Adsorption of lactic acid from fermentation broth and aqueous solutions on Zeolite molecular sieves

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 isotherms 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 in batch mode. Henry's constant dependency on temperature was derived from Van't Hoff's equation. The heat of adsorption was calculated as (29 +/- 17) kJ/mol. The kinetics of adsorption was investigated in column studies where the breakthrough and elution curves were measured. 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. (c) 2005 Elsevier Ltd. All rights reserved.