Introduction

The separation of solutes by means of liquid membranes is based on a simple and well-established idea: two completely miscible liquid phases, separated by a third liquid, immiscible with either of them, can exchange solutes, provided there is a difference between their chemical potentials in the two phases and provided the intermediate liquid is able to transport them. In most cases the two miscible liquids, denoted hereafter as donor and acceptor phases, are aqueous solutions and the third (membrane) phase is an organic liquid. The configuration involving two organic solutions separated by an aqueous membrane is less popular.

The growing interest in the recovery and separation of solutes by means of liquid membranes may be related to the advantages of this separation method over the related separation operations - solid membranes and solvent extraction - as well as to the recent development of efficient liquid membrane techniques and contactors.

The main advantage of liquid membranes over polymer ones is the higher flux, owing to the very much higher diffusion coefficients of solutes in liquids than in solids. Moreover, some liquid membrane techniques allow a convective diffusion regime instead of a molecular one, which also increases fluxes. Another advantage of liquid membranes is the availability of a great number of substances which, when added to the liquid membrane phase, increase selectivity.

A liquid-membrane process can be regarded as a combination of extraction and a stripping process, which take place simultaneously in the same device. In solvent extraction, both the extractant amount and the distribution coefficient of the solute play essential roles for process efficiency, whereas in liquid membrane separation the selectivity is controlled by the kinetics of the transport process. In contrast to solvent extraction, in liquid membrane separation the amount of transferred solute is not proportional to the amount of the solvent used, in this case the membrane liquid. The relatively small amount of the latter permits the use of various highly efficient and selective - even expensive - carriers.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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