Evans-Polanyi (BEP) relationship for O-H, and C-O bond formation or cleavage on Ni(111), Ni(100), and Ni(211) were incorporated to accelerate computational analysis and generate trends on other transition metals (e.g., Cu, Au, Pt). To improve the numerical quality of micro-kinetic modeling, later interactions of main surface reaction intermediates were proven to be critical and incorporated successfully into the kinetic models. Finally, evidence of support playing a role in the enhancement of catalyst activity and the impact on future modeling will be discussed. DFT will be a powerful tool for understanding and even predicting catalyst performance and is shaping our approach to catalysis research. Such molecular-level information obtained from computational methods will undoubtedly guide the design of new catalyst materials with high precision.
Author:
Publisher: Elsevier
ISBN: 0080548512
Category : Technology & Engineering
Languages : en
Pages : 357
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Book Description
Since 1987, the Petroleum Division of the American Chemical Society (ACS) has sponsored at 3 year intervals an international symposium on fluid cracking catalysts (FCC) technology. This volume collects the recent progress of this technology as reported in the papers presented during the 232th National Meeting of the ACS in San Francisco, September 10-14, 2006.Sixty-six years after the introduction of the fluid cracking catalyst process, it remains the main process of gasoline generation for the estimated 237 millions cars on US roads. Catalysts testing and evaluation still remains a subject of interest, debate and controversy. Lambda sweep testing, testing of SOx, NOx and combustion promoters have been discussed in details together with catalyst evaluation for atmospheric residues and metal contaminated oils cracking.Of particular interest has been the introduction of novel concept in process design aimed at improving cracked product selectivity such as two-stage risers for better gasoline and olefins production and downer technology for high severity processes . The importance of solid state nuclear magnetic resonance (NMR) in the study of crude oils, catalysts and reaction products are illustrated by several examples. Two contributions describe the use of predictive methods to understand FCC aging and deactivationand personal overviews of the development of SOx and combustion promoters technology are presented.* Presents findings from the tri-annual international symposium on fluid cracking catalysts (FCC) technology, sponsored by the Petroleum Division of the American Chemical Society (ACS) * Two contributions describe the use of predictive methods to understand FCC aging and deactivation* Personal overviews by the authors of the development of SOx and combustion promoters technology
Author: Marco A. Sanchez-Castillo
Publisher:
ISBN:
Category :
Languages : en
Pages : 222
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Author: Paul B. Venuto
Publisher: Marcel Dekker
ISBN:
Category : Science
Languages : en
Pages : 176
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Author: Anton Mlinar
Publisher:
ISBN:
Category :
Languages : en
Pages : 123
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Book Description
The oligomerization of propene to produce higher molecular weight molecules was investigated as a model reaction pathway for the synthesis of liquid transportation fuels and fuel additives from C2 to C5 light olefins. In this scheme, light olefins could come from a variety of sources including the cracking of petroleum, as a byproduct in the production of hydrocarbons from synthesis gas during Fisher-Tropsch synthesis, or from the dehydration of alcohols created during biomass fermentation. Transformation of these light olefins into heavier molecules could allow for future production of transportation fuels from many carbon-rich sources, including natural gas, coal, and biomass, instead of the current system that relies almost exclusively on petroleum. Microporous and mesoporous Brønsted acidic and exchanged nickel materials are the most common heterogeneous catalysts for the oligomerization of light olefins into heavier products. Much is unknown about the role of the catalyst in influencing the oligomer size and the degree of oligomer branching - both characteristics crucial to the production of high quality liquid fuels - making the selection and design of appropriate oligomerization catalysts challenging. It was therefore the goal of this dissertation to establish how the catalyst site, proximity of sites, and catalyst support influence the final product distribution of oligomers. The discussion begins with an examination of the role of the acid site density in the Brønsted acidic zeolite H-MFI on the activity and selectivity to propene dimers. An increase in the aluminum site density, represented by a decrease in the catalyst Si/Al ratio from 140 to 10, was determined to decrease the conversion of propene to heavier products from 75% to 10% at 548 K. Examination of the reaction pathways for oligomer formation using kinetic analyses and DFT simulations indicate that site density influences the relative rates of oligomer growth and desorption. Specifically, the high loading of hydrocarbons in zeolites with low Si/Al ratios limit oligomer growth beyond the dimer lowering the propene conversion, as fewer oligomers are formed, but also increasing dimer selectivity due to the smaller concentration of long oligomers required for secondary cracking reactions. Regardless of the Si/Al ratio in H-MFI, the activity of the Brønsted acid sites for oligomer cracking and aromatic formation limit the control over the product distribution with these catalysts. To achieve better oligomer control and limit secondary oligomer reactions, heterogeneous nickel-exchanged aluminosilicates were explored. These materials can achieve near complete conversion of ethene to oligomers with > 98% selectivity at high olefin pressures; however, the manner in which these catalysts convert light olefins into heavier products is not understood. Therefore, to determine any potential benefit to using these catalysts over Brønsted acidic zeolites, the reaction mechanism, state of nickel sites, and influence of catalyst support were investigated to determine their roles in catalyst activity and oligomer branching. A series of Ni-exchanged Na-X zeolites with various nickel loadings were successfully synthesized via aqueous ion exchange with nickel (II) nitrate and explored as propene oligomerization catalysts. Characterization of Ni-Na-X indicates that Ni remains Ni2+ both after synthesis and under reaction conditions, contrary to previous reports. Although all catalysts were > 98% selective to oligomers at 453 K and 1-5 bar propene pressure, the catalyst activity was determined to be a strong function of the nickel loading. At high nickel loadings, the catalyst is active immediately upon exposure to propene but deactivates rapidly to 0% conversion. As the nickel loading is decreased below 1 wt%, however, the catalyst exhibits low initial activity and instead activates with time on stream, before deactivating and reaching a non-zero steady-state activity after more than 2000 min of time on stream. Development of a reaction network and subsequent microkinetic model indicates that the activation period is caused by migration of Ni2+ cations from inaccessible positions of the zeolite to the supercage, where catalysis occurs. The subsequent catalyst deactivation is caused by complexation of nearby sites within the zeolite supercage leaving only isolated Ni2+ sites active at steady state. Once an understanding of the time on stream activity profile was established, the role of the support on the catalyst activity and degree of dimer branching was examined. Exchanging the non-catalytic co-cation in the zeolite, Na+ in Ni-Na-X, for other alkali metal and alkaline earth co-cations was determined to influence both the propene oligomerization activity and dimer isomer distribution. Specifically, Li+, the smallest alkali metal co-cation, and Sr2+, the largest alkaline earth co-cation examined, led to the highest dimer branching and catalyst activity per Ni2+ cation in their respective groups. It was determined that this effect was caused by both larger cations expanding the zeolite lattice and alkali metal cations present in the zeolite supercage taking up otherwise open pore volume. This led to the conclusion that space around the Ni2+ cations in the supercage is what governs catalytic activity and dimer branching in these catalysts. The realization that space around the Ni2+ site controls catalyst activity led to the exploration of larger mesoporous aluminosilicate structures as potentially more active propene oligomerization catalysts. To this end, Ni-exchanged MCM-41 and MCM-48 (pore size = 23 Å) and SBA-15 (pore size = 57 Å) were synthesized and examined as oligomerization catalysts. It was determined that the same principles established in zeolites for making an active catalyst, such as high Ni2+ dispersion, were still applicable to these larger-pored systems. As predicted, further increasing the space around the active site did increase the catalyst activity with the highest activity per Ni2+ site existing for the SBA-15 material. The decreased steric constraints from the support in these structures, however, led to increased trimer production as well as catalyst deactivation caused by heavy molecules depositing in the pores. The more open environment also resulted in less control over the degree of dimer branching causing all mesoporous catalysts to produce a 49/51 mixture of branched to linear dimers at 453 K and 1 bar propene pressure.
Author: C.Richard A. Catlow
Publisher: Elsevier
ISBN: 0128050586
Category : Technology & Engineering
Languages : en
Pages : 372
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Book Description
Modelling and Simulation in the Science of Micro- and Meso-Porous Materials addresses significant developments in the field of micro- and meso-porous science. The book includes sections on Structure Modeling and Prediction, Synthesis, Nucleation and Growth, Sorption and Separation processes, Reactivity and Catalysis, and Fundamental Developments in Methodology to give a complete overview of the techniques currently utilized in this rapidly advancing field. It thoroughly addresses the major challenges in the field of microporous materials, including the crystallization mechanism of porous materials and rational synthesis of porous materials with controllable porous structures and compositions. New applications in emerging areas are also covered, including biomass conversion, C1 chemistry, and CO2 capture. Authored and edited by experts in the field of micro- and meso-porous materials Includes introductory material and background both on the science of microporous materials and on the techniques employed in contemporary modeling studies Rigorous enough for scientists conducting related research, but also accessible to graduate students in chemistry, chemical engineering, and materials science
Author: University of Mississippi. Department of Chemical Engineering
Publisher:
ISBN:
Category : Catalytic cracking
Languages : en
Pages : 36
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Book Description
