Accelerated Coalescence in Phase Separation of Partially Miscible Solvents

在一项由美国国家科学基金会资助的研究中，一种新的液-液萃取工艺正在研究中，该工艺利用了具有溶解度临界点的部分可混溶溶剂的特性。在此过程中，首先将临界混合物与待分离的溶质一起加热到临界温度以上，形成均匀溶液，然后冷却到混相曲线以下的热力学不稳定区域，在此溶剂分离成共存相。这个新工艺不仅是可行的，而且是非常有利的，尤其是在处理易于乳化或形成稳定分散体的体系时。例如，它可以在不使用离心机的情况下处理发酵液，这是一项对生物分离具有深远影响的技术突破。新分离工艺的高效率是由于一种从未在文献中报道过的现象：当共存曲线以下淬火后的相分离时，聚结不仅大大加快，而且对溶剂和溶质杂质的敏感性远低于等温操作。采用新的分离技术，可以使发酵液的聚结时间减少三个数量级，而传统的等温分离过程会形成稳定的分散体和乳剂。拟议的研究打算利用光散射和摄影技术详细调查这种加速聚结现象，并试图制定定量的理论解释。本研究的结果将对理解溶剂萃取中阻碍聚合的一般现象具有科学和技术意义，并将对由于共存曲线上的冷却或加热而导致的部分混相混合物的相分离提供一些启示。

In a research effort presently funded by NSF a novel liquid- liquid extraction processes is being investigated, which capitalizes on the properties of partially miscible solvents with a critical point of solubility. In this process the critical mixture, together with the solute to be separated, is first heated above its critical temperature, where it forms a uniform solution, and then cooled to the thermodynamically unstable region below the miscibility curve where the solvents separate into who coexisting phases. This new process was shown not only to be feasible, but also to extremely advantageous, above all when dealing with systems that tend to emulsify or form stable dispersions. For example, it can handle a fermentation broth without using a centrifuge, which is a technical breakthrough with far-reaching implications in bioseparation. The high efficiency of the new separation process is due to a phenomenon that has never been reported in the literature: when phases separation after quenching below the coexistence curve, coalescence is not only greatly accelerated, but it is much less sensitive to impurities of both solvents and solutes than during isothermal operations. The coalescence times of a fermentation broth can be reduced by three orders of magnitude by using the new separation technique in place of the traditional isothermal process, in which cause the formation of stable dispersions and emulsions. The proposed research intends to investigate this phenomenon of accelerated coalescence in detail, using light-scattering and photographic techniques, accompanied by an attempt to formulate a quantitative theoretical explanation. The results of this study will be of both scientific and technical interest in understanding the general phenomenon of hindered coalescence in solvent extraction and will shed some light on the phase separation of partially miscible mixtures due to cooling or heating across the coexistence curve.