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液-液-液三相（以下简称三液相）萃取是近年来发展起来的新型萃取分离技术。目前应用报道最多的是一类由有机油相、富聚合物中相和富盐下相构成的三液相萃取体系。开展此类三液相体系相分离动态和成相机理的研究，不仅可加深对复杂液相体系成相过程的科学认识，也为相关设备的设计及三液相萃取工业化应用的控制方法提供数据支持。 第一部分研究了由有机油相、富聚合物中相和富盐下相构成的三液相体系的动态成相行为特征。通过改变各成相组分的质量百分比，研究了三液相体系形成过程中的控速步骤及体系组成对于成相平衡时间的影响。发现在三液相体系成相过程中，富盐下相是一个连续相，分散的富聚合物水滴和油滴在连续的富盐下相中各自聚并和上浮，分别与富盐下相分离。随后富聚合物中相和油上相的分离继续进行，直到三液相体系成相完成。此过程中富聚合物相为分散相，油相可视为其连续相。当体系组成沿着不同操作线变动时，油相的形成均以油滴聚并作为控速步骤；但聚合物相的形成可能从液滴聚并控速变为液滴移动控速或二者混合控速。体系的成相平衡时间取决于其中富聚合物中相的成相速率和它的平衡体积。构建了三液相体系成相速率和体系性质之间的定量模型。 第二部分详细研究了成相盐种类对三液相体系动态成相行为的影响及原因。发现对于不同成相盐构成的三液相体系，富盐下相达到平衡体积的时间几乎一样。然而，随着成相盐阴离子或阳离子盐析能力的增大，富聚合物中相和油上相之间的分离会逐渐减慢。对相关原因做了详细地理论分析。一方面，成相盐离子盐析能力的增大会减小油滴之间的范德华引力以及油滴和富聚合物相介质之间的亲疏水差异程度，同时增大了油滴之间的空间斥力。另一方面，富聚合物滴之间的范德华引力和聚合物滴与油相介质间的亲疏水差异程也逐渐减小。因此，油上相和富聚合物中相的成相速率都减慢，从而导致二者分离速率降低。 第三部分在成功构建一个可用于盐湖卤水中锂和硼、镁同步分离的三液相萃取模型的基础上，关注了体系动态成相机理及对目标物分配行为的影响。发现在该体系中，锂在油相和硼在富聚合物相中的分配速率，取决于体系动态成相过程中油相和富聚合物相体积的增大速率。这是因为锂和硼分配进目标相的量由锂、硼各自目标相的体积以及其中锂、硼的浓度所决定。随着时间的推移，油相和富盐下相以及富聚合物相和富盐下相的分离速率很快完成，但油相和富聚合物相的分离速率慢。含锂油滴在富聚合物相介质中聚并成相时锂的浓度不再变化，含硼富聚合物滴在油相介质中聚并成相时硼的浓度也不变。但含锂油滴和含硼富聚合物滴聚并成相使得油相和富聚合物相的体积逐渐增大。所以影响油相和富聚合物中相体积变化的动态成相行为是锂和硼在目标相中分配的量的主要决定因素。 第四部分用不同分子量的聚合物构建了一系列萃取体系，用于盐湖卤水锂、硼、镁的分离，从成相的角度探究了锂和硼进入目标主体相的动态机理。PEG分子量增大使得富聚合物相粘度持续增大，但富聚合物相粘度对锂和硼分配速率的影响能力不具有持续性，这与锂、硼动态分配机理的改变有关。当富聚合物相粘度小时，锂和硼动态分配的依赖于“融合”机理，即含锂油滴和含硼富聚合物滴各自融合以实现相分离，分别将锂和硼分配进油相和富聚合物中相的主体相中。这种机理下目标物分配速率受控于富聚合物相的粘度。当富聚合物相粘度增大到一定程度后，锂和硼的分配依赖于熵驱动的油滴/油膜自发消失机理，即中上相分散带中的含锂油滴/油膜体积逐渐减小，油相主体相体积逐渐增大，最终实现含锂油相和含硼富聚合物相的完全分离。这种机理下目标物分配速率与富聚合物相的粘度无关。;Three-liquid-phase extraction is a newly developed technology for extraction and separation processes. Three-liquid-phase system (TLPS), which is composed of organic oil phase, polymer-rich middle phase and salt-rich bottom phase, is the most reported TLPS in literatures. Investigation on phase separation dynamics and phase-forming mechanism of such TLPS is not only benefit for our scientific understanding in complex systems containing multiple liquid phases, but provides supporting data that are needed for design of appropriate extraction separators and formulation of operation rules for future industrial application of three-liquid phase separation technology.In this dissertation, dynamic phase forming behavior of three-liquid-phase system (TLPS) composed of organic oil phase, polymer-rich middle phase and salt-rich bottom phase was investigated in detail. With changing mass composition of phase-forming components, the rate-control process in formation of such a TLPS was recognized, as well as the effect of system composition on the phase-forming equilibrium time (tE) of TLPS. It found that dynamic forming process of TLPS was in fact a course of dispersive polymer and organic oil droplets aggregated and separated out respectively from continuous salt aqueous bottom phase. After that the separation between polymer-rich phase and oil phase was still continued, until phase formation of TLPS completed. During separation of polymer-rich and oil phases, the former was the dispersed phase while the latter could be seen as the continuous phase of the former. Formation rate of organic oil phase was controlled mainly by coalescence rate of dispersed oil droplets; however, the rate-determining process for formation of polymer middle phase may change from drop sedimentation to coalescence or codetermined by both, when mass composition of the TLPS changed along different operation lines. The value of tE depends on formation rate of the polymer middle phase and its equilibrium volume. A quantitative correlation of phase separation rate of TLPS with its physicochemical properties was given.Effect of phase-forming salt on the dynamic behavior of phase formation of TLPS was also studied. It found that the species of salts exhibited almost no effect on the separation rate of oil top phase and polymer middle phase from salt aqueous bottom phase; however separation between oil top phase and polymer middle phase became slow with the increase of salting-out ability of the ions present in the slats. Theoretical analysis was provided in detail. On one hand, the Van der Waals attraction potential energy among dispersed oil drops and the media of polymer-rich phase decreased, while the energy from steric repulsion increased with increasing the salting-out ability. On the other, the Van der Waals attraction potential energy among dispersed polymer-rich aqueous drops and the media of oil phase decreased, too. Therefore, both decrease in the formation rate of the oil top and polymer-rich middle phases resulted into decrease in the rate of separation between them. Based on a TLPS which was successful in simultaneous separation of lithium from boron and magnesium in salt lake brine, the effect of dynamic phase forming behavior of TLPS on the dynamic partition behavior of objectives was focused. Results showed that the partition rate of lithium into the oil phase and that of boron into the polymer-rich middle phase was mainly governed by the increase rate of volume of their target phases during phase formation process of TLPS. This was because that the mass of lithium or boron partitioning into their target phases was determined by the volume of the phase and the concentration of lithium or boron in it. The separations between oil and polymer-rich drops from the salt bottom phase finished very quickly, but the separation between oil and polymer-rich phase was slow. With time went on, the concentrations of lithium in oil drops in the media of polymer-rich phase and that of boron in polymer-rich drops in the media of oil phase were fixed, but the volume of oil and polymer-rich bulk phases were increased along with separation of the two phases, which enhanced the mass of lithium and boron partitioning into their target bulk phases. Mechanism of dynamic partition behavior of targets in TLPS was explored from view of phase formation. Series molecular weights of polymers were employed to form TLPSs for extraction and separation of lithium from boron and magnesium in salt lake brine. It found that the rheological property of system continued to decrease with increasing the polymer molecular weight. But the effect of rheological property of system on the partition behavior of lithium and boron was not durative. This was attributed to the change in partitioning mechanism of lithium and boron. When the viscosity of polymer-rich middle phase was low, the partition of lithium and boron depended on separation of B-containing polymer-rich drops and Li-containing oil drops achieved by the two drops merging with their bulk phases respectively. By such “merging” mechanism the partition rate of lithium and boron was governed by the rheological property of system. Whilst, when viscosity of polymer-rich phase increased to a certain extent, separation of B-containing polymer-rich drops and Li-containing oil drops was completed by shrink of oil drops/films and expansion of oil bulk phase under driven of entropy. Thus, the partition rate of lithium and boron was independent of the rheological property of system.
|林洁媛. 液-液-液三相萃取体系相分离动态和成相机理研究[D]. 中国科学院研究生院,2018.|
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