<p>The adsorption of residual organic molecules generated during the metabolic activity of bacteria was investigated.</p> <p>At first a number of potential adsorbants and ion exchange resins were selected with different average pore diameters and specific surface areas.</p> <p>The adsorption (removal) capacity of these materials was evaluated through the determination of their adsorption isotherms on a residual organics solution, obtained from an activated sludge reactor, that operated with Phenol as a substrate.</p> <p>On the basis of these isotherms Filtrasorb 400, an activated Carbon with 35Aº average pore diameter and 1200 m²/g specific surface area, was selected as the best adsorbant. Subsequently a fluidized bed biological reactor was used to study the direct adsorption of the residual organics produced by the biofilms on the Filtrasorb 400 particles supporting the growth. A phenol solution was fed to the reactor and different Oxygen to Phenol ratios were applied.</p> <p>The adsorption of the residual organics molecules generated by the biological growth in a fluidized bed biological reactor proved feasible and independent of the Oxygen to Phenol ratio applied. The Phenol removal efficiency of the reactor was determined by the Oxygen supplied. The removal reached 100% whenever residual Oxygen was present in the effluent of the reactor (no Oxygen limitation).</p> <p>Specific reaction rates higher than the ones reported in the literature were observed.</p> <p>The removal of the residual organics resulted in a stable effluent pH.</p> <p>The monitoring of the height of the expanded bed that developed biological growth is a parameter that can be used to monitor the total volume of biological films in the reactor. A volume yield can also be calculated.</p> / Master of Engineering (ME)

<p>Herein is reported a theoretical and experimental evaluation of liquid exclusion chromatography (LEC) for the measurement of particle size distribution (PSD) and diameter averages for colloidal spheres of various compositions.</p> <p>Correction factors for axial dispersion have been derived for a general detector whose signal is proportional to the number of particles time particle diameter to the power gamma (γ) where γ varies from zero to six. This general detector includes a turbidimeter (γ=6) and a refractometer (γ=3).</p> <p>Equipment and operational variables and their effect on resolution were investigated experimentally. These included packing and pore sizes, bed length and carrier liquid flowrate.</p> <p>The use of LEC for the off-line monitoring of the growth of latex particles was investigated for the surfactant-free emulsion polymerization of two monomer systems-styrene and vinyl acetate.</p> <p>LEC can be used to quantitatively measure the size distribution and diameter averages of both organic latices and inorganic particles in the submicron range in an off-line analytical mode. LEC is sufficiently rapid for the off-line monitoring of latex particle growth in emulsion polymerization. With some modification it could be used in an online mode as a sensor for reactor control.</p> / Master of Engineering (ME)

<p>Polyurethanes have been a material of choice for the fabrication of many conventional blood-contact devices such as vascular grafts, cardiac assist devices and total artificial hearts. Although these applications have had some success for short term applications there is a major limitation in their use for long term applications. The deficiency of the current devices and their associated materials arises from the foreign nature of these prostheses with respect to the body. Most often these devices initiate a natural physiological response that defends the body by attacking the foreign surfaces. When the materials contact with blood, the response is a series of events which lead to the eventual formation of a thrombus. In turn this often results in the dislodging of microscopic thrombi which can embolize and cause strokes.</p> <p>There is therefore a need to better understand the interactions of blood with polyurethanes and to develop polyurethanes of improved blood compatibility. In this thesis the proposition is explored that improved materials may be achieved by incorporating chemical functional groups that are known to be important in the interactions of vascular and other components tending to prevent thrombogenesis. These components are the plasma proteins, the blood cells and the endothelium. Thus functional groups have been incorporated covalently into "conventional" polyurethanes as follows: (1) sulfonate groups which are an important component of the vascular wall and of the anticoagulant heparin, (2) certain amino acid moieties which are involved in the neutralization of clotting enzymes particularly serine proteases, (3) hydrocarbon chains which might be expected to bind albumin, a passivating protein, from blood, and (4) polyethylene oxide chains which might be expected to simulate the hydrogel-like nature of quiescent blood cell/plasma interfaces and which have been shown by others to minimize interactions with proteins.</p> <p>The novel polyurethane materials were extensively characterized for several aspects of bulk and surface properties and response to plasma proteins. The functionalized materials were found to have greatly modified properties relative to conventional non-functionalized polyurethanes. Using differential scanning calorimetry and Fourier transform infra-red spectroscopy it was possible to associate this modified behaviour with the formation of Ionic clusters within the microdomain structures of the polyurethanes.</p> <p>The different functional groups of the sulfonated and derivatized polymers allow the materials to achieve very high levels of water uptake. These elevated water levels give a hydrogel-like character to the polymers which in turn yields very low contact angle values. Furthermore, it would appear from ESCA (electron spectroscopy for chemical analysis) surface analysis data and the time dependence of sessile drop contact angle data that the material surface in air is substantially different than when the surface is contacted with an aqueous medium.</p> <p>Measurements of the adsorption of fibrinogen from plasma and buffer were carried out using radiolabelling methods. The specific functionality of the different materials combine with their hydrogel-like nature to yield fibrinogen adsorption patterns in plasma that are unique and different from previously studied polyurethanes. Some of the materials were evaluated for their ability to delay plasma clotting times using standard thrombin time measurements. The results would suggest that sulfonaed and some derivatized polyurethanes may be capable of deactivating thrombin, which is a key enzyme in the formation of fibrin, the primary constituent of blood clots.</p> <p>The work of this thesis makes the following contributions: (i) a general method of introducing chemical function into the hard segment of polyurethanes involving reaction of amine or hydroxyl groups with sulfonyl chloride, (ii) improved understanding of polyurethane ionomer structure. (iii) methods of controlling protein interactions and water uptake of polyurethanes by incorporation of specific functional groups.</p> / Doctor of Philosophy (PhD)

<p>Relevant mechanisms involved in the heterogeneous free radical polymerization of vinyl chloride have been identified including elementary chemical reactions. physical phenomena of polyvinylchloride particle formation and reactant species distributions in phases during polymerization. A comprehensive reactor model for batch and semi-batch processes has been developed on the basis of these mechanisms. The present model accounts for comprehensive elementary chemical reactions, for the effect of diffusion-controlled reactions, for the monomer and initiator distributions among phases and for radical migration between monomer and polymer phases during polymerization. Wide ranging kinetic data covering commercially significant conversion and reaction temperature ranges were measured in the present investigation to better understand the mechanisms involved and to estimate model parameters. The present model predictions are in excellent agreement with experimental data obtained in the present work and independently in other laboratories. The model allows one to predict reactor pressure development; monomer conversion histories; polymerization rates; the critical conversion at the end of two phase polymerization; the limiting conversion for polymerization at temperatures below the polyvinylchloride glassy-state transition temperature; instantaneous and accumulated molecular weight averages and distributions, and other kinetic features of vinyl chloride polymerization over temperature and conversion ranges of commercial interest.</p> <p>The effect of polymerization conditions on polymer properties, especially the thermal stability of polyvinylchloride, has been elucidated. Deterioration of the thermal stability of polymer at high conversions is attributed to a decrease in monomer concentration. The secondary reactions which form the defect structures in polyvinylchloride are favoured at high conversions because of the increase in radical and polymer concentrations and the decrease in monomer concentration. The defect structures which are responsible for the low thermal stability of polyvinylchloride can be minimized significantly by using a semi-batch process at high conversions. Significant improvement in thermal stability of polyvinylchloride at high productivity by semi-batch processing at the monomer vapour pressure was demonstrated in the present investigation.</p> <p>A novel method for monitoring monomer conversion online during the suspension polymerization of vinyl chloride was developed in the present study. This method provides an effective tool not only for vinyl chloride polymerization kinetic studies but also can be adapted for use with other monomer and comonomer systems.</p> / Doctor of Philosophy (PhD)

<p>The kinetics of free-radical polymerization with and without crosslinking have been studied both theoretically and experimentally using methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) as a model system.</p> <p>The mechanisms involved in the auto-acceleration of polymerization rate due to both chain physical entanglement and/or chemical crosslinking of polymerchains have been further elucidated using on-line electron spin resonance techniques (ESR). It was found that the observed radical trapping effect is associated with the conversion rate auto-acceleration phenomenon and that there exist two radical populations during the auto-acceleration period. The polymerization system is therefore heterogeneous with respect to the radical environment. The trapped radical fraction has been estimated by both post-effect measurement of radical concentration and deconvolution of the ESR signal. Crosslinking has been found to significantly enhance auto-acceleration and radical trapping. The radical concentrations found using large concentrations of crosslinker reach levels as high as 10⁻³ molar. The stability of the radicals trapped on the polymer network has been studied at temperatures up to 180ºC to assess the potential of the so-called reactive gels for various applications.</p> <p>Radical concentrations versus time were measured by ESR for the copolymerization of MMA/EGDMA over the entire ranges of monomer composition and conversion. Together with conversion measurements, this provides a set of comprehensive kinetic data suitable for the estimation of individual rate constants for propagation, termination and also the initiation efficiency. It was found that these kinetic rate constants and the initiation efficiency fall simultaneously and dramatically when the polymerization system approaches its glass state. The free-radical gelation of MMA/EGDMA system under adiabatic conditions has also been investigated. These kinetic data permits severe testing of existing kinetic gelation models and suggest the need for further effort to develop more realistic models. For the theoretical work done in this thesis. the effort was directed to the development of more realistic kinetic models. Progress has been made in the following aspects: (1) A general method was developed to acount for chain-length dependent bimolecular terminatioll ofpolymer radicals for linear chain systems. With this method, there is no need to propose the full form of the bivariate distribution function which accounts for the dependence ofthe termination constanton the chain lengthsofterminatingpolymerradicals. (2) The Tobita-Hamielec kinetic model for free-radical polymerization with crosslinking was re-examined. The governing moment equations using the pseudo-kinetic rate constant method has been derived to include gel population and extended for asymmetric divinyl monomers.Anewsemi-statistical gelationmodel wasderived. Thismodel clearly illustrates the influenceofcrosslinkdensity distributiononotheraspectsofpolymernetworkformation. Problems in post-gelation modelling were addressed and discussed in terms of further development to provide a more realistic kinetic model. (3) A comprehensive kinetic model for the chemical modification of prepolymer in reactive processing using free-radical initiator has been derived. This model equationswhen solved give the full molecularweight distribution at different degrees of chain scission, long chain branching, crosslinking and grafting (processing time, type and level of initiator and additive). A general scheme for kinetic parameter estimation bas been also suggested.</p> / Doctor of Philosophy (PhD)

<p>The availability of fast, reproducible on-line instrumentation plays a critical role in paving the way for improvements in the productivity and product quality of industrial processes. In the polymer latex industry, one of the primary reasons for the lack of adequate instrumentation is that the traditional on-line sensors for density, viscosity, light scattering and absorption seldom respond to only one property; instead, their response is a function of many latex properties. If, however, these sensors respond differently to latex property changes, a novel approach to instrumentation is to use information from several of them to infer several quality variables simultaneously. This thesis applies this concept to two latex systems. The first is the continuous emulsion polymerization of poly(vinyl acetate). A density meter and the single wavelength UV turbidity of a diluted sample are used to track solids fraction and mean particle size on a pilot scale reactor. To sensor-latex property relationships are derived from a mechanistic understanding of the system. The standard deviation of the solids fraction measurement is 0.8% of value, for the mean diameter, it is 3%. The second process is the batch copolymerization of styrene and methyl methacrylate (MMA). Two spectrometers, covering a wavelength range from 190 nm to 1800 nm were used to predict the weight fractions of water, styrene and MMA monomer, poly(styrene), and poly(MMA). The standard deviations of the composition measurements were between 0.2 and 1.2 weight percent. The sensor-latex property relationships were arrived at by an empirical, multivariate calibration. The important implications of these results are that: (1) the number of sensors that could be considered for on-line analyzers is greatly increased; and (2) this methodology may be successful for previously intractable instrumentation problems. Also, potentially any latex property that can be measured in the laboratory can be included in the calibration, provided the property of interest has a reproducible effect on the response of the sensor.</p> / Doctor of Philosophy (PhD)

<p>The recovery of BaSO₄ mineral slimes (-10 microns) from silica using dispersed and dissolved air flotation, was studied. Experiments were performed in a modified commercial batch flotation machine. The influence of flotation variables such as collector concentration, concentration of silica depressant, pH, aeration and mineral purity on flotation parameters were also examined.</p> <p>Experimental evidence suggests that dissolved air flotation results in enhanced BaSO₄ recovery over that normally achieved using dispersed air flotation for a limited range of experimental conditions. This range is characterized by poor BaSO₄ flotation conditions such as low pH or collector concentration. The flotation of BaSO₄ was found to be strongly influenced by variables which regulate the surface chemistry of the mineral, such as collector concentration, pH, silica depressant and mineral purity. It was also speculated that mechanical transfer or gangue into the froth may be a critical factor in the upgrading of barite ores.</p> / Master of Engineering (ME)

<p>Adsorption rates and equilibria of several gases on 4A zeolite powder were measured with the aid of a constant pressure, variable volume apparatus. Data are presented for Ar, CH₄, N₂, C₂H₆, CO, CO₂ and O₂ at various temperatures between -150ºC and +20ºC. In calculating diffusivities, due account was taken of the fact that the zeolite particles were cubes having a range of sizes.</p> <p>Equilibrium data are represented by Martin's version of the viral equation for two - dimensional non-ideal cases.</p> <p>Diffusivities generally increase with adsorbate concentration and this tendency is more marked for gases which can strongly interact with the sodium cations in the 4A zeolite crystal structures. Entropies and enthalpies of activation for diffusion are presented and explained in terms of the molecular properties and heats of adsorption for the various adsorbates.</p> / Doctor of Philosophy (PhD)

<p>This study considers control problems associated with robust stability and performance of linear, time-invariant multivariable controllers. The robust stability and performance problems considered here are determined exclusively by the steady-state properties of closed-loop systems, and therefore they are independent of controller design and tuning methods. New approaches, one based on geometric interpretations and the other on singular value decomposition, are proposed to analyze the effects of steady-state model mismatches. The new analysis approaches are able to distinguish the critical differences between a process and its model that cause the control problems, and to identify the crucial process characteristics that must be preserved in the model if the closed-loop system is to be robust. This study shows that these properties are related to specific geometric differences and to particular elements in the singular value decomposition matrices, and that it is the structure rather than the magnitude of multivariate model mismatch that dominates the robustness properties. These results explain the fact that many nonlinear processes can be controlled by linear controllers with robustness over a wide range of operating conditions, in spite of the large mismatch magnitudes arising from process nonlinearities. Physical examples of these processes are given in this thesis. The analysis results are also used to specify new criteria for experimental designs to identify linear models that lead to robust multivariable controllers. The new experimental designs are based on minimizing model uncertainities in the multivariate model structure rather than simply the mismatch magnitude. The significance of the new experimental design approach is that it can identify robust models that yields high-performance control even for ill-conditioned processes. These robust identification designs usually require input perturbations that are drastically different from traditional designs.</p> / Doctor of Philosophy (PhD)

<p>This research deals primarily with the design and implementation aspects of model based digital control algorithms. The performance of model based digital controllers degrades whenever the process input saturates or the process model is significantly different from the true process. Simulations and experiments have been performed to identify the saturation problems in model based controllers and four algorithms were proposed to compensate for this problem. The saturation problem was generalized to cover all situations where the output computed by the model based controller cannot be applied to the actual process. This includes actuator saturation, operator override, temporary actuator failure and asynchronous control. A generalized implementation scheme of model based controllers was proposed and a dramatic performance improvement was observed by using such an implementation scheme. The second part of the thesis focuses on the robustness aspect of model based controllers. The work reported here takes a time domain, rather than the traditional frequency domain approach. A new stability theorem and corollaries for uncertain systems have been derived and applied to simulated processes. A new analysis method, Error Band Method (EBM), has been developed to analyse the performance of a dynamic uncertain control system. Monte Carlo simulations have been performed to verify the validity of this approach. The method was extended to include controller design and controller comparisons. This methodology provides a different perspective to the analysis and design of uncertain model based digital control system.</p> / Doctor of Philosophy (PhD)