No abstract

Solvent selection for extractive fermentation for propionic acid was conducted with three systems: Alamine 304‐1 (trilaurylamine) in 2‐octanol, 1‐dodecanol, and Witcohol 85 NF (oleyl alcohol). Among them, the solvent containing 2‐octanol exhibited the highest partition coefficient in acid extraction, but it was also toxic to propionibacteria. The most solvent‐resistant strain among five strains of the microorganism was selected. Solvent toxicity was eliminated via two strategies: entrapment of dissolved toxic solvent in the culture growth medium with vegetable oils such as corn, olive, or soybean oils; or replacement of the toxic 2‐octanol with nontoxic Witcohol 85 NF. The complete recovery of acids from the Alamine 304‐1/Witcohol 85 NF was also realized with vacuum distillation. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 454‐461, 1998.

Production of propionic acid by fermentation is hindered by low productivity and product inhibition. Cell immobilization to increase productivity and extractive fermentation to reduce product inhibition were investigated. Propionic acid concentration in the extractive fermentation was maintained at 13 g•L-1 by concurrent extraction with a Iiquid extractant consisting of 40 % (v/v) Alamine" 304-1 (trilaurylamine) in Witcohol" 85 NF (oleyl alcohol). A final concentration of71 g-L-1 propionic acid was obtained in non extractive mode. Yields of propionic and acetic acids were doubled and higher overall productivities were obtained in the extractive fermentation. The extractant also exhibited selectivity for propionic acid over acetic acid, thus partially purifying the former. In both fermentation modes, productivity was enhanced by cell immobilization in calcium alginate beads. An economie analysis of a modified version of the fermentation based on several favorable assumptions showed that the extractive fermentation can, at best, approach economie feasibility at an annual production of 4.7 x 10 7 kg. For the assumed conditions, the production cost of the propionic acid was US$ 1.16•kg-'; this cost was reduced to US$ 0.94•kg-' when the value of the acetic acid byproduct was included.

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