Solvent extraction one of the oldest approaches of separation known, remains one of the most well-known methods operating on an industrial scale. With the availability of variety of solvents as well as commercial equipment, liquid–liquid extractions finds applications in fields like chemicals and bio-products, food, polymer, pharmaceutical industry etc. Liquid–liquid extraction process is particularly suitable for biorefinery process (through conversion using microorganisms), featuring mild operational conditions and ease of control of process. The principles, types, equipment and applications of liquid–liquid extraction for bioproducts are discussed. Currently various intensification techniques are being applied in the field of liquid–liquid extraction for improving the process efficiency like hybrid processes, reactive extraction, use of ionic liquids etc, which are gaining importance due to the cost associated with the downstream processing of the fermentation products (20–50% of total production cost).
Experimental and theoretical perspectives of reactive extraction of gallic acid (GA) from aqueous solutions using tri-n-butyl phosphate (TBP) and tri-n-octylamine (TOA) as extractant dissolved in three nontoxic natural oils, namely, rice bran oil, sunflower oil, and soybean oil, are investigated. The solvent's extractability is observed in an order of sunflower oil > rice bran oil > soybean oil and rice bran oil > sunflower oil > soybean oil with TOA and TBP, respectively. The theoretical insights of reaction mechanisms for the extraction of GA are estimated in the form of overall equilibrium constants (K E ), stoichiometric coefficients (m), individual equilibrium constants (K 11 , K 12 , K 21 ), and concentrations (C 11 , C 12 , and C 21 ) of various complexes formed between extractant and acid.
Reactive extraction of propionic acid was studied using Aliquat 336 in different diluents (2-octanol and oleyl alcohol). Effects of temperature and water co-extraction on extraction of propionic acid were determined. Study of these parameters is important to design an efficient recovery process for propionic acid recovery. The knowledge of effect of temperature is essential for designing the extraction and backextraction step. Extraction was found to increase with increasing temperature upto 40 o C whereupon it decreases. This suggested that extraction should be performed at temperature around 40 o C, and back extraction at temperature > 60 o C. Water coextraction was found to be highest at low Aliquat concentrations. With increase in acid concentration an increase in co-extracted water was found.
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