Phase separation of solvent mixtures with a critical point of miscibility.
Item
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Title
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Phase separation of solvent mixtures with a critical point of miscibility.
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Identifier
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AAI9946171
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identifier
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9946171
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Creator
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Gupta, Rajan.
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Contributor
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Advisers: Reuel Shinnar | Roberto Mauri
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Date
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1999
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical
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Abstract
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In this work, the dynamics of phase separation in liquid mixtures, phase separation in the presence of surfactants, and a novel separation process of liquid-liquid extraction have been studied.;In the first part of this work, we study the phase segregation of a partially miscible liquid mixture when it is quenched to a temperature T deeply below its critical point of miscibility Tc, with |T-Tc| / Tc ∼ 0.1. In the case of initially homogeneous mixture, we observe the formation of single phase microdomains, which grow linearly in time in the range of 10--400 pm, indicating that phase segregation is driven by convection, and not by diffusion. While these domains are interconnected dendritic structures when the mixture had critical composition, they appear to be spherical drops in the off-critical case. On the other hand, when the mixture is initially segregated everywhere, with the exception of a millimeter-thick region, a sharp interface appears a few seconds after the quench, with no visible drops forming. Using a dimensional analysis of the governing equations based on the model H, we show that phase separation is governed by the convection induced by capillary forces, and not by diffusion. In addition, we determine an expression estimating the growth rate of single-phase domains, which is in very good agreement with our experimental results.;In the second part of this work, we show that the presence of surface-active compounds does not influence the settling time of a partially miscible liquid mixture as it phase separates. On the other hand, when the same mixture, in its two-phase state, is agitated isothermally, its settling time greatly increases if surfactants are added. This phenomenon is monitored microscopically, and is explained theoretically applying the model H, showing that during phase transition the capillary forces induce a net attraction between droplets which greatly dominates the repulsive forces due to the presence of surfactants.;Finally, we describe a new liquid-liquid extraction process, which capitalizes on the properties of partially miscible solvents. It consists in first mixing the system to be extracted with a primary solvent, which is soluble with the native solvent, and subsequently adding a modifier, which is insoluble with either the native or the primary solvent. This process has the advantage that the resulting separation of the solvents is very rapid, even in the presence of emulsion-forming impurities. In addition, the extraction efficiency of the new process may be ten times higher than that of the traditional liquid-liquid extraction. The new process is thought of having significant advantages in the extraction of products from fermentation broths, plants and other natural sources.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
