Microreactor, system and method for investigating a solid-fluid chemical reaction in a microreactor

Abstract

Embodiments of the present disclosure may include a microreactor for investigating solid-fluid chemical reactions, the microreactor including an inlet section including a first inlet microchannel. Embodiments may also include an outlet section including an outlet microchannel. Embodiments may also include a reaction section including. Embodiments may also include a reaction chamber configured to hold one or more solid particles. In some embodiments, the reaction chamber may be arranged in fluid communication with the first inlet microchannel and the outlet microchannel. In some embodiments, the microreactor may be configured to be observed by one or more experimental techniques under reaction conditions comprising liquid and / or supercritical carbon dioxide conditions.

Description

[0001] MICROREACTOR, SYSTEM AND METHOD FOR INVESTIGATING A SOLID-FLUID CHEMICAL REACTION IN A MICROREACTOR

[0002] The present patent disclosure concerns a microreactor for investigating solid-fluid chemical reactions, a system for investigating a solid-fluid chemical reaction in a microreactor, and a method for investigating a solid-fluid chemical reaction in a microreactor. Particular embodiments concern microreactors for studying solid-fluid chemical reactions wherein the fluid is or comprises liquid or supercritical carbon dioxide.

[0003] Carbon capture is of increasing interest for storing carbon in any other place than in the earth’s atmosphere. One way of capturing carbon dioxide is using minerals, often metal oxide or metal silicate bearing materials, such as olivine. Some of these materials form carbonate materials such as calcite, magnesite, and dolomite, which are very stable and can often be used industrially. The reaction rate of these minerals with carbon dioxide at ambient temperature and pressure is, however, very low.

[0004] One way to increase the reaction rate is by changing the reaction conditions, such as temperature and pressure, and by changing reactant concentrations. Finding improved conditions, however, may take a long time. One way of studying reactions is by using microreactors or microchannel reactors. These are devices wherein chemical reactions take place in a confinement with typical lateral dimensions below 1 mm. These microreactors are known for having a fine degree of process control.

[0005] It is an object, among objects, to provide improved microreactors, systems and methods for investigating a solid-fluid chemical reaction in a microreactor.

[0006] To this end, there is provided a microreactor for investigating solid-fluid chemical reactions, the microreactor comprising: an inlet section comprising a first inlet microchannel; an outlet section comprising an outlet microchannel; and a reaction section comprising a reaction chamber configured to hold one or more solid particles, wherein the reaction chamber is arranged in fluid communication with the first inlet microchannel and the outlet microchannel, wherein the microreactor is configured to be observed by one or more experimental techniques under reaction conditions.

[0007] With this microreactor, solid-fluid reactions can be investigated over a large range of experimental conditions and with in situ and / or operando experimental techniques, unavailable, at least in combination, for other methods of investigating chemical reactions. Embodiments of the present disclosure may include the reaction conditions being or comprising liquid and / or supercritical carbon dioxide conditions. These conditions may include pressures above 60 bar at room temperature (liquid carbon dioxide) and 73 bar and temperatures above 31 °C (supercritical carbon dioxide). This allows the investigation of unexplored chemical reactions and reaction conditions for reactions between solids, such as minerals that are reactive to carbon dioxide, and liquid and supercritical carbon dioxide.

[0008] Embodiments of the present disclosure may include a microreactor for investigating solid-fluid chemical reactions, the microreactor including an inlet section including a first inlet microchannel. Embodiments may also include an outlet section including an outlet microchannel. Embodiments may also include a reaction section. The reaction section may include a reaction chamber configured to hold one or more solid particles. In some embodiments, the reaction chamber may be arranged in fluid communication with the first inlet microchannel and the outlet microchannel. In some embodiments, the microreactor may be configured to be observed by one or more experimental techniques under reaction conditions.

[0009] In some embodiments, the one or more experimental techniques may include one or more optical experimental techniques. In some embodiments, the reaction chamber may be optically transparent from at least one side. This allows for optical experimental techniques to be used on, e.g., the reaction chamber or any of the microchannels. The optical experimental techniques may include one or more of: optical spectroscopy; optical microscopy; UV / VIS spectroscopy; Raman spectroscopy; Raman microscopy; fluorescence spectroscopy; fluorescence microscopy; infrared spectroscopy; and infrared microscopy.

[0010] In some embodiments, the microreactor may be configured to be operated at pressures of at least 20 bar, preferably at least 50 bar, most preferably at least 90 bar. In some embodiments, preferably the microreactor may be configured to be operated at a pressure in the range of 90 to 300 bar, more preferably 100 to 250 bar.

[0011] In some embodiments, the microreactor may be configured to be operated at pressures of at least 73 bar, preferably at least 80 bar, most preferably at least 100 bar, wherein preferably the microreactor is configured to be operated at a pressure in the range of 73 to 300 bar, more preferably 90 to 250 bar.

[0012] Embodiments of the present disclosure may also include a microreactor comprising an acoustic wave generator configured to transmit acoustic waves towards the reaction chamber. The acoustic wave generator may be or comprise a piezoelectric element, such as a piezoelectric transducer. In another embodiment, the acoustic wave generator may be an interdigital transducer, which may generate acoustic surface waves. The substrate may in this embodiment be a piezoelectric substrate, such as quarts or lithium niobate.

[0013] Embodiments of the present disclosure may also include microreactor according to any one of the preceding claims. In some embodiments, the inlet section may include a second inlet microchannel. The first and second inlet channels preferably connect at a microchannel junction of the microreactor. The junction may be in fluid communication with the reaction chamber. Another fluid may be introduced via the second inlet. Plug flow may be used to feed the reaction chamber with fluid.

[0014] For example, water can be introduced in the second inlet channel. When carbon dioxide is introduced via the first inlet, a plug flow of carbon dioxide and water can be introduced into the reaction chamber. Transport of carbon dioxide into the water and water into the carbon dioxide will occur at the interfaces. Inside plugs there will be internal convection because of the shear of the microchannel walls acting on the edges of the plug. This internal convection both along the longitudinal direction of the microchannel(s) and in the lateral direction, which may enhance mixing within a plug.

[0015] In some embodiments, the reaction chamber may include a particle barrier at or near an outlet end thereof. The particle barrier may comprise a plurality of blocking elements with openings arranged therebetween. The blocking elements may be formed by etching a substrate, in particular by etching away the openings such that the blocking elements are formed. The particle barrier may alternatively comprise a frit.

[0016] In some embodiments, the first inlet microchannel may be configured such that solid particles are able to pass through towards the reaction chamber. In this way, the reaction chamber can be filled with the solid particles. This may be done via the first inlet microchannel.

[0017] In some embodiments, the reaction chamber may be a first reaction chamber, the microreactor further including a second reaction chamber in fluid connection with the inlet section. The second reaction chamber may be positioned downstream of, and in fluid communication with, the first reaction chamber. The microreactor is preferably configured such that the first reaction chamber is able to operate at first reaction conditions, and the second reaction chamber is able to operate at second reaction conditions, different from the first reaction conditions. The temperature may differ, or the pressure may differ, or both. Also, the fluid composition added to the second reaction chamber may differ from the fluid composition added to the first reaction chamber, for example, by changing the corresponding microchannel diameters of two input fluids. Additionally, the second reaction chamber may comprise a different material as a solid reactant than the first reaction chamber.

[0018] In some embodiments, one or both of the first and second reaction chambers may have a width, as seen in cross section that is at least two, preferably five, times as large as the width of the microchannels connected at respectively the inlet side of the respective reaction chamber and the outlet side of the respective reaction chamber.

[0019] Embodiments may also include a pressure drop section arranged between the first reaction chamber and the second reaction chamber and configured to reduce the fluid pressure at the second reaction chamber.

[0020] In some embodiments, the pressure drop section may include a pressure drop microchannel having a cross sectional surface area that is smaller than a cross sectional surface area of the first inlet microchannel. In some embodiments, the cross sectional surface area of the pressure drop microchannel may be between 0.01% and 10% of the cross sectional surface area of the first inlet microchannel, such as 0.1%. In some embodiments, the pressure drop microchannel may have a V-shape in cross-section.

[0021] In some embodiments, the microreactor may be configured to be heated at a reaction section side opposite the inlet section or at or near the reaction section such that, when heat is applied to the microreactor, a thermal gradient exists in first direction along the microreactor. In this way, a reaction can be studied at least for varying temperatures in situ. In some embodiments, the second reaction chamber may be offset along the first direction relative to the first reaction chamber.

[0022] In some embodiments, the microreactor may be configured such that the fluid pressure is reduced in a second direction different from the first direction. In some embodiments, the second direction may be perpendicular to the first direction. In some embodiments, the second reaction chamber may be offset along the second direction relative to the first reaction chamber.

[0023] Embodiments may also include indicating chambers each arranged in fluid connection with the inlet section and configured as an indicator of a phase of fluid present in the indicating chambers. In some embodiments, the indicating chambers may be offset relative to each other along the first direction. In some embodiments, the indicating chambers may be offset relative to each other along the second direction. Embodiments of the present disclosure may include a thermal barrier between the reaction section and the inlet section and / or the outlet section.

[0024] In some embodiments, the inlet section may include a third inlet microchannel. In some embodiments, the third inlet microchannel may be configured such that a reactive fluid flow is able to flow to react with fluid exiting the reaction chamber. A second fluid microchannel junction may be provided, connecting the third inlet microchannel to a microchannel that is in fluid connection with the outlet microchannel or directly to the outlet microchannel. The reaction section may comprise he second fluid microchannel junction.

[0025] In some embodiments, the microchannels have, in cross section, a width in the range of 5 to 1000 pm, preferably 50 to 300 pm, and a height in the range of 5 to 1000 pm, preferably 50 to 300 pm.

[0026] Embodiments of the present disclosure may include a base in which the microchannels and reaction chamber are formed, and a transparent cover or top fixedly connected to the base and arranged to close the microchannels and reaction chamber. In some embodiments, the base may be made of silicon, quartz, or lithium niobate. In some embodiments, the transparent cover may be made of glass, quartz, sapphire, or magnesium fluoride. The glass may be borosilicate glass.

[0027] In some embodiments, the reaction section is configured to be heated to a temperature in the range of 31 °C to 300 °C, in the range of 70 °C to 300 °C, 85 °C to 275 °C, 90 °C to 250 °C or in the range of 150 °C to 250 °C. These temperature ranges are especially suited for studying reactions with supercritical carbon dioxide.

[0028] According to a second aspect, there is provided a system comprising a microreactor according to any one of the embodiments of the first aspect; and a carbon dioxide feed system configured to feed an input of the microreactor with liquid or supercritical carbon dioxide, preferably liquid carbon dioxide.

[0029] The carbon dioxide feed system may comprise a pressurized carbon dioxide container configured to output liquid carbon dioxide. The pressurized carbon dioxide container may have a pressure in the range of 55 - 65 bar. The pressurized carbon dioxide container may comprise a dip needle for extracting the liquid carbon dioxide. The carbon dioxide feed system may comprise one or more pumps configured to receive liquid carbon dioxide and configured to output liquid or supercritical carbon dioxide to the first input microchannel of the microreactor. The pumps may be syringe pumps. The pumps may be cooled to a temperature below 31 °C, preferably a temperature in the range of 5 - 20 °C. At these temperatures and pressures the carbon dioxide is in a liquid state . Once the carbon dioxide is in the microreactor and heated, keeping the pressure above about 74 bar, the carbon dioxide transitions to its supercritical state. In this way, solid-fluid reactions with supercritical carbon dioxide can occur in the microreactor.

[0030] According to a third aspect, there is provided a method for investigating a solid-fluid chemical reaction in a microreactor, the method including placing one or more solid particles in a reaction chamber of the microreactor. Embodiments may also include introducing a fluid flow to one or more inlets of the microreactor. Embodiments may also include allowing the fluid to flow through the reaction chamber such that the solid-fluid chemical reaction occurs. Embodiments may also include observing the solid particles and / or the fluid in the microreactor using one or more experimental techniques. In some embodiments, the chemical reaction may be allowed to occur at a pressure of at least 50 bar. In some embodiments, the chemical reaction is allowed to occur at liquid carbon dioxide or supercritical carbon dioxide conditions.

[0031] Embodiments may also include using a microreactor according to the first aspect and / or a system according to the second aspect to perform the method steps.

[0032] It will be understood that technical advantages and effects associated with features and / or embodiments of one aspect, apply to the corresponding, similar or equivalent features and / or embodiments of the other aspects. It will also be apparent that the features of the various aspects and / or embodiments thereof may be applied to the other aspects and / or embodiments thereof.

[0033] Brief Description of the Drawings

[0034] The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present disclosure. The above and other advantages of the features and objects of the disclosure will become more apparent, and the aspects and embodiments will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

[0035] FIG. 1 A is a schematic drawing illustrating a microreactor, according to some embodiments of the present disclosure; FIG. IB is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0036] FIG. 2 is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0037] FIG. 3 is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0038] FIG. 4 is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0039] FIG. 5 is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0040] FIG. 6 is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0041] FIG. 7 is a block diagram illustrating a microreactor, according to some embodiments of the present disclosure;

[0042] FIG. 8 is a block diagram illustrating a system comprising a microreactor, according to some embodiments of the present disclosure;

[0043] FIG. 9 is an image showing a microreactor according to some embodiments of the present disclosure;

[0044] FIG. 10 is an image showing a reaction chamber of a microreactor filled with solid particles according to some embodiments of the present disclosure;

[0045] FIG. 10 is a microscope image showing a reaction chamber of a microreactor filled with solid particles according to some embodiments of the present disclosure;

[0046] FIG. 12 is an image showing a microreactor according to some embodiments of the present disclosure;

[0047] FIG. 13 is a schematic drawing illustrating a microreactor, according to some embodiments of the present disclosure;

[0048] FIG. 14 is an image with inverted colours, showing a microreactor, according to some embodiments of the present disclosure;

[0049] FIG. 15 is an image showing the pressure dop section and indicator chambers of the microreactor according to FIG. 14;

[0050] FIG. 16 is a flowchart illustrating method for investigating a solid-fluid chemical reaction in a microreactor, according to some embodiments of the present disclosure;

[0051] FIG. 17 is a schematic drawing of a cross-section of a microchannel of a microreactor, according to some embodiments of the present disclosure;

[0052] FIG. 18 is a schematic drawing of a cross-section of an inlet microchannel of a microreactor, according to some embodiments of the present disclosure; FIG. 19 is a schematic drawing of a cross-section of a pressure drop microchannel of a microreactor, according to some embodiments of the present disclosure; and

[0053] FIG. 20 is a schematic drawing illustrating a microreactor, according to some embodiments of the present disclosure;

[0054] FIG. 21 is a schematic drawing indicating an example of detecting magnesium ions with a fluorophore-based analytical fluid reacting with magnesium ions in a microreactor according to some embodiments of the present disclosure;

[0055] FIG. 22 is a microscope image showing fluorescence of an analytical compound reacting with metal ions in a microreactor according to some embodiments of the present disclosure;

[0056] FIG. 23 is a graph of measured fluorescence intensity versus magnesium concentration in the microfluidic channel.

[0057] FIG. 24 is a schematic drawing illustrating a microreactor, according to some embodiments of the present disclosure;

[0058] FIG. 25 is a schematic drawing illustrating a microreactor, according to some embodiments of the present disclosure;

[0059] FIG. 26 is a graph of measured fluorescence intensity versus detection wavelength for various temperatures of the fluid in the microfluidic channel; and

[0060] FIG. 27 is a graph of measured fluorescence intensity versus detection wavelength for various pressures of the fluid in the microfluidic channel.

[0061] Detailed Description of Preferred Embodiments

[0062] FIG. 1A is a schematic drawing of a microreactor 100 according to some embodiments of the present disclosure. FIG. IB is a block diagram that describes the microreactor 100. In some embodiments, the microreactor 100 includes an inlet section 110, an outlet section 120, and a reaction section 130. The inlet section 110 includes a first inlet microchannel 112. The outlet section 120 includes an outlet microchannel 122. The reaction section 130 includes a reaction chamber 132 configured to hold one or more solid particles. The reaction chamber 132 is arranged in fluid communication with the first inlet microchannel 112 and the outlet microchannel 122. The microreactor 100 is configured to be observed by one or more experimental techniques under reaction conditions.

[0063] In some embodiments, the one or more experimental techniques may include one or more optical experimental techniques. The reaction chamber 132 may be optically transparent from at least one side. In some embodiments, the microreactor may be configured to be operated at pressures of at least 73 bar, preferably at least 80 bar, most preferably at least 100 bar, wherein preferably the microreactor is configured to be operated at a pressure in the range of 73 to 300 bar, more preferably 90 to 250 bar. FIG. 2 is a block diagram that describes microreactor 200, according to some embodiments of the present disclosure. In some embodiments, the microreactor 200 includes an acoustic wave generator 210 configured to transmit acoustic waves towards the reaction chamber. The acoustic waves may be ultrasound waves. The acoustic wave generator may be or comprise a piezoelectric element, such as a piezoelectric transducer. Alternatively, or additionally, the microreactor may comprise a substrate that is a piezoelectric material. In this way, the solid particles may be agitated by ultrasound energy. This allows the investigation of whether, for instance, carbonate passivation layers that are formed at the surface of the mineral particles can be at least partially broken in order to increase a reaction rate with carbon dioxide. The acoustic wave generator 210 may be positioned adjacent to the reaction chamber 132. Alternatively, the acoustic wave generator 210 may be positioned at an opposite side of the substrate relative to the reaction chamber 132. Unless mentioned otherwise, the microreactor 200 may comprise the same features as other microreactors, such as microreactor 100, mentioned herein.

[0064] FIG. 3 is a block diagram that describes microreactor 300, according to some embodiments of the present disclosure. In some embodiments, the inlet section 320 may include a second inlet microchannel 322. Unless mentioned otherwise, the microreactor 300 may comprise the same features as other microreactors, such as microreactor 100, mentioned herein.

[0065] FIG. 7 is a block diagram that describes microreactor 1100, according to some embodiments of the present disclosure. In some embodiments, the microreactor 1100 may include a base 1110 and a transparent cover or top 1120 fixedly connected to the base 1110 and arranged to close the microchannels and reaction chamber, such that the microchannels and reaction chamber are formed. Preferably the base 1110 may be made of silicon, quartz, or lithium niobate. Preferably the transparent cover or top 1120 may be made of glass, quartz, sapphire, magnesium fluoride. Preferably the top 1120 is made of borosilicate glass. When silicon and glass, such as borosilicate glass, are used, the glass can be bonded to the silicon using anodic bonding, e.g. at 400 °C under inert (nitrogen or argon) atmosphere, with a bonding potential of 400 V for 20 min. The resulting bond strength between the silicon and glass is higher than the fracture strength of the glass. Before bonding, the substrates may be cleaned as described on p. 165, middle paragraph of R.M. Tiggelaar et al., Chemical Engineering Journal 131 (2007), pp. 163- 170, which is incorporated herein by reference in its entirety.

[0066] In an embodiment, the microchannels are formed by etching the substrate, such as silicon, with deep reactive ion etching, thus creating a rectangular or square cross sectional shape. An example is shown in FIG. 17, in which the substrate 110 is shown in which the microchannel 1116 is etched. The substrate 1110 is covered by the cover 1120, such that the microchannel 1116 is closed.

[0067] In an embodiment, the inlet and / or outlet microchannels formed by etching the silicon using deep reactive ion etching (DRIE) combined with HF etching of the glass cover, thereby creating a square or rectangular geometry in the silicon and a semicircular or dome-shape, seen in cross section, in the glass. This dome shape allows for attaching microtubing and / or capillaries (e.g. fused silica capillaries) with adhesive inside the inlet and outlet channels of the microreactor, thus allowing for an increased operating pressure. An example is shown in FIG. 18. The width of the dome may be, for instance, 400 pm, and the depth into the glass may be, for example, 100 pm. As an example, the inlets may have a matching width and depth of 400 pm. In this example, the inlet may be followed by a channel with a width of 100 pm and a depth of 300 pm.

[0068] The pressure drop section may comprise pressure drop microchannels 1124. In an embodiment, these microchannels 1124 are etched using potassium hydroxide etching, which, when using silicon as the substrate, results in a triangular geometry as shown in FIG. 19. The pressure drop section contains triangular structures with a width of 10 microns and a depth of 7 microns. The pressure drop section may have a length in the range of 0. 1 cm to 10 cm, preferably 0.5 cm to 5 cm, such as 1.4 cm.

[0069] FIG. 4 is a block diagram that describes microreactor 400, according to some embodiments of the present disclosure. In some embodiments, the reaction chamber 420 may include a particle barrier 422 at an outlet end thereof. Preferably the first inlet microchannel may be configured such that solid particles may be able to pass through towards the reaction chamber 420. In FIG. 1A, the reaction chamber 132 comprises a similar particle barrier 422. Unless mentioned otherwise, the microreactor 400 may comprise the same features as other microreactors, such as microreactor 100, mentioned herein. FIGS. 10 and 11 show respective microscope images of a reaction chamber 132 with particle barrier 422. Particles can be seen which are blocked from flowing out of the reaction chamber in the flow direction (to the right in FIG. 10, and to the top in FIG. 11).

[0070] The particle barrier 422 may comprise a plurality of blocking elements 424 with openings 426 (FIG. 11) arranged therebetween. The blocking elements 424 may be formed by etching a substrate, such as a silicon substrate, in particular by etching away the substrate to form the openings 426, such that the blocking elements are formed. Examples of etching are described, for instance, in relation to FIGS. 17 to 19. The particle barrier may alternatively comprise a frit. FIG. 5 is a block diagram that describes microreactor 500, according to some embodiments of the present disclosure. In some embodiments, the microreactor 500 may include a second reaction chamber 512 in fluid connection with the inlet section. The reaction chamber 132 may be a first reaction chamber 132. Unless mentioned otherwise, the microreactor 500 may comprise the same features as other microreactors, such as microreactor 100, mentioned herein.

[0071] In some embodiments, the microreactor 100 is configured to be heated at a reaction section side 140 opposite the inlet section, located at side 142, or at or near the reaction section such that, when heat may be applied to the microreactor 100, a thermal gradient exists in a first direction 701 along the microreactor 100. In an embodiment, the second reaction chamber is offset along the first direction 701 relative to the first reaction chamber 132. This is described in further detail in relation to FIG. 13.

[0072] The microreactor may be configured such that the fluid pressure may be reduced in a second direction 702 different from the first direction 701. The second direction 702 (FIG. 14) may be perpendicular to the first direction 701. In some embodiments, the second reaction chamber is offset along the second direction 702 relative to the first reaction chamber 132.

[0073] FIG. 6 is a block diagram that describes microreactor 900, according to some embodiments of the present disclosure. In some embodiments, the inlet section 920 may include a third inlet microchannel 922. The third inlet microchannel 922 may be configured such that a reactive fluid flow may be able to flow to react with fluid exiting the reaction chamber. Unless mentioned otherwise, the microreactor 600 may comprise the same features as other microreactors, such as microreactor 100, mentioned herein.

[0074] Referring to FIG. 1A, the microreactor 100 may comprise a first microchannel junction 114, connecting the first inlet microchannel 112 and the second inlet microchannel 322. A first microchannel 116 connects the first microchannel junction 114 with the reaction chamber 132.

[0075] The microreactor 100 may further comprise the third inlet microchannel 922. A second fluid microchannel junction 124 is provided, connecting the third inlet microchannel 922 to a second microchannel 126 that is in fluid connection with the outlet microchannel 122. An analytical fluid, such as water comprising hydroxide ions, may be introduced via the third inlet microchannel 922. If the fluid exiting the reaction chamber 132 comprises components that respond to the presence of the analytical fluid, this may be observed with a suitable experimental technique. For instance, if Mg2+is present in the fluid exiting the reaction chamber 132, then the presence of hydroxide ions causes the precipitation of magnesium hydroxide, which can be observed with optical means, such as a microscope.

[0076] In an embodiment, the analytical fluid is a fluorescent agent, fluorescent probe or fluorophore that fluoresces when in a solution together with metal ions dissolved by a reaction with the solid particles, such as magnesium ions, calcium ions or iron ions. One example of a fluorescent agent for magnesium ions is a fluorescent molecule generally known as Mag-fura-2, which is a tetrapotassium salt with UIPAC name tetrapotassium;2-[6-[bis(carboxylatomethyl)amino]-5- (carboxylatomethoxy)-l-benzofuran-2-yl]-l,3-oxazole-5-carboxylate, as described in The Molecular Probes Handbook, 11th edition, chapter 19, pp. 862-864. Another example of a fluorescent agent is 3, 5 -dichlorosalicylaldehyde (BCSA). Fluorescent agents exist also for other metal ions, such as calcium ions and iron ions.

[0077] The microscope can be equipped with appropriate fdters to limit the light spectrum observed by the microscope to be close to the fluorescent wavelength or wavelength-band such that the determination of the metal ion concentration can be improved. For example, the signal to noise ratio may be improved.

[0078] A schematic drawing of the working principle in a microreactor for measuring magnesium ion concentration using a fluorophore is indicated in FIG. 21. A part of a schematic microreactor is shown, including a part of the reaction chamber 132, the third inlet microchannel 922, the outlet channel 122 and the junction 124. A reaction chamber outlet microchannel 133 connects an outlet of the reaction chamber 132 with the junction 124. In this case olivine particles 2101 are drawn. Other solid materials can be used and the same principle will apply, when the reaction results in release of dissolved ions, such as metal ions (e.g. magnesium, calcium or iron) that are detectable with an appropriate fluorophore or other fluorescent light generating analytical fluid. As is visible in the example of Fig. 21, the analytical fluid comprising fluorophore is allowed to flow through the third inlet microchannel 922 and meets the effluent with Mg-ions at the junction 124. The microreactor is operated under laminar flow conditions in this example, and intermixing of the analytical fluid and the effluent occurs at the interface of the two flows, resulting in fluorescent light to be released (indicated as green colour in the Fig. 21 as originally fded in colour). The temperature and pressure indicated in FIG. 21 are merely an example of the conditions in the reaction chamber. The method of detecting ions in the effluent coming from the reaction chamber works irrespective of the conditions in the reaction chamber.

[0079] It is an option that the junction 124 is distanced from the reaction chamber 132 such that the temperature at the junction 124 is lower than the reaction chamber 132. It is an option that the area around the junction 124 is temperature controlled using a separate heater or cooling element, such that the effluent coming from the reaction chamber 132 is brought to a temperature different from, typically lower than, the temperature in the reaction chamber 132.

[0080] Actual microscope images of an actual microreactor seen under a microscope are shown in Fig. 22. The corresponding area that is shown in each image is indicated by rectangle 2103 in Fig. 21. The white dotted lines are added to the images in order to indicate the edges of the microchannels. The top image shows the analytical fluid, which has a lighter colour than the effluent, coming in from the third inlet channel 922. The effluent comprises no magnesium ions in this case. An interface 2201 can be seen to be formed between the two laminar flows. The flow in all images is from the junction 124 to the outlet side 122, in the figures to the left.

[0081] The middle image is for a magnesium ion concentration of 500 pM in the effluent. It can be seen that the brightness is increased at the interface 2201. The bottom image is for a magnesium ion concentration of 1000 pM in the effluent. An even higher brightness is observed at the interface 2201.

[0082] Data for similar microscope images as Fig. 22, but with the microscope equipped with suitable optical filters, is shown in Fig. 23. The fluorescence intensity scales linearly with the magnesium ion concentration in the effluent. For example, a linear response between fluorescence intensity and magnesium ion concentration for concentrations between 125 and 1250 pM is observed. Even low concentrations below 200 pM can be accurately determined. The ROI rectangle 2105 in Fig. 21 is an example of an area that can be used to determine the fluorescence intensity. This method of detecting ion concentration in the effluent is highly effective. In addition, for example, this method can be used for studying reactions between metal silicate containing solid particles and aqueous carbon dioxide, in which metal ions are dissolved into the aqueous carbon dioxide. The data shown in Fig. 23 is measured with an analytical fluid comprising a fluorescent agent being 3, 5 -dichlorosalicylaldehyde.

[0083] FIG. 26 shows the fluorescent intensity as a function of wavelength of the fluorescent agent 3, 5 -dichlorosalicylaldehyde (BCSA) mentioned above for various selected temperatures 30 °C, 90 °C and 137 °C. More temperatures were measured. The data allows the response of the fluorescent agent is calibrated for temperature. The data show that the fluorescent agent can be used at the temperatures of interest, for example for carbonization of minerals at elevated temperature. FIG. 27 shows similar plots for the same fluorescent agent but versus pressure. More pressures than the ones shown in the plot have been measured. The data show that the fluorescent agent can be used at the pressures of interest, for example for carbonization of minerals at elevated pressure.

[0084] The reactive fluid or analytical fluid based upon 3,5-dichlorosalicylaldehyde (BCSA) comprises at least 80% by weight, preferably 90% by weight, of a polar and protic solvent, not being water. The presence of too much water may cause a substantial unwanted fluorescence response from the BCSA. The analytical fluid may comprise a suitable amount, such as 1 - 20 wt%, 1-15 wt% or 2-10 wt%, of a buffer for neutralizing the pH of the fluid in which the magnesium ions and achieving a pH in the range of 6.5 to 7.5, preferably 6.8 to 7.2. The buffer may be a Good’s buffer, for example be HEPES (4-(2 -hydroxyethyl)- 1- piperazineethanesulfonic acid) or PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid)) or a combination thereof. The analytical fluid in this case may in addition comprise water. In this way, the analytical fluid is able to provide sufficient fluorescence signal to detect magnesium ions in concentrations below 100 pM.

[0085] A method of determining a magnesium ion concentration in a fluid flow may be as follows. The fluid flow may have a temperature in the range of 31 °C to 300 °C, in the range of 90 °C to 250 °C, or in the range of 150 °C to 250 °C, and may have a pressure in the range of 10 bar to 300 bar. The method comprises obtaining a sample of the fluid flow, mixing the sample with a reactive fluid or analytical fluid comprising a fluorescent probe, the fluorescent probe being 3,5-dichlorosalicylaldehyde to form a fluorescent sample, recording a fluorescent signal from the fluorescent sample, and determining the magnesium ion concentration based on the recorded fluorescent signal. The determining may be based on a calibration curve such as the one shown in FIG. 23. In addition, the determining may comprise a correction of the fluorescence signal based on the curves shown in FIG. 26 and / or FIG. 27.

[0086] The obtaining of a sample of the fluid flow may be performed by obtaining a small parallel flow of the fluid flow, or by taking out a sample of the fluid flow using suitable means. In the latter case, the fluorescence may be performed at a different pressure and temperature than the fluid flow, but this should not have an effect on the determination when performing the above noted calibration(s), for example. The fluorescence signal may be recorded using a camera and suitable optics, which may be a microscope or lenses, depending on the measurement setup. An optical fdter may furthermore be used, to focus on the fluorescence signal from magnesium ions together with the fluorescent probe, which for BCSA is at a wavelength of about 500 nm. A filter may thus filter out light having a wavelength above 520 or 540 nm, for example.

[0087] This method of determining a magnesium ion concentration can be performed with any of the herein disclosed microreactors and the third and fourth inlet channels. However, this method is also suitable for larger reactors, such as continuous reactors, or batch reactors, that are used to allow minerals such as olivine to react with carbon dioxide to form magnesium carbonate. Magnesium ions also dissolve, and it may be beneficial to track the magnesium ion concentration in the fluid flow at various places within the reactor, for example, or at various times.

[0088] FIG. 24 is microscope image that shows an example microreactor 2400, according to some embodiments of the present disclosure. Unless mentioned otherwise, the microreactor 2400 may comprise the same features as other microreactors, such as microreactor 100, 900 or 1200, mentioned herein. Microreactor 2400 comprises a fourth inlet microchannel 2424 which is microfluidically connected to the junction 2424, which is otherwise the same as junction 124. The fourth inlet microchannel 2424 allows additional analytical fluid to be mixed at the junction 2424 with the fluid coming from the reactor through microchannel 133. Preferably the analytical fluid flows through the microchannel 2432 and 2442 are similar or the same, within 10% variation or less . This speeds up the mixing of the analytical fluid with the fluid comprising the magnesium or other metal ions. With similar or equal flows, the mixing can be sped up by a factor of two. In these reactors, generally the fluid flows are laminar, so the mixing is mostly, if not all, the result of diffusion.

[0089] FIG. 25 is microscope image that shows an example microreactor 2500, according to some embodiments of the present disclosure. Unless mentioned otherwise, the microreactor 2500 may comprise the same features as other microreactors, such as microreactor 100, 900, 1200, or 2500 mentioned herein. Compared to microreactor 2400, the microreactor 2500 has a reaction chamber 2532 that has a smaller diameter than the reaction chamber 132 of the microreactor 2400. Although the volume is smaller, it has been observed that, especially at high pressure, the reaction chamber with a larger diameter can be relatively weak and can exhibit leaking. With the microreactor 2500, this problem is solved by strengthening the reaction chamber 2532.

[0090] FIG. 9 is microscope image that shows an example microreactor 800, according to some embodiments of the present disclosure. The microreactor 800 includes three thermal barriers 810 between the reaction section 130 and the inlet section 110. The thermal barriers 810 are formed in this example by complete removal of the substrate. Optionally, the cover can be removed as well. Unless mentioned otherwise, the microreactor 800 may comprise the same features as other microreactors, such as microreactor 100, mentioned herein.

[0091] FIG. 8 is a block diagram that describes a system 1300 comprising a microreactor 1310 according to any one of the embodiments described herein, and a carbon dioxide feed system 1320 configured to feed an input of the microreactor 1310 with liquid or supercritical carbon dioxide, preferably liquid carbon dioxide. The system 1300 may further comprise a heating system 1330 for heating the microreactor 1310. The heater system 1330 may comprise a heater and a heater controller. The heaters may be implemented with one or more Peltier elements provided on one or more copper blocks. Another option is to use PID-controlled cartridge heaters embedded in one or more copper blocks. The microreactor may then be attached to the heatable copper blocks, e.g. with thermal paste or adhesive, in order to at least heat the reaction chamber of the microreactor. The inlet side of the microreactors, such as inlet side 142 of microreactor 100, may be cooled, for instance using coolant flowing through a holder for holding the microreactor. The coolant may originate from a thermoelectric recirculating chiller system as described below. Alternatively, the inlet side can be cooled using Peltier elements.

[0092] The microreactor, the reaction section and / or the reaction chamber may be configured to be heated to a temperature in the range of 31 °C to 300 °C, 85 °C to 275 °C, 90 °C to 250 °C, in the range of 100 °C to 300 °C, or in the range of 150 °C to 250 °C. Temperatures within these ranges are suitable especially for investigating a reaction between metal silicate bearing materials, such as olivine. In these ranges, the carbon dioxide can be in its supercritical state.

[0093] The carbon dioxide feed system 1320 may comprise a pressurized carbon dioxide container configured to output liquid carbon dioxide. The pressurized carbon dioxide container may have a pressure in the range of 55 - 65 bar. The pressurized carbon dioxide container may comprise a dip needle for extracting the liquid carbon dioxide.

[0094] The carbon dioxide feed system may comprise one or more pumps configured to receive liquid carbon dioxide and configured to output liquid or supercritical carbon dioxide to the first input microchannel of the microreactor. The pumps may be syringe pumps. The pumps may be cooled to a temperature below 31 °C, preferably a temperature in the range of 5 - 20 °C, for instance using Peltier elements or using a thermoelectric recirculating chiller system, such as a ThermoRack 401 thermoelectric recirculating chiller SW10472. Coolant may be pumped through tubes wrapped around the syringe of the syringe pumps. At these temperatures and pressures the carbon dioxide is in a liquid state. Once the carbon dioxide is in the microreactor and heated, keeping the pressure above about 74 bar, the carbon dioxide transitions to its supercritical state. In this way, solid-fluid reactions with supercritical carbon dioxide can occur in the microreactor. Pressure control may be done using pressure sensors and pressure controllers known in the art.

[0095] FIG. 12 shows a microscope image of a microreactor 1000 according to another embodiment. In this embodiment, the reaction chamber 132 is implemented as a microchannel. The solid particles are stopped by the particle barrier 422. The solid particles, such as olivine particles, will then be spread out at least partially along the first direction 701, and are therefore subject to different temperatures when the temperature gradient is applied. In FIG. 12, particles lying closer to the particle barrier 422 are warmer than the ones further away, that is, more towards the inlet 112. With this embodiment of the microreactor, it is possible to investigate differences of the solid-fluid reactions as a function of temperature. For instance, olivine particles can be seen to shrink faster at certain temperatures than at other temperatures.

[0096] FIG. 13 shows a schematic drawing of a microreactor 500 according to an embodiment of the present disclosure. The microreactor 500 includes an inlet section 510, an outlet section 120, and a reaction section 530. The inlet section 510 includes a first inlet microchannel 512. The outlet section 520 includes an outlet microchannel 522. The reaction section 530 includes a first reaction chamber 532 and a second reaction chamber 534, which is offset along the first direction 701 relative to the first reaction chamber 532. The first 532 and second 534 reaction chambers are arranged in fluid communication with the first inlet microchannel 512 and the outlet microchannel 522, via the downstream microchannel 526. The first reaction chamber 532 is connected to the inlet 512 and outlet 522 via microchannel 542. The second reaction chamber 532 is connected to the inlet 512 and outlet 522 via microchannel 544.

[0097] In this embodiment, the microreactor 500 further comprises a third reaction chamber 536 which is offset in the first direction 701 relative to both the first 532 and second 534 reaction chambers, and a fourth reaction chamber 558 which is offset in the first direction 701 relative to all of the first 532, second 534 and third 536 reaction chambers. Each reaction chamber comprises, as an example, one solid particle, respectively particle 562, 564, 566 and 568.

[0098] In this way, each reaction chamber can be operated at a different temperature, when a temperature gradient is present along the first direction 701. This can be achieved by heating from the reaction chamber size 140 of the microreactor 500. The reaction chambers are arranged with the first chamber 532 at the warmest part of microreactor 500, while the second, third and fourth reaction chambers are each in a cooler part of the microreactor 500. This arrangement can be reversed, i.e. that the first reaction chamber is in the coolest part, and the fourth reaction chamber is in the warmest part, or can be otherwise arranged, not in any particular order.

[0099] The first reaction chamber 532 is closed laterally with first lateral cap 552, which closes an opening for allowing the solid particle 562 to be put into the first reaction chamber 532. The same holds for the second reaction chamber 534, capped by second lateral cap 554. The third reaction chamber 536 is capped laterally by third lateral cap 556, similar to the first reaction chamber 532. The fourth reaction chamber 538 is capped laterally by fourth lateral cap 558 similar to the first reaction chamber 532.

[0100] When in use, this configuration results in a stationary situation at the solid particle, i.e. without or with very little fluid flow. Alternatively, each of the caps 552, 554, 556 and 558 may comprise a separate outlet channel, or microchannel in fluid communication with the outlet channel 522, such that a fluid flow along the solid particles can be achieved.

[0101] Although this example microreactor 500 comprises four reaction chambers, this can be adapted to two, three, four or more. The reaction chambers 532, 534, 536 and 538 may be implemented as the reaction chamber 132 of the microreactor 100. In this case, the microreactor 500 preferably comprises separate downstream microchannels for each reaction chamber, connected to the outlet microchannel 522.

[0102] FIG. 14 shows a microscope grayscale image, with inverted colours, of a microreactor 1400, according to an embodiment of the present disclosure. The microreactor 1400 comprises a first reaction section 630 and a second reaction section 632. The microreactor 1400 may have a third reaction section 634 and may have a fourth reaction section 636. Each reaction section is in this example arranged to have four reaction chambers such as the microreactor 500 of FIG. 13. Each reaction section could alternatively have one, two, three, or more reaction chambers.

[0103] The microreactor 1400 includes at least one pressure drop section 622 arranged between the first reaction section 630 and the second reaction section 632 and configured to reduce the fluid pressure at the second reaction section 632, for instance by 5 bar.

[0104] In some embodiments, the pressure drop section 622 may include a pressure drop microchannel 624. The pressure drop microchannel 624 may include a cross sectional surface area that is smaller than a cross sectional surface area of the first inlet microchannel. Preferably the cross sectional surface area of the pressure drop microchannel 624 is between 0.01% and 10% of the cross sectional surface area of downstream microchannel 526. The pressure drop microchannel 624 is emphasized with added black lines in the microscope image for sake of clarity.

[0105] In some embodiments, indicating chambers 680 are provided, each arranged in fluid connection with the inlet section and configured as an indicator of a phase of fluid present in the indicating chambers. In some embodiments, the indicating chambers 680 may be offset relative to each other along the first direction 701. The indicating chambers may additionally or alternatively be offset relative to each other along the second direction 702.

[0106] FIG. 15 is an enlarged microscope grayscale image, with inverted colours, of a microreactor during manufacture of the microchannels. The image shows the pressure drop section 622 comprising a pressure drop microchannel 624, partially etched, together with the indicating chambers 680. The pressure drop microchannel 624 can be seen clearly. In the image, the microchannel 624 is contrasted by both black and white colour, due to optical effects / artifacts when taking the image.

[0107] FIG. 20 is a schematic drawing of a microreactor 2000 according to embodiments of the present disclosure. The microreactor 2000 is similar to the microreactor 500 and to the microreactor 1400. The microreactor 2000 includes an inlet section 2010, an outlet section 2020, a first reaction section 2030 and a second reaction section 2040. The inlet section 2010 includes a first inlet microchannel 2012. The outlet section 2020 includes an outlet microchannel 2022. The first reaction section 2030 includes a first reaction chamber 2032 and a second reaction chamber 2034, which is offset along the first direction 701 relative to the first reaction chamber 2032.

[0108] The first 2032 and second 2034 reaction chambers are each arranged in fluid communication with the first inlet microchannel 2012 and the outlet microchannel 2022, via, among others, the downstream microchannel 2062. The first reaction chamber 2032 is connected to the inlet 2012 and outlet 2022 via microchannel 2014. The second reaction chamber 2034 is fed via a first bridge microchannel 2015 between the first and second reaction chambers. Contrary to the microreactor 500, in the microreactor 2000, it is possible to have continuous flow through each of the reaction chamber. Since the flow is in a downward direction in this figure, the particle or particles in the reaction chambers remain in the lower end of the reaction chambers.

[0109] In this embodiment, the microreactor 2000 further comprises a third reaction chamber 2036 which is offset in the first direction 701 relative to both the first 2032 and second 2034 reaction chambers. Each reaction chamber may comprise, as an example, one solid particle, respectively. The third reaction chamber 2036 is connected to the inlet 2012 and outlet 2022 via second bridge microchannel 2016. Each reaction section is in this example comprises three reaction chambers. Each reaction section could alternatively have one, two, three, or more reaction chambers.

[0110] The reaction chambers are arranged with the first chamber 2032 at the coolest part of microreactor 2000, while the second, third and fourth reaction chambers are each in an increasingly warmer part of the microreactor 2000. This arrangement can be reversed, i.e. that the first reaction chamber is in the warmest part, and the fourth reaction chamber is in the coolest part, or can be otherwise arranged, not in any particular order.

[0111] The microreactor 2000 further comprises the second reaction section 2040. The microreactor 2000 may have a third reaction section and may have a fourth reaction section and so on. The microreactor 2000 includes at least one pressure drop section 622 arranged between the first reaction section 630 and the second reaction section 632 and configured to reduce the fluid pressure at the second reaction section 632, for instance by 5 bar, similar to microreactor 1400.

[0112] The second reaction section 2040 includes a fourth reaction chamber 2042, a fifth reaction chamber 2044, and a sixth reaction chamber 2046, which are offset relative to each other along the first direction 701. The fourth to sixth reaction chambers are each arranged in fluid communication with the first inlet microchannel 2012, via the microchannel 2052, and the outlet microchannel 2022, via the downstream microchannel 2062. The fifth reaction chamber 2044 is fed via a third bridge microchannel 2055 between the fourth and fifth reaction chambers. The sixth reaction chamber 2046 is connected to the inlet 2012 and outlet 2022 via second bridge microchannel 2056.

[0113] The first 2030 and second 2040 reaction sections in microreactor 2000 have respective reactor chambers most suitable for single solid particles. Alternatively, the first 2030 and second 2040 reaction sections may comprise reaction chambers as the reaction chamber 132 of FIGS 1, 9 or 12. The same holds for the reaction section 530 of microreactor 500 (FIG. 13) and reaction sections 630, 632, 634 and 634 of microreactor 1400 (FIG. 14). Each of these alternative reaction chambers may thus also comprise a particle barrier, such as the particle barrier 422.

[0114] In order for each reaction chamber of the first 2030 and / or second 2040 reaction sections to have a comparable or equal flow rate, the microreactor 2000 may comprise one or more flow adapting sections downstream of the respective reaction section. In FIG. 20, for the first reaction section 2030 this is embodied by meandering microchannel 2035 and meandering microchannel 2037. For the second reaction section 2040, this is embodied by meandering microchannel 2045 and meandering microchannel 2037. These meandering microchannels cause the effective path length experienced by fluid flowing from the respective reaction chambers 2034 and 2036 to be comparable or equal to the effective path length experienced by fluid flowing from the first reaction chamber 2032.

[0115] In the microreactor 2000, the second reaction section 2040 will receive fluid which may have reaction products that were produced in the first reaction section 2030. Although this may influence the reaction conditions of the second reaction section, the advantage is that screening of the reaction conditions with varying temperatures and pressures while still having a continuous flow is possible.

[0116] FIG. 16 is a flowchart that describes method for investigating a solid-fluid chemical reaction in a microreactor, according to some embodiments of the present disclosure. In some embodiments, at 1210, the method may include placing one or more solid particles in a reaction chamber of the microreactor. At 1220, the method may include introducing a fluid flow to one or more inlets of the microreactor. At 1230, the method may include allowing the fluid to flow through the reaction chamber such that the solid-fluid chemical reaction occurs. At 1240, the method may include observing the solid particles and / or the fluid in the microreactor using one or more experimental techniques. In some embodiments, the chemical reaction may be allowed to occur at a pressure of at least 50 bar, preferably at least 73 bar.

[0117] The solid particles may be metal oxide or metal silicate bearing materials. The metal oxide or metal silicate bearing materials may comprise magnesium, iron, calcium and / or silicon. According to an embodiment, the metal silicate bearing material is olivine. According to another embodiment, the metal silicate bearing material is serpentine. The fluid that is introduced at step 1220 may comprise liquid carbon dioxide fed via the first inlet microchannel. The liquid carbon dioxide may be mixed with water which is fed via the second inlet microchannel.

[0118] Various other steps that are part of methods according to embodiments of the present disclosure are described in relation to FIGS. 1 to 15 and FIGS. 17 to 19.

[0119] Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below.

Claims

CLAIMS1. Microreactor for investigating solid-fluid chemical reactions, the microreactor comprising: an inlet section comprising a first inlet microchannel; an outlet section comprising an outlet microchannel; and a reaction section comprising; a reaction chamber configured to hold one or more solid particles, wherein the reaction chamber is arranged in fluid communication with the first inlet microchannel and the outlet microchannel; wherein the microreactor is configured to be observed by one or more experimental techniques under reaction conditions comprising liquid and / or supercritical carbon dioxide conditions.

2. Microreactor according to claim 1, wherein the one or more experimental techniques comprise one or more optical experimental techniques, wherein the reaction chamber is optically transparent from at least one side.

3. Microreactor according to claim 1 or 2, wherein the microreactor is configured to be operated at pressures of at least 73 bar, preferably at least 80 bar, most preferably at least 100 bar, wherein preferably the microreactor is configured to be operated at a pressure in the range of 73 to 300 bar, more preferably 90 to 250 bar.

4. Microreactor according to any one of the preceding claims, comprising an acoustic wave generator configured to transmit acoustic waves towards the reaction chamber.

5. Microreactor according to any one of the preceding claims, wherein the inlet section comprises a second inlet microchannel.

6. Microreactor according to any one of the preceding claims, wherein the reaction chamber comprises a particle barrier at an outlet end thereof, wherein preferably the first inlet microchannel is configured such that solid particles are able to pass through towards the reaction chamber.

7. Microreactor according to any one of the preceding claims, wherein the reaction chamber is a first reaction chamber, the microreactor further comprising a second reaction chamber in fluid connection with the inlet section.SUBSTITUTE SHEET (RULE 26)8. Microreactor according to claim 7, comprising a pressure drop section arranged between the first reaction chamber and the second reaction chamber and configured to reduce the fluid pressure at the second reaction chamber.

9. Microreactor according to claim 8, wherein the pressure drop section comprises a pressure drop microchannel having a diameter that is smaller than a diameter of the first inlet microchannel, wherein preferably the diameter of the pressure drop microchannel is between 0.01% and 10% of the diameter of the first inlet microchannel.

10. Microreactor according to any one of the preceding claims, wherein the microreactor is configured to be heated at a reaction section side opposite the inlet section or at or near the reaction section such that, when heat is applied to the microreactor, a thermal gradient exists in first direction along the microreactor.

11. Microreactor according to claim 10, in dependence of claim 7, wherein the second reaction chamber is offset along the first direction relative to the first reaction chamber.

12. Microreactor according to claim 10 or 11, in dependence of claim 8, wherein the microreactor is configured such that the fluid pressure is reduced in a second direction different from the first direction, wherein preferably the second direction is perpendicular to the first direction.

13. Microreactor according to claim 12, wherein the second reaction chamber is offset along the second direction relative to the first reaction chamber.

14. Microreactor according to any one of claims 10 to 13, comprising indicating chambers each arranged in fluid connection with the inlet section and configured as an indicator of a phase of fluid present in the indicating chambers.

15. Microreactor according to claim 14, wherein the indicating chambers are offset relative to each other along the first direction.

16. Microreactor according to claim 14 or 15, in dependence of 8, wherein the indicating chambers are offset relative to each other along the second direction.SUBSTITUTE SHEET (RULE 26)17. Microreactor according to any one of the preceding claims, comprising a thermal barrier between the reaction section and the inlet section.

18. Microreactor according to any one of the preceding claims, wherein the inlet section further comprises a third inlet microchannel, wherein the third inlet microchannel is configured such that a reactive fluid flow is able to flow to react with fluid exiting the reaction chamber.

19. Microreactor according to claim 18, comprising a microchannel junction arranged to microfluidically connect the third inlet to the outlet microchannel.

20. Microreactor according to any one of the preceding claims, wherein the microchannels have, in cross section, a width in the range of 5 to 1000 pm, preferably 50 to 300 pm, and a height in the range of 5 to 1000 pm, preferably 50 to 300 pm.

21. Microreactor according to any one of the preceding claims, comprising: a base in which the microchannels and reaction chamber are formed; and a transparent cover fixedly connected to the base and arranged to close the microchannels and reaction chamber, wherein preferably the base is made of silicon, quartz, or lithium niobate, wherein preferably the transparent cover is made of glass, quartz, sapphire, magnesium fluoride.

22. Microreactor according to any one of the preceding claims, wherein the reaction section is configured to be heated to a temperature in the range of 31 °C to 300 °C, in the range of70 °C to 300 °C, 90 °C to 250 °C, or in the range of 150 °C to 250 °C.

23. Method for investigating a solid-fluid chemical reaction in a microreactor, the method comprising: placing one or more solid particles in a reaction chamber of the microreactor; introducing a fluid flow to one or more inlets of the microreactor; allowing the fluid to flow through the reaction chamber such that the solid-fluid chemical reaction occurs; and observing the solid particles and / or the fluid in the microreactor using one or more experimental techniques.SUBSTITUTE SHEET (RULE 26)24. Method according to claim 22, wherein the chemical reaction is allowed to occur at a pressure of at least 50 bar and wherein the fluid is or comprises liquid carbon dioxide or supercritical carbon dioxide.

25. Method according to claim 21 or 22, wherein the observing comprises recording a particle size of the solid particles over time and determining a reaction parameter based on the recorded particle size of the solid particles over time.

26. Method according to any one of claims 23 to 25, wherein the reaction chamber is heated to a temperature in the range of 31 °C to 300 °C, in the range of 90 °C to 250 °C, or in the range of 150 °C to 250 °C.

27. Method according to any one of claims 23-26, wherein a microreactor according to any one of claims 1 to 22 is used.

28. Method according to claim 27, in dependence of claim 18, wherein a reactive fluid is provided to the third inlet such that it is able to react with the fluid exiting the reaction chamber.

29. Method according to claim 28, wherein the fluid exiting the reaction chamber comprises metal ions, wherein the reactive fluid comprises a metal-ion-sensitive analytical fluid that emits fluorescent light when in a solution together with metal ions.

30. Method according to claim 29, wherein the metal-ion-sensitive analytical fluid is or comprises a fluorescent agent, fluorescent probe or fluorophore, wherein optionally: the metal ions comprise magnesium, calcium and or iron; and / or when the metal ions comprise magnesium, the metal-ion-sensitive analytical fluid is or comprises tetrapotassium;2-[6-[bis(carboxylatomethyl)amino]-5-(carboxylatomethoxy)- 1 - benzofuran-2-yl]-l ,3-oxazole-5-carboxylate or 3,5-dichlorosalicylaldehyde.

31. System for investigating a solid-fluid chemical reaction in a microreactor, comprising: a microreactor according to any one of claims 1 to 22; and a carbon dioxide feed system configured to feed an input of the microreactor with liquid or supercritical carbon dioxide.

32. System according to claim 31 , comprising a heating system for heating the microreactor.SUBSTITUTE SHEET (RULE 26)33. System according to claim 32, wherein the heating system is configured to heat at least a part of the microreactor to a temperature in the range of 31 °C to 300 °C, in the range of 90 °C to 250 °C, or in the range of 150 °C to 250 °C.

34. Method of determining a magnesium ion concentration in a fluid flow, wherein the fluid flow has a temperature in the range of 31 °C to 300 °C, in the range of 90 °C to 250 °C, or in the range of 150 °C to 250 °C, and a pressure in the range of 10 bar to 300 bar, comprising obtaining a sample of the fluid flow; mixing the sample with a reactive fluid or analytical fluid comprising a fluorescent probe, the fluorescent probe being 3,5-dichlorosalicylaldehyde to form a fluorescent sample; recording a fluorescent signal from the fluorescent sample; determining th? magnesium ion concentration based on the recorded fluorescent signal.SUBSTITUTE SHEET (RULE 26)

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