# Recent Advances in Muconic Acid Extraction Process
## 4 Muconic Acid Extraction
### Solvent Screening  
Several researchers have investigated muonic acid extraction using different organic systems (Table 2). According to [PERSON] et al. (2019) [24], for carboxylic acid extraction, two main types of solvents can be used: physical and reactive (that interacts with the acids to form complexes). A mixture of these two will generate a composite solvent. The use of conventional organic solvents (hexane, methyl isobutyl ketone) generates a number of drawbacks, including toxicity, environmental contamination, low process safety, problematic solvent regeneration, and detrimental effects on microorganism activity, which makes direct extraction difficult. To address these problems and to respect the requirements of Green Chemistry, more sustainable solvents have been proposed and developed during the past three decades: canola oil or ionic liquids (organic salts with a melting point lower than 100 \({}^{\circ}\)C). Due to their particular features (low vapor pressure, low combustibility, wide liquid range, and good thermal stability), ILs are used in ionic-liquid-based extraction as diluents and/or extractants for solvent extraction [48]. From the data presented in Table 2, very high K can be observed in ionic liquids (Cyphos and Cytop IL) while analyzing classic solvents, butanol was the most effective. In general, there are two types of diluents: active and inactive. Due to the presence of functional groups, the active diluents (ketone, alcohol) are often polar in character and serve as effective solvating media for ion pairs. Because they are non-polar, inactive diluents like hexane have very poor acid distribution (Table 2) and poor polar complex solvation. These diluents are helpful in the stripping of acid because they prevent the third phase from forming at greater acid concentrations in the organic phase. Tertiary amines and ionic liquids have strong extractability, but because they are viscous and corrosive, they must always be utilized with a diluent that also influences the organic phase's physical characteristics, including density, viscosity, and surface tension. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Organic Phase** & **Extraction Conditions** & **K/Yield, \%** & **Ref.** \\ \hline \multicolumn{4}{c}{Physical Solvents} \\
1-butanol & & 6.146 & [49] \\ isoamyl alcohol & 2.846 & [49] \\ methyl ethyl ketone & 5 mL equal volumes at both aqueous & 1.180 & [49] \\ methyl isobutyl ketone & & 120 rpm for two hours in a & 1.074 & [49] \\ di-isobutyl ketone & temperature-controlled water bath & 0.672 & [49] \\ iso-butanol & shaker & 3.948 & [49] \\ n-hexane & initial acid concentration: & 0.636 & [49] \\ dimethyl glutamate & 0.005–0.007 mol/kg & 2.951 & [49] \\ ethyl propionate & & 1.941 & [49] \\ diethyl carbonate & & 1.199 & [49] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Muonic acid single system extraction [24; 49; 50; 51; 52]. Over a temperature range of 25 to 75 \({}^{\circ}\)C, the solubility data of muonic acid (cis-cis) in polar solvents such as water, ethanol, 2-propanol, and acetic acid have been calculated by [PERSON] et al. [53]. The results proved an exothermic process, increased solubility with rising temperature for the investigated domain, and the following order for solvent efficiency: water < acetic acid < 2-propanol < ethanol. [PERSON] et al. analyzed water soluble amines for extraction, propylamine and tri-n-propylamine, and proved not to be applicable for MA reactive extraction (extraction yield < 1%) [52]. The ion interactions between the solvent and the carboxylic acid molecules are extremely important for the formation of weak physical bonds between them. Since the intermolecular hydrogen bonds formed by acid molecules are substantially weaker than those observed between acid and water molecules, carboxylic acids typically remain as monomers in the aqueous phase.