Fermentation and separation of lactic acid.

摘要

The recovery of lactic acid from fermentation broth and aqueous solutions was studied by adsorption on Silicalite molecular sieves. Batch experiments were used to measure the adsorption isotherm of the lactic acid on Silicalite. A linear correlation was found for both solutions. Silicalite showed a higher adsorptive capacity in the case of the aqueous solution than that of the fermentation broth. Henry's constants were estimated as 2 ± 0.7 L/Kg and 1 ± 0.5 L/Kg for the aqueous and broth solutions, respectively. The effect of temperature on adsorption was also studied batch mode. Henry's constant dependency on temperature was derived from Vant Hoffs equation. The heat of adsorption was calculated as (7 ± 4) × 103 Cal/mol.; The kinetics of adsorption was investigated in column studies where the breakthrough and elution curves were measured. A linear driving force model (LDF) was used to model the breakthrough behavior of the fermentation broth solution. The overall mass-transfer coefficient determined by fitting the model to the experimental breakthrough data was found 36.5 ± 7.7 hr −1. The adsorption process was controlled by the internal diffusion in the Silicalite pellets rather than the diffusion through the fluid film around the pellet. The fluid phase resistance was estimated as 21% of the overall resistance. The glucose presence in the fermentation broth had a negligible effect on lactic acid breakthrough curve in the studied range.; An integrated fermentation-adsorption system with cell recycle was proposed and simulated for efficient lactic acid fermentation. This method has the advantage of eliminating the inhibitory effect of lactic acid on cells' growth and productivity. Numerical simulations showed increased productivity over batch fermentation without pH-control with a two-fold increase of production in most cases.