Embossing-Free Permeate Carrier for Ultrahigh Pressure Reverse Osmosis.

Abstract

Membrane brine concentration (MBC) offers the ability to concentrate brines at lower energy and cost compared to thermal brine concentration (TBC), thus expanding the global opportunities for minimum and zero liquid discharge (M/ZLD). Ultrahigh-pressure reverse osmosis (UHPRO) and osmosis-assisted RO (OARO) MBC processes operate between 80 and 120 bar, depending on the specific process configuration. Herein, we show that operating commercial RO membranes on top of commercial permeate carriers (PCs) at such high pressures leads to both RO membrane compaction and embossing, which initially cause reduced water permeability and elevated permeate backpressure, respectively. Eventually, the polyamide (and polysulfone) layer can rupture, resulting in the irreversible loss of salt rejection at applied pressures of 80 to 120 bar. Optical and SEM images confirmed through-thickness mechanical imprinting that aligned with the structural features of the PCs, establishing a clear causal relationship between embossing and performance decline. Finally, we designed an embossing-free permeate carrier (EFPC) composed of two soft tricot mesh layers sandwiching a rigid stainless-steel mesh. This EFPC eliminated embossing-enhanced permeate backpressure and membrane damage, enabling commercial RO membranes to sustain stable water flux and salt rejection up to 120 bar. Overall, this study demonstrates that advancements in UHPRO/OARO technology must incorporate both compaction-resistant membranes and EFPCs to fully realize the potential of MBC technology.