Effect of Spacer Configuration on the Characteristics of FO Membranes: Alteration of Permeation Characteristics by Membrane Deformation and Concentration Polarization

Abstract

Membrane deformation is a significant problem in osmotically driven membrane processes, as it restricts practical operating conditions and reduces overall process performance due to unfavorable alteration of membrane permeation characteristics. In this respect, a spacer plays a crucial role, as it dictates the form and extent of membrane deformation in association with concentration polarization (CP), which is also influenced by spacer-induced hydrodynamic behavior near the membrane surface. These two roles of spacers on membrane permeation characteristics are inherently inseparable with the coexistence of hydraulic and osmotic pressures. Here, we suggest a novel analytical method to differentially quantify the proportions of effective osmotic pressure drop caused by membrane deformation and CP. Furthermore, we tested two different FO membranes with three different spacer configurations to define and discuss different forms of membrane deformation and their effects on membrane permeation characteristics. The differential analysis revealed the effect of spacer configuration on effective osmotic pressure drop in membrane deformation (up to ∼201% of variation) is much greater than that in CP (up to ∼20.1% of variation). In addition, a combined configuration of a feed spacer and tricot spacer demonstrated its ability of mitigating membrane deformation with lower selectivity loss and channel pressure drop under pressurization.

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

“…The experimental data presented in this study are extracted from previous studies, whereby the membrane active-layer faced the feed-side (for desalination and high fouling solutions) [3,17,21]. Additionally, most of the CP models in the literature typically agree that dilutive ICP occurs within the support structure of the membrane on the draw-side, and ECP occurs in the boundary layer on the feed-side [6,[10][11][12]19]. As the feed solution used is deionised water the, ECP in the feed can be neglected (i.e., no solute in the feed).…”

“…While PAO is the use of FO with applied pressure assisting flux performance, even within regular FO processes it has been observed that 0.5 bar of pressure is needed to circulate fluid in 8-inch FO modules [17]. The resultant transmembrane pressure (TMP) has been found to cause the deformation of the membrane into the draw-channel, resulting in the draw-channel contraction recently studied in the literature [18][19][20][21]. Furthermore, the applied TMP has been observed to cause a long-term compaction of the membrane after operation with moderate (1-2.5 bar) pressure [3].…”

“…This has led to spacer designs that offer low mechanical support as a tradeoff for unimpeded fluid flow, and hence a lower pressure drop [17,18,21]. While the impact of draw-spacer contraction has been reported on pressure drops and fouling potential, the effects studied have been on the relative contribution of deformation against CP effects [19].…”

Oxygen Enrichment Membranes for Kuwait Power Plants: A Case Study

“…This means that the membrane is the best choice for the generation of 30 mol% oxygen in terms of capital and operating costs, as shown in Table 1. Nevertheless, it should be noted that the membrane performance might decrease with time due to the accumulation of the gas in the boundary layer [14][15][16]. This phenomenon is known as concentration polarization and can be reduced by increasing the feed gas velocity [17].…”

Novel Hole-Pillar Spacer Design for Improved Hydrodynamics and Biofouling Mitigation in Membrane Filtration

“…Although these proposed novel spacer designs indicate favorable progress for enhanced ltration membranes, several constraints are still encountered and hamper their commercialization and industrial implementation. It includes the design complexity 26,29 , the handling di culty 27,29 , the risk of membrane deformation/damage 24,25,30 , and the high energy requirements 22,25,28 .…”