Bipolar Membrane Electrodialysis Stack Research Articles

Thermal effect of the stack in a bipolar membrane electrodialysis: Mechanism, risk, size effect and salt effect

Thermal effect inevitably occurred in a bipolar membrane electrodialysis (BMED) stack impacts its energy efficiency and potentially damages non-metallic components. Up to now, thermal mechanism and impacts within a BMED stack remain incompletely understood. Thus, thermal mechanism and impacts within the stack were investigated using the validated equivalent circuit model of a BMED system. Its results revealed that currents/Joule effect in the main circuit were dominant compared to those in the external circuit. The proportion of Joule heat in the main circuit exceeds 99.00 %, while that in the external circuit was less than 1.00 %. Joule heat generated in the outermost slot of the maximum conductivity compartment was obvious, while that in any position of the main circuit within the minimum conductivity compartment was also significant. Thermal impacts of non-metallic components were affected by the heat transfer of solution thermal effect. Besides, these effects which included current distribution, Joule effect, and thermal risk, were mainly affected by the size of the element at spacer, and the conductance provided by the salt and its products. Larger size of slots/ducts at spacer reduced the heat transfer efficiency at their location, while that of main channel enhanced the heat transfer efficiency between membranes and solution. Low conductivity salts and corresponding products pose a greater thermal risk for BMED stack. Meanwhile, these effects would be aggravated from the lab- to large-scale BMED stack. These findings can enhance the comprehension of the involved processes for optimizing BMED technique, thereby accelerating its development.

Improving ammonia nitrogen removal and recovery by BMED stack optimization: The effect of ion exchange membrane thickness

Bipolar membrane electrodialysis (BMED) has emerged as an efficient and promising technology for the removal and recovery of ammonia nitrogen. Despite its potential, the optimization of BMED systems for enhanced performance and energy efficiency remains a critical challenge, particularly in the context of varying ion exchange membrane (IEM) thicknesses. Membranes with a thickness of < 80 µm have low resistance and are mainly used for processes requiring low energy consumption. Membranes with a thickness of 80–250 µm have moderate resistance and high ion selectivity and are widely used for electrodialysis applications. Membranes with a thickness of > 250 µm have higher ion selectivity than commercial membranes with a thickness of 80–250 µm and are suitable for processes that demand high purity. This study investigates the effect of IEM thickness ranging from 16–400 µm on BMED performance for ammonia nitrogen removal and recovery, and energy consumption. The BMED configuration comprising five cell triplets consisting of a cation exchange membrane, bipolar membrane, and anion exchange membrane was employed. The thickness of IEMs was divided into three categories: 16–17 µm (PCEM/ PAEM), 100–150 µm (CD100/AD100, InnoSep-C/InnoSep-A), and 380–400 µm (MC-3470/MA-3475). In membranes with a thickness of 100–150 µm, the ammonia nitrogen removal was exceptionally high at 99.2 %, with a recovery of 98.7 % (CD100/AD100: 100 µm) at a current density of 80 mA/cm2, and the system exhibited low specific energy consumption (SEC) of 8.87 kWh/kg-N (InnoSep-C/InnoSep-A: 150 µm) at a current density of 20 mA/cm2. However, when using the thinnest IEMs (PCEM: 16 µm, PAEM: 17 µm), an increase in total ammonia nitrogen loss (10.21–22.01 %) led to a reduction in ammonia nitrogen recovery. Conversely, when using the thickest IEMs (MC-3470: 380 µm, MA-3475: 400 µm), the SEC was extremely high (30.98–126.67 kWh/kg-N), making them unsuitable for the BMED process for ammonia nitrogen removal and recovery. Based on these experimental results, it is suggested to use an optimal thickness of IEM within the range of 80–250 µm in the BMED systems to achieve a balanced performance, maximizing ammonia nitrogen removal and recovery while minimizing the SEC. Consequently, the present study provides a comprehensive understanding of the effects of the IEM thicknesses on the BMED systems and could offer a practical perspective for optimizing the BMED stack with respect to improving the removal and recovery rate of ammonia nitrogen and reducing the energy consumption.

Intricacies of caustic production from industrial green liquor using bipolar membrane electrodialysis

Lime based causticization of green liquor (GL, rich in Na2CO3) to white liquor (rich in NaOH) followed by lime recycling in pulp and paper mills is an energy intensive and environmentally hazardous technique. Recently membrane electrolysis is proposed to be an alternative to this, where use of single cation exchange membrane (CEM) between two electrodes limits the processing volume of the feed stream. This can be overcome through BMED (bipolar membrane electrodialysis) technique, where multiple cell pairs can be applied to process larger feed volume. Current report investigates optimization of NaOH production from synthetic-GL using a BMED stack with variation of current density (25, 50, 75 and 100 mA·cm−2), GL concentration (100%, 75%, and 50% v/v), and feed temperature (27, 40 and 50 ℃) along with multiple cell pair arrangement (1, 2 and 3). With 50 mA·cm−2, ~1.6 mol·L−1 of NaOH could be produced from 500 mL of synthetic-GL in 5 h using a three-cell pair BMED setup (effective area of 32 cm2 per cell pair), where current efficiency and energy consumption estimates were ~88.0% and ~4.7 kWh·kg−1, respectively. Under identical conditions, NaOH production performance from industrial-GL was quite comparable (deviation < 5%) to that of synthetic-GL.

A mathematical model of the external circuits in a bipolar membrane electrodialysis stack: Leakage currents and Joule heating effect

Leakage currents existing in a bipolar membrane electrodialysis (EDBM) stack caused loss of coulombic efficiency, ranged from approximately 0.9% to 12%, and created undesirable heat that impaired its operation. A mathematical model for electrical analog of a cell pair, predicting leakage currents and Joule heating effect of the external circuits in a EDBM stack was developed by considering the electrochemical process as an electrical analog circuit. Current and potential balance equations was used to define the equivalent network, and differential calculus was applied to solve these equations. Leakage current model was validated with experimental and simulated results. On this basis, leakage currents and Joule heating effect in a pilot-scale EDBM stack were analyzed. The results revealed that leakage currents in external circuits were distributed symmetrically around the membrane stack and were significantly affected by the number of cell pairs, current density, and element resistivity. Moreover, Joule heating effect in the external circuit in the stack was quantitatively analyzed and the temperature effect was dominated by the slot closed to the electrode cell in the acid compartment. This was most pronounced (raised by 12.18 ℃ in 0.3 s) during the termination stage. Using these findings, EDBM stacks can be improved and the optimal spacers and a more reasonable process can be designed, which could boost the development of EDBMs.

Ammonia separation from wastewater using bipolar membrane electrodialysis

AbstractNitrogen pollution is a serious environmental challenge in natural water and thus selective ammonia separation in wastewater treatment is of great importance to decrease the nitrogen load to natural water systems. Bipolar membrane electrodialysis (BMED) is a relatively new ion exchange membrane technology that can be used for ammonia recovery from wastewater as a beneficial substance. A bench‐scale BMED stack with seven pairs of bipolar membrane (BPM) and a cation exchange membrane (CEM) was operated under various voltage applications to separate ammonia from dewatering centrate (liquid downstream from dewatering of anaerobically digested wastewater sludge). Ammonia in the wastewater was rapidly separated (up to 87% in 30 min) and recovered as ammonium hydroxide solution using the BMED stack. We found that the maximum rate of ammonium separation was governed by the concentration polarization near CEMs rather than water transport into BPMs. In addition, even with the significantly high organic level in dewatering centrate (408 mg/L as total suspended solids), high efficient ammonia separation was maintained over 8 repeated BMED operations without any pretreatment of the feed wastewater, indicating effective organic fouling control with regular chemical cleaning. Furthermore, BMED operation for 30 minutes at 5.0 V per cell pair was found to be ideal for high purity ammonium hydroxide production and low electrical energy consumption. Based on the high separation efficiency and low energy consumption, we suggest that BMED be further investigated as an attractive option for ammonia separation and recovery from wastewater.

A Mathematical Model of the External Circuits in a Bipolar Membrane Electrodialysis Stack: Leakage Currents and Joule Heating Effect

A Mathematical Model of the External Circuits in a Bipolar Membrane Electrodialysis Stack: Leakage Currents and Joule Heating Effect

Ammonium sulfate production from wastewater and low-grade sulfuric acid using bipolar- and cation-exchange membranes

Conventional electrodialysis can be used to recover ammonia from dewatering centrate (i.e., down-stream wastewater from digested sludge dewatering). However, ionic impurities of the recovered ammonia solution are still a limiting factor for broad applications of ion-exchange membranes (IEMs) in wastewater treatment and resource recovery. In this study, an electrodialysis stack with bipolar membranes (BPMs) and cation exchange membranes (CEMs) but without anion exchange membranes (AEMs) was examined under various operation conditions to demonstrate high-purity ammonium sulfate production using low-grade sulfuric acid and dewatering centrate. Two significant benefits of removing AEMs from the bipolar membrane electrodialysis (BMED) are no more membrane fouling problems on AEMs and complete exclusion of impurity anions (e.g., chloride ions) in the recovered ammonium sulfate solution. A higher applied voltage condition (30 V over 7 pairs of CEM and BPM) resulted in a substantially high ammonia recovery (88.4%) and concentration (4.34 g-N/L) in 90 min. The ammonia recovery and concentration were also improved by increasing the flow rate through the BMED stack. The lowest electric energy consumption in the membrane stack was 9.6 kW h/kg-N, indicating energy efficient production of high-purity ammonium sulfate from wastewater. The amount of divalent cation scales accumulated in the BMED stack was linearly proportional to the average electric current, implying that the scaling problem can be controlled by reducing the applied voltage. Even with the scale accumulation, the electric current generation (i.e., separation performance) was hardly affected during the experiment. These findings demonstrated the strong potential of AEM-lacking BMED for practical ammonia separation from wastewater with reduced impurities.

Integration of Bipolar Membrane Electrodialysis with Ion-Exchange Absorption for High-Quality H3PO2 Recovery from NaH2PO2.

H3PO2 has emerged as an indispensable reducing agent for electroless nickel plating. Commercial preparation of H3PO2, with high purity and low cost, is a great challenge. In this work, a novel technique by the integration of bipolar membrane electrodialysis (BMED) with ion-exchange absorption was designed to prepare high-quality H3PO2 aqueous solution. The critical parameters, such as voltage drop, NaH2PO2 concentration, and different types of anion-exchange membranes, were systematically investigated. Continuous experiments indicated that a high yield of up to 80.06% with a low energy consumption of 4.99 kW h/kg was achieved under optimal operation conditions (voltage drop of 20 V, feed concentration of 15 wt % NaH2PO2, and anion-exchange membrane of AHA). Moreover, leakage of Na+ ions through the bipolar membrane was observed. By using T-52H cation-exchange resin, the final concentration of Na+ ions in H3PO2 aqueous solution was reduced to 20.91 mg/L. Subsequently, a long-term experiment was performed to evaluate the stability of the BMED stack, and the concentration of H3PO2 in the acid compartment reached 4.15 mol/L. Under optimal conditions, the H3PO2 production cost was estimated at $0.937 kg–1, which was competitive and economically friendly for industrial application.

Mathematical modelling and experimental investigation of CO2 absorber recovery using an electro-acidification method

Conventionally, CO2 is recovered using heat stripping method in the carbon capture and sequestration process (CCS), which requires a large amount of energy, and an amine treatment unit to remove heat stable salt (HSS). The energy consumed in CO2 recovery accounts for a large fraction of the total energy required for the CCS process. In this work, a novel electro-acidification method using bipolar membrane electrodialysis (BMED) was proposed as an alternative for simultaneous carbon absorber regeneration and HSS removal. The BMED stack was designed and integrated with a hollow fiber membrane contactor. The theoretical energy consumption for CO2 recovery were estimated through mathematical modelling, which was as low as 2 MJ/kg-CO2 (including HSS removal). The practical energy consumption is higher than the calculated due to trapped CO2. The findings of this study have important implications for the understanding of the integrated membrane process for carbon management with lower energy consumption.

Sustainable treatment of desulfurization wastewater by ion exchange and bipolar membrane electrodialysis hybrid technology

Residual Ca2+ and Mg2+ in chemically softened desulfurization wastewater may form hydroxides which block the pores of cationic exchange membranes (CEM) during bipolar membrane electrodialysis (BMED) used for acid and base recovery. In this study, ion exchange was investigated as a polishing treatment prior to BMED for sustainable treatment of desulfurization wastewater. Adsorption of Ca2+ and Mg2+ from desulfurization wastewater was investigated using three chelating resins (Amberlite IRC 747, Lewatit TP 208 and Lewatit TP 260) in batch adsorption studies as a function of contact time (0–720 min), solution pH (6.0–11.0), salinity (35–140 g L−1) and temperature (298–318 K). Langmuir isotherm fitted the experimental data better than Freundlich isotherm, and the pseudo second-order kinetics describe the adsorption behavior well. Evaluation of thermodynamic parameters (G°, free energy; S°, enthalpy change; and H°, entropy change) demonstrated that ion exchange of Ca2+ and Mg2+ from desulfurization wastewater was feasible, favorable and endothermic in nature. The activation energies for Ca2+ and Mg2+ adsorption using TP 208 were 58.5 kJ mol−1 and 73.6 kJ mol−1 respectively >TP 260 of 38.6 kJ mol−1 and 47.9 kJ mol−1 > IRC 747 of 36.9 kJ mol−1 and 39.5 kJ mol−1. Column studies showed that the breakthrough points of Ca2+ and Mg2+ by IRC 747 both advanced with increasing bed height and that the Thomas model can adequately describe the breakthrough curves. The effluent of resin columns was injected into a BMED stack with high-purity acid (99.3%) and base (99.0%) produced. The product acid and base was reutilized to regenerate and transform the saturated chelating resins, respectively, and proved to be effective with duplicate cycles.

Process Economic Evaluation of Resource Valorization of Seawater Concentrate by Membrane Technology

In this study, a process design consisting of chemical precipitation, electrodialysis with monovalent-selective membranes, and bipolar membrane electrodialysis (BMED) is proposed to valorize seawater concentrate discharged from an RO (reverse osmosis) plant for the production of acid/base and coarse salt with high purity. After pre-precipitation and electrodialysis with monovalent-selective membranes, a high purity of coarse salt (∼92%) was obtained. Furthermore, the effect of current density and feed concentration of the BMED process on the production of acid/base with high purity was investigated. It is acceptable to attain acid/base with a purity of ∼95%/∼85% when operating at a current density of 10 mA/cm2 and a feed conductivity of 100 mS/cm by applying the screened BMED stack. Finally, the total process cost for the acid/base production was estimated at $0.50/kg at the current density of 10 mA/cm2, which is appropriate and competitive for industrial application.

Recovery of citric acid from fermented liquid by bipolar membrane electrodialysis

The process of recovering citric acid from fermented liquid by bipolar membrane electrodialysis (BMED) was studied. Two bipolar membranes and one cation exchange membrane were stacked to form a two-compartment BMED stack configuration. The effects of the current density, initial concentration of sodium citrate, and structure of the acid compartment (AC) and base compartment (BC) on the performance of the BMED process were investigated. Filling mixed-bed ion exchange resins in BC could decrease the compartment resistance and led to a pure base solution for reuse. The highest acid recovery of 97.1% was achieved with 3.3% initial sodium citrate under a current density of 40 mA cm−1. Additionally, a decrease of voltage across AC by filling cation exchange resins restricted the migration of H+ ions from AC to BC. A higher initial concentration of sodium citrate has an adverse effect on the recovery of citric acid. BC with a bipolar membrane (BPM) exhibited lower energy consumption and a higher recovery rate of citric acid. BMED appears to be a promising technology for recovering citric acid from fermented liquid.

Electrochemical Ion-Exchange Regeneration and Fluidized Bed Crystallization for Zero-Liquid-Discharge Water Softening.

This research investigated the use of an electrochemical system for regenerating ion-exchange media and for promoting the crystallization of hardness minerals in a fluidized bed crystallization reactor (FBCR). The closed-loop process eliminates the creation of waste brine solutions that are normally produced when regenerating ion-exchange media. A bipolar membrane electrodialysis stack was used to generate acids and bases from 100 mM salt solutions. The acid was used to regenerate weak acid cation (WAC) ion-exchange media used for water softening. The base solutions were used to absorb CO2 gas and to provide a source of alkalinity for removing noncarbonate hardness by WAC media operated in H(+) form. The base solutions were also used to promote the crystallization of CaCO3 and Mg(OH)2 in a FBCR. The overall process removes hardness ions from the water being softened and replaces them with H(+) ions, slightly decreasing the pH value of the softened water. The current utilization efficiency for acid and base production was ∼75% over the operational range of interest, and the energy costs for producing acids and bases were an order of magnitude lower than the costs for purchasing acid and base in bulk quantities. Ion balances indicate that the closed-loop system will accumulate SO4(2-), Cl(-), and alkali metal ions. Acid and base balances indicate that for a typical water, small amounts of base will be accumulated.

Extraction of Amphoteric Amino Acid by Bipolar Membrane Electrodialysis: Methionine Acid as a Case Study

Methionine is an important amino acid to block the autophagy in cells. In industry, the production of methionine through the hydantoin pathway generates a huge amount of inorganic salts (i.e., Na2SO4), reducing the product purity. In this work, an efficient bipolar membrane electrodialysis (BMED) technology was proposed to extract high-purity methionine from the mother liquor of reaction. Lab-scale experiments were conducted with an optimized BMED stack at a current density of 150 A/m2. The energy consumption and current efficiency were acceptable, reaching 2.156 kWh/kg NaOH and 75.10%, respectively. Specifically, the base, i.e., NaOH, with a high concentration generated in BMED stack can be used for effective adsorption of H2CO3, in view of reducing the emission of CO2. Furthermore, a simulation of cation migration during the BMED operation was performed on the basis of the relationship between pH and the concentration of different ion species. From the simulation, it is critical to control the pH at ∼4....

Production of Acids and Bases for Ion Exchange Regeneration from Dilute Salt Solutions Using Bipolar Membrane Electrodialysis

The acids and bases used for ion exchange regeneration contribute significantly to the increasing salinity of potable water supplies. This research investigated the use of bipolar membrane electrodialysis (BMED) for producing acids and bases from dilute salt solutions that are produced during reverse osmosis or evaporative cooling. Using single pass BMED, acids and bases were produced with concentrations equal to ∼75% of the feed salt concentration with current utilizations >75%. Current utilization increased with increasing feed salt concentrations due to decreased leakage current through the monopolar membranes. The maximum current density at which the BMED stack could be operated depended on the feed salt concentration and the flow velocity and was limited by water dissociation at the interface between the diluate solutions and the monopolar membranes. The stack resistance was dominated by the bipolar membranes, even for the most dilute feed solutions. The energy required per mole of acid or base produ...

Bipolar membrane electrodialysis in aqua–ethanol medium: Production of salicylic acid

To overcome the low solubility of salicylic acid (SAH) in the production process by bipolar membrane electrodialysis (BMED), the water–ethanol mixture as solution medium was introduced in the BMED technique. The results indicated that the highest acid concentration was obtained when ethanol content was 50v/v%, and the current efficiency reached 98.2%. Moreover, the BMED stack of BP–C (BP, bipolar membrane; C, cation exchange membrane) configuration was proved as most cost-effective configuration, and using this configuration the highest current efficiency could reach 99.6% and the lowest energy consumption was 2.1kWhkg−1.

Regenerating spent acid produced by HZSM-5 zeolite preparation by bipolar membrane electrodialysis

A large amount of acid wastewaters containing sodium chloride (NaCl) is usually generated during the production of HZSM-5 zeolite (H-form Zeolite Socony Mobile Five). It can cause contamination of the environment if discharged directly. In this study, a method was reported to regenerate hydrochloric acid (HCl) and sodium hydroxide (NaOH) from the acid wastewater by bipolar membrane electrodialysis (BMED). The effects of operation parameters, such as initial base concentration and current density, on the spent acid solution regeneration were investigated. The results indicated that the initial concentration of sodium hydroxide had little or no effect on the acid wastewater regeneration. But it was also demonstrated that current density have a great influence on the acid wastewater regeneration, and a higher current density applied to the BMED stack usually resulted in lower current efficiency and higher energy consumption. After the operation of BMED process, the comparison between the recycled acid solution and the pure acid solution illustrates the recycled acid solution by BMED process can replace the pure acid solution completely. Therefore, this experiment can not only achieve the elimination of environmental pollution, but also the recycling of resources.

Clean post-processing of 2-amino-1-propanol sulphate by bipolar membrane electrodialysis for industrial processing of 2-amino-1-propanol

2-Amino-1-propanol (AMP) is a key intermediate compound in the production of antibiotics, with increasing demand in industry. In this study, we propose a newly designed bipolar membrane electrodialysis (BMED) system with a novel three-compartment configuration for the processing of AMP from the AMP sulphate solution. The operational parameters were investigated for optimizing the performance of this novel BMED stack, compared to the traditional two-compartment BMED stack in the pilot scale experiment. The experimental results indicate that this novel type of BMED stack offers a better performance for AMP processing than the conventional two-compartment BMED stack. The optimum performance was observed at the current density ranging from 40 to 60mAcm−2 and a spacer thickness of 0.70mm. The corresponding current efficiency and energy consumption reached up to 53.4% and 3.135kWhkg−1, respectively. The two-compartment BMED stack was found to have a low current efficiency (39.8%) and a high energy consumption (3.864kWhkg−1). Pilot-scale experiments for an industrial application of this novel BMED stack have been applied, demonstrating that the BMED process is feasible and economically alternative for AMP purification in the industry.

Treatment of simulated brominated butyl rubber wastewater by bipolar membrane electrodialysis

A large amount of wastewaters containing sodium bromide (NaBr) is usually generated during the production of brominated butyl rubber; it can cause contamination of the environment. In this study, a method was reported to regenerate hydrobromic acid (HBr) and sodium hydroxide (NaOH) from a simulated NaBr wastewater by bipolar membrane electrodialysis (BMED). Sodium hydroxide may be recycled in the neutralization washing process of preparing the brominated butyl rubber. The effects of operation parameters, such as sodium bromide concentration, current density, and initial acid and base concentrations, on regeneration were analyzed, on the basis of proper energy consumption and current efficiency. The results indicated that a low energy consumption and a high current efficiency were achieved when the concentration of sodium bromide was in the range of 11,000–16,000 mg/L with both the initial concentration of the acid and base at about 0.10 mol/L. Additionally, it was also demonstrated that a high current density applied to the BMED stack usually resulted in both higher energy consumption and current efficiency. Finally, a discharged NaBr concentration of 133.9 mg/L, which was far below the discharge standard of water pollutants for industry, could be obtained from the initial concentration of 16,000 mg/L after the operation of BMED process for 3.5 h. Therefore, this process cannot only achieve the elimination of environmental pollution, but also the recycling of resources.

Alcohol splitting for the production of methyl methoxyacetate: Integration of ion-exchange with bipolar membrane electrodialysis

As a green technology for organic synthesis, alcohol splitting by using bipolar membrane electrodialysis (BMED) is restricted from industrial practice due to the unacceptable electrical resistance of the organic medium. This research proposes an integration strategy to reduce the electrical resistance, i.e., filling ion-exchange resins in a BMED stack. This strategy is adopted for the production of methyl methoxyacetate in methanol, and the performance of 4 kinds of ion-exchange resins are assessed in terms of the voltage drop, product yield, and current efficiency. Under the experimental conditions, the lowest voltage drop was achieved by using D201 macroreticular anion-exchange resin, and the voltage drop decreased by 44.3–61.4%. However, there was a slight decrease in the product yield and current efficiency due to the adsorption of methyl methoxyacetate onto the resins. As a compromise, 201*7 gel-type anion-exchange resin is the best choice.