Download or read book Kinetic Studies of Selective Ethylene Oligomerization Processes of Chromium Based Catalyst Systems written by Anina Tonia Wöhl and published by . This book was released on 2009 with total page 111 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Characterization and Catalytic Activity of Chromium Complexes written by Joanna Gurnham and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: There has been a growing demand for specific linear alpha olefins in the polyethylene industry in order to control polymer rheology. This growing demand thereby increases the need for highly active and selective ethylene oligomerization catalysts. Chromium-based catalysts continue to be of high interest for this application due to this metal's versatility in both selective and non selective ethylene oligomerization. Ligand design is an important consideration in oligomerization chemistry: the ability of the ligand to stabilize low valent chromium and to support a two-electron redox process will allow the catalytic systems to follow the selective ring expansion mechanism for oligomerization. Chelating aminophosphane based ligands, previously studied by our group, have been shown to support both tri- and tetramerization of ethylene. We have explored modifications of one of the NP arms by replacing with a different coordinating group in an attempt to further stabilize the monovalent state of chromium and increase selectivity. Other ligands explored in this work are pyrrole based ligands, which have shown high activity and selectivity towards ethylene oligomerization. One example of this is the commercial Chevron-Phillips system. Recently, the co-polymerization of CO2 with epoxides has been studied as an environmentally friendly route to convert CO2 into biodegradable polymers. The first successful catalytic system to achieve these results consisted of a diethyl-zinc complex. More recently, aluminum, chromium, cadmium and cobalt have been studied as polycarbonate catalysts. To date, the only reported chromium catalysts for CO2-epoxide copolymerization are Cr-salen and Cr-porphyrin complexes, studied by Darrensbourg and Holmes, respectively. We were particularly interested in finding new chromium-based complexes able to catalyze epoxide/CO2 copolymerization by using molecules with the nitrogen donor motif embedded in different functions such as neutral pyridines with anionic pendants, pyrroles with either imine or amine pendants, or a combination of these.

Download or read book Catalysis and Kinetics Molecular Level Considerations written by Guy B. Marin and published by Academic Press. This book was released on 2013-12-24 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in Chemical Engineering was established in 1960 and is the definitive serial in the area. It is one of great importance to organic chemists, polymer chemists, and many biological scientists. Written by established authorities in the field, the comprehensive reviews combine descriptive chemistry and mechanistic insight and yield an understanding of how the chemistry drives the properties. This volume covers the topic of catalysis and kinetics and aspects in chemical engineering. Control and optimization of process systems Polyelectrolytes Propane dehydrogenation and selective oxidation of hydrogen Chromium catalysts for ethylene polymerization and oligomerization Computational simulation of rare Earth catalysis

Download or read book The Challenge of Selectivity in Ethylene Oligomerization written by Indira Thapa and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of the Factors Affecting the Selectivity of Catalytic Ethylene Oligomerization written by Khalid Albahily and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past decade, advances in ethylene oligomerization have witnessed explosive growth of interest from both commercial and academic standpoint, with chromium metal invariably being the metal of preference. A common feature in this literature was the extended long debate regarding the mechanism, metal oxidation states responsible for selectivity and the role of the ligand. This thesis work embarked on the isolation and characterization of new active intermediates called "single component catalysts" (or self activating) to address two important questions: (1) how the catalyst precursors re-arrange upon activation and (2) the real oxidation state of the activated species. Four different ligands systems have been examined for this purpose. The first part is a study on the NPIIIN ligand which can be described as a dynamic and non-spectator ligand. Upon aluminum alkyl activation, a series of single component chromium catalysts for selective ethylene oligomerization and polymerization have been isolated, fully characterized and tested. New selective single component chromium(I) catalysts have also been isolated and tested positively for ethylene trimerization. The second part includes a new series of chromium complexes based on the NPVN ligand. This ligands enabled to obtain the first polymer-free extremely active catalytic system. In both NPN ligand systems, a new activation pathway was discovered by using vinyl Grignard reagent [(CH2=CH)MgCl] as activator and/or reducing agent. The third part explores new modified pyrrole-chromium complexes which were found to be highly active and selective ethylene trimerization catalysts. This part was a continuation of previous work from our lab to complete the mechanistic picture of this highly successful pyrrole-chromium catalyst independently commercialized by Phillips-Chevron and Mitsubishi. Interestingly upon aluminum alkyl treatment, the first example of a Schrock-type chromium ethylidene complex has been isolated and characterized and found to be a potent catalyst for selective ethylene trimerization. Finally, the other ligands introduced in this thesis are new systems called pyridine-SNS and Si-SNS that introduce some modification to the known commercial SNS catalyst (Sasol technology). The introduction of a pyridine ring or a silyl unit in the ligand scaffold has allowed to understand the mechanism of action of this remarkable system.

Download or read book Mechanisms and Kinetics of Ethylene Oligomerization Over Nickel based Heterogeneous Catalysts written by Gabriel Viana Sueth Seufitelli and published by . This book was released on 2021 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present research describes the kinetics and mechanisms of the ethylene oligomerization over nickel-based solid catalysts at subcritical and supercritical ethylene conditions. The Ni-H-Beta catalyst was used due to its high activity for the conversion of ethylene into higher alkenes. Initially, the role of nickel and Brønsted sites on the ethylene oligomerization over Ni-H-Beta catalysts is investigated. According to the catalyst characterization results, nickel is present on the catalyst surface as Ni2+, from the free NiO phase and highly dispersed Ni2+ interacting with the catalyst’s lattice oxygen. Ethylene sorption results indicate that ethylene dissociates over two active sites upon adsorption over the Ni-H-Beta. Further characterization via pyridine sorption suggests that the presence of non-coordinated Ni2+ or Brønsted sites decreases the probability for the formation of the active sites on the catalyst surface. Then, the kinetics of ethylene oligomerization over the Ni-H-Beta are discussed. A kinetic model was developed for temperatures varying between 50 and 100°C and pressures varying between 5 and 28 atm. The results indicate the butene and hexene are formed via a series of ethylene coordination-insertion steps and the formation of octene follows the co-oligomerization of ethylene and desorbed butene. In the present study, we refer to the pathway involving co-oligomerization of butene and hexene as "cascade co-oligomerization". A detailed reaction network is proposed and modeled based on the Langmuir-Hinshelwood-Hougen-Watson kinetics. After studying the mechanisms and kinetics of the ethylene oligomerization under subcritical conditions, the solubility of coke in supercritical ethylene is discussed. The solubility of coke in ethylene was investigated at 30, 50, and 75°C and pressures ranging from 1 to 68 bar; conditions previously screened by our research group for ethylene oligomerization. The approach uses n-decane as a model compound to simulate coke formed during the catalytic process. A detailed thermodynamic model is developed for the solubility of n-decane in subcritical and supercritical ethylene. Beyond the ethylene critical point (P = 50.3 bar and T = 9.4°C) the solubility of n-decane in ethylene at 30°C reaches a maximum value of 3.0%; close to the value observed at 50 and 75°C, under the same pressure. Comparison of kinetic and solubility data show that the transport of products from the catalyst to the bulk of the supercritical fluid is a function of the reaction temperature. At low temperatures (30°C), coke dissolution rates are higher than apparent coke production rates. However, at high temperatures (60 and 90°C), coke dissolution rates are not able to outcompete the high rates of coke formation. The last step of the study with the Ni-H-Beta catalyst involves a kinetic model under supercritical ethylene conditions. The kinetic data under supercritical conditions are modeled based on the Langmuir-Hinshelwood-Hougen-Watson kinetics. Three different reaction limiting steps are compared: adsorption, chain-growth, and desorption. The model that assumes desorption of products as the reaction limiting step provides the best fitting of the kinetic data among the models proposed in the present work. Therefore, the slow desorption of products from the catalyst surface to the bulk of supercritical ethylene limits the reaction. This result is consistent with the result obtained in the solubility study.Based on the previous solubility and kinetic studies, a novel catalyst is designed for the oligomerization of supercritical ethylene. This catalyst is composed of nickel supported on mesoporous SIRAL support. We report the production of liquid products at 50, 100, and 200°C and 40 and 65 bar operating at both single and dual reactor configurations. The novel Ni-SIRAL catalyst is able to oligomerize ethylene at supercritical conditions without experiencing deactivation. The liquid product is composed of linear alkenes and a substantial fraction of cycloalkanes (8.5 wt. %). A high yield for liquid hydrocarbons of 60.8 wt. % is reported at 200oC and 65 bar.

Download or read book Oligomerization and Polymerization of Ethylene by Phenoxy imine Titanium Catalysts written by Astrid Cordier and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 1-hexene is one of the most important olefin used as comonomer for the production of value-added polyethylenes (HDPE, LLDPE). In the field of selective ethylene trimerization employing titanium-based catalysts, specific single tridentate phenoxy-imine complexes (SFI) display the highest activity and 1-hexene selectivity upon activation with methylaluminoxane (MAO). However, ethylene polymerization is an unavoidable side reaction affecting both 1-hexene selectivity and process operations. Although being a major drawback, the causes of polymerization remain a grey area since few studies were dedicated to its deciphering. To handle this challenge , an original “polymer-to-catalyst” strategy was implemented. An extensive temperature study (26-80°C) revealed that the highest 1-hexene activity is reached between 30 °C and 40 °C while polymer production is prominent above 50 °C. Polyethylenes obtained were analyzed by SEC, NMR DSC, and advanced segregation techniques (CEF, SIST, rheology). Molar masses above 10^5 g mol-1 were identified along with a 1-hexene content below 1 mol %. An increase of dispersity (Ɖ > 2) with temperature was ascribed to an evolution from single to multi-site polymerization catalysis. Kinetic studies proved that polymer is continuously produced even at short reaction time, for any reaction temperature. Other parameters (addition of 1-hexene, hydrogen and use of trimethylaluminum) were found to impair the trimerization selectivity and/or activity of the system. Nevertheless, it was possible to lower the selectivity in polyethylene by premixing the complex with MAO. After analyzing the possible routes for the polymerization catalyst formation, the hypotheses of temperature and MAO-induced complex alterations were considered. Regarding the latter, a molecular ligand-free Ziegler-Natta catalyst, modeled using TiCl4/MAO, and the synthesized (FI)Ti(III)Cl2 activated by MAO could not explain polymer production in the SFI system. Formation of a polymerization species upon thermal alteration of the SFI complex was evidenced. This [O-,N,O-]-type species displays common features regarding catalytic response to 1-hexene compared to the polymerization catalyst in the SFI system although it could not reach the same catalytic performances. The formation of a bis(phenoxy-imine) complex (FI)2TiCl2 was evidenced in this thesis and is a promising avenue worth exploring. Eventually, although the exact species has not yet been identified, this work enabled to guide the focus of further investigations on activation process and complex rearrangement by ligand mobility.

Download or read book Computational Design and Analysis of Molecular Ethylene Oligomerization Catalysts written by Doo Hyun Kwon and published by . This book was released on 2019 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: Linear alpha olefins (LAOs) are key petrochemical precursors for the synthesis of larger polymers, detergents, plasticizers, and lubricants. Most catalytic ethylene oligomerization processes generate a wide distribution of LAO carbon chain lengths. A major ongoing industrial challenge is to develop homogeneous catalysts that result in selective and tunable ethylene oligomerization to 1-hexene and 1-octene alkenes. Quantum mechanical calculations coupled with rapidly advancing technology have enabled the ability to calculate small molecule systems with high accuracy. Employing computational models to advance from empirical to quantitative prediction of product selectivities has become an active area of exploration. In this work, we demonstrate the development and use of a density-functional theory (DFT) transition-state model that provides highly accurate quantitative prediction of phosphinoamidine (P,N) Cr catalysts for controllable selective ethylene trimerization and tetramerization. This model identified a new family of highly selective catalysts that through computational-based ligand design results in a predictable shift from 1-hexene selectivity to 1-octene. Subsequent experimental ligand synthesis and catalyst testing verified the quantitative computational predictions. DFT calculations also provide key insights to factors controlling catalytic activity and present important design criteria for the development of active Cr-based ethylene oligomerization systems. Non-selective ethylene transformations, referred to as full range processes, provide access to a range of LAOs (C4-C20) that are used to produce polyethylene, surfactants, and other commercial products. During full-range oligomerizations, undesired byproducts degrade the purity of LAOs mostly consisting of branched oligomers. Computational mechanistic investigations reveal the origin of linear versus branched selectivity in Fe-catalyzed ethylene oligomerization reactions.

Download or read book Towards Selective Ethylene Tetramerization written by Yacoob Shaikh and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: There is an increasing trend towards advancing the understanding and development of ethylene oligomerization catalysts, both in academia and industry. The metal of choice in this chemistry is invariably chromium, which has shown great versatility in selective trimerization/tetramerization, non-selective oligomerization and polymerization of ethylene. While much success has been achieved in ethylene trimerization, the same con not be said about tetramerization catalysis. Aminophosphine based ligands have demonstrated their ability towards selective 1-octene production, however, the popular PNP catalyst is able to achieve only 70% selectivity. In order to explore the possibility of developing and enhancing the selectivity of chromium based ethylene tetramerization catalyst, this thesis work was undertaken. The ligand systems we chose for our work were bidentate aminophosphine based (PN(CH2)nNP), which has yielded interesting selective oligomerization. Subtle modifications were found to result in drastic changes in selectivity, from tetramerization (PN(CH2)3NP) to trimerization (PN(CH2)2NP). We managed to successfully develop the first truly selective (over 90%) 1-octene catalyst with polymer-free behavior. Further modifications on the ligand framework, where one atom of Si was used to link the two NP units, resulted in non-selective oligomerization, in which case we determined that the oxidation-state of chromium is a key player. We explored other modifications on our selective ligands in which one of the arms on the bidentate ligand was replaced with a base-donor amine, phosphine or pyridine, and resulted in interesting selectivity changes. The final modification that we tested was a novel N(CH2)2P ligand and found it to be a highly active, non-selective oligomerization catalyst.

Download or read book Catalytic and Process Study of the Selective Hydrogenation of Acetylene and 1 3 Butadiene written by Ruijun Hou and published by Springer. This book was released on 2017-01-05 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis offers novel methods for catalyst and process design for the selective hydrogenation of acetylene and 1,3-butadiene. The author predicts the properties of supported Pd–Ni bimetallic catalysts using density functional theory (DFT) calculations and temperature-programmed desorption (TPD). The excellent correlation between model surfaces and supported catalysts demonstrates the feasibility of designing effective bimetallic catalysts for selective hydrogenation reactions. The author also proposes a method for designing non-precious metal catalysts to replace precious metals. She modifies the process of selective hydrogenation of acetylene by coupling the selective adsorption to the selective hydrogenation in the liquid phase, as a result of which the ethylene selectivity is greatly improved and heat transfer is greatly enhanced. Lastly, by analyzing the mechanism of liquid-phase hydrogenation, the author proposes a multi-stage slurry bed reactor for industrial applications.“/p>

Download or read book The Privileged Pincer Metal Platform Coordination Chemistry Applications written by Gerard van Koten and published by Springer. This book was released on 2015-08-27 with total page 381 pages. Available in PDF, EPUB and Kindle. Book excerpt: The series Topics in Organometallic Chemistry presents critical overviews of research results in organometallic chemistry. As our understanding of organometallic structure, properties and mechanisms increases, new ways are opened for the design of organometallic compounds and reactions tailored to the needs of such diverse areas as organic synthesis, medical research, biology and materials science. Thus the scope of coverage includes a broad range of topics in pure and applied organometallic chemistry, where new breakthroughs are being achieved that are of significance to a larger scientific audience. The individual volumes of Topics in Organometallic Chemistry are thematic. Review articles are generally invited by the volume editors.

Download or read book Olefin Polymerization written by Walter Kaminsky and published by Wiley-VCH. This book was released on 2006-08-18 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: With an enormous velocity, olefin polymerization has expanded to one of the most significant fields in polymers since the first industrial use about 50 years ago. In 2005, 100 million tons of polyolefins were produced - the biggest part was catalyzed by metallorganic compounds. The Hamburg Macromolecular Symposium 2005 with the title "Olefin Polymerization" involved topics such as new catalysts and cocatalysts, kinetics, mechanism and polymer reaction engineering, synthesis of special polymers, and characterization of polyolefins. The conference combined scientists from different disciplines to discuss latest research results of polymers and to offer each other the possibility of cooperation. This is reflected in this volume, which contains invited lectures and selected posters presented at the symposium.

Download or read book The Selective Oligomerization of Ethylene Using Chromium Diphosphine Catalysts and the Synthesis and Reactivity of Group 7 Carbonyl Derivatives Relevant to Synthesis Gas Conversion written by Paul Richard Elowe and published by . This book was released on 2009 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Deactivation and Regeneration of Zeolite Catalysts written by M. Guisnet and published by World Scientific. This book was released on 2011 with total page 359 pages. Available in PDF, EPUB and Kindle. Book excerpt: In chemical processes, the progressive deactivation of solid catalysts is a major economic concern and mastering their stability has become as essential as controlling their activity and selectivity. For these reasons, there is a strong motivation to understand the mechanisms leading to any loss in activity and/or selectivity and to find out the efficient preventive measures and regenerative solutions that open the way towards cheaper and cleaner processes. This book covers in a comprehensive way both the fundamental and applied aspects of solid catalyst deactivation and encompasses the state-of-the-art in the field of reactions catalyzed by zeolites. This particular choice is justified by the widespread use of molecular sieves in refining, petrochemicals and organic chemicals synthesis processes, by the large variety in the nature of their active sites (acid, base, acid-base, redox, bifunctional) and especially by their peculiar features, in terms of crystallinity, structural order and textural properties, which make them ideal models for heterogeneous catalysis. The aim of this book is to be a critical review in the field of zeolite deactivation and regeneration, by collecting a series of contributions by experts in the field which describe the factors, explain the techniques to study the causes and suggest methods to prevent (or limit) catalyst deactivation. At the same time, an anthology of commercial processes and exemplar cases provides the reader with theoretical insights and practical hints on the deactivation mechanisms and draws attention to the key role played by the loss of activity on process design and industrial practice.

Download or read book The Selective Oligomerization of Ethylene with Metal organic Frameworks written by Eric Daniel Metzger and published by . This book was released on 2018 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: The benefits of heterogeneous catalysis for industry and the society at large cannot be overstated, with approximately 90% of all industrial catalysis being performed with heterogeneous catalysts. Despite the undeniable operational advantages of heterogeneous catalysts, several large volume industrial processes involved in the production of commodity chemicals remain impenetrable to solid catalysts. Among them are the selective dimerization of ethylene and the selective trimerization of ethylene, which require fine steric and electronic tuning to optimize the production of the desired olefin. In this thesis, I describe the development of new heterogeneous catalysts to address the lack of activity and selectivity found among heterogeneous catalysts for selective ethylene oligomerizations, with an emphasis on developing new metal-organic framework (MOF) catalysts for the selective dimerization of ethylene to 1-butene. The ability to tune the catalytically active site of a solid at the molecular level places MOFs in prime position to answer challenges in heterogeneous catalysis that no other class of solids has been able to address. Chapter 2 of this thesis describes the development of Ni-MFU-4/, a nickel-substituted MOF with excellent activity and selectivity for the dimerization of ethylene to 1-butene. Although the active sites in the MOF are designed to mimic homogeneous Nitrispyrazolylborate dimerization catalysts, the selectivity observed for the solid catalyst is considerably higher than that of the homogeneous system, highlighting the importance of active site isolation in the porous solid. Chapter 3 details a combination of studies utilizing isotopic labeling and mechanistic probes to demonstrate that Ni-MFU-4/ dimerizes ethylene via the Cossee-Arlman mechanism. Chapter 4 reports the preparation of Ni-CFA-1, a related heterogeneous ethylene dimerization catalyst that is far more synthetically accessible than Ni- MFU-4/. Lastly, chapter 5 relays initial results towards the development of MOF-based ethylene trimerization catalysts.

Download or read book The Role of Aluminate in the Activation of Catalytic Systems for Ethylene Oligomerization written by Ahmed Alzamly and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The reaction mechanisms followed by ethylene polymerization and selective oligomerization (tri- and tetramerization) are conceptually very different, being a non-redox chain growth and a redox metallacycle ring expansion pathway respectively. With chromium being the metal of choice, metal oxidation states and the variation of ancillary ligand able to support specific metal oxidation states responsible for selective trimerization, tetramerization or nonselective oligomerization/polymerization were varied. In this research project we have explored a broad range of novel pyridine containing modified PN ligand scaffolds with the aim of probing the role of the pyridine donor substituent in stabilizing lower oxidation states and ultimately affecting the selectivity of the ethylene in the catalytic cycle. In this study, pyridine PNP pincer ligands in conjunction with chromium salts and alkylaluminium activators have been explored. Their catalytic activities toward ethylene oligomerization were rationalized through the isolation of different chromium-aluminate intermediates in different oxidation states during the catalytic reaction. Moreover, we explored other pyridine modification of NNP type ligand. Its anionic ligand shows a rare example of a Cr(II) hydride cluster which shows a high activity as a nonselective ethylene oligomerization catalyst. Finally, a cyclic PNPN type ligand was explored. The ligand enabled the isolation of a mix-valent Cr(I)/Cr(II) species which was found to be inactive toward ethylene oligomerization due to its geometric constraint.

Download or read book Development and Mechanistic Studies of the Chromium Tetramethyltetraazaannulene Catalyst System for the Copolymerization of Carbon Dioxide and Epoxides written by Shawn Brendan Fitch and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A prominent goal of scientists is to develop products and processes to meet the ever-growing needs of society. Today's needs include products that are economical, specialized, and made through processes with minimal impact on the environment. One such product that serves an important and widespread need is poly(bisphenol A carbonate) for its physical properties and ease of synthesis and processing. However, this polymer does not meet the growing need of being environmentally benign as production involves carcinogenic, chlorinated solvents and toxic monomers that can leach out from the polymer product. An answer to this new demand is the development of a different process for the production of polycarbonate plastics utilizing carbon dioxide and epoxides. Carbon dioxide is an attractive monomer that is cheap and nontoxic, and its utilization signifies an important contribution to counteract global greenhouse emissions. The stability of carbon dioxide has posed a significant and complex challenge towards its utilization. Epoxides are attractive since they are synthesized from a wide variety of olefins, both naturally occurring and those derived from petroleum. The exploration of catalysts to facilitate the coupling of epoxides to carbon dioxide to afford polycarbonates has been under investigation in the Darensbourg lab for fifteen years, and has lead to the development of several successful systems such as zinc bisphenoxides and chromium salens. This dissertation focuses on the development of another successful catalyst system, chromium tetramethyltetraazaannulene, and further elucidation of the mechanism by which polycarbonates are formed. Herein, aspects of the copolymerization process using this system will be discussed in detail, such as cocatalyst and pressure dependence, catalyst derivatization, and kinetic and mechanistic investigations. The end result of these investigations is the development of the most active chromium-based catalyst for the copolymerization of cyclohexene oxide and carbon dioxide and a better understanding of how the copolymer product is produced.