Electrodialysis With Bipolar Membranes Research Articles

Functionalized biopolymer based bipolar membrane with poly ethylene glycol interfacial layer for improved water splitting

This study investigates the effect of poly ethylene glycol (PEG) of different molecular weight (MW) as interfacial layer (IL) of bipolar membrane (BPM) for water dissociation. Chitosan (CS) was modified to N-methylene phosphonic chitosan (PC) and quaternized chitosan (QC), for preparing cation- and anion-exchange layer (CEL and AEL, respectively) of BPM. Different BPMs were prepared by layer-by-layer solution casting method (in aqueous media to achieve the good adhesion between layers) using PEG of different MWs (200–3400 Da) as IL. CEL and AEL with good ion-exchange properties were separately evaluated for their physicochemical and electrochemical characterizations. All BPMs with IL (PEG) were evaluated from current–voltage ( I– V) curves and water dissociation efficiency. The experimental results proved the excellent catalytic activity of PEG for water dissociation, which further improved with its MW. Furthermore, electrodialysis with bipolar membrane (EDBPM) experiments confirmed the occurrence of water dissociation at BPM interface and thus formation of acid and base.

Production of low-phytate soy protein isolate by membrane technologies: Impact of salt addition to the extract on the purification process

Previously, the advantages of combining electrodialysis with bipolar membranes (EDBM) to acidify a soy protein extract to pH 6 with ultrafiltration/diafiltration (UF/DF) using a 100 kDa membrane to produce a soy protein isolate (SPI) with low phytic acid to protein ratio were demonstrated. However, some limitations related to the fouling of ED spacers by precipitated proteins and to the flux decline during UF/DF at pH 6 were observed. Therefore the purpose of this work was to study the impact of adding KCl (0.12 M or 0.24 M) to the starting extract on the efficiency of both processes and on the solubility of the resulting isolates. Results indicated that adding KCl to the initial extract increased the productivity of EDBM by approximately two times and reduced proportionally its energy requirement. This was in large part due to the prevention of ED spacer fouling. Permeate flux during UF/DF was improved by as much as 20% when compared to the flux measured for the purification of pH 6 extracts without added salt. The phytic acid to protein ratio for pH 6 isolates obtained from the addition of KCl to the initial extract were also found to be lower than for isolates produced at pH 9 or by isoelectric precipitation at pH 4.5, but higher than for the pH 6 isolates obtained without addition of KCl to the initial extract. For the pH range 2–3.5, solubility of these isolates was improved when compared to the one of isolate pH 9, but it was similar to the one of the isolate pH 4.5. Production of added-value soy protein isolate is limited by the presence of high amount of phytic acid in the isolate produced by traditional isoelectric precipitation process. We presented previously an approach combining electrodialysis with bipolar membranes (EDBM) with ultrafiltration/diafiltration (UF/DF) for the production of soy protein isolate with low phytic acid to protein ratio and with improved solubility. However, fouling of the electrodialysis spacers by precipitated proteins was observed in the electrodialysis cell which limited practical industrial application of the approach. This problem was solved by the addition of KCl (0.12 M KCl or 0.24 M KCl) to the initial soy protein extract at pH 9 prior to its pH adjustment to 6 by EDBM. It resulted in the improvement of the EDBM productivity by more than 2 times and in a proportional decrease in its energy consumption. Flux during UF/DF at pH 6 was also improved by as much as 20% when KCl was added to the starting extract. In addition, the added KCl was found to be easily removed by UF/DF with the resulting isolates having a final protein content of 94 % which was found similar to the isolate obtained without addition of salt to the starting extract. Although the isolates produced from extracts with added KCl were found to have slightly lower solubility for the pH range of 2 to 3.5 than isolates produced from extract without addition of salt, their solubility was similar or better that for the isolates produced by traditional isoelectric precipitation process and with a lower phytic acid to protein ratio. These isolates could be considered as valuable ingredients for the formulation of fruit juice beverages or power juices, considering that the pH of these liquid food products is around 3.5. ► Adding KCl to pH 9 extract prevented fouling of ED cell by protein precipitation. ► Permeate flux for UF/DF pH 6 is improved for the extracts with added KCl. ► Isolates from extract with added KCl have better solubility than the one at pH 9.0.

Integration of conventional electrodialysis and electrodialysis with bipolar membranes for production of organic acids

To reduce the cost of electrodialysis with bipolar membranes (EDBM) for production of organic acids, conventional electrodialysis (CED) was integrated with EDBM, i.e., CED supplied concentrated organic salts as the feed to EDBM. To assess the adaptability of this integration, sodium gluconate was chosen as a model agent for production of gluconic acid. Results indicated that this integration could achieve an apparent current efficiency higher than 100% and low energy consumption due to the inward concentration of gluconate and electrode reactions in CED. Besides, the process cost of CED–EDBM was estimated to be $0.31 kg −1, which was less than that of EDBM ($0.39 kg −1). This integration not only made the production cost-effective but also kept the operation of EDBM stable.

Optimization of electrodialysis with bipolar membranes by using response surface methodology

Response surface methodology (RSM), a facile tool for optimization, was employed to determine the optimum conditions for production of organic acids by using electrodialysis with bipolar membranes (EDBM). In particular, gluconic acid was chosen as the model organic acid, and the Box-Behnken center-united experimental design was used to quantify the effects of current density, electrolyte concentration, and feed concentration on the process cost. According to the ridge and canonical analysis, the optimum conditions were as follows: current density, 44.83 mA cm −2; electrolyte concentration, 0.12 mol dm −3; feed concentration, 0.15 mol dm −3. Moreover, the experimental results were in good agreement with the predictions, suggesting that RSM was a good tool for modeling the process of EDBM.

Win−Win Coupling in Electrodialysis with Bipolar Membranes (EDBM) for Cleaner Production

An obstacle to the development of electrodialysis with bipolor membranes (EDBM) technology—high fixed cost—can be cleared away by allocating the investment among factories or plants, but it requires that EDBM couple two processes inside and provide respective products cost-effectively. To assess the process coupling, piperazine sulfate (PzH2SO4) and sodium gluconate (NaGlu) were used as model agents for Pz regeneration and HGlu production, respectively. The results showed that the highest current efficiency was achieved at the highest current density, and the lowest energy consumption at the highest feed concentration. The process cost was estimated to be $0.80 kg−1 Pz and $0.17 kg−1 HGlu in the coupled operation, which were less than those in separate operations—$0.96 kg−1 Pz and $0.24 kg−1 HGlu. Apart from environmental benignity, the process coupling in EDBM can achieve a win−win economy due to allocation of investment and economies of scale.

Galacturonic Acid Recovery from Pectin Rich Agro-Wastes by Electrodialysis with Bipolar Memranes

Pectin rich agro wastes can be utilised for manufacture of galacturonic acid. Pectin is a complex polysaccharide found in the primary cell walls and intercellular regions of higher plants. Backbone of pectin molecules is composed of galacturonic acid as a monomer. Galacturonic acid and derivates are valuable raw materials in food and cosmetic industries as acidic agents and for production of vitamin C. In this work the aim was to produce galacturonic acid from citrus pectin and sugar beet pulp. The hydrolysate of pectin contains mainly carbohydrates (oligo- and monosaccharides) and galacturonic acid. Electrodialysis with bipolar membranes (EDBM) represents an efficient technology to separate charged compounds from a solution. To remove galacturonic acid, EDBM seems a suitable process, because galacturonic acid is present as a charged compound in the solution. To obtain galacturonic acid from hydrolysate of pectin laboratory experiments were performed, similar to the system applied by Novalic et al. for recovery of other organic acids. An ED stack containing anion and cation selective and bipolar membranes was applied to obtain GA from hydrolysate.

Influence of process variables on the production of bovine milk casein by electrodialysis with bipolar membranes

The food and drink industry is one of the largest industrial sectors worldwide. Milk is one of the most important raw materials employed due to both its unique nutritional value and important functional properties. However, the functionality of the various components in milk could be employed more effectively if they were available separately. The aim of this work is the evaluation of the performance of an electro membrane technology, electrodialysis with bipolar membranes (EDBM), in the separation of casein from milk. The influence of the main operation variables, i.e., milk concentration (2.5–10 wt.%) and current density (100–400 A m −2), has been analysed. Several process parameters have been recorded while the energy consumption calculations have also been performed in order to compare this membrane technology with the conventional process. Obtained results demonstrate the technical viability of EDBM and the high influence of selected variables in the separation of casein from milk. As a result, high purity casein of 95% purity was achieved by EDBM technology instead of the 85% purity casein obtained by the conventional process. The use of clean technologies, as EDBM, will contribute towards the sustainable development of this sector.

Simultaneous regeneration of formic acid and carbonic acid from oxalate discharge by using electrodialysis with bipolar membranes (EDBM)

The feasibility was tested on simultaneous generation of formic acid and carbonic acid from oxalate discharge by using two-compartment electrodialysis with bipolar and anion exchange membranes. The process performances were evaluated by considering such factors as the molar ratio of sodium formate to sodium carbonate, and current density. The results indicated that current efficiency could attain 72% and 21% for the generation of formic acid and carbonic acid, respectively. The energy consumption was 4.3–16.6 kWh kg −1 for formic acid and 20.1–96.3 kWh kg −1 for carbonic acid. When the molar ratio of sodium formate to sodium carbonate was in the range of 0.5–2, formate anions would be the main current carriers through the anion exchange membrane, and the molar concentration of formic acid could achieve 12 times that of carbonic acid in the product solution. This can be mainly ascribed to the high permselectivity of the anion exchange membrane for formate anions. Notably, a third competitive species – OH − – is not negligible in the acid reclaiming system by using EDBM.

Synthesis of [EMIM]OH via bipolar membrane electrodialysis – precursor production for the combinatorial synthesis of [EMIM]-based ionic liquids

A new environmentally benign process for the production of aqueous solutions of [EMIM]OH is reported. Electrodialysis with bipolar membranes (EDBM) was implemented for the first time to produce this hydroxide-based precursor in 5% concentration in water from the non-toxic bulk ionic liquid [EMIM][EtOSO3] at the kg-scale. The results are discussed with regard to ease of operation, productivity and obtained product quality. Moreover, several structurally new ionic liquids were synthesized by reaction of the aqueous precursor solution with different acids, such as, e.g., H2SiF6 or hexafluoroacetylacetone. But also the synthesis of well-established ionic liquids, such as, e.g., [EMIM][BF4] has been carried out using the hydroxide intermediate and the full procedure is compared to well-established ion metathesis protocols.

A new model for characterization of bipolar membrane electrodialysis of brine

Electrodialysis with bipolar membranes (EDB) is an attractive/promising technique of converting unnecessary salt into corresponding acid and base. The efficiency of this process depends on the quality of bipolar and monopolar (anion- and cation-exchange) membranes constituting a repeating unit of an EDB stack. Thus, the choice of membranes is essential. A new model to characterize each kind of membrane in the EDB stack individually is proposed. The model is fitted to the experimental results of laboratory-scale electrodialysis of industrial brine using commercially available membranes (Neosepta: BP-1, AMX, and CMX; and FumaTech: FAB and FKB). It was found that the efficiency of the bipolar membrane BP-1 is ca. 90%. For both sets of membranes (Neosepta and FumaTech) anion-exchange membranes showed lower selectivity than cation-exchange ones. For j = 75 mA/cm 2 the ionic selectivity of monopolar Neosepta membranes was slightly better than that of the FumaTech membranes. However, because of reduced water transport the FAB anion-exchange membrane (FumaTech) was more efficient in the production of more concentrated acid. The accuracy of determination of the model parameter was better when a significantly large charge passed through the EDB stack.

Electrodialysis with Bipolar Membranes for Sustainable Development

Electrodialysis with bipolar membranes (EDBM) is a kind of technology that integrates solvent and salt dissociation. It can realize salt conversion without second salt pollution or provide H+ and OH-/alkoxide ions in situ without salt introduction. Thus, it inherently possesses economical and environmental benefits. Moreover, its technological compatibility gives rise to new functions when it couples with other technologies, such as complexion, ion exchange, extraction, and adsorption. In view of the above peculiarities, EDBM has found many interesting applications in chemistry, food processing, biochemical industries, and environmental protection. However, its development has been restricted by such factors as lack of recognition of its contribution to industrial ecology, high membrane cost, insufficient research investment, and scarce operation experience. This paper compiles an introduction to this technology from the perspective of industrial ecology and conducts an extensive examination into EDBM applications. Its purpose is to gather synergic strength from academia, industry, and government to perfect EDBM for sustainable development.

Modeling of weak acid production by the EDB method

The electrodialysis with bipolar membrane (EDB) of organic acid salts is an alternative way of the production of organic acids. In this work a model of the basic EDB cell consisting of three compartments (acid, salt, base) is presented. The transport of ions through monopolar ion-exchange membranes is described by the extended Nernst–Planck equation, assuming the Donnan equilibrium at the boundary solution|membrane. The diffusion of undissociated acid and the electro-osmotic flow of water is taken into account. The model predicts how the efficiency of salt conversion, the resistance of cell, the volumes of acid, salt, and base solutions change with time for a given current density. The simulation results are presented for the acetic acid. The influence of nonideality of membranes and of the acid dissociation constant on the efficiency of acid production is shown.

Electrodialysis as a useful technique for lactic acid separation from a model solution and a fermentation broth

A two-stage electrodialysis (ED) method was used for lactic acid recovery. In the first step sodium lactate was concentrated with desalting electrodialysis using ion exchange membranes Ralex (Mega, Czech Republic). The second step was the electroconversion of sodium lactate to lactic acid by electrodialysis with bipolar membranes (EDBM) Neosepta (Tokuyama Corp., Japan). The lactic acid was recovered from model solutions and from real fermentation broth as well. The trials with model solutions were focused on determination of the suitable conditions for electrodialysis experiments and on investigation of the time course under different conditions. The fermentation broth from lactic acid fermentation had to be pretreated before electrodialysis experiments. The pretreatment consisted of ultrafiltration, decolourisation and removing of multivalent metal ions. In the first ED step the final lactate concentration of 175 g/l was obtained and afterwards the final lactic acid concentration of 151 g/l was reached in the second ED step.

Recovery of citric acid from fermentation broths by electrodialysis with bipolar membranes

An hybrid membrane process for the recovery of citric acid from fermentation broth's which involves electrodialysis with bipolar membranes (EDBM) is being developed. In this paper the results of EDBM tests performed in a laboratory pilot loop are presented. The most suitable cell configuration and related process parameters have been determined. A comparison of membrane performances of different manufacturers is also presented.

Production of organic acids by bipolar electrodialysis: realizations and perspectives

Currently, the production of organic acids continues to increase significantly for traditional applications (additives for food and pharmaceutical industries) as well as for new ones (biodegradable plastics industry). This results in a growing demand for alternative process solutions such as Electrodialysis with Bipolar Membranes (EDBM). These must be simultaneously economically attractive and have a low impact on the environment. In this context, this article details the performance and economical figures related to an industrial EDBM plant operated for the production of organic acids. In addition, a complete downstream (from the fermentation) process based on combined electrodialysis steps for purification/concentration and conversion is proposed in the case of lactic acid.

Electrodialysis with Bipolar Membranes: Principles, Optimization, and Applications

This paper is an overview of the bipolar membrane technology. The process of electrodialysis with bipolar membrane (EDBM) along with the different EDBM process configurations are presented. Some ways of optimization of both the bipolar membranes and the EDBM technology are envisaged. Most of the applications relate to the production or recovery of organic acids while the first plant has been commissioned by 1986 at Washington Steel (USA) for the recovery of HF/HNO3 from waste pickling liquors. In the last few years, there has been increasing interest in using bipolar electrodialysis stacks in chemical and agro industrial processes to directly acidify or basify process streams without the addition of chemicals. This attractive feature of this technology has contributed to the implementation of several plants in fermentation process for the production of organic and amino acids.

Application of electrodialysis within fine chemistry

Abstract Several fine chemicals and pharmaceutical products are obtained by multi-step processes involving, amongst others, the neutralization of acid and basic solutions which lead to the formation of salts. Two routes using electrodialysis with bipolar membranes (EDBM) can be followed: (i) the conversion of the salt into the corresponding acid and basic solutions, or (ii) the neutralization of the alkali salts of the required organic acid by EDBM instead of carrying out the acid hydrolysis. Within a European Research Program the feasibility of both electrodialysis processes for amino acid production have been studied. The first type of process seemed to be not very attractive because of too high losses of amino acid and because of economical reasons. The second type of ED process was carried out in a batch mode of operation with a fixed current density of 1000 A/m2 until the stack voltage increased to 30 V, then the acidification was continued at a fixed voltage and the current density was decreased to 400 A/m2. The current efficiency found varied between 85 and 97%. The technological aspects are discussed, e.g. how to avoid precipitation of the amino acid in the membrane stack, the maximum achievable concentrations of the neutralized amino acid and of the basic solution produced.

Recovery of organic acids with high molecular weight using a combined electrodialytic process

When organic acids having molecular weights of around 200 kg kmol −1 or more are recovered using electrodialysis with bipolar membranes (EDB) in a three compartment arrangement, mass transfer (conversion rate) is rather low and energy consumption is relatively high. One of the problems lies in the coupled system between anion exchange membranes and bipolar membranes. In order to reduce the bipolar membrane area, a high transport rate through the anion exchange membranes is necessary. This, however, leads to an unpropotionately high energy consumption. In this study an attempt was made to improve the process by splitting the three compartment EDB into a conventional ED, and a two compartment system with bipolar and cation exchange membranes. This means, the bipolar membrane area will be determined by the transport rates of Na + through the cation exchange membrane, which is advantageous. However, the equivalent Na + amount must be transported two times. The organic acids separated were gluconic and citric acid. The results showed that in both cases an improvement of the technology appears possible. The bipolar membrane area can be significantly reduced, which from the economic point of view is very important. Normally, energy and membrane costs are to a certain degree variable. Thus, the degree to which the process can be made more economical has to be considered case by case.

Desalination of surface water to industrial water with lower impact on the environment: Part 4: Treatment of effluents from water desalination stages for reuse and balance of the new technological concept for water desalination

Within the framework of our new technological concept for the desalination of surface water to industrial water, the production of a mixed acid and a mixed base by electrodialysis with bipolar membranes (EDBM) from effluents was one main objective of the study. After optimized pretreatment, reverse osmosis (RO) or electrodialysis reversal (EDR) concentrates and regenerates from cation and anion exchangers can be used as feed solutions for the production of an acid and a base by EDBM. The products obtained fulfill the requirements for ion exchanger regeneration chemicals. A material balance of the new technological concept for typical river water shows that—in comparison with conventional methods for the production of desalinated water—there is less raw water consumption, less wastewater is generated and fewer commercial chemicals are needed.