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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Oxidation of Orthoxylene in a Transported Bed Reactor

Wainwright, Sebastian Mark 02 1900 (has links)
<p>The objective of this research program was to evaluate a gas-solid contacting reactor (called a transported bed reactor) in which the solid catalyst is conveyed upward in a vertical pipe by the gaseous reactants/products; at the top of the reactor the solids are separated from the gas stream and recirculated through the system. The reaction employed in this evaluation was the oxidation of orthoxylene on a vanadia on silica gel catalyst.</p> <p>This oxidation reaction was studied separately on the same catalyst in a bench-scale fixed bed reactor over a range of temperatures, oxygen and orthoxylene concentrations and flow rates to provide conversions from 1 to 100% and considerable variation in selectivity. Reaction products were analyzed at short on-stream times and after considerable reaction times. These results indicated that reaction rates on freshly oxidized catalyst are much higher than those observed after steady-state has been achieved; selectivity to organic oxidation products is also improved significantly. Reaction studies are also carried out with other catalysts, notably a titania based one, and these results are similar in general behaviour but differ in some important details. Kinetic parameters in the Redox or steady-state adsorption models are evaluated.</p> <p>This reaction was carried out in a pilot scale transported bed reactor, 3/4 in. O.D. by 27 ft. long. Solid hold-up was measured by activating quick shut-off values. It was demonstrated that stable operation could be achieved at very high solids loadings (solid/gas ratios up to 250 and voidages from 0.60 to 0.86). It is demonstrated that the high reaction rates and selectivities can be exploited in such reactors. Suggestions for further research on such reactor systems are included.</p> / Doctor of Philosophy (PhD)
82

Computer Control of A Reciprocating Plate Extraction Column

Kusuma, Indra 11 1900 (has links)
<p>This work discusses the control of a pilot scale (15 cm Dia.) Karr reciprocating extraction column. The system used is Kerosene dispersed in water, in which mass transfer does not occur.</p> <p>The control scheme developed were tested for servo tracking and regulator control of the holdup of the dispersed phase, the manipulated variance was frequency of the reciprocating plates. Holdup was determined from an empirical correlation using an on-line measurement of column differential pressure.</p> <p>Dynamic tests indicated the process to be nonlinear and assymmetric in time constant, deadtime and gain. A deadtime was observed between manipulating plate frequency and hold-up of the dispersed phase.</p> <p>Various controllers were tested; PI ( in feedback or feed forward mode or the combination), Dahlin algorithm. These were compared to the performance of minimum variance controller and S.T.R. All controllers were implemented using a 16 bit microprocessor.</p> <p>The Dahlin and Minimum variance controllers have been demonstrated to handle process with deadtime better than the PI controller, because they both have deadtime compensator.</p> <p>It was shown that the S.T.R. is superior over all fixed parameters controllers in handling the non-linearity of the process.</p> / Master of Engineering (ME)
83

Modelling and Discrimination Studies in a Catalytic Fluidized Bed Reactor

Shaw, Sholto Douglas Ian 03 1900 (has links)
<p>The object of this research program was to develop a strategy and methodology for modelling existing large-scale chemical reactors by coupling bench-scale studies with plant data.</p> <p>By way of example, the hydrogenolysis of n-butane on a 10% nickel on silica gel catalyst was carried out in a pilot-scale fluidized bed reactor (8 in. in diameter by 3 ft. bed depth). Integral reaction data were obtained from a small fixed bed reactor, packed with the same catalyst. A kinetic model, based on adsorption-desorption and reaction of activated hydrocarbon species, was developed and the ten kinetic parameters in it were estimated from the packed bed data. Statistical methods for the design of experiments for parameter estimated and for model discrimination were employed. This chemical kinetic model was used with a number of available two-phase mechanistic models to describe the fluid mechanical behaviour in fluidized beds. A catalyst activity and an interchange factor, which provides a prediction of the interchange of gas between the bubble and the emulsion phase in a fluidized bed were estimated from the plant data. Statistical methods were used to plan the experiments to allow a combination of maximum discrimination among models and a test of the models over the full range of possible operating conditions. A model discrimination criterion which takes into account the effect of errors in parameter estimates is developed and applied to determine the best model for this system at two fluidized bed heights.</p> <p>Fluidized bed models are evaluated in the light of this experience. Some of the problems associated with obtaining estimates of parameters in one experimental system and applying them in another are delineated. General guidelines are indicated for modelling large industrial-scale reactors.</p> / Doctor of Philosophy (PhD)
84

Aluminum Hydrolysis Effects on Phosphorus Removal from Wastewaters

Diamadopoulos, Evangelos 06 1900 (has links)
<p>It is widely recognized that phosphorus removal from wastewaters by coagulation with aluminum salts is brought about not by the aluminum ion itself but by the hydrolysis products of the metal ion.</p> <p>The present work investigated the effectiveness of the aluminum polymeric species in phosphorus removal. These species were formed by partially neutralizing an aluminum chloride solution with sodium hydroxide under controlled conditions and they were given the name PBAC for Polymerized Basic Aluminum Chloride. The results were compared with those obtained using Alum, the most commonly employed aluminum coagulant. Although the removal of phosphorus from wastewaters was the main objective, the work extended to other areas such as supernatant suspended solids removal, sludge filtrability and organics removal.</p> <p>The factors that were found to influence the efficiency of the coagulants were:</p> <p>(i) The aging time of the aluminum polymers,</p> <p>(ii) The OH:Al molar ratio in the preparation of PBAC,</p> <p>(iii) The Al:P molar ratio (Aluminum dosage),</p> <p>(iv) The pH,</p> <p>(v) The presence in the wastewater of other ionic species.</p> <p>It was found that the removal of phosphorus could be adequately explained by a model involving complex formation and precipitation. It was shown, however, that the removal of organics cannot be attributed to a strictly chemical interaction and other mechanisms should be considered as well.</p> / Master of Engineering (ME)
85

Opposing Free and Forced Convective Heat Transfer to Turbulent Air Flow in a Verticle Pipe

Khosla, Kumar Jagjit 11 1900 (has links)
<p>The interaction between the opposing free and forced convection has been studied, by first defining the limits of the onset of flow reversal, through flow visualisation experiments involving the cooling of upward flowing hot water. From dynamic similarity considerations, these experiments were used to define the operating conditions, for experiments involving the heating of downward flowing air, to ensure unidirectional flow. Radial measurements of the temperature and velocity were made, in a 24 in. long, 8.054 in. diameter test section, with fully developed turbulent air flow entering its inlet. The inlet Reynolds numbers ranged from 7500 to 37500, the test section wall temperature was maintained constant for any run; the temperature range covered was 122ºF to 890ºF. Some temperature profiles exhibited unusual behaviour and this indirectly indicated flow reversal in situations where it was expected from the dynamic similarity considerations.</p> <p>The partial differential equations for the conservation of mass, momentum and energy were solved numerically by an implicit finite difference formulation. Good agreement between the predictions and the observations was obtained for negligible buoyancy force; while deviations increased with an increase in the relative magnitude of the buoyancy force. During the various attempts to resolve this discrepancy, it was felt that a change in the turbulence structure might have occurred. The effective conductivity profiles, calculated from the measured temperature profiles indicated an increase in the turbulent activity with increasing free-forced convection interaction. Heat transfer rates were found to be 215% higher than those obtained from pure forced convection considerations, for Gr/Re² ~ 0.90.</p> / Doctor of Philosophy (PhD)
86

Polymerization Kinetics and Properties of Vinyl Polymers

Abdel-Alim, Hazem Ahmed 09 1900 (has links)
<p>This thesis has been written as three self-consistent parts. Part One reports on experimental and theoretical investigation of the kinetics of the bulk polymerization of vinyl chloride. Part Two found its origin in Part One and resulted from the need of unambiguous characterization of the polymer synthesized. Molecular aggregation can interfere with the interpretation of all classical methods of polymer characterization in addition to gel permeation chromatography. Part Three resulted from an independent study performed by the author to broaden his knowledge in the field of polymer science and engineering in the area of polymer rheology. The results of this study were very successful and made a significant contribution to polymer rheology and therefore are reported herein. Some details of these three Parts follow under separate headings.</p> / Doctor of Philosophy (PhD)
87

Polymer Reactor Design, Optimization and Control in Latex Production Technology

Penlidis, Alexander 09 1900 (has links)
<p>During continuous emulsion polymerization of many monomers (e.g. vinyl acetate, vinyl chloride), sustained oscillations (limit cycles) occur in conversion and all the latex and polymer properties. This creates severe problems with the commercial application of continuous reactors. As shown by Pollock (1984) advanced control theory is inadequate for controlling these reactors. However, it was shown that the limit cycle behaviour could be eliminated through redesign of the reactor train configuration. The redesigned production train was shown via simulation to be free of oscillations and to offer greatly increased flexibility in controlling particle size and monomer conversion.</p> <p>In this thesis the mathematical model of Kiparissides (1978) and Pollock (1984), based on a particle age distribution analysis and incorporating detailed chemistry and physics of the polymerization phenomena involved, is modified and is used to simulate the dynamic behaviour of these reactors for different modes of process operation (batch, semi-batch and continuous train) and monomer systems (PVAc, PVc).</p> <p>Experimental studies which demonstrate the improved dynamic performance of the redesigned reactor system are carried out in a pilot plant stainless steel reactor train with on-line monitoring of monomer conversion with a set of on- line densitometers. Control of the final latex particle size and conversion is achieved through manipulation of the initiator feed rate to the first particle nucleating reactor, and the split of the monomer and water flow rates between the first two reactors of the train.</p> <p>The effect of monomer arid water soluble impurities on the emulsion polymerization of Case I monomers is further investigated both theoretically and experimentally. Experimental identification and verification of the main source of stochastic disturbances in these systems was thus obtained.</p> / Doctor of Philosophy (PhD)
88

Application of Adaptive Control to a Reciprocating Plate Liquid-Liquid Solvent Extraction Column

Camurdan, Cihan Mehmet 09 1900 (has links)
<p>An experimental investigation of the application of direct digital control (DDC) has been carried out with continuous chemical processing equipment, namely a liquid-liquid solvent extraction column. The type of extractor used was the Karr reciprocating plate column.</p> <p>Steady state simulations of the column were carried out using both a semi-empirical model for studying the hydrodynamics of the column, and a mechanistic model for studying the mass transfer characteristics of the column. The results of these simulations were used to interpret the closed loop response characteristics of the column. Two types of control schemes were studied; (i) an adaptive self tuning regulator (STR), (ii) the Dahlin algorithm.</p> <p>Though the dispersed phase holdup is not the primary control variable, its control is essential to prevent the hydrodynamic instability. The frequency of reciprocation was used to control the holdup. The relationship between the frequency of reciprocation and the dispersed phase holdup is highly nonlinear therefore an adaptive controller (in this work, a self tuning regulator) has to be used to control this process. Previous work on holdup control has been extended to include a wider, range of operating conditions and prevention of covariance windup by using an empirical discounting factor.</p> <p>The primary control objective was the control of the extract concentration. This was done in two ways. The first scheme was a cascaded control to manipulate the frequency of reciprocation whereby the inner loop was the holdup control. An STR-STR cascade arrangement was compared with cascade a PI-STR arrangement. It was found that the restrictions imposed on the outer loop meant that the PI-STR arrangement, was as effective as the STR-STR arrangement. The second control scheme manipulated the continuous phase flow rate with (MIMO) and without (SISO) the simultaneous control of the holdup via manipulation of the frequency of reciprocation. A variable dead time Dahlin controller was used to control the extract concentration in this second control scheme. In the MlMO case, decoupling was not necessary since one loop had a positive gain while the other had a negative gain and so the interactions were constructive.</p> / Doctor of Philosophy (PhD)
89

Measurement and Modelling of Long Chain Branching

Thomas, Sydney 02 1900 (has links)
<p>The measurement and modelling of long chain branching (LCB) in free-radical chain growth polymerization is examined. A new method, the "instantaneous" property method, is presented for the calculation of the full molecular weight distribution(MWD) of branched polymers when the branching is due to chain transfer to polymer. The method is shown to be accurate and consistent with the method of moments, the method that is generally used to calculate molecular weight averages. The method can give additional detail about the MWD of the various branched families in the polymeric mixture. Such information can be quite useful in correlating processing properties with molecular structure. Two polymers that produce LCB when polymerized were examined. Bulk polymerization of vinyl acetate (VAc) and p-methyl styrene were carried out. Gel permeation chromatography. intrinsic viscosity and low angle laser light scattering measurements were used to measure molecular weight averages and LCB frequencies. Two methods were used to calculate LCB frequencies and they both gave results that were consistent with the method of moments. The "instantaneous" method was applied to the data from the polymerization of PPMS since for this polymer LCB is due to chain transfer to polymer. The predictions from the "instantaneous" method, when compared to the method of moments and the experimental data, were shown to be of acceptable accuracy.</p> / Doctor of Philosophy (PhD)
90

Modelling the Competitive Adsorption of 1,1,2-Trichloroethane with Naturally Occurring Background Organics onto Activated Carbon

Narbaitz, Martin Roberto January 1985 (has links)
<p>Activated carbon adsorption is the most widely considered process for the removal from drinking water of low level toxic chemicals as well as many other organic substances. The adsorption of these compounds involves complex competitive interactions which are not well understood, however, they are crucial to the design of safe and cost effective adsorbers. To obtain a better understanding of competitive adsorption as observed in water treatment adsorber, at the time of a toxic spill, a three part study was conducted with a representative bisolute mixture. The mixture consisted of a toxic chemical (1,1,2-trichloroethane (TCEA)) and the naturally occurring organic substance from a northern river considered as a single compound and measured as TotaI Organic Carbon.</p> <p>The first part of this study consisted of single solute adsorption and desorption experiments as well as blsolute equiIibrium experiment. The adsorption of TCEA was found to be completely reversible, while that of the background organics was virtually irreversible. The bIsolute experiments showed that the background organics substantIally decreased the adsorption capacIty of TCEA, while the adsorption capacity of the background organics was only marginally reduced by the presence of TCEA. The predictive multisolute Isotherm models in the literature could not describe the experimental data. Two other models, which assume that a fraction of the adsorption does not involve competition, were found to describe the data successfully.</p> <p>The second part of this study investigated the rates of adsorption from one-adsorbate and two-adsorbate soIutions. The data of both single adsorbate kinetic experIments were described very well by the homogeneous surface diffusion model. The adsorption of the background organic was very slow, yet it was not necessary to utilize separate terms for the slow and rapid adsorption mechanisms. All of the adsorption occurred by the slow mechanism. The slow adsorption phenomenon, which is suspected to occur in very small pores, appears to be related to the irreversible adsorption observed during equilibrium studies. The background organics that adsorbed by the slow mechanism were virtually not desorbable, while TCEA which adsorbed completely reversibly, did not show any slow adsorption during the kinetics. As expected from the large difference in the values of the diffusion coefficients, to properly model the bisolute batch kinetic experimental data, diffusional interactions such as cross diffusion terms had to be included.</p> <p>The third part of this investigation was a column study involving six different phases, each with a different feed solution. The results were consistent with the equilibrium predictions. Phase IV showed that an expected and potentially dangerous large scale desorption of previously adsorbed toxic organics, caused by a substantial increase in the feed background organics, did not occur. The elution of TCEA actually decreased, probably due to cross diffusional interactions. The column experiment also confirmed that due to competitive interactions and to the increasing loading of background organics on the carbon with time, the adsorbers became substantially less effective at treating toxic spills as the operation cycle proceeded.</p> / Doctor of Philosophy (PhD)

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