Insights into the Influence of Membrane Permeability and Structure on Osmotically-Driven Membrane Processes

Abstract

The success of osmotically-driven membrane (OM) technology relies critically on high-performance membranes. Yet trade-off of membrane properties, often further complicated by the strongly non-linear dependence of OM performance on them, imposes important constraint on membrane performance. This work systematically characterized four typical commercial osmotic membranes in terms of intrinsic separation parameters, structure and surface properties. The osmotic separation performance and membrane scaling behavior of these membranes were evaluated to elucidate the interrelationship of these properties. Experimental results revealed that membranes with smaller structural parameter (S) and higher water/solute selectivity underwent lower internal concentration polarization (ICP) and exhibited higher forward osmosis (FO) efficiency (i.e., higher ratio of experimental water flux over theoretical water flux). Under the condition with low ICP, membrane water permeability (A) had dominant effect on water flux. In this case, the investigated thin film composite membrane (TFC, A = 2.56 L/(m2 h bar), S = 1.14 mm) achieved a water flux up to 82% higher than that of the asymmetric cellulose triacetate membrane (CTA-W(P), A = 1.06 L/(m2 h bar), S = 0.73 mm). In contrast, water flux became less dependent on the A value but was affected more by membrane structure under the condition with severe ICP, and the membrane exhibited lower FO efficiency. The ratio of water flux (Jv TFC/Jv CTA-W(P)) decreased to 0.55 when 0.5 M NaCl feed solution and 2 M NaCl draw solution were used. A framework was proposed to evaluate the governing factors under different conditions and to provide insights into the membrane optimization for targeted OM applications.

Effect of titanium oxide/reduced graphene (TiO2/rGO) addition onto water flux and reverse salt diffusion thin-film nanocomposite forward osmosis membranes

“…In AL-DS mode, the concentrated DS on one side of the active layer reduces driving force and water flux slightly. DS mode also reduces water flux, but flux is still higher than AL-FS mode (Wei et al 2021 ). Water flow is higher with DI water compared to 0.1 M NaCl feed in AL-FS and AL-DS modes.…”

Wrinkled CNTs@PLLA Composite Membranes for Enhanced Separation Performance

“…Smaller pores, however, lead to the loss of the latter, and vice versa. This is the well-known trade-off effect in separation [ 1 , 2 , 3 , 4 ]. So far, much effort has been made to break this effect.…”

Thin‐film nanocomposite forward osmosis membrane with polydopamine @UiO‐66‐NH2‐modified polypropylene support and its antifouling property

“…25 However, the use of PP membrane as the support layer of FO membrane is rare because of the strong hydrophobicity of PP membrane. 26 Although the hydrophilic group is introduced into the polymer surface by plasma or chemical modification, the hydrophilic property of the polymer gradually returns to the hydrophobic state with time. 27 The use of dopamine greatly improves the hydrophilicity of PP membrane on the surface of the membrane and in the inner pores, so it can effectively induce PP membrane to be hydrophilic.…”

“…The excellent pore structure and thinness of PP membrane favors the reduction in membrane structure parameters of the support, thereby decreasing the internal concentration polarization (ICP) 25 . However, the use of PP membrane as the support layer of FO membrane is rare because of the strong hydrophobicity of PP membrane 26 . Although the hydrophilic group is introduced into the polymer surface by plasma or chemical modification, the hydrophilic property of the polymer gradually returns to the hydrophobic state with time 27 .…”