Applications of Bipolar Membrane Electrodialysis
Eurodia Industrie and its main shareholder Tokuyama Corporation have designed, built, and started up several bipolar membrane electrodialysis plants for the production of various specialty chemicals (many are confidential ar our customers request). In addition, several key employees of Ameridia are experienced with the design and operation of bipolar membrane electrodialysis systems thanks to their involvement with Aqualytics, one of the first companies to commercialize the technology (now closed down).
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Production of specialty inorganic and organic acids: several operating plants
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pH adjustment in chemical processing
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Recovery of NaOH/H2SO4 from waste sodium sulfate
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Production of HCl & NaOH for IX resins
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Conversion of salts of KOH, NaOH, NH4OH, etc.
Conventional Production
If the acid is produced by fermentation, selected microorganisms are used to convert the carbohydrate feedstock. Most of these microorganisms cannot work efficiently in acidic conditions and a base is added to the fermenter to maintain the desired high pH. In these cases, the acid is produced as the salt and must be converted to the acid outside of the fermenter. Conventionally, the conversion of the organic salt into the acid is handled by either acidification/ crystallization or ion exchange resins. In either case, a strong mineral acid, such as sulfuric acid, must be used, with safety and corrosion issues and at a cost. Even more, the acidification results in a by-product salt such as CaSO4 or Na2SO4 that must be either precipitated or crystallized, filtered and for which an outlet has to be found. Additionally, organic acid yields can be low as there can be significant losses of product in the precipitation step or in the ion exchange columns. After the by-product separation, the organic acid has to be processed through extensive purification steps to remove residual impurities from the fermentation. The acid products can also be contaminated with the anion from the strong acid.
These conventional methods generate wastes or unwanted byproducts. By bipolar membrane electrodialysis, the acidification of organic acids can be clean, without a salt waste, and in some cases, can simultaneously concentrate and purify the organic acid.
Advantages of Bipolar Membrane Electrodialysis
Bipolar membrane electrodialysis can be used to directly acidify the organic salt without the addition of chloride or sulfate anions, thus eliminating the formation of the unwanted salt byproduct and all the handling and disposal problems. Instead, the H+ ions generated from the water splitting occurring in the bipolar membranes cleanly acidifies the organic salt solution. At the same time, the salt cations, either potassium, sodium or ammonium, are converted in the base that is valuable to the fermentation process. Additionally, in some cases, product concentration and purification may take place, decreasing the demand for the downstream purification.
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