# Recent Advances in Muconic Acid Extraction Process
## 3 Reactive Extraction  
Extraction represents the operation of separating the components of a liquid or solid mixture based on their solubility difference in one or more solvents. If the extraction takes place only through the physical phenomena of solubilization and diffusion, the extraction is physical, and if, during the process, a complex is formed between the extractant and the carboxylic acid, the extraction is reactive [12]. Both methods can be applied in the case of direct extraction without biomass separation or by recirculating part of the fermentation broth [34]. Since 1960, due to the advantages compared to classical separation techniques, studies on reactive extraction have been developed especially for important organic compounds obtained through chemical or biochemical synthesis: carboxylic acids, amino acids, antibi \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **Details** & **Ref.** \\ \hline \multirow{4}{*}{Melting point} & 194–196 \({}^{\circ}\)C (cis,cis-muconic acid) & [30] \\  & 191 \({}^{\circ}\)C (cis,trans-muconic acid) & [29] \\  & 300 \({}^{\circ}\)C (trans, trans-muconic acid) & [29] \\  & 1 g/L (cis,cis-muconic acid) & [31] \\ Solubility in water & 5.2 g/L (cis,trans-muconic acid) & [31] \\  & 0.1 g/L (trans,trans-muconic acid) & [29] \\ Stability & Stable under normal conditions & [30] \\  & 2.9 (cis,cis-muconic acid) (pka1) & [29] \\ Acidity constant, & 3.57 (cis,cis-muconic acid)(pka2) & [29] \\ pKA & 2.9 (cis,trans muonic acid) & [29] \\  & 3.4 (trans,trans-muconic acid) & [29] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 2: Commercial products obtained from muonic acid. otics, etc. Reactive extraction was developed in order to obtain an efficient separation [35] and requires the presence of an extractant which can be dissolved in the organic phase but has some solubility in the aqueous phase. However, it is essential that the product of the reaction between the solute and the extractant be hydrophobic [36]. The efficiency of reactive extraction depends on the physical and chemical characteristics of the solute: hydrophobicity and acid-base properties; on the properties of the extractant: reactivity, the ability to form hydrophobic compounds with the solute, and on separation conditions: pH, mixing intensity, concentration level, etc. Due to these conditions, the interaction mechanism between solute and extractant, the optimal extraction conditions in correlation with the separation factors, and the extraction mechanism are the main directions of study in reactive extraction [37; 38; 39]. The mechanism of reactive extraction presents particularities specific to each extraction system, the general case being presented in Figure 3[12]. The mechanism presented assumes the fact that the solubility of the system components in the other phase is zero, and separation is achieved by the following stages [40]:  
* diffusion of the extractant at the separation interface between the two phases;
* diffusion of the solute at the separation interface between the two phases;
* interfacial reaction between solute and extractant;
* diffusion of the acid-extractant complex resulting from the interfacial reaction in the organic phase. In certain cases, depending on the solubility of the components of the extraction system in the other phase, the site of the reaction between the solute and the extractant can be located either in the vicinity of the interface or in the aqueous phase. Taking into account the steps involved in the reactive extraction, the determinant of the speed of the global process can be diffusion or complex formation, the process being diffusional and kineticly limited. The relative importance of the two types of resistance is established by studying the effect of the intensification of the mixing of the phases on the degree of extraction or on the solute rate of mass transfer.