1,720,975 research outputs found
Distributed secondary gas injection via a fractal injector: A nature-inspired approach to improving conversion in fluidized bed reactors
No full textThe conversion in bubbling fluidized bed reactors is suppressed because the interphase mass transfer and gas-solid contact in bubbling fluidized bed reactors are often poor. Most of the gas is present in the form of bubbles, which have low surface-to-volume ratios and are nearly devoid of catalyst particles. The chaotic behaviour of the bubbles is difficult to predict and can change with reactor size, making scale-up very difficult. The work in this thesis presents a novel approach to overcoming these difficulties in bubbling fluidized beds. Nature uses branching, fractal structures, which greatly facilitate mass transfer in natural systems, such as trees and lungs. These structures scale easily, which is a very important feature as the organism grows. This approach can also be applied to fluidized beds. A fractal injector was developed for both quasi 2-D and 3-D beds to distribute a portion of the total gas flow throughout the fluidized bed. To determine the effect of this distributed secondary gas injection on the properties of a gas-solid fluidized bed, the study is split into four topics: the effect on the hydrodynamics of the fluidized bed, the mechanisms leading to the observed changes in the hydrodynamics, the residence time and macroscopic mixing of the gas, and the influence on the performance of the reactor. The results indicate that secondary gas injection via a fractal injector effectively reduces the bubble diameter by up to 30% (~70% reduction in the volume) and increases the gas-solid contact. It is shown that these effects lead to a higher conversion and selectivity in a bubbling fluidized bed reactor. Mechanisms for these effects are proposed.Applied Science
Fundamentals of tri-block copolymer self-assembly in solutions, and its relation to nano-templating
No full textThe purpose of this thesis is to obtain a better understanding of the formation mechanism of mesoporous silica materials, such as SBA-15 that use block copolymers as templating agents. Despite the fact that these materials are now extensively synthesized, the fundamental role of the different synthesis variables has not been determined on the basis of a detailed physical chemical study. Such a synthesis typically starts with the formation of spherical micelles that are converted into long cylindrical micelles during silica hydrolysis and condensation. As a result, a silica matrix with hexagonally ordered mesopores is obtained, after removing the micelles by extraction or calcination. The interactions between the block copolymer and the various additives (silica, acids, salts, solvents) during the first steps of the synthesis in solution are believed to play an important role in the creation of these highly structured materials. Therefore, the emphasis of this thesis lays on providing fundamental information on the self-assembly process of the tri-block copolymer P123 (EO20PO70EO20), typically used in the synthesis of SBA-15, at conditions that mimic those of mesoporous materials synthesis as closely as possible.DelftChemTechApplied Science
Aerosol assisted synthesis of nanostructured silica
No full textZeolites are microporous aluminosilicates that have broad applications especially in industrial processes like fluidized catalytic cracking (FCC) owing to their unique properties with respect to both activity and selectivity. However, the micropores of zeolites may in some cases limit their catalytic performance due to restricted molecular transport induced by similar size of the diffusing hydrocarbons and the micropore size. This had led researchers to develop mesoporous silica materials (pore sizes in the range of 2 and 50 nm) as catalyst supports for enhanced molecular transport. Mesoporous silica are usually prepared using the conventional sol-gel synthesis which takes several days and the final morphology is often irregular. The present thesis deals with the use of a continuous aerosol reactor process involving evaporation induced self-assembly (EISA) that allows synthesis of mesoporous silica (using a tri-block co-polymer, P123 as a templating agent) within several seconds. The synthesis in general involves a large number of experimental parameters. In order to explore this high dimensional experimental space, a factorial design of experiments was employed to study the effect of important variables, namely the precursor composition and the tubular reactor temperature, on the textural properties of the final product. This methodology allows simultaneous investigation of the influence of multiple parameters, which is advantageous over the traditional form of experimentation in the nanomaterials community, where only one variable is changed at a time. It allows exploration over a wider range of conditions to highlight the true nature (global/local) of trends that are often misinterpreted as a universal occurrence in conventional experimental trials. Using contours, this method exclusively determined multiple conditions for achieving a required surface area and pore volume. It also illustrated the variation of these properties over a wider domain of experimental conditions. Additionally, novel mesoporous silica and silica-alumina materials were synthesized using a laboratory spray drier by self-assembly of nanosized silica and alumina particles, using P123 as a structure directing agent. The materials possessed extraordinary steam stability and showed good potential when their performance was tested in pulse cracking experiments. The method offers exciting opportunities for further industrial development as part of mesoporous zeolite composites.Applied Science
Reply to Comment on 'Diffusion of water and sodium counter-ions in nanopores of beta-lactoglobulin crystal: A molecular simulation study'
No full textApplied Science
Mesoporous diphosphine-transition metal complex catalyst for hydroformylation
No full textThe invention pertains to a diphosphine-transition metal complex comprising a diphosphine-transition metal ligand that is covalently bonded to an insoluble mesoporous support having an average pore diameter of from 4.5 nm to 50 nm, characterized in that the ligand as attached to the support has the formula: wherein R is aryl, C1-C4 alkyl, aralkyl, alkylaryl; C1-C4 alkoxy, aralkoxy, or alkylaryloxy; P is a phosphorous atom; M is a transition metal; X is a bond, CH2, 0, S or NH2; Y is C or N; A is a linking moiety which is bonded to the mesoporous support; the ring formed by X, Y and the two aromatic rings is a 5- or 6-membered ring; and wherein the aromatic rings may be unsubstituted or substituted.; The invention further relates to the use of the diphosphine- transition metal complex as a catalyst in a reaction selected from hydroformylation, hydrogenation, carbonylation or carbon-carbon coupling.Delft University of Technolog
Testing the consistency of the Maxwell-Stefan formulation when predicting self-diffusion in zeolites with strong adsorption sites
No full textApplied Science
Heterogeneity explains features of "anomalous" thermodynamics and statistics
No full textApplied Science
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