One of the most important issues in suspension polymerisation process is the control of the final particle size distribution (PSD) as this is an indicator for both quality and financial matters. For polymer manufacturers, a narrow PSD is always welcome. The conventional reactors, e. g. stirred tank reactors, generally produce particles of a rather broad PSD. As a result, to explore a new type of polymerisation devices becomes a challenging task. The objectives of this PhD study are to apply a novel mixing apparatus, the oscillatory baffled reactor (OBR), to batch polymerisation of MMA and Styrene (crosslinked) and to characterise all the major aspects of the OBR involved in the pioneering work, with a view to assessing its potential for industrial applications. In order to carry out such investigations, a 1.2 litre batch jacketed OBR system with temperature control and on-line data acquisition units was designed and built. In addition, an off-line image capture system was set up f or droplet studies. From heat transfer study in the OBR, it was found that the temperature profiles across and along the reactor were uniform and a heat transfer correlation was obtained. The oil-water dispersion in the OBR was then investigated for various baffle designs, dispersed phase fractions and the levels of surfactants, enabling the optimal baffle type and parameters to be identified. In order to understand the droplet behaviour in the OBR, the droplet size distribution (DSD) was examined on dispersion uniformity, oscillation time, operational conditions, baffle thickness and the level of surfactant addition. It was found that the DSDs were very uniform within the reactor and the oscillation frequency and amplitude had the same effect on controlling the DSDs. Finally, a series of PMMA and PS tests were successfully conducted in the OBR, indicating that the polymer PSD can be controlled by adjusting both oscillation conditions and the baffle orifice diameter and that the OBR has the potential to produce uniform polymer particles at high oscillation frequencies. A correlation between droplet sizes with no reaction and final polymer particle sizes was established, which can be used to predict the final polymer sizes.

No description available.

No description available.

As a byproduct of incomplete combustion, soot attracts increasing attentions as extensive researches exploring serious health and environmental effects from soot particles. Soot emission reduction requires a comprehensive understanding of the mechanism for polycyclic aromatic hydrocarbons and of soot formation and aging processes. Therefore, advanced experimental techniques and numerical simulations have been conducted to investigate this procedure. In order to investigate the effects of dimethyl ether (DME) mixing on soot particle size distribution functions (PSDFs), DME was mixed in premixed ethylene/oxygen/argon at flames at the equivalence ratio of 2.0 with a range of mixing ratio from 0% to 30% of the total carbon fed. Two series of atmospheric pressure flames were tested in which cold gas velocity was varied to obtain different flame temperatures. The evolution of PSDFs along the centerline of the flame was determined by burner stabilized stagnation probe and scanning mobility particle sizer (SMPS) techniques, yielding the PSDFs for various separation distances above the burner surface. Meanwhile, the flame temperature profiles were carefully measured by a thermocouple and the comparison to that of simulated laminar premixed burner-stabilized stagnation flame was satisfactory. Additionally, to understand the chemical role of DME mixing in soot properties, characterization measurements were conducted on soot samples using thermo-gravimetric analysis (TGA) and elemental analysis (EA). Results of the evolution of PSDFs and soot volume fraction showed that adding DME into ethylene flame could reduce soot yield significantly. The addition of DME led to the decrease of both the soot nucleation rate and the particle mass growth rate. To explain the possible mechanism for the observation, numerical simulations were performed. Although DME addition resulted in the slight increase of methyl radicals from pyrolysis, the decrease in acetylene and propargyl radicals inhibited the production of polycyclic aromatic hydrocarbons. At the same time, the addition of DME gave rise to the increase of the flame temperatures, which favored the production of OH radicals. The incremental concentration of OH radicals promoted the oxidation rate of soot particles. Additionally, soot samples from flames with higher DME mixing ratios showed higher O/C, H/C mass ratios and thus better oxidation characteristics. In summary, the addition of DME reduces soot emission in two ways: on the one hand, it inhibits soot nucleation and mass/size growth, then the production of soot particles decreases; on the other hand, it promotes soot oxidation process by increasing the concentration of OH radicals and improving the oxidation behavior of the soot particles, then more particles are oxidized. Both of them are responsible for the reduction of soot emissions at the presence of DME.

No description available.

As commercially manufactured nanomaterials become more commonplace, they have the potential to enter ecological and biological environments sometime during their lifecycle of production, distribution, use or disposal. Despite rapid advances in the production and application of nanomaterials, little is known about how nanomaterials may interact with the environment or affect human health. This research investigates an environmental application of nanomaterials and characterizes the physicochemical properties of commonly manufactured nanomaterials in environmental health and safety studies. Characterization of nanomaterials for applications and environmental health and safety studies is essential in order to understand how physicochemical properties correlate with chemical, ecological, or biological response or lack of response. Full characterization includes determining the bulk and surface properties of nanomaterials. Bulk characterization methods examine the shape, size, phase, electronic structure and crystallinity, and surface characterization methods include surface area, arrangement of surface atoms, surface electronic structure, surface composition and functionality. This work investigates the selective catalytic reduction (SCR) of NO2 to N2 and O2 with ammonia on nanocrystalline NaY, Aldrich NaY and nanocrystalline CuY using in situ Fourier transform infrared (FTIR) spectroscopy. It was determined that the kinetics of SCR were 30% faster on nanocrystalline NaY compared to commercial NaY due to an increase in external surface area and external surface reactivity. Copper-cation exchanged nanocrystalline Y resulted in an additional increase in the rate of SCR as well as distinct NO2 and NH3 adsorption sites associated with the copper cation. These superior materials for reducing NOx could contribute to a cleaner environment. This work consists of characterization of commonly manufactured or synthesized nanomaterials and studies of nanomaterials in specific environmental conditions. Bulk and surface characterization techniques were used to examine carbon nanotubes, titanium dioxide nanoparticles, bare silver nanoparticles and polymer-coated silver nanoparticles, and copper nanoparticles. Lithium titanate nanomaterial was collected from a manufacturing facility was also characterized to identify occupational health risks. Particle size distribution measurements and chemical composition data showed the lithium titanate nanomaterial forms larger micrometer agglomerates, while the nanoparticles present were due to incidental processes. A unique approach was applied to study particle size during dissolution of nanoparticles in aqueous and acidic conditions. An electrospray coupled to a scanning mobility particle sizer (ES-SMPS) was used to determine the particle size distribution (PSD) of bare silver nanoparticles in nitric acid and copper nanoparticles in hydrochloric acid. The results show unique, size-dependent dissolution behavior for the nanoparticles relative to their micrometer sized counterparts. This research shows size-dependent properties of nanomaterials can influence how they will be transported and transformed in specific environments, and the behavior of larger sized materials cannot be used to predict nanomaterial behavior. The type of nanomaterial and the media it enters are important factors for determining the fate of the nanomaterial. These studies will be important when considering measures for exposure control and environmental remediation of nanomaterials.

This thesis is based on observations of the physical properties of wheat flour dough using ultrasonic measurements. Three frequency ranges were used in the study, low frequencies (near 40 kHz), intermediate frequencies (1 to 5 MHz, where bubble resonance effects are apparent), and high frequencies (near 20 MHz). Doughs mixed under different head space air pressures, from vacuum to atmospheric pressure, as well as under nitrogen, were studied at low frequency to investigate their relaxation behavior. Subsamples from ambient dough and vacuum dough displayed differences in the dependence of velocity and attenuation on time after compression, but no post mixing relaxation effect was apparent. A critical headspace pressure of approximately 0.16 atmospheres determined whether vacuum-like or ambient-like relaxation was observed. A peak in attenuation and changes in ultrasonic velocity were observed around the bubble resonance frequency, and these ultrasonic parameters changed substantially as a function of time. A bubble resonance model was used to interpret the results around the bubble resonance frequency, and bubble size distributions were estimated for ambient and vacuum dough from the ultrasonic data. For the high frequency range, a molecular relaxation model was used to interpret the results. Different fast relaxation times were observed for ambient dough (5 ns) and vacuum dough (1 ns). This relaxation time may be associated with conformational rearrangements in glutenin inside the dough matrix. These experiments have enabled dough relaxation to be probed over a very wide range of time scales (from ns to hours), and will lead to a better understanding of the role of dough matrix and gas cell effects on the physical properties of wheat flour doughs. / October 2007

This thesis is based on observations of the physical properties of wheat flour dough using ultrasonic measurements. Three frequency ranges were used in the study, low frequencies (near 40 kHz), intermediate frequencies (1 to 5 MHz, where bubble resonance effects are apparent), and high frequencies (near 20 MHz). Doughs mixed under different head space air pressures, from vacuum to atmospheric pressure, as well as under nitrogen, were studied at low frequency to investigate their relaxation behavior. Subsamples from ambient dough and vacuum dough displayed differences in the dependence of velocity and attenuation on time after compression, but no post mixing relaxation effect was apparent. A critical headspace pressure of approximately 0.16 atmospheres determined whether vacuum-like or ambient-like relaxation was observed. A peak in attenuation and changes in ultrasonic velocity were observed around the bubble resonance frequency, and these ultrasonic parameters changed substantially as a function of time. A bubble resonance model was used to interpret the results around the bubble resonance frequency, and bubble size distributions were estimated for ambient and vacuum dough from the ultrasonic data. For the high frequency range, a molecular relaxation model was used to interpret the results. Different fast relaxation times were observed for ambient dough (5 ns) and vacuum dough (1 ns). This relaxation time may be associated with conformational rearrangements in glutenin inside the dough matrix. These experiments have enabled dough relaxation to be probed over a very wide range of time scales (from ns to hours), and will lead to a better understanding of the role of dough matrix and gas cell effects on the physical properties of wheat flour doughs.

This thesis is based on observations of the physical properties of wheat flour dough using ultrasonic measurements. Three frequency ranges were used in the study, low frequencies (near 40 kHz), intermediate frequencies (1 to 5 MHz, where bubble resonance effects are apparent), and high frequencies (near 20 MHz). Doughs mixed under different head space air pressures, from vacuum to atmospheric pressure, as well as under nitrogen, were studied at low frequency to investigate their relaxation behavior. Subsamples from ambient dough and vacuum dough displayed differences in the dependence of velocity and attenuation on time after compression, but no post mixing relaxation effect was apparent. A critical headspace pressure of approximately 0.16 atmospheres determined whether vacuum-like or ambient-like relaxation was observed. A peak in attenuation and changes in ultrasonic velocity were observed around the bubble resonance frequency, and these ultrasonic parameters changed substantially as a function of time. A bubble resonance model was used to interpret the results around the bubble resonance frequency, and bubble size distributions were estimated for ambient and vacuum dough from the ultrasonic data. For the high frequency range, a molecular relaxation model was used to interpret the results. Different fast relaxation times were observed for ambient dough (5 ns) and vacuum dough (1 ns). This relaxation time may be associated with conformational rearrangements in glutenin inside the dough matrix. These experiments have enabled dough relaxation to be probed over a very wide range of time scales (from ns to hours), and will lead to a better understanding of the role of dough matrix and gas cell effects on the physical properties of wheat flour doughs.

No description available.