Nanofiltration membranes broaden the use of membrane separation technology

Most reverse osmosis (RO) research has concentrated on the development of single-pass seawater membranes. The success of these high rejection membranes has created interest in other applications requiring less demanding salt rejection, or desiring the elimination of salt from a feed stream (diafiltration), or having severe chemical resistance requirements. All would prefer to operate at lower net driving pressures than demanded by the high rejection membranes. This paper reports on the characteristics of three such tailored membranes. These membranes have been designated as “quo;nanofiltration”quo; membranes to distinguish them from the “quo;hyperfiltration”quo; seawater membranes. The first is XP45, a polyamide membrane with a low sodium chloride rejection that makes it an excellent candidate for applications such as the processing of salty cheese wheys and pharmaceutical preparations. The second is NF70, another polyamide, a low pressure membrane with rejections suited for converting mildly brackish water and organic-laden raw water to potable water that meets WHO standards. The third is XP20, a new developmental membrane for the maintenance of electroless copper plating baths.