Chemical and Biomolecular Engineering - Theses
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ItemStudies on modeling and scale-up of ceramic hybrid pulsed column( 2018)Extraction of lithium from chloride brine in salt lakes is a separation process of great importance. It is also a promising industrial field where solvent extraction columns are likely to be used. However, the extraction solution is corrosive to traditional stainless steel column because of its high chloride content, therefore a type of novel anti-corrosive ceramic hybrid pulsed column is designed and tested in order to be considered for industrial applications, as well as a ceramic standard pulsed sieve plate column for comparison. The hydrodynamics of the two columns are tested under pilot plant conditions. For each column, effects of pulsation intensity and two phase velocities on holdup, characteristic velocity and Sauter mean diameter are investigated. Holdup of ceramic hybrid pulsed column is higher by around 50%. Correlations are proposed to predict holdup for both columns with ARD of 5.9% and 9.3% respectively. Characteristic velocity, which is key parameter in calculating column throughput, is investigated and modelled. Results show that characteristic velocities of ceramic pulsed sieve plate column are larger. Sauter mean diameter of ceramic hybrid pulsed column is smaller by around 30%. Correlations are proposed to predict the Sauter mean diameter, d_32, with ARD of 13.6% and 4.2% respectively. The higher holdup and smaller d_32 in the ceramic hybrid pulsed column contribute to larger mass transfer area and hence better mass transfer efficiency. Axial dispersion and mass transfer parameters, which are important to determine column height, are tested with a standard liquid-liquid system with medium interfacial tension, 30% TBP in Shellsol 2046–water with acetic acid as solute. Axial dispersion coefficients, E_c, of the ceramic hybrid pulsed column are less by around 50%. Effects of pulsation and two phase velocities on E_c are investigated. Correlations are proposed to predict E_c with ARD of 6.0% and 6.9% respectively. The height of overall mass transfer unit, H_ocp, of the ceramic hybrid pulsed column is less by around 40%, indicating better mass transfer efficiency. Effects of pulsation and two phase velocities on H_ocp are investigated. Volumetric mass transfer coefficients, K_oc a, for both columns are calculated. K_oc a of the ceramic hybrid pulsed column is higher by around 50%. Correlations are proposed to predict K_ox a with ARD of 12.0% and 7.0% respectively. Under proper operating condition, height of transfer unit of ceramic hybrid pulsed column can reach as low as 0.2m, showing very good efficiency. Two-phase computational fluid dynamics (CFD) models for the two columns are developed with commercial software ANSYS FLUENT. Hydrodynamic performance including two-phase distribution and velocity fields are generated. Holdup and axial dispersion coefficients are studied systematically, and CFD successfully predicts the higher holdup and lower axial dispersion coefficients for the ceramic hybrid pulsed column in experiments. CFD gives reasonable predictions for the trends of holdup and axial dispersion coefficients with pulsation intensity and two phase velocities. Predicted axial dispersion coefficients with this method are accurate. However the breakage and coalescence phenomenon of drop swarms is so complicated that the development of more accurate prediction method for holdup based on population balance model (PBM) still needs further research. A pilot ceramic hybrid pulsed column for lithium extraction from salt lake brine is designed for industrial applications. Physical properties are tested for the real system from Qinghai province, China. A MATLAB program is coded under the framework of design from first principles for the demonstration column, and its applicability is validated with experimental data. Program simulations are performed to investigate the effects of key operating parameters including two phase flow ratio and pulsation intensity. With considerations of volumetric efficiency and solvent reprocessing cost, these two parameters are determined to be V_c:V_d=1:1 and Af=1.0cm/s respectively. The demonstration column diameter and height are determined with the MATLAB program, under the operating conditions determined previously. To reach an annual yield of 10 tons/year and 99% lithium recovery in the extraction section, the demonstration column needs to have an effective height of 1.8m and an internal diameter of 0.36m.
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ItemThe use of a Y-Y shaped microfluidic device for the study of solvent extraction kinetics( 2012)Solvent extraction (SX) is usually defined as the process of transferring a substance from one liquid to another liquid phase for the purpose of purification and/or concentration. The commercial importance of SX processes is widely recognised in the metallurgical, pharmaceutical, “food and beverage”, petrochemical, nuclear, catalysis, polymer and material industry. SX is often considered to be the most efficient method of separating valuable products from complex liquid mixtures. Thus, SX is widely exploited in the production of precious metals and fine chemical products and constitutes one of the most important unit operations in the chemical industry. SX systems have been investigated under a variety of experimental conditions in both equilibrium and kinetic studies. Kinetics is important since it is intimately related to the mechanism of extraction, it has a major role in the choice of industrial operation conditions and it ultimately determines the size of the contacting equipment. Today a number of short residence time contactors are being proposed in which kinetics of extraction are becoming more important. However, due to the heterogeneous nature of these reactions, kinetic measurements are difficult. Therefore, mechanisms of extraction are not well understood. Indeed, a long term debate about the actual site of the extraction reaction seems still far from being concluded. Depending on the technique exploited for the kinetic study, different authors have often reported different mechanisms and/or contrasting conclusions. In order to thoroughly understand the mechanism of SX reactions, new tools to overcome limitations of traditional extraction kinetics techniques are necessary. Microfluidics is potentially one of these innovative tools. Microfluidics, the science and the technology that deals with the manipulation of small amount of fluids in microchannels, has proved to be a revolutionary tool in many fields of chemistry, physics and engineering. A few studies have already demonstrated the possibility to implement analytical techniques on microfluidic platforms. These include chromatography, electrophoresis as well as SX. The first report on SX procedures integrated on a microfluidic device was reported by Kitamori and co-workers in 2000. Since then, studies in this field have mushroomed in the literature. However, despite potential advantages that microfluidics could offer such as the high contact area per unit volume, the high throughput per total system volume and a significant reduction in the chemical quantities, some major complications also arise in the microenvironment. The fluid flow control is difficult and the full understanding of physical and chemical phenomena at this scale is still yet to be achieved. Consequently, very few studies on SX mechanistic have been attempted in a microdevice. In this thesis, the use of a Y-Y shaped microfluidic device for the study of solvent extraction kinetics relevant for the hydrometallurgical industry is demonstrated. The following contributions are discussed: i) a homogeneous (aq/aq) diffusion study of the Co(II) ion is carried out, ii) an improved stabilisation of a water/oil interface in the Y-Y shaped microchannel is achieved by coupling a guide structure with a glass wall surface treatment, iii) the heterogeneous diffusion of a probe molecule (8-hydroxyquinoline) is investigated and thoroughly explained in light of different mass transport models, each corresponding to different levels of approximation, iv) the extraction of Co(II) and Fe(III) by di (2-ethylhexyl) phosphoric acid (DEHPA) is performed in the microchannel and modelled; the extraction of Co(II) as well as that of Fe(III) are shown to occur in a regime controlled by the reaction kinetics. Consequences on mechanistic aspects are discussed and v) a prototype microfluidic device that integrated a UV-Vis detection system is also proposed. The functioning of the prototype is demonstrated and preliminary results on in situ detection of concentrated species are reported. Applications of the device to study concentrated SX systems such as those encountered in the hydrometallurgical industry are presented.