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ABSTRACT
Microchannel devices are promising tools to intensify the liquid–liquid extraction and reaction processes. To realize multi-stage extraction, which is widely implemented in industrial processes, several microchannel devices are required. However, the use of many microchannel devices, which are relatively expensive, may lead to an increased cost of equipment. To reduce the required number of microchannel devices, in this study, a circulation-extraction method (CEM) was developed. In this approach, aqueous and organic liquids were circulated among the liquid holding vessels and the microchannel device. In this manner, multi-stage extraction could be realized using a single microchannel device, by periodically replacing the extractant in the vessel with the unused liquid. To improve the productivity of multi-stage extraction, the productivity of each extraction stage must be improved by optimizing parameters that affect the productivity. Herein, the effects of different parameters on the extraction performance of the CEM were investigated by performing a single-stage extraction experiment pertaining to the extraction of phenol from dodecane to water. Furthermore, the CEM was compared with the conventional flow-through-extraction method (FTEM), which can achieve the target extraction efficiency by implementing the flow of liquids in the microchannel once, in terms of the space–time yield (STY) and energy consumption (ε). The results indicated that a larger liquid circulation flow rate and channel length in the CEM corresponded to the earlier attainment of the target extraction efficiency. For both the CEM and FTEM, STY was an ascending function of ε. Under the same liquid flow rate, the highest STY was obtained at the shortest channel length for the CEM (755 L-liquid L-channel−1 h−1), and this value was higher than that for the FTEM (584 L-liquid L-channel−1 h−1). Thus, the CEM could effectively replace the FTEM as a multi-stage extraction process performed using only a single microchannel device.
Nomenclature
| C | = | solute concentration (mol m−3) |
| E | = | extraction efficiency (%) |
| F | = | flow rate (ml min−1) |
| Ka | = | volumetric mass transfer coefficient (s−1) |
| LC | = | channel length (m) |
| ∆P | = | Pressure drop (kPa) |
| t | = | circulation time (s) |
| tE | = | circulation time to achieve the target extraction efficiency (s) |
| τ | = | residence time in the microchannel (s) |
| τε | = | residence time in the microchannel to achieve the target extraction efficiency (s) |
| STY | = | space-time yield (L-liquid L-channel−1 h−1) |
| V | = | liquid volume in the vessel (ml) |
| VC | = | volume of microchannel (L) |
| α, β | = | arbitrary constant |
| ε | = | energy consumption (J L-liquid−1) |
| Subscripts and superscripts | ||
| org | = | organic phase |
| T | = | two-phase |
| Ves | = | in vessel |
| MD | = | in microchannel device |
| in | = | at inlet |
| out | = | at outlet |
| cir | = | circulation-extraction method |
| flow | = | flow-through-extraction method |
| 0 | = | at initial state |
| * | = | at equilibrium state |