Enantioseparation of chiral aromatic acids in process intensified liquid–liquid extraction columns

Abstract

Enantioselective liquid-liquid extraction (ELLE) is a powerful alternative to common technologies for separation of racemic mixtures. The first application of ELLE for aromatic acids in liquid-liquid extraction columns is described. The ELLE is investigated experimentally and theoretically for phenylsuccinic acid (PSA) as a representative for aromatic acids. A racemic mixture of (R/S)-PSA is separated with hydroxypropyl-b-cyclodextrin as selector molecule. The ELLE obtained the highest operative selectivity (a op 5 1.8-2) for low pH-values and temperatures. Because of the low operative selectivity, a countercurrent process is necessary to separate both enantiomers completely. The countercurrent process is investigated in process intensified extraction columns (Ø in 5 15 mm) with a high number of equilibrium stages. The experiments demonstrate a good symmetric separation with an enantiomeric excess of 60% and yields of 80% for both enantiomers. Finally, the back extraction is investigated to recycle the selector molecule and increase the efficiency.

Single stage and countercurrent extraction of 5-hydroxymethylfurfural from aqueous phase systems

“…In summary, the pulsation in future HMF extractions should be kept as low as possible but high enough to avoid flooding in the column. Hence, a compromise has to be found between high extraction efficiency and robust fluid dynamics [21]. A pulsation frequency of 0.2 Hz was not applicable on that throughput indicating the flooding limit.…”

“…The same phenomenon is the reason for smaller throughput of the column because back mixing increases with decreasing rising velocity. Therefore, it is possible to apply the column also with these high concentrations, but a compromise with the throughput has to be found again [21,45].…”

“…It is an objective to enable a high but defined energy input to the system because it is crucial to control hydrodynamics and thus mass transfer and extraction efficiency [19][20][21][22][23][24][25]. To achieve this, the 50 stirred cells are divided by star-shaped stator internals with open area fraction of approximately 25% to minimize backflow.…”

Optimization study on continuous separation of equol enantiomers using enantioselective liquid–liquid extraction in centrifugal contactor separators

“…Hydroxypropyl-␤-cyclodextrin (HP-␤-CD, Fig. 2) as chiral extractant in ELLE has been studied in the past [24][25][26] .…”

“…The below relations derived according to the single stage extraction model and detailed information about the single stage extraction model is reported in our previous work[26].…”