Extraction Of Propionic Acid From Fermentation Broth By Ion-exchange Chromatography

The propionic acid is an important feed mould inhibitor and industrial product, which is mainly produced by chemical methods. With the serious pollution, high cost and severe operating conditions by chemical synthesis, not to match the trend that environmental awareness is becoming more and more stronger, so the process of propionic acid fermentation has been the hot topic.The growth of microorganism needs certain buffer system and the appropriate pH. The propionic acid of metabolism synthesis, in fact, in the form of propionic acid salt exists in the fermentation broth. Meanwhile, in view of the properties of propionic acid itself, it is unable to use the traditional calcium salt method to produce propionic acid because of its high solubility. The propionic acid of Biological production on the market is in the form of calcium propionate at present, instead of propionic acid. How to extract the propionic acid radical from the fermented broth and make it into propionic acid is an urgent problem which needs to solve.Ion-exchange chromatography and the main problem of propionic acid extraction process is studied in this paper. Firstly, reducing the competitive effect about the active group of anion resins through optimizing the medium; secondly, removing the pigment in the fermentation broth with the membrane filtration method; then the adsorption capacity of 7 kinds of ion-exchange resins with different properties for propionic acid in the fermentation broth was investigated and the effects of fermentation broth acidification methods and pH value on the resin adsorption capacity were studied; finally the elution processes with different concentrations of H2SO4 were analyzed and the feasibility of in series multi-column chromatography to increase the yield of propionic acid was discussed. This Paper main research results are as follows:1. The optimization of the fermentation medium and removing pigment of the fermentation brothUsing the present fermentation medium as the initial medium, removing the(NH4)2SO4 and KH2PO4 in the fermentation medium under the premise that didn't influence the production of propionic acid, for the sake of eliminating the competitive effect for anion exchange resin reactive group, to increase the anion exchange resin adsorption capacity for propionic acid. Then removing pigment with ultrafiltration membrane of different apertures to reduce the color degree and increase the purity of production. The conclusions were as follows:(1) There were no effects on propionic acid production phase and yield after removal of inorganic salt, meanwhile, it could save the cost of production in a way.(2) The selected 7 kinds of ion-exchange resins had a higher adsorption capacity for propionic acid in the fermentation medium which removed the(NH4)2SO4 and KH2PO4, the result proved that SO42- and H2PO4- would compete the active group of anion exchange resin.(3) Both the propionic acid concentration and color degree of fermentation broth would reduce with the filter membrane aperture decreasing. The color degree of fermentation broth would decrease to 2 degree when the filter membrane aperture was selected as 5 kDa. In consideration of propionic acid yield and color degree change of fermentation broth, the filter membrane aperture of 5 kDa was selected in this paper.2. The optimization on propionic acid absorption-desorption processThe effects of fermentation broth acidification methods and pH value on the resin adsorption capacity were studied, and a high concentration propionic acid eluant was obtained. H2SO4 was selected as the desorption solution instead of conventional NaOH in this paper, to make propionic acid enrich through increasing H2SO4 concentration, finally removing the SO42- of eluant in calcium salt precipitation method. The conclusions were as follows:(1) The effects of fermentation broth acidification methods and p H value on the resin adsorption capacity were studied, and D001 H-type cation exchange resin acidization method was determined.(2) When pH value decreased to 3 from 6.5, the static state adsorption capacity of ZGD630 increased from 54.34 mg/g to 110 mg/g dry beads, with a dynamic adsorption capacity of 152.5 mg/g. The highest propionic acid concentration during the elution process(4 mol/L H2SO4) reached 81.8 g/L, which was 2.12 times of the original fermentation broth concentration. Removing the SO42- of eluant in calcium salt precipitation method, and obtain molecular state propionic acid solution.(3) A propionic acid yield of 62.15% was obtained with in series three-column combined chromatography, a significant improvement compared to the one-column chromatography.(4) The purity of calcium propionate increased from 35.45 % to 75.94 %, which was 2.14 times of the original fermentation broth. The result proved that it could not only enrich propionic acid but also remove other impurities in the fermentation broth via ion-exchange resins, and improve the purity of propionic acid in the final product.