High-Pressure Nanofiltration for Brine Concentration: The Critical Role of Support-Layer Compaction

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Nanofiltration (NF) membranes are explored for low-salt-rejection reverse osmosis (LSRRO) in concentrating high-salinity brines.
• Understanding NF membrane performance under elevated pressures is crucial for applications like minimal or zero liquid discharge (MLD/ZLD).

Purpose of the Study:

• To systematically evaluate the feasibility of NF membranes for LSRRO under high operating pressures.
• To develop a predictive framework for NF membrane performance under elevated pressures.

Main Methods:

• Experimental evaluation of a commercial NF membrane under elevated pressures.
• Structural characterization of membrane components (active and support layers).
• Development of a theoretical framework integrating polymer thermodynamics, kinematics, and porous-media transport.

Main Results:

• The selective active layer remained stable, but the porous support layer compacted significantly under high pressure.
• Water permeance declined substantially due to support layer compaction.
• The developed framework accurately predicted pressure-dependent permeance and identified compaction resistance as key for high-pressure performance.

Conclusions:

• Membrane performance at high pressures is primarily dictated by the mechanical robustness of the support layer.
• NF membrane design for LSRRO and MLD/ZLD applications must prioritize resistance to compaction.
• A predictive, mechanistically informed framework is established for evaluating and designing NF membranes for challenging brine concentration applications.