Pressure Retarded Osmosis Applications Research Articles

Membrane distillation & pressure retarded osmosis hybrid system using thermally rearranged nanofibrous membranes

To increase the efficiency of a closed-loop hybrid system consisting of membrane distillation (MD) and pressure retarded osmosis (PRO) processes, thermally rearranged nanofibrous membranes (TR-NFMs) via electrospinning were proposed in this study. Two fluorine-based modifications were performed on TR-NFMs to optimize their affinity with water. Hydrophobicity of TR-NFM was enhanced by atmospheric plasma coating (TR-NFM-Rx) to increase liquid entry pressure of water (LEPw) for MD applications. On the other hand, for PRO applications, gas-phase direct fluorination was applied on TR-NFM (TR-NFM-Fx) to improve its hydrophilicity by replacing the C–H bond of a TR polymer with a C–F bond. Before measuring the performance of the hybrid system, the MD performance was calculated from the mass transfer model based on the temperature and concentration of the solution to confirm the operating conditions of the MD-PRO hybrid system. The resulting TR-NFM-R40 showed an excellent water flux of 51.5 L/m2 hr at 70 °C despite a 3 M NaClaq operating solution that is unfavorable for MD performance. In the PRO process, thin film composite membrane (TR-TFC-F5) also exhibited outstanding power density of 120 W/m2 at 27 bar using 3 M NaClaq and D.I. water as operating and feed solutions, respectively. During 180 h continuous operation of MD-PRO hybrid system, the resulting average power density was about 90 W/m2 and average MD water flux was about 45–50 L/m2 hr at 70 °C using 3 M NaClaq operating solution. In conclusion, the developed TR membranes for MD-PRO hybrid system provides an insight into the future of energy harvesting technology.

Tubular PAN/CNC thin film nanocomposite (TFN) pressure retarded osmosis (PRO) membrane: fabrication and preliminary evaluation in desalination process

The pressure retarded osmosis (PRO) process requires high performance, high flux, high rejection, and resistant membranes under harsh conditions. Since conventional phase-inversion membranes are insufficient to permit the required water flux, alternative membrane fabrication methods need to be developed. Many studies have recently been carried out to fabricate strong enough nanofiber PRO membranes resistant to higher pressure while providing high flux and high rejection rates. This work aims to fabricate tubular nanofiber PRO membranes by the electrospinning technique. In the study, cellulose nanocrystals (CNCs) were added to polyacrylonitrile (PAN) polymer solution to fabricate nanocomposite nanofiber PRO membranes. According to the scanning electron microscopy (SEM), FT-IR, dynamic mechanical analysis, porometer, and contact angle analysis results, it is concluded that PAN and CNCs provided a complete mixture, and the addition of CNCs increased the mechanical strength in the PAN membranes, which is the crucial phenomena in PRO applications. In this study, the newly fabricated membrane achieves a higher PRO water flux of 405.38 LMH using 1 M NaCl and a DI as feed water. The corresponding salt flux is found as 2.10 gMH, which is higher than our previous study. The selectivity of the reversed flux represented by the ratio of the water flux to the reversed salt flux (Jw/Js) was able to be kept as high as 193.03 L/g for PRO operation. As far as we know, the performance of the work-developed membrane in this study has shown better performance than all PRO membranes reported in the literature previously.Graphic abstract

Use of Pressure-Retarded-Osmosis to reduce Reverse Osmosis energy consumption by exploiting hypersaline flows

Power production from salinity gradients, the so-called Pressure Retarded Osmosis (PRO), has been actively investigated and tested since the 70s for its reliability and controllability. Besides these advantages, it seems a promising green solution since it allows the dilution of highly concentrated brines and the specific energy consumption of desalination plants. Most of PRO applications, though, use freshwater as feed solution, which in some locations may be scarce or dedicated to other uses. In the present paper, PRO is researched for hypersaline solutions (brine and seawater), and a sensitivity analysis is carried out over the most significant parameters that affect the system performance: draw and feed velocities, hydrostatic pressure-osmotic pressure difference ratio and membrane length. The PRO model is then coupled to a simplified Reverse Osmosis (RO) plant into two novel integrated desalination plant layouts to quantify the PRO impact on the specific energy consumption. The two layouts are simulated with both a commercial and an experimental membrane, with a view to membrane technology improvement.

Pressure-retarded osmosis for enhanced oil recovery

Pressure-retarded osmosis (PRO) is a membrane-based process that has been used historically to harness the osmotic energy of saline feed solutions. While conventional PRO applications target seawater (SW) /freshwater solution pairings, this paper focuses on an innovative high salinity gradient PRO application for waterflooding (WF) in the petroleum industry. WF is an industry-wide practice wherein produced water (PW) or SW is injected into the geological formation to displace hydrocarbons and increase oil production at the wellhead. PW represents the largest volume waste stream in oil production and harnessing its osmotic energy in a PRO application converts that waste stream into an asset leading to higher oil production while simultaneously reducing pumping energy requirements and enhancing injectivity.In this application, hypersaline PW at 28% total dissolved solids (TDS) is the draw solution and SW at 3.5% TDS is the feed. In contrast with hydroturbine (HT) & reverse osmosis (RO) applications where the economic benefit is energy, in WF, the primary benefit is additional oil production and a secondary benefit is energy savings. With the PW/SW solution pairing, PRO economics were compared for the WF, HT, and RO applications. The key economic metric is the “dollars of economic benefit derived per module per year” and for WF, that benefit is estimated at $71,700/module-year while the HT and RO configurations were found to return <$500/module-yr. Based on these findings, it is recommended that the application of PRO for WF be investigated further, to better define pretreatment requirements, commercial membrane performance limits and other environmental considerations.

Tailoring the porous structure of hollow fiber membranes for osmotic power generation applications via thermally assisted nonsolvent induced phase separation

For osmotic power generation using the pressure retarded osmosis (PRO) process, mechanically robust membranes with high osmotic water flux are needed to obtain high power density from a given osmotic pressure difference. Particularly in the case of support-free hollow fiber membranes (HFMs), the pressure tolerance is a critical factor in maximizing power density when operating at high applied pressure with concentrated brine. Here, mechanically robust integrally-skinned asymmetric (ISA) HFMs were developed by combining the nonsolvent induced phase separation (NIPS) with the quenching, into a facile approach called the thermally assisted NIPS (T-NIPS) method, to tailor the membrane structure for PRO applications. The prepared T-NIPS membranes exhibited two distinct layers: a dense ISA outer layer and an isoporous inner layer. Compared to conventional NIPS HFMs, the T-NIPS HFMs showed much higher power density and collapse pressure, up to 5.5 W/m2 and 18 bar, respectively. The effect of pore forming agents on the membrane structure during the T-NIPS process, and on PRO performance, were studied. In addition, the power density and the pressure tolerance were further enhanced by optimizing the membrane dimensions and structure of the T-NIPS HFMs.

Tuning water content in polymer dopes to boost the performance of outer-selective thin-film composite (TFC) hollow fiber membranes for osmotic power generation

The lack of effective membranes greatly hinders the use of pressure retarded osmosis (PRO) to harvest renewable osmotic energy. In comparison to the flat sheet and inner-selective hollow fiber configurations, the development of outer-selective hollow fiber membranes is much slower although it may be more attractive for real PRO applications. This study demonstrates that tuning the water content in polymer dopes can be an effective means to simultaneously enhance the mechanical robustness and water transport properties, boosting the PRO performance of outer-selective thin-film composite (TFC) hollow fiber membranes. Fundamental properties of polymer dopes with different water content and their influence on the hollow fiber supports as well as resultant TFC membranes were systematically investigated. With a low water content of 2wt% in the polymer dope, the newly developed TFC membrane not only has the smallest structural parameter, highest toughness, and largest water permeability among all membranes studied but also displays an impressive peak power density of 10.05W/m2 at 22bar using 1M NaCl and DI water as feeds. To our best knowledge, this is the highest power density of outer-selective TFC PRO hollow fiber membranes reported in the literature. Mathematical models predict that approximately 25% performance increase can be further achieved if the external concentration polarization (ECP) effect is minimized. This study may provide useful insights to design high performance outer-selective TFC hollow fiber membranes for osmotic power generation.

A high-performance and fouling resistant thin-film composite membrane prepared via coating TiO2 nanoparticles by sol-gel-derived spray method for PRO applications

Abstracts Pressure retarded osmosis (PRO) is an attractive process for capturing renewable energy that requires high-performance and fouling-resistant membranes. Herein, we report a novel surface coating method that increases the water flux and organic fouling resistance of PRO membranes. The support layer of a commercial TFC was coated with TiO2 nanoparticles (TNPs) via a sol-gel-derived spray coating method. This TNP coating imparted hydrophilic properties and a negative charge to the membrane surface. A TNP-coated membrane (TNP1.0) showed a 25% increase in water flux and a 50% decrease in reverse salt flux. The flux reduction of the TNP membrane was 32% less than that of a commercial TFC membrane in the presence of humic acid foulants. This suggests that a high-performance and fouling-resistant PRO membrane can be prepared using a TiO2 sol-gel-derived spray coating method.

Modeling of a forward osmosis and a pressure-retarded osmosis spiral wound module using the Spiegler-Kedem model and experimental validation

Abstract A mathematical model is developed for a spiral wound module for both forward osmosis (FO) and pressure-retarded osmosis (PRO) applications. This model is obtained by combining the membrane transport, external concentration polarization, and internal concentration polarization models with the pressure drop and mass balance equations for both the feed as well as the draw solutions. The Spiegler-Kedem (SK) model is used for describing the local mass transport in the active layer of the membrane. In addition, a new expression is established for determining the internal concentration polarization in the support layer of the membrane. A nonlinear constrained optimization technique is then applied, along with the experimental data for FO and PRO, to predict the unknown parameters of the mathematical model for the spiral wound module. To ensure the validity of the proposed model and predicted parameters, the model is again used to predict and compare the performance of the module at a variety of operating conditions. Apart from this, the product recovery and the energy extraction efficiency of the module at a variety of operating conditions are also analyzed. Lastly, we have tried to answer the question, whether the Solution Diffusion (SD) based model or the SK based model is better for design and analysis, and for obtaining the optimal operating conditions for both FO as well as PRO applications.

Pressure Retarded Osmosis (PRO): Past experiences, current developments, and future prospects

Pressure Retarded Osmosis (PRO) has attracted worldwide attention with respect to its salinity gradient energy production potential, and low energy desalination applications. PRO processes, which use Seawater Reverse Osmosis (SWRO) brine as draw solutions, have a higher potential of being applied to any new, and existing membrane based seawater desalination systems, as an energy production and/or conservation process. Hydraulic pressure is applied on a high salinity draw solution, and the hydraulic pressure of the high salinity draw solution can be kept relatively constant during operation, even though the volumetric flow rate is to be increased. Therefore, the draw side of the PRO process can be considered near-isobaric, in most cases. The harvested Gibbs free energy of mixing, and the volumetric expansion can explain this near-isobaric behavior of the draw side in the PRO process. Thus, PRO can be used to multiply the internal energy of the draw solution with respect to the ratio of the permeated water flux. Even though PRO has very high theoretical potential for energy production and/or recovery, there are several shortcomings, which should be answered before the realization of the scale up applications, such as; thermodynamic process optimization, high power density membranes, and high efficiency hydraulic pressure conversion and recovery systems. This review gives detailed information about the PRO process including; (1) theoretical background, (2) membranes for PRO, (3) experimental and large scale applications, and (4) economic feasibility of PRO applications.

Design and Performance of HTI's Thin Film Composite Membrane for Forward Osmosis and Pressure Retarded Osmosis Applications

Design and Performance of HTI's Thin Film Composite Membrane for Forward Osmosis and Pressure Retarded Osmosis Applications