Counter-current liquid-liquid extraction process in a submillimeter conduit.

Abstract

TITLE: Countercurrent liquid-liquid extraction process in a submillimeter conduit The invention relates to a countercurrent liquid-liquid extraction process in a submillimeter conduit, the process comprising the following steps implemented from an initial train of liquid drops in the conduit, said train being composed of an alternation of drops of a first liquid (LM) and a second liquid (LNM) less wetting than the first liquid and immiscible with the first liquid, one of the two liquids having a component to be extracted towards the other of the two liquids: a) apply a first pressure gradient along the conduit so as to generate a visco-inertial flow displacing a first volume of drop train according to said first gradient and generating a film of first liquid having moved in the opposite direction to said first gradient, the film being located between the drops of second liquid and the conduit;b) stop the application of the first pressure gradient; c) apply a second pressure gradient along the conduit, in the opposite direction to the first pressure gradient applied in step a), so as to generate a visco-capillary flow displacing a second volume of droplet train along said second gradient; and d) stop the application of the second pressure gradient. Figure for the abbreviation: Figure 3;

Description

Title of the invention: Countercurrent liquid-liquid extraction process in a submillimeter conduit. Technical field of the invention

[0001] The present invention relates to the field of liquid-liquid extraction.

[0002] Liquid-liquid extraction is a process consisting of bringing two immiscible or slightly miscible liquid phases into contact so as to allow a mass exchange of a component from one phase to the other. Summary of the invention

[0003] There are many liquid-liquid extraction processes. For example, reference may be made to the article by C. Xu and T. Xie, “Review of Microfluidic Liquid-Liquid Extractors”, Ind. Eng. Chem. Reas., vol. 56, no. 27, pp. 7593-7622 (2017), doi:10.2021 / acs.iecr.7b01712 (PA1), which references several of the techniques proposed to date.

[0004] Among these, liquid-liquid extraction processes utilizing a submillimeter conduit in which extraction can take place are particularly sought after.

[0005] By "submillimeter" conduit, it is appropriate to understand a conduit having two dimensions not exceeding one millimeter. Most often, this conduit has a circular cross-section, but the invention can be applied to other cross-sectional shapes, for example, square cross-sections.

[0006] Indeed, the miniaturization of a liquid-liquid extraction process in a submillimeter conduit presents several advantages.

[0007] A primary advantage lies in the reduction of the volumes of liquid involved. This is particularly true when the liquids in question are hazardous or rare and expensive. This is the case, for example, with liquids containing a radiochemical component to be extracted, which can be encountered in medical or pharmaceutical applications. Furthermore, in the event of liquid loss into the environment, the volumes involved greatly reduce the risks.

[0008] A second advantage lies in the permanent containment of the liquids within the conduit. This containment is obviously beneficial for hazardous liquids, for example, those containing radiochemicals. The risk of liquid loss is also reduced. Furthermore, the containment allows for easy handling of the liquid components, thus enabling simplified automation.

[0009] Finally, a third advantage lies in achieving extraction performance levels that are difficult to obtain on a larger scale. Indeed, miniaturization allows, in a way general increase in the densities of material flow extracted from one liquid phase to the other, due to the higher ratio between the exchange surface area between the two liquid phases with respect to the volume occupied by each liquid phase.

[0010] There are then two main approaches to ensure extraction of component between two immiscible liquid phases in a submillimeter conduit.

[0011] The first approach consists of circulating the two liquid phases in co-current (same direction).

[0012] PA1 references several proposed co-current techniques, including techniques using a submillimeter conduit. In co-current flow, liquid-liquid exchange cannot exceed the extraction efficiency of a single contact stage between liquids, and therefore extraction is generally low in quantity. A co-current technique that is nonetheless effective is described in greater detail in JR Bums and C. Radshaw, "The intensification of rapid reactions in multiphase systems using flow in capillaries," Lab Chip, 2001, doi:10.1039 / bl02818a (PA2). It consists of using a train of droplets of two immiscible liquid phases, each of which completely wets the submillimeter conduit. This results in an alternation of a droplet of one liquid phase and a droplet of the other liquid phase, and so on along the conduit.The droplet train can be generated by ensuring that the two liquid phases meet at a T-junction upstream of the conduit.

[0013] The second approach consists of circulating the two liquid phases in counter-current flow (opposite directions). Counter-current flow has the advantage of allowing the liquids to be brought into contact through several extraction stages, resulting in a quantitative transfer from one liquid phase to the other.

[0014] Various techniques have been proposed to implement this countercurrent approach, which are well presented in the PA1 review. These include, in particular, the countercurrent liquid-liquid extraction processes a) discontinuous multi-stage and b) continuous.

[0015] Discontinuous multi-stage processes are particularly complex to implement, either because of the setups they require, or because they involve delicate physico-chemical processes to separate the two liquid phases after their contact, and this for each stage. Extraction is generally carried out discontinuously, between two stages.

[0016] Continuous processes b) require maintaining a constant separation between the two phases. The most common method is to implement a (solid) separating membrane between the two counter-currently flowing liquid phases. Besides the simplicity of the associated setup, the confinement of each of the two liquid phases is therefore significantly simpler than with discontinuous multi-stage processes. In a membrane process, one of the control parameters is the size of the pores of the membrane through which the extraction of a component from one liquid phase to another can take place (mass transfer).

[0017] However, these membrane processes suffer from several drawbacks: - limiting the pressure difference on either side of the membrane, at the risk of compromising the mechanical integrity of the membrane; - the limitation of mass transfer across the membrane (resistance provided by the size of the pores, the thickness and tortuosity of the membrane, but also the diffusion boundary layer on either side of each face of the membrane).

[0018] It is therefore difficult to design a membrane thick enough (to withstand the pressure difference) while ensuring optimal mass transfer from one liquid phase to the other. Miniaturizing the device to implement a countercurrent membrane liquid-liquid extraction process thus presents intrinsic physical limitations, which are accompanied by performance losses for the extraction process.

[0019] Other techniques exist that are based on a continuous countercurrent liquid-liquid extraction process. Among these are countercurrent chromatography processes. Here, the separation of the liquid phases is maintained throughout the extraction by a radial acceleration field (centrifugal force) applied to a millimeter-thick duct wound around a coil. The difference in mass density between the two liquid phases is used to ensure separation, as the centrifugal force experienced by each of the two liquid phases is not the same. For example, see Y. Ito & RL Bowman, “Countercurrent chromatography with flow-through coil planet centrifuge,” Science, vol. 173, no. 3995, pp. 420–422, Jul. 1971, doi.10.1126 / science.173.3995.420 (PA3). However, this approach is not very conducive to miniaturization, as the separation effect becomes increasingly difficult to achieve with miniaturization.Following a similar approach, a gravitational field is used instead of a centrifugal force to separate the liquid phases. However, here too, below a certain size, the separation of the liquid phases is no longer effective. The performance losses of the liquid-liquid extraction process then become significant.

[0020] An objective of the invention is to propose a counter-current liquid-liquid extraction process in a submillimeter conduit with improved performance.

[0021] To this end, the invention proposes a counter-current liquid-liquid extraction process in a submillimeter conduit, the process comprising the following steps implemented starting from an initial train of liquid droplets in the conduit, said train being composed of alternating droplets of a first liquid and a second liquid less wetting than the first liquid and immiscible with the first liquid, one of the two liquids having a component to be extracted towards the other of the two liquids: a) apply a first pressure gradient along the conduit so as to generate a visco-inertial flow moving a first volume of droplet train along said first gradient and generating a film of first liquid having moved in the opposite direction to said first gradient, the film being located between the drops of second liquid and the conduit; b) stop the application of the first pressure gradient; (c) apply a second pressure gradient along the conduit, in the opposite direction to the first pressure gradient applied in step (a), so as to generate a visco-capillary flow displacing a second volume of droplet train along said second gradient; and d) stop the application of the second pressure gradient

[0022] The method according to the invention may also include other features, among which the following features, taken alone or in combination:

[0023] - step d) begins when the second volume of droplet train is displaced during step c) equals the first volume of droplet train displaced during step a);

[0024] - we repeat Ni times steps a) to d), with Ni a natural number greater than or equal to the unit;

[0025] - the train of drops is regular;

[0026] - at the end of step d), steps a) to d) having been advantageously repeated Ni times, A volume of the first liquid is located at one end of the conduit, and the process then comprises the following steps: A) withdraw the volume of first liquid from the conduit through the end of the conduit where said volume is located; B) generate a train of liquid drops in the conduit through the conduit end through which the volume of first liquid was withdrawn in step A), said train being composed of an alternation of a drop of the first liquid and a drop of the second liquid;

[0027] - at the end of step B), it includes a step C) consisting of implementing the steps a) to d);

[0028] - we repeat step C) N2 times, with N2 a natural number greater than or equal to one;

[0029] - we repeat steps A) and B) N3 times), with N3 a natural number greater than or equal to the unit;

[0030] - the train of drops generated in step B) is regular. Brief description of the figures

[0031] Other features and advantages of the invention will become apparent during the course of the Reading the detailed description that follows, for understanding of which one should refer to the attached drawings, and for which:

[0032] Fig. 1 represents a simplified diagram of a device capable of implementing a liquid-liquid extraction process according to the invention;

[0033] Fig. 2 represents a submillimeter conduit comprising a train of liquid drops, formed by an alternation of a drop of first liquid and of second liquid less wetting than the first liquid and not miscible with the first liquid, from which the process according to the invention is implemented;

[0034] Fig. 3, which includes 4 diagrams, represents one period of oscillation, namely the respective counter-current displacements of the first liquid drops and the second liquid drops, during the implementation of the process according to the invention;

[0035] Fig.4, which includes 3 diagrams, represents the evolution during the repeated implementation of several oscillation periods according to the successive diagrams of Fig.3, of the initial droplet train represented on Fig.2;

[0036] Fig. 5, which includes 3 diagrams, represents other steps of the process according to the invention aimed at generating a new train of liquid drops formed from an alternation of a drop of first liquid and a drop of second liquid;

[0037] Fig. 6 is a simplified diagram of a device actually made to implement the process according to the invention. Detailed description of the invention

[0038] The invention proposes a counter-current liquid-liquid extraction method in a submillimeter conduit.

[0039] We start from a situation in which a train of liquid drops is provided in the conduit, said train being composed of an alternation of drops of a first liquid LM and a second liquid LNM less wetting than the first liquid and not miscible with the first liquid, one of the two liquids also comprising a component to be extracted towards the other of the two liquids.

[0040] The method according to the invention then aims to implement the following steps: a) apply a first pressure gradient along the conduit so as to generate a visco-inertial flow moving a first volume of droplet train along said first gradient and generating a film of first liquid having moved in the opposite direction to said first gradient, the film being located between the drops of second liquid and the conduit; b) stop the application of the first pressure gradient; (c) apply a second pressure gradient along the conduit, in the opposite direction to the first pressure gradient applied in step (b) so as to generate a visco-capillary flow displacing a second volume of droplet train along said second gradient; and d) stop the application of the second pressure gradient.

[0041] The implementation of steps a) to d) defines an oscillation period.

[0042] This can be better understood with the support of figures 1 to 3.

[0043] Figure 1 shows a device capable of implementing the process described above. Figure 2 shows the initial situation with the train of droplets of the two liquid phases involved. Finally, Figure 3 shows the physical phenomena involved in explaining the counter-current movement of the two liquid phases present in the submillimeter conduit during the implementation of the steps of the process according to the invention.

[0044] Figure 1 shows a first open flask Fl containing the first liquid LM and a second closed flask F2 containing the second liquid LNM. The two flasks Fl and F2 are connected by a submillimeter conduit CS, the ends of which E1 and E2 are immersed respectively in the first liquid LM of the first flask Fl and the second liquid LNM of the second flask F2. The fact that the second flask F2 is closed allows its pressure to be controlled by any suitable means (not shown), while the first flask Fl, being open, remains at ambient (atmospheric) pressure. A pressure gradient can therefore be applied along the submillimeter conduit.

[0045] In the starting situation, namely before implementing the process according to the invention as described above, we start from the situation represented in [Fig.2].

[0046] This train of drops can be obtained using two reservoirs (not shown in [Fig. 1]), one for the first liquid LM and the other for the second liquid LNM, each reservoir being connected by a capillary to an inlet of a T-fitting whose outlet opens into the submillimeter duct. In the initial situation, there is therefore an alternation of a drop of the first liquid and a drop of the second liquid along the submillimeter duct CS.

[0047] As can be seen in [Fig. 2], the initial droplet train is not necessarily regular, nor are the droplet volumes equal. Indeed, in order to perform the liquid-liquid exchange operation, it is possible to inject into the submillimeter conduit CS a desired ratio, denoted a, between the average flow rate QLM of the first liquid and the average flow rate Qlnm of the second liquid. This ratio is therefore written a = QLM / Q LNM. Depending on this ratio a, in particular, the droplet train will be more or less regular. A regular train is, however, advantageous in order to avoid excessively degrading performance.

[0048] Diagram 1 of [Fig. 3] is an enlarged view of [Fig. 2] at the level of a drop of second liquid. It shows a single drop of second liquid LNM, on either side of which is a drop of first liquid LM. Each drop of liquid, when stationary, is in contact with the inner wall of the submillimeter conduit CS, and there is an interface between the drop of second liquid LNM and each drop of first liquid LM, under the effect of surface tension (the liquids are immiscible).

[0049] From this situation, step a) is implemented.

[0050] To achieve this, the pressure in the second flask F2 is made lower than the pressure in the first flask Fl. The resulting pressure gradient then pushes the entire train of drops towards the second flask F2. A first volume of the drop train is thus displaced in the direction of the pressure gradient applied during this step (i.e., from left to right, as indicated by the double arrow in diagram 2 of [Fig. 3]). The pressure difference must be sufficiently large to generate forward movement in a visco-inertial flow regime. In this flow regime, viscous forces and inertial forces (acceleration) are significant due to the velocity generated by the pressure gradient.Surface tension forces (capillary forces), particularly those acting on the inner wall of the submillimeter duct CS (which, unlike surface tension forces, do not change with flow velocity), are then negligible compared to viscous and inertial forces. In this flow regime, a droplet of the second liquid LNM tends to elongate and move away from the inner wall of the submillimeter duct, and a film of the first liquid then forms between the droplet of the second liquid and the inner wall of the submillimeter duct CS. The first liquid LM forming the film originates from the droplet of the first liquid located to the right of the droplet of the second liquid LNM. The first liquid feeding the film therefore moves in the opposite direction to the pressure gradient applied during this step a).However, there is indeed an overall movement of the drops of the first liquid and the drops of the second liquid in the direction of the pressure gradient applied during this step a).

[0051] At step b), the application of this pressure gradient is then stopped.

[0052] Diagram 3 of [Fig. 3] shows a relaxation where the droplet of second liquid LNM re-adhes to the inner wall of the submillimeter conduit CS. This re-adhesion phenomenon also implies that the first liquid of the film is displaced to the left, causing the film to disappear. The situation is then comparable to the initial situation, except that the train of droplets as a whole, and therefore in particular the droplet of second liquid, has moved in the direction of the gradient applied in step a), and that the first liquid has moved from the droplet of first liquid LM located to the right of the droplet of second liquid LNM towards the droplet of first liquid located to the left of the droplet of first liquid.

[0053] There has therefore been a relative exchange between the first liquid and the second liquid.

[0054] At this stage, however, the entire volume of liquid (namely the entire train of drops) present in the submillimeter conduit has moved to the right, in direction of vial F2.

[0055] In step c), a pressure gradient is applied between the two flasks Fl, F2, which is opposite to the pressure gradient applied in step a). This can be achieved by increasing the pressure at the second flask F2. Furthermore, the pressure gradient applied during step c) is lower (in absolute value) than that applied during step a) so that the flow regime is a visco-capillary regime (flow velocity, in absolute value, lower than for step a). In this flow regime, the predominant forces are viscous forces and surface tension (capillary) forces. Inertial forces are negligible. This flow regime has the effect of displacing the droplets of the first liquid and the droplets of the second liquid in the direction imposed by the pressure gradient, namely from right to left towards the first flask Fl.This time, the portion of the first liquid likely to be retained on the capillary wall is very small (in practice negligible). This is what we observe in diagram 4 of [Fig.3].

[0056] Step c) makes the general counter-current movement between the two liquid phases effective. This counter-current movement can be more or less significant.

[0057] We then stop at step d) the application of this gradient.

[0058] At the end of step d), we find ourselves in a situation similar to the starting situation (diagram 1 of [Fig.3]), except that the drops of second liquid have moved to the right and the drops of first liquid have moved to the left.

[0059] Advantageously, step d) is implemented when the second volume of droplet train displaced during step c) equals the first volume of droplet train displaced during step a). This implies that the final volume of droplet train displaced is zero. There has then been a total countercurrent displacement between the two liquid phases, i.e., without any overall movement of the initial droplet train (initial = diagram 1 of [Fig. 3]).

[0060] The performance of this liquid-liquid extraction process is very interesting.

[0061] This is related, on the one hand, to the large exchange surface area available between the two liquid phases that the process implements, ab initia, with the starting droplet train, and on the other hand, to the fact that a stable interface between the two liquid phases (first liquid and second, less wetting liquid) is maintained during the implementation of steps a) to d). This stability is particularly linked to pressure control (essentially a longitudinal pressure gradient) which is substantially the same at a given section of the submillimeter conduit and therefore at a first / second liquid interface at that section. The applied pressure gradient also ensures the counter-current movement of the two phases liquids to ensure the desired extraction.

[0062] The process according to the invention is particularly well-suited to miniaturizing the device for its implementation. Indeed, the miniaturization of the submillimeter conduit (which may imply greater viscous and capillary forces) can be compensated for by the pressure gradient applied during the process to obtain the aforementioned operation (visco-inertial regime followed by visco-capillary regime), without compromising the efficiency of the extraction process; quite the contrary. In fact, all other things being equal, miniaturization makes it possible to increase the surface area exchange ratio between droplets of the two liquid phases relative to their respective volumes.

[0063] The device is also relatively simple (no moving mechanical parts, no multi-stages, no membrane likely to undergo high pressure differences at the interface between the two liquid phases, etc.).

[0064] Advantageously, steps a) to d) can be repeated Ni times, with Ni a natural number greater than or equal to one. This allows, as can be understood, the set of drops of the second liquid to be moved towards the second flask F2 and the set of drops of the first liquid to the first flask FL

[0065] However, by repeating steps a) to d) of the process according to the invention a number of times, it can be observed that the train of drops tends to generate large drops of liquid (whether for the first liquid or for the second liquid), the smaller drops in fact tending to aggregate into the larger ones.

[0066] This can be observed in [Fig.4].

[0067] This gradually leads to a situation where the drops become increasingly larger (diagram 1 to diagram 3 in [Fig. 4]). Diagram 3 in [Fig. 4] corresponds to a particularly advanced stage of this phenomenon.

[0068] Thus, by continuing these oscillations, the entire second liquid risks ending up at the right end and the first liquid at the left end without any alternation. Consequently, the train of drops is progressively destroyed due to the respective movements of the two liquids. Now, in light of what has been explained previously, it is clear that it is the alternation of drops of the first and second liquids in a train of drops that allows the liquids to move in opposite directions.

[0069] To avoid this situation, it is necessary to regenerate the droplet train, in particular after a given number Ni of oscillation periods.

[0070] Otherwise, this may have an impact on the extraction performance of the process since the contact surfaces between a drop of first liquid and second liquid tend to decrease (assuming that the extraction of a component of a The transfer of liquid phase from one to the other could not be almost entirely achieved, for example in the situation shown in diagram 3 of [Fig. 4]). Most importantly, this can impact the volumetric flow rate of the process, in other words, the quantity of component extracted per unit of time by the process. Indeed, this flow rate is higher when the droplet train is composed of a multitude of small droplets, namely, droplets of short lengths.

[0071] Therefore, it may sometimes be useful to ensure that we remain in a situation close to scheme 1 of [Fig.4], before implementing steps a) to d) of the liquid-liquid extraction process according to the invention again.

[0072] Therefore, at the end of step d), steps a) to d) having been advantageously repeated Ni times, a volume of first liquid is located at one end of the conduit.

[0073] The process may then advantageously include the following additional steps: A) withdraw the volume of first liquid from the conduit through the end of the conduit where said volume is located; B) generate a train of liquid drops in the conduit through the conduit end through which the volume of first liquid was withdrawn in step A), said train being composed of an alternation of one drop of the first liquid LM and one drop of the second liquid LNM.

[0074] Here too, the train of drops is advantageously regular, for the reasons already mentioned above.

[0075] This is explained in support of [Fig.5].

[0076] In this figure, still starting from the situation in [Fig.2], after the implementation of Ni repetitions of steps a) to d), we find ourselves in the situation of diagram 1 in [Fig.5], which is therefore likely to be that of diagram 3 in [Fig.4].

[0077] In this case, the volume of the first liquid is withdrawn from the side of the first flask Fl, as shown in diagram 2 of [Fig.5].

[0078] Next, a new droplet train is generated according to step B), as shown in diagram 3 of [Fig. 5]. A new droplet train, with small droplets, is then injected into the submillimeter conduit. This maintains an optimal situation, ensuring an optimal volumetric treatment flow rate and reducing the risk of performance losses in the extraction process.

[0079] By adjusting the volume removed in step A) and the respective volumes of the two liquids reinjected into the submillimeter conduit in step B), the relative exchange of the two liquid phases (or relative "hold-up" of the phases, according to Anglo-Saxon terminology) can then be controlled. In other words, the ratio between the magnitude of the respective countercurrent flow rates and the volume of each of the liquid phases.

[0080] Recall that a = Qlm / Qlnm is the ratio of the average flow rate of the first liquid to the average flow rate of the second liquid. Let fi be the ratio of the volume of the first liquid to the volume of the second liquid. Let V be the volume of the first liquid withdrawn in step A), VLM the volume of the first liquid injected in step B), and VLNM the volume of the second liquid also injected in step B to generate the droplet train. We can then impose operation according to a given ratio a while guaranteeing a given ratio [3]. More precisely, we have V-VLM = a*VLNM, while also imposing that P = Vlm / Vlnm-

[0081] Thus, the process allows counter-current extraction according to a given ratio of flow rates of the liquid phases and a given ratio of the volumes of said liquid phases.

[0082] We can then add a step C) consisting of implementing steps a) to d).

[0083] Advantageously, we can repeat step C) N2 times, with N2 a natural number greater than or equal to one.

[0084] Similarly, if it proves useful, steps A) and B) may be repeated N3 times, with N3 a natural number greater than or equal to one.

[0085] We will now present a concrete example of implementation in support of [Fig.6]. [Fig.6] is a representation in progress, namely neither in the initial state nor in the final state.

[0086] The entire implementation can be automated, and moreover managed remotely.

[0087] A concrete assembly is envisaged with two syringes SI, S2, one of which includes a The first liquid is a mixture of ISANE 185 and tributylphosphate (TBP) at 30% by mass. The second liquid is a mixture of water and nitric acid, with a molarity of 4M. The second liquid is less wetting than the first, and the two liquids are immiscible. In this example, the component to be extracted from one liquid phase to the other in the liquid-liquid extraction process is nitric acid, which is therefore initially in the second liquid to be extracted into the first. The resulting mixtures are immiscible. Each syringe has a Cl, C2 capillary at its outlet, with the capillaries joining at a distribution tee that opens into a submillimeter CS channel.The submillimeter tube CS is made of polytetrafluoroethylene (PTFE), with a circular cross-section, an internal diameter of 750 µm, and a length of 1.8 m. The submillimeter tube CS is laid flat on a table. At the other end of the submillimeter tube, there is a vial F for collecting the liquid. In an alternative embodiment, the submillimeter tube can be wound around a cylinder with a diameter greater than 2 cm; this works equally well.

[0088] The initial state is as follows.

[0089] The submillimeter duct CS is filled with the first liquid. Syringe S1 is empty. Syringe S2 is filled with µL of the second liquid. Capillaries C1 and C2 are filled with their respective liquids. Flask F is filled with the first liquid. The tip of the submillimeter duct CS is immersed in the first liquid at the interface between the air and the free surface of the first liquid.

[0090] 46 pL of the first liquid is then aspirated into the syringe SI by pulling on the piston PI of the syringe SL

[0091] A train of drops of first liquid and second liquid is then injected.

[0092] Once the train of drops of first liquid and drop of second liquid has been generated, steps a) to d) of the process are then implemented.

[0093] Step a) generates a visco-inertial flow with an average flow velocity of 0.4 m / s in the submillimeter conduit. This is achieved by a pusher action on the piston PI of the syringe SI containing the first liquid, which applies an overpressure at the T-junction, relative to the pressure at the flask F. And step c) generates a visco-capillary flow with an average flow velocity of 0.04 m / s in the submillimeter conduit. This is achieved by pulling on the piston PI of the syringe SL. This implies a vacuum at the T-fitting relative to the pressure at the vial F. The duration of this step c) is 10 times longer than the duration of step a) such that after one oscillation period, the total volume (first liquid + second liquid) injected into the submillimeter conduit is zero.

[0094] Steps a) to d) are implemented Ni = 10 times in succession.

[0095] At the end of these 10 repetitions (or 10 periods of oscillation), the drops of second liquid advance approximately 15cm in the submillimeter conduit towards the flask F (which corresponds to a displaced volume of 66 pL).

[0096] Next, steps A) and B) of the process explained previously (cycle) are implemented.

[0097] Thus, 64 pL of wettable liquid is withdrawn (step A) from the submillimeter conduit CS from the T-piece to the syringe SL. This is done at a flow rate of 15 pL / s.

[0098] Then (step B)), 32 pL of the second liquid and 32 pL of the first liquid are simultaneously injected through the T-fitting at the same flow rate of 5 pL / s for each liquid, so as to obtain a train of drops formed by a regular alternation of drops of the first liquid and the second liquid. This is done by pressing the pistons P1, P2. The ratio a, as defined previously, is therefore a = 1 in this example.

[0099] The steps described above were then repeated according to 313 oscillation periods (= Ni + N2) and according to N3 = 31 cycles, so that the flask F is emptied of its first liquid and consequently filled entirely with second liquid.

[0100] The procedure described above has the following characteristics: - an extraction performance equivalent to that of a multi-stage, counter-current liquid-liquid extraction process with 3.2 theoretical stages over 1.8m of submillimeter duct, and - an average flow rate of 0.5 pL / s.

Claims

Demands

1. A countercurrent liquid-liquid extraction process in a submillimeter conduit, the process comprising the following steps carried out from an initial train of liquid drops in the conduit, said train being composed of an alternation of drops of a first liquid (LM) and drops of a second liquid (LNM) less wetting than the first liquid and immiscible with the first liquid, one of the two liquids having a component to be extracted towards the other of the two liquids: a) apply a first pressure gradient along the conduit so as to generate a visco-inertial flow displacing a first volume of drop train along said first gradient and generating a film of first liquid having moved in the opposite direction to said first gradient, the film being located between the drops of second liquid and the conduit; b) stop the application of the first pressure gradient;(c) apply a second pressure gradient along the conduit, in the opposite direction to the first pressure gradient applied in step (a) so as to generate a visco-capillary flow displacing a second volume of droplet train along said second gradient; and (d) stop the application of the second pressure gradient.

2. The method according to claim 1, characterized in that step d) is started when the second volume of drop train displaced during step c) equals the first volume of drop train displaced during step a).

3. A method according to any one of the preceding claims, characterized in that steps a) to d are repeated Ni times, with Ni a natural number greater than or equal to one.

4. A method according to any one of the preceding claims, characterized in that the train of drops is regular.

5. A method according to any one of the preceding claims, wherein, after step d), steps a) to d) have been advantageously repeated N times, a volume of first liquid is localized at one end of the conduit, characterized in that it then comprises the following steps: A) withdrawing the volume of first liquid from the conduit through the end of the conduit where said volume is located; B) generating a train of liquid droplets in the conduit through the end of conduit through which the volume of first liquid was withdrawn in step A), said train being composed of an alternation of a drop of the first liquid (LM) and a drop of the second liquid (LNM).

6. A method according to the preceding claim, characterized in that, at the end of step B), it comprises a step C) consisting of carrying out steps a) to d).

7. Method according to the preceding claim, characterized in that step C is repeated N2 times), with N2 a natural number greater than or equal to one.

8. A method according to any one of claims 5 to 7, characterized in that steps A) and B) are repeated N3 times, with N3 a natural number greater than or equal to one.

9. A method according to any one of claims 6 to 8, characterized in that the train of drops generated in step B) is regular.

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