The thin-film composite low pressure reverse osmosis membranes

Abstract

Reverse osmosis systems are generally designed and utilized on the basis of reference membrane water flux and desalting performance at 28 Kg/cm 2 (400 psi) net driving pressure (NDP). Low commercial stage are capable of equivalent performance at 14 Kg/cm 2 (200 psi) NDP. Further, possibly, super low pressure (SLP) membranes are capable of equivalent performanec at 7 Kg/cm 2 (100 psi) NDP. These LP and SLP membranes offer immediately obvious savings in energy cost for reverse osmosis desalting and water reclamation. In addition, they can make a most important contribution to reduced membrane replacement cost and improved permeate quality when operating on high salinity feeds at higher recevery levels. Two new series and four types of thin-film composite LP and/or SLP reverse osmosis membranes have been developed. These membranes, designated UTC series, give superior performance in such area as water flux, salt rejection, chemical stability and microbiological resistance. UTC-20 & 40 series membranes are designed for use at pressure of 5–15 kg/cm 2 (71–213 psi). UTC-20 series membranes are available in two grades. UTC-20 HR membrane has a high water flux over 2.4 m 3/m 2 day (60 gfd) and NaCl rejection above 70 % at 15 kg/cm 2. UTC-20 HF membrane has a very high water flux over 3.5 m 3/m 2 day (86 gfd) and NaCl rejection above 50 % at 15 kg/cm 2, while the magnesium sulfate rejections of UTC-20 HR & 20 HF membranes are above 99.0 %, respectively. UTC-40 series membranes are also available in two grades. UTC-40 HR membrane has high NaCl rejections above 98 % and 1.0 m 3/m 2 day (24.5 gfd) water flux at 15 kg/cm 2. UTC-40 HF membrane has very high water flux above 2.5 m 3/m 2 day (61.5 gfd) and over 90 % sodium chloride rejection at 15 kg/cm 2. UTC-20 & 40 series membrane are directed to use in the market for ultrapure water production and brackish water desalination at low or super low operating pressure. These new composite membranes have been successfully manufactured in continuous flat sheet form and wound into the spiral elements.