Chemical and Biomolecular Engineering - Theses

Permanent URI for this collection

http://hdl.handle.net/11343/354

Filters

2012 1
1
Reset filters

Settings
Statistics
Citations
Subject: solvent extraction × Author: Ciceri, Davide ×

Search Results

Now showing 1 - 1 of 1
  • Item
    Thumbnail Image
    The use of a Y-Y shaped microfluidic device for the study of solvent extraction kinetics
    Ciceri, Davide ( 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.