大宗化学品工业：大宗化学品工业中的膜分离技术？ 前面提及的另外一种膜分离过程——渗透气化中液体混合物中脱出蒸汽，或者是在气体或蒸汽渗透中，从混合物中脱出某种气体，这种分离过程采用了一种和反渗透类似的扩散机理。所有的这些扩散过程均需要成膜材料连续致密，常常采用片状或管状的高分子膜，而不能采用陶瓷膜。 超滤是另外一种位于过滤范畴边缘的情况，可以采用超滤的方法从大分子溶液中分离溶剂，也可以从胶体悬浮液中分离液体。不同滤膜的种类常用其所能截留颗粒的尺寸来区分，对于微滤膜来说，其所能截留颗粒尺寸的变化范围是从0.05μm (50nm)到3μm，而这很难满足超滤的要求。超滤的截留范围有时用截留直径表示(3-100nm或者是0.03-0.1μm)，有时折算成近似的截留分子质量，所用单位为原子质量单位道尔顿，此时超滤的截留范围约为从5000d (5kd) 到250kd。 纳滤的截留范围可以定义为0.8nm-8.0nm或者是200 d -14000d，而反渗透的截留范围可以达到200 d，但是，做这样的定义并不是非常有意义。 a similar diffusion mechanism applies for the other membrane processes mentioned above – of a vapour out of a liquid mixture for pervaporation, or of one gas out of a mixture for gas or vapour permeation. these diffusion processes all require the continuity of material represented by a polymeric membrane, in sheet or tubular form, and cannot be undertaken in ceramic materials. ultrafiltration is another borderline case as it is used to separate solvents from solutions of very large molecules, as well as the liquid from a suspension of colloidal solids. while it is normal to describe microfiltration membranes in terms of a retained particle size, the range being from 0.05μm (50nm) to 3μm, this is more difficult with ultrafiltration, for which the range is sometimes quoted in diameter terms (3-100nm or 0.03-0.1μm), and sometimes as an approximate molecular weight, in terms of daltons, the unit of atomic weight – when ultrafiltration covers from about 5000d (5kd) up to about 250kd. although not quite so meaningful, nanofiltration can be defined as covering 0.8- 8.0nm or 200-14000d, with reverse osmosis running up to 200d.查看更多
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