Electroanalysis with a single microbead of phosphate binding resin (FerrIX™) mounted in epoxy film

Commercial resin microbeads are widely applied in ion exchange and extraction. Here, a single anion-selective and phosphate binding resin microbead (FerrIX™) is mounted into an epoxy membrane and investigated by 4-electrode membrane voltammetry and membrane impedance spectroscopy. Anion transport properties are observed to dominate associated with three distinct potential domains: (I) a low bias ohmic potential domain (dominant at high electrolyte concentration), (II) a concentration polarisation potential domain, and (III) an over-limiting potential domain. Voltammetric responses show transient diffusion-migration features at higher scan rates and quasi-steady state features at lower scan rates. Inherent microbead conductivity is shown to be linked to two resistive elements, electrolyte concentration dependent and independent, in series. The effects of phosphate binding are revealed as transient pattern in impedance spectroscopy data. Preliminary data suggest phosphate concentration-dependent peak features in the imaginary impedance versus frequency plot due to phosphate binding into the microbead. Graphical abstract

Analysis of Concentration Polarisation in Full-Size Spiral Wound Reverse Osmosis Membranes using Computational Fluid Dynamics

A three-dimensional model for the simulation of concentration polarisation in a full-scale spiral wound reverse osmosis (RO) membrane element was developed. The model considered the coupled effect of complex spacer geometry, pressure drop and membrane filtration. The simulated results showed that, at a salt concentration of 10,000 mg/L and feed pressure of 10.91 bar, permeate flux decreased from 27.6 L/(m2 h) (LMH) at the module inlet to 24.1 LMH at the module outlet as a result of salt accumulation in the absence of a feed spacer. In contrast, the presence of the spacer increased pressure loss along the membranes, and its presence created vortices and enhanced fluid velocity at the boundary layer and led to a minor decrease in flux to 26.5 LMH at the outlet. This paper underpins the importance of the feed spacer’s role in mitigating concentration polarisation in full-scale spiral wound modules. The model can be used by both the industry and by academia for improved understanding and accurate presentation of mass transfer phenomena of full-scale RO modules by different commercial manufacturers that cannot be achieved by experimental characterization of the mass transfer coefficient or by CFD modelling of simplified 2D flow channels.

Impact of Forward Osmosis Operating Pressure on Deformation, Efficiency and Concentration Polarisation with Novel Links to CFD

Forward osmosis (FO) modules currently suffer from performance efficiency limitations due to concentration polarisation (CP), as well as pressure drops during operation. There are incentives to further reduce CP effects, as well as optimise spacer design for pressure drop improvements and mechanical support. In this study, the effects of applying transmembrane pressure (TMP) on FO membrane deformation and the subsequent impact on module performance was investigated by comparing experimental data to 3D computational fluid dynamics (CFD) simulations for three commercial FO modules. At a TMP of 1.5 bar the occlusion of the draw-channel induced by longitudinal pressure hydraulic drop was comparable for the Toray (16%) and HTI modules (12%); however, the hydraulic perimeter of the Profiera module was reduced by 46%. CFD simulation of the occluded channels indicated that a change in hydraulic perimeter due to a 62% increase in shear strain resulted in a 31% increase in the Reynolds number. This reduction in channel dimensions enhanced osmotic efficiency by reducing CP via improved draw-channel hydrodynamics, which significantly disrupted the external concentration polarization (ECP) layer. Furthermore, simulations indicated that the Reynolds number experienced only modest increases with applied TMP and that shear strain at the membrane surface was found to be the most important factor when predicting flux performance enhancement, which varied between the different modules. This work suggests that a numerical approach to assess the effects of draw-spacers on pressure drop and CP can optimize and reduce investment in the design and validation of FO module designs.

Comprehensive Review on High Hydrogen Permselectivity of Palladium Based Membranes: Part I

Palladium based membranes are widely used for supplying ultra-high purity hydrogen to a polymer electrolyte fuel cell (PEFC) installed on small vehicles and various electronic devices. Compared to pressure swing adsorption (PSA), the use of palladium based membrane is more economical for small size (small capacity) applications. The transportation of hydrogen through a palladium based membrane is governed by Sieverts’ Law and quantified with Fick’s First Law. Since the 20th century, the fabrication of high-performance palladium based membrane for enhanced hydrogen recovery performance has become practical. However, along with the improvement in hydrogen recovery performance, concentration polarisation becomes unavoidable because hydrogen permeation flux starts to affect hydrogen concentration at the membrane surface. Various parametric studies have investigated the effects of membrane thickness, hydrogen molar fraction and total upstream and downstream pressures on concentration polarisation level. The influence of membrane temperature, permeability, type and number of species in the hydrogen mixture, diffusivity of the hydrogen mixture, system configurations and flow patterns are also reported and comprehensively reviewed in this paper. Part II will complete the presentation.

Comprehensive Review on High Hydrogen Permselectivity of Palladium Based Membranes: Part II

This article completes the presentation of various techniques reducing concentration polarisation in palladium based membranes for supplying ultra-high purity hydrogen to a polymer electrolyte fuel cell (PEFC), such as the implementation of baffles and the use of microchannel configuration. The present paper also reviews and reports the current methods for estimating hydrogen permeation flux under concentration polarisation influence, which will be a useful guide for academics and industrial practitioners.