Design Guideline for Passive Microextractors: From Cocurrent Flow to

Subscriber access provided by UNIV OF LOUISIANA

Separations

Design Guideline for Passive Microextractors: From Co-current flow to Counter-current flow Tingliang Xie, Shan Jing, and Cong Xu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05639 • Publication Date (Web): 16 Apr 2019 Downloaded from http://pubs.acs.org on April 17, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Design Guideline for Passive Microextractors: From Co-current flow to Counter-current flow Tingliang Xie, Shan Jing, Cong Xu*

Institute of Nuclear and New Energy Technology, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Tsinghua University, Beijing, 100084, P.R China.

*Corresponding

author:

*Tel: 86-10-89796075; Fax: 86-10-62771740; E-mail: [email protected].

Abstract: Passive counter-current microextractors with high throughputs have potentially broad applications in industrial-scale solvent extraction and hazardous waste disposal. To date, no design guideline has been available for developing such microextractors based on passive co-current microextractors. In this study, an oscillating feedback microextractor was chosen as an example system to provide a clear roadmap for bridging the gap between passive coand counter-current microextractors and achieving high-throughput counter-current microextraction. Four steps were necessary, namely, (1) determination of the counter-current flow arrangement strategy, (2) selection and modification of a primary passive co-current microextractor, (3) establishment of a passive single-unit counter-current microextractor, and (4) parallelization of the passive single-unit counter-current microextractor with the aim of achieving high throughput. The development from a passive co-current microextractor to a passive and high-throughput counter-current microextractor was demonstrated using the

1 / 41

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

oscillating feedback microextractor. Keywords: liquid-liquid extraction, passive micromixer, high throughput, co-current, counter-current, microfluidics 1. Introduction Liquid-liquid solvent extraction is an important process used to separate target species from a mixture based on solubility differences. Microfluidics has proven to be a rapid, low-cost, and high-efficiency technology in many fields, such as analysis, synthesis, separation, and pelleting.1 Microextraction is used to perform liquid-liquid solvent extraction in microscale contactors, i.e., microextractors, and has been proven highly efficient for multiple-component separation.2–5 Microextractors can be classified into two main types: active microextractors and passive microextractors. Unlike active microextractors, passive microextractors achieve extraction by relying solely on specially designed microchannel configurations, without any moving parts or external energy input.6 Therefore, passive microextractors are easier to fabricate and operate, which allows them to be efficiently and widely used in liquid-liquid microextraction. In recent years, many studies on passive microextractors have been reported. However, to date, most of these studies have focused on ordered flow microextractors such as droplet, slug, and laminar flow microextractors,5,7–11 and little attention has been paid to disordered flow microextractors.12,13 In droplet microextractors,5 to generate ordered droplets, the flow rate of

2 / 41


Page 2 of 61

Page 3 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the dispersed phase should be much lower than that of the continuous phase. As for the slug flow microextractors,7-9 the slugs are often produced at small total flow rates with appropriate flux ratios. Consequently, it is difficult to realize high total throughput. In laminar flow microextractors,10,11 a stable phase interface must be maintained. Therefore, both phases must have low flow rates to prevent one phase from penetrating the other, which limits the total throughput. In contrast with these ordered flow microextractors, the most prominent feature of disordered flow microextractors is that much smaller droplets can be produced at high throughputs in a disordered mode. Therefore, disordered flow microextractors are not applicable to analysis and fine synthesis, but they may have advantages in industrial-scale extraction, which requires high throughput and high efficiency. However, less attention has been focused on disordered flow microextractors with high throughputs,12,13 whereas a large number of studies have examined fluid mixing processes for miscible liquids.14,15 Furthermore, another crucial problem needs to be addressed in practice. All the abovementioned microextractors7–13 involve co-current microextraction, in which the mass transfer limit is determined by the phase equilibrium. As a result, only one equilibrium stage can be achieved, resulting in a low extraction efficiency. Compared with co-current extraction, counter-current extraction is a common method to increase the recovery efficiency because of its higher mass transfer driving force. Thus, it is logical to direct construction efforts towards counter-current microextractors. However, the construction of microscale counter-current extractors is difficult because the surface tension forces are dominant over the inertial force

3 / 41



and gravity. To date, many studies have been published concerning counter-current microextractors,16–33 which can mainly be classified into three groups, namely, multistage counter-current microextractors, continuous counter-current microextractors, and hybrid counter-current microextractors, in accordance with the mass transfer mode and flow patterns. In multistage counter-current microextractors, solutes are transferred from one phase to another in a discrete mode. 19,21,22,30 Two problems need to be solved to establish multistage counter-current microextractors. The first is the need to compensate for the pressure losses that occur at each stage, and the second is the completion of phase separation. To overcome these two problems, the use of some mechanical components, such as check valves and pumps, is inevitable, and precise pressure control is also essential. In short, multistage counter-current microextractors are active and costly. Moreover, as the check valves and pumps are implemented on the macroscale, excessively large volumes are needed, and the parallelization of tens or hundreds of these parts constitutes a significant investment. Meanwhile, simultaneous and precise control of the pressures in tens or hundreds of multistage counter-current microextractors would undoubtedly be too complicated. Consequently, the practical application of active multistage counter-current microextractors may be limited. In continuous counter-current microextractors, solutes are transferred between two phases in a differential mode.16-18,25–28,31,32 A distinguishing feature of continuous counter-current microextractors is that a continuous and stable interface is required between the two liquids,

4 / 41


Page 4 of 61

Page 5 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


but complete phase separation is not required. Consequently, the interstage pumps and check valves required in multistage counter-current microextractors can be eliminated, and thus, continuous counter-current microextractors are operated in a passive mode. The main difficulty in continuous counter-current microextractors is maintaining a continuous and stable interface between two liquids against the shear force generated by the counter-current flow.34,35

Both

the

membrane-assisted

method16,17

and

surface-tension-assisted

method18,25–27,31,32 have been used to help maintain a stable interface, in which the flow rates of both phases, the surface properties, the physical and chemical properties of both liquids, and the pressures of the inlets and outlets must be controlled precisely. This method is thus very difficult and too complicated for scaling-up from one to tens or hundreds of continuous counter-current microextractors. Clearly, the above two kinds of counter-current microextractors are not suitable for passive and high-throughput microextraction. Conversely, hybrid counter-current microextractors with disordered flows can meet the requirements. To date, only two hybrid counter-current microextractors have been investigated. One is based on a vortex flow microextractor,33 and the other is based on an oscillating feedback microextractor (OFM).23,29 Overall, passive, high-throughput, and robust counter-current microextractors remain a challenge. Passive counter-current microextractors (PCMs) originate from passive co-current microextractors, but not every passive co-current microextractor can be developed into a PCM, particularly if high throughput is required. The difficulty lies in changing a co-current

5 / 41



Page 6 of 61

flow arrangement into a counter-current flow arrangement against the shear force and the surface tension but remaining the same micromixing mechanisms. Compared with the co-current flow, the significant shear force at the interface between two phases can easily destroy the counter-current flow, and the surface tension dominant over the gravity and inertial forces also leads to a difficulty in phase separation. As a result, there still is a vast gap between passive co-current microextractors and PCMs, which has limited the application of high-throughput PCMs in practice. In this study, a design guideline was established to bridge this gap, and an OFM was adopted to demonstrate the successful development of a high-throughput

PCM

from

a

passive

co-current

microextractor.

Importantly,

a

counter-current microextractor can be established according to the guideline to breakthrough equilibrium limit in co-current microextraction. 2. Design guideline The aim of this study was to establish a high-throughput PCM based on a passive co-current microextractor. The target microextractor required three features: a passive mode, a counter-current flow arrangement, and a high throughput. As achieving these three features in a single design step would be difficult, the stepwise design method shown in Figure 1 was adopted. The design guideline consists of four steps. The first step is the determination of the counter-current flow arrangement strategy, i.e., how to transfer two phases in opposite directions and separate the two phases to be mixed. In this step, the counter-current mode of the two phases must first be determined. Then the conveying mode and the separation method

6 / 41


Page 7 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of the two phases can be determined. As mentioned in Introduction, the hybrid counter-current microextractors are more suitable for high-throughput and robust PCMs compared the multistage and continuous counter-current microextractors. However, the latter two microextractors still have their merits for constructing other unique counter-current flow arrangements such as ordered and precisely-controlled counter-current microextraction without the requirements of high-throughput and/or passive operation. The second step is the selection and modification of a passive co-current microextractor based on the counter-current flow arrangement strategy. This step is a basis to construct the target microextractor, i.e., the high-throughput and robust PCM. The reason is that almost all counter-current microextractors have been developed based on co-current ones to be realized easily. In the step, the flow pattern must first be determined according to the counter-current flow mode determined in Step I. As mentioned in Introduction, although there are four kinds of flow patterns in microchannels, only the disordered flow pattern meets the hybrid counter-current flow mode. The order flow patterns such as the laminar, droplet, and slug flow patterns are available for the multistage and continuous flow modes in Step I. After choosing the flow pattern, the adaption of the co-current microextractor has further to be made to fit the counter-current flow mode. This is because the counter-currently conveying mode and separation method of the two phases are necessary for the counter-current flow mode but are not needed by the co-current flow mode. The third step is the construction of a single-unit counter-current microextractor consisting of several modified co-current microextractors. Finally, the fourth step is parallelization of the single-unit microextractor to a multiple-unit

7 / 41



microextractor using the numbering-up method, followed by verification of its extraction performance. In this work, a passive microextractor, i.e., the OFM, was adopted to demonstrate how a co-current microextractor can be developed into a high-throughput counter-current microextractor using the design guideline.

Figure 1. Design guideline for high-throughput PCMs 3. Experiments 3.1 Microextractor fabrication All the microextractors used in this work were fabricated using two layers of transparent poly methyl methacrylate (PMMA) plates. The microchannels were machined on one PMMA plate using a precision machine tool. Then, the slotted plate and another smooth plate were

8 / 41


Page 8 of 61

Page 9 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


clamped together using a fixture and immersed in absolute ethyl alcohol at 40 °C. The clamped PMMA plates were subjected to ultrasonication for 30–80 min. As a result, the two PMMA plates were bonded to each other to form a complete microextractor. The fabricated microextractor was then used for tests after washing with deionized water. A detailed description of the microextractor fabrication process has been reported previously.12,29 3.2 Apparatus Two precise syringes (Longer Precision Pump Co., Ltd., Baoding, China, LSP01-1BH, stroke resolution: 0.156 m) were adopted to pump two immiscible phases into the microextractor simultaneously. The densities of the two phases were measured using a densitometer (Den Di-1, Beijing YILUDA Co. Ltd., Beijing, China), and a rotary viscosimeter (DV-1, Fungilab Co., Barcelona, Spain) was used to measure the viscosities. The surface tension was measured using an interface tensiometer (BZY-1, Shanghai Hengping Instrument Factory, Shanghai, China). 3.3 Chemical reagents The extraction performance was characterized by extracting tetravalent metal zirconium ions (1137 mg Zr4+/L) from an aqueous nitric acid solution (5.58 M HNO3) into a 30% tributyl phosphate (TBP)/kerosene solution. This immiscible two-phase system (aqueous HNO3 and TBP/kerosene) has been extensively used in spent nuclear fuel processing and in ore processing. The Zr4+ concentrations in the raffinate and the eluent were determined using inductively coupled plasma atomic absorption spectroscopy (ICP) (SPECTRO ARCOS FHX

9 / 41



Page 10 of 61

76004553, SPECTRO Analytical Instruments GmbH, Kleve, Germany). All tests were performed within the temperature range of 22–23 °C. Analytically pure TBP and HNO3 were purchased from Beijing Chemicals Factory (Beijing, China). The kerosene was purchased from Jinzhou Refinery Factory (Liaoning, China). Analytical-grade Zr(NO3)4·5H2O was purchased from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). The densities and viscosities of the two phases are presented in Table 1. The interfacial tension of the 30% TBP/kerosene–HNO3 (Zr4+) solution was 8.0 mN/m. Table 1 Viscosities and densities of the microextraction solutions Feed material Organic phase solution

Density (kg/m3) 815.1

Viscosity (mPa·s) 1.92

Aqueous phase solution

1165.6

1.44

4. Demonstration of the design guideline 4.1 Step I: Determination of the counter-current flow arrangement strategy As shown in Figure 1, the core of the design guideline is the single-unit counter-current microextractor. To implement a counter-current flow arrangement strategy, three issues need to be considered. The first is what kind of counter-current microextractor should be used. The second is how to transfer the two immiscible phases in opposite directions. The third is whether phase separation is necessary and how it can be realized. As mentioned above, there are three kinds of counter-current microextractors, namely, multistage, continuous, and hybrid flow microextractors. Given the requirement of high

10 / 41


Page 11 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


throughput, hybrid counter-current microextractors were adopted here.29,35,36 In a hybrid counter-current microextractor, the transport of the two phases in opposite directions and phase separation can be realized using alternative pulse feeding of the two phases and internal droplet aggregation. The details of this strategy are depicted in Figure 2 and can be described as follows. A complete operating cycle consists of four stages: droplet aggregation stage I, the organic phase feeding stage, droplet aggregation stage II, and the aqueous phase feeding stage. 

Droplet aggregation stage I (Figure 2-A): small droplets (red color) aggregate into large

droplets owing to the surface tension. Furthermore, a clear interface between the organic phase (yellow color) and aqueous phase (red color) is formed owing to the density difference. Consequently, phase separation can be achieved in this stage. 

Organic phase feeding stage (Figure 2-B): the organic phase is rushed into the rectangular

cavity (N + 1) through the bottom inlet channel. The aqueous phase (dispersed phase) in the bottom section (Figure 2-A) is broken into small droplets by the rushing organic phase owing to the high shear force, and the small droplets are distributed throughout the rectangular cavity. In addition, the original organic phase (continuous phase) in the top section of the rectangular cavity (N + 1) is transferred into the rectangular cavity (N).

11 / 41



Figure 2. Hybrid counter-current microextractor strategy 

Droplet aggregation stage II (Figure 2-C): this stage is similar to droplet aggregation

stage I (Figure 2-A). 

Aqueous phase feeding stage (Figure 2-D): the aqueous phase is rushed into the

rectangular cavity (N) through the top inlet channel and broken up into small droplets owing to the high shear force. The original aqueous phase in the bottom section of the rectangular cavity (N) is transferred into the rectangular cavity (N + 1). The above strategy for constructing a passive counter-current flow arrangement can be implemented by repeating the four stages. Here, fresh organic and aqueous phases continually replace the original ones in every cavity, and both the original phases are transferred in opposite directions. It should be noted that during the feeding stage of one phase, the other

12 / 41


Page 12 of 61

Page 13 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


phase is expected not to escape from the local cavity. The undesirable escape results in back-mixing against the counter-current flow arrangement and consequently degrades the extraction performance. The back-mixing may occur under some inappropriate operating conditions such as excessive driving pressure and too short aggregation period. The subsequent steps must be determined based on the above strategy to solve the three issues. 4.2 Step II: Selection and modification of a passive co-current microextractor 4.2.1 Structural modification As mentioned above, the OFM shown in Figure 3-A and investigated previously by us was selected as the basis for further modification.12 Further, Figure 3-B illustrates three mixing mechanisms of water single-phase flow (density, 1000 kg/m3, and viscosity, 1.0 mPa·s) in two-dimensions, including the oscillating flow mixing, the recirculation flow mixing, and the vortex flow mixing. The three mixing mechanisms were simulated by a commercial CFD software (ANSYS Fluent 16.1). As shown in Figure 3-B, the fluid through the feedback channels can contribute to the growth of the recirculation vortex, which can increase the flow resistance along the side. As a result, the inlet fluid is bent towards the opposite side owing to the expanded recirculation vortex, and then a similar phenomenon occurs. Consequently, the flow oscillation can be produced. And a detailed description was presented in our previous paper.12 The modification must solve the three issues raised in Step I. As a result, the primary

13 / 41



co-current OFM (Figure 3-A) was modified to obtain the new co-current microextractor shown in Figure 3-C. The dimensions of this microextractor are presented in Figure 3-D. Here, the main modification was to place two identical basic OFMs oppositely and connect them using a straight chamber to enable phase mixing and phase separation. The cavities in Figure 2 were replaced by such modified OFMs. The modified OFM can be divided into five sections: the inlet section, the bottom extraction section, the middle extraction section, the upper extraction section, and the outlet section. Effectively, both the bottom and upper extraction sections are the identical co-current OFMs constructed of a mixing chamber, a splitter, two feedback channels, and an inlet/outlet channel. Given the counter-current flow arrangement shown in Figure 2, one of the two opposite OFMs will ensure sufficient mixing, regardless of whether the aqueous phase or the organic phase is fed in. Namely, the two phases always enter one of both OFMs whether they are transferred from bottom to top or otherwise. When the two phases rush into the OFM, the Coanda effect (wall attachment phenomena) forces the liquid flow to oscillate and then generate vortex flows and internal recirculation.12 The three flow patterns have the strong shear force and effectively break up the dispersed phase into small droplets, resulting in efficient mass transfer. It should be noted that the two phases flow in parallel and mix with each other during every feeding stage for the counter-current microextractor established based on the strategy in Step I. Thus, there is another important issue required to be determined in Step II. It is whether the parallel flow pattern enables a sufficiently high extraction efficiency. A series of tests was conducted consequently to examine the extraction efficiency, as described in the following section.

14 / 41


Page 14 of 61

Page 15 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Furthermore, the larger channel size of the middle extraction section can reduce the influence of the surface tension and is beneficial to droplet aggregation under the influence of gravity. The rapid aggregation facilitates phase separation consequently. Overall, the inclusion of the top and bottom OFMs in a cavity lays a foundation for establishing a counter-current flow arrangement with high-efficiency mass transfer. Associating with the pulse feeding of the two phases mentioned in Step I and detail in the following Step III, a real counter-current extraction process can be constructed. The phase separation also can be realized by the wide middle section. Therefore, this structural modification provides the basis for solving the issues mentioned in Step I.

Figure 3. Diagram of the modified microextractor available for the counter-current flow arrangement: (A) primary OFM, (B) three mixing mechanisms, (C) configuration of the

15 / 41



modified microextractor, and (D) dimensions of the modified microextractor (depth: 2.0 mm). 1: bottom expanded inlet/outlet channel; 2: bottom inlet/outlet channel; 3: divergent chamber; 4: feedback channel; 5: barrier; 6: splitter; 7: upper inlet/outlet channel; 8: top expanded inlet/outlet channel; 9: inlet section; 10: bottom extraction section; 11: middle extraction section (mixer–settler section); 12: upper extraction section; 13: outlet section

Figure 4. Diagram of the modified microextractor available for co-current microextraction: (A) configuration and (B) dimensions (depth: 1.0 mm). 1: Inlet port; 2: Y-type feed channel; 3: inlet channel; 4: divergent chamber; 5: feedback channel; 6: barrier; 7: splitter; 8: outlet channel; 9: outlet port; 10: inlet section; 11: bottom extraction section; 12: middle extraction section; 13: upper extraction section; 14: outlet section

16 / 41


Page 16 of 61

Page 17 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4.2.2 Verification of the modified microextractor with co-current flow The modified microextractor (Figure 3) available for the counter-current flow arrangement was adapted as shown in Figure 4 to examine its co-current microextraction performance. Here, the inlet channel was split into two branches to allow simultaneous feeding of the two phases. The experimental flowchart is shown in Figure 5.

Figure 5. Schematic diagram of the co-current microextraction experiments using the modified microextractor In all the tests described in the section, the flux ratio R (= Qor/Qaq, where Qor and Qaq are the fluxes of the organic phase and the aqueous phase, respectively) was kept at 1.0. To evaluate the co-current extraction performance, the extraction extent E was defined as D/De. D is the ratio between the Zr concentration in the organic phase and that in the aqueous phase after passing through the microextractor, and De is D at equilibrium. The condition E = 100% represents the completion of a co-current extraction process. In addition, the overall volumetric mean mass transfer coefficient ka was calculated as follows:

17 / 41



R*  Qaq (Caq,in  Caq,out )  kaVΔC

ka 

ΔCm 

Qaq (Caq,in  Caq,out ) VΔCm

* * (Caq,in  Caq,in )  (Caq,out  Caq,out ) *  (C  Caq,in )  ln  aq,in  *  (Caq,out  Caq,out ) 

Page 18 of 61

(1)

(2)

(3)

Where R* is the extraction rate, Caq,in is the Zr concentration in the inlet aqueous phase, Caq,out is the Zr concentration in the outlet aqueous phase, k is the overall mass transfer coefficient, a is the mass transfer area between the two phases per unit volume, and ΔCm is the logarithmic * mean concentration of Zr. Caq,in is the equilibrium Zr concentration in the inlet aqueous phase * that corresponds to the actual Zr concentration in the inlet organic phase. Caq,out is the

equilibrium Zr concentration in the outlet aqueous phase that corresponds to the actual Zr concentration in the outlet organic phase. Figures 6 shows the experimental results for co-current microextraction at different Reynolds numbers. The Reynolds number of the aqueous phase was defined as Reaq = ρaqduaq/μaq, where d is the inlet channel width and uaq is the velocity of the aqueous phase at the inlet channel. The residence time tR was defined as tR = V/(Qaq + Qor), where V is the volume of the microextractor. As shown in Figure 6, the extraction extent increases with increasing Reaq, though the residence time decreases. In addition, at lower Reynolds numbers (Reaq < 393.5), the extraction extent shows no apparent change with increases in Reaq. This phenomenon can be explained as follows: at lower Reynolds numbers (lower volumetric flow

18 / 41


Page 19 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rates), the dispersed phase is not effectively broken up into small droplets, so the mass transfer is dominated by the molecular diffusion resulting from molecular thermal motion. However, at higher Reynolds numbers (Reaq > 393.5), the dispersed phase is forcefully broken up into small droplets owing to the produced vortex flow, oscillating flow, and feedback flow.12 Therefore, the mass transfer specific surface area increases significantly, resulting in a corresponding enhancement of mass transfer. Consequently, the extraction extent E and the overall volumetric mean mass transfer coefficient ka increase with increasing Reynolds numbers, although the residence time decreases. It must be noted that the extraction extent E at lower Reynolds numbers is somewhat lower, which indicates decreased extraction performance for the co-current flow pattern. As a result, when the Reynolds number for counter-current microextraction falls in the lower region, several modified microextractors must be adopted to ensure a high extraction efficiency. However, the co-current extraction efficiency of the modified microextractor is sufficient to construct a counter-current microextraction system.

Figure 6. Co-current microextraction performance at different Reynolds numbers

19 / 41



In summary, it is necessary to examine the extraction performance of the modified co-current microextractor. The goal is to determine whether the modified co-current microextractor satisfies the requirements to further construct a counter-current microextractor. The higher is the performance of the modified co-current microextractor, the less is the stages to be required in the counter-current microextractor. Too many stages of the counter-current microextractor can lead to high flow resistance and consequently low throughput. As a result, an original co-current microextractor should be carefully modified to obtain extraction performance as high as possible. 4.3 Step III: Single-unit counter-current microextractor It is well known that co-current flow microextraction cannot exceed one theoretical separation stage owing to the phase equilibrium, which results in a low extraction efficiency. In contrast, counter-current microextraction is commonly used as a method to increase the extraction efficiency. In this step, the modified microextractor (Figure 3-C) was developed into a complete counter-current microextraction system. 4.3.1 Construction To account for the above-discussed lower co-current microextraction performance at lower Reynolds numbers, a single-unit counter-current microextractor must consist of several of the modified microextractors. As depicted in Figure 7, four of the modified microextractors (Figure 3-C) were connected to each other end to end. A sketch of the complete counter-current microextraction system is shown in Figure 8. The system can be divided into

20 / 41


Page 20 of 61

Page 21 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Diagram of the single-unit counter-current microextractor consisting of four modified microextractors (depth: 2.0 mm) two modules: the control module and the microextraction module. The main components of the control module were four solenoid valves (ZCC-1P, Shanghai Juliang Solenoid Manufacturing Co., Shanghai, China) and a timing controller. The opening and closing of the four solenoid valves were controlled by the timing controller, through which the flow flux could be adjusted. In addition, a pressure-regulating valve (Type 70, Marsh Bellofram Co., Nottingham, UK) was used to adjust the pressure in the compressed gas buffer tank. The microextraction module was constructed using an organic phase settler, an aqueous phase settler, and the single-unit microextraction section. The organic phase settler was connected to Hole-I, and the aqueous phase settler was connected to Hole-II in the single-unit microextraction section. The pressures in the organic and aqueous phase settlers were

21 / 41



Page 22 of 61

monitored using online pressure sensors and recorded by a computer so that the pressure drop over the entire microextraction module could be determined.

Figure 8. Schematic diagram of the experimental setup for the single-unit counter-current microextractor Table 2 Control of the operating stage using different states of the four solenoid valves (○ valve open, ● valve closed) Stage

V-LC

V-LV

V-HC

V-HV

Organic phase feeding stage Droplet aggregation stage I Aqueous phase feeding stage Droplet aggregation stage II

● ● ○ ●

○ ○ ● ○

○ ● ● ●

● ○ ○ ○

Counter-current extraction, i.e., the strategy determined in Step I, was achieved using the flowchart shown in Figure 8. The details of the working principle can be found elsewhere.29 Briefly, a complete operating cycle consists of four stages: a) the organic phase feeding stage,

22 / 41


Page 23 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


b) droplet aggregation stage I, c) the aqueous phase feeding stage, and d) droplet aggregation stage II. As listed in Table 2, different operating stages are triggered depending on the specific states of the valves V-LC, V-LV, V-HC, and V-HV, controlled by the programmable timing controller (Figure 8). During the organic phase feeding stage, the fresh organic phase (light phase) in the aqueous phase settler (heavy phase) was fed into the modified microextractors in the microextraction section. In any of the four modified microextractors, the local organic phase in the upper section was driven into the next microextractor (on the left side), prior to the local aqueous phase accumulated in the bottom section. It was then mixed with the local aqueous phase in the next microextractor to achieve mass transfer. Consequently, the local organic phase was transported into the next microextractor towards the left, but most of the local aqueous phase remained in place. Subsequently, droplet aggregation stage I was triggered, in which the two phases (organic and aqueous phases) in each microextractor were separated by gravity into a top layer that was rich in the organic phase and a bottom layer that was rich in the aqueous phase. Subsequently, the aqueous phase feeding stage began. The aqueous phase in the organic phase settler was driven into the four modified microextractors. During this stage, the local aqueous phase in the bottom section of every microextractor was driven into the next microextractor (on the right side) prior to the local organic phase that was accumulated in the top section. It was then mixed with the local organic phase in the next microextractor. Similarly, most of the local organic phase remained in place, but the local aqueous phase tended to move towards the right during this stage. Droplet aggregation stage II began following the aqueous phase feeding stage, and the phase

23 / 41



Page 24 of 61

separation process was similar to that in droplet aggregation phase I. All four stages were repeated, thereby achieving complete counter-current microextraction. 4.3.2 Verification of the single-unit counter-current microextractor The extraction performance was used to verify the single-unit counter-current microextractor. The various parameters used to evaluate the extraction performance are defined as follows. The extraction efficiency X is given by:

X 

Caq_in  Caq_raf Caq_in

(4)

Where Caq_in is the initial solute concentrations in the aqueous phase feed solution and Caq_raf is the solute concentration of the aqueous phase layer (raffinate) in the aqueous phase settler. When the raw solution in the aqueous or organic phase settler was completely transported, a syringe with a long needle was used to remove the samples from the aqueous phase settler. Similarly, the maximum solute recovery efficiency Xe for co-current extraction can be represented as:

Xe 

Caq_in  Caq_e Caq_in

(5)

Where Caq_e is the equilibrium solute concentration in the aqueous phase for a co-current extraction process. Here Xe was measured in an agitated vessel where temperatures and flux

24 / 41


Page 25 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ratios (or phase ratios) identical to those used for counter-current extraction in PCMs. Furthermore, an index λ was defined to evaluate the extraction performance and assess the extent to which counter-current extraction was achieved.



X Xe

(6)

It is well known that severe back-mixing during extraction can cause deviations from the counter-current flow, leading to a co-current flow or a complete mixing flow. Complete back-mixing in the counter-current flow extraction process give a λ value of 1.0 (at phase equilibrium) or less than 1.0 (under nonequilibrium conditions). Consequently, λ ≤ 1.0 indicates that an unsuccessful counter-current flow arrangement was achieved, whereas λ > 1.0 indicates that a counter-current flow arrangement was successfully achieved. Thus, larger λ values correspond to a successful counter-current flow and excellent extraction performance. In addition, as for the counter-current microextraction, the volume flow rates for the organic phase Fo and aqueous phase Fa were expressed using the following equations:

Fo  Vo,f tcycle

(7)

Fa  Va,f tcycle

(8)

Where Vo,f and Va,f are the time-averaged volumes transported during one feeding stage for the organic phase and aqueous phase, respectively, and tcycle is the total duration of the four stages in one operating cycle, i.e., tcycle = toc + tI + tac + tII. Vo,f and Va,f were calculated using the total

25 / 41



Page 26 of 61

volume of the transported phases during the entire operating period. In addition, the parameters Rv,o/m and Rv,a/m were defined as follows:

Rv ,o / m  Vo , f N *Vm Rv ,a / m  Va , f N *Vm

(9) (10)

Where N is the number of the units for the countercurrent extraction system (namely, N = 1 for the single-unit counter-current microextractor, and N = 4 for the four-unit counter-current microextractor). And Vm is the volume of the modified microextractor (i.e., the main mixing zone marked by the red rectangle in Figure 3). Thus, Rv,o/m and Rv,a/m characterize the ratio of liquid amount in each modified microextractor that will be replaced by the feeding phase during the feeding stage. Excessively high values of Rv,o/m and Rv,a/m indicate that the feeding phase caused the mixing zone to break down, resulting in severe back-mixing. In addition, the flux ratio for the counter-current extraction can be defined as following:

Rcounter  Fo Fa

(11)

A series of tests was conducted using the single-unit PCM to assess the dependence of the extraction performance on the phase feeding times. The results are presented in Figure 9. In this case, the pressure drop ΔP over the microextraction module was maintained at a constant value of 40 kPa. The durations of droplet aggregation stage I (tI) and droplet aggregation stage II (tII) were preset to tI = tII = 3.0 s. Further, the durations of the organic phase feeding stage (toc) and the aqueous phase feeding stage (tac) were set to be identical. As shown in Figure 9-A,

26 / 41


Page 27 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Rv,o/m and Rv,a/m increase with increasing toc (tac). The flux ratio Rcounter (Figure 9-B), extraction efficiency X (Figure 9-C) and extraction performance index λ (Figure 9-D) did not change significantly with increasing phase feeding times. However, it should be noted that all the λ values were larger than unity at different phase feeding times. Therefore, it can be confirmed that the counter-current extraction process was successfully established in the single-unit PCM, yielding excellent counter-current extraction efficiencies.

Figure 9. Changes in (A) the dimensionless feeding volume during one cycle, (B) flux ratio, (C) the extraction efficiency, and (D) the extraction performance index with phase feeding times in the single-unit PCM In summary, a single-unit counter-current microextractor with high efficiencies is expected because it is the core to construct a multiple-unit counter-current microextractor with high

27 / 41



throughput. In addition, the optimized operating conditions can also be determined through performance verification. When the extraction performance is not satisfied with the requirements of the counter-current extraction, it is necessary to come back to Step I and then Steps II and III to improve all modifications. 4.4 Step IV: Parallelization—multiple-unit counter-current microextractor In the final step, the single-unit counter-current microextractor was parallelized by the numbering-up method to obtain throughputs as high as possible.

Figure 10. Overall configuration and dimensions of the four-unit counter-current microextractor 4.4.1 Construction A four-unit PCM (shown in Figure 10) was proposed based on the single-unit PCM (shown in Figure 7). As illustrated in Figure 10, four identical single-unit PCMs were machined on a PMMA plate (210 mm (length) × 103 mm (width) × 6 mm (depth)). Two tree-like channel networks comprising two layers (22 branch channels) were used to distribute the feed flow

28 / 41


Page 28 of 61

Page 29 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


into every sub-PCM and collect the outlet flow from every sub-PCM. The flowchart shown in Figure 8 is also applicable to the four-unit PCM, except that the four-unit microextractor shown in Figure 10 should be used to replace the single-unit microextractor shown in Figure 7. Moreover, the operating procedure is also identical to that described in Step III. 4.4.2 Verification of the four-unit PCM 4.4.2.1 Pressure drop First, the pressure drops between the organic and aqueous phase settlers were measured using the pressure sensors installed at the top of the two settlers. Figure 11 shows the typical trend for the pressure drop signal over an operating cycle in which the durations of each stage were preset to toc = 0.7 s, tI = 18.0 s, tac = 0.7 s, and tII = 18.0 s. A rectangular pressure drop wave was generated. Thus, it can be considered that each of the two phases was transported under a constant driving pressure during the feeding stages.

Figure 11. Pressure drops in the operating system over one cycle

29 / 41



Page 30 of 61

Figure 12. Throughputs for the single- and four-unit PCMs Table 3 Throughputs of PCMs published in the literature Type of PCM

Operating system

F (mL/min)

(surface-modification-assisted)18

Continuous Continuous (membrane- assisted)16 Continuous (membrane- assisted)17 This paper (single-unit) This paper (four-unit)

toluene (cobalt tri)/water 0.3 × 10-3–2.0 × 10-3 n-heptane (propanol)/water 0.02–0.5 n-heptane (benzyl alcohol)/water 0.04–0.4 4+ TBP/kerosene–HNO3 (Zr ) /water 0.79-1.43 TBP/kerosene–HNO3 (Zr4+) /water 2.65-4.04

4.4.2.2 Throughputs The total throughput F is equal to the sum of Fo and Fa. Figure 12 shows the experimental throughput results for when the durations of the feeding stages toc and tac were identical and the droplet aggregation times tI and tII were both 3.0 s. It can be seen that the total throughput of the four-unit PCM is 2.82–3.56 times larger than that of the single-unit PCM under the same conditions. In addition, as the duration of the feeding stage increases, F increases up to a maximum of 4.04 mL/min (four-unit PCM), which significantly exceeds the throughput values of 3.0 × 10-4 to 0.5 mL/min obtained with most common PCMs (showed in Table 3). Clearly, the total throughput can be significantly increased by numbering-up the single-unit

30 / 41


Page 31 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PCM. 4.4.2.3 Extraction performance A series of tests was conducted using the four-unit PCM to assess the dependence of the extraction performance on the phase feeding time or droplet aggregation time. The pressure drop ΔP over the microextraction module was maintained at a constant value of 40 kPa. (1) Influence of the phase feeding time Figure 13 shows the influence of the duration of the phase feeding stages and droplet aggregation stages on the performance of the four-unit PCM. As for the influence of the phase feeding time, the durations of the droplet aggregation stages tI and tII were set to 3.0 s, and the durations of the feeding stages tac and toc were always kept identical. As shown in Figure 13-A, Rv,o/m and Rv,a/m increase with increasing toc (tac). In Figure 13-B, the flux ratio Rcounter (Rcounter = Fo/Fa) has no apparent change with the increase of toc (tac). In Figure 13-C, a maximum value for the extraction efficiency X can be observed at toc (tac) = 0.7 s. It is clear that the mixing time in each mixing zone of the four-unit PCM is proportional to the duration of the feeding stage. In addition, increasing toc (tac) also increases flow rate (Reynolds number) and consequently intensify the oscillation, vortexes, and internal recirculation. The aqueous phase is therefore effectively broken up into small droplets, thus increasing the specific surface area for mass transfer. As a result, the extraction efficiency increases with increasing toc (tac). However, other phenomena should also be noted, as shown in Figure 13-A. Specifically, Rv,o/m and Rv,a/m also increase with increasing toc (tac). Considering the organic phase feeding

31 / 41



stage as an example, an increased Rv,o/m indicates that the greater amount of accumulated aqueous phase at the bottom of each mixing zone will be entrained into the next mixing zone by the fed organic phase. However, this is not the expected distribution for establishing a perfect counter-current flow in a PCM. In the perfect PCM, the fed organic phase should only drive the organic phase accumulated in the top layer of each mixing zone into the next mixing zone. The aqueous phase accumulated in the bottom layer should remain in the mixing zone and not enter the next mixing zone.29 A similar outcome is expected during the feeding stage of the aqueous phase. Based on these phenomena, a perfect counter-current PCM can be implemented. However, some local aqueous and local organic phases are always entrained by the fed organic phase during the organic phase feeding stage and the fed aqueous phase during the aqueous phase feeding stage, respectively. As a result, unexpected back-mixing occurs, which leads to an inefficient counter-current flow and a lower extraction efficiency. Thus, the extraction efficiency is dependent on the combined effect of the mass transfer specific surface area and the extent of back-mixing. Consequently, the optimal extraction efficiency was observed at toc = 0.7 s. Figure 13-D depicts the effect of the phase feeding time on λ. The λ values are larger than unity at all phase feeding times. Thus, it can be confirmed that a counter-current extraction process was established in the four-unit PCM, which yielded excellent counter-current extraction efficiencies.

32 / 41


Page 32 of 61

Page 33 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13. Effects of phase feeding time and droplet aggregation time on (A) the dimensionless feeding volume during one cycle, (B) flux ratio, (C) the extraction efficiency, and (D) the extraction performance index in the four-unit PCM (2) Influence of the droplet aggregation time As for the influence of the droplet aggregation time, the durations of the phase feeding stages were set as tac = toc = 0.7 s, and the durations of the droplet aggregation stages tI and tII

33 / 41



were always identical. As shown in Figure 13-A, Rv,o/m and Rv,a/m increase with increasing tI (tII). This phenomenon can be explained as follows: as tI (tII) increases, better phase separation can be achieved, which can effectively prevent the liquids from back-mixing. Therefore, in a single cycle, more of the organic phase can be transferred from the aqueous phase settler to the organic phase settler, and more of the aqueous phase can be transferred in the opposite direction. Consequently, Rv,o/m and Rv,a/m increase as tI (tII) increases. Furthermore, as showed in Figure 13-B, the flux ratio Rcounter has no apparent change with the increase of the tI (tII). In addition, the extraction efficiency X (shown in Figure 13-C) and the extraction performance index λ (shown in Figure 13-D) increase with increasing tI. Two factors can contribute to this result. First, as tI (tII) increases (i.e., the residence time increases), the values of X and λ should increase. Second, better phase separation can be achieved with a larger value of tI (tII). Consequently, less liquid back-mixing occurs and the mass transfer driving force increases, so as to increase the extraction efficiency X and extraction performance index λ. Furthermore, it should be noted that all the λ values are larger than unity, indicating that a counter-current extraction process was successfully established in the four-unit PCM. Overall, the distribution channel mode and the counter-current flowchart have to satisfy the parallelization requirements to enable the high-throughput and high extraction efficiency. The tree-like distribution channel mode is more suitable for the hybrid counter-current flow arrangement than the ladder-like distribution channel mode. This is because the ladder-like channel network generally has a larger volume than the tree-like channel network. The phase

34 / 41


Page 34 of 61

Page 35 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


separation, therefore, tends to occur in the large volume, making the system difficult to control. Moreover, it can be confirmed that the extraction efficiency of the four-unit PCM at a throughput of 4.04 mL/min was approximately 1.86 times greater than the best co-current extraction

efficiency.

Therefore,

the

presented

design

guideline

of

constructing

high-throughput PCMs through parallelization was successfully achieved. 5. Conclusions The study used an OFM as an example to present a clear guideline for bridging the gap between passive co- and counter-current microextractors. According to the guideline, the basic co-current microextractor was sequentially endowed with three critical features, namely, passive operation, a counter-current flow, and a high throughput. Finally, a high-throughput PCM was successfully established. The final PCM not only exhibited a throughput of 4.04 mL/min, which is much larger than that of most common PCMs in the literature, but also a high extraction efficiency not limited by the phase equilibrium. The established design guideline can facilitate the utilization of PCMs in practical applications associated with chemical extraction and separation processes.

Acknowledgment

This work was supported by the National Natural Science Foundation of China (No. 21776152 and No. 21576149).

References

35 / 41



(1) Whitesides, G. M. The origins and the future of microfluidics. Nature. 2006, 442, 368-373. (2) Muranaka, Y.; Nakagawa, H.; Masaki, R.; Maki, T.; Mae, K. Continuous 5-Hydroxymethylfurfural production from monosaccharides in a microreactor. Ind. Eng. Chem. Res. 2017, 56, 10998-11005. (3) Nemer, M. B.; Roberts, C. C.; Hughes. L.G.; Wyatt, N.B.; Brooks, C. F.; Rao, R. Drop mass transfer in a microfluidic chip compared to a centrifugal contactor. AIChE J. 2014, 60, 3071-3078.

(4) Tsaoulidis, D.; Angeli, P. Effect of channel size on liquid-liquid plug flow in small channels. AIChE J. 2016, 62, 315-324.

(5) Zhao, Y. C.; Chen, G. W.; Yuan, Q. Liquid–liquid two-phase mass transfer in the T-junction microchannels. AIChE J. 2007, 53, 3042-3053. (6) Huang, H.; Chen, Z.; Yan, X. Simultaneous determination of serotonin and creatinine in urine by combining two ultrasound‐assisted emulsification microextractions with on‐column stacking in capillary electrophoresis. J Sep. Sci. 2012, 35, 436-444. (7) Jiang, F.; Yin, S.; Srinivasakannan, C.; Li, S.; Peng, J. Separation of lanthanum and cerium from chloride medium in presence of complexing agent along with EHEHPA (P507) in a serpentine microreactor. Chem. Eng. J. 2018, 334, 2208-2214. (8) Sattari-Najafabadi, M.; Esfahany, M. N. N. Intensification of liquid-liquid mass transfer in

36 / 41


Page 36 of 61

Page 37 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a circular microchannel in the presence of sodium dodecyl sulfate. Chem. Eng. Process. 2017, 117, 9-17. (9) Yin, S.; Pei, J.; Peng, J.; Zhang, L.; Srinivasakannan, C. Study on mass transfer behavior of extracting La (III) with EHEHPA (P507) using rectangular cross-section microchannel. Hydrometallurgy 2018, 175, 64-69. (10) Kolar, E.; Catthoor, R. P.; Kriel, F. H.; Sedev, R.; Middlemas, S.; Klier, E.; Priest, C. Microfluidic solvent extraction of rare earth elements from a mixed oxide concentrate leach solution using Cyanex® 572. Chem. Eng. Sci. 2016, 148, 212-218. (11) Kagawa, T.; Ohno, M.; Seki, T.; Chikama, K. Online determination of copper in aluminum alloy by microchip solvent extraction using isotope dilution ICP-MS method. Talanta 2009, 79, 1001-1005. (12) Xu, C.; Chu, Y. An oscillating feedback microextractor with asymmetric feedback channels. Chem. Eng. J. 2014, 253, 438-447. (13) Xu, C.; Dai, Y. High-throughput production of droplets using mini hydrodynamic focusing devices with recirculation. Ind. Eng. Chem. Res. 2015, 54, 6551-6558. (14) Fu, L. M.; Ju, W. J.; Tsai, C. H.; Hou, H. H.; Yang, R. J.; Wang, Y. N. Chaotic vortex micromixer utilizing gas pressure driving force. Chem. Eng. J. 2013, 214, 1-7. (15) Hong, C. C.; Choi, J. W.; Ahn, C. H. A novel in-plane passive microfluidic mixer with modified Tesla structures. Lab Chip 2004, 4, 109-113.

37 / 41



Page 38 of 61

(16) Hereijgers, J.; Callewaert, M.; Lin, X.; Verelst, H.; Breugelmans, T.; Ottevaere, H.; De Malsche, W. A high aspect ratio membrane reactor for liquid–liquid extraction. J. Membrane Sci. 2013, 436, 154-162. (17) Hereijgers, J.; van Oeteren, N.; Denayer, J. F.; Breugelmans, T.;

De Malsche, W.

Multistage counter-current solvent extraction in a flat membrane microcontactor. Chem. Eng. J. 2015, 273, 138-146. (18) Aota, A.; Nonaka, M.; Hibara, A.; Kitamori, T. Counter-current laminar microflow for highly efficient solvent extraction. Angew. Chem. Int. Edit. 2007, 46, 878-880.

(19) Holbach, A.; Kockmann, N. Counter-current arrangement of microfluidic liquid-liquid droplet flow contactors. Green Process Synth. 2013, 2, 157-167.

(20) Jaritsch, D.; Holbach, A.; Kockmann, N. Counter-current extraction in microchannel flow: current status and perspectives. J Fluid Eng. 2014, 136, 091211.

(21) Wall, G. P. A micro-mixer-settler for laboratory continuous counter-current solvent extraction. AERE CE/R 1730, Harwell, Berks, U.K., 1955.

(22) Li, S. W.; Jing, S.; Luo, Q.; Chen, J.; Luo, G. S. Bionic system for counter-current multi-stage microextraction. RSC Adv. 2012, 2, 10817-10820.

(23) Xie, T. L.; Xu, C. High-throughput counter-current microextraction in passive mode. Lab Chip. 2018, 18, 1471-1484.

38 / 41


Page 39 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24) Halperin, J.; Oliver, J. H.; McDowell, W. C. A micro mixer settler for the rapid solvent extraction of radioactive nuclides. Lanthanide and Actinide Research. 1986, 1, 179.

(25) Hibara, A.; Nonaka, M.; Hisamoto, H.; Uchiyama, K.; Kikutani, Y.; Tokeshi, M.; Kitamori, T. Stabilization of liquid interface and control of two phase confluence and separation in glass microchips by utilizing octadecylsilane modification of microchannels. Anal. Chem. 2002, 74, 1724-1728.

(26) Aota, A.; Hibara, A.; Kitamori, T. Interface of micro counter-current flows in microchips. Anal. Chemistry. 2007, 79, 3919-3924.

(27) Aota, A.; Hibara, A.; Sugii, Y.; Kitamori, T. Shape of the liquid-liquid interface in micro counter-current flows. Anal. Sci. 2012, 28, 9-12. (28) Viernes, N. O.; Chemistry at liquid-liquid interfaces: co- and counter-current extraction and biologically active membranes in microchannels; Master Thesis, University of Illinois, Urbana-Champaign, USA, 2015.

(29) Xu, C.; Jing, S.; Chu, Y. F. Counter-current droplet-flow-based mini extraction with pulsed feeding and without moving parts. AIChE J. 2016, 62, 3685-3698. (30) Weeranoppanant, N.; Adamo, A.; Saparbaiuly, G.; Rose, E.; Fleury, C.; Schenkel, B.; Jensen, K. F. Design of multistage counter-current liquid−liquid extraction for small-scale applications. Ind. Eng. Chem. Res. 2017, 56, 4095-4103.

39 / 41



(31) Aota, A.; Mawatari, K.; Kitamori, T. Parallel multiphase microflows: fundamental physics, stabilization methods and applications. Lab Chip 2009, 9, 2470-2476. (32) Watanabe, M. An inkjet-printed microfluidic device for liquid-liquid extraction. Analyst. 2011, 136, 1420-1424. (33) Xie, T. L.; Jing, S.; Xu, C. Co-current and counter-current extraction based on a novel three-dimensional vortex microextractor. Chem. Eng. Res. Des. 2017, 128, 37-48. (34) Hellé, G.; Mariet, C.; Cote, G. Microfluidic tools for the liquid-liquid extraction of radionuclides in analytical procedures. Procedia Chemistry. 2012, 7, 679-684. (35) Zhao. B, Viernes, N. O.; Moore, J. S.; Beebe, D. J. Control and applications of immiscible liquids in microchannels. J. Am. Chem. Soc. 2002, 124, 5284-5285. (36) Xu, C.; Xie, T. L. Review of microfluidic liquid-liquid extractors. Ind. Eng. Chem. Res. 2017, 56, 7593-7622.

40 / 41


Page 40 of 61

Page 41 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Abstract Graphics

41 / 41




Page 42 of 61

Page 43 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. Hybrid countercurrent microextractor strategy 165x123mm (300 x 300 DPI)



Figure 3. Diagram of the modified microextractor available for the counter-current flow arrangement: (A) primary OFM, (B) three mixing mechanisms, (C) configuration of the modified microextractor, and (D) dimensions of the modified microextractor (depth: 2.0 mm). 1: bottom expanded inlet/outlet channel; 2: bottom inlet/outlet channel; 3: divergent chamber; 4: feedback channel; 5: barrier; 6: splitter; 7: upper inlet/outlet channel; 8: top expanded inlet/outlet channel; 9: inlet section; 10: bottom extraction section; 11: middle extraction section (mixer–settler section); 12: upper extraction section; 13: outlet section 127x91mm (300 x 300 DPI)


Page 44 of 61

Page 45 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Diagram of the modified microextractor available for cocurrent microextraction: (A) configuration and (B) dimensions (depth: 1.0 mm) 129x108mm (300 x 300 DPI)



Figure 5. Schematic diagram of the cocurrent microextraction experiments using the modified microextractor 129x66mm (300 x 300 DPI)


Page 46 of 61

Page 47 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


297x216mm (150 x 150 DPI)



Figure 7. Diagram of the single-unit countercurrent microextractor consisting of four modified microextractors (depth: 2.0 mm) 99x134mm (300 x 300 DPI)


Page 48 of 61

Page 49 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. Schematic diagram of the experimental setup for the single-unit countercurrent microextractor 129x84mm (300 x 300 DPI)



Figure 9. Changes in (A) the dimensionless feeding volume during one cycle, (B) flux ratio, (C) the extraction efficiency, and (D) the extraction performance index with phase feeding times in the single-unit PCM 79x50mm (300 x 300 DPI)


Page 50 of 61

Page 51 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60







Page 52 of 61

Page 53 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60





Figure 10. Overall configuration and dimensions of the four-unit countercurrent microextractor 129x74mm (300 x 300 DPI)


Page 54 of 61

Page 55 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


152x62mm (300 x 300 DPI)



Figure 12. Throughputs for the single- and four-unit PCMs 79x60mm (300 x 300 DPI)


Page 56 of 61

Page 57 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13. Effects of phase feeding time and droplet aggregation time on (A) the dimensionless feeding volume during one cycle 69x75mm (300 x 300 DPI)



Figure 13. Effects of phase feeding time and droplet aggregation time on (B) flux ratio 68x75mm (300 x 300 DPI)


Page 58 of 61

Page 59 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13. Effects of phase feeding time and droplet aggregation time on (C) the extraction efficiency 67x75mm (300 x 300 DPI)



Figure 13. Effects of phase feeding time and droplet aggregation time on (D) the extraction performance index in the four-unit PCM 68x75mm (300 x 300 DPI)


Page 60 of 61

Page 61 of 61 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


131x67mm (300 x 300 DPI)


Design Guideline for Passive Microextractors: From Cocurrent Flow to

Recommend Documents