Download or read book Impact of Physical Properties of Silica on the Reaction Kinetics of Silica Supported Metallocenes and Polyethylene Morphology written by Muhammad Ahsan Bashir and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polyolefins account for more than half of the world's plastic production and about 80% of these polyolefins are commercially produced with heterogeneous olefin polymerization catalysts such as Phillips, Ziegler-Natta and metallocenes. Trouble-free plant operation due to low fouling of the reactor or other plant equipment, relatively stable catalytic activity, good polymer morphology and high polymer bulk densities can be achieved by employing heterogeneous olefin polymerization catalysts. On the other hand, heterogenization of the olefin polymerization catalysts lead to drastic reduction in their activities and broadening of the polymer molar mass distribution which is undesirable in some cases because it can influence the processability and mechanical properties of the polyolefin grade. Various explanations have been proposed in the open literature to explain these effects of catalyst immobilization which mainly include existence of diffusion resistance to (co)-monomer(s) transport at the active sites during polymerization and the change of the active site(s) behavior due to immobilization leading to multiple site types on the final supported catalyst. Nevertheless, both of these explanations have a connection with the physical properties (e.g., particle size, surface area, pore volume, pore diameter etc.) of the support because the support can impact the nature of the final active species formed on it, dispersion of the active species throughout the support particles and, last but not the least, the intraparticle diffusion of (co)-monomer(s) during polymerization. Metallocenes are considered as single-site catalysts and any changes in the nature of the active site(s) upon their immobilization on a support or during the course of polymerization due to mass transfer resistance can be detected from the broadening of polyolefin molar mass distribution. Therefore, the present work is an attempt to study the effects of physical properties of silica supported metallocenes on their ethylene polymerization kinetics as well as on the morphology of the produced polyethylene. For this purpose, the surface chemistry of the used commercial silica supports was fixed by dehyroxylating all of them at 600 °C, whereas, the final metal loadings of the supported catalysts were nearly kept constant by preparing them under identical conditions. Furthermore, slurry and gas phase polymerization protocols along with the used aluminum alkyl scavenger (which can also induce chemical effects on the catalytic behavior of supported metallocenes) were also fixed by testing different polymerization protocols and scavengers. Such systematic study has allowed us to attribute the observed differences in the reaction kinetics of the supported metallocenes, explicitly, to the differences in the physical parameters of the silica supports and, consequently, to the existence of diffusion resistance to (co) monomer(s) transport at the active site(s) during the course of polymerization.
Download or read book Silica written by Peter J. Heaney and published by Walter de Gruyter GmbH & Co KG. This book was released on 2018-12-17 with total page 624 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume 29 of Reviews in Mineralogy provides an updated silica review which focuses on the most recent developments. This book describes the crystal structures and phase transitions of silica and its stuffed derivatives; bridges the relationship between the microstructural character of real silica minerals and the behavior of silica in the geological environment; covers Quantum mechanical considerations of the Si-O bond; shows how calculations based upon first-principles theory can explain and predict silica transitions at high temperatures and pressures; covers spectroscopic analyses of silica and how they reveal vibrational behaviors in response to variations in temperature, pressure, and composition and finally details the uses of silica for industrial purposes.
Download or read book The Properties of Silica written by Robert Browning Sosman and published by . This book was released on 1927 with total page 870 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Characterization and Chemical Modification of the Silica Surface written by E.F. Vansant and published by Elsevier. This book was released on 1995-04-25 with total page 573 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxide surface materials are widely used in many applications, in particular where chemically modified oxide surfaces are involved. Indeed, in disciplines such as separation, catalysis, bioengineering, electronics, ceramics, etc., modified oxide surfaces are very important. In all cases, the knowledge of their chemical and surface characteristics is of great importance for the understanding and eventual improvement of their performances. This book reviews the latest techniques and procedures in the characterization and chemical modification of the silica surface, presenting a unified and state-of-the-art approach to the relevant analysis techniques and modification procedures, covering 1000 references integrated into one clear concept.
Download or read book Adsorption on Silica Surfaces written by Eugene Papirer and published by CRC Press. This book was released on 2000-04-05 with total page 774 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Progresses from theoretical issues to applications. Contains a historical overview, in-depth considerations of various scenarios of silica adsorption, and results from the latest research. Invaluable for broad coverage of the expanding field of silica research."
Download or read book The properties of silica an introduction to the properties of substances in the solid non conducting state written by Robert B. Sosman and published by . This book was released on 1961 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Chemical and Physical Effects of Silica Fume on the Microstructure and Mechanical Properties of Concrete written by Rachel Jean Detwiler and published by . This book was released on 1988 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of Siloxane Ring Strain and Cation Charge Density on the Formation of Coordinately Unsaturated Metal Sites on Silica written by and published by . This book was released on 2015 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: Amorphous silica (SiO2) is commonly used as a support in heterogeneous catalysis. However, due to the structural disorder and temperature induced change of surface morphology, the structures of silica supported metal catalysts are difficult to determine. Most studies are primarily focused on understanding the interactions of different types of surface hydroxyl groups with metal ions. In comparison, the effect of siloxane ring size on the structure of silica supported metal catalysts and how it affects catalytic activity is poorly understood. Here, we have used density functional theory calculations to understand the effect of siloxane ring strain on structure and activity of different monomeric Lewis acid metal sites on silica. In particular, we have found that large siloxane rings favor strong dative bonding interaction between metal ion and surface hydroxyls, leading to the formation of high-coordinate metal sites. In comparison, metal-silanol interaction is weak in small siloxane rings, resulting in low-coordinate metal sites. The physical origin of this size dependence is associated with siloxane ring strain, and, a correlation between metal-silanol interaction energy and ring strain energy has been observed. In addition to ring strain, the strength of the metal-silanol interaction also depends on the positive charge density of the cations. In fact, a correlation also exists between metal-silanol interaction energy and charge density of several first-row transition and post-transition metals. The theoretical results are compared with the EXAFS data of monomeric Zn(II) and Ga(III) ions grafted on silica. In conclusion, the molecular level insights of how metal ion coordination on silica depends on siloxane ring strain and cation charge density will be useful in the synthesis of new catalysts.
Download or read book A Study of the Morphology of Silica Supported MoO3 written by Abhay Kumar Datta and published by . This book was released on 1990 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied Science Technology Index written by and published by . This book was released on 2000 with total page 1688 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Colloidal Silica written by Horacio E. Bergna and published by CRC Press. This book was released on 2005-12-19 with total page 926 pages. Available in PDF, EPUB and Kindle. Book excerpt: In spite of the apparent simplicity of silica's composition and structure, scientists are still investigating fundamental questions regarding the formation, constitution, and behavior of colloidal silica systems. Colloidal Silica: Fundamentals and Applications introduces new information on colloid science related to silica chemistry as well
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 Multimodal Polymers with Supported Catalysts written by Alexandra Romina Albunia and published by Springer. This book was released on 2019-01-16 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides an overview of polyolefine production, including several recent breakthrough innovations in the fields of catalysis, process technology, and materials design. The industrial development of polymers is an extraordinary example of multidisciplinary cooperation, involving experts from different fields. An understanding of structure-property and processing relationships leads to the design of materials with innovative performance profiles. A comprehensive description of the connection between innovative material performance and multimodal polymer design, which incorporates both flexibility and constraints of multimodal processes and catalyst needs, is provided. This book provides a summary of the polymerization process, from the atomistic level to the macroscale, process components, including catalysts, and their influence on final polymer performance. This reference merges academic research and industrial knowledge to fill the gaps between academic research and industrial processes. · Connects innovative material performance to the flexibility of multimodal polymer design processes; · Provides a comprehensive description of the polymerization process from the atomic level to the macroscale; · Presents a polyhedric view of multimodal polymer production, including structure, property, and processing relationships, and the development of new materials.
Download or read book Introduction to Industrial Polypropylene written by Dennis B. Malpass and published by John Wiley & Sons. This book was released on 2012-07-02 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: This introductory text is an important resource for new engineers, chemists, students, and chemical industry personnel to understand the technical aspects of polypropylene which is the 2nd largest synthetics polymer in manufactured output. The book considers the following topics: What are the principal types of polypropylene and how do they differ? What catalysts are used to produce polypropylene and how do they function? What is the role of cocatalysts and how have they evolved over the years? How are industrial polypropylene catalysts tested and the resultant polymer evaluated? What processes are used in the manufacture of polypropylene? What are the biopolymer alternatives to polypropylene? What companies are the major industrial manufacturers of polypropylene? What is the environmental fate of polypropylene?
Download or read book Metallocene based Polyolefins written by John Scheirs and published by Wiley. This book was released on 2000-01-21 with total page 600 pages. Available in PDF, EPUB and Kindle. Book excerpt: With contributions from leading international experts, thisessential book gives comprehensive coverage of all areas ofmetallocene catalysts and metallocene-based polyolefins includingdetails of the very latest developments. The manufacture of polyolefins by metallocene catalysts representsa revolution in the polymer industry. The last five years inparticular have seen a dramatic increase in the volume of researchinto metallocenes and the maturing of metallocene technology. The following areas are covered in this comprehensive book:catalyst structure, comonomer incorporation, polymerizationmechanisms and conditions, reactor configurations, specialproperties, comparison with conventional polyolefins, rheologicaland processing behavior and fields of application. This is an invaluable book for plastics engineers, polymerchemists, physicists, materials scientists, and all those workingin the plastics manufacturing and processing industries.
Download or read book Polymer Science and Engineering written by National Research Council and published by National Academies Press. This book was released on 1994-01-01 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polymers are used in everything from nylon stockings to commercial aircraft to artificial heart valves, and they have a key role in addressing international competitiveness and other national issues. Polymer Science and Engineering explores the universe of polymers, describing their properties and wide-ranging potential, and presents the state of the science, with a hard look at downward trends in research support. Leading experts offer findings, recommendations, and research directions. Lively vignettes provide snapshots of polymers in everyday applications. The volume includes an overview of the use of polymers in such fields as medicine and biotechnology, information and communication, housing and construction, energy and transportation, national defense, and environmental protection. The committee looks at the various classes of polymersâ€"plastics, fibers, composites, and other materials, as well as polymers used as membranes and coatingsâ€"and how their composition and specific methods of processing result in unparalleled usefulness. The reader can also learn the science behind the technology, including efforts to model polymer synthesis after nature's methods, and breakthroughs in characterizing polymer properties needed for twenty-first-century applications. This informative volume will be important to chemists, engineers, materials scientists, researchers, industrialists, and policymakers interested in the role of polymers, as well as to science and engineering educators and students.
Download or read book Handbook of Thermoplastics written by Olagoke Olabisi and published by CRC Press. This book was released on 2016-02-03 with total page 976 pages. Available in PDF, EPUB and Kindle. Book excerpt: This new edition of the bestselling Handbook of Thermoplastics incorporates recent developments and advances in thermoplastics with regard to materials development, processing, properties, and applications. With contributions from 65 internationally recognized authorities in the field, the second edition features new and updated discussions of seve
