Accelerated Coalescence in Phase Separation of Partially Miscible Solvents

在目前由NSF资助的一项研究工作中，正在研究一种新型的液-液萃取方法，该方法利用了具有溶解度临界点的部分混溶溶剂的性质。在该过程中，临界混合物与待分离的溶质一起首先被加热到其临界温度以上，在此其形成均匀溶液，然后冷却到溶解度曲线以下的溶剂不稳定区域，在此溶剂分离成共存相。这种新工艺不仅可行，而且非常有利，尤其是在处理倾向于分散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。新分离过程的高效率是由于文献中从未报道过的现象：当淬火后相分离低于共存曲线时，聚结不仅大大加速，而且对溶剂和溶质的杂质的敏感性远远低于等温操作。用这种新的分离技术代替传统的等温过程，使发酵液的聚结时间缩短了三个数量级，从而形成稳定的分散液和乳状液。拟议的研究旨在详细调查这种加速聚结的现象，使用光散射和摄影技术，并试图制定一个定量的理论解释。这项研究的结果将是科学和技术的兴趣，在理解的一般现象，阻碍聚结溶剂萃取，并将揭示一些光的相分离的部分互溶的混合物，由于冷却或加热的共存曲线。

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.