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The direct reactive extraction of propionic acid from Propionibacterium acidipropionici broths with solutions of tri‐n‐octylamine in dichloromethane, n‐butyl acetate or n‐heptane underlined the strong negative influence of the cells, due to the blockage of the interface by their adsorption. The magnitude of this effect <#>depends on the affinity of the cells for the organic phase, which is more important for n‐heptane, but only at biomass concentrations below 18 g L–1 d.w. (dry weight). Moreover, the interfacial mass transfer of the acid is also controlled by the solvent polarity, and is accelerated from n‐heptane to dichloromethane and by the addition to the organic phase of 1‐octanol as a phase modifier. The influences of the biomass concentration, the rotation speed and the solvent dielectric constant were included in a mathematical model describing the solute mass flow from the aqueous to the organic phase.

These experiments were focused on the reactive extraction of succinic acid from Actinobacillus succinogenes suspensions with TOA dissolved in butyl acetate without and with 1-octanol. The results underlined the strong negative influence of cells on interfacial mass transfer rate, due to the physical barrier created at the interface by their adsorption. Thus, the mass flow recorded for the pure aqueous phase exceeded about 6.8−7.8 times that reached for aqueous suspension with a biomass concentration of 27 g L −1 d.w., this difference becoming more pronounced at higher pH-values of the aqueous phase. The negative influence of bacterial cells is attenuated by 1-octanol addition into the solvent phase. This effect was described by means of the amplification factor, which is over 1 for all discussed extraction systems containing 1-octanol. The influences of the extraction parameters and interfacial mechanism have been included in a mathematical model describing the acid mass flow from aqueous suspension to the organic phase, the average deviation from the experimental values being ±4.33%.

Formic and acetic acids could be selectively removed from the mixture with succinic acid by facilitated pertraction with tri-noctylamine (TOA). The pertraction selectivity is positively influenced by increasing the pH-gradient between the feed and stripping phases and carrier concentration in liquid membrane up to 70 g/L, as well as by lowering the mixing intensity of the two aqueous phases, TOA concentration exhibiting the most important influence. The cumulated influences of the considered parameters have been included in a mathematical model describing the pertraction of these carboxylic acids by means of the selectivity factor. The proposed model offers a good concordance with the experimental values of selectivity factor, the average deviation being of 5.22%.

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The reactive extraction of propionic acid from simulated broths with apparent viscosity varying between 5 and 20 cP has been studied. The reactive extraction has been carried out with TOA dissolved in three solvents with different dielectric constants (dichloromethane, butyl acetate, n-heptane) without and with 1-octanol as phase modifier. The results indicated that the mechanism of the interfacial reaction between acid and extractant was not modified compared to the extraction from pure aqueous solutions, but the separation efficiency has been significantly affected. Thus, the extraction degree and extraction constant have been reduced by increasing the viscosity of aqueous phase, effect that was partially counteracted by adding 1octanol in solvent phase. The most important influence of alcohol addition was recorded for the solvent with the lowest polarity, namely n-heptane.

The reactive extractions of propionic acid with TOA dissolved in three solvents with different dielectric constants (dichloromethane, butyl acetate, n-heptane) without and with 1-octanol as phase modifier have been comparatively analyzed. The results indicated that the mechanism of the interfacial reaction between acid and extractant is controlled by the organic phase polarity. In absence of 1-octanol, the structures of the extracted complexes are RCOOH.Q 2 for dichloromethane and butyl acetate, respectively (RCOOH) 2 Q 4 for n-heptane. These structures are modified by adding 1-octanol and become RCOOH.Q for extraction in dichloromethane or butyl acetate, respectively RCOOH.Q 2 for extraction in n-heptane. Although the presence of 1-octanol improves the extraction efficiency, it leads to the reduction of extraction constants for all considered solvents, influence that is more significant for n-heptane.