Membrane applications bipolar membranes

Water Splitting A modified electrodi ysis arrangement is used as a means of regenerating an acid and a base from a corresponding salt. For instance, NaCl may be used to produce NaOH and HCl. Water sphtting is a viable alternative to disposal where a salt is produced by neutralization of an acid or base. Other potential applications include the recovery of organic acids from their salts and the treating of effluents from stack gas scrubbers. The new component required is a bipolar membrane, a membrane that sphts water into H and OH". At its simplest, a bipolar membrane may be prepared by... 

An analysis of the individual PEM components offers evidence of almost unbroken R D see Fig. 13.10 (Jochem et al., 2007). The overall importance of the membrane is striking. Furthermore, the numbers of annual applications for bipolar plates (BPP) and the gas-diffusion layer (GDL) decrease after 2002, while the increase in membrane applications flattens out. This correlates with the equally lower number of fuel cell patents in the field of mobile applications. 

There has been an accelerated interest in polymer electrolyte fuel cells within the last few years, which has led to improvements in both cost and performance. Development has reached the point where motive power applications appear achievable at an acceptable cost for commercial markets. Noticeable accomplishments in the technology, which have been published, have been made at Ballard Power Systems. PEFC operation at ambient pressure has been validated for over 25,000 hours with a six-cell stack without forced air flow, humidification, or active cooling (17). Complete fuel cell systems have been demonstrated for a number of transportation applications including public transit buses and passenger automobiles. Recent development has focused on cost reduction and high volume manufacture for the catalyst, membranes, and bipolar plates. 

Bazinet, L., Lamarche, F., Labrecque, R., Toupin, R., Boulet, M., and Ippersiel, D. 1997. Electroacidification of soybean proteins for the production of isolate. Food Technol. 51(9), 52-56, 58, 60. Bazinet, L., Lamarche, F., and Ippersiel, D. 1998. Bipolar-membrane electrodialysis Applications of electrodialysis in the food industry. Trends in Food Sci. Technol. 9, 107-113. 

Electrodialysis is by far the largest use of ion exchange membranes, principally to desalt brackish water or (in Japan) to produce concentrated brine. These two processes are both well established, and major technical innovations that will change the competitive position of the industry do not appear likely. Some new applications of electrodialysis exist in the treatment of industrial process streams, food processing and wastewater treatment systems but the total market is small. Long-term major applications for ion exchange membranes may be in the nonseparation areas such as fuel cells, electrochemical reactions and production of acids and alkalis with bipolar membranes. 

Electromembrane processes such as electrolysis and electrodialysis have experienced a steady growth since they made their first appearance in industrial-scale applications about 50 years ago [1-3], Currently desalination of brackish water and chlorine-alkaline electrolysis are still the dominant applications of these processes. But a number of new applications in the chemical and biochemical industry, in the production of high-quality industrial process water and in the treatment of industrial effluents, have been identified more recently [4]. The development of processes such as continuous electrodeionization and the use of bipolar membranes have further extended the range of application of electromembrane processes far beyond their traditional use in water desalination and chlorine-alkaline production. 

In addition to the monopolar membrane described above a large number of special property membranes are used in various applications such as low-fouling anion-exchange membranes used in certain wastewater treatment applications or composite membranes with a thin layer of weakly dissociated carboxylic acid groups on the surface used in the chlorine-alkaline production, and bipolar membranes composed of a laminate of an anion- and a cation-exchange layer used in the production of protons and hydroxide ions to convert a salt in the corresponding acids and bases. The preparation techniques are described in detail in numerous publications [13-15]. 

Problems in the practical application of bipolar membrane electrodialysis In addition to the precipitation of multivalent ions in the base containing flow stream and the stability of the ions in strong acids and bases a serious problem is the contamination of the products by salt ions that permeate the bipolar membrane. In particular, when high concentrations of acids and bases are required the salt contamination is generally high [28] as illustrated in Figure 5.13 that illustrates the conversion of... 

The future for electrodialysis-based wastewater treatment processes appears bright. The dilute concentrations of metals in the waste streams do not degrade or foul the cation or anion exchange membranes. The concentrate streams are recirculated to build up their metal content to a level that is useful for further recovery or direct return to the process stream. Ongoing research in the development of cheaper cation exchange membranes, and stable anion exchange and bipolar membranes will allow electrodialysis-based applications to become more competitive with other treatments. 

Electrodialysis with bipolar membranes (EDBMs) [23] was applied recently to the production of mineral and organic acids [24-36], inhibition of enzymatic browning [37-39], and separation of protein [40-44]. These applications are based on water dissociation at the interface of a bipolar membrane (BPM) coupled with monopolar membrane action. A recent up-to-date overview gives the possibilities and the economic relevance of BPM technology [45]. 

Bazinet L, Lamarche E, and Ippersiel D. Bipolar-membrane electrodialysis An application of electrodialysis for the food industry. Trends Food Sci. Tech. 1998 9 107-113. 

These applications are based on water dissociation at the interface of a bipolar membrane and are coupled with the action of the monopolar membrane action. Deacidification and acid production, however, entail conventional ED. In the recovery of organic acids from fermentation broths the elimination of cations has often been a major problem, as fermentation typically performs better in pHs significantly above the pfC, of the acid produced. Bipolar membranes offer a solution to the elimination... 

H. Muller and H. Putter, Preparation method of bipolar membranes, Jpn. Pat. JP 61-207444 (unexamined application). 

H.P. Rapp, G. Eigenberger and H. Strathmann, Electrodialysis with bipolar membranes - theory and application , Proc. of ICOM 96 The 1996 International Congress on Membranes and Membrane Processes), Yokohama, Aug. 18-23, p. 506-507. 

The practical use of bipolar membranes for the recovery of acids and bases from the corresponding salts by electrodialytic water dissociation in the early 80 s by Liu et al. [9] opened a multitude of new applications in chentical industry and in waste water treatment. The combination of electrodialysis with conventional ion-exchange technology and the use of conducting spacers are both commercially and technically very interesting variations of the basic process [10]. 

Electrodialysis was developed first for the desalination of saline solutions, particularly brackish water. The production of potable water is still currently the most important industrial application of electrodialysis. But other applications, such as the treatment of industrial effluents [45], the production of boiler feed water, demineralization of whey [46], de-acidification of fruit juices [47], etc. are gaining increasing importance with large-scale industrial installations. An application of electrodialysis which is limited regionally to Japan has gained considerable commercial importance. This is the production of table salt from sea water. Diffusion dialysis and the use of bipolar membranes have significantly expanded the application of electrodialysis in recent years [48]. 

Bipolar membranes have recently gained increasing attention as efficient tools for the production of acids and bases from the corresponding salts by electrically forced water dissociation. The process, which has been known for many years, is economically very attractive and has a multitude of possible applications [55]. So far, however, the large-scale use of the process has been rather limited because of the shortcomings of today s bipolar membranes, which have to meet certain requirements as far as their water splitting capability, their electrical properties and chemical stability is concerned. But recent progress in the development of efficient bipolar membranes have increased the technical and industrial importance of this process. 

Bazinet, L., Lamarche, F., and Ippersiel, D. (1998) Bipolar membrane electrodialysis Applications of electrodialysis in the food industry. Trends in Food Science and Technology 9, 107-113. 

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