The invention relates to an ultrasound liquid manipulating system and more specifically a system for manipulation of a liquid-liquid system or a gas-liquid system using an interval-contact reactor.

Background of the invention

Miniaturization of chemical reactors is a promising field of reactor design to improve mass and energy transfer. An important unit operation in chemical processes is liquid- liquid (or solvent) extraction, for which microstructured devices are also studied. Liquid-liquid extractions consist of heterogeneous systems of immiscible liquids. Microreactors can provide intensified effects for such systems owing to the different flow patterns that can be generated as a result of the mixing elements used and the flow rate applied. The various flow patterns generated can provide very high interfacial areas, shorter diffusion lengths and internal mixing effects, even under laminar flow conditions. To accommodate for sufficient throughput in order to match the industrial production capabilities, methodologies such as the numbering up have been developed, which involves introducing identical parallel flow channels. However, numbering up may lead to an excessive amount of parallel channels in order to reach the desired throughput. To reduce the need for numbering up, increase of the rates of reaction, separation or transport may be a better approach. In extraction processes, intensified mixing of the immiscible phases or of the liquid volumes close to the interfaces of the immiscible phases is appropriate to increase the extraction rate. There are many methods developed for improving the mixing effects, which are broadly classified as passive and active. Passive methodology involves using innovative structures, splits, curvatures and obstructions in the microstructure to intensify mixing. A two-phase system that is of interest is the hydrolysis of p-nitrophenyl acetate. This is an instantaneous pseudo-first order reaction which is mass-transfer controlled. Plouffe et al. in "Liquid-liquid flow regimes and mass transfer in various micro-reactors", Chem. Eng. J. (2014) 15-17, compared the performance of this reaction with several of the passive elements available and saw that these were not really effective in improving the performance of this system, which was quantified in terms of the conversion and the volumetric mass transfer coefficient. Plouffe et al. then proceeded to improve the performance of the system by changing the solvent to one that has an increased solubility with the aqueous phase and ensuring parallel flow in the two phase system. As this may not always be feasible, an alternative method is to utilize external forms of energy to improve the mixing effects. This approach is called an active methodology.

There are many active methods available, with ultrasound being one of them. When ultrasound in the frequency range of 20 kHz to 2 MHz is applied to a liquid it is known to create cavitation bubbles, which in turn causes various chemical and physical effects within the liquid medium. In the case of solvent extraction the physical effects are of more importance. The physical effects are a result of cavitation bubbles formation, vibration and collapse, which cause improved internal circulation that enhances the mass transfer resulting in faster and increased conversion. When ultrasound is applied to a liquid-liquid system, more specifically for extraction purposes, an emulsion of one of the phases in the other is created. This formation of emulsion leads to increased interfacial areas between the two immiscible phases resulting in an enhanced mass transfer flux between the phases. The mechanism of this emulsion formation by ultrasound has already been discussed by different researchers.

There are many methodologies developed for combining ultrasound with microreactors, the most common of which is having the microstructured device suspended in a liquid medium and ultrasound being applied to the medium for effective transfer. In most cases this is achieved by making use of an ultrasonic bath. These methods were proved to be effective in improving the performance of the hydrolysis reaction. Such methods are, however, accompanied by different disadvantages such as dissipation of power in the liquid medium, inhomogeneous ultrasonic field, non-reproducibility and dependence of the performance on the make and type of the ultrasonic bath used. Therefore there is a need for a novel and different approach for the direct application of ultrasound to the microreactor without using a liquid medium for energy transfer.

Summary of the invention

It is an object of embodiments of the present invention to provide an efficient approach for the direct application of ultrasound to a microreactor without using a liquid medium for energy transfer. Embodiments of the present invention may be directed to liquid- liquid systems or to gas-liquid systems.

The above objective is accomplished by a method and device according to the present invention.

In a first aspect the present invention provides devices for manipulation of fluids, the device comprising:

- an ultrasonic oscillation source;

- a reactor base, whereby the reactor base comprises at least one channel;

- a fluid carrier for carrying a fluid stream, said fluid carrier adapted to be positioned in said at least one channel;

characterized in that the fluid carrier is intermittently in direct contact with the at least one channel defining at least two distinct contact areas in the channel. In some embodiments, at least one contact area may be provided.

In preferred embodiments a plurality of channels are provided such to enable a residence time to produce significant improvement in the process as compared to the direct contact device.

In preferred embodiments the at least one channel is defined by two walls and a longitudinal surface, whereby the fluid carrier is intermittently in direct contact with the longitudinal surface of the channels. In some embodiments the channel may have a V- or U-groove cross-section.

In preferred embodiments a channel is defined by successive through-holes provided in the reactor base, whereby the fluid carrier is intermittently in direct contact with the through-holes.

It is an advantage of embodiments of the present invention that the fluid carrier is not in contact with the reactor base along its entire surface, but only at specific contact points or areas. These contact points will work as a local antenna enabling a maximum and efficient transmission of the vibrations into the fluid carrier by direct contact with the transducer and thereby eliminating the dependence on the far field distance. The intermittent direct contact between the fluid carrier and the at least one channel may be obtained by a plurality of distanced supporting protrusions in the channel. The number of contact point may be between 2 and 10, and may be for example 5. It is an advantage of embodiments of the present invention that when an emulsified bubble or droplet passes in the fluid carrier over such a contact area or local antenna, the ultrasound causes the emulsified aqueous phase to split up. The plurality of antenna's may cause these bubbles to split up repetitively at successive antennas or at each successive antenna. Even though there is an increase in the interfacial area by the emulsification, this change in size of the emulsified aqueous phase due to the repetitive splitting and coalescence, can provide additional interfacial area, thereby increasing the mass transfer between the phases and further improving the yield of the process. It is an advantage of embodiments of the present invention that introduction of intervals along the channels for direct contact transfer of ultrasound to the microchannel was found to be effective in improving the performance of the reactive extraction process. The intervals brought two major advantages: in first aspect the points of high intensity became concentrated at the intervals and secondly the intervals caused a repetitive change in the size of the emulsified aqueous phase which contributed to additional improvement in mass transfer between the two immiscible phases. In embodiments of the present invention the quantity of intervals is preferably determined by considering for example, amongst others the total size of the base plate, the used wavelength of the ultrasonic oscillation source, the design of the transducer and the total length of the channel pass laying on top of the transducer.

In a specific embodiment with channel length of x cm and ultrasound wavelength of y cm, the best configuration in terms of number of intervals was found to be five intervals per x cm of channel and per y cm of wavelength. The improvement in yield of the hydrolysis reaction was found to be highest for the five interval design compared to the direct contact design at all the residence times for the operating conditions studied. In some embodiments, the presence of five intervals was found to result in the best design. When studying the variation in residence time the percentage improvement in the sonicated yield for the interval design over the direct contact design was between 23 to 13% and in terms of the volumetric mass transfer coefficient between 29 to 17 %.

In preferred embodiments at least five contact points are provided.

In preferred embodiments a plurality of contact points are provided, whereby said plurality of contact points are distributed in a spatial pattern.

It is an advantage of embodiments of the present invention that when the fluid carrier is in direct contact with the channels at a specific fixed interval, the high intensities of the generated signal are distributed or focused amongst each contact area or point. In preferred embodiments a plurality of contact points are provided at a same distance from each other.

In preferred embodiments the device further comprises a cover plate, said cover plate adapted to at least partially cover the reactor base.

In preferred embodiments the fluid carrier is made of a material adapted to absorb signals generated by the ultrasonic oscillation source. In further preferred embodiments, the material is an acoustic soft or hard material. In yet further preferred embodiments, the material is not chemically reactive with the fluid and/or an optical transparent material. In a specific example, the material may be Teflon or perfluoroalkoxy (PFA).

It is an advantage of embodiments of the present invention that when a soft material is provided the latter does not corrode due to usage.

In preferred embodiments the reactor base comprising the fluid carrier is attached on the ultrasonic oscillation source.

The channel may be a volume substantially larger than the fluid carrier. The channel may comprise supporting elements such that at different distances from the ultrasonic oscillation source one or more fluid carriers can be positioned.

The supporting elements may be configured such that a plurality of fluid carriers can be supported, each fluid carrier being positioned at a distinct distance from the ultrasonic oscillation source. The supporting elements may be configured for supporting the fluid carriers at predetermined distances from the ultrasonic oscillation source, one of these distances being lambda/2 from the ultrasonic oscillation source, wherein lambda is the wavelength of the ultrasonic oscillation source.

The supporting elements may be configured for supporting the fluid carriers by through holes in the supporting elements through which the fluid carriers pass. In preferred embodiments the fluid carrier is attached by means of clamping or gluing, for example by using a two part glue or any other glue with good acoustic impedance characteristics. The tightness of attaching by means of a screw is important as it is the link between the ultrasonic transducer and the reactor plate. The tightness should be as tight as possible. Currently a 10 mm screw is used at the center of a 80X80 mm plate. In preferred embodiments the ultrasonic oscillation source comprises a waveform generator and an amplifier.

In preferred embodiments the device may be a microreactor.

In preferred embodiments the reactor base may be metal plate, for example an aluminum metal plate.

In preferred embodiments the fluid carrier may be a tube.

In preferred embodiments in between the intervals, cavities are present and a liquid is provided in said cavities or openings, which stabilizes the temperature of the reaction liquid present in the fluid carrier. In preferred embodiments the liquid provided in said cavities or openings is a heating or cooling liquid.

In a second aspect devices according to embodiments of the present invention may be used for liquid-liquid extraction.

In a third aspect the present invention provides methods for manufacturing a device for manipulation of fluids, said method comprising:

- providing an ultrasonic oscillation source;

- providing a reactor base, whereby the reactor base comprises at least one channel;

- providing a fluid carrier for carrying a fluid stream, said fluid carrier adapted to be positioned in said at least one channel and said fluid carrier comprising a continuous outer surface; characterized in that the fluid carrier is intermittently in direct contact with at least one channel defining at least two distinct contact areas.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief description of the drawings

FIG. 1 (a) illustrates a schematic representation of a reactor according to embodiments of the invention, (b) illustrates a cross section of single channel direct-contact type reactor known in the art, and (c) illustrates a cross section of a single channel of an interval-contact type reactor according to embodiments of the present invention. FIG. 2 schematically illustrates details of a single interval as indicated in Fig. 1 (c). FIG. 3(a)-(c) schematically illustrate different arrangements of intervals provided in a channel, Fig. 3(a) illustrates a cross-section of a specific embodiment where the channel comprises three interval contact arrangement, Fig. 3 (b) illustrates a cross- section of a specific embodiment where the channel has five interval contacts and finally Fig. 3 (c) illustrates a specific embodiment providing a channel having seven contacts.

FIG. 4 illustrates a microreactor known in the art and its process and electrical connections.

FIG. 5 illustrates the chemical reaction related to the hydrolysis of p- nitrophenylacetate.

FIGs. 6 (a)-(b) illustrate thermal imaging of the ultrasound reactor plate of a microreactor of (a) the direct contact type as known in the art and (b) interval contact type according to embodiments of the present invention.

FIGs. 7 (a)-(e) illustrate behavior of emulsified slug at an interval in embodiments of the present invention. FIG. 8 illustrates variation of yield with number of intervals per channel of a reactor plate used in embodiments of the present invention. Error bars calculated on the basis of three replicates. (If no error bars are shown they are smaller than the symbol). FIG. 9 illustrates a thermal profile of a plate comprising intervals according to embodiments of the present invention, more specifically comprising seven intervals per channel of the reactor plate.

FIG. 10 illustrates variation of extraction yield with reactor design type. Error bars calculated on the basis of three replicates. (If no error bars are shown they are smaller than the symbol).

FIG. 11 illustrates variation of temperature between outlet and inlet with residence time of a microreactor based on direct contact as known in the art and on interval contact according to embodiments of the present invention. Error bars calculated on the basis of three replicates. (If no error bars are shown they are smaller than the symbol).

FIG. 12 illustrates variation of volumetric mass transfer coefficient with reactor design type. Error bars calculated on the basis of three replicates. (If no error bars are shown they are smaller than the symbol).

FIG. 13 illustrates an alternative embodiment of a microreactor according to embodiments of the present invention.

FIG. 14 illustrates a microreactor with multiple layers, according to an embodiment of the present invention.

FIG. 15 illustrates the variation in yield at different levels of a multiple layer microreactor, illustrating features of embodiments of the present invention.

FIG. 16 illustrates a thermal image of a multiple layer microreactor, illustrating features of embodiments of the present invention.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

Any reference signs in the claims shall not be construed as limiting the scope.

In the different drawings, the same reference signs refer to the same or analogous elements. Detailed description of illustrative embodiments

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Where in embodiments of the present invention reference is made to "microreactor", reference may be made to a reactor comprising channel widths up to 2 mm or larger. Where in embodiments of the present invention reference is made to intermittently indirect contact, reference is made to two elements that are not in contact over their whole length but are in direct contact with each other at different distinct points, i.e. at points distanced from each other, also referred to as intervals.

In a first aspect, the present invention relates to a device for manipulation of fluids. The latter includes liquid or solvent extraction, but is not limited thereto. The device comprising an ultrasonic oscillation source, a reactor base comprising at least one channel, and a fluid carrier for carrying a fluid stream, said fluid carrier adapted to be positioned in said at least one channel. According to embodiments of the present invention, the fluid carrier is intermittently in direct contact with the at least one channel defining at least two distinct contact areas in the channel.

It is to be noted that the system under study can be a gas in a liquid (e.g. bubbles) as well as a liquid in a liquid (droplet). The system thus may be a gas-liquid system or a liquid-liquid system.

The introduction of intervals along the channel(s) for direct contact transfer of ultrasound to the microchannels was found to be effective in improving the performance of the reactive extraction process. The intervals brought about two major improvements to the design. Firstly, the points of high temperature became concentrated at the intervals and, secondly, the intervals caused a repetitive change in the size of the emulsified aqueous phase which contributed to additional improvement in mass transfer between the two immiscible phases. The best configuration in terms of number of intervals was found to be five intervals per channel for this particular reactor size and geometry, although embodiments of the present invention are not limited thereto. The improvement in yield of the hydrolysis reaction was found to be the highest for the five-intervals design compared to the direct-contact design at all residence times for the operating conditions studied. When studying the variation in residence time the improvement in the extraction yield under sonication conditions for the interval design, compared to the direct-contact design was between 23 to 13 % and in terms of the interfacial mass transfer area between 29 to 17 %. Embodiments of the present invention provide novel reactors, preferably microreactors, suitable for ultrasound-assisted action on liquid-liquid systems or gas- liquid systems. Examples of possible action are extraction, emulsification, separation, stripping, absorption, distillation, etc. . Reactors according to embodiments of the present invention are suitable for ultrasound-assisted treatment of a fluid, e.g. a fluid stream. By way of illustration, effects of ultrasound-assisted treatment will be discussed with reference to effects on liquid-liquid extraction for emulsified aqueous phases, but embodiments are not limited thereto and other applications of ultrasound- assisted treatment also are envisaged. Embodiments of the present invention introduce short contact intervals in a microchannel tubing of the microreactor, along the reactor plate channel, in order to advantageously have a more focused transmission of the ultrasound. The non-contacted parts of the tubing are still under the influence of the ultrasound as a result of the pseudo-sonicated zone created by the adjacent intervals.

The effect of introduction of these elements was first studied by comparing the thermal profiles with and without the presence of intervals and it was found that the maximum intensities along the channel become focused at these intervals. The influence of the intervals on a sonicated two-phase flow was studied and revealed a repetitive splitting (at the intervals) and coalescence (downstream from the interval) of the emulsified aqueous phase. This dynamic change in the size of the emulsified aqueous phase introduces additional interfacial area and improves the mass transfer between the phases. The number of intervals were varied between three, five and seven, but other intervals could also be provided. However, five intervals showed the best performance resulting in a preferred embodiment. On comparing the five-interval design with a direct-contact design it was shown that the interval design gave the best improvement in yield for the process conditions studied.

In some embodiments, a device wherein one or more fluid carriers are supported at different distances from the ultrasound oscillation source is provided, such that the overall length of the fluid carriers or the number of fluid carriers wherein ultrasonic treatment can be performed can be increased. The system then operates in a stacked mode by providing different layers, levels or planes wherein fluid carriers can be positioned.

By way of illustration, embodiments of the present invention not being limited thereto, some examples will now further be discussed with reference to the drawings. This will illustrate standard and optional features of the exemplary embodiments shown.

The reactor assembly according to the present invention is similar to the direct- contact type reactors known in the art, which is illustrated in FIG. 1(a). The reactor 100 in Fig. 1(a) comprises a reactor plate 102, e.g. a metal like an aluminum plate, of for example 4 mm thickness and dimensions of 80x80 mm, with at least one, e.g. four channels, preferably square shaped in cross-section, cut through the plate 102. These channels preferably have the same dimensions as the outer diameter of the tubing 104 to be placed in them. The four channels account for four passes through the sonicated zone. The tubing 104 is preferably PFA (perfluoroalkoxy) tubing with an internal diameter of 0.8 mm and outer diameter of 1.6 mm, which is preferably held in place in the channels, e.g. in the square channels, with a cover plate 106, e.g. a Plexiglas cover plate of 5 mm thickness, fixed to the reactor plate 102, e.g. bolted at the four corners on top of the aluminum plate. The entire assembly is bolted onto a transducer 110 whose input parameters are then controlled by a wave form generator and amplifier combination (FIG. 1 (a)).

In the direct-contact type reactor as illustrated in Fig. 1(a) the applicant realized that a pseudo-sonicated zone is present, which showed sonication activity in a region of the tube that was not embedded in the reactor plate 102. This region existed for a distance of up to 8 cm away from the reactor plate 102, both at the inlet and outlet of the reactor 100. This behavior was also observed in the tubing bends in between the sonicated passes, which are also outside the reactor plate as illustrated in Fig. 1(a). The cross section of a part of a single channel of the direct-contact reactor is shown in FIG. 1 (b), where it can be seen that the tube is in contact with the reactor plate along the full length of the channel. Based on the pseudo-sonicated zone observed in the direct- contact type the applicant, it was hypothesized that the contact with the entire length of the channel may not be really required, so that by reducing the contact length it may be possible to have a more focused transmission of sound at specific points along the channels length.

With this insight, the applicant developed a design where the tubing is not in contact with the plate along its entire length as shown in FIG. 1 (c), but only at specific points e.g. contact intervals 120. For reference purpose we will term these points of contacts as intervals 120. Each interval 120 (as detailed schematically in FIG. 2) may have a width as small as possible, whereby at least 1mm of contact length is present. The height must be sufficient enough to prevent contact with the non-contact surface even when the ultrasonic vibrations are applied. In one particular embodiment, the width may be 1mm and the height may be 2.4mm from the bottom of the plate, although embodiments are not limited to these specific dimensions and other dimensions also can be used. . The space between the intervals is in one example at a height of 1.6 mm from the bottom of the plate. This arrangement made sure that the tubing is in contact with the bottom part of the channel only at the intervals and this makes only the intervals to be at the same height at which the tubing was in contact in the direct-contact type. We assume with this configuration that, instead of the entire length of channel transmitting the sound waves in the form of one single element, the individual intervals act as different focused transmission points along the length of the channel. The parts of the tubing that are not in contact with the intervals will still be under the influence of the ultrasound as a result of the pseudo-sonicated zone created by the adjacent intervals.

Embodiments of the present invention are based on contacting the tubing with the reactor plate at intervals, whereby the number of intervals can be varied. In embodiments the number of interval elements was varied to determine the ideal number required along each channel for an effective transfer of the ultrasound using specific materials.

FIG. 13 schematically illustrates an alternative embodiment where a channel is defined by successive through-holes provided in the reactor base, whereby the fluid carrier is intermittently in direct contact with the through-holes, as the fluid carrier is positioned inside the through-holes. The reactor 1300 and the contact intervals 1302 are shown.

In addition, in some embodiments, like illustrated in FIG. 13, a water bath may be provided, whereby said liquid, e.g. water bath, is provided in the channel or cavities defined by the space of the fluid carrier not in direct contact with the reactor plate, which are present in between the intervals, and whereby said liquid is adapted to heat/cool the fluid and fluid carrier. The liquid may be provided by means of a liquid input or output mechanism, as indicated by "liquid medium in/out" on the figure. Alternatively, also a gas may be used for heating or cooling the fluid and fluid carrier. The fluid or liquid entrance 1304 is shown in FIG. 13.

The introduction of temperature control by a matching mini-ultrasonic-bath is obtained by providing a supply for the temperature-control medium. Such a temperature-control medium may e.g. be pumped through the channel. In one embodiment, the medium is pumped through two elbows with push-in fittings provided at both ends of the hollowed-out area, which act as inlet and exit points. A watertight sealing may be provided. For the fluid-fluid system, the temperature-control medium can also facilitates transfer of the ultrasound from the transducer to the reaction mass, thus providing an indirect contact between the source and the sonicated system. This method of sonication holds an advantage over conventional horn setups as it prevents the reaction mass coming in direct contact with the sonication source, thereby avoiding metal contamination by erosion through ultrasound source surface cavitation. Variations of three, five and seven intervals along each channel were studied. They were arranged along the channel as shown in FIG. 3. With this arrangement three plates were manufactured to perform the required experiments. The thermal profile of the plates for different variations in the design and process parameters were also studied with a thermal camera with spatial resolution of 1.36 mrad.

An extraction device comprising an ultrasound transducer according to the present invention is illustrated in FIG. 4. The device preferably comprises two pumps, e.g. syringe pumps, that pump the fluid, in the present example aqueous and organic phases, through a T-junction with a selected flow rate (between 0.1 and 1.0 ml/min) to form the desired flow pattern. In all flow rates that are selected the slug flow persists. In all the experiments both the aqueous and the organic streams are pumped at the same flow rate (i.e. phase ratio 1:1). The total length of tubing used is 58 cm out of which the first 9 cm constitute the distance from the T-junction to the reactor plate, the next 40 cm the sonicated section and finally 9 cm, being the distance from the reactor plate outlet to the separating flask. From the T-junction the two phase system flows into the designed reactor after which 2 ml of the phases is collected in a separating flask and separated by gravity separation.

In FIG. 4 the process connections (left hand side) as well as the electrical connections (right hand side) are shown. FIG. 4 illustrates syringe pumps 402 for providing an aqueous stream 404 and an organic steam 406. These streams are mixed in a mixing and flow pattern generation zone 412 . Just before entering the reactor and just after leaving the reactor, a pseudo-sonification zone 414 is present. In the reactor 410, a sonification zone 416 is present. At the exit of the reactor 410 a high speed camera 408 may be positioned. Once the liquid has passed the reactor and the exit pseudo- sonification zone 414, a settling and separation zone 418 is present, ending in a separating flask 422. The electrical components comprise a waveform generator 430, an amplifier 432 providing a signal to the transducer 434 of the reactor plate 410, and a cooling fan 436.

The ultrasound wave characteristics frequency, amplitude and shape of the wave may be controlled by a Picotest G5100A waveform generator. The signal is sent to the transducer through an E&l 1020L RF amplifier. The transducer is a multi- frequency type which can operate at frequencies of 20, 40 & 60 kHz (Ultrasonics World MPI-7850D-20-40-60 H). A cooling fan is used to keep the transducer cool, to avoid variations in power and to avoid overheating of the reactor plate.

In a first example a reaction of interest is the hydrolysis of p-nitrophenyl acetate, as this has been well described in terms of solvent extraction and acoustic enhancement and therefore allows good comparison. This is a reactive extraction process which is illustrated in FIG. 5. The organic input stream is p-nitrophenyl acetate dissolved in toluene at a concentration of 0.05 M, while the aqueous phase consists of a 0.5 M NaOH solution. This is an instantaneous reaction and hence it is mass transfer controlled. As an excess of NaOH is used, this reaction can be considered as a pseudo- first order reaction. When the sodium p-nitrophenolate is formed in the water phase, the solution turns yellow, which can be utilized to quantify its concentration in a UV- 1601 Shimadzu spectrophotometer at a wavelength of 400 nm.

The effect of introducing the intervals along the length of the channel according to embodiments of the present invention was first studied in terms of the thermal profile of the reactor plate when sonicated for a certain amount of time. Both the direct-contact type and the interval-contact type with 5 intervals were subjected to a frequency of 20 kHz, at an amplitude of 590 m.V and net applied electrical power of 20 W. The thermal profile was then observed after a period of 30 min with the thermal camera. The images obtained are shown in FIG. 6. From the images obtained it can be seen that for the direct-contact type known to the skilled person, the high temperature area in the channel is spread in a non-uniform way along the length of the channel, whereas the introduction of the intervals in the interval-type reactor seems to concentrate the high temperature points at the intervals. Also it is to be noted from the images that the high intensity points of the interval-contact type are at a higher temperature (average of 37.1°C - 41°C at the intervals) than the direct-contact type (average of 32.2°C - 35.1°C along the channels). Considering that the temperature variation is approximately proportional to the ultrasound intensity variation along the plate, we perceive that the objective of focusing the ultrasound at defined points along the channel is met with this design.

In addition to the thermal profile of the reactor plate, the behavior of the two- phase system was also observed with a high speed camera (Photron Fastcam Mini UX- 100). In preferred embodiments PFA tubing used which is hydrophobic, as a result the organic phase is the continuous phase and the aqueous phase is the dispersed phase. There was an emulsification of the aqueous phase by the organic phase upon sonication of the direct-contact type reactor. A similar initiation mechanism which made use of the vibration of either clusters of small bubble or individual large bubbles formed in the continuous phase was observed in the interval-type reactor as in the direct-type contact reactor. In addition to this emulsification, a specific behavior was observed along the interval points of especially the third and the fourth pass of the tubing, where the emulsified aqueous phase appeared to split, as shown in FIG. 7. Sonication of the two-phase flow causes the regularity of the segmented phases to be disturbed by alternately causing coalescence and subsequent splitting up again. The increase in interfacial area by emulsification, may be combined in this case with the increase in mixing by the repetitive cycles of coalescence and phase splitting, thereby increasing the mass transfer between the phases and further improving the yield of the process. Hence, this design seems to be beneficial for the desired fluids interaction.

Having studied the effect of the presence of the interval on the design and fluid flow characteristics, the next step is to obtain the ideal number of intervals along each channel according to embodiments of the present invention. The sonicated reactive extraction of p-nitrophenyl acetate experiment was carried out in each of these plates at a frequency of 20.3 kHz, amplitude of 590 m.V and the net applied power of 20 W. In all the experiments both the aqueous and the organic streams are pumped at the same flow rate (i.e. phase ratio 1:1). The extraction yields obtained at different residence times are plotted in (FIG. 8). From the graph it is very evident that irrespective of the number of intervals there is always an improvement in the yield by sonication (e.g. non-silent). Comparing the three intervals designs (circles), the lowest yield at all residence times was obtained for the 3 interval arrangement, which is possibly related to insufficient contact length (i.e. three times 1 mm). In the three- interval design the contact length per channel is reduced by a factor of 26 in comparison to the direct-contact type. Comparing the five-intervals (diamonds) and the seven-intervals designs (triangles), it is seen that the highest yield was obtained for the five-intervals type, even though the contact length for the 7 intervals is greater (7 mm compared to 5 mm for the five-intervals type). To better understand this, the thermal profile of both reactor plates was captured with the thermal camera after sonication at the same operating conditions for a period of 30 minutes. The infrared image for the five-intervals type was already shown in FIG. 6(b), while that for the seven-intervals design is shown in FIG. 9. Form the thermal profile it is seen that there is a clear difference in the temperature distribution along the surface of the plate depending on the number of intervals. The five-interval design shows a higher temperature both overall and at the intervals. Higher temperature is considered to represent better power transmission along the channel, and hence the five-interval design provides better transmission of power, resulting in better yield of the extraction process.

The five-intervals design (circles) was compared to the direct-contact type (triangle) known in the art at a frequency of 20.3 kHz, amplitude of 590 m.V and net applied power of 20 W at the same residence times in terms of the yield obtained for the sonicated hydrolysis reaction of p-nitrophenyl acetate. The results obtained are shown in FIG. 10. From the results it is evident that the five-interval design according to the present invention advantageously performs better at all the residence times compared to the direct-contact type. The causes of this improvement were investigated. Firstly, the temperature difference between the inlet and outlet of the reactor plate was measured at the same ultrasound parameters and residence times. The results obtained are plotted in FIG. 11. From the estimation of temperature differences it is seen that there are no large differences in temperature between the two designs leading to the conclusion that in terms of the calorimetric power delivered to the reaction liquid, there is no real difference. This is unexpected because the contact length of the interval type is reduced by a factor of 16 in comparison to the direct-contact type. The only other parameter that can really influence the yield is the interfacial area. The fluctuating change in size of the dispersed phase due to the influence of the presence of the interval seems to be providing the additional improvement in mass transfer, resulting in higher yields for the interval design.

The improvement in mass transfer was quantified by the estimation of the volumetric mass transfer coefficient (Kia). Kia was calculated for this reaction utilizing the method proposed by Ramshaw & Burns in "The intensification of rapid reactions in multiphase systems using slug flow in capillaries", Lab Chip. 1 (2001) 10-15. The equation used is as follows:

Kia= -1A In(l-a)

The variation of Kia with residence time for the two design types is shown in FIG. 12. Considering the results obtained for the silent condition, it is seen that as a result of the nature of the equation used the Kia value seems to exhibit an asymptotic behaviour at higher residence time. With sonication the entire curve shifts upward with the asymptote reached faster. The highest values of Kia are observed for the interval- contact type which shows an improvement in the Kia. values in the range of 85 to 58 % (at residence times of 87 s to 9.7 s respectively) with respect to the silent condition.

As the temperature differences between the inlet and the outlet streams of both the interval and direct contact are almost similar it can be assumed that the Ki values are similar and that the increase in the Kia value can be attributed to the increase in the interfacial area available for mass transfer due to the splitting and combining of the emulsified aqueous slugs. The improvement in the interfacial area is in the range of 29 to 17 % with respect to the direct-contact design.

The space between the contact points was explored for provision of temperature control. To realise this, a two-step approach was applied whereby firstly temperature control was induced using direct contact method design parameters and whereby direct contact elements were introduced as intervals. The step of temperature control was achieved by suspending the tubing in a temperature controlled and sonicated liquid medium, leading to an indirect transfer of ultrasound termed the indirect contact reactor. The direct contact elements were introduced at regular intervals along the tubing. Open as well as closed intervals were assessed. In open interval design, the fluid carrier is mainly supported by the supporting elements. In closed interval design, the fluid carrier is in contact at a certain position but substantially along the circumference of the fluid carrier. The reactor design which incorporates both the interval and indirect approaches of ultrasound transfer is termed the hybrid contact reactor. The hybrid reactors performed better than the indirect contact reactor (20 to 27% higher yield) for lower residence times of < 45 s and similar for higher residence times. Comparing the two hybrid designs (open and closed intervals), even though their performance was similar the closed interval gave more stable and distinct yields. The design showed a relative performance similar to the interval contact design which gave the highest yields thus far for the same operating conditions. It was found that the device can work as a continuous emulsifier.

By way of illustration, embodiments of the present invention not being limited thereto, an example of a multilayer microreactor is further discussed with reference to FIG. 14 to FIG. 16.

The multilevel interval reactor 1400 according to the example discussed herein has a fixed volume that can be sonicated. The volume is dependent on the length of the tubing which in turn is governed by the diameter and hence the bending radius available for this diameter. The dimensions also factor into the number and position of the channels thereby determining the length of the sonicated tube. The volume that can be sonicated limits the throughput of a device. A solution to increase the throughput for a given plate size is proposed here by providing multiple levels at which the tubing can be placed. These levels can either be used for parallel or series operation. The addition of levels advantageously is done at locations at points of oscillation maximums. These points are determined to be at a height of λ/2 or at half wavelength. This theory was tested in the interval contact design by placing tubes at the closest proximity 1410 to the transducer (0 level, similar to the single level interval reactor) , λ/4 level 1412 and λ/2 level 1414. The design proposed is as shown in FIG. 14. The intervals 1402 and the end intervals 1404 are also shown.

The reactor comprises a top and bottom plate which act as supports for the intervals. The intervals are held in place, e.g. using two screws at the top and bottom of the plates. All the intervals are of similar dimensions except at the entry and exist to facilitate the placement of flat end fittings to hold the tubing in place. The thickness of the intervals was selected to be 2.5 mm to facilitate the placement of screws to hold the intervals in place. The assembly is connected to a transducer with a 10 mm screw placed at the bottom of the plate. In order to evaluate the performance of the system, the hydrolysis of the p- nitrophenylacetate was tested. The experiments were conducted for similar residence times of 27 s and compared to the silent condition. The results obtained are as shown in FIG. 15. The levels were also observed with a thermal camera and the image obtained is as shown in FIG. 16. FIG. 15 shows an improvement in yield for the levels 0 and λ/2. The yield obtained in silent and at level λ/4 are almost similar, showing there is little or no improvement. The improvement in level zero is what is expected as it is in the near field of operation. The improvement in λ/2 shows that there is an oscillation maximum at this point and it can be exploited for improvement in throughput. The improvement is further supported by the thermal image in FIG. 3, which shows a higher heating rate at the zero and λ/2 levels.

Reference numbers

100 reactor

102 reactor plate

104 tubing

106 cover plate

110 transducer

120 contact intervals

402 syringes

404 aquaous stream

406 organic stream

408 high speed camera

410 reactor

412 mixing and flow pattern generation zone

414 pseudo-sonification zone

416 sonification zone

418 settling and separation zone

422 separating bottle.

430 waveform generator

432 amplifier

434 transducer

436 cooling fan

1300 exemplary reactor

1302 fluid inlet

1400 other exemplary reactor

1402 intervals

1404 end intervals