This invention generally relates to coatings for composite polyamide membranes. Polyamide membranes are commonly used in a variety of fluid separations. One particular class of such membranes include a microporous support with a “thin film” or “discriminating” polyamide layer which may formed by an interfacial reaction as described in U.S. Pat. No. 4,277,344 to Cadotte et al. The properties of such membranes may be modified by the addition of various additives, coatings and post-treatments as described in: U.S. Pat. No. 5,755,964; U.S. Pat. No. 6,878,278; and US 2009/0159527 to Mickols et al. and US 2008/0269417 to Belfer et al. Additional techniques include coating composite membranes with various polymers, e.g. polyoxazoline as described in US 2008/0185332 and US 2009/0194479 to Niu et al., poly(hexmethylenebiguanide) hydrochloride as described in U.S. Pat. No. 7,491,334 to Comstock, polyamide-polyether block copolymers as described in U.S. Pat. No. 7,490,725 to Pinnau et al. and various copolymers as described in US 2005/0056589 to Hendel et al. One interesting class of polymer coatings includes polyalkylene oxide compounds such as those described in U.S. Pat. No. 6,280,853 to Mickols, US 2007/0251883 and US 2009/0220690 to Niu et al. and U.S. Pat. No. 6,913,694 to Koo et al. Such polyalkylene oxide compounds may be combined with other polymers including polyoxazoline compounds as described in US 2008/0185332 and US 2009/0194479 to Niu et al. or polyacrylamide as described in US 2010/0143733 to Mickols. The entire content of each of the preceding references is incorporated herein by reference.
While coatings of polyalkylene oxide compounds have been shown to reduce fouling of composite polyamide membranes, further improvements in membrane performance are still desired.