The Research On Tartaric Acid Production By Bipolar Membrane Electrodialysis

Organic acids have extensive and close contact with human life, which arewidely used in food, beverage, pharmaceutical, cosmetic, chemical synthesis andbiochemistry. There are two ways to produce organic acid, chemical synthesis andfermentation. No matter fermentation or chemical synthesis, organic acids separation,concentration, purification is needed in post-processing. Traditional purificationprocesses include sedimentation, acidification, precipitation, crystallization and ionexchange step. Precipitation acidification process consumes large amounts of acid andbase, which also produces large amounts of solid waste. Traditional organic acidproduction and purification of these shortcomings do not meet the requirements ofgreen chemistry and energy saving, there is an urgent need for alternative processes.In order to achieve the goal of energy saving and green chemicals, we need a moreeconomical and environment-friendly technology.BPED (Bipolar membrane electrodialysis) can be applied to this area. If a directelectrical potential is established between bipolar membrane, water dissociationoccurs at the interphase of it, forming H~+and OH~-. Metal cations and anions of agiven organic salt combine with H~+and OH~-forming alkali and organic acidrespectively. Organic acid produced by this method has high purity, and the cost ofpost-processing is reduced. The alkali, which is by-product, can be applied to theorganic acid fermentation process, in this way it has no secondary pollution.Tartaric acid production by bipolar membrane is a starting point of this research.We focus on the energy-saving and other common problems of electrodialysis in thispaper, and the main conclusions are as follows:1. Due to low solubility of potassium hydrogen tartrate in aqueous solution, theconfiguration of experimental membrane stack is BP-A-C. In order to reduce the highresistance of the acid compartment which is caused by the low resolution of tartaricacid, strong acid ion exchange resin is added to the acid compartment.Experimental results show that adding ion exchange membrane reduces the operating voltage andthe energy consumption under the same current density. In some extend, adding ionexchange resin reduce the tartaric acid production. But comparing with the decreaseof energy consumption this method still has a tremendous positive performance.2. Under the same conditions, we add the ion exchange resins to ED(electrodislysis). The results are similar to the bipolar membrane electrodialysis. Theexperiment extends the application range of adding ion exchange resin.3. Considering the complexity of adding tiny resin to large-scale electrodialyzer,conductive spacer carved from cation exchange membrane is used in the pilot scaleexperiment. Experimental results show that the conductive spacer effectively reducesthe operating voltage, reducing energy consumption. Comparative experiment iscarried out between the Germany bipolar membrane and domestic bipolar membrane.The results show the tartaric acid yield and current efficiency of domestic bipolarmembrane should be improved in future.4. The process cost of four experiments is estimated according to theexperimental results, and there is a pair-wise comparison in accordance with theexperimental scale.(1) In small scale the accounting result of process cost show that：no matter BPED or ED, the total production cost increase with the current density;adding resin can reduce the total production cost and energy consumption costsignificantly; the total production cost of BPED is higher than ED,which is caused bythe expensive price of bipolar membrane.(2) In pilot scale, the tatal production costand energy consumption cost decrease with the current rising. The use of conductivespacer reduces the cost of energy consumption, and the decreased range of totalproduction cost is smaller than the decreased range of energy consumption cost,because of the reduce of tartaric acid production after adding the conductivespacer.The cost using domestic bipolar membrane is less than that of Germany bipolarmembrane.5. We also investigate the problem of pollution in the bipolar membraneelectrodialysis process; the results basically reproduce the phenomenon of pollution inthe literature. Cation exchange membrane is mainly affected by inorganic pollutants, and anion exchange membrane is mainly affected by organic pollutants. For example,the phenomenon of pollution increases with the holmic acid concentration and currentintensity.The results of this study show that add of ion exchange resin and conductivespacer effectively reduces the energy consumption of tartaric acid production byBPED. There is no doubt that this technology can also be extended to the productionprocess of other organic acids.