Profiled Ion Exchange Membranes: A Comprehensible Review

Abstract

Profiled membranes (also known as corrugated membranes, micro-structured membranes, patterned membranes, membranes with designed topography or notched membranes) are gaining increasing academic and industrial attention and recognition as a viable alternative to flat membranes. So far, profiled ion exchange membranes have shown to significantly improve the performance of reverse electrodialysis (RED), and particularly, electrodialysis (ED) by eliminating the spacer shadow effect and by inducing hydrodynamic changes, leading to ion transport rate enhancement. The beneficial effects of profiled ion exchange membranes are strongly dependent on the shape of their profiles (corrugations/patterns) as well as on the flow rate and salts' concentration in the feed streams. The enormous degree of freedom to create new profile geometries offers an exciting opportunity to improve even more their performance. Additionally, the advent of new manufacturing methods in the membrane field, such as 3D printing, is anticipated to allow a faster and an easier way to create profiled membranes with different and complex geometries.

Keywords: 3D printing; corrugated membranes; electrodialysis; hydrodynamic; ion exchange membranes; mass transfer; membrane capacitive deionization; profiled membranes; reverse electrodialysis; thermal pressing.

Figure 1

Profiled membranes with straight ridges parallel to the flow direction: (a) SEM-image of a cross-section of the profiled cation-exchange membrane (CEM). Reproduced with permission from Reference [19]. Copyright 2011 Elsevier; (b) Photo of 1 × 1 cm² section of profiled CEM after more than 60 days of reverse electrodialysis (RED) stack operation, in which air sparging was applied as an antifouling strategy. Reproduced with permission from Reference [21]. Copyright 2016 American Chemical Society.

Figure 2

Surface morphology of tailor-made profiled membranes with: (a) waves and (b) pillars corrugations. Reproduced with permission from Reference [22]. Copyright 2014 Elsevier.; velocity fields, obtained by computational fluid dynamics (CFD), around pillar structures with (c) round, (d) diamond, and (e) tear shape, for a flow direction indicated by the upward arrow on the right. Reproduced with permission from Reference [25]. Copyright 2010 Elsevier.

Figure 3

An illustrative scheme of correlation of membrane fouling with topography of profiled membranes in cross-flow filtration for water treatment. Re stands for Reynolds number. Particles are represented in red and the prismatic membrane surface pattern by blue triangles. The bending arrows illustrate particles entering and leaving locally created flow vortexes Reproduced with permission from Reference [33]. Copyright 2016 Elsevier.

Figure 4

Velocity fields, obtained by particle tracking velocimetry (PTV), of fluid flow between sub-corrugated membranes for Reynold numbers (based on half the channel height), Re_h of 10 and 100 in a RED application. Reproduced with permission from Reference [36]. Copyright 2014 Elsevier.

Figure 5

Chevron profiled membranes used in RED: (a) SEM image of the surface morphology, (b) segment of a channel formed by chevron profiled membranes; (c) map of mass transfer coefficient, obtained by CFD, at two linear flow velocity of 1.0 cm/s, (d) comparison, based on CFD simulations, of the ratio (θ) between net power density obtainable in RED stacks with different configurations and the one obtainable in RED stack with empty channels, (e) experimental net power density obtained in RED stacks with different configurations. Reproduced with permission from References [45,46]. Copyright 2016 and 2017, respectively, Elsevier.

Figure 6

Economic evaluation of an ammonium nitrate treatment process using different anion-exchange membranes (AEM), in which Ralex AMH, MA-41 and MA-40 are flat, MA-41p is a profiled (subscript “p”) version of MA-41, which surface denoted by (a) is shown on the right with a scale bar of 100 μm. ^aPrices are given for the year 2011. (Reproduced with permission from Reference [49]. Copyright 2016 Elsevier).

Figure 7

Different possible pathways for preparation of profiled ion exchange membranes: (a) hot pressing; (b) membrane casting (Adapted from Reference [22]); (c) Direct 3D printing (Reproduced with permission from Reference [52]. Copyright 2016 American Chemical Society.); (d) 3D printing on top of a commercial membrane (Reproduced with permission from Reference [53]. Copyright 2018 Timon Rijnaarts).

Figure 8

Illustrative examples (from References [52,60] of micro-patterned profiled ion exchange membranes prepared by 3D printing, (Reproduced with permission, Copyright 2016 and 2018, respectively, American Chemical Society).