This thesis is concerned with the study of different effects in protein ultrafiltration including device configuration, solution chemistry and membrane charge In the recent and more established literature membrane fouling remains a challenging problem that limits the wider application of ultrafiltration. Thus, investigations which can aid understanding and potentially reduce membrane fouling are of particular interest and in this study the problem has been addressed from several different angles Polyethersulfone membranes were studied at varying pH and two ionic strengths using bovine serum albumm and lysozyme as the model proteins. The study was conducted both in a stirred cell and a crossflow configuration in order to evaluate the influence of different system hydrodynamics on filtration This work was further substantiated through the application of filtration models An attempt was also made to modify the membrane surface by low temperature plasma modification with the intention to preferentially alter the characteristics of the membrane surface Both unmodified and plasma-modified polyethersulfone membranes were characterised using a range of analytical methods including flux data, streaming potential, contact angle and MWCO measurements to aid results interpretation. The research showed that MWCO data quoted by manufacturers is mostly greater than that obtained during laboratory studies The MWCO technique was also used to highlight differences between the unmodified and plasma-modified membranes demonstrating that the modification resulted in a membrane with tighter pores in the lower molecular weight region. Concentration polarisation effects were found to be reduced as a result of the plasmamodification The study of protein filtration at different pH and ionic strengths demonstrated that ionic strength effects were more pronounced than pH effects It was also shown that changes m the ionic strength can be used to alter the degree of protein rejection for the given system concentration polarisation was found to be higher during crossflow filtration compared to stirred cell filtration The thesis adds to existing knowledge in the area of ultrafiltration emphasizing the importance of device configuration, solution chemistry as well as the potential of charged membranes

In the bio/pharmaceutical industry, fermentation is extremely important in pharmaceutical development, and in microbial research. However, new fermentor designs are needed to improve production and reduce costs of complex systems such as cultivation of mammalian cells and genetically engineered micro-organisms. Traditionally, stirred tank design is driven by the oxygen transfer capability needed to achieve cell growth. However, design methodologies available for stirred tank fermentors are insufficient and many times contain errors. The aim of this research is to improve the design of production scale stirred tank fermentors through the development of dimensionless correlations and by providing information on aspects of fermentor tanks that can aid in oxygen mass transfer. This was accomplished through four key areas. Empirical studies were used to quantify the mass transfer capabilities of several different reactors. Computational fluid dynamics (CFD) was used to assess the impact of certain baffle and impeller geometries. Correction schemes were developed and applied to the experimental data. Dimensionless correlations were created from corrected experimental data to act as a guide for future production scale fermentor design. The methods for correcting experimental data developed in this research have proven to be accurate and useful. Furthermore, the correlations found from the corrected experimental data in this study are of great benefit in the design of production scale stirred tank fermentors. However, when designing a stirred tank fermentor of a different size, further experimentation should be performed to refine the correlations presented.

Extensive use of stirred vessels in the process industries for various operations has attracted researchers to study the mixing mechanisms and its effects on the processes. Among the various flow-measuring methods, Particle Image Velocimetry (PlV) technique has become more popular in comparison to LDA and HW A methods because of its ability to provide instantaneous velocity fields. The present study uses this technique to investigate the flowfields and turbulent properties in a 290mm vessel stirred by Rushton Disc turbine (RDT) and Pitched blade turbine (PBT) impellers. Angle-resolved instantaneous flow-fields were obtained using 2-D and 3-D PlV technique. Flows in the RDT were examined. The distribution of out-of-plane vorticity and turbulent properties such as rms velocities, Reynolds stresses and turbulent kinetic energy was discussed. The flow number and power number of the RDT impeller were obtained as 0.83 and 5.16 respectively. Flows generated by the PBT impeller were examined in more detail. For this purpose, a multiblock approach was developed which allowed analysing larger fields of view with reasonably higher resolution. Whole vessel was thus mapped and various turbulent properties were examined. The mean flow-fields, out-of-plane vorticity and turbulent properties such as Reynolds stresses, turbulent kinetic energy and turbulent energy dissipation rates were estimated at different angle of blade rotation. The variation of the trailing vortex axis was obtained. The pumping number and power number ofPBT impeller was obtained as 0.86 and 1.52 respectively. Using this information, an integral length scales were estimated using 2-D FFT autocorrelation, which showed that these length scales vary significantly through out the vessel. It is demonstrated that assuming constant length scale through out the vessel could underestimate dissipation rate up to 25% in the impeller discharge. A kinetic energy balance was carried out around the PBT blades. It is shown that around 44% of the total power consumed by the impeller is dissipated within the impeller. The average rate of dissipation of kinetic energy was 39 times higher in the impeller region than the average dissipation rate in the vessel. Using LDA and PIV techniques, macro-instabilities (Ml) were studied. Spectral analysis was done using LOMB algorithm, which showed the presence of a dimensionless frequency of O.013-0.0174N in the RDT and PBT impellers. The frequency of Ml varied linearly with the impeller speed. The maximum broadening of turbulence levels due to the presence of Ml was around 20% for the PBT and 18% for the RDT impeller. The effect of mixing on the feed locations was studied using PlV measurements. Results showed that there is no direct effect of feed coming out of the feed pipe on the flow distribution, however, due to feed pipe, there was a wake formation close to the feed pipe. The low Reynolds number in the wake can affect local mixing conditions close to the feed pipe. At the end, angle-resolved Reynolds stresses were calculated and was noticed that flows in the vessel were isotropic in the bulk of the vessel however, anisotropic flow was noticed in the impeller stream.

Research Doctorate - Doctor of Philosophy (PhD) / This thesis describes a study in which the aim was to develop an improved method for computational fluid dynamics (CFD) modelling of gas-liquid flow in mechanically-stirred tanks. Stirred tanks are commonly used in the process industries for carrying out a wide range of mixing operations and chemical reactions, yet considerable uncertainties remain in design and scale-up procedures. Computational modelling is of interest since it may assist in investigating the detailed flow characteristics of stirred tanks. However, as shown by a review of the literature, a range of limitations have been evident in previously published modelling methods. In the development of the modelling method, single-phase liquid flow was firstly considered, as a basis for extension to multiphase flow. A finite volume method was used to solve the equations for conservation of mass and momentum, in conjunction with the k-epsilon turbulence model. Simulation results were compared with experimental measurements for tanks stirred by a Rushton turbine and by a Lightnin A315 impeller. Comparison was made between different methods which account for impeller motion. Accuracy was assessed in terms of the prediction of velocities, power and flow numbers, the presence of trailing vortices, pressures around the impeller, and the turbulent kinetic energy and dissipation rate. The effect of grid density was investigated. For gas dispersion in a liquid, the modelling method employed the Eulerian-Eulerian two-fluid equations, again in conjunction with the k-espilon turbulence model. The correct specification of the equations was firstly reviewed. Different forms of the turbulent dispersion force were compared. For the drag force, it was found that existing correlations did not properly account for the effect of turbulence in increasing the bubble drag coefficient. By analysing literature data, a new equation was proposed to account for this increase in drag. For the prediction of bubble size, a bubble number density equation was introduced, which takes into account the effects of break-up and coalescence. The modelling method also allows for gas cavity formation behind impeller blades. Simulations of gas-liquid flow were again carried out for tanks stirred by a Rushton turbine and by a Lightnin A315 impeller. Again, the impeller geometry was included explicitly. A series of simulations were carried out to test the individual effects of various alternative modelling options. With the final method, based on developments in this study, simulation results show reasonable overall agreement in comparison with experimental data for bubble size, gas volume fraction, overall gas holdup and gassed power draw. In comparison to results based on previously published modelling methods, a significant improvement has been demonstrated. However, a number of limitations have been identified in the modelling method, which can be attributed either to the practical limitations on computer resources, or to a lack of understanding of the underlying physics. Recommendations have been made regarding investigations which could assist with further improvement of the CFD modelling method.

A jet-stirred reactor was designed and constructed in the Clean Combustion Research Center (CCRC) at King Abdullah University of Science and Technology (KAUST); was validated with n-heptane, iso-octane oxidation and cyclohexene pyrolysis. Different configurations of the setup have been tested to achieve good agreement with results from the literature. Test results of the reactor indicated that installation of a pumping system at the downstream side in the experimental apparatus was necessary to avoid the reoccurrence of reactions in the sampling probe. Experiments in ethyl levulinate oxidation were conducted in the reactor under several equivalence ratios, from 600 to 1000 K, 1 bar and 2 s residence time. Oxygenated species detected included methyl vinyl ketone, levulinic acid and ethyl acrylate. Ethylene, methane, carbon monoxide, hydrogen, oxygen and carbon dioxide were further quantified with a gas chromatography, coupled with a flame ionization detector and a thermal conductivity detector. The ethyl levulinate chemical kinetic model was first developed by Dr. Stephen Dooley, Trinity College Dublin, and simulated under the same conditions, using the Perfect-Stirred Reactor code in Chemkin software. In comparing the simulation results with experimental data, some discrepancies were noted; predictions of ethylene production were not well matched. The kinetic model was improved by updating several classes of reactions: unimolecular decomposition, H-abstraction, C-C and C-O beta-scissions of fuel radicals. The updated model was then compared again with experimental results and good agreement was achieved, proving that the concerted eliminated reaction is crucial for the kinetic mechanism formulation of ethyl levulinate. In addition, primary reaction pathways and sensitivity analysis were performed to describe the role of molecular structure in combustion (800 and 1000 K for ethyl levulinate oxidation in the jet-stirred reactor).

This work offers a well-developed understanding of the mixing process inside Jet- Stirred Reactors (JSR’s) with different geometries. Due to the difficulty of manufacturing these JSR’s made in quartz, existing JSR configurations were assessed with certain modifications and optimal operating conditions were suggested for each reactor. The effect of changing the reactor volume, the nozzle diameter and shape on mixing were both studied. Two nozzle geometries were examined in this study, a crossed shape nozzle and an inclined shape nozzle. Overall, six reactor configurations were assessed by conducting tracer experiments - using the state-of-art technologies of high-speed cameras and laser absorption spectroscopy- and Computational Fluid Dynamics (CFD) simulations. The high-speed camera tracer experiment gives unique qualitative information – not present in the literature – about the actual flow field. On the other hand, when using the laser technique, a more quantitative analysis emerges with determining the experimental residence time distribution (RTD) curves of each reactor. Comparing these RTD curves with the ideal curve helped in eliminating two cases. Finally, the CFD simulations predict the RTD curves as well as the mixing levels of the JSR’s operated at different residence times. All of these performed studies suggested the use of an inclined nozzle configuration with a reactor diameter D of 40mm and a nozzle diameter d of 1mm as the optimal choice for low residence time operation. However, for higher residence times, the crossed configuration reactor with D=56mm and d=0.3mm gave a nearly perfect behavior.

Soot formation mechanisms have been a target of intense research for decades. The various stages in the soot formation mechanism have been accepted and recognized, nevertheless, the nucleation stage, which corresponds to the transition from gas phase polycyclic aromatic hydrocarbons (PAH) to condensed particles, is controversial. Pyrene dimerization is considered by many models to be the first step in soot nucleation. In this work, a jet-stirred reactor (JSR) in the temperature range of 700 – 1200 K was used to perform pyrene pyrolysis and to study the various dimerization Nascent particles were chemically analyzed using Fourier-transform ion cyclotron resonance high resolution mass spectrometry (FT-ICR MS) with a laser desorption ionization (LDI) source. Simulations were realized based on a simple kinetic model using CHEMKIN-PRO, which addressed three different dimerization pathways: 1) physical dimerization of two pyrene molecules (P-DIM), 2) physical dimerization between a pyrene molecule and a pyrenyl radical (PR-DIM), and/or 3) chemical dimerization between two pyrenyl radicals (C-DIM). The detected species presented 202 and 402 Da masses in the mass spectra with different intensities. At higher temperatures, the formation rate was enhanced due to the sensibility of particle formation to the reaction temperature. The first temperature regime was identified at 700 – 900 K, where the detected species contained only pyrene molecules, stacked by Van der Waals forces (P-DIM). In the 900–1100 K range, the formation of pyrenyl radicals was considered, and the production of PR-DIM was favored. In the higher temperature range (1100–1200 K), the greater species' mass were located and related to the dimerization of two pyrenyl radicals (C-DIM). The temperature increase was reflected in the production of higher concentrations of the pyrenyl radical, resulting in the dominance of the chemical dimerization pathway at 1200 K. The use of different initial concentrations of pyrene in the simulations did not significantly affect the outcome. Results of the experiment were reflected in the simulations, based on the model used, revealing the tendency of the three dimerization pathways, the decreased survival rate of physically-formed dimers, and the enhanced production of chemically-linked dimers at high temperatures.

Rapid consumption of energy storage and serious environmental pollution demand more advanced combustion strategies and more renewable fuels. Development of chemical kinetic models and suitable selection of fuels are key factors in evolving and optimizing new engine and combustion concepts. Alkenes are typical composition of gasoline as well as typical intermediates in the oxidation of larger alkanes and alcohol, while isoprene is one of the important alkenes impacting both the atmospheric pollution and energy depletion. Isoprene is one of the most important species in the atmosphere chemistry, dominating the carbon flux emitted by vegetation and accounting for forty percent of non-methane biogenic emissions globally. Isoprene has been recognized not only as a noteworthy precursor to polycyclic aromatic hydrocarbons but also as a promising fuel additive. Isoprene has been extensively investigated in the atmosphere chemistry, but its role as a critical diolefin in combustion chemistry has received less attention. Only A few researchers studied isoprene chemistry by carrying out pyrolysis experiments and theoretical calculations. To better understand the combustion chemistry of isoprene, this work presents a detailed experimental and kinetic modeling investigation. This study explored the chemical kinetics of isoprene oxidation in ignition delay times and speciation measurements. Our shock tube experiments for ignition delay times covered the temperatures of 680 – 1470 K, pressures of 1 – 30 bar, and equivalence ratios of 0.5 – 2. We measured laser-based time-resolved CO speciation in a low-pressure shock tube at temperatures of 900 – 1470 K, pressures of 1 and 4 bar, and equivalence ratios of 0.5 and 1. Major species concentrations were measured in a jet-stirred reactor at 680 – 1280 K, 1 bar, and φ = 0.5 – 2. Afterwards, we used 1,3-butadiene as a basis to develop fuel-specific isoprene sub-mechanism and coupled it with a C0-C5 core sub-mechanism. Finally we developed a comprehensive kinetic model including 1585 species and 6884 reactions and achieved a good agreement between the model’s predictions and the experiments. To our knowledge, this study is the first comprehensive effort to describe the process and provides valuable insights into isoprene oxidation. The work reported in the thesis also facilitates the better understanding of combustion chemistry of diolefins.

Crystallization is a key unit operation in the fine chemical and pharmaceutical industries, many of which employ batch stirred vessels for crystallization. Although using stirred vessels for crystallization has advantages such as better mixing and faster cooling, one of the disadvantages is that due to the presence of mechanical parts in the vessel such as baffles, impeller etc., crystals break up while stirring and generate unwanted secondary nucleation. This process contributes to a wide crystal size distribution with a smaller than desired mean crystal size. For studying crystal breakage phenomenon, experimentalists choose to use nonsolvents for crystal breakage experiments to isolate breakage from simultaneously occurring phenomena such as Ostwald-ripening, aging and agglomeration. Although performing experiments in non-solvents eliminates other phenomena and helps isolate breakage, the results can not always be correlated to saturated solutions due to density and viscosity differences between the two conditions. In this research, the effects of Ostwald ripening, aging and agglomeration on the crystal size and shape distributions are quantitatively measured. Micro and macro scale experiments were performed in both non-solvents and saturated solutions and the results were compared to determine the effects. Both in situ focused beam reflectance method (FBRM) and off-line analyses were performed to characterize the crystal size distributions. Results from experiments show that there is significant difference between the breakage behavior of crystals in non-solvents and in saturated solutions, mplying significant impacts of Ostwald ripening, aging, agglomeration and dissolution in saturated solutions. Calculations using Zwietering correlation also show that the difference between the viscosities and densities in the two systems may also be a contributing factor to the difference in the breakage profiles. It was also found that growth rates of crystals can differ when they are subjected to stress and strain. In macroscale experiments, dissolution was found to have a significant impact on the crystal size distribution. Abrasion was found to be the dominating fracture mechanism for most systems. Extent of breakage and morphological changes were found to be dependent on stirring rates, suspension density, shape and hardness of crystals and the type of system.

<p> This dissertation describes an investigation into the free radical polymerization of styrene in continuous stirred tank reactors (CSTR's). The aim was to develop a steady state polymerization model which would accurately predict conversion and molecular weight distribution (MWD) up to high conversion. </p> <p> The dissertation is divided into three self-contained parts. Part I describes the testing and development of polymerization kinetics using a single CSTR. The single CSTR model is described. Theoretical and experimental conversions and MWD's are compared and discussed. </p> <p> Part II describes the development of a model for a system of CSTR's. It is based upon the single CSTR model and the kinetics developed in Part I. Theoretical and experimental results for a three reactor system are compared and discussed. </p> <p> Part III describes the development of gel permeation chromatography (GPC) for measuring MWD. Molecular weight and resolution calibration data are presented and discussed. Four methods of chromatogram interpretation that correct for imperfect resolution are compared. </p> / Thesis / Doctor of Philosophy (PhD)