Study On Separation Of Propionic Acid Coupled With Vitamin B₁₂ Fermentation

Fermentation production of propionic acid (PA) and vitamin B12 (VB12) is greatly inhibited by propionic acid that is the product of fermentation. By the removal of propionate acid, high concentration of propionic acid and VB12 was obtained. In this thesis, PA has been separated by adsorption. Adsorption behaviors and the selectivity were studied by using static methods including the static equilibrium adsorption, the adsorption thermo dynamics properties and the kinetics of adsorption. The good operation conditions including adsorption, washing, desorption and regeneration, have been confirmed by dynamic adsorption methods. Then PA has been separated from the fermentation broth.Through the resin selection experiments,the 330 resin showed a better capability among kinds of resins.The key step 330 resin is chosed to investigate kinetics and thermodynamics of propionic acid on ion-exchange resin. The results show that the Langmuir adsorption isotherm was suitable for describing the adsorption process. During the adsorption process, the adsorption behavior of propionic acid on resin was belong to the partical diffusion control step. Using alkalescence anion exchange 330 resin to absorb propionic acid from fermentation broth, the expanded bed adsorption and desorption process of propionic acid were investigated systematically with the selected resin, and the optimized operation conditions were obtained as follows:pH 5.0, the concentration of propionic acid 10 g·L-1, 20 min and the flow velocity 710 mL·min-1, under the above conditions, the dynamic adsorption capacity reached 57.73 mg·g-1. When the concentration of NaOH 3 mol·L-1, flow velocity 1.32 mL·min-1, the desorption rate reached 93.2%。An coupling bioprocess for in situ propionic acid recovery coupled with fermentation of vitamin B12 was established based on this technology. By decreasing the concentration of propionic acid, the inhibition of propionic acid to Propionicbacterium freudenreichii was lightened dramatically. High density of cell and vitamin B12 were abtained comparing to the Fed-batch fermentation, the yield of vitamin B12 and propionic acid increased 26.69% and 36.63%, respectively.