No description available.

Air emissions from the combustion of fossil fuel, including carbon dioxide, sulfur dioxide, nitrogen dioxide and nitric oxide, have caused severe health and environmental problems. The post-combustion wet scrubbing has been employed for control of carbon dioxide and sulfur dioxide emissions. However, it is restricted by the sparingly water soluble nitric oxide, which accounts for 90-95% of nitrogen oxides. It is desirable and cost-effective to remove nitric oxide from flue gas by existing wet scrubbers for reduced capital costs and foot prints. In this research, absorption of nitric oxide from simulated flue gas using three different absorbents was first conducted in a bubble column system at room temperature and atmospheric pressure. Through performance comparison, ammoniacal cobalt(II) solutions were chosen as the optimum absorbent for nitric oxide absorption. Then the effects of fresh absorbent composition, pH value and temperature on nitric oxide absorption were investigated. Experimental results showed that the best initial NO removal efficiency of 96.45% was measured at the inlet flow rate of 500 mL·min-1; the room temperature of 292.2 K; the pH value of 10.50; and the concentrations of cobalt(II) solution, NO and O2 of 0.06 mol·L-1, 500 ppmv and 5.0%, respectively. For in-depth understanding of NO absorption into ammoniacal cobalt(II) complexes, equilibrium constants of reactions between nitric oxide and penta- and haxa-amminecobalt(II) solutions, respectively were determined using a bubble column reactor, in which the operation was performed continuously with respect to gas phase and batch-wise with respect to liquid phase. The experiments were conducted at temperatures from 298.2 to 310.2 K and pH from 9.06 to 9.37, all under atmospheric pressure. All experimental data fitted well to the following equations: K_NO^5=1.90×10^7 exp(3598.5/T) and K_NO^6=3.56×10^11 exp(1476.4/T), which give the enthalpy of reactions between NO and penta- and hexa-amminecobalt (II) nitrates as ∆H^5=-29.92 kJ·mol^(-1) and ∆H^6=-12.27 kJ·mol^(-1). In kinetic study, a number of experiments were conducted in a home-made double-stirred reactor at temperatures of 298.2 and 303.2 K and pH from 8.50 to 9.87 under atmospheric pressure. The reaction rate constants were calculated with the use of enhancement factor derived for gas absorption accompanied by parallel chemical reactions. The reaction between NO and pentaaminecobalt(II) was first order with respect to NO and pentaamminecobalt(II) ion, respectively. Similarly, the reaction between NO and hexaaminecobalt(II) was also first order with respect to NO and hexaamminecobalt(II) ion, respectively. The forward reaction rate constants of these two reactions were 6.43×10^6 and 1.00×10^7 L·mol-1·s-1, respectively at 298.2 K, and increased to 7.57×106 and 1.12×107 L∙mol-1∙s-1, respectively at 303.2 K. Furthermore, regeneration of used absorbent was attempted but fails. None of the additives tested herein including potassium iodide (KI), sodium persulphate (Na2S5O8) and activated carbon (AC) showed capability of regeneration at room temperature and atmospheric pressure. In addition, the effect of oxygen was investigated. With ammoniacal cobalt(II) compounds a positive effect of oxygen on NO absorption was observed. Calculated NO amount absorbed into the aqueous solution showed that with the oxygen the absorption reaction could be considered as irreversible. This fact was probably the reason for the failure of regeneration of the tested reagents. Last but not least, volumetric liquid-phase mass transfer coefficient, kLa, in some popular industrial absorbers including bubble column (BC), conventional stirred tank reactor (CSTR) and gas-inducing agitated tank (GIAT) were determined by modeling removal of oxygen from water. The experimental results could be well interpreted by mathematical models with 90% of deviations less than ±10 %.

No description available.

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

Acid treatments have predominantly been conducted using HCl for its availability, high rock dissolving power and soluble reaction products. At high temperatures, rapid spending of the acid with carbonates prevents deeper penetration distance into the formations. Alternative fluids such as acetic and formic acid have lent themselves to retarded reaction rates, low corrosivity and reduced tendency to form acid/oil sludge in asphaltene-rich crudes but for high reaction rate problems. Chelating agents, with the added advantage of complexing with alkali-earth metals in carbonates to form water-soluble products that are thermally stable at high temperature, have been introduced as stimulation fluids. Glutamic acid diacetic acid (GLDA) ethylenediaminetetraacetic acid (EDTA) and hydroxyethylenediaminetriacetic acid (HEDTA) are aminopolycarboxylic acids that were studied. To predict the spending of chelating agents relative to simple organic acids at temperatures between 150 and 250˚F, the chemical kinetics of dolomite dissolution in these acid solutions were investigated over different reaction conditions in a rotating disk apparatus. Samples of the reacted acids from the reactor were collected and then analyzed with inductively coupled plasma (ICP). Analyses of the experimental data were carried out to determine kinetic parameters of the heterogeneous reactions needed for matrix stimulation of dolomitic reservoirs. Experimental results indicated that dolomite dissolution rates increased in all the acid solutions as the disk rotational speeds increased at 150, 200, and 250˚F. The dissolution of dolomite in 0.886 M GLDA was found to be surface-reaction limited at lower temperatures and mass-transfer limited at highest temperature. GLDA with the lowest reaction rates and relative diffusion coefficient demonstrated retardation before spending with deeper penetration capability for productivity and injectivity improvement.

iv The recovery of lactic acid from its dilute aqueous solutions is a major problem. The ester of lactic acid, namely, methyl lactate has a wide range of applications. The esterification of an aqueous solution of lactic acid with methanol is a reversible reaction. As excess of amount water is present in the reaction mixture, the conversion is greatly restricted by the chemical reaction equilibrium limitations. In this study the esterification kinetics of lactic acid with methanol both in the absence and presence of an ion exchange resin as a heterogeneous acid catalyst was investigated with isothermal batch experiments between 40 - 70 0 C and at atmospheric pressure. Self-polymerization of lactic acid was enlightened by considering the hydrolysis reaction of lactoyllactic acid at the reaction temperatures and at various initial concentrations. Both homogeneous and heterogeneous reaction rate constants were evaluated. Methyl lactate process development was also investigated. The process was based on the recovery of 10% lactic acid by reaction with methanol in a absorption column using ion-exchange resin Lewatit SPC-112 H+. The effect of various parameters including lactic acid concentration or reactant molar ratio, lactic acid feed flow rate, methanol and inert carrier rate on reactor performance were studied. The reaction of methyl lactate formation over the ion exchange resin catalyst was observed to be slower than the mass transfer rate whereas mass transfer of methanol in gas phase was the limiting step for methanol transfer to the liquid mixture. Mass transfer of water from liquid phase to the gas phase was controlled by the mass transfer resistance of liquid phase. Thus, it can be concluded that the counter-current gas-liquid reactors with acidic solid catalysts can be used as simultaneous reaction and separation equipment.

A mathematical model is developed to study the coupled heat and moisture transfer through a fabric system that consists of a single layer of fabric and an air gap. Properties of air and moisture are sensitive to temperature and hence are assumed to be functions of local temperature. Therefore the model is applicable to a broad range of boundary conditions. A numerical scheme is proposed to solve the distributions of temperature and moisture concentration throughout the layers, from which the thermal and evaporative resistances of the fabric system can be evaluated. Experiments are conducted for two particular fabrics using a sweating guarded hotplate, and the data show good agreement with the model predictions. Using this model, the effects of parameters in environmental conditions, air gap and material properties on the thermal and evaporative resistances are studied. This work provides fundamental basis for the optimization of garment fit and material properties to achieve good performance for the clothing system.

The heat flux demands for electronics cooling applications are quickly approaching the limits of conventional thermal management systems. To meet the demand of next generation electronics, a means for rejecting high heat fluxes at low temperatures in a compact system is an urgent need. To answer this challenge, in this work a gasketed chevron plate heat exchanger in conjunction with a slurry consisting of highly endothermic solid ammonium carbamate and a heat transfer fluid. A reduced-order 1-dimensional model was developed and used to solve the coupled equations for heat, mass, and momentum transfer. The feasibility of this chosen design for satisfying the heat rejection load of 2kW was also explored in this study. Also, a decomposition reaction using acetic acid and sodium bicarbonate was conducted in a plate heat exchanger (to simulate a configuration similar to the ammonium carbamate reactions). This enabled the experimental validation of the numerical predictions for the momentum transfer correlations used in this study (which in turn, are closely tied to both the heat transfer correlations and chemical kinetics models). These experiments also reveal important parameters of interest that are required for the reactor design. A numerical model was developed in this study and applied for estimating the reactor size required for achieving a power rating of 2 kW. It was found that this goal could be achieved with a plate heat exchanger weighing less than 70 kg (~100 lbs) and occupying a volume of 29 L (which is roughly the size of a typical desktop printer). Investigation of the hydrodynamic phenomena using flow visualization studies showed that the flow patterns were similar to those described in previous studies. This justified the adaptation of empirical correlations involving two-phase multipliers that were developed for air-water two-phase flows. High-speed video confirmed the absence of heterogeneous flow patterns and the prevalence of bubbly flow with bubble sizes typically less than 0.5 mm, which justifies the use of homogenous flow based correlations for vigorous gas-producing reactions inside a plate heat exchanger. Absolute pressure measurements - performed for experimental validation studies - indicate a significant rise in back pressure that are observed to be several times greater than the theoretically estimated values of frictional and gravitational pressure losses. The predictions from the numerical model were found to be consistent with the experimental measurements, with an average absolute error of ~26%

Hollow fibre and spiral wound membrane (SWM) modules are the most common commercially available membrane modules. The latter dominate especially for RO, NF and UF and are the focus of this study. The main difficulty these types of modules face is concentration polarisation. In SWM modules, the spacer meshes that keep the membrane leaves apart also help reduce the effects of concentration polarisation. The spacer filaments act as flow obstructions, and thus encourage flow destabilisation and increase mass transfer enhancement. One of the detrimental aspects of the use of spacers is an increase of pressure losses in SWM modules. This study analyses the mechanisms that give rise to mass transfer enhancement in narrow spacer-filled channels, and investigates the relationship between flow destabilisation, energy losses and mass transfer. It shows that the regions of high mass transfer on the membrane surface correlate mainly with those regions where the fluid flow is towards the membrane. Based on the insights gained from this analysis, a series of multi-layer spacer designs are proposed and evaluated. In this thesis, a Computational Fluid Dynamics (CFD) model was used to simulate steady and unsteady flows with mass transfer in two- and three-dimensional narrow channels containing spacers. A solute with a Schmidt number of 600 dissolving from the wall and channel Reynolds numbers up to 1683 were considered. A fully-developed concentration profile boundary condition was utilised in order to reduce the computational costs of the simulations. Time averaging and Fourier analysis were performed to gain insight into the dynamics of the different flow regimes encountered, ranging from steady flow to vortex shedding behind the spacer filaments. The relationships between 3D flow effects, vortical flow, pressure drop and mass transfer enhancement were explored. Greater mass transfer enhancement was found for the 3D geometries modelled, when compared with 2D geometries, due to wall shear perpendicular to the bulk flow and streamwise vortices. Form drag was identified as the main component of energy loss for the flow conditions analysed. Implications for the design of improved spacer meshes, such as extra layers of spacer filaments to direct the bulk flow towards the membrane walls, and filament profiles to reduce form drag are discussed.