# Recent Advances in Muconic Acid Extraction Process
## 4 Muconic Acid Extraction
### Reactive Extraction Systems Used for MA Separation  
Due to the low extraction efficiency obtained in physical extraction for classical solvents and the very high cost and viscosity for reactive solvents, the use of a mixture between physical and reactive solvents (extractants) was analyzed for improving the separation performance, obtaining composite solvents (includes an extractant that interacts with the acid and a diluent to enable the complexation of the acid). Diluents are used to change the basicity of the extractant, which affects the formation of a third phase (a stable emulsion usually formed at the aqueous-organic interface composed of aggregates of the extractant and the complex), the stability of the acid-extractant complex, and extractant loading (the ratio between acid concentration and extractant concentration in the organic phase). Different extractants (Table 3) dissolved in organic solvents were considered for muonic acid separation: hydrophobic amines, ionic liquids, and organophosphorus compounds [49; 50; 51; 52].  
Comparing the results from Tables 2 and 3, it is evident that the extractant addition in the organic phase strongly increased the MA distribution coefficient. This is especially obvious for hexane: K increased from 0.636 to 5.868 when TBP was added and 11.264 for TOPO, leading to the conclusion that organophosphorus compounds can effectively be used in MA reactive extraction. Comparing extraction efficiency achieved for amines to those for organophosphorus compounds, superior values may be observed. Additionally, as the amine's alkyl chain length increased (from six to eight carbon atoms), the process yield improved (from 76.07% to 94.08%). An interesting fact was noted: for the same alkyl chain length, the process efficiency was higher for secondary amine (DOA) compared to the tertiary one (TOA), from 94.08% to 96.13%, due to less steric hindrance in the complex formation. The distribution coefficient for ionic liquids decreased once the diluent was added to the organic phase (from 510 for Cyphos IL101 to 51.3 for Cyphos IL101+ canola oil), but its values were still well above the distribution coefficients for all other reactive extraction systems (Table 3).  
\begin{table}
\begin{tabular}{c c c c} \hline
**Organic Phase** & **Extraction Conditions** & **K/Yield, \%** & **Ref.** \\ \hline  & aqueous phase pH 4.25 \(\pm\) 0.05 & & \\ polypropylene glycol 4000 & 20\% (\(\
icefrac{{v}}{{v}}\)) solvent & 5.78 & [50] \\  & shaken vigorously at 30 \({}^{\circ}\)C for 30 min & & \\  & Reactive solvents & & \\ CYTOP 503 & 37.9 & [51] \\ CYPHOS IL101 & 20\% (\(\
icefrac{{v}}{{v}}\)) solvent & 510 & [51] \\ CYPHOS IL104 & 399 & [51] \\ Aliquat 336 & & & 93.7 & \\ Tri-octylamine & aqueous phase pH 4.25 & 3.4, 94.08\% & [52] \\ Tributylphosphate & & 6.4 & [51] \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._Tri-n-butyl phosphate, TBP--10 to 50% by volume, and tri-n-octylphosphine oxide, TOPO--4% to 16% by volume, in various solvents (alcohols, esters, ketones, and alkane) for MA concentration of 0.007 mol/kg (Table 3) [49] have shown extraction degrees between 70 and 93%. Tri-n-octyl amine, TOA, extracted MA with an efficiency of 95% when dissolved in ethyl oleate, but the formation of a third phase, located at the interface but within the organic phase, was observed for this system. In order to overcome this drawback, several phase modifiers were analyzed: ethanol, 1-butanol, 1-pentanol, 1-octanol, and 1-dodecanol, from which only ethanol was not able to prevent third-phase formation. The use of butanol allowed an extraction degree of 95.66% in the system with TOA and ethyl oleate [52].