Bioprocessing solvent extraction

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

Groot WJ, Soedjak HS, Donck PB, ban der Fans RGJM, Luyben KCAM, and Timmer JMK, Butanol recovery from fermentations by hquid-hquid extraction and membrane solvent extraction. Bioprocess Engineering 1990, 5, 203-216. 

Solvent extraction is used extensively to recover chemicals from natural products. Solvents are used to extract and concentrate natural oils and products in the bioprocessing industries (nutraceu-tical, food, pharmaceutical, feed, cosmetic, biotechnology) in quantities from grams to metric tons. Biotechnology applications include the recovery of primary and secondary metabolites [4]. Extraction is used to recover vegetable oils and food products. It is used to process a variety of materials including groundnut, mustard seed, soybean, pahn kemal, sunflower, rice bran, copra, cottonseed, and minor oil seeds like neem, mahua, watermelon seed, castor seed, and so on. 

Finally, the esterification reaction with styrallyl alcohol and acetic acid was carried out under natural reaction conditions using esterification catalysts such as citric acid or by means of bioprocess reactions using commercial esterforming enzymes (5). The catalytic conversion of styrallyl alcohol to styrallyl acetate did not change the stereoisomer ratio. The resulting stereoisomeric mixture of styrallyl acetate was recovered and purified by solvent extraction followed by fractional distillation. 

Rates of gas-liquid, liquid-liquid, and solid-liquid mass transfer are important and often control the overall rates in bioprocesses. For example, the rates of oxygen absorption into fermentation broth often control the overall rates of aerobic fermentation. Ihe extraction of some products from a fermentation broth, using an immiscible solvent, represents a case of liquid-liquid mass transfer. Solid-liquid mass transfer is important in some bioreactors using immobilized enzymes. 

In this review, recent progress on integrated bioprocessing, including in situ adsorption using polymeric resins, in situ extraction with adequate solvents, application of cyclodextrins, and the use of aqueous two-phase systems, are summarized and their advantages and disadvantages are described in detail. 

The recovery phase of a bioprocess begins once the products are freely suspended in a solution, either in the supernatant from the solid-liquid separation or in the lysate from the cellular disruption. Extraction is the process of separating the desired components in a liquid solution by contact with another insoluble liquid into which the desired product will be selectively extracted. This process is also commonly known as liquid-liquid extraction. The solvent-rich phase is called the extract and the residual liquid from which the desired product has been removed is called the raffinate. 

As if the low distribution coefficient does not present enough of an obstacle, extraction of acetic acid from fermentation broths is made still more unattractive by the high pH of the solutions. For the bioprocesses being evaluated, acetic acid will be produced in a solution with a pH of about 6.0. The pK of acetic acid is 4.8 and thus, at a pH of 6.0, virtually all the acetic acid produced in solution exists as an acetate ion. Current extraction/recovery schemes entail acidification (with HCl, for example) to convert the acetate ion to free acetic acid. Then the free acid can be extracted with an organic solvent. If CO2 IS used as the extractant, HCl is not required. Carbonic acid from the C02-water equilibrium will neutralize part, but not all, of the acetate ion this can be determined from a material and charge balance of species in solution. 

Dinculescu D, Guzin-Stoica A, Dobre T, Floarea O (2000) Experimental investigation of citric acid reactive extraction with solvent recycling. Bioprocess Eng 22 529-532 Pinacci P, Radaelli M (2002) Recovery of citric acid from fermentation broths by electrodialysis with bipolar membranes. Desalination 148 177-179... 

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