Membrane Separation Technology Research

The separation of Li⁺ and [Bmim]⁺(1-Butyl-3-methylimidazolium) using a cation exchange membrane in an electric field is studied in this work. The effects of the type of cation exchange membrane, current density, total cation concentration, temperature, and anion types on the separation efficiency are investigated. The results indicate that it is feasible to achieve the efficient separation of Li⁺ and [Bmim]⁺ using the selectivity of cation exchange membranes under an electric field. The CIMS membrane (a type of cation exchange membrane produced by ASTOM Corporation) shows obvious selectivity of Li⁺ from [Bmim]⁺. When the current density is 5 mA/cm² and the feed concentrations of Li⁺ and [Bmim]⁺ are 0.3 mol/L and 0.2 mol/L, respectively, the selective transport coefficient of CIMS can reach 5.9 in the first 120 min of the process. The separation efficiency can be effectively improved by reducing the current density and increasing the total cation concentration. Decreasing the feed temperature can slightly improve the separation efficiency. Changing the type of anion in the feed from chloride to acetate has no detectable effect on the separation. Full article

This work aims to theoretically investigate the effect of both the fixed charge density of ion exchange membranes and the ionic strength of the treated aqueous NaCl solution on the generated Donnan potential at thermodynamic equilibrium conditions. The direct objective of our work is to calculate the equilibrium concentration of the Cl⁻ co-ion inside a swelled cation-exchange membrane equilibrated with a water/NaCl system. Two activity coefficient models are employed, i.e., the Debye–Huckel (DH) model (as a reference model) and the Meissner model, which is known for its applicability in treating concentrated solutions. Experimental data available in the literature for Donnan potential are used to verify model predictions. Our study confirms that a high fixed charge density is required to counterbalance the deterioration in membrane selectivity encountered in high-salinity systems. The DH model can be safely used to predict the Donnan potential for feed compositions up to 0.1 M. At higher compositions, the DH model significantly overestimates the predicted (absolute) Donnan potential compared to the Meissner model. The osmotic pressure resulting from the difference in ionic concentration between the membrane phase and the feed phase is found to have insignificant effects on the Donnan potential. The equilibrium computations and methodology are presented in a general way that enables handling multivalent electrolyte systems such as CaCl₂. Full article

In this paper, refined sugar wastewater (RSW) is treated by electrodialysis (ED) coupled with an upflow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). The salt in RSW was first removed by ED, and then the remaining organic components in RSW were degraded by a combined UASB and MBR system. In the batch operation of ED, the RSW was desalinated to a certain level (conductivity < 6 mS·cm⁻¹) at different dilute to concentrated stream volume ratios (V_D/V_C). At the volume ratio of 5:1, the salt migration rate J_R and COD migration rate J_COD were 283.9 g·h⁻¹·m⁻² and 13.84 g·h⁻¹·m⁻², respectively, and the separation factor α (defined as J_COD/J_R) reached a minimum value of 0.0487. The ion exchange capacity (IEC) of ion exchange membranes (IEMs) after 5 months of usage showed a slight change from 2.3 mmol·g⁻¹ to 1.8 mmol·g⁻¹. After the ED treatment, the effluent from the tank of the dilute stream was introduced into the combined UASB-MBR system. In the stabilization stage, the average COD of UASB effluent was 2048 mg·L⁻¹, and the effluent COD of MBR was maintained below 44–69 mg·L⁻¹, which met the discharge standard of water contaminants for the sugar industry. The coupled method reported here provides a viable idea and an effective reference for treating RSW and other similar industrial wastewaters with high salinity and organic contents. Full article

Wastewater reclamation has gradually become an important way to cope with the global water crisis. Ultrafiltration plays an imperative part as a safeguard for the aim but is often limited by membrane fouling. Effluent organic matter (EfOM) has been known to be a major foulant during ultrafiltration. Hence, the primary aim of this study was to investigate the effects of pre-ozonation on the membrane fouling caused by EfOM in secondary wastewater effluents. In addition, the physicochemical property changes of EfOM during pre-ozonation and the subsequent influence on membrane fouling were systemically investigated. The combined fouling model and the morphology of fouled membrane were adopted to scrutinize the fouling alleviation mechanism by pre-ozonation. It was found that membrane fouling by EfOM was dominated by hydraulically reversible fouling. In addition, an obvious fouling reduction was achieved by pre-ozonation with 1.0 mg O₃/mg DOC. The resistance results showed that the normalized hydraulically reversible resistance was reduced by ~60%. The water quality analysis indicated that ozone degraded high molecular weight organics such as microbial metabolites and aromatic protein and medium molecular weight organics (humic acid-like) into smaller fractions and formed a looser fouling layer on the membrane surface. Furthermore, pre-ozonation made the cake layer foul towards pore blocking, thereby reducing fouling. In addition, there was a little degradation in the pollutant removal performance with pre-ozonation. The DOC removal rate decreased by more than 18%, while UV₂₅₄ decreased by more than 20%. Full article

The goals of the present investigation are to study and to model pale lager beer dealcoholization via reverse osmosis (RO). Samples were dealcoholized at a temperature of 15 ± 1 °C. An Alfa Laval RO99 membrane with a 0.05 m² surface was used. The flux values were measured during the separations. The ethanol content, extract content, bitterness, color, pH, turbidity, and dynamic viscosity of beer and permeate samples were measured. The initial flux values were determined using linear regression. The initial ethanol flux ($J_{EtOH 0}$) values were calculated from the initial flux values and the ethanol content values. A 2^P full factorial experimental design was applied, and the factors were as follows: transmembrane pressure (TMP): 10, 20, 30 bar; retentate flow rate (Q): 120, 180, 240 L/h; $J_{EtOH 0}$ was considered as the response. The effect sizes of the significant parameters were calculated. The global maximum of the objective function was found using a self-developed Grid Search code. The changes in the analytical parameters were appropriate. The TMP had a significant effect, while the Q had no significant effect on the $J_{EtOH 0}$. The effect size of the TMP was 1.20. The optimal value of the factor amounted to TMP = 30 bar. The predicted $J_{EtOH 0}$ under the above conditions was 121.965 g/m² h. Full article

In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries. Full article

A large pore size Poly(vinylidene fluoride) (PVDF) membrane was prepared by the V-NIPS method using PVDF/N, N-dimethylacetamide (DMAc)/Polyvinyl pyrrolidone (PVP)/Polyethylene glycol (PEG) system. Firstly, the effect of different additive ratios on the membrane morphology and pore size was studied, and it was found that when the PVP:PEG ratio was 8:2, PVDF membranes with a relatively large pore size tend to be formed; the pore size is about 7.5 µm. Then, the effects of different exposure time on the membrane morphology and pore size were investigated, and it was found that as the vapor temperature increased, the pores on the surface of the membrane first became slightly smaller and then increased. Finally, the effects of different vapor temperatures on the membrane properties were discussed. The results showed that the as-prepared membrane exhibited suitable capillary flow rate and similar performance compared with a commercially available membrane in colloidal gold tests. The likely cause is that the amount of negative charge is less and the capillary migration rate is too fast. This paper provides a reference for the preparation of PVDF colloidal gold detection membrane. Full article

The inclusion of membrane-based oxygen-fired combustion in power plants is considered an emerging technology that could reduce carbon emissions in a more efficient way than cryogenic oxygen-fired processes. In this paper, a techno-economic assessment was developed for a 863 MW_el,net power plant to demonstrate whether this CCS technique results in a reduction in efficiency losses and economic demand. Four configurations based on oxygen transport membranes were considered, while the benchmark cases were the air combustion process without CO₂ capture and a cryogenic oxygen-fired process. The type of driving force through the membrane (3-end or 4-end), the point of integration into the oxy-fuel combustion process, the heating system, and the pollutant control system were aspects considered in this work. In comparison, the efficiency losses for membrane-based alternatives were lower than those in the cryogenic oxygen-fired process, reaching savings of up to 14% net efficiency. Regarding the specific energy consumption for CO₂ capture, the configuration based on the oxygen transport membrane unit with 4-end mode and hot filtration presented 1.01 kW_el,net,·h/kg_{CO2 captured} with 100% CO₂ recovery, which is an improvement of 11% compared with the cases using cryogenic oxygen. Comparing economic aspects, the specific investment costs for cases based on the oxygen transport membrane unit varied between 2520 and 2942 $/kW_el,net·h. This was between 39.6 and 48.2% above the investment for the reference case without carbon capture. However, its hypothetical implantation could suppose a savings of 10.7% in terms of investment cost compared with cryogenic oxygen-based case. In terms of the levelized cost of electricity and the cost of CO₂ avoidance, the oxygen transport membrane configurations achieved more favorable results compared with the cryogenic route, reaching savings up to 14 and 38%, respectively. Although oxygen transport membrane units are currently not mature for commercial-scale applications, the results indicated that its application within carbon capture and storage technologies can be strongly competitive. Full article

Dual membrane hybrid systems generally produce reclaimed water for non-potable uses by blending microfiltered biologically treated sewage effluent (BTSE) and reverse osmosis (RO) permeate. This reclaimed water is found to contain a significant amount of micro-pollutants, which possibly cause toxicity effects to aquatic organisms and plants when exposed to it. Therefore, removing such pollutants from the reclaimed water before reaching the community is highly emphasized nowadays. The currently used treatment of the RO treatment of microfiltered BTSE is energy intensive and not cost effective. This paper focuses on less costly and efficient membrane-based hybrid treatment systems such as the microfiltration-adsorption (MF-GAC) hybrid system, Nano filter (NF) and RO in the removal of micro-pollutants from the microfiltered BTSE. Both the MF-GAC hybrid system and NF (with NTR 729HF membrane) removed 70 to 95% of micropollutants from microfiltered BTSE. The removal depends on the hydrophobicity, charge, and size of the micropollutants. RO was excellent in removing more than 90% of pollutants, while MF was inefficient, as the latter primarily depends on the size exclusion mechanism. Based on the finding, it is suggested to treat only a portion of microfiltered BTSE through the MF-GAC or NF membrane before blending with RO permeate to enhance the removal of micro-pollutants from reclaimed water. The development of sustainable hybrid systems for the removal of all micropollutants of different chemical and physical properties is the key for the water reclamation. Full article

Two-dimensional (2D) MXene materials have recently been the focus of membrane research due to their unique properties, such as their single-atomic-layer thickness, flexibility, molecular filtration abilities and microstructural similarities with graphene, which is currently the most efficient precursor material for gas separation applications. In addition, the potential to process nanoscale channels has motivated investigations of parameters which can improve membrane permeability and selectivity. Interlayer spacing and defects, which are still challenging to control, are among the most crucial parameters for membrane performance. Herein, the effect of heat treatment on the d-spacing of MXene nanosheets and the surface functionalization of nanolayers was shown regarding its impact on the gas diffusion mechanism. The distance of the layers was reduced by a factor of over 10 from 0.345 nm to 0.024 nm, the defects were reduced, and the surface functionalization was maintained upon treatment of the Ti₃C₂ membrane at 500 °C under an Ar/H₂ atmosphere as compared to 80 °C under vacuum. This led to a change from Knudsen diffusion to molecular sieving, as demonstrated by single-gas permeation tests at room temperature. Overall, this work shows a simple and promising way to improve H₂/CO₂ selectivity via temperature treatment under a controlled atmosphere. Full article

This study reports on the impact of elevated recovery (i.e., 80%, 85%, and 90%) on the fouling and performance of air gap membrane distillation (AGMD) with real seawater and landfill leachate wastewater samples using polytetrafluoroethylene (PTFE) polymer membranes. Increasing the feed temperature from 55 °C to 65 °C improved the water flux of seawater and wastewater and shortened the operating time by 42.8% for all recoveries. The average water flux in the 80%, 85%, and 90% recovery experiments at the 65 °C feed temperature was 32%, 37.32%, and 36.7% higher than the case of 55 °C for the same recoveries. The water flux decline was more severe at a higher temperature and recovery. The highest flux decline was observed with a 90% recovery at 65 °C feed temperature, followed by an 85% recovery at 65 °C. Close examination of the foulants layer revealed that seawater formed a cake fouling layer made predominantly of metal oxides. In contrast, the landfill leachate fouling was a combination of pore blocking and cake formation, consisting mainly of carbonous and nitrogenous compounds. Physical cleaning with deionized (DI) water at 55 °C and 65 °C and chemical cleaning with hydrogen peroxide (H₂O₂) were investigated for their efficiency in removing membrane foulants. Analytical results revealed that seawater fouling caused membrane pore blockage while wastewater fouling formed a porous layer on the membrane surface. The results showed that membrane cleaning with hydrogen peroxide restored >97% of the water flux. Interestingly, the fouling factor in seawater tests was 10%, while it was 16% for the wastewater tests. Full article