Application Of Continuous Ion Exchange In L-lactic Acid Separation

L-lactic acid is an important organic acid, widely used, and the prospects fordevelopment are extremely impressive. It’s greatly significant to solve the problemsof the separation process of L-lactic acid, which are high cost, low efficiency, andenvironmental pollution. For fermentation broth composition was complex,difficult to purify, this paper adopted flocculation process to pretreat fermentationbroth, and optimize the process parameters. Based on the results of staticadsorption and fixed-bed ion exchange, the continuous ion exchange process andthe preliminary design of continuous ion exchange process and partition schemewere obtained. Parameters of continuous ion exchange process were to optimizatedand established and achieved the economic and efficient separation of L-lactic acid.The main research results are as follows:(1) By single-factor and response surface experiments, the operating conditionsof flocculation process for the pretreatment of L-lactic acid ammonium wereoptimized. The results were as followed: the dosage of magnesium sulfate (MgSO4)was2‰, he dosage of calcium hydroxide (Ca (OH)2) was5‰, the dosage ofactivated carbon was7‰, the temperature of flocculation was80°C, the time offlocculation was40min. Under these conditions, the removal rate of residual sugarwas30.32%, the removal rate of protein was90.96%and L-lactic acid ammoniumloss rate was3.22%.(2) Through the resin screening experiments, the good resin was filtered,732resin, which was completely exchanged rapidly within1min, and it’s adsorptioncapacity can reach345.97mg/g. The relatively best desorption agent was0.5mol/LH2SO4by the study of desorption agent and its concentration.(3) Through single factor experiments, the only significant factor that was onlypH value of the static ion-exchange was established, and the relatively best ionexchange effect was obtained when the pH ranged4-5. The adsorption isotherms ofL-lactic acid ammonium and732resin was established, and the fitting equationresulted Langmuir type. The flow rate and height to diameter ratio of fixed bed ionexchange process were studied, and the optimum flow rate was40mL/min, therelatively best height to diameter ratio was7.5:1, breakthrough time was21.5min,desorption time was60min, the desorption rate was up to96%. Under the optimalconditions, the adsorption curve and desorption curve of fixed bed were drawed. (4) Based on the results of static adsorption and fixed-bed ion exchange, thecontinuous ion exchange process and the partition scheme for the separation ofL-lactic acid was devised.The effect of flow rates of exchange area on continuousion exchange was investigated, and the relatively best flow rates of exchange area（1-6#）、washing area after the exchange（18-20#）、regeneration area（12-17#）、washing area after regeneration（9-11#）、top water area with product（7-8#）were40、40、140、35and20mL/min respectively. And concentration of each export showscyclical change steadily.(5) By camparing and analyzing continuous ion exchange process with thefixed bed ion exchange process in production of L-lactic acid, acid consumptionand water consumption, continuous ion exchange greatly improved the dailyproduction of the product, reduced acid and water consumption.