Reverse osmosis membrane compaction and embossing at ultra-high pressure operation

Abstract

Herein, we describe the performance (i.e., flux and rejection) of commercially-available, thin film composite brackish water RO (BWRO), seawater RO (SWRO) and high-pressure RO (HPRO) membranes operating at pressures from 14 bar (200 psi) to 207 bar (3000 psi). For each membrane material, we elucidate the impacts to performance using a porous metal frit and woven tricot mesh permeate carrier materials from commercial HPRO, SWRO, BWRO and tap water RO (TWRO) membrane modules. The water permeability of all tested membranes declines with increasing pressure, whereas rejection behaves differently for different combinations of membrane type and permeate carrier. Cross-sectional SEM and FIB-SEM images confirm permanent reduction of the polysulfone support membrane thickness (38% to 60%) as well as collapse of support membrane skin layer pores – both of which may contribute to the observed performance decline. Also, at ultra-high pressures, permeate carrier materials with higher porosity cause greater embossing and, ultimately, coating film damage (defect formation) that leads to increased salt passage (loss of salt rejection). In contrast, the permeate carriers with lower porosity still lost water permeability, but maintained higher rejection. Finally, all of the observed compaction/embossing-related performance decline occurs within about 60 min after a membrane coupon was exposed to ultra-high pressure.