大宗化学品工业：大宗化学品工业中的膜分离技术？ 我们应该注意到的很重要的一点是反渗透技术（仅仅在45年前，标志着膜分离历史的开始）和纳滤技术并不符合传统的过滤的概念，例如，传统意义上的从悬浮固体或液滴中分离出液体的方法，主要是利用过滤介质来拦截固体颗粒和液滴，这些介质带有大量的且尺寸适当的通孔。在这个过程中，过滤液体并不发生相变。 反渗透（和纳滤）与之相比主要是利用待分离物质在溶液中的扩散。当膜的两侧存在较高的压差时，溶液中的溶剂就会溶解到成膜物质中，在其中扩散移动，最终移到包含有纯净溶剂的另一侧。反渗透（和纳滤）并不是一种很理想的分离方法，主要是因为在溶剂扩散移动过程中，溶液中的溶质由于具有一定的扩散能力也必然要随之扩散。但是，由于溶剂的扩散系数要远远高于溶质，因此，分离过程实际上已基本完成。 it is important to note that reverse osmosis (with which the whole history of membrane separations began, just 45 years ago) and nanofiltration are not filtration processes in the normally accepted sense of the word, i.e. a separation of fluid from suspended solid particles or liquid droplets whereby the fluid passes without change of phase through a barrier by means of pores that are continuous from one side of the barrier to the other, and whose size is such as to hold back the particles of droplets. reverse osmosis (and nanofiltration) by contrast operate by diffusion from a solution. under the high differential pressure across the membrane, the solvent from the solution actually dissolves in the material of the membrane, diffuses across it and transfers out into the clean solvent on the other side. it is not a perfect separation, because the dissolved species from the feed solution have a definite ability to diffuse through it as well, but the diffusion coefficient for the solvent is so much higher than that for the solute that the separation is virtually complete.查看更多
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